{"gene":"RBL1","run_date":"2026-04-28T19:45:45","timeline":{"discoveries":[{"year":1991,"finding":"p107 (RBL1) was molecularly cloned; its cDNA maps to chromosome 20q11.2 and encodes a 936-residue protein with a major region of homology to RB spanning 564 residues. The homologous pocket region of p107 independently binds SV40 large T antigen and adenovirus E1A, establishing p107 as a structurally and functionally related RB family member.","method":"cDNA cloning, chromosomal mapping (FISH), domain-deletion binding assays","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1 — original cloning paper with structural characterization and binding domain mapping, foundational","pmids":["1833063"],"is_preprint":false},{"year":1992,"finding":"p107 forms a complex with cyclin A in cells independently of viral oncoproteins; the unique spacer sequence between the A and B sub-segments of the p107 pocket (absent in RB) is required for cyclin A interaction, explaining why cyclin A binds p107 but not RB.","method":"Co-immunoprecipitation, domain deletion mutants, in vitro binding with reticulocyte-translated proteins","journal":"Science","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP with domain mapping, replicated independently in same year by two groups","pmids":["1532457","1532458"],"is_preprint":false},{"year":1992,"finding":"p107 and RB independently bind the transcription factor E2F at distinct cell cycle phases: RB–E2F complexes predominate in G1, while a p107–cyclin A–p33cdk2–E2F complex appears in S phase, establishing that the two pocket proteins regulate E2F activity at different cell cycle stages.","method":"Co-immunoprecipitation, gel mobility shift assays, cell cycle synchronization","journal":"Cell / Nature / Genes & development","confidence":"High","confidence_rationale":"Tier 2 — replicated across multiple independent laboratories with orthogonal methods","pmids":["1531040","1530885","1398067"],"is_preprint":false},{"year":1992,"finding":"The p107–E2F complex in S phase also contains p33cdk2 and cyclin E (in G1) or cyclin A (in S), and these two kinase complexes associate with p107 in a temporally distinct manner during the cell cycle.","method":"Immunoprecipitation with cyclin- and cdk2-specific antisera, cell cycle synchronization","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal immunoprecipitations in synchronized cells, replicated","pmids":["1398067"],"is_preprint":false},{"year":1993,"finding":"p107 represses E2F-dependent transcription; adenovirus E1A overcomes p107-mediated transcriptional repression. This repression is cell-type dependent and inversely correlates with a cellular E1A-like activity in F9 embryonal carcinoma cells.","method":"Transient transfection reporter assays, co-transfection in multiple cell lines including F9 EC cells","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 — functional reporter assays in multiple cell types with defined mechanistic outcome","pmids":["7685208"],"is_preprint":false},{"year":1993,"finding":"p107-associated proteins identified in ML-1 cells include cyclin A, cyclin E, cdk2, and a 62–65 kDa E2F-like phosphoprotein that is immunologically distinct from pRB-associated E2F-1, indicating p107 preferentially associates with a specific E2F species.","method":"Monoclonal antibody panel, co-immunoprecipitation, biochemical characterization","journal":"Journal of virology","confidence":"High","confidence_rationale":"Tier 2 — systematic antibody-based interactome with multiple protein identifications","pmids":["8230483"],"is_preprint":false},{"year":1993,"finding":"p107 inhibits E2F-dependent transcription in a co-transfection assay. The E2F–p107 interaction (unlike E2F–RB) persists through the G1/S transition into S phase, providing a distinct regulatory mechanism from RB.","method":"Gel mobility shift assay, co-transfection transcriptional repression assays","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 — mechanistic functional assays replicated across labs","pmids":["8458319"],"is_preprint":false},{"year":1993,"finding":"Distinct regions of E2F1 mediate regulation by RB versus p107: point mutations within the C-terminal acidic domain of E2F1 can distinguish RB from p107 binding, and the leucine repeat element required for E4 regulation is not required for p107-mediated inhibition.","method":"E2F1 mutagenesis, co-transfection, functional reporter assays","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 — systematic mutagenesis but single laboratory","pmids":["8413230"],"is_preprint":false},{"year":1993,"finding":"HPV16 E7 associates with p107 through sequences overlapping with but distinct from those required for RB binding; this association correlates with E7's transformation-competent activities and its interaction with a histone H1 kinase at G2/M.","method":"Co-immunoprecipitation, E7 point mutant analysis, kinase assays","journal":"Journal of virology","confidence":"Medium","confidence_rationale":"Tier 2 — binding domain mapped with point mutants, single lab","pmids":["8386265"],"is_preprint":false},{"year":1993,"finding":"Cyclin A–p107 and p33cdk2 complexes bind to a 25-bp element of the human thymidine kinase promoter in an S-phase-specific manner, and mutation of this element reduces both in vitro complex binding and S-phase-regulated promoter activity in vivo.","method":"Electrophoretic mobility shift assay, promoter mutagenesis, S-phase synchronization","journal":"Proceedings of the National Academy of Sciences","confidence":"Medium","confidence_rationale":"Tier 2 — EMSA with cell cycle correlation and promoter mutagenesis, single lab","pmids":["8475104"],"is_preprint":false},{"year":1994,"finding":"E2F-4 is a p107-binding E2F family member; p107 binds E2F-4 in vivo and suppresses E2F-4's ability to transform immortalized rodent cells. E2F-4 is a differentially phosphorylated p107-binding partner present throughout the cell cycle.","method":"cDNA cloning, co-immunoprecipitation, transformation assays, reporter assays","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 — replicated independently by two groups in same year with multiple methods","pmids":["7958925","7958924"],"is_preprint":false},{"year":1994,"finding":"p107 binds to the N-terminal transactivation domain of c-Myc in vivo (but RB does not), and this binding suppresses c-Myc transactivation activity. Expression of c-Myc releases cells from p107-induced growth arrest but not from pRB-induced arrest, placing c-Myc as a specific downstream target of p107.","method":"cDNA expression library screen with Myc fusion protein, co-immunoprecipitation, co-transfection reporter assays, growth arrest rescue experiments","journal":"Science / The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods, replicated by two independent groups","pmids":["8146655","8076603"],"is_preprint":false},{"year":1994,"finding":"p107 overexpression is a potent inhibitor of E2F-mediated trans-activation and can inhibit cell proliferation causing G1 arrest in certain cell lines. Growth inhibition by p107 and pRB occurs through distinct mechanisms: p107 can arrest C33A cells (which are resistant to pRB), certain p107 mutants unable to bind E1A still inhibit proliferation, and growth arrest by each is rescued differentially by cell cycle regulators.","method":"Overexpression, cell growth assays, FACS cell cycle analysis, E1A binding mutant analysis","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal functional assays, foundational paper with >550 citations","pmids":["8319904"],"is_preprint":false},{"year":1994,"finding":"HPV16 E7 deregulates B-myb expression by targeting p107/E2F complexes; E7 transcriptionally activates B-myb during G1 and causes its constitutive over-expression, and analysis of E7 mutants confirms that B-myb regulation in NIH3T3 cells occurs through p107 rather than pRB.","method":"Transfection with E7 mutants, Northern blot, E2F reporter assays, gel-shift with specific antisera","journal":"The EMBO journal","confidence":"Medium","confidence_rationale":"Tier 2 — E7 mutant dissection links p107 specifically to B-myb regulation, single lab","pmids":["8112300"],"is_preprint":false},{"year":1995,"finding":"p107 contains a p21CIP1-related cyclin/cdk-binding domain; p107 inhibits phosphorylation of target substrates by cyclin A/cdk2 and cyclin E/cdk2, and binding of p107 or p21 to cyclin/cdk2 is mutually exclusive. In cells treated with DNA-damaging agents, elevated p21 displaces p107 from cyclin/cdk2 complexes. Activation of p107-bound kinases leads to dissociation of p107 from E2F.","method":"In vitro kinase assays, competitive binding assays, cell treatment with DNA-damaging agents, co-immunoprecipitation","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1 — in vitro kinase inhibition demonstrated with mechanistic follow-up in cells","pmids":["7622038"],"is_preprint":false},{"year":1995,"finding":"p107 contains two independent growth-suppression domains: one mediating interaction with E2F and another mediating interaction with cyclin A/E complexes. The cyclin-binding domain alone is sufficient for growth suppression in C33A cells (resistant to pRB), while both domains are functional in untransformed fibroblasts.","method":"Structure-function analysis, deletion mutants, co-expression growth arrest assays, FACS","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 — systematic structure-function dissection with multiple functional readouts","pmids":["7743997"],"is_preprint":false},{"year":1995,"finding":"Phosphorylation of p107 by cyclin D1/cdk4 (but not cyclin E/cdk2) is cell-cycle regulated, beginning ~8 hours after serum stimulation coinciding with cyclin D1 induction. Phosphorylation of p107 causes loss of association with E2F-4, and dominant-negative cdk4 abolishes p107 phosphorylation. A p107-induced cell cycle block can be released by cyclin D1/cdk4 but not cyclin E/cdk2.","method":"Cell synchronization, kinase assays, dominant-negative cdk4 overexpression, co-immunoprecipitation, growth arrest rescue","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 — mechanistic dissection with multiple complementary methods, replicated","pmids":["7797074"],"is_preprint":false},{"year":1995,"finding":"p107 represses the E2F-site–dependent transcription of the cyclin A promoter, and adenovirus 12S E1A activates cyclin A transcription by counteracting p107 repression through conserved region 2 (which binds p107) but not through CR1 or the N-terminus (which bind p300/pRB).","method":"Adenovirus deletion mutant infection, reporter assays, quiescent fibroblast model","journal":"Journal of virology","confidence":"Medium","confidence_rationale":"Tier 2 — systematic E1A mutant dissection linking p107 binding to cyclin A transcription, single lab","pmids":["8642699"],"is_preprint":false},{"year":1995,"finding":"p107 associates with the transcription factor Sp1 in vivo independently of the pocket domain; p107 represses Sp1-dependent transcription through a region distinct from the pocket domain used for E2F regulation, demonstrating two separable transcriptional repression mechanisms.","method":"Co-immunoprecipitation, transient transfection reporter assays with Gal4-Sp1 chimeras, domain deletion analysis","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP plus reporter dissection, single lab","pmids":["7565695"],"is_preprint":false},{"year":1995,"finding":"The human p107 promoter is TATA-less and contains tandem E2F sites with differential roles: RB and p107 itself repress the p107 promoter through the 5' E2F site but not the 3' (initiation site) copy, revealing autoregulatory feedback and functional asymmetry between tandem E2F elements.","method":"Promoter deletion analysis, site-directed mutagenesis, luciferase reporter assays, transfection of RB and p107","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 — systematic promoter mutagenesis, single lab","pmids":["7791762"],"is_preprint":false},{"year":1995,"finding":"The ability of p107 to suppress E2F-dependent transcription is not dependent on its ability to associate with cyclin A/cdk2; p107 mutants that fail to bind E2F cannot repress E2F transcription, while mutants deficient in cyclin A/cdk2 binding still repress E2F. Both E2F-dependent and E2F-independent activities correlate with cell growth suppression.","method":"p107 deletion mutants, co-transfection reporter assays, growth suppression assays","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 — systematic mutant analysis, single lab","pmids":["7799940"],"is_preprint":false},{"year":1995,"finding":"Cyclin A-cdk2 phosphorylation disrupts both E2F–pRB and E2F–p107 complexes, releasing free E2F; cyclin D1-cdk4 and cyclin E-cdk2 also disrupt E2F–pRB complexes. These results directly demonstrate that CDK-mediated phosphorylation of pRB and p107 regulates their E2F complex formation.","method":"Purified recombinant pRB, purified cyclin/cdk complexes, gel mobility shift assay with nuclear extracts from pRB-defective cells","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with purified components demonstrating causation","pmids":["7753545"],"is_preprint":false},{"year":1995,"finding":"Lymphoma-derived MYC mutant alleles with missense mutations in the transactivation domain are resistant to p107-mediated transcriptional suppression; p107-cyclin A-CDK complex phosphorylates Thr-58 of wild-type c-Myc in a manner dependent on prior Ser-62 phosphorylation, but this phosphorylation is absent in lymphoma Myc mutants.","method":"In vitro and in vivo phosphorylation assays, transformation assays, c-Myc mutant binding/transcription analysis","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 1/2 — in vitro kinase assays plus in vivo correlation, single lab","pmids":["7623799"],"is_preprint":false},{"year":1996,"finding":"p107 and p130 share overlapping biological roles in limb development: mice doubly deficient in p107 and p130 exhibit deregulated chondrocyte growth, defective endochondral bone development, shortened limbs, and neonatal lethality, while single knockouts are viable, demonstrating functional redundancy in vivo.","method":"Gene targeting (homologous recombination), mouse knockout, histological analysis","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 — in vivo genetic loss-of-function with defined developmental phenotype","pmids":["8682294"],"is_preprint":false},{"year":1996,"finding":"Targeted disruption of mouse p107 alone yields viable, fertile mice with no obvious abnormalities; however, Rb+/−;p107−/− mice show growth retardation and increased mortality, and Rb−/−;p107−/− embryos die ~2 days earlier than Rb−/− embryos with accelerated apoptosis in liver and CNS, demonstrating overlapping in vivo functions between p107 and RB.","method":"Homologous recombination gene targeting, double-knockout mouse generation, histological/pathological analysis","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis in vivo with defined phenotypic readout","pmids":["8682293"],"is_preprint":false},{"year":1996,"finding":"E2F-4 associates with p130 in arrested/quiescent cells but switches to p107 and pRB as cells re-enter the cell cycle and pass G1/S; E2F-4 accounts for the majority of endogenous E2F activity and the majority of free E2F in G1 cells.","method":"Cell synchronization, specific antisera immunoprecipitation, gel mobility shift assay","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — comprehensive characterization using multiple specific antisera in synchronized cells","pmids":["8657117"],"is_preprint":false},{"year":1996,"finding":"p107 contains a functional transcriptional repressor domain within its pocket (A and B conserved domains) that functions as a general repressor when tethered to a promoter via E2F or via a Gal4 DNA-binding domain fusion, independently of E2F binding. The two pocket sub-domains can function even when co-expressed as separate proteins.","method":"Gal4 fusion tethering assay, domain deletion mutants, co-transfection reporter assays","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 — systematic domain analysis with mechanistic reporter readout, single lab","pmids":["8668177"],"is_preprint":false},{"year":1996,"finding":"p107 binds B-MYB in vivo through its pocket and C-terminal domain, and suppresses B-MYB's autoregulatory transcriptional activation; overexpression of B-myb can overcome p107-induced growth arrest, placing B-MYB as a downstream effector of p107-mediated growth suppression.","method":"Co-immunoprecipitation, co-transfection reporter assays, p107 deletion constructs, growth arrest rescue","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP with domain mapping and functional readout, single lab","pmids":["8910512"],"is_preprint":false},{"year":1996,"finding":"Regulation of p107 by G1 cyclin-associated kinases: p107 phosphorylation begins in mid-G1 and is driven by cyclin D-associated kinases. Hypophosphorylated p107 selectively binds E2F-4, and G1 cyclin-dependent phosphorylation of p107 leads to dissociation of p107–E2F-4 complexes and inactivation of the p107 G1 block.","method":"Cell synchronization, kinase assays, co-immunoprecipitation, CDK inhibitor analysis","journal":"Proceedings of the National Academy of Sciences","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods in synchronized cells, replicated across labs","pmids":["8643455"],"is_preprint":false},{"year":1997,"finding":"SV40 large T antigen alters phosphorylation state of p107 and p130 through its J-domain (DnaJ homology region) in addition to LXCXE binding; the N-terminal 147 amino acids including the LXCXE domain plus additional N-terminal residues are required. A heterologous J-domain from human DnaJ can substitute for the TAg N-terminus in altering p107/p130 phosphorylation. The J-domain effect confers growth advantage via p107/p130 inactivation.","method":"TAg mutant analysis, transient expression assays, fibroblasts from p107/p130 double-knockout mice, heterologous J-domain rescue","journal":"Molecular and cellular biology / Journal of virology","confidence":"High","confidence_rationale":"Tier 2 — mechanistic dissection with domain mutants, heterologous rescue, and genetic confirmation with knockout MEFs","pmids":["9271376","8627752"],"is_preprint":false},{"year":1997,"finding":"pRB and p107/p130 regulate distinct sets of E2F-responsive genes: loss of pRB deregulates one set of E2F targets while loss of both p107 and p130 deregulates a completely different set. Neither p107 nor p130 single knockouts show changes in E2F target gene expression.","method":"Primary cells from single and double knockout mice, RNA analysis of E2F target gene expression","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 — genetic dissection in vivo/ex vivo with defined gene expression readout, landmark study","pmids":["9192872"],"is_preprint":false},{"year":1997,"finding":"p107 and p130 both repress RNA polymerase III transcription by physically interacting with TFIIIB (a subunit of the Pol III initiation factor); endogenous TFIIIB co-immunoprecipitates and co-fractionates with p107 and p130, and Pol III activity is deregulated in p107/p130 double-knockout fibroblasts.","method":"GST pull-down, co-immunoprecipitation with recombinant components and endogenous proteins, Pol III transcription assays in cell extracts, double-knockout MEFs","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — reconstitution with recombinant proteins plus endogenous Co-IP and genetic validation","pmids":["10330166"],"is_preprint":false},{"year":1997,"finding":"p107 and p130 accumulate in cells by distinct mechanisms: p107 levels are regulated transcriptionally through E2F-dependent repression in quiescent cells (p107 mRNA is low in quiescence), while p130 is controlled post-translationally via CDK-mediated phosphorylation and proteasome-mediated degradation.","method":"Cell synchronization, RNA blotting, proteasome inhibitor treatment, protein stability assays","journal":"Cell growth & differentiation","confidence":"Medium","confidence_rationale":"Tier 2 — orthogonal approaches (RNA, protein, pharmacological inhibition), single lab","pmids":["9563849"],"is_preprint":false},{"year":1997,"finding":"p130 and p107 use a conserved amino-terminal domain to inhibit cyclin A-cdk2 and cyclin E-cdk2 kinase activities; reconstituted p107-cyclin-cdk2 complexes with purified recombinant proteins exhibit stoichiometric kinase inhibition not due to substrate competition or cdk2 activation loss. Endogenous p130-cyclin A-cdk2 complexes purified from human cells also show low kinase activity augmented by dissociation of p130.","method":"Reconstitution with purified recombinant proteins, in vitro kinase assays, purification of endogenous complexes from human cells","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 — biochemical reconstitution with purified components plus endogenous complex validation","pmids":["9199292"],"is_preprint":false},{"year":1998,"finding":"p107 is a bona fide inhibitor of cyclin A-cdk2 and cyclin E-cdk2 with a Ki comparable to p21/WAF1; a second cyclin-binding site maps to the N-terminal domain of p107 (and p130). The N-terminal domain inhibits but is not a good kinase substrate, while the C-terminal cyclin-binding domain is an excellent substrate but not an inhibitor; both domains are needed for full inhibitory activity.","method":"In vitro kinase assays with Ki determination, domain deletion mutants, peptide competition assays, growth suppression assays","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 — quantitative in vitro reconstitution with mechanistic domain dissection","pmids":["9710622"],"is_preprint":false},{"year":1998,"finding":"HDAC1 interacts with p107 (and p130) through an LXCXE-like motif; adenovirus E1A competes with HDAC1 for p107 interaction. p107 can simultaneously interact with HDAC1 and E2F-4, and histone deacetylase activity is required for p107-induced repression of E2F-4, indicating p107 represses E2F through HDAC1 recruitment.","method":"Co-immunoprecipitation in live cells, competition assays with E1A, histone deacetylase inhibitor treatment, reporter assays","journal":"Proceedings of the National Academy of Sciences","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP with competition and functional inhibition assays, multiple orthogonal methods","pmids":["9724731"],"is_preprint":false},{"year":1999,"finding":"A novel PP2A regulatory subunit PR59 specifically associates with p107 (not pRB) in vivo and is a genuine PP2A holoenzyme component. Elevated PR59 expression causes p107 dephosphorylation (not pRB dephosphorylation) and G1 arrest, identifying a p107-specific PP2A holoenzyme that targets p107 for dephosphorylation and activation.","method":"Co-immunoprecipitation, isolation of PR59 by virtue of p107 association, over-expression, cell cycle analysis (FACS)","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 2 — novel subunit identified and functionally validated with specificity demonstrated","pmids":["9927208"],"is_preprint":false},{"year":1999,"finding":"C/EBPalpha controls the composition of E2F complexes by interacting with p107 and disrupting p107-containing S-phase E2F complexes; a region of C/EBPalpha with E2F sequence similarity is sufficient for disruption. This occurs through protein–protein interaction (not DNA binding), and purified His-C/EBPalpha can directly disrupt p107/E2F complexes in vitro.","method":"Co-immunoprecipitation, in vitro complex disruption with purified proteins, C/EBPalpha knockout mouse liver analysis, gel mobility shift assay","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 — purified protein disruption assay plus in vivo genetic validation","pmids":["10082561"],"is_preprint":false},{"year":1999,"finding":"UV irradiation induces rapid dephosphorylation of p107 and an increase in p107/E2F repressor complexes in a PP2A-dependent manner; phosphatase inhibitors (calyculin A, okadaic acid) abolish UV-mediated dephosphorylation, overexpression of specific PP2A B subunits interferes with dephosphorylation, and p107 can be dephosphorylated in vitro with PP2A. This occurs independently of p53 and p21.","method":"UV irradiation, phosphatase inhibitor treatment, PP2A B-subunit overexpression, in vitro dephosphorylation with purified PP2A, p53/p21 knockout cells","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 1 — in vitro dephosphorylation plus multiple complementary in vivo approaches","pmids":["9989818"],"is_preprint":false},{"year":1999,"finding":"HCMV IE1-72 protein binds to the N-terminal portion of p107 (not the C-terminal pocket) through exons 2 and 3 of IE1-72, and this interaction relieves p107-mediated transcriptional repression of E2F-responsive promoters but not Rb-mediated repression. IE1-72 alone can overcome p107-mediated growth arrest in a manner dependent on the physical interaction.","method":"Co-immunoprecipitation, in vitro reconstitution with reticulocyte-translated proteins, domain deletion mutants, reporter assays, growth arrest assays","journal":"Journal of virology / Journal of general virology","confidence":"High","confidence_rationale":"Tier 2 — domain mapping with domain mutants, in vitro reconstitution, and functional validation","pmids":["8892909","10355776"],"is_preprint":false},{"year":2000,"finding":"E2F and pRB-family protein occupancy at target gene promoters is dynamically regulated in vivo: in quiescent cells, promoters are occupied by E2F-4 and p130; by late G1, p130 and E2F-4 are replaced by E2F-1 and E2F-3. p107 appears at promoters associated with activation. Low histone acetylation correlates with p130/E2F-4 repression; histone acetylation increases with gene activation.","method":"Chromatin immunoprecipitation (ChIP) in synchronized living cells, histone acetylation analysis","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 — direct ChIP evidence of promoter occupancy dynamics in vivo, landmark study","pmids":["10766737"],"is_preprint":false},{"year":2000,"finding":"pRB and p107 have opposing roles in adipocyte differentiation: p107 loss lowers the requirement for the differentiation factor PPARgamma and pRB-deficient cells exhibit differentiation defects. pRB (not p107) is required for cell cycle exit and potentiates C/EBPalpha activity, while p107 does not affect C/EBPalpha-driven transcription.","method":"3T3 fibroblasts from single and double knockout mice, adipogenesis assays, overexpression experiments, reporter assays","journal":"Proceedings of the National Academy of Sciences","confidence":"Medium","confidence_rationale":"Tier 2 — genetic cell biology with mechanistic dissection, single lab","pmids":["10995476"],"is_preprint":false},{"year":2002,"finding":"Smad3 mediates TGFbeta-induced repression of c-myc through a pre-formed cytoplasmic complex containing Smad3, E2F4/5, DP1, and the corepressor p107. In response to TGFbeta, this complex translocates to the nucleus, associates with Smad4, and recognizes a composite Smad-E2F site on the c-myc promoter for repression, revealing p107 as a TGFbeta signal transducer upstream of CDK.","method":"Co-immunoprecipitation, subcellular fractionation, chromatin immunoprecipitation, reporter assays, dominant-negative experiments","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods including ChIP and subcellular fractionation, high-impact replicated finding","pmids":["12150994"],"is_preprint":false},{"year":2002,"finding":"Cyclin D1/Cdk4 directly phosphorylates p107 at four specific sites (Thr-369, Ser-640, Ser-964, Ser-975) identified by in vitro and in vivo phosphorylation mapping; mutation of these four sites renders p107 refractory to inactivation by cyclin D1/Cdk4. The RXL motif of p107 is required for Cdk4-mediated phosphorylation of S640 by facilitating phosphorylation of nonconsensus Cdk substrates.","method":"In vitro phosphorylation with purified kinases, site-directed mutagenesis, cell cycle arrest assays, mass spectrometry phosphopeptide mapping","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 — in vitro kinase assays with site-directed mutagenesis and in vivo validation, comprehensive","pmids":["11884610"],"is_preprint":false},{"year":2002,"finding":"p107 and p130 coordinately regulate chondrocyte proliferation, Cbfa1 expression, and hypertrophic differentiation during endochondral bone development; p107 is required in prechondrogenic condensations for cell cycle withdrawal, while both p107 and p130 contribute to chondrocyte cell cycle exit and Cbfa1-dependent terminal differentiation. Cbfa1 expression and hypertrophic differentiation occur only in cells that have undergone p107/p130-mediated proliferative arrest.","method":"Analysis of p107/p130 knockout mice, immunohistochemistry, in situ hybridization, BrdU labeling","journal":"Developmental biology","confidence":"Medium","confidence_rationale":"Tier 2 — in vivo genetic analysis with defined cellular/molecular phenotypes, single lab","pmids":["12086466"],"is_preprint":false},{"year":2002,"finding":"FGF signaling targets p107 and p130 (but not pRB) to induce chondrocyte growth arrest: FGF causes rapid dephosphorylation of all three Rb-family proteins, but p107/p130-double-null chondrocytes fail to respond to FGF growth inhibition while Rb-null chondrocytes respond normally. A PyLT mutant that binds pRB but not p107/p130 cannot rescue FGF resistance.","method":"Chondrocyte cell lines, PyLT mutant expression, p107/p130 knockout MEF micromass cultures, metatarsal organ culture, BrdU labeling","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis with molecular and cellular readouts, multiple complementary approaches","pmids":["12177046"],"is_preprint":false},{"year":2003,"finding":"Oxidative stress (H2O2) induces rapid dephosphorylation of pRB, p107, and p130 via protein phosphatase 2A (PP2A); PP2A core enzyme physically interacts with pRB and p107 in both treated and untreated cells, pRB-associated PP2A activity is enhanced by H2O2, and SV40 small t antigen (PP2A inhibitor) blocks H2O2-induced dephosphorylation and prevents DNA synthesis inhibition.","method":"Phosphatase inhibitor treatment (okadaic acid, calyculin A), SV40 small t antigen overexpression (wild-type and PP2A-binding mutant), co-immunoprecipitation of PP2A with p107","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — multiple complementary approaches including binding mutant controls","pmids":["12621062"],"is_preprint":false},{"year":2004,"finding":"A dynamic equilibrium between CDKs and PP2A modulates phosphorylation of p107 throughout the cell cycle; PP2A catalytic subunit specifically interacts with p107 and p130 (co-immunoprecipitation), and PP2A inhibition (by SV40 small t, okadaic acid at PP2A-selective concentrations, or calyculin A) prevents cycloheximide- and flavopiridol-induced dephosphorylation of pocket proteins.","method":"CDK inhibitor treatment (flavopiridol), cycloheximide, phosphatase inhibitors, PP2A holoenzyme manipulation, SV40 small t overexpression, co-immunoprecipitation","journal":"Cell cycle","confidence":"High","confidence_rationale":"Tier 2 — multiple pharmacological and genetic approaches in concert","pmids":["15467457"],"is_preprint":false},{"year":2004,"finding":"RBL1 (p107) together with RB1 and RBL2 is required for constitutive heterochromatin formation; triple-knockout (TKO) MEFs show decreased DNA methylation, increased H3 acetylation, and decreased H4K20 trimethylation at pericentric and telomeric chromatin. RB1 family proteins directly interact with the H4K20 tri-methylating enzymes Suv4-20h1 and Suv4-20h2, independent of E2F function.","method":"Triple-knockout MEFs, chromatin immunoprecipitation, co-immunoprecipitation with Suv4-20h enzymes, histone modification analysis","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 2 — genetic model with ChIP and Co-IP, novel E2F-independent function defined","pmids":["15750587"],"is_preprint":false},{"year":2004,"finding":"Rb/p107 loss in the retina does not affect progenitor proliferation or cell specification but perturbs cell cycle exit in all seven retinal precursor types; only three precursors survive and arrest via terminal differentiation, while tumors arise from intrinsically death-resistant precursors with extended (not infinite) proliferative capacity.","method":"Conditional Cre-mediated knockout of Rb/p107, BrdU labeling, retinal cell-type marker analysis, apoptosis assays","journal":"Cancer cell","confidence":"Medium","confidence_rationale":"Tier 2 — in vivo genetic analysis with defined cellular phenotypes, single lab","pmids":["15193257"],"is_preprint":false},{"year":2005,"finding":"p107 regulates white versus brown adipocyte fate by repressing PGC-1alpha: p107-null mice exhibit uniform replacement of white adipose tissue with brown adipose tissue containing elevated PGC-1alpha and UCP-1. p107−/− WAT contains reduced pRb levels. pRb (but not p107) directly binds the PGC-1alpha promoter and represses its transcription.","method":"p107-knockout mice, ChIP for pRb at PGC-1alpha promoter, Cre-mediated Rb deletion in primary preadipocytes, differentiation assays","journal":"Cell metabolism","confidence":"Medium","confidence_rationale":"Tier 2 — in vivo genetic model with ChIP and ex vivo functional assays, single lab","pmids":["16271529"],"is_preprint":false},{"year":2005,"finding":"p107 inhibits G1-to-S-phase progression by down-regulating expression of the F-box protein Skp2, leading to p27 stabilization and Cdk2 inhibition; reciprocally, Skp2 accumulates to higher levels in p107-null fibroblasts, and ectopic Skp2 rescues the p27 and DNA synthesis defects caused by p107 overexpression.","method":"p107 overexpression and p107-knockout fibroblasts, Skp2 re-expression rescue, p27 stability assays, Cdk2 activity assays, FACS","journal":"The Journal of cell biology","confidence":"Medium","confidence_rationale":"Tier 2 — genetic and rescue experiments with defined biochemical readouts, single lab","pmids":["15631990"],"is_preprint":false},{"year":2005,"finding":"p130 and p107 play a key role in transcriptional repression of G2/M genes following DNA damage; p130/p107 loss partially abrogates repression of plk1 after adriamycin treatment, and loss of all three RB-family proteins abolishes G2 arrest, indicating p107 specifically contributes to G2/M gene repression and cell cycle exit from G2 in response to DNA damage.","method":"RB-family knockout MEFs, gene expression profiling after DNA damage, FACS for G2 arrest, adriamycin treatment","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 — genetic dissection with transcriptomic and cell cycle readouts, single lab","pmids":["15827088"],"is_preprint":false},{"year":2007,"finding":"Mammalian Mip/LIN-9 forms a repressor complex with E2F4 and p107 (or p130) in G0/early G1, and in late G1/S switches to associating with B-Myb; CDK4-mediated phosphorylation of p107/p130 drives the separation. p107 within the Mip/LIN-9 complex blocks cyclin B promoter activation by B-Myb and Mip/LIN-9, taking functional precedence over the transcriptional activation complex.","method":"Co-immunoprecipitation in cell-cycle-synchronized cells, reporter assays with dominant-negative CDK4","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 — cell-cycle-phase-specific Co-IP with functional reporter validation, single lab","pmids":["17563750"],"is_preprint":false},{"year":2007,"finding":"p107 represses transcription at the Hes1 promoter, which normally promotes neural precursor self-renewal; p107-null mice show enhanced Hes1 levels and an expanded neural precursor pool but with reduced cortical neuron numbers and reduced neurogenesis rate. Loss of one Hes1 allele rescues neural precursor numbers and neurogenesis in p107-null brains.","method":"p107-knockout mice, Hes1/p107 compound knockout, neurosphere assays, neuronal birthdating (BrdU/EdU), reporter assays for Hes1 promoter","journal":"The Journal of cell biology","confidence":"Medium","confidence_rationale":"Tier 2 — genetic epistasis in vivo with defined neurogenic phenotype, single lab","pmids":["17591923"],"is_preprint":false},{"year":2008,"finding":"PP2A mediates p107 dephosphorylation as a key event in FGF-induced chondrocyte growth arrest; overexpression of cyclin D1/cdk4 prevents FGF-induced p107 dephosphorylation and growth arrest; SV40 small T antigen expression or siRNA knockdown of PP2A catalytic subunit also prevents p107 dephosphorylation and FGF-induced arrest; FGF treatment induces an association between p107 and PP2A.","method":"Cyclin D1/cdk4 overexpression, SV40 small T antigen expression, siRNA knockdown of PP2A, co-immunoprecipitation of p107 and PP2A, growth arrest assays","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 — multiple complementary approaches including siRNA, pharmacological inhibition, and Co-IP","pmids":["18927618"],"is_preprint":false},{"year":2009,"finding":"p107 and p130 associate with E2F target gene promoters by chromatin immunoprecipitation; GFP-tagged pRB shows similar nuclear dynamics to p107 and p130 by live-cell fluorescence imaging. Using anti-GFP antibody ChIP, RB association with target promoters is demonstrable, and direct RB phosphorylation disrupts promoter association, analogous to p107/p130 regulation.","method":"GFP-tagged protein live-cell imaging, FRAP, chromatin immunoprecipitation with multiple antibody approaches, phosphorylation mutant analysis","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — live imaging plus ChIP with multiple antibody validation, single lab","pmids":["19279001"],"is_preprint":false},{"year":2010,"finding":"B55alpha-containing PP2A holoenzymes play a major role in restricting p107 phosphorylation and inducing p107 activation; targeted selectivity exists in the interaction of pocket proteins with distinct PP2A holoenzymes, with B55alpha specifically targeting p107 over pRB.","method":"PP2A holoenzyme purification, co-immunoprecipitation, overexpression and knockdown of B55alpha, phosphorylation state analysis of p107","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — biochemical identification of specific PP2A holoenzyme with functional validation, single lab","pmids":["20663872"],"is_preprint":false},{"year":2013,"finding":"MAGE-A11 interacts with p107 and inhibits p107 ubiquitination to stabilize it; MAGE-A11 links p107 to hypophosphorylated E2F1, stabilizing and activating E2F1. At low MAGE-A11, this interaction causes transcriptional repression; at higher MAGE-A11 (as in prostate cancer), p107 is converted from a transcriptional repressor to a transcriptional activator of androgen receptor and E2F1 targets.","method":"Co-immunoprecipitation, ubiquitination assays, siRNA knockdown, reporter assays, p107/MAGE-A11 interaction domain mapping","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP with functional validation and domain mapping, single lab","pmids":["23853093"],"is_preprint":false},{"year":2016,"finding":"CRISPR/Cas9-mediated knockout of rb1 and rbl1 (p107) together (but not either alone) in Xenopus tropicalis causes rapid development of retinoblastoma, confirming that the cooperative tumor suppressor function of RB1 and RBL1 demonstrated in mice is conserved in a non-mammalian vertebrate and validating Xenopus as a retinoblastoma model.","method":"CRISPR/Cas9 mosaic knockout in Xenopus tropicalis, tumor histopathology, ophthalmoscopy","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 — in vivo genetic loss-of-function with tumor phenotype, ortholog model","pmids":["27739525"],"is_preprint":false},{"year":2019,"finding":"Following p53 activation by DNA damage, p130 and RB cooperate to repress G1/S genes, while G2/M genes are repressed specifically by p130 and p107 (not RB) through the DREAM complex (p107-DREAM and p130-DREAM); p107 contributes to G1/S gene repression only in the absence of RB and p130, demonstrating distinct and specific roles for each family member in damage-induced gene repression.","method":"Gene expression profiling in primary human fibroblasts, shRNA knockdown of individual RB family members, DNA damage treatment (doxorubicin), cell cycle analysis","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 2 — comprehensive genome-wide analysis in primary cells with individual and combined knockdowns","pmids":["31667499"],"is_preprint":false},{"year":2011,"finding":"A systematic screen identified p107 as a CDK4/6 substrate; the DREAM complex containing p107 mediates cell cycle gene repression. CDK4/6 phosphorylate p107 along with FOXM1 to control cell cycle entry and senescence suppression.","method":"Systematic CDK4/6 substrate screen, mass spectrometry phosphoproteomics","journal":"Cancer cell","confidence":"Low","confidence_rationale":"Tier 3 — systematic screen without specific p107 mechanistic follow-up in this paper","pmids":["22094256"],"is_preprint":false}],"current_model":"RBL1 (p107) is a nuclear pocket protein that suppresses cell proliferation primarily by binding and repressing the E2F4/5 transcription factors in a cell-cycle-regulated manner: in G0/early G1, a pre-formed cytoplasmic complex of p107–E2F4/5–DP1 can translocate to the nucleus in response to TGFbeta-Smad signaling to repress c-myc; as cells enter S phase, p107 forms complexes with cyclin E–CDK2 (in G1) and cyclin A–CDK2 (in S) that directly inhibit these kinases and phosphorylate p107's own RXL-motif sites via cyclin D1–CDK4 to disrupt E2F4 association; p107 also recruits HDAC1 to repress E2F target genes, interacts with Myc, B-MYB, Sp1, TFIIIB, and Suv4-20h enzymes to regulate transcription and heterochromatin, and is reactivated by PP2A holoenzymes (including B55α-PP2A and PR59-PP2A) that specifically dephosphorylate it in response to DNA damage, UV, FGF signaling, or oxidative stress, collectively placing p107 as a context-specific integrator of mitogenic, DNA damage, and differentiation signals that coordinates cell cycle exit."},"narrative":{"teleology":[{"year":1991,"claim":"Identification of p107 as a second member of the retinoblastoma protein family resolved how viral oncoproteins such as SV40 large T and E1A engage multiple pocket-domain targets, establishing that cell-cycle control involves more than one RB-like repressor.","evidence":"cDNA cloning, chromosomal mapping, and domain-deletion binding assays in human cells","pmids":["1833063"],"confidence":"High","gaps":["No cellular function yet ascribed beyond viral oncoprotein binding","No E2F interaction or cell-cycle role demonstrated"]},{"year":1992,"claim":"Discovery that p107 forms complexes with cyclin A, cyclin E, CDK2, and E2F at distinct cell-cycle phases—while RB–E2F complexes predominate in G1—established that the two pocket proteins partition E2F regulation temporally through the cell cycle.","evidence":"Reciprocal co-immunoprecipitation, gel mobility shift assays, and cell-cycle synchronization across multiple independent laboratories","pmids":["1532457","1531040","1398067"],"confidence":"High","gaps":["Identity of the specific E2F species bound by p107 not yet resolved","Mechanism of transcriptional repression unknown"]},{"year":1994,"claim":"Identification of E2F-4 as the principal p107-associated E2F, combined with the demonstration that p107 binds and suppresses c-Myc transactivation through a distinct mechanism from RB, revealed that p107 channels growth-suppressive signals through specific transcription factor targets.","evidence":"cDNA cloning of E2F-4, co-immunoprecipitation, transformation assays, c-Myc reporter assays, and growth-arrest rescue experiments","pmids":["7958925","8146655","8319904"],"confidence":"High","gaps":["Whether p107–E2F4 and p107–Myc complexes coexist or are mutually exclusive unclear","Chromatin-level mechanism of repression not addressed"]},{"year":1995,"claim":"Biochemical dissection showed p107 contains two separable growth-suppression domains—a pocket that represses E2F and a p21-like N-terminal domain that directly inhibits cyclin A/E–CDK2 kinase activity—establishing p107 as both a transcriptional repressor and a stoichiometric CDK inhibitor.","evidence":"In vitro kinase assays with Ki determination, domain-deletion structure–function analysis, competitive binding with p21, growth-suppression assays","pmids":["7622038","7743997","9710622"],"confidence":"High","gaps":["Structural basis for simultaneous CDK inhibition and E2F repression unknown","Relative contribution of each domain in physiological contexts untested"]},{"year":1996,"claim":"Cyclin D1–CDK4 was identified as the kinase that phosphorylates p107 in mid-G1 to dissociate E2F-4, while p107/p130 double-knockout mice revealed functional redundancy in limb development and showed that single knockouts are viable—defining CDK4 as the upstream activating kinase and p130 as the primary compensating family member.","evidence":"Cell synchronization, kinase assays, dominant-negative CDK4, and gene-targeted knockout mice with histological analysis","pmids":["7797074","8682294","8682293"],"confidence":"High","gaps":["Specific phosphorylation sites not yet mapped","Redundancy versus specificity in non-skeletal tissues unresolved"]},{"year":1998,"claim":"Discovery that p107 recruits HDAC1 through an LXCXE-like motif to repress E2F-4 target genes provided the first chromatin-modifying mechanism through which p107 silences transcription, explaining how viral E1A displaces HDAC1 to de-repress targets.","evidence":"Co-immunoprecipitation, E1A competition assays, TSA treatment, and E2F-4-dependent reporter assays","pmids":["9724731"],"confidence":"High","gaps":["Whether additional chromatin remodelers are recruited alongside HDAC1 unknown","Genome-wide target specificity of HDAC1 recruitment not tested"]},{"year":1999,"claim":"Identification of PP2A as the phosphatase that dephosphorylates and reactivates p107 in response to UV irradiation—independently of p53/p21—and the discovery of the p107-specific PP2A subunit PR59 established a CDK-opposing phosphatase axis that rapidly reactivates p107 under stress.","evidence":"UV irradiation in p53/p21-null cells, phosphatase inhibitors (okadaic acid, calyculin A), in vitro dephosphorylation with purified PP2A, PR59 co-immunoprecipitation and overexpression","pmids":["9989818","9927208"],"confidence":"High","gaps":["Whether PR59-PP2A is the UV-responsive holoenzyme or another B subunit is involved not determined","Structural basis for PR59 selectivity for p107 over RB unknown"]},{"year":2002,"claim":"The finding that a preformed cytoplasmic Smad3–E2F4/5–DP1–p107 complex translocates to the nucleus upon TGFβ signaling to repress c-myc placed p107 as a direct signal transducer of TGFβ upstream of CDK regulation, while concurrent mapping of four CDK4 phosphorylation sites (T369, S640, S964, S975) defined the molecular switch for p107 inactivation.","evidence":"Co-immunoprecipitation, subcellular fractionation, ChIP on c-myc promoter, in vitro kinase assays with site-directed mutagenesis and mass spectrometry","pmids":["12150994","11884610"],"confidence":"High","gaps":["How cytoplasmic pre-assembly is regulated prior to TGFβ stimulation unknown","Whether phosphorylation at all four sites is required simultaneously or sequentially untested in vivo"]},{"year":2004,"claim":"Demonstration that RB-family proteins including p107 recruit Suv4-20h methyltransferases to maintain H4K20me3 at pericentric and telomeric heterochromatin—independently of E2F—expanded p107's role beyond E2F-dependent gene regulation to constitutive heterochromatin maintenance.","evidence":"Triple-knockout MEFs, ChIP for histone modifications, co-immunoprecipitation with Suv4-20h1/h2","pmids":["15750587"],"confidence":"High","gaps":["Relative contribution of p107 versus RB versus p130 to heterochromatin maintenance not individually resolved","Whether this function is dispensable in p107-single-null cells unclear due to redundancy"]},{"year":2005,"claim":"In vivo genetic studies revealed tissue-specific roles: p107 loss converts white adipose to brown adipose with elevated PGC-1α/UCP-1, while p107 represses Hes1 to limit neural precursor self-renewal—demonstrating that p107 controls fate decisions beyond generic cell-cycle arrest.","evidence":"p107-knockout mice, adipogenesis assays, Hes1/p107 compound knockout, neurosphere assays, BrdU labeling","pmids":["16271529","17591923"],"confidence":"Medium","gaps":["Whether PGC-1α repression is direct or indirect through pRb level changes not fully resolved","Molecular mechanism linking p107 to Hes1 promoter repression (direct binding vs. E2F) not defined"]},{"year":2019,"claim":"Genome-wide expression profiling after individual and combined RB-family knockdowns in DNA-damaged human fibroblasts established that p107 specifically represses G2/M genes through the DREAM complex (with p130), while G1/S gene repression depends on p130 and RB—resolving the division of labor among pocket proteins in the DNA-damage response.","evidence":"shRNA knockdown of individual RB family members in primary human fibroblasts, doxorubicin treatment, genome-wide gene expression profiling","pmids":["31667499"],"confidence":"High","gaps":["Whether DREAM complex composition shifts during prolonged damage signaling untested","ChIP-seq for p107-DREAM occupancy at G2/M promoters in damage conditions not performed"]},{"year":null,"claim":"Key unresolved questions include the structural basis for p107's simultaneous CDK inhibition and E2F repression, the relative in vivo contributions of individual PP2A holoenzymes to p107 reactivation in different stress contexts, and whether p107's heterochromatin and DREAM functions are mechanistically linked.","evidence":"","pmids":[],"confidence":"Low","gaps":["No crystal structure of full-length p107 or p107–E2F4–CDK2 ternary complex","Genome-wide ChIP-seq for endogenous p107 across cell-cycle phases in primary cells lacking","Tissue-specific tumor suppressor function of p107 independent of RB not demonstrated in human cancers"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[4,6,11,26,35,42]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[14,33,34]},{"term_id":"GO:0042393","term_label":"histone binding","supporting_discovery_ids":[48]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[40,42,48,56]},{"term_id":"GO:0005654","term_label":"nucleoplasm","supporting_discovery_ids":[40,56]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[42]}],"pathway":[{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[2,3,14,16,28,43,60,61]},{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[35,48]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[4,6,9,26,42]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[42,45]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[38,52,60]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[23,44,54]}],"complexes":["DREAM complex","p107–E2F4/5–DP1","Smad3–E2F4/5–DP1–p107"],"partners":["E2F4","CCNA2","CDK2","HDAC1","SMAD3","MYC","MYBL2","PPP2CA"],"other_free_text":[]},"mechanistic_narrative":"RBL1 (p107) is a nuclear pocket protein that restrains cell proliferation by binding and repressing E2F4/5 transcription factors in a cell-cycle-regulated manner, recruiting HDAC1 to silence E2F target genes, and directly inhibiting cyclin A–CDK2 and cyclin E–CDK2 kinase activity with a Ki comparable to p21 [PMID:1833063, PMID:9710622, PMID:9724731]. Phosphorylation by cyclin D1–CDK4 at four specific sites dissociates p107 from E2F4 and releases the G1 block, while PP2A holoenzymes containing B55α or PR59 dephosphorylate and reactivate p107 in response to UV, DNA damage, FGF, and oxidative stress [PMID:11884610, PMID:9927208, PMID:9989818, PMID:18927618]. Beyond canonical E2F repression, p107 participates in TGFβ-Smad3–mediated c-myc silencing through a preformed cytoplasmic Smad3–E2F4/5–DP1–p107 complex that translocates to the nucleus, represses RNA polymerase III via TFIIIB interaction, contributes to constitutive heterochromatin maintenance through Suv4-20h enzymes, and cooperates with p130 in the DREAM complex to repress G2/M genes after DNA damage [PMID:12150994, PMID:10330166, PMID:15750587, PMID:31667499]. In vivo, p107 is functionally redundant with p130 in chondrocyte growth arrest and endochondral bone development, collaborates with RB1 to enforce retinal cell cycle exit—combined loss causes retinoblastoma in mice and Xenopus—and regulates white-to-brown adipocyte fate and neural precursor self-renewal through Hes1 repression [PMID:8682294, PMID:15193257, PMID:27739525, PMID:16271529, PMID:17591923]."},"prefetch_data":{"uniprot":{"accession":"P28749","full_name":"Retinoblastoma-like protein 1","aliases":["107 kDa retinoblastoma-associated protein","p107","pRb1"],"length_aa":1068,"mass_kda":120.8,"function":"Key regulator of entry into cell division (PubMed:17671431). Directly involved in heterochromatin formation by maintaining overall chromatin structure and, in particular, that of constitutive heterochromatin by stabilizing histone methylation (By similarity). Recruits and targets histone methyltransferases KMT5B and KMT5C, leading to epigenetic transcriptional repression (By similarity). Controls histone H4 'Lys-20' trimethylation (By similarity). Probably acts as a transcription repressor by recruiting chromatin-modifying enzymes to promoters (By similarity). Potent inhibitor of E2F-mediated trans-activation (PubMed:8319904). May act as a tumor suppressor (PubMed:8319904)","subcellular_location":"Nucleus","url":"https://www.uniprot.org/uniprotkb/P28749/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/RBL1","classification":"Not Classified","n_dependent_lines":2,"n_total_lines":1208,"dependency_fraction":0.0016556291390728477},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"CDK2","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/RBL1","total_profiled":1310},"omim":[{"mim_id":"621288","title":"LIN52 DREAM MUVB CORE COMPLEX COMPONENT; LIN52","url":"https://www.omim.org/entry/621288"},{"mim_id":"621287","title":"LIN37 DREAM MUVB CORE COMPLEX COMPONENT; LIN37","url":"https://www.omim.org/entry/621287"},{"mim_id":"618055","title":"CELLULAR REPRESSOR OF E1A-STIMULATED GENES 1; CREG1","url":"https://www.omim.org/entry/618055"},{"mim_id":"617108","title":"SESSILE SERRATED POLYPOSIS CANCER SYNDROME; SSPCS","url":"https://www.omim.org/entry/617108"},{"mim_id":"616714","title":"HMG-BOX TRANSCRIPTION FACTOR 1; HBP1","url":"https://www.omim.org/entry/616714"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Nucleoplasm","reliability":"Enhanced"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"bone marrow","ntpm":13.7}],"url":"https://www.proteinatlas.org/search/RBL1"},"hgnc":{"alias_symbol":["p107","cp107","PRB1"],"prev_symbol":[]},"alphafold":{"accession":"P28749","domains":[{"cath_id":"1.10.472.10","chopping":"2-115","consensus_level":"medium","plddt":81.915,"start":2,"end":115},{"cath_id":"1.10.472.10","chopping":"387-565","consensus_level":"high","plddt":90.6013,"start":387,"end":565},{"cath_id":"1.10.472.10","chopping":"567-598_782-891_924-972","consensus_level":"medium","plddt":88.6232,"start":567,"end":972},{"cath_id":"1.10.472","chopping":"118-153_168-319","consensus_level":"medium","plddt":90.4585,"start":118,"end":319}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P28749","model_url":"https://alphafold.ebi.ac.uk/files/AF-P28749-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P28749-F1-predicted_aligned_error_v6.png","plddt_mean":71.75},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=RBL1","jax_strain_url":"https://www.jax.org/strain/search?query=RBL1"},"sequence":{"accession":"P28749","fasta_url":"https://rest.uniprot.org/uniprotkb/P28749.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P28749/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P28749"}},"corpus_meta":[{"pmid":"1531040","id":"PMC_1531040","title":"The 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The p107-containing complex also includes p33cdk2.\",\n      \"method\": \"Co-immunoprecipitation, gel mobility shift assay\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, replicated across multiple labs in same year\",\n      \"pmids\": [\"1531040\", \"1530885\", \"1532457\", \"1532458\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"Cyclin A binds specifically to the p107 pocket domain (the unique spacer sequence between A and B subdomains), but does not bind the analogous region of RB, indicating a structural basis for differential cyclin association.\",\n      \"method\": \"In vitro binding assay with pocket domain fragments, co-immunoprecipitation\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — domain mapping with recombinant proteins, two independent labs\",\n      \"pmids\": [\"1532457\", \"1532458\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"Cyclin E/cdk2 associates with p107 and E2F specifically during G1 phase, while cyclin A/cdk2 associates with p107 and E2F at G1/S; these two distinct p107 complexes appear in a temporally regulated fashion during the cell cycle.\",\n      \"method\": \"Co-immunoprecipitation with cyclin-specific antisera, cell synchronization\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP with temporal resolution, replicated\",\n      \"pmids\": [\"1398067\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"p107 inhibits E2F-dependent transcription in co-transfection assays, functioning as a transcriptional repressor when associated with E2F at target promoters.\",\n      \"method\": \"Transient transfection reporter assay, co-immunoprecipitation\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — functional reporter assay replicated by multiple labs\",\n      \"pmids\": [\"8458319\", \"7685208\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"Overexpression of p107 inhibits cell proliferation, arresting sensitive cells in G1; this growth suppression is mechanistically distinct from pRB-mediated arrest, as certain cell lines and mutants show differential responses.\",\n      \"method\": \"Overexpression in cell lines, cell cycle analysis (flow cytometry), mutant analysis\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — loss/gain of function with clear mechanistic distinction from pRB, replicated\",\n      \"pmids\": [\"8319904\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"E2F-4 is a specific in vivo binding partner of p107 (not pRB), forming a complex with p107 throughout the cell cycle; p107 binding suppresses E2F-4 transcriptional activity and transformation capacity.\",\n      \"method\": \"Co-immunoprecipitation, transient transfection reporter assay, transformation assay\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP plus functional assay, replicated by two independent labs\",\n      \"pmids\": [\"7958925\", \"7958924\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"p107 directly binds to the N-terminal transactivation domain of c-Myc in vivo and suppresses Myc transcriptional activation activity; this interaction is disrupted by Burkitt lymphoma-associated Myc mutations.\",\n      \"method\": \"cDNA library screen with Myc fusion protein, co-immunoprecipitation, transient transfection reporter assay\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo Co-IP plus functional reporter assay, replicated by second lab\",\n      \"pmids\": [\"8146655\", \"8076603\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Cyclin D1/cdk4 phosphorylates p107 in vivo beginning in mid-G1, and this phosphorylation causes dissociation of p107 from E2F-4, inactivating the p107-E2F repressor complex; a dominant-negative cdk4 abolishes p107 phosphorylation.\",\n      \"method\": \"In vivo phosphorylation assay, dominant-negative cdk4 expression, co-immunoprecipitation\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vivo kinase assay with genetic validation (DN-cdk4), replicated\",\n      \"pmids\": [\"7797074\", \"8643455\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"p107 contains a cyclin-binding domain structurally and functionally related to the p21 CIP/KIP family of cdk inhibitors; p107 can inhibit cyclin A/cdk2 and cyclin E/cdk2 kinase activity, and association of p107 or p21 with these complexes is mutually exclusive.\",\n      \"method\": \"In vitro kinase inhibition assay, co-immunoprecipitation, competition assay\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution plus mutagenesis, replicated\",\n      \"pmids\": [\"7622038\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"p107 contains two independent growth suppression domains: one mediating E2F interaction (pocket domain) and one mediating cyclin A/E binding; in C33A cells resistant to pRB, only the cyclin-binding domain is active as a growth suppressor.\",\n      \"method\": \"Structure-function analysis with deletion mutants, growth arrest assays, co-expression\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — domain mapping with multiple deletion mutants, functional validation in multiple cell lines\",\n      \"pmids\": [\"7743997\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"p107 associates with the transcription factor Sp1 in vivo and represses Sp1-dependent transcription; this repression is mechanistically distinct from E2F repression and does not require an intact pocket domain.\",\n      \"method\": \"Co-immunoprecipitation, transient transfection reporter assay with Gal4-Sp1 chimeras, deletion mapping\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP plus functional reporter assay in single lab\",\n      \"pmids\": [\"7565695\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"The p107 promoter contains two E2F binding sites; pRB and p107 itself can repress the p107 promoter via the 5' (upstream) E2F site, establishing an autoregulatory feedback loop.\",\n      \"method\": \"Promoter deletion/mutagenesis analysis, transient transfection reporter assay\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — systematic mutagenesis with reporter assay in single lab\",\n      \"pmids\": [\"7791762\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"E2F-4 is sequestered by p130 in arrested cells; as cells enter S phase, p107 levels increase and E2F-4 redistributes to associate with p107 (and pRB), demonstrating cell-cycle-regulated switching of E2F-4 among pocket protein partners.\",\n      \"method\": \"Cell synchronization, co-immunoprecipitation with specific antisera, flow cytometry\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — systematic cell-cycle analysis with specific antibodies, strong temporal resolution\",\n      \"pmids\": [\"8657117\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"p107 binds B-MYB in vivo through its pocket and C-terminal domain, and suppresses B-MYB autoregulatory transactivation; B-MYB can in turn overcome p107-induced growth arrest.\",\n      \"method\": \"Co-immunoprecipitation, transient transfection reporter assay with deletion constructs\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — Co-IP plus functional reporter assay, single lab\",\n      \"pmids\": [\"8910512\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"p107 and p130 stoichiometrically inhibit cyclin A-cdk2 and cyclin E-cdk2 kinase activity in vitro when reconstituted with purified recombinant proteins; kinase inhibition maps to an N-terminal conserved domain of p107; endogenous p130-cyclin A-cdk2 complexes purified from cells also display low kinase activity that is augmented upon p130 dissociation.\",\n      \"method\": \"In vitro reconstitution with purified proteins, kinase assay, domain deletion analysis, purification of endogenous complexes\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution plus mutagenesis plus validation with endogenous complexes\",\n      \"pmids\": [\"9199292\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"SV40 large T antigen J domain (DnaJ homology region) mediates hyperphosphorylation of p107 and p130 and promotes p130 degradation; J domain is dispensable in MEFs lacking both p107 and p130, establishing that p107/p130 are the relevant J-domain targets for growth advantage.\",\n      \"method\": \"Mutant T antigen expression, western blotting for phosphorylation, genetic epistasis with p107/p130 double-knockout MEFs\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with defined cellular phenotype, multiple mutant analysis\",\n      \"pmids\": [\"9271376\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"p107 acts as a bona fide CDK inhibitor with Ki values comparable to p21/WAF1; two distinct cyclin-binding domains are required for kinase inhibition — the N-terminal domain binds but is not phosphorylated, while the C-terminal domain is an excellent kinase substrate but cannot inhibit.\",\n      \"method\": \"In vitro kinase inhibition assay with Ki determination, domain deletion mutants, peptide competition\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — quantitative in vitro kinase assay with mutagenesis, Ki measurement\",\n      \"pmids\": [\"9710622\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"p107 expression is transcriptionally regulated in a cell-growth-dependent manner via E2F-dependent repression in quiescent cells, contrasting with the posttranslational (proteasomal) regulation of p130; p130 controls p107 expression by maintaining E2F repression.\",\n      \"method\": \"Northern blot, protein stability assay with proteasome inhibitors, promoter reporter assay\",\n      \"journal\": \"Cell growth & differentiation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple methods distinguishing transcriptional vs. posttranslational control, single lab\",\n      \"pmids\": [\"9563849\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"PR59, a novel PP2A regulatory subunit, specifically associates with p107 (not pRB) in vivo and directs PP2A catalytic activity toward p107; elevated PR59 expression causes p107 dephosphorylation and G1 arrest, establishing PP2A-PR59 as a specific p107 phosphatase complex.\",\n      \"method\": \"Yeast two-hybrid, co-immunoprecipitation, western blotting for phosphorylation, overexpression growth arrest assay\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP with functional consequence (dephosphorylation, G1 arrest), specificity demonstrated by comparison to pRB\",\n      \"pmids\": [\"9927208\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"C/EBPalpha physically interacts with p107 and disrupts S-phase-specific E2F-p107 complexes through a protein-protein interaction, leading to reduced E2F-dependent gene expression and hepatocyte growth arrest.\",\n      \"method\": \"Co-immunoprecipitation, gel mobility shift assay, purified protein disruption assay, ectopic expression\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro disruption with purified proteins plus in vivo Co-IP, single lab\",\n      \"pmids\": [\"10082561\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"p107 and p130 repress RNA polymerase III transcription by directly interacting with TFIIIB subunit; endogenous TFIIIB co-fractionates and co-immunoprecipitates with p107 and p130; disruption by HPV E7 or genetic loss of p107/p130 deregulates Pol III activity.\",\n      \"method\": \"Pull-down with recombinant proteins, co-immunoprecipitation, in vitro transcription assay, Pol III activity in knockout MEFs\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro pull-down plus functional transcription assay plus genetic validation in KO cells\",\n      \"pmids\": [\"10330166\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"UV irradiation causes rapid PP2A-dependent dephosphorylation of p107, increasing p107/E2F repressor complexes; this dephosphorylation is blocked by phosphatase inhibitors (calyculin A, okadaic acid) and by overexpression of specific PP2A B subunits, and occurs independently of p53/p21.\",\n      \"method\": \"Western blotting for phosphorylation states, phosphatase inhibitor treatment, PP2A B subunit overexpression, p107 dephosphorylation in vitro with PP2A\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal approaches (inhibitors, genetic, in vitro), p53/p21-independence established\",\n      \"pmids\": [\"9989818\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"A preformed cytoplasmic complex containing Smad3, E2F4/5, DP1, and p107 translocates to the nucleus in response to TGFbeta signaling and associates with Smad4 to repress c-myc transcription via a composite Smad-E2F element; p107 acts as a corepressor upstream of CDK signaling in the TGFbeta pathway.\",\n      \"method\": \"Co-immunoprecipitation, chromatin immunoprecipitation, subcellular fractionation, reporter assay, site-directed mutagenesis of promoter elements\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — ChIP, Co-IP, fractionation, promoter mutagenesis in single rigorous study\",\n      \"pmids\": [\"12150994\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Cyclin D1/Cdk4 directly phosphorylates p107 at four specific sites (Thr-369, Ser-640, Ser-964, Ser-975) in vitro and in vivo; the RXL motif of p107 is required for Cdk4-mediated phosphorylation of nonconsensus sites; non-phosphorylatable p107 mutants at these sites are resistant to cyclin D1/Cdk4-mediated reversal of growth suppression.\",\n      \"method\": \"In vitro kinase assay with purified Cdk4, site-directed mutagenesis of phosphorylation sites, co-immunoprecipitation, cell cycle arrest assay\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro kinase assay with site mutagenesis plus in vivo validation\",\n      \"pmids\": [\"11884610\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Oxidative stress (H2O2) induces rapid dephosphorylation of p107 via PP2A; PP2A catalytic subunit physically interacts with p107 in both treated and untreated cells; this dephosphorylation contributes to inhibition of DNA synthesis.\",\n      \"method\": \"Co-immunoprecipitation of PP2A with p107, phosphatase inhibitor assay (okadaic acid, calyculin A), SV40 small t antigen overexpression, kinase inhibition assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — four independent lines of evidence including PP2A-specific tools, reciprocal Co-IP\",\n      \"pmids\": [\"12621062\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"PP2A with B55α regulatory subunit specifically interacts with p107 and constitutes the major PP2A holoenzyme responsible for restricting p107 phosphorylation state; distinct PP2A holoenzymes show selectivity for different pocket proteins.\",\n      \"method\": \"Proteomic identification, co-immunoprecipitation, knockdown of B55α, phosphorylation state analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — proteomics plus functional Co-IP, single lab\",\n      \"pmids\": [\"20663872\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"p107 inhibits G1-to-S progression by transcriptionally repressing expression of the F-box protein Skp2, leading to accumulation of p27; ectopic Skp2 restores DNA synthesis in p107-overexpressing cells, and p107-/- MEFs have elevated Skp2.\",\n      \"method\": \"Overexpression and knockout analysis, western blotting, rescue experiment with Skp2 expression, DNA synthesis assay\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — gain and loss of function with epistasis (Skp2 rescue), single lab\",\n      \"pmids\": [\"15631990\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"p107 represses transcription at the Hes1 promoter in neural progenitors; loss of p107 leads to elevated Hes1 and an expanded progenitor pool with impaired commitment to neuronal fate; Hes1 heterozygosity rescues neurosphere numbers and neurogenesis defects in p107-null mice.\",\n      \"method\": \"Reporter assay for Hes1 promoter, p107-/- mouse analysis, Hes1/p107 double-mutant genetic epistasis, neuronal birthdating\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis in vivo plus promoter reporter assay, clear phenotypic rescue\",\n      \"pmids\": [\"17591923\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Mammalian Mip/LIN-9 forms a repressor complex with p107 (or p130) and E2F4 specifically in G0/early G1; CDK4-mediated phosphorylation of p107 dissociates this complex, releasing Mip/LIN-9 to associate with B-Myb in late G1/S; p107 blocks B-Myb/Mip/LIN-9-mediated cyclin B promoter activation.\",\n      \"method\": \"Co-immunoprecipitation at specific cell cycle phases, phospho-specific co-IP, reporter assay, p107 overexpression epistasis\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — cell-cycle-resolved Co-IP plus functional epistasis, single lab\",\n      \"pmids\": [\"17563750\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"FGF signaling activates PP2A to dephosphorylate p107 in chondrocytes; overexpression of cyclin D1/Cdk4 prevents FGF-induced p107 dephosphorylation and growth arrest; knockdown of PP2A catalytic subunit or inhibition by SV40 small T antigen prevents both p107 dephosphorylation and FGF-induced arrest; FGF treatment induces physical association of p107 with PP2A.\",\n      \"method\": \"siRNA knockdown of PP2A, SV40 small T antigen overexpression, cyclin D1/Cdk4 overexpression, co-immunoprecipitation, western blotting for p107 phosphorylation\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal approaches establishing PP2A-p107 axis in FGF response, Co-IP of endogenous complex\",\n      \"pmids\": [\"18927618\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"p107 and p130 are required for FGF-mediated growth inhibition in chondrocytes; p107/p130 double-knockout chondrocytes fail to arrest in response to FGF, while single knockouts show only partial impairment; pRB is not involved in this response.\",\n      \"method\": \"Primary chondrocyte cultures from knockout mice (p107-/-, p130-/-, p107-/-/p130-/-), metatarsal bone rudiment FGF treatment, BrdU incorporation, viral oncoprotein complementation (PyLT mutants)\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic epistasis with multiple single and compound KOs plus mechanistic dissection with viral oncoprotein mutants\",\n      \"pmids\": [\"12177046\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"p107 is part of the DREAM complex (with E2F4, DP, MuvB) and specifically mediates repression of G2/M genes (but not G1/S genes) in response to p53/p21 activation; p130-DREAM represses G1/S genes while p107-DREAM represses G2/M genes.\",\n      \"method\": \"Gene expression profiling, chromatin immunoprecipitation, genetic deletion of RB family members in primary human fibroblasts, DNA damage (p53 activation)\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genome-wide gene expression plus ChIP with multiple genetic conditions\",\n      \"pmids\": [\"31667499\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"MAGE-A11 interacts with p107 and inhibits its ubiquitination, stabilizing p107; MAGE-A11 links p107 to hypophosphorylated E2F1, stabilizing and activating E2F1; at high MAGE-A11 levels, p107 switches from transcriptional repressor to activator in prostate cancer cells.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, siRNA knockdown, reporter assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — Co-IP with functional consequence, single lab\",\n      \"pmids\": [\"23853093\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"p107 interacts in vivo with Rb and p130-related proteins via its pocket domain to interact with adenovirus E1A, SV40 T antigen, and HPV E7 oncoproteins; HPV16 E7 binds p107 through sequences overlapping with but distinct from RB-binding sequences.\",\n      \"method\": \"Co-immunoprecipitation, two-hybrid, point mutation analysis of E7\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — multiple viral oncoprotein binding studies, single lab per paper\",\n      \"pmids\": [\"8386265\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"Human cytomegalovirus IE1-72 protein binds the N-terminal region of p107 (distinct from the C-terminal pocket domain where viral oncoproteins typically bind) and relieves p107-mediated transcriptional repression of E2F-responsive promoters; IE1-72 overcomes p107-induced growth suppression in a manner dependent on this protein-protein interaction.\",\n      \"method\": \"Co-immunoprecipitation in vivo and in vitro, reporter assay, domain mapping with deletion mutants, growth arrest rescue assay\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo and in vitro Co-IP plus functional reporter and growth assay with mutants, single lab\",\n      \"pmids\": [\"8892909\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"p107 and p130, but not pRB, mediate transcriptional repression of G2/M genes (including plk1) in response to DNA damage; cells lacking all three RB family proteins fail to accumulate at 4N DNA content after adriamycin treatment, indicating cooperative roles in G2 arrest.\",\n      \"method\": \"Gene expression analysis, partial and complete RB family genetic deletion, DNA content analysis by flow cytometry\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic deletion with defined gene expression and cell cycle phenotypes, single lab\",\n      \"pmids\": [\"15827088\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Cyclin A/cdk2 phosphorylation of p107 leads to dissociation of the p107/cyclin/cdk2/E2F complex; both E2F-p107 and E2F-pRB complexes are disrupted by phosphorylation by cyclin A-cdk2 in vitro using purified components.\",\n      \"method\": \"In vitro phosphorylation with purified cyclins/CDKs, gel mobility shift assay\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro assay with purified components directly demonstrating phosphorylation-dependent complex disruption\",\n      \"pmids\": [\"7753545\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"p107 (RBL1) is a transcriptional repressor and CDK inhibitor that operates in a cell-cycle-regulated manner: in G1 it associates with E2F4/5 (and Mip/LIN-9) to repress E2F-target gene promoters including G2/M genes; cyclin E/cdk2 binds p107 in G1 and cyclin A/cdk2 binds it at G1/S, and p107 stoichiometrically inhibits both kinases through a p21-like N-terminal domain; CDK4/cyclin D1 phosphorylates p107 at specific sites (facilitated by an RXL docking motif) to release E2F and relieve growth suppression, while PP2A (directed by B55α or PR59 subunits) specifically dephosphorylates p107 to reactivate it in response to signals such as UV, oxidative stress, or FGF; p107 also directly binds and suppresses c-Myc and B-MYB transactivation domains, represses Sp1-dependent and RNA Pol III transcription, and participates as a preformed cytoplasmic complex with Smad3/E2F4 that translocates to the nucleus to mediate TGFβ-dependent c-myc repression.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\nI'll systematically classify each paper, then extract discoveries only from KEPT papers about RBL1 (p107, the canonical human protein encoded by RBL1/retinoblastoma-like 1).\n\n**EXCLUDE list:**\n- Paper [29] (retrieved): PRB1 = Trichoderma proteinase B gene — SYMBOL COLLISION, fungal gene\n- Paper [46] (retrieved): prb1 overexpression in Trichoderma — SYMBOL COLLISION\n- Paper [47] (retrieved): FTS/Hook/p107(FHIP) — the \"p107\" here is FHIP (a different 107-kDa protein), NOT RBL1\n- Paper [49] (retrieved): RBL-1 = rat basophilic leukemia cell line — ALIAS COLLISION (cell line, not gene)\n- Paper [58] (curated-equivalent in retrieved): PRB1 = yeast proteinase B — SYMBOL COLLISION\n- Paper [83] (retrieved): PRB1 yeast proteinase B mapping — SYMBOL COLLISION\n- Paper [84] (retrieved): prb1 Trichoderma atroviride — SYMBOL COLLISION\n- Paper [88] (retrieved): PRB1 Saccharomyces cerevisiae — SYMBOL COLLISION\n- Paper [100] (retrieved): PRB1/PRB2/PRB4 = salivary proline-rich proteins — ALIAS COLLISION\n- Paper [56] (retrieved): pRb1-cyclin D1-cdk4/6-p16 pathway in endometrial carcinoma — expression/correlation study, no mechanistic finding about p107 specifically; focuses on pRb1, not p107\n- Papers from curated list: [1],[2],[3],[4],[5],[6],[7],[11],[12] — large-scale interactome/genomic resource papers without specific p107 mechanistic findings\n- Paper curated [5]: VIRMA/m6A — unrelated\n- Paper [59] (retrieved): domain superfamily analysis — computational prediction only (Tier 4)\n\nAll remaining papers about p107 (RBL1) canonical protein are KEEP.\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1991,\n      \"finding\": \"p107 (RBL1) was molecularly cloned; its cDNA maps to chromosome 20q11.2 and encodes a 936-residue protein with a major region of homology to RB spanning 564 residues. The homologous pocket region of p107 independently binds SV40 large T antigen and adenovirus E1A, establishing p107 as a structurally and functionally related RB family member.\",\n      \"method\": \"cDNA cloning, chromosomal mapping (FISH), domain-deletion binding assays\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — original cloning paper with structural characterization and binding domain mapping, foundational\",\n      \"pmids\": [\"1833063\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"p107 forms a complex with cyclin A in cells independently of viral oncoproteins; the unique spacer sequence between the A and B sub-segments of the p107 pocket (absent in RB) is required for cyclin A interaction, explaining why cyclin A binds p107 but not RB.\",\n      \"method\": \"Co-immunoprecipitation, domain deletion mutants, in vitro binding with reticulocyte-translated proteins\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP with domain mapping, replicated independently in same year by two groups\",\n      \"pmids\": [\"1532457\", \"1532458\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"p107 and RB independently bind the transcription factor E2F at distinct cell cycle phases: RB–E2F complexes predominate in G1, while a p107–cyclin A–p33cdk2–E2F complex appears in S phase, establishing that the two pocket proteins regulate E2F activity at different cell cycle stages.\",\n      \"method\": \"Co-immunoprecipitation, gel mobility shift assays, cell cycle synchronization\",\n      \"journal\": \"Cell / Nature / Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — replicated across multiple independent laboratories with orthogonal methods\",\n      \"pmids\": [\"1531040\", \"1530885\", \"1398067\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"The p107–E2F complex in S phase also contains p33cdk2 and cyclin E (in G1) or cyclin A (in S), and these two kinase complexes associate with p107 in a temporally distinct manner during the cell cycle.\",\n      \"method\": \"Immunoprecipitation with cyclin- and cdk2-specific antisera, cell cycle synchronization\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal immunoprecipitations in synchronized cells, replicated\",\n      \"pmids\": [\"1398067\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"p107 represses E2F-dependent transcription; adenovirus E1A overcomes p107-mediated transcriptional repression. This repression is cell-type dependent and inversely correlates with a cellular E1A-like activity in F9 embryonal carcinoma cells.\",\n      \"method\": \"Transient transfection reporter assays, co-transfection in multiple cell lines including F9 EC cells\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — functional reporter assays in multiple cell types with defined mechanistic outcome\",\n      \"pmids\": [\"7685208\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"p107-associated proteins identified in ML-1 cells include cyclin A, cyclin E, cdk2, and a 62–65 kDa E2F-like phosphoprotein that is immunologically distinct from pRB-associated E2F-1, indicating p107 preferentially associates with a specific E2F species.\",\n      \"method\": \"Monoclonal antibody panel, co-immunoprecipitation, biochemical characterization\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — systematic antibody-based interactome with multiple protein identifications\",\n      \"pmids\": [\"8230483\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"p107 inhibits E2F-dependent transcription in a co-transfection assay. The E2F–p107 interaction (unlike E2F–RB) persists through the G1/S transition into S phase, providing a distinct regulatory mechanism from RB.\",\n      \"method\": \"Gel mobility shift assay, co-transfection transcriptional repression assays\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic functional assays replicated across labs\",\n      \"pmids\": [\"8458319\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"Distinct regions of E2F1 mediate regulation by RB versus p107: point mutations within the C-terminal acidic domain of E2F1 can distinguish RB from p107 binding, and the leucine repeat element required for E4 regulation is not required for p107-mediated inhibition.\",\n      \"method\": \"E2F1 mutagenesis, co-transfection, functional reporter assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — systematic mutagenesis but single laboratory\",\n      \"pmids\": [\"8413230\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"HPV16 E7 associates with p107 through sequences overlapping with but distinct from those required for RB binding; this association correlates with E7's transformation-competent activities and its interaction with a histone H1 kinase at G2/M.\",\n      \"method\": \"Co-immunoprecipitation, E7 point mutant analysis, kinase assays\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — binding domain mapped with point mutants, single lab\",\n      \"pmids\": [\"8386265\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"Cyclin A–p107 and p33cdk2 complexes bind to a 25-bp element of the human thymidine kinase promoter in an S-phase-specific manner, and mutation of this element reduces both in vitro complex binding and S-phase-regulated promoter activity in vivo.\",\n      \"method\": \"Electrophoretic mobility shift assay, promoter mutagenesis, S-phase synchronization\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — EMSA with cell cycle correlation and promoter mutagenesis, single lab\",\n      \"pmids\": [\"8475104\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"E2F-4 is a p107-binding E2F family member; p107 binds E2F-4 in vivo and suppresses E2F-4's ability to transform immortalized rodent cells. E2F-4 is a differentially phosphorylated p107-binding partner present throughout the cell cycle.\",\n      \"method\": \"cDNA cloning, co-immunoprecipitation, transformation assays, reporter assays\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — replicated independently by two groups in same year with multiple methods\",\n      \"pmids\": [\"7958925\", \"7958924\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"p107 binds to the N-terminal transactivation domain of c-Myc in vivo (but RB does not), and this binding suppresses c-Myc transactivation activity. Expression of c-Myc releases cells from p107-induced growth arrest but not from pRB-induced arrest, placing c-Myc as a specific downstream target of p107.\",\n      \"method\": \"cDNA expression library screen with Myc fusion protein, co-immunoprecipitation, co-transfection reporter assays, growth arrest rescue experiments\",\n      \"journal\": \"Science / The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods, replicated by two independent groups\",\n      \"pmids\": [\"8146655\", \"8076603\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"p107 overexpression is a potent inhibitor of E2F-mediated trans-activation and can inhibit cell proliferation causing G1 arrest in certain cell lines. Growth inhibition by p107 and pRB occurs through distinct mechanisms: p107 can arrest C33A cells (which are resistant to pRB), certain p107 mutants unable to bind E1A still inhibit proliferation, and growth arrest by each is rescued differentially by cell cycle regulators.\",\n      \"method\": \"Overexpression, cell growth assays, FACS cell cycle analysis, E1A binding mutant analysis\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal functional assays, foundational paper with >550 citations\",\n      \"pmids\": [\"8319904\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"HPV16 E7 deregulates B-myb expression by targeting p107/E2F complexes; E7 transcriptionally activates B-myb during G1 and causes its constitutive over-expression, and analysis of E7 mutants confirms that B-myb regulation in NIH3T3 cells occurs through p107 rather than pRB.\",\n      \"method\": \"Transfection with E7 mutants, Northern blot, E2F reporter assays, gel-shift with specific antisera\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — E7 mutant dissection links p107 specifically to B-myb regulation, single lab\",\n      \"pmids\": [\"8112300\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"p107 contains a p21CIP1-related cyclin/cdk-binding domain; p107 inhibits phosphorylation of target substrates by cyclin A/cdk2 and cyclin E/cdk2, and binding of p107 or p21 to cyclin/cdk2 is mutually exclusive. In cells treated with DNA-damaging agents, elevated p21 displaces p107 from cyclin/cdk2 complexes. Activation of p107-bound kinases leads to dissociation of p107 from E2F.\",\n      \"method\": \"In vitro kinase assays, competitive binding assays, cell treatment with DNA-damaging agents, co-immunoprecipitation\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro kinase inhibition demonstrated with mechanistic follow-up in cells\",\n      \"pmids\": [\"7622038\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"p107 contains two independent growth-suppression domains: one mediating interaction with E2F and another mediating interaction with cyclin A/E complexes. The cyclin-binding domain alone is sufficient for growth suppression in C33A cells (resistant to pRB), while both domains are functional in untransformed fibroblasts.\",\n      \"method\": \"Structure-function analysis, deletion mutants, co-expression growth arrest assays, FACS\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — systematic structure-function dissection with multiple functional readouts\",\n      \"pmids\": [\"7743997\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Phosphorylation of p107 by cyclin D1/cdk4 (but not cyclin E/cdk2) is cell-cycle regulated, beginning ~8 hours after serum stimulation coinciding with cyclin D1 induction. Phosphorylation of p107 causes loss of association with E2F-4, and dominant-negative cdk4 abolishes p107 phosphorylation. A p107-induced cell cycle block can be released by cyclin D1/cdk4 but not cyclin E/cdk2.\",\n      \"method\": \"Cell synchronization, kinase assays, dominant-negative cdk4 overexpression, co-immunoprecipitation, growth arrest rescue\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic dissection with multiple complementary methods, replicated\",\n      \"pmids\": [\"7797074\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"p107 represses the E2F-site–dependent transcription of the cyclin A promoter, and adenovirus 12S E1A activates cyclin A transcription by counteracting p107 repression through conserved region 2 (which binds p107) but not through CR1 or the N-terminus (which bind p300/pRB).\",\n      \"method\": \"Adenovirus deletion mutant infection, reporter assays, quiescent fibroblast model\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — systematic E1A mutant dissection linking p107 binding to cyclin A transcription, single lab\",\n      \"pmids\": [\"8642699\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"p107 associates with the transcription factor Sp1 in vivo independently of the pocket domain; p107 represses Sp1-dependent transcription through a region distinct from the pocket domain used for E2F regulation, demonstrating two separable transcriptional repression mechanisms.\",\n      \"method\": \"Co-immunoprecipitation, transient transfection reporter assays with Gal4-Sp1 chimeras, domain deletion analysis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP plus reporter dissection, single lab\",\n      \"pmids\": [\"7565695\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"The human p107 promoter is TATA-less and contains tandem E2F sites with differential roles: RB and p107 itself repress the p107 promoter through the 5' E2F site but not the 3' (initiation site) copy, revealing autoregulatory feedback and functional asymmetry between tandem E2F elements.\",\n      \"method\": \"Promoter deletion analysis, site-directed mutagenesis, luciferase reporter assays, transfection of RB and p107\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — systematic promoter mutagenesis, single lab\",\n      \"pmids\": [\"7791762\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"The ability of p107 to suppress E2F-dependent transcription is not dependent on its ability to associate with cyclin A/cdk2; p107 mutants that fail to bind E2F cannot repress E2F transcription, while mutants deficient in cyclin A/cdk2 binding still repress E2F. Both E2F-dependent and E2F-independent activities correlate with cell growth suppression.\",\n      \"method\": \"p107 deletion mutants, co-transfection reporter assays, growth suppression assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — systematic mutant analysis, single lab\",\n      \"pmids\": [\"7799940\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Cyclin A-cdk2 phosphorylation disrupts both E2F–pRB and E2F–p107 complexes, releasing free E2F; cyclin D1-cdk4 and cyclin E-cdk2 also disrupt E2F–pRB complexes. These results directly demonstrate that CDK-mediated phosphorylation of pRB and p107 regulates their E2F complex formation.\",\n      \"method\": \"Purified recombinant pRB, purified cyclin/cdk complexes, gel mobility shift assay with nuclear extracts from pRB-defective cells\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with purified components demonstrating causation\",\n      \"pmids\": [\"7753545\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Lymphoma-derived MYC mutant alleles with missense mutations in the transactivation domain are resistant to p107-mediated transcriptional suppression; p107-cyclin A-CDK complex phosphorylates Thr-58 of wild-type c-Myc in a manner dependent on prior Ser-62 phosphorylation, but this phosphorylation is absent in lymphoma Myc mutants.\",\n      \"method\": \"In vitro and in vivo phosphorylation assays, transformation assays, c-Myc mutant binding/transcription analysis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1/2 — in vitro kinase assays plus in vivo correlation, single lab\",\n      \"pmids\": [\"7623799\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"p107 and p130 share overlapping biological roles in limb development: mice doubly deficient in p107 and p130 exhibit deregulated chondrocyte growth, defective endochondral bone development, shortened limbs, and neonatal lethality, while single knockouts are viable, demonstrating functional redundancy in vivo.\",\n      \"method\": \"Gene targeting (homologous recombination), mouse knockout, histological analysis\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo genetic loss-of-function with defined developmental phenotype\",\n      \"pmids\": [\"8682294\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"Targeted disruption of mouse p107 alone yields viable, fertile mice with no obvious abnormalities; however, Rb+/−;p107−/− mice show growth retardation and increased mortality, and Rb−/−;p107−/− embryos die ~2 days earlier than Rb−/− embryos with accelerated apoptosis in liver and CNS, demonstrating overlapping in vivo functions between p107 and RB.\",\n      \"method\": \"Homologous recombination gene targeting, double-knockout mouse generation, histological/pathological analysis\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis in vivo with defined phenotypic readout\",\n      \"pmids\": [\"8682293\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"E2F-4 associates with p130 in arrested/quiescent cells but switches to p107 and pRB as cells re-enter the cell cycle and pass G1/S; E2F-4 accounts for the majority of endogenous E2F activity and the majority of free E2F in G1 cells.\",\n      \"method\": \"Cell synchronization, specific antisera immunoprecipitation, gel mobility shift assay\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — comprehensive characterization using multiple specific antisera in synchronized cells\",\n      \"pmids\": [\"8657117\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"p107 contains a functional transcriptional repressor domain within its pocket (A and B conserved domains) that functions as a general repressor when tethered to a promoter via E2F or via a Gal4 DNA-binding domain fusion, independently of E2F binding. The two pocket sub-domains can function even when co-expressed as separate proteins.\",\n      \"method\": \"Gal4 fusion tethering assay, domain deletion mutants, co-transfection reporter assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — systematic domain analysis with mechanistic reporter readout, single lab\",\n      \"pmids\": [\"8668177\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"p107 binds B-MYB in vivo through its pocket and C-terminal domain, and suppresses B-MYB's autoregulatory transcriptional activation; overexpression of B-myb can overcome p107-induced growth arrest, placing B-MYB as a downstream effector of p107-mediated growth suppression.\",\n      \"method\": \"Co-immunoprecipitation, co-transfection reporter assays, p107 deletion constructs, growth arrest rescue\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP with domain mapping and functional readout, single lab\",\n      \"pmids\": [\"8910512\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"Regulation of p107 by G1 cyclin-associated kinases: p107 phosphorylation begins in mid-G1 and is driven by cyclin D-associated kinases. Hypophosphorylated p107 selectively binds E2F-4, and G1 cyclin-dependent phosphorylation of p107 leads to dissociation of p107–E2F-4 complexes and inactivation of the p107 G1 block.\",\n      \"method\": \"Cell synchronization, kinase assays, co-immunoprecipitation, CDK inhibitor analysis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods in synchronized cells, replicated across labs\",\n      \"pmids\": [\"8643455\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"SV40 large T antigen alters phosphorylation state of p107 and p130 through its J-domain (DnaJ homology region) in addition to LXCXE binding; the N-terminal 147 amino acids including the LXCXE domain plus additional N-terminal residues are required. A heterologous J-domain from human DnaJ can substitute for the TAg N-terminus in altering p107/p130 phosphorylation. The J-domain effect confers growth advantage via p107/p130 inactivation.\",\n      \"method\": \"TAg mutant analysis, transient expression assays, fibroblasts from p107/p130 double-knockout mice, heterologous J-domain rescue\",\n      \"journal\": \"Molecular and cellular biology / Journal of virology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic dissection with domain mutants, heterologous rescue, and genetic confirmation with knockout MEFs\",\n      \"pmids\": [\"9271376\", \"8627752\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"pRB and p107/p130 regulate distinct sets of E2F-responsive genes: loss of pRB deregulates one set of E2F targets while loss of both p107 and p130 deregulates a completely different set. Neither p107 nor p130 single knockouts show changes in E2F target gene expression.\",\n      \"method\": \"Primary cells from single and double knockout mice, RNA analysis of E2F target gene expression\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic dissection in vivo/ex vivo with defined gene expression readout, landmark study\",\n      \"pmids\": [\"9192872\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"p107 and p130 both repress RNA polymerase III transcription by physically interacting with TFIIIB (a subunit of the Pol III initiation factor); endogenous TFIIIB co-immunoprecipitates and co-fractionates with p107 and p130, and Pol III activity is deregulated in p107/p130 double-knockout fibroblasts.\",\n      \"method\": \"GST pull-down, co-immunoprecipitation with recombinant components and endogenous proteins, Pol III transcription assays in cell extracts, double-knockout MEFs\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reconstitution with recombinant proteins plus endogenous Co-IP and genetic validation\",\n      \"pmids\": [\"10330166\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"p107 and p130 accumulate in cells by distinct mechanisms: p107 levels are regulated transcriptionally through E2F-dependent repression in quiescent cells (p107 mRNA is low in quiescence), while p130 is controlled post-translationally via CDK-mediated phosphorylation and proteasome-mediated degradation.\",\n      \"method\": \"Cell synchronization, RNA blotting, proteasome inhibitor treatment, protein stability assays\",\n      \"journal\": \"Cell growth & differentiation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — orthogonal approaches (RNA, protein, pharmacological inhibition), single lab\",\n      \"pmids\": [\"9563849\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"p130 and p107 use a conserved amino-terminal domain to inhibit cyclin A-cdk2 and cyclin E-cdk2 kinase activities; reconstituted p107-cyclin-cdk2 complexes with purified recombinant proteins exhibit stoichiometric kinase inhibition not due to substrate competition or cdk2 activation loss. Endogenous p130-cyclin A-cdk2 complexes purified from human cells also show low kinase activity augmented by dissociation of p130.\",\n      \"method\": \"Reconstitution with purified recombinant proteins, in vitro kinase assays, purification of endogenous complexes from human cells\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — biochemical reconstitution with purified components plus endogenous complex validation\",\n      \"pmids\": [\"9199292\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"p107 is a bona fide inhibitor of cyclin A-cdk2 and cyclin E-cdk2 with a Ki comparable to p21/WAF1; a second cyclin-binding site maps to the N-terminal domain of p107 (and p130). The N-terminal domain inhibits but is not a good kinase substrate, while the C-terminal cyclin-binding domain is an excellent substrate but not an inhibitor; both domains are needed for full inhibitory activity.\",\n      \"method\": \"In vitro kinase assays with Ki determination, domain deletion mutants, peptide competition assays, growth suppression assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — quantitative in vitro reconstitution with mechanistic domain dissection\",\n      \"pmids\": [\"9710622\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"HDAC1 interacts with p107 (and p130) through an LXCXE-like motif; adenovirus E1A competes with HDAC1 for p107 interaction. p107 can simultaneously interact with HDAC1 and E2F-4, and histone deacetylase activity is required for p107-induced repression of E2F-4, indicating p107 represses E2F through HDAC1 recruitment.\",\n      \"method\": \"Co-immunoprecipitation in live cells, competition assays with E1A, histone deacetylase inhibitor treatment, reporter assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP with competition and functional inhibition assays, multiple orthogonal methods\",\n      \"pmids\": [\"9724731\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"A novel PP2A regulatory subunit PR59 specifically associates with p107 (not pRB) in vivo and is a genuine PP2A holoenzyme component. Elevated PR59 expression causes p107 dephosphorylation (not pRB dephosphorylation) and G1 arrest, identifying a p107-specific PP2A holoenzyme that targets p107 for dephosphorylation and activation.\",\n      \"method\": \"Co-immunoprecipitation, isolation of PR59 by virtue of p107 association, over-expression, cell cycle analysis (FACS)\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — novel subunit identified and functionally validated with specificity demonstrated\",\n      \"pmids\": [\"9927208\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"C/EBPalpha controls the composition of E2F complexes by interacting with p107 and disrupting p107-containing S-phase E2F complexes; a region of C/EBPalpha with E2F sequence similarity is sufficient for disruption. This occurs through protein–protein interaction (not DNA binding), and purified His-C/EBPalpha can directly disrupt p107/E2F complexes in vitro.\",\n      \"method\": \"Co-immunoprecipitation, in vitro complex disruption with purified proteins, C/EBPalpha knockout mouse liver analysis, gel mobility shift assay\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — purified protein disruption assay plus in vivo genetic validation\",\n      \"pmids\": [\"10082561\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"UV irradiation induces rapid dephosphorylation of p107 and an increase in p107/E2F repressor complexes in a PP2A-dependent manner; phosphatase inhibitors (calyculin A, okadaic acid) abolish UV-mediated dephosphorylation, overexpression of specific PP2A B subunits interferes with dephosphorylation, and p107 can be dephosphorylated in vitro with PP2A. This occurs independently of p53 and p21.\",\n      \"method\": \"UV irradiation, phosphatase inhibitor treatment, PP2A B-subunit overexpression, in vitro dephosphorylation with purified PP2A, p53/p21 knockout cells\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro dephosphorylation plus multiple complementary in vivo approaches\",\n      \"pmids\": [\"9989818\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"HCMV IE1-72 protein binds to the N-terminal portion of p107 (not the C-terminal pocket) through exons 2 and 3 of IE1-72, and this interaction relieves p107-mediated transcriptional repression of E2F-responsive promoters but not Rb-mediated repression. IE1-72 alone can overcome p107-mediated growth arrest in a manner dependent on the physical interaction.\",\n      \"method\": \"Co-immunoprecipitation, in vitro reconstitution with reticulocyte-translated proteins, domain deletion mutants, reporter assays, growth arrest assays\",\n      \"journal\": \"Journal of virology / Journal of general virology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — domain mapping with domain mutants, in vitro reconstitution, and functional validation\",\n      \"pmids\": [\"8892909\", \"10355776\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"E2F and pRB-family protein occupancy at target gene promoters is dynamically regulated in vivo: in quiescent cells, promoters are occupied by E2F-4 and p130; by late G1, p130 and E2F-4 are replaced by E2F-1 and E2F-3. p107 appears at promoters associated with activation. Low histone acetylation correlates with p130/E2F-4 repression; histone acetylation increases with gene activation.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP) in synchronized living cells, histone acetylation analysis\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct ChIP evidence of promoter occupancy dynamics in vivo, landmark study\",\n      \"pmids\": [\"10766737\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"pRB and p107 have opposing roles in adipocyte differentiation: p107 loss lowers the requirement for the differentiation factor PPARgamma and pRB-deficient cells exhibit differentiation defects. pRB (not p107) is required for cell cycle exit and potentiates C/EBPalpha activity, while p107 does not affect C/EBPalpha-driven transcription.\",\n      \"method\": \"3T3 fibroblasts from single and double knockout mice, adipogenesis assays, overexpression experiments, reporter assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic cell biology with mechanistic dissection, single lab\",\n      \"pmids\": [\"10995476\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Smad3 mediates TGFbeta-induced repression of c-myc through a pre-formed cytoplasmic complex containing Smad3, E2F4/5, DP1, and the corepressor p107. In response to TGFbeta, this complex translocates to the nucleus, associates with Smad4, and recognizes a composite Smad-E2F site on the c-myc promoter for repression, revealing p107 as a TGFbeta signal transducer upstream of CDK.\",\n      \"method\": \"Co-immunoprecipitation, subcellular fractionation, chromatin immunoprecipitation, reporter assays, dominant-negative experiments\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods including ChIP and subcellular fractionation, high-impact replicated finding\",\n      \"pmids\": [\"12150994\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Cyclin D1/Cdk4 directly phosphorylates p107 at four specific sites (Thr-369, Ser-640, Ser-964, Ser-975) identified by in vitro and in vivo phosphorylation mapping; mutation of these four sites renders p107 refractory to inactivation by cyclin D1/Cdk4. The RXL motif of p107 is required for Cdk4-mediated phosphorylation of S640 by facilitating phosphorylation of nonconsensus Cdk substrates.\",\n      \"method\": \"In vitro phosphorylation with purified kinases, site-directed mutagenesis, cell cycle arrest assays, mass spectrometry phosphopeptide mapping\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro kinase assays with site-directed mutagenesis and in vivo validation, comprehensive\",\n      \"pmids\": [\"11884610\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"p107 and p130 coordinately regulate chondrocyte proliferation, Cbfa1 expression, and hypertrophic differentiation during endochondral bone development; p107 is required in prechondrogenic condensations for cell cycle withdrawal, while both p107 and p130 contribute to chondrocyte cell cycle exit and Cbfa1-dependent terminal differentiation. Cbfa1 expression and hypertrophic differentiation occur only in cells that have undergone p107/p130-mediated proliferative arrest.\",\n      \"method\": \"Analysis of p107/p130 knockout mice, immunohistochemistry, in situ hybridization, BrdU labeling\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo genetic analysis with defined cellular/molecular phenotypes, single lab\",\n      \"pmids\": [\"12086466\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"FGF signaling targets p107 and p130 (but not pRB) to induce chondrocyte growth arrest: FGF causes rapid dephosphorylation of all three Rb-family proteins, but p107/p130-double-null chondrocytes fail to respond to FGF growth inhibition while Rb-null chondrocytes respond normally. A PyLT mutant that binds pRB but not p107/p130 cannot rescue FGF resistance.\",\n      \"method\": \"Chondrocyte cell lines, PyLT mutant expression, p107/p130 knockout MEF micromass cultures, metatarsal organ culture, BrdU labeling\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with molecular and cellular readouts, multiple complementary approaches\",\n      \"pmids\": [\"12177046\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Oxidative stress (H2O2) induces rapid dephosphorylation of pRB, p107, and p130 via protein phosphatase 2A (PP2A); PP2A core enzyme physically interacts with pRB and p107 in both treated and untreated cells, pRB-associated PP2A activity is enhanced by H2O2, and SV40 small t antigen (PP2A inhibitor) blocks H2O2-induced dephosphorylation and prevents DNA synthesis inhibition.\",\n      \"method\": \"Phosphatase inhibitor treatment (okadaic acid, calyculin A), SV40 small t antigen overexpression (wild-type and PP2A-binding mutant), co-immunoprecipitation of PP2A with p107\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple complementary approaches including binding mutant controls\",\n      \"pmids\": [\"12621062\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"A dynamic equilibrium between CDKs and PP2A modulates phosphorylation of p107 throughout the cell cycle; PP2A catalytic subunit specifically interacts with p107 and p130 (co-immunoprecipitation), and PP2A inhibition (by SV40 small t, okadaic acid at PP2A-selective concentrations, or calyculin A) prevents cycloheximide- and flavopiridol-induced dephosphorylation of pocket proteins.\",\n      \"method\": \"CDK inhibitor treatment (flavopiridol), cycloheximide, phosphatase inhibitors, PP2A holoenzyme manipulation, SV40 small t overexpression, co-immunoprecipitation\",\n      \"journal\": \"Cell cycle\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple pharmacological and genetic approaches in concert\",\n      \"pmids\": [\"15467457\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"RBL1 (p107) together with RB1 and RBL2 is required for constitutive heterochromatin formation; triple-knockout (TKO) MEFs show decreased DNA methylation, increased H3 acetylation, and decreased H4K20 trimethylation at pericentric and telomeric chromatin. RB1 family proteins directly interact with the H4K20 tri-methylating enzymes Suv4-20h1 and Suv4-20h2, independent of E2F function.\",\n      \"method\": \"Triple-knockout MEFs, chromatin immunoprecipitation, co-immunoprecipitation with Suv4-20h enzymes, histone modification analysis\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic model with ChIP and Co-IP, novel E2F-independent function defined\",\n      \"pmids\": [\"15750587\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Rb/p107 loss in the retina does not affect progenitor proliferation or cell specification but perturbs cell cycle exit in all seven retinal precursor types; only three precursors survive and arrest via terminal differentiation, while tumors arise from intrinsically death-resistant precursors with extended (not infinite) proliferative capacity.\",\n      \"method\": \"Conditional Cre-mediated knockout of Rb/p107, BrdU labeling, retinal cell-type marker analysis, apoptosis assays\",\n      \"journal\": \"Cancer cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo genetic analysis with defined cellular phenotypes, single lab\",\n      \"pmids\": [\"15193257\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"p107 regulates white versus brown adipocyte fate by repressing PGC-1alpha: p107-null mice exhibit uniform replacement of white adipose tissue with brown adipose tissue containing elevated PGC-1alpha and UCP-1. p107−/− WAT contains reduced pRb levels. pRb (but not p107) directly binds the PGC-1alpha promoter and represses its transcription.\",\n      \"method\": \"p107-knockout mice, ChIP for pRb at PGC-1alpha promoter, Cre-mediated Rb deletion in primary preadipocytes, differentiation assays\",\n      \"journal\": \"Cell metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo genetic model with ChIP and ex vivo functional assays, single lab\",\n      \"pmids\": [\"16271529\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"p107 inhibits G1-to-S-phase progression by down-regulating expression of the F-box protein Skp2, leading to p27 stabilization and Cdk2 inhibition; reciprocally, Skp2 accumulates to higher levels in p107-null fibroblasts, and ectopic Skp2 rescues the p27 and DNA synthesis defects caused by p107 overexpression.\",\n      \"method\": \"p107 overexpression and p107-knockout fibroblasts, Skp2 re-expression rescue, p27 stability assays, Cdk2 activity assays, FACS\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic and rescue experiments with defined biochemical readouts, single lab\",\n      \"pmids\": [\"15631990\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"p130 and p107 play a key role in transcriptional repression of G2/M genes following DNA damage; p130/p107 loss partially abrogates repression of plk1 after adriamycin treatment, and loss of all three RB-family proteins abolishes G2 arrest, indicating p107 specifically contributes to G2/M gene repression and cell cycle exit from G2 in response to DNA damage.\",\n      \"method\": \"RB-family knockout MEFs, gene expression profiling after DNA damage, FACS for G2 arrest, adriamycin treatment\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic dissection with transcriptomic and cell cycle readouts, single lab\",\n      \"pmids\": [\"15827088\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Mammalian Mip/LIN-9 forms a repressor complex with E2F4 and p107 (or p130) in G0/early G1, and in late G1/S switches to associating with B-Myb; CDK4-mediated phosphorylation of p107/p130 drives the separation. p107 within the Mip/LIN-9 complex blocks cyclin B promoter activation by B-Myb and Mip/LIN-9, taking functional precedence over the transcriptional activation complex.\",\n      \"method\": \"Co-immunoprecipitation in cell-cycle-synchronized cells, reporter assays with dominant-negative CDK4\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — cell-cycle-phase-specific Co-IP with functional reporter validation, single lab\",\n      \"pmids\": [\"17563750\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"p107 represses transcription at the Hes1 promoter, which normally promotes neural precursor self-renewal; p107-null mice show enhanced Hes1 levels and an expanded neural precursor pool but with reduced cortical neuron numbers and reduced neurogenesis rate. Loss of one Hes1 allele rescues neural precursor numbers and neurogenesis in p107-null brains.\",\n      \"method\": \"p107-knockout mice, Hes1/p107 compound knockout, neurosphere assays, neuronal birthdating (BrdU/EdU), reporter assays for Hes1 promoter\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis in vivo with defined neurogenic phenotype, single lab\",\n      \"pmids\": [\"17591923\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"PP2A mediates p107 dephosphorylation as a key event in FGF-induced chondrocyte growth arrest; overexpression of cyclin D1/cdk4 prevents FGF-induced p107 dephosphorylation and growth arrest; SV40 small T antigen expression or siRNA knockdown of PP2A catalytic subunit also prevents p107 dephosphorylation and FGF-induced arrest; FGF treatment induces an association between p107 and PP2A.\",\n      \"method\": \"Cyclin D1/cdk4 overexpression, SV40 small T antigen expression, siRNA knockdown of PP2A, co-immunoprecipitation of p107 and PP2A, growth arrest assays\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple complementary approaches including siRNA, pharmacological inhibition, and Co-IP\",\n      \"pmids\": [\"18927618\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"p107 and p130 associate with E2F target gene promoters by chromatin immunoprecipitation; GFP-tagged pRB shows similar nuclear dynamics to p107 and p130 by live-cell fluorescence imaging. Using anti-GFP antibody ChIP, RB association with target promoters is demonstrable, and direct RB phosphorylation disrupts promoter association, analogous to p107/p130 regulation.\",\n      \"method\": \"GFP-tagged protein live-cell imaging, FRAP, chromatin immunoprecipitation with multiple antibody approaches, phosphorylation mutant analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — live imaging plus ChIP with multiple antibody validation, single lab\",\n      \"pmids\": [\"19279001\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"B55alpha-containing PP2A holoenzymes play a major role in restricting p107 phosphorylation and inducing p107 activation; targeted selectivity exists in the interaction of pocket proteins with distinct PP2A holoenzymes, with B55alpha specifically targeting p107 over pRB.\",\n      \"method\": \"PP2A holoenzyme purification, co-immunoprecipitation, overexpression and knockdown of B55alpha, phosphorylation state analysis of p107\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — biochemical identification of specific PP2A holoenzyme with functional validation, single lab\",\n      \"pmids\": [\"20663872\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"MAGE-A11 interacts with p107 and inhibits p107 ubiquitination to stabilize it; MAGE-A11 links p107 to hypophosphorylated E2F1, stabilizing and activating E2F1. At low MAGE-A11, this interaction causes transcriptional repression; at higher MAGE-A11 (as in prostate cancer), p107 is converted from a transcriptional repressor to a transcriptional activator of androgen receptor and E2F1 targets.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assays, siRNA knockdown, reporter assays, p107/MAGE-A11 interaction domain mapping\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP with functional validation and domain mapping, single lab\",\n      \"pmids\": [\"23853093\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"CRISPR/Cas9-mediated knockout of rb1 and rbl1 (p107) together (but not either alone) in Xenopus tropicalis causes rapid development of retinoblastoma, confirming that the cooperative tumor suppressor function of RB1 and RBL1 demonstrated in mice is conserved in a non-mammalian vertebrate and validating Xenopus as a retinoblastoma model.\",\n      \"method\": \"CRISPR/Cas9 mosaic knockout in Xenopus tropicalis, tumor histopathology, ophthalmoscopy\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo genetic loss-of-function with tumor phenotype, ortholog model\",\n      \"pmids\": [\"27739525\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Following p53 activation by DNA damage, p130 and RB cooperate to repress G1/S genes, while G2/M genes are repressed specifically by p130 and p107 (not RB) through the DREAM complex (p107-DREAM and p130-DREAM); p107 contributes to G1/S gene repression only in the absence of RB and p130, demonstrating distinct and specific roles for each family member in damage-induced gene repression.\",\n      \"method\": \"Gene expression profiling in primary human fibroblasts, shRNA knockdown of individual RB family members, DNA damage treatment (doxorubicin), cell cycle analysis\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — comprehensive genome-wide analysis in primary cells with individual and combined knockdowns\",\n      \"pmids\": [\"31667499\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"A systematic screen identified p107 as a CDK4/6 substrate; the DREAM complex containing p107 mediates cell cycle gene repression. CDK4/6 phosphorylate p107 along with FOXM1 to control cell cycle entry and senescence suppression.\",\n      \"method\": \"Systematic CDK4/6 substrate screen, mass spectrometry phosphoproteomics\",\n      \"journal\": \"Cancer cell\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — systematic screen without specific p107 mechanistic follow-up in this paper\",\n      \"pmids\": [\"22094256\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"RBL1 (p107) is a nuclear pocket protein that suppresses cell proliferation primarily by binding and repressing the E2F4/5 transcription factors in a cell-cycle-regulated manner: in G0/early G1, a pre-formed cytoplasmic complex of p107–E2F4/5–DP1 can translocate to the nucleus in response to TGFbeta-Smad signaling to repress c-myc; as cells enter S phase, p107 forms complexes with cyclin E–CDK2 (in G1) and cyclin A–CDK2 (in S) that directly inhibit these kinases and phosphorylate p107's own RXL-motif sites via cyclin D1–CDK4 to disrupt E2F4 association; p107 also recruits HDAC1 to repress E2F target genes, interacts with Myc, B-MYB, Sp1, TFIIIB, and Suv4-20h enzymes to regulate transcription and heterochromatin, and is reactivated by PP2A holoenzymes (including B55α-PP2A and PR59-PP2A) that specifically dephosphorylate it in response to DNA damage, UV, FGF signaling, or oxidative stress, collectively placing p107 as a context-specific integrator of mitogenic, DNA damage, and differentiation signals that coordinates cell cycle exit.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"RBL1 (p107) is a multifunctional cell-cycle regulator that represses E2F-dependent transcription and directly inhibits cyclin-dependent kinase activity to control G1/S and G2/M progression. p107 associates with E2F4/5 and the DREAM/MuvB complex to repress target promoters—including G2/M genes, Skp2, Hes1, and c-myc—while a p21-like N-terminal domain stoichiometrically inhibits cyclin A/cdk2 and cyclin E/cdk2 with Ki values comparable to p21 [PMID:9710622, PMID:7622038, PMID:31667499]. CDK4/cyclin D1 phosphorylates p107 at specific sites (requiring an RXL docking motif) to dissociate E2F and relieve transcriptional repression, whereas PP2A holoenzymes containing B55α or PR59 regulatory subunits dephosphorylate p107 to reactivate repressor function in response to UV, oxidative stress, and FGF signaling [PMID:11884610, PMID:9927208, PMID:9989818, PMID:18927618]. Beyond canonical E2F targets, p107 participates in a cytoplasmic Smad3/E2F4 complex that translocates to the nucleus upon TGFβ signaling to repress c-myc, directly suppresses c-Myc and B-MYB transactivation, and represses RNA polymerase III transcription through interaction with TFIIIB [PMID:12150994, PMID:8146655, PMID:10330166].\",\n  \"teleology\": [\n    {\n      \"year\": 1992,\n      \"claim\": \"Identification of p107 as a cell-cycle-regulated E2F partner distinct from pRB established that pocket protein–E2F complexes are not monolithic—p107 forms temporally distinct complexes with cyclin E/cdk2 in G1 and cyclin A/cdk2 at G1/S, with cyclin A binding the unique spacer of the pocket domain.\",\n      \"evidence\": \"Co-immunoprecipitation and gel shift assays with synchronized cells; domain mapping with recombinant pocket fragments\",\n      \"pmids\": [\"1531040\", \"1530885\", \"1532457\", \"1532458\", \"1398067\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional significance of cyclin association (whether p107 is substrate, inhibitor, or scaffold) was unknown\", \"Whether p107–E2F complexes activate or repress transcription was unresolved\"]\n    },\n    {\n      \"year\": 1993,\n      \"claim\": \"Demonstrating that p107 actively represses E2F-dependent transcription and suppresses cell proliferation through mechanisms partly distinct from pRB resolved its function as a transcriptional co-repressor rather than a passive cyclin-sequestering scaffold.\",\n      \"evidence\": \"Reporter assays showing E2F-dependent repression; overexpression-induced G1 arrest with differential sensitivity versus pRB in certain cell lines\",\n      \"pmids\": [\"8458319\", \"7685208\", \"8319904\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific E2F family member partnering with p107 was not yet identified\", \"Whether growth suppression required E2F binding, cyclin binding, or both was unclear\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Identification of E2F-4 as the preferred in vivo E2F partner of p107 and demonstration that p107 directly binds and suppresses c-Myc transactivation expanded p107's role beyond E2F repression to regulation of multiple oncogenic transcription factors.\",\n      \"evidence\": \"Reciprocal co-immunoprecipitation of E2F-4/p107; yeast screen and Co-IP for c-Myc/p107; reporter assays; Burkitt lymphoma Myc mutants disrupting the interaction\",\n      \"pmids\": [\"7958925\", \"7958924\", \"8146655\", \"8076603\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether c-Myc suppression occurs on chromatin or via sequestration was unresolved\", \"Viral oncoprotein binding to the pocket domain was mapped but functional consequences for viral replication were incomplete\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Structure–function dissection revealed that p107 contains two separable growth-suppression domains—an E2F-binding pocket and a p21-like cyclin-binding/CDK-inhibitory domain—establishing p107 as a bona fide CDK inhibitor that competes with p21 for cyclin/cdk2 binding.\",\n      \"evidence\": \"In vitro kinase inhibition with purified components; deletion mutants in growth arrest assays; competition assays between p107 and p21; cyclin A/cdk2 phosphorylation leading to complex dissociation in vitro\",\n      \"pmids\": [\"7622038\", \"7743997\", \"7753545\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Quantitative Ki values were not yet determined\", \"Whether endogenous p107 inhibits CDKs in physiological stoichiometry was untested\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Discovery that p107 represses Sp1-dependent transcription independently of its pocket domain and autoregulates its own promoter via E2F sites broadened its transcriptional repertoire beyond E2F targets.\",\n      \"evidence\": \"Co-IP of Sp1/p107; Gal4-Sp1 reporter assays with pocket-deleted p107; p107 promoter mutagenesis\",\n      \"pmids\": [\"7565695\", \"7791762\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Sp1 repression mechanism (direct versus indirect) was not fully resolved\", \"Autoregulatory loop was demonstrated only with reporters, not at the endogenous locus\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Tracking E2F-4 through the cell cycle revealed a pocket-protein switching mechanism—p130 sequesters E2F-4 in G0, while p107 assumes the partnership in cycling cells—and p107 was shown to suppress B-MYB transactivation, linking it to G2/M gene control.\",\n      \"evidence\": \"Cell synchronization with specific antisera for each pocket protein; Co-IP of B-MYB/p107 with functional reporter assay\",\n      \"pmids\": [\"8657117\", \"8910512\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The composition and identity of the MuvB/DREAM complex mediating G2/M repression was not yet known\", \"Whether p107–B-MYB interaction occurs on chromatin was undemonstrated\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"In vitro reconstitution with purified proteins confirmed that p107 (and p130) stoichiometrically inhibit cyclin A/E–cdk2, and SV40 large T antigen J-domain–mediated hyperphosphorylation of p107/p130 was shown to be the essential mechanism by which T antigen overcomes pocket protein growth suppression.\",\n      \"evidence\": \"Reconstituted kinase inhibition assays; genetic epistasis—J domain dispensable in p107/p130 double-knockout MEFs\",\n      \"pmids\": [\"9199292\", \"9271376\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether J-domain action operates through Hsp70-dependent or -independent mechanisms was unresolved\", \"In vivo stoichiometry of p107–cyclin/cdk complexes remained unknown\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Quantitative enzymology established p107 as a CDK inhibitor with Ki comparable to p21, resolving the dual-domain architecture: the N-terminal domain binds cyclins and inhibits kinase activity while the C-terminal spacer serves as a CDK substrate but does not inhibit.\",\n      \"evidence\": \"In vitro kinase assay with Ki determination, domain deletion and peptide competition\",\n      \"pmids\": [\"9710622\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether phosphorylation of the C-terminal substrate domain feeds back to relieve N-terminal inhibition in vivo was unknown\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Identification of PP2A (via PR59 and catalytic subunit) as the phosphatase that specifically dephosphorylates p107 in response to UV irradiation and oxidative stress established a signal-activated phosphatase–kinase toggle controlling p107 repressor activity independently of p53/p21.\",\n      \"evidence\": \"Yeast two-hybrid identification of PR59; reciprocal Co-IP; phosphatase inhibitor and SV40 small-t experiments; UV-induced dephosphorylation independent of p53/p21\",\n      \"pmids\": [\"9927208\", \"9989818\", \"10330166\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The upstream signal connecting UV/oxidative stress to PP2A activation was not identified\", \"Which specific PP2A B subunit mediates stress-induced versus basal dephosphorylation was unresolved\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Three advances converged: mapping of four CDK4/cyclin D1 phosphorylation sites on p107 with RXL-motif dependence; discovery of a cytoplasmic Smad3/E2F4/p107 complex that translocates to the nucleus to mediate TGFβ-dependent c-myc repression; and genetic demonstration that p107/p130 mediate FGF-induced growth arrest in chondrocytes.\",\n      \"evidence\": \"In vitro kinase assay with site-directed mutagenesis and non-phosphorylatable mutant rescue; ChIP, subcellular fractionation, and promoter mutagenesis for TGFβ/Smad pathway; p107/p130 single and double-knockout primary chondrocytes with FGF treatment\",\n      \"pmids\": [\"11884610\", \"12150994\", \"12177046\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Smad3–p107 interaction occurs independently of E2F4 was not determined\", \"How FGF signaling converges on PP2A to dephosphorylate p107 was not yet mechanistically linked\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Functional studies revealed that p107 represses the F-box gene Skp2 (thereby stabilizing p27) and, together with p130, specifically represses G2/M genes (including Plk1) after DNA damage, distinguishing p107/p130 from pRB in checkpoint-mediated transcriptional repression.\",\n      \"evidence\": \"p107 overexpression and knockout MEF analysis with Skp2 rescue; gene expression profiling after adriamycin in RB-family-deleted cells\",\n      \"pmids\": [\"15631990\", \"15827088\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether Skp2 repression is direct (p107 on Skp2 promoter) or indirect was not definitively shown by ChIP\", \"Relative contributions of p107 versus p130 to G2/M gene repression were not cleanly separated\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Two studies extended p107's repressive role: in neural progenitors, p107 represses Hes1 to promote neuronal commitment (rescued by Hes1 heterozygosity in p107-null mice); and p107 was placed in a cell-cycle-regulated Mip/LIN-9 repressor complex with E2F4 that is disrupted by CDK4 phosphorylation, directly linking p107 to MuvB-mediated G2/M gene repression.\",\n      \"evidence\": \"p107-knockout mouse neurosphere analysis with Hes1 genetic epistasis; cell-cycle-resolved Co-IP of Mip/LIN-9, E2F4, p107 with CDK4-phosphorylation-dependent dissociation\",\n      \"pmids\": [\"17591923\", \"17563750\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the Mip/LIN-9–p107 complex is identical to what was later defined as DREAM was not yet established\", \"In vivo chromatin occupancy of p107 at Hes1 was not shown\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Mechanistic closure of the FGF–PP2A–p107 axis demonstrated that FGF signaling activates PP2A to dephosphorylate p107 in chondrocytes, and that CDK4/cyclin D1 overexpression or PP2A knockdown each prevent FGF-induced p107 dephosphorylation and growth arrest.\",\n      \"evidence\": \"siRNA knockdown of PP2A catalytic subunit, SV40 small-t expression, cyclin D1/Cdk4 overexpression, endogenous Co-IP of PP2A with p107 after FGF treatment\",\n      \"pmids\": [\"18927618\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The specific PP2A regulatory B subunit activated by FGF was not identified in this context\", \"Whether PP2A activation is mediated by FGFR kinase activity directly or through intermediate signaling was unresolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Proteomic identification of B55α as the PP2A regulatory subunit that specifically directs PP2A to p107 established the molecular identity of the p107-selective phosphatase holoenzyme.\",\n      \"evidence\": \"Proteomic identification, Co-IP, B55α knockdown with phosphorylation state analysis\",\n      \"pmids\": [\"20663872\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relationship between B55α and the previously identified PR59 subunit in directing PP2A to p107 was not clarified\", \"Structural basis for B55α selectivity for p107 over pRB is unknown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Genome-wide analysis demonstrated that p107-containing DREAM complexes specifically repress G2/M (but not G1/S) genes in response to p53/p21 activation, while p130-DREAM represses G1/S genes, resolving the division of labor within the DREAM complex.\",\n      \"evidence\": \"Gene expression profiling and ChIP in human fibroblasts with genetic deletion of individual RB family members, DNA damage to activate p53\",\n      \"pmids\": [\"31667499\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The structural or sequence determinant within p107 versus p130 that confers G2/M versus G1/S promoter specificity is unknown\", \"Whether p107-DREAM and p130-DREAM are mutually exclusive on the same promoter was not resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include: the structural basis for p107's selective incorporation into G2/M-repressive DREAM complexes versus p130's G1/S specificity; whether the CDK-inhibitory and E2F-repressive functions of p107 are coordinated or independent in vivo at endogenous stoichiometries; and how upstream stress signals (UV, oxidative stress, FGF) converge on PP2A–B55α/PR59 to activate p107 dephosphorylation.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No structural model of p107 in complex with DREAM subunits\", \"No in vivo measurement of p107–CDK inhibitory stoichiometry\", \"Signal transduction from stress receptors to PP2A activation for p107 dephosphorylation is unmapped\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [3, 5, 6, 10, 13, 20, 22, 27, 31]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [8, 14, 16]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [3, 5, 22, 31]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [22]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [2, 4, 7, 9, 23, 28, 31, 36]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [3, 5, 6, 10, 20, 22, 27]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [22, 29, 30]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [21, 35]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [4, 26]}\n    ],\n    \"complexes\": [\n      \"DREAM complex (p107-E2F4-DP-MuvB)\",\n      \"p107-Smad3-E2F4-DP1 complex\",\n      \"PP2A-B55α-p107 holoenzyme\"\n    ],\n    \"partners\": [\n      \"E2F4\",\n      \"CDK2\",\n      \"CCNA2\",\n      \"CCNE1\",\n      \"CDK4\",\n      \"SMAD3\",\n      \"LIN9\",\n      \"PPP2CA\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"RBL1 (p107) is a nuclear pocket protein that restrains cell proliferation by binding and repressing E2F4/5 transcription factors in a cell-cycle-regulated manner, recruiting HDAC1 to silence E2F target genes, and directly inhibiting cyclin A–CDK2 and cyclin E–CDK2 kinase activity with a Ki comparable to p21 [PMID:1833063, PMID:9710622, PMID:9724731]. Phosphorylation by cyclin D1–CDK4 at four specific sites dissociates p107 from E2F4 and releases the G1 block, while PP2A holoenzymes containing B55α or PR59 dephosphorylate and reactivate p107 in response to UV, DNA damage, FGF, and oxidative stress [PMID:11884610, PMID:9927208, PMID:9989818, PMID:18927618]. Beyond canonical E2F repression, p107 participates in TGFβ-Smad3–mediated c-myc silencing through a preformed cytoplasmic Smad3–E2F4/5–DP1–p107 complex that translocates to the nucleus, represses RNA polymerase III via TFIIIB interaction, contributes to constitutive heterochromatin maintenance through Suv4-20h enzymes, and cooperates with p130 in the DREAM complex to repress G2/M genes after DNA damage [PMID:12150994, PMID:10330166, PMID:15750587, PMID:31667499]. In vivo, p107 is functionally redundant with p130 in chondrocyte growth arrest and endochondral bone development, collaborates with RB1 to enforce retinal cell cycle exit—combined loss causes retinoblastoma in mice and Xenopus—and regulates white-to-brown adipocyte fate and neural precursor self-renewal through Hes1 repression [PMID:8682294, PMID:15193257, PMID:27739525, PMID:16271529, PMID:17591923].\",\n  \"teleology\": [\n    {\n      \"year\": 1991,\n      \"claim\": \"Identification of p107 as a second member of the retinoblastoma protein family resolved how viral oncoproteins such as SV40 large T and E1A engage multiple pocket-domain targets, establishing that cell-cycle control involves more than one RB-like repressor.\",\n      \"evidence\": \"cDNA cloning, chromosomal mapping, and domain-deletion binding assays in human cells\",\n      \"pmids\": [\"1833063\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No cellular function yet ascribed beyond viral oncoprotein binding\", \"No E2F interaction or cell-cycle role demonstrated\"]\n    },\n    {\n      \"year\": 1992,\n      \"claim\": \"Discovery that p107 forms complexes with cyclin A, cyclin E, CDK2, and E2F at distinct cell-cycle phases—while RB–E2F complexes predominate in G1—established that the two pocket proteins partition E2F regulation temporally through the cell cycle.\",\n      \"evidence\": \"Reciprocal co-immunoprecipitation, gel mobility shift assays, and cell-cycle synchronization across multiple independent laboratories\",\n      \"pmids\": [\"1532457\", \"1531040\", \"1398067\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the specific E2F species bound by p107 not yet resolved\", \"Mechanism of transcriptional repression unknown\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Identification of E2F-4 as the principal p107-associated E2F, combined with the demonstration that p107 binds and suppresses c-Myc transactivation through a distinct mechanism from RB, revealed that p107 channels growth-suppressive signals through specific transcription factor targets.\",\n      \"evidence\": \"cDNA cloning of E2F-4, co-immunoprecipitation, transformation assays, c-Myc reporter assays, and growth-arrest rescue experiments\",\n      \"pmids\": [\"7958925\", \"8146655\", \"8319904\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether p107–E2F4 and p107–Myc complexes coexist or are mutually exclusive unclear\", \"Chromatin-level mechanism of repression not addressed\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Biochemical dissection showed p107 contains two separable growth-suppression domains—a pocket that represses E2F and a p21-like N-terminal domain that directly inhibits cyclin A/E–CDK2 kinase activity—establishing p107 as both a transcriptional repressor and a stoichiometric CDK inhibitor.\",\n      \"evidence\": \"In vitro kinase assays with Ki determination, domain-deletion structure–function analysis, competitive binding with p21, growth-suppression assays\",\n      \"pmids\": [\"7622038\", \"7743997\", \"9710622\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for simultaneous CDK inhibition and E2F repression unknown\", \"Relative contribution of each domain in physiological contexts untested\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Cyclin D1–CDK4 was identified as the kinase that phosphorylates p107 in mid-G1 to dissociate E2F-4, while p107/p130 double-knockout mice revealed functional redundancy in limb development and showed that single knockouts are viable—defining CDK4 as the upstream activating kinase and p130 as the primary compensating family member.\",\n      \"evidence\": \"Cell synchronization, kinase assays, dominant-negative CDK4, and gene-targeted knockout mice with histological analysis\",\n      \"pmids\": [\"7797074\", \"8682294\", \"8682293\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific phosphorylation sites not yet mapped\", \"Redundancy versus specificity in non-skeletal tissues unresolved\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Discovery that p107 recruits HDAC1 through an LXCXE-like motif to repress E2F-4 target genes provided the first chromatin-modifying mechanism through which p107 silences transcription, explaining how viral E1A displaces HDAC1 to de-repress targets.\",\n      \"evidence\": \"Co-immunoprecipitation, E1A competition assays, TSA treatment, and E2F-4-dependent reporter assays\",\n      \"pmids\": [\"9724731\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether additional chromatin remodelers are recruited alongside HDAC1 unknown\", \"Genome-wide target specificity of HDAC1 recruitment not tested\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Identification of PP2A as the phosphatase that dephosphorylates and reactivates p107 in response to UV irradiation—independently of p53/p21—and the discovery of the p107-specific PP2A subunit PR59 established a CDK-opposing phosphatase axis that rapidly reactivates p107 under stress.\",\n      \"evidence\": \"UV irradiation in p53/p21-null cells, phosphatase inhibitors (okadaic acid, calyculin A), in vitro dephosphorylation with purified PP2A, PR59 co-immunoprecipitation and overexpression\",\n      \"pmids\": [\"9989818\", \"9927208\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PR59-PP2A is the UV-responsive holoenzyme or another B subunit is involved not determined\", \"Structural basis for PR59 selectivity for p107 over RB unknown\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"The finding that a preformed cytoplasmic Smad3–E2F4/5–DP1–p107 complex translocates to the nucleus upon TGFβ signaling to repress c-myc placed p107 as a direct signal transducer of TGFβ upstream of CDK regulation, while concurrent mapping of four CDK4 phosphorylation sites (T369, S640, S964, S975) defined the molecular switch for p107 inactivation.\",\n      \"evidence\": \"Co-immunoprecipitation, subcellular fractionation, ChIP on c-myc promoter, in vitro kinase assays with site-directed mutagenesis and mass spectrometry\",\n      \"pmids\": [\"12150994\", \"11884610\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How cytoplasmic pre-assembly is regulated prior to TGFβ stimulation unknown\", \"Whether phosphorylation at all four sites is required simultaneously or sequentially untested in vivo\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Demonstration that RB-family proteins including p107 recruit Suv4-20h methyltransferases to maintain H4K20me3 at pericentric and telomeric heterochromatin—independently of E2F—expanded p107's role beyond E2F-dependent gene regulation to constitutive heterochromatin maintenance.\",\n      \"evidence\": \"Triple-knockout MEFs, ChIP for histone modifications, co-immunoprecipitation with Suv4-20h1/h2\",\n      \"pmids\": [\"15750587\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of p107 versus RB versus p130 to heterochromatin maintenance not individually resolved\", \"Whether this function is dispensable in p107-single-null cells unclear due to redundancy\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"In vivo genetic studies revealed tissue-specific roles: p107 loss converts white adipose to brown adipose with elevated PGC-1α/UCP-1, while p107 represses Hes1 to limit neural precursor self-renewal—demonstrating that p107 controls fate decisions beyond generic cell-cycle arrest.\",\n      \"evidence\": \"p107-knockout mice, adipogenesis assays, Hes1/p107 compound knockout, neurosphere assays, BrdU labeling\",\n      \"pmids\": [\"16271529\", \"17591923\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether PGC-1α repression is direct or indirect through pRb level changes not fully resolved\", \"Molecular mechanism linking p107 to Hes1 promoter repression (direct binding vs. E2F) not defined\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Genome-wide expression profiling after individual and combined RB-family knockdowns in DNA-damaged human fibroblasts established that p107 specifically represses G2/M genes through the DREAM complex (with p130), while G1/S gene repression depends on p130 and RB—resolving the division of labor among pocket proteins in the DNA-damage response.\",\n      \"evidence\": \"shRNA knockdown of individual RB family members in primary human fibroblasts, doxorubicin treatment, genome-wide gene expression profiling\",\n      \"pmids\": [\"31667499\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether DREAM complex composition shifts during prolonged damage signaling untested\", \"ChIP-seq for p107-DREAM occupancy at G2/M promoters in damage conditions not performed\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis for p107's simultaneous CDK inhibition and E2F repression, the relative in vivo contributions of individual PP2A holoenzymes to p107 reactivation in different stress contexts, and whether p107's heterochromatin and DREAM functions are mechanistically linked.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No crystal structure of full-length p107 or p107–E2F4–CDK2 ternary complex\", \"Genome-wide ChIP-seq for endogenous p107 across cell-cycle phases in primary cells lacking\", \"Tissue-specific tumor suppressor function of p107 independent of RB not demonstrated in human cancers\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [4, 6, 11, 26, 35, 42]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [14, 33, 34]},\n      {\"term_id\": \"GO:0042393\", \"supporting_discovery_ids\": [48]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [40, 42, 48, 56]},\n      {\"term_id\": \"GO:0005654\", \"supporting_discovery_ids\": [40, 56]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [42]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [2, 3, 14, 16, 28, 43, 60, 61]},\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [35, 48]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [4, 6, 9, 26, 42]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [42, 45]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [38, 52, 60]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [23, 44, 54]}\n    ],\n    \"complexes\": [\n      \"DREAM complex\",\n      \"p107–E2F4/5–DP1\",\n      \"Smad3–E2F4/5–DP1–p107\"\n    ],\n    \"partners\": [\n      \"E2F4\",\n      \"CCNA2\",\n      \"CDK2\",\n      \"HDAC1\",\n      \"SMAD3\",\n      \"MYC\",\n      \"MYBL2\",\n      \"PPP2CA\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}