{"gene":"CSTF2","run_date":"2026-06-09T22:57:19","timeline":{"discoveries":[{"year":1996,"finding":"CstF-64 is a limiting subunit of the CstF complex; its accumulation is specifically repressed in primary B cells, and overexpression of CstF-64 is sufficient to switch IgM heavy chain pre-mRNA processing from the membrane-bound (µm) to secreted (µs) form. CstF has higher affinity for the µm poly(A) site, and the µm site is stronger in a reconstituted in vitro processing reaction.","method":"Reconstituted in vitro polyadenylation/processing assay, overexpression in B cell lines, affinity measurements","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstituted in vitro processing, overexpression rescue, affinity measurements; replicated in subsequent work","pmids":["8945520"],"is_preprint":false},{"year":1998,"finding":"A 10-fold decrease in CstF-64 concentration in the DT40 B cell line specifically and dramatically reduces IgM heavy chain mRNA accumulation; further reduction causes reversible G0/G1 cell cycle arrest, and depletion leads to apoptotic cell death, demonstrating unexpected roles for CstF-64 in regulating gene expression and cell growth.","method":"Gene disruption of endogenous CstF-64 replaced with regulatable transgene in DT40 cells; cell cycle and apoptosis assays","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean genetic KO with regulatable transgene, multiple phenotypic readouts (mRNA accumulation, cell cycle, apoptosis)","pmids":["9885564"],"is_preprint":false},{"year":1996,"finding":"CstF-64 (64 kDa subunit) and CPSF 100 kDa are concentrated in discrete nuclear foci ('cleavage bodies') closely associated with coiled bodies; these foci are transcription-dependent and contain newly synthesized RNA, revealing dynamic transcription-coupled subnuclear localization of the 3'-cleavage machinery.","method":"Immunofluorescence with monoclonal antibodies, alpha-amanitin/DRB transcription inhibition, immunogold electron microscopy, BrU labeling of nascent RNA","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal microscopy methods (IF, EM immunogold, nascent RNA labeling) with functional perturbation by transcription inhibition","pmids":["8654386"],"is_preprint":false},{"year":2003,"finding":"The N-terminal RNA recognition motif (RRM) of CstF-64 recognizes GU-rich downstream sequence elements; the C-terminal helix of the RRM unfolds upon RNA binding and extends into the hinge domain where interactions with other polyadenylation assembly factors occur, suggesting this conformational change initiates assembly of the polyadenylation complex. Consecutive U residues are required for strong CstF-GU interaction.","method":"NMR structure determination of the RRM domain free and RNA-bound; mutagenesis of RNA contacts","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — NMR structure with RNA binding validation and mutagenesis, replicated by subsequent structural/biophysical studies","pmids":["12773396"],"is_preprint":false},{"year":2005,"finding":"The protein-RNA interface of CstF-64 RRM acquires significant micro-to-millisecond timescale mobility upon binding GU-rich RNA, while the free protein is uniformly rigid. This dynamic behavior at the binding interface is proposed to allow binding to diverse GU-rich sequences while discriminating against non-GU-rich RNAs.","method":"NMR relaxation dynamics measurements of CstF-64 RRM free and bound to two GU-rich RNA sequences","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — NMR relaxation with two different RNA substrates in a single rigorous study","pmids":["15769465"],"is_preprint":false},{"year":2006,"finding":"The C-terminal domains of CstF-64 and its yeast orthologue Rna15 fold into a three-helix bundle with an uncommon topological arrangement. This domain mediates interaction with Pcf11, and this interaction is critical for mRNA 3'-end processing but dispensable for transcription termination.","method":"NMR structure determination of C-terminal domains; mutagenesis of conserved surface residues; in vitro 3'-end processing assays with Rna15 mutants","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — NMR structure combined with mutagenesis and functional in vitro processing assays","pmids":["17116658"],"is_preprint":false},{"year":2009,"finding":"The hinge domain of CstF-64 is essential for interaction with CstF-77 and for nuclear localization; nuclear import of a preformed CstF complex is an essential step in polyadenylation. Loss of the hinge domain abolishes CstF-64-dependent polyadenylation activity as measured by a reporter assay.","method":"SLAP (stem-loop luciferase assay for polyadenylation) with CstF-64 domain deletion/mutation constructs; co-immunoprecipitation; immunofluorescence localization","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (reporter assay, Co-IP, IF localization) in a single study","pmids":["19887456"],"is_preprint":false},{"year":2009,"finding":"EV71 3C protease cleaves CstF-64 at position 251 (N-terminal P/G-rich domain) and at multiple sites near position 500 (C-terminus). This cleavage inactivates CstF-64 and inhibits host cell 3'-end pre-mRNA processing and polyadenylation; impairment is rescued by adding purified recombinant CstF-64 protein.","method":"In vitro cleavage assay with recombinant 3Cpro and CstF-64; site-directed mutagenesis to map cleavage sites; in vitro polyadenylation assay with 3Cpro-treated nuclear extract; rescue by recombinant CstF-64","journal":"PLoS pathogens","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro cleavage with mutagenesis mapping of cleavage sites, functional rescue in polyadenylation assay","pmids":["19779565"],"is_preprint":false},{"year":2010,"finding":"CstF-64 binds CstF-77 and symplekin mutually exclusively through its hinge domain. The CstF-64–symplekin interaction is limiting for histone RNA 3'-end processing but relatively unimportant for cleavage/polyadenylation. Nuclear accumulation of CstF-64 depends on its binding to CstF-77 but not to symplekin. CstF-64τ can compensate for loss of CstF-64 but has lower affinity for CstF-77 and is less stable.","method":"Identification of CstF-64 and symplekin mutants that distinguish the two interactions; co-immunoprecipitation; complementation assays in cell lines; 3'-end processing assays","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP with structure-function mutants, functional processing assays, localization studies; multiple orthogonal approaches","pmids":["21119002"],"is_preprint":false},{"year":2000,"finding":"A variant form of CstF-64, termed tauCstF-64, is encoded by an autosomal gene (Cstf2t) on mouse chromosome 19 and is specifically expressed in meiotic and postmeiotic germ cells to compensate for X-chromosome inactivation of the somatic CstF-64. The tauCstF-64 protein contains a Pro→Ser substitution in its RNA-binding domain and significant changes in the region interacting with CstF-77.","method":"cDNA cloning; chromosomal mapping; immunoblot; 2D-PAGE; antibody reactivity; proteolytic digest pattern comparison","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — cDNA cloning with biochemical characterization (immunoblot, 2D-PAGE, proteolytic mapping); single lab","pmids":["11113135"],"is_preprint":false},{"year":2001,"finding":"In C. elegans, CstF-64 forms a complex with the SL2 snRNP (but not SL1 or other U snRNAs), linking mRNA 3'-end formation with SL2-specific trans-splicing. Stem/loop III of SL2 RNA is required for both SL2 identity and association with CstF-64.","method":"Immunoprecipitation of complex with anti-CstF-64 antibody; mutational analysis of SL2 RNA stem-loops; in vivo trans-splicing assays","journal":"Genes & development","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal IP with mutational dissection of RNA determinants; single lab","pmids":["11581161"],"is_preprint":false},{"year":2007,"finding":"CstF-64 RBD has higher affinity for poly(U) than tauCstF-64 RBD, while tauCstF-64 has higher affinity for poly(GU). A region C-terminal to the RBD (not Pro-41 alone) is important for RNA sequence recognition and differential affinity.","method":"RNA cross-linking Kd measurements with poly(G), poly(A), poly(C), poly(U), and poly(GU) ribopolymers; mutagenesis of CstF-64 RBD residues","journal":"The Biochemical journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — quantitative binding assay with mutagenesis; single lab","pmids":["17029590"],"is_preprint":false},{"year":2014,"finding":"CstF-64 supports ESC pluripotency and cell cycle progression by promoting correct 3'-end processing (non-polyadenylation) of replication-dependent histone mRNAs; loss of CstF-64 results in increased histone mRNA polyadenylation, lengthened G1, and loss of pluripotency. τCstF-64 partially compensates and is recruited to the histone mRNA 3'-end processing complex.","method":"CstF-64 knockout ESCs; RT-PCR and Northern analysis of histone mRNA polyadenylation; cell cycle analysis; pluripotency marker assays; τCstF-64 knockdown in Cstf2-deficient ESCs","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with multiple phenotypic readouts and partial rescue analysis; single lab","pmids":["24957598"],"is_preprint":false},{"year":2018,"finding":"The carboxy-terminus of CstF-77 enhances CstF-64 RNA binding activity by altering how the RRM of CstF-64 engages RNA, increasing RRM stability and thus the affinity of the CstF complex for RNA. CstF-64 nuclear localization depends on CstF-77 binding; excess CstF-64 accumulates in the cytoplasm, possibly by interacting with cytoplasmic RNAs.","method":"NMR spectroscopy of recombinant CstF-64 RRM-Hinge and CstF-77 CTD; reverse genetics; RNA binding assays; immunofluorescence localization","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 / Strong — NMR structure-function with reverse genetics and multiple orthogonal assays (binding, localization) in a single rigorous study","pmids":["30257008"],"is_preprint":false},{"year":2018,"finding":"CSTF2 promotes 3'UTR shortening of RAC1 by cotranscriptionally binding to a GUAAU motif at the proximal polyadenylation site of RAC1, which attenuates recruitment of transcription elongation factors AFF1 and AFF4, causing defects in elongation and favoring proximal poly(A) site usage.","method":"RNA sequencing; chromatin immunoprecipitation (ChIP) for CSTF2 and transcription elongation factors; 3'UTR isoform analysis; CSTF2 knockdown/overexpression with migration/invasion assays","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP showing cotranscriptional binding with functional consequences; single lab","pmids":["30143523"],"is_preprint":false},{"year":2020,"finding":"A missense mutation in the RRM of CSTF2 (p.D50A) causes intellectual disability in males. This mutation changes the electrostatic potential of the RRM, leading to greater (altered on-rate) RNA binding affinity and reduced C/P efficiency, altering polyadenylation sites in over 1300 brain-expressed genes.","method":"Reporter gene C/P assay; NMR structure and chemical shift perturbation of D50A RRM; genome-wide poly(A) site analysis in knock-in mice","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 / Strong — NMR structural characterization, in vivo reporter assay, genome-wide APA analysis; multiple orthogonal methods in one study","pmids":["32816001"],"is_preprint":false},{"year":2022,"finding":"Electrostatic attraction is the dominant force in CSTF2 RRM binding to U-rich RNA; RNA binding is accompanied by enthalpy-entropy compensation and changes in picosecond-to-nanosecond timescale protein dynamics. Competition between fast high-affinity RNA binding and efficient correct C/P is demonstrated in vivo.","method":"Mutagenesis of surface-charged residues; NMR spectroscopy; biophysical binding assays (ITC, SPR); in vivo C/P reporter assay","journal":"Biophysical journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — mutagenesis combined with NMR and multiple biophysical assays plus in vivo C/P reporter","pmids":["35090899"],"is_preprint":false},{"year":2023,"finding":"CSTF2 co-transcriptionally regulates m6A installation on target gene transcripts by slowing RNA Pol II elongation rate during transcription; CSTF2-regulated m6As are predominantly recognized by IGF2BP2, an m6A reader that stabilizes mRNAs.","method":"Transcriptomic m6A profiling (MeRIP-seq) in PDAC tissues; CSTF2 knockdown/overexpression with m6A and RNA Pol II elongation analysis; RIP for IGF2BP2","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — MeRIP-seq and Pol II elongation assays with KD/OE; single lab, mechanistic follow-up needs more orthogonal validation","pmids":["37816727"],"is_preprint":false},{"year":2024,"finding":"CSTF2 RRM binds U-rich RNA through a multistep binding process involving differences in ps-ns dynamics and potential structural changes in the C-terminal α-helix, as determined by NMR titration, spin relaxation, paramagnetic relaxation enhancement, and rigid-body docking.","method":"NMR titration and spin relaxation; paramagnetic relaxation enhancement; rigid-body docking","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — multiple NMR methods in a single rigorous structural study; consistent with prior structural work","pmids":["39305233"],"is_preprint":false},{"year":2025,"finding":"CSTF2 diminishes CXCL10 expression by promoting poly(A) polymerase alpha (PAPα) binding to the 3'UTR of CXCL10 RNA, resulting in shortened poly(A) tails and compromised CXCL10 RNA stability, thereby suppressing iαβT cell infiltration and anti-tumor immunity in PDAC.","method":"RIP assay for CSTF2 and PAPα binding to CXCL10 3'UTR; poly(A) tail length assay; CSTF2 KO mouse models and co-culture immune assays; Forsythoside B inhibitor targeting CSTF2 RRM","journal":"Cell death and differentiation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RIP with poly(A) tail length measurement and functional immune readouts; single lab","pmids":["39972059"],"is_preprint":false},{"year":2025,"finding":"CSTF2 shortens the 3'UTR of PGK1 pre-mRNA by binding near its proximal polyadenylation site, leading to loss of m6A sites that would otherwise be recognized by YTHDF2 (promoting degradation), thereby increasing PGK1 protein levels and enhancing glycolysis under hypoxia. Hypoxia-induced m6A near the proximal poly(A) site is recognized by YTHDC1, which recruits CSTF2 to further enhance PGK1 3'UTR shortening.","method":"RIP-seq for CSTF2 binding; m6A-seq; 3'UTR isoform analysis; CSTF2 KO in HCC cell lines and xenograft models; YTHDF2/YTHDC1 co-IP; masitinib inhibitor screen","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple binding and sequencing assays with in vivo xenograft validation; single lab","pmids":["39514400"],"is_preprint":false},{"year":2014,"finding":"Loss of CstF-64 in mouse ESCs results in loss of differentiation potential toward the endodermal lineage, which is necessary for cardiomyocyte specification; endodermal signaling from conditioned medium of XEN stem cells restores cardiomyocyte differentiation in CstF-64-knockout cells, placing CstF-64 upstream of endoderm-dependent cardiac specification.","method":"CstF-64 knockout ESCs (Cstf2E6); endoderm/mesoderm/cardiac differentiation assays; conditioned medium rescue experiment; marker expression analysis","journal":"Stem cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with differentiation assays and conditioned medium rescue; single lab","pmids":["25460602"],"is_preprint":false}],"current_model":"CSTF2 (CstF-64) is the RNA-binding subunit of the trimeric CstF complex that recognizes GU-rich downstream sequence elements in pre-mRNAs through its N-terminal RRM domain (via predominantly electrostatic, dynamically mobile interactions), recruits the complex to poly(A) sites, and is rate-limiting for cleavage and polyadenylation efficiency; its nuclear localization depends on binding CstF-77 through its hinge domain, which also mediates mutually exclusive interactions with symplekin for histone mRNA 3'-end processing; CstF-64 concentration is a key regulatory lever for alternative poly(A) site selection (e.g., IgM heavy chain switching in B cell differentiation), and it additionally co-transcriptionally regulates m6A deposition and 3'UTR length by modulating RNA Pol II elongation rate, with downstream consequences for mRNA stability, cell cycle progression, ESC pluripotency, and tumor biology."},"narrative":{"mechanistic_narrative":"CSTF2 (CstF-64) is the RNA-binding subunit of the cleavage stimulation factor (CstF) complex that recognizes GU/U-rich downstream sequence elements in pre-mRNAs and is rate-limiting for the efficiency and site selection of 3'-end cleavage and polyadenylation [PMID:8945520, PMID:12773396]. Its N-terminal RRM engages GU-rich RNA through predominantly electrostatic contacts, with the C-terminal helix unfolding upon binding and the protein-RNA interface acquiring micro-to-millisecond mobility that permits recognition of diverse GU-rich sequences while discriminating against non-GU RNAs [PMID:12773396, PMID:15769465, PMID:35090899]. The hinge domain anchors CstF-64 into the complex by binding CstF-77, an interaction required for nuclear import and for full RNA-binding activity, and which is mutually exclusive with symplekin binding that instead drives histone mRNA 3'-end processing [PMID:19887456, PMID:21119002, PMID:30257008]. Because CstF-64 is present at limiting concentration, its abundance sets a regulatory lever for alternative poly(A) site selection, exemplified by the switch from membrane-bound to secreted IgM heavy chain during B cell differentiation, and its depletion arrests the cell cycle and triggers apoptosis [PMID:8945520, PMID:9885564]. CstF-64 supports embryonic stem cell pluripotency and cell cycle progression by promoting correct non-polyadenylated processing of replication-dependent histone mRNAs and gates endoderm-dependent cardiac differentiation [PMID:24957598, PMID:25460602]. Beyond canonical processing, CSTF2 acts co-transcriptionally to shorten 3'UTRs (e.g., RAC1, PGK1) by binding proximal poly(A) sites and modulating RNA Pol II elongation, with downstream effects on m6A deposition recognized by readers such as IGF2BP2, YTHDF2, and YTHDC1, linking it to mRNA stability, glycolysis, and tumor immunity [PMID:30143523, PMID:37816727, PMID:39514400]. A missense mutation (p.D50A) in the RRM that alters its electrostatic potential and RNA binding causes X-linked intellectual disability and shifts poly(A) site usage across more than 1300 brain-expressed genes [PMID:32816001].","teleology":[{"year":1996,"claim":"Established that CstF-64 abundance, rather than mere presence, governs poly(A) site choice — explaining how a constitutive processing factor can act as a developmental switch.","evidence":"Reconstituted in vitro processing, overexpression in B cell lines, and affinity measurements at IgM heavy chain poly(A) sites","pmids":["8945520"],"confidence":"High","gaps":["Mechanism by which CstF-64 levels are repressed in primary B cells not resolved","Generalizability to other alternative poly(A) site genes not yet tested"]},{"year":1996,"claim":"Localized the 3'-cleavage machinery to transcription-dependent subnuclear foci, linking CstF-64 to active transcription sites.","evidence":"Immunofluorescence, immunogold EM, BrU nascent RNA labeling, and transcription inhibition","pmids":["8654386"],"confidence":"High","gaps":["Functional significance of cleavage body foci for processing efficiency unclear"]},{"year":1998,"claim":"Showed CstF-64 has unexpected roles beyond housekeeping 3'-end processing by linking its dosage to cell cycle progression and survival.","evidence":"Regulatable transgene replacing endogenous CstF-64 in DT40 cells with cell cycle and apoptosis readouts","pmids":["9885564"],"confidence":"High","gaps":["Which target mRNAs drive the G0/G1 arrest and apoptosis not identified","Direct vs indirect effects not separated"]},{"year":2000,"claim":"Identified a germ-cell paralog (tauCstF-64/Cstf2t) that compensates for X-inactivation of CstF-64 during spermatogenesis, revealing tissue-specific specialization of the subunit.","evidence":"cDNA cloning, chromosomal mapping, immunoblot, 2D-PAGE, and proteolytic mapping","pmids":["11113135"],"confidence":"Medium","gaps":["Functional consequences of the RRM Pro→Ser substitution not characterized in this study","Single-lab characterization"]},{"year":2001,"claim":"Connected CstF-64 to trans-splicing in C. elegans through specific association with the SL2 snRNP, expanding its role beyond cis 3'-end formation.","evidence":"Reciprocal IP and mutational dissection of SL2 RNA stem-loops with in vivo trans-splicing assays","pmids":["11581161"],"confidence":"Medium","gaps":["Relevance to mammalian CstF-64 function unknown","Molecular contacts mediating SL2 association not mapped"]},{"year":2003,"claim":"Defined the structural basis of GU-rich element recognition and proposed an RNA-induced conformational change in the RRM C-terminal helix that initiates complex assembly.","evidence":"NMR structure of the RRM free and RNA-bound with mutagenesis of RNA contacts","pmids":["12773396"],"confidence":"High","gaps":["Coupling between helix unfolding and downstream factor recruitment not directly demonstrated"]},{"year":2005,"claim":"Explained how a single RRM tolerates diverse GU-rich sequences by showing binding induces interface mobility rather than rigid lock-and-key recognition.","evidence":"NMR relaxation dynamics of the RRM free and bound to two GU-rich RNAs","pmids":["15769465"],"confidence":"High","gaps":["Functional link between dynamics and in vivo poly(A) site selection not established at this stage"]},{"year":2006,"claim":"Separated the C-terminal domain's role in 3'-end processing (via Pcf11) from transcription termination, dissecting distinct functions of the subunit.","evidence":"NMR structure of C-terminal domains, surface mutagenesis, and in vitro processing assays with Rna15 mutants","pmids":["17116658"],"confidence":"High","gaps":["Conservation of the Pcf11 interaction surface in human CstF-64 not directly tested here"]},{"year":2007,"claim":"Quantified differential RNA-binding specificity between CstF-64 and tauCstF-64, mapping determinants to a region C-terminal to the RBD rather than a single residue.","evidence":"RNA cross-linking Kd measurements across homopolymers with RBD mutagenesis","pmids":["17029590"],"confidence":"Medium","gaps":["In vivo consequences of differential affinity for poly(A) site choice not assessed","Single-lab assay"]},{"year":2009,"claim":"Established the hinge domain as essential for CstF-77 binding and nuclear import, defining preformed-complex nuclear entry as a required step in polyadenylation.","evidence":"SLAP reporter assay with domain deletions, Co-IP, and IF localization","pmids":["19887456"],"confidence":"High","gaps":["Import receptor/pathway for the CstF complex not identified"]},{"year":2009,"claim":"Revealed CstF-64 as a target of viral subversion, with EV71 3C protease cleaving and inactivating it to shut down host 3'-end processing.","evidence":"In vitro cleavage with site mapping, polyadenylation assay on protease-treated extract, and recombinant rescue","pmids":["19779565"],"confidence":"High","gaps":["In vivo contribution of CstF-64 cleavage to viral replication during infection not quantified"]},{"year":2010,"claim":"Showed the hinge mediates mutually exclusive CstF-77 versus symplekin binding, partitioning CstF-64 between canonical poly(A) processing and histone mRNA 3'-end processing.","evidence":"Interaction-discriminating mutants, reciprocal Co-IP, complementation, and processing assays","pmids":["21119002"],"confidence":"High","gaps":["How the choice between CstF-77 and symplekin is regulated in cells not defined"]},{"year":2014,"claim":"Linked CstF-64 to stem cell biology by showing it enforces correct non-polyadenylated histone mRNA processing required for pluripotency and cell cycle, and gates endoderm-dependent cardiac differentiation.","evidence":"CstF-64 knockout ESCs with histone mRNA, cell cycle, pluripotency, and differentiation assays plus conditioned-medium rescue","pmids":["24957598","25460602"],"confidence":"Medium","gaps":["Direct vs secondary effects on histone processing not fully separated","Single-lab studies"]},{"year":2018,"claim":"Demonstrated co-transcriptional 3'UTR shortening as a CSTF2 function, acting by attenuating elongation factor recruitment to favor proximal poly(A) sites, with cancer phenotypes.","evidence":"RNA-seq, ChIP for CSTF2 and AFF1/AFF4, 3'UTR isoform analysis, and migration/invasion assays on RAC1","pmids":["30143523"],"confidence":"Medium","gaps":["Mechanism of elongation factor attenuation not structurally defined","Single-lab"]},{"year":2018,"claim":"Showed CstF-77 binding allosterically enhances CstF-64 RNA-binding activity by stabilizing the RRM, coupling complex assembly to affinity.","evidence":"NMR of RRM-Hinge with CstF-77 CTD, reverse genetics, binding assays, and IF localization","pmids":["30257008"],"confidence":"High","gaps":["Quantitative contribution of this enhancement to in vivo site selection not measured"]},{"year":2020,"claim":"Provided a direct disease link, showing an RRM missense mutation that increases RNA-binding on-rate reduces processing efficiency and causes X-linked intellectual disability with genome-wide poly(A) site shifts.","evidence":"Reporter C/P assay, NMR of D50A RRM, and genome-wide poly(A) site analysis in knock-in mice","pmids":["32816001"],"confidence":"High","gaps":["How altered poly(A) site usage translates to neuronal dysfunction not resolved"]},{"year":2022,"claim":"Defined electrostatics as the dominant binding force and revealed a competition between fast high-affinity RNA binding and correct cleavage/polyadenylation, reframing the D50A defect mechanistically.","evidence":"Surface-charge mutagenesis, NMR, ITC/SPR, and in vivo C/P reporter","pmids":["35090899"],"confidence":"High","gaps":["Structural intermediate driving the affinity-vs-efficiency tradeoff not directly visualized"]},{"year":2024,"claim":"Refined the binding mechanism to a multistep process involving ps-ns dynamics and C-terminal helix structural change, extending the dynamic recognition model.","evidence":"NMR titration, spin relaxation, paramagnetic relaxation enhancement, and rigid-body docking","pmids":["39305233"],"confidence":"High","gaps":["Atomic-resolution bound-state structure not obtained"]},{"year":2025,"claim":"Connected CSTF2-driven 3'UTR shortening to m6A biology and disease, showing it removes or remodels m6A sites recognized by reader proteins to control mRNA stability, glycolysis, and anti-tumor immunity.","evidence":"RIP/RIP-seq, m6A-seq, poly(A) tail length assays, reader co-IPs, KO mouse and xenograft models for CXCL10 and PGK1","pmids":["37816727","39972059","39514400"],"confidence":"Medium","gaps":["Direct causal chain from elongation modulation to specific m6A site loss not fully reconstituted","Single-lab studies per target"]},{"year":null,"claim":"How CstF-64 abundance, post-translational state, and competition between high-affinity binding and efficient processing are integrated to control alternative poly(A) site choice genome-wide in different cell types remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No genome-wide model linking CstF-64 dosage to tissue-specific APA outcomes","Regulation of CstF-64 levels in vivo poorly defined","Atomic structure of the RNA-bound complex incomplete"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[3,4,11,16,18]},{"term_id":"GO:0140098","term_label":"catalytic activity, acting on RNA","supporting_discovery_ids":[0,5,6,7]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[6,8,13]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[6,13]},{"term_id":"GO:0005654","term_label":"nucleoplasm","supporting_discovery_ids":[2]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[13]}],"pathway":[{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[0,3,6,8]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[14,17]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[15,19,20]}],"complexes":["CstF complex"],"partners":["CSTF3","SYMPK","PCF11","PAPOLA","IGF2BP2","YTHDF2","YTHDC1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P33240","full_name":"Cleavage stimulation factor subunit 2","aliases":["CF-1 64 kDa subunit","Cleavage stimulation factor 64 kDa subunit","CSTF 64 kDa subunit","CstF-64"],"length_aa":577,"mass_kda":61.0,"function":"One of the multiple factors required for polyadenylation and 3'-end cleavage of mammalian pre-mRNAs. This subunit is directly involved in the binding to pre-mRNAs","subcellular_location":"Nucleus","url":"https://www.uniprot.org/uniprotkb/P33240/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CSTF2","classification":"Not Classified","n_dependent_lines":70,"n_total_lines":1208,"dependency_fraction":0.057947019867549666},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"CPSF6","stoichiometry":0.2},{"gene":"RBM14","stoichiometry":0.2},{"gene":"SNRPA","stoichiometry":0.2},{"gene":"SNRPB","stoichiometry":0.2},{"gene":"SNRPC","stoichiometry":0.2},{"gene":"SSRP1","stoichiometry":0.2},{"gene":"TOP1","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/CSTF2","total_profiled":1310},"omim":[{"mim_id":"611968","title":"CLEAVAGE STIMULATION FACTOR, 3-PRIME PRE-RNA, SUBUNIT 2, 64-KD, TAU VARIANT; CSTF2T","url":"https://www.omim.org/entry/611968"},{"mim_id":"602388","title":"SYMPLEKIN; SYMPK","url":"https://www.omim.org/entry/602388"},{"mim_id":"301116","title":"INTELLECTUAL DEVELOPMENTAL DISORDER, X-LINKED 113; XLID113","url":"https://www.omim.org/entry/301116"},{"mim_id":"300907","title":"CLEAVAGE STIMULATION FACTOR, 3-PRIME PRE-RNA, SUBUNIT 2, 64-KD; CSTF2","url":"https://www.omim.org/entry/300907"},{"mim_id":"194355","title":"X BOX-BINDING PROTEIN 1; XBP1","url":"https://www.omim.org/entry/194355"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Nucleoplasm","reliability":"Enhanced"},{"location":"Nuclear bodies","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in 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CstF has higher affinity for the µm poly(A) site, and the µm site is stronger in a reconstituted in vitro processing reaction.\",\n      \"method\": \"Reconstituted in vitro polyadenylation/processing assay, overexpression in B cell lines, affinity measurements\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstituted in vitro processing, overexpression rescue, affinity measurements; replicated in subsequent work\",\n      \"pmids\": [\"8945520\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"A 10-fold decrease in CstF-64 concentration in the DT40 B cell line specifically and dramatically reduces IgM heavy chain mRNA accumulation; further reduction causes reversible G0/G1 cell cycle arrest, and depletion leads to apoptotic cell death, demonstrating unexpected roles for CstF-64 in regulating gene expression and cell growth.\",\n      \"method\": \"Gene disruption of endogenous CstF-64 replaced with regulatable transgene in DT40 cells; cell cycle and apoptosis assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean genetic KO with regulatable transgene, multiple phenotypic readouts (mRNA accumulation, cell cycle, apoptosis)\",\n      \"pmids\": [\"9885564\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"CstF-64 (64 kDa subunit) and CPSF 100 kDa are concentrated in discrete nuclear foci ('cleavage bodies') closely associated with coiled bodies; these foci are transcription-dependent and contain newly synthesized RNA, revealing dynamic transcription-coupled subnuclear localization of the 3'-cleavage machinery.\",\n      \"method\": \"Immunofluorescence with monoclonal antibodies, alpha-amanitin/DRB transcription inhibition, immunogold electron microscopy, BrU labeling of nascent RNA\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal microscopy methods (IF, EM immunogold, nascent RNA labeling) with functional perturbation by transcription inhibition\",\n      \"pmids\": [\"8654386\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"The N-terminal RNA recognition motif (RRM) of CstF-64 recognizes GU-rich downstream sequence elements; the C-terminal helix of the RRM unfolds upon RNA binding and extends into the hinge domain where interactions with other polyadenylation assembly factors occur, suggesting this conformational change initiates assembly of the polyadenylation complex. Consecutive U residues are required for strong CstF-GU interaction.\",\n      \"method\": \"NMR structure determination of the RRM domain free and RNA-bound; mutagenesis of RNA contacts\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — NMR structure with RNA binding validation and mutagenesis, replicated by subsequent structural/biophysical studies\",\n      \"pmids\": [\"12773396\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"The protein-RNA interface of CstF-64 RRM acquires significant micro-to-millisecond timescale mobility upon binding GU-rich RNA, while the free protein is uniformly rigid. This dynamic behavior at the binding interface is proposed to allow binding to diverse GU-rich sequences while discriminating against non-GU-rich RNAs.\",\n      \"method\": \"NMR relaxation dynamics measurements of CstF-64 RRM free and bound to two GU-rich RNA sequences\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — NMR relaxation with two different RNA substrates in a single rigorous study\",\n      \"pmids\": [\"15769465\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"The C-terminal domains of CstF-64 and its yeast orthologue Rna15 fold into a three-helix bundle with an uncommon topological arrangement. This domain mediates interaction with Pcf11, and this interaction is critical for mRNA 3'-end processing but dispensable for transcription termination.\",\n      \"method\": \"NMR structure determination of C-terminal domains; mutagenesis of conserved surface residues; in vitro 3'-end processing assays with Rna15 mutants\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — NMR structure combined with mutagenesis and functional in vitro processing assays\",\n      \"pmids\": [\"17116658\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"The hinge domain of CstF-64 is essential for interaction with CstF-77 and for nuclear localization; nuclear import of a preformed CstF complex is an essential step in polyadenylation. Loss of the hinge domain abolishes CstF-64-dependent polyadenylation activity as measured by a reporter assay.\",\n      \"method\": \"SLAP (stem-loop luciferase assay for polyadenylation) with CstF-64 domain deletion/mutation constructs; co-immunoprecipitation; immunofluorescence localization\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (reporter assay, Co-IP, IF localization) in a single study\",\n      \"pmids\": [\"19887456\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"EV71 3C protease cleaves CstF-64 at position 251 (N-terminal P/G-rich domain) and at multiple sites near position 500 (C-terminus). This cleavage inactivates CstF-64 and inhibits host cell 3'-end pre-mRNA processing and polyadenylation; impairment is rescued by adding purified recombinant CstF-64 protein.\",\n      \"method\": \"In vitro cleavage assay with recombinant 3Cpro and CstF-64; site-directed mutagenesis to map cleavage sites; in vitro polyadenylation assay with 3Cpro-treated nuclear extract; rescue by recombinant CstF-64\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro cleavage with mutagenesis mapping of cleavage sites, functional rescue in polyadenylation assay\",\n      \"pmids\": [\"19779565\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"CstF-64 binds CstF-77 and symplekin mutually exclusively through its hinge domain. The CstF-64–symplekin interaction is limiting for histone RNA 3'-end processing but relatively unimportant for cleavage/polyadenylation. Nuclear accumulation of CstF-64 depends on its binding to CstF-77 but not to symplekin. CstF-64τ can compensate for loss of CstF-64 but has lower affinity for CstF-77 and is less stable.\",\n      \"method\": \"Identification of CstF-64 and symplekin mutants that distinguish the two interactions; co-immunoprecipitation; complementation assays in cell lines; 3'-end processing assays\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP with structure-function mutants, functional processing assays, localization studies; multiple orthogonal approaches\",\n      \"pmids\": [\"21119002\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"A variant form of CstF-64, termed tauCstF-64, is encoded by an autosomal gene (Cstf2t) on mouse chromosome 19 and is specifically expressed in meiotic and postmeiotic germ cells to compensate for X-chromosome inactivation of the somatic CstF-64. The tauCstF-64 protein contains a Pro→Ser substitution in its RNA-binding domain and significant changes in the region interacting with CstF-77.\",\n      \"method\": \"cDNA cloning; chromosomal mapping; immunoblot; 2D-PAGE; antibody reactivity; proteolytic digest pattern comparison\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — cDNA cloning with biochemical characterization (immunoblot, 2D-PAGE, proteolytic mapping); single lab\",\n      \"pmids\": [\"11113135\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"In C. elegans, CstF-64 forms a complex with the SL2 snRNP (but not SL1 or other U snRNAs), linking mRNA 3'-end formation with SL2-specific trans-splicing. Stem/loop III of SL2 RNA is required for both SL2 identity and association with CstF-64.\",\n      \"method\": \"Immunoprecipitation of complex with anti-CstF-64 antibody; mutational analysis of SL2 RNA stem-loops; in vivo trans-splicing assays\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal IP with mutational dissection of RNA determinants; single lab\",\n      \"pmids\": [\"11581161\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"CstF-64 RBD has higher affinity for poly(U) than tauCstF-64 RBD, while tauCstF-64 has higher affinity for poly(GU). A region C-terminal to the RBD (not Pro-41 alone) is important for RNA sequence recognition and differential affinity.\",\n      \"method\": \"RNA cross-linking Kd measurements with poly(G), poly(A), poly(C), poly(U), and poly(GU) ribopolymers; mutagenesis of CstF-64 RBD residues\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — quantitative binding assay with mutagenesis; single lab\",\n      \"pmids\": [\"17029590\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"CstF-64 supports ESC pluripotency and cell cycle progression by promoting correct 3'-end processing (non-polyadenylation) of replication-dependent histone mRNAs; loss of CstF-64 results in increased histone mRNA polyadenylation, lengthened G1, and loss of pluripotency. τCstF-64 partially compensates and is recruited to the histone mRNA 3'-end processing complex.\",\n      \"method\": \"CstF-64 knockout ESCs; RT-PCR and Northern analysis of histone mRNA polyadenylation; cell cycle analysis; pluripotency marker assays; τCstF-64 knockdown in Cstf2-deficient ESCs\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with multiple phenotypic readouts and partial rescue analysis; single lab\",\n      \"pmids\": [\"24957598\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"The carboxy-terminus of CstF-77 enhances CstF-64 RNA binding activity by altering how the RRM of CstF-64 engages RNA, increasing RRM stability and thus the affinity of the CstF complex for RNA. CstF-64 nuclear localization depends on CstF-77 binding; excess CstF-64 accumulates in the cytoplasm, possibly by interacting with cytoplasmic RNAs.\",\n      \"method\": \"NMR spectroscopy of recombinant CstF-64 RRM-Hinge and CstF-77 CTD; reverse genetics; RNA binding assays; immunofluorescence localization\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — NMR structure-function with reverse genetics and multiple orthogonal assays (binding, localization) in a single rigorous study\",\n      \"pmids\": [\"30257008\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"CSTF2 promotes 3'UTR shortening of RAC1 by cotranscriptionally binding to a GUAAU motif at the proximal polyadenylation site of RAC1, which attenuates recruitment of transcription elongation factors AFF1 and AFF4, causing defects in elongation and favoring proximal poly(A) site usage.\",\n      \"method\": \"RNA sequencing; chromatin immunoprecipitation (ChIP) for CSTF2 and transcription elongation factors; 3'UTR isoform analysis; CSTF2 knockdown/overexpression with migration/invasion assays\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP showing cotranscriptional binding with functional consequences; single lab\",\n      \"pmids\": [\"30143523\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"A missense mutation in the RRM of CSTF2 (p.D50A) causes intellectual disability in males. This mutation changes the electrostatic potential of the RRM, leading to greater (altered on-rate) RNA binding affinity and reduced C/P efficiency, altering polyadenylation sites in over 1300 brain-expressed genes.\",\n      \"method\": \"Reporter gene C/P assay; NMR structure and chemical shift perturbation of D50A RRM; genome-wide poly(A) site analysis in knock-in mice\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — NMR structural characterization, in vivo reporter assay, genome-wide APA analysis; multiple orthogonal methods in one study\",\n      \"pmids\": [\"32816001\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Electrostatic attraction is the dominant force in CSTF2 RRM binding to U-rich RNA; RNA binding is accompanied by enthalpy-entropy compensation and changes in picosecond-to-nanosecond timescale protein dynamics. Competition between fast high-affinity RNA binding and efficient correct C/P is demonstrated in vivo.\",\n      \"method\": \"Mutagenesis of surface-charged residues; NMR spectroscopy; biophysical binding assays (ITC, SPR); in vivo C/P reporter assay\",\n      \"journal\": \"Biophysical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — mutagenesis combined with NMR and multiple biophysical assays plus in vivo C/P reporter\",\n      \"pmids\": [\"35090899\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CSTF2 co-transcriptionally regulates m6A installation on target gene transcripts by slowing RNA Pol II elongation rate during transcription; CSTF2-regulated m6As are predominantly recognized by IGF2BP2, an m6A reader that stabilizes mRNAs.\",\n      \"method\": \"Transcriptomic m6A profiling (MeRIP-seq) in PDAC tissues; CSTF2 knockdown/overexpression with m6A and RNA Pol II elongation analysis; RIP for IGF2BP2\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — MeRIP-seq and Pol II elongation assays with KD/OE; single lab, mechanistic follow-up needs more orthogonal validation\",\n      \"pmids\": [\"37816727\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CSTF2 RRM binds U-rich RNA through a multistep binding process involving differences in ps-ns dynamics and potential structural changes in the C-terminal α-helix, as determined by NMR titration, spin relaxation, paramagnetic relaxation enhancement, and rigid-body docking.\",\n      \"method\": \"NMR titration and spin relaxation; paramagnetic relaxation enhancement; rigid-body docking\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — multiple NMR methods in a single rigorous structural study; consistent with prior structural work\",\n      \"pmids\": [\"39305233\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CSTF2 diminishes CXCL10 expression by promoting poly(A) polymerase alpha (PAPα) binding to the 3'UTR of CXCL10 RNA, resulting in shortened poly(A) tails and compromised CXCL10 RNA stability, thereby suppressing iαβT cell infiltration and anti-tumor immunity in PDAC.\",\n      \"method\": \"RIP assay for CSTF2 and PAPα binding to CXCL10 3'UTR; poly(A) tail length assay; CSTF2 KO mouse models and co-culture immune assays; Forsythoside B inhibitor targeting CSTF2 RRM\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RIP with poly(A) tail length measurement and functional immune readouts; single lab\",\n      \"pmids\": [\"39972059\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CSTF2 shortens the 3'UTR of PGK1 pre-mRNA by binding near its proximal polyadenylation site, leading to loss of m6A sites that would otherwise be recognized by YTHDF2 (promoting degradation), thereby increasing PGK1 protein levels and enhancing glycolysis under hypoxia. Hypoxia-induced m6A near the proximal poly(A) site is recognized by YTHDC1, which recruits CSTF2 to further enhance PGK1 3'UTR shortening.\",\n      \"method\": \"RIP-seq for CSTF2 binding; m6A-seq; 3'UTR isoform analysis; CSTF2 KO in HCC cell lines and xenograft models; YTHDF2/YTHDC1 co-IP; masitinib inhibitor screen\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple binding and sequencing assays with in vivo xenograft validation; single lab\",\n      \"pmids\": [\"39514400\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Loss of CstF-64 in mouse ESCs results in loss of differentiation potential toward the endodermal lineage, which is necessary for cardiomyocyte specification; endodermal signaling from conditioned medium of XEN stem cells restores cardiomyocyte differentiation in CstF-64-knockout cells, placing CstF-64 upstream of endoderm-dependent cardiac specification.\",\n      \"method\": \"CstF-64 knockout ESCs (Cstf2E6); endoderm/mesoderm/cardiac differentiation assays; conditioned medium rescue experiment; marker expression analysis\",\n      \"journal\": \"Stem cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with differentiation assays and conditioned medium rescue; single lab\",\n      \"pmids\": [\"25460602\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CSTF2 (CstF-64) is the RNA-binding subunit of the trimeric CstF complex that recognizes GU-rich downstream sequence elements in pre-mRNAs through its N-terminal RRM domain (via predominantly electrostatic, dynamically mobile interactions), recruits the complex to poly(A) sites, and is rate-limiting for cleavage and polyadenylation efficiency; its nuclear localization depends on binding CstF-77 through its hinge domain, which also mediates mutually exclusive interactions with symplekin for histone mRNA 3'-end processing; CstF-64 concentration is a key regulatory lever for alternative poly(A) site selection (e.g., IgM heavy chain switching in B cell differentiation), and it additionally co-transcriptionally regulates m6A deposition and 3'UTR length by modulating RNA Pol II elongation rate, with downstream consequences for mRNA stability, cell cycle progression, ESC pluripotency, and tumor biology.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"CSTF2 (CstF-64) is the RNA-binding subunit of the cleavage stimulation factor (CstF) complex that recognizes GU/U-rich downstream sequence elements in pre-mRNAs and is rate-limiting for the efficiency and site selection of 3'-end cleavage and polyadenylation [#0, #3]. Its N-terminal RRM engages GU-rich RNA through predominantly electrostatic contacts, with the C-terminal helix unfolding upon binding and the protein-RNA interface acquiring micro-to-millisecond mobility that permits recognition of diverse GU-rich sequences while discriminating against non-GU RNAs [#3, #4, #16]. The hinge domain anchors CstF-64 into the complex by binding CstF-77, an interaction required for nuclear import and for full RNA-binding activity, and which is mutually exclusive with symplekin binding that instead drives histone mRNA 3'-end processing [#6, #8, #13]. Because CstF-64 is present at limiting concentration, its abundance sets a regulatory lever for alternative poly(A) site selection, exemplified by the switch from membrane-bound to secreted IgM heavy chain during B cell differentiation, and its depletion arrests the cell cycle and triggers apoptosis [#0, #1]. CstF-64 supports embryonic stem cell pluripotency and cell cycle progression by promoting correct non-polyadenylated processing of replication-dependent histone mRNAs and gates endoderm-dependent cardiac differentiation [#12, #21]. Beyond canonical processing, CSTF2 acts co-transcriptionally to shorten 3'UTRs (e.g., RAC1, PGK1) by binding proximal poly(A) sites and modulating RNA Pol II elongation, with downstream effects on m6A deposition recognized by readers such as IGF2BP2, YTHDF2, and YTHDC1, linking it to mRNA stability, glycolysis, and tumor immunity [#14, #17, #20]. A missense mutation (p.D50A) in the RRM that alters its electrostatic potential and RNA binding causes X-linked intellectual disability and shifts poly(A) site usage across more than 1300 brain-expressed genes [#15].\",\n  \"teleology\": [\n    {\n      \"year\": 1996,\n      \"claim\": \"Established that CstF-64 abundance, rather than mere presence, governs poly(A) site choice — explaining how a constitutive processing factor can act as a developmental switch.\",\n      \"evidence\": \"Reconstituted in vitro processing, overexpression in B cell lines, and affinity measurements at IgM heavy chain poly(A) sites\",\n      \"pmids\": [\"8945520\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which CstF-64 levels are repressed in primary B cells not resolved\", \"Generalizability to other alternative poly(A) site genes not yet tested\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Localized the 3'-cleavage machinery to transcription-dependent subnuclear foci, linking CstF-64 to active transcription sites.\",\n      \"evidence\": \"Immunofluorescence, immunogold EM, BrU nascent RNA labeling, and transcription inhibition\",\n      \"pmids\": [\"8654386\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional significance of cleavage body foci for processing efficiency unclear\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Showed CstF-64 has unexpected roles beyond housekeeping 3'-end processing by linking its dosage to cell cycle progression and survival.\",\n      \"evidence\": \"Regulatable transgene replacing endogenous CstF-64 in DT40 cells with cell cycle and apoptosis readouts\",\n      \"pmids\": [\"9885564\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which target mRNAs drive the G0/G1 arrest and apoptosis not identified\", \"Direct vs indirect effects not separated\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Identified a germ-cell paralog (tauCstF-64/Cstf2t) that compensates for X-inactivation of CstF-64 during spermatogenesis, revealing tissue-specific specialization of the subunit.\",\n      \"evidence\": \"cDNA cloning, chromosomal mapping, immunoblot, 2D-PAGE, and proteolytic mapping\",\n      \"pmids\": [\"11113135\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequences of the RRM Pro\\u2192Ser substitution not characterized in this study\", \"Single-lab characterization\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Connected CstF-64 to trans-splicing in C. elegans through specific association with the SL2 snRNP, expanding its role beyond cis 3'-end formation.\",\n      \"evidence\": \"Reciprocal IP and mutational dissection of SL2 RNA stem-loops with in vivo trans-splicing assays\",\n      \"pmids\": [\"11581161\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relevance to mammalian CstF-64 function unknown\", \"Molecular contacts mediating SL2 association not mapped\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Defined the structural basis of GU-rich element recognition and proposed an RNA-induced conformational change in the RRM C-terminal helix that initiates complex assembly.\",\n      \"evidence\": \"NMR structure of the RRM free and RNA-bound with mutagenesis of RNA contacts\",\n      \"pmids\": [\"12773396\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Coupling between helix unfolding and downstream factor recruitment not directly demonstrated\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Explained how a single RRM tolerates diverse GU-rich sequences by showing binding induces interface mobility rather than rigid lock-and-key recognition.\",\n      \"evidence\": \"NMR relaxation dynamics of the RRM free and bound to two GU-rich RNAs\",\n      \"pmids\": [\"15769465\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional link between dynamics and in vivo poly(A) site selection not established at this stage\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Separated the C-terminal domain's role in 3'-end processing (via Pcf11) from transcription termination, dissecting distinct functions of the subunit.\",\n      \"evidence\": \"NMR structure of C-terminal domains, surface mutagenesis, and in vitro processing assays with Rna15 mutants\",\n      \"pmids\": [\"17116658\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Conservation of the Pcf11 interaction surface in human CstF-64 not directly tested here\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Quantified differential RNA-binding specificity between CstF-64 and tauCstF-64, mapping determinants to a region C-terminal to the RBD rather than a single residue.\",\n      \"evidence\": \"RNA cross-linking Kd measurements across homopolymers with RBD mutagenesis\",\n      \"pmids\": [\"17029590\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo consequences of differential affinity for poly(A) site choice not assessed\", \"Single-lab assay\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Established the hinge domain as essential for CstF-77 binding and nuclear import, defining preformed-complex nuclear entry as a required step in polyadenylation.\",\n      \"evidence\": \"SLAP reporter assay with domain deletions, Co-IP, and IF localization\",\n      \"pmids\": [\"19887456\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Import receptor/pathway for the CstF complex not identified\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Revealed CstF-64 as a target of viral subversion, with EV71 3C protease cleaving and inactivating it to shut down host 3'-end processing.\",\n      \"evidence\": \"In vitro cleavage with site mapping, polyadenylation assay on protease-treated extract, and recombinant rescue\",\n      \"pmids\": [\"19779565\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo contribution of CstF-64 cleavage to viral replication during infection not quantified\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Showed the hinge mediates mutually exclusive CstF-77 versus symplekin binding, partitioning CstF-64 between canonical poly(A) processing and histone mRNA 3'-end processing.\",\n      \"evidence\": \"Interaction-discriminating mutants, reciprocal Co-IP, complementation, and processing assays\",\n      \"pmids\": [\"21119002\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How the choice between CstF-77 and symplekin is regulated in cells not defined\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Linked CstF-64 to stem cell biology by showing it enforces correct non-polyadenylated histone mRNA processing required for pluripotency and cell cycle, and gates endoderm-dependent cardiac differentiation.\",\n      \"evidence\": \"CstF-64 knockout ESCs with histone mRNA, cell cycle, pluripotency, and differentiation assays plus conditioned-medium rescue\",\n      \"pmids\": [\"24957598\", \"25460602\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct vs secondary effects on histone processing not fully separated\", \"Single-lab studies\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Demonstrated co-transcriptional 3'UTR shortening as a CSTF2 function, acting by attenuating elongation factor recruitment to favor proximal poly(A) sites, with cancer phenotypes.\",\n      \"evidence\": \"RNA-seq, ChIP for CSTF2 and AFF1/AFF4, 3'UTR isoform analysis, and migration/invasion assays on RAC1\",\n      \"pmids\": [\"30143523\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of elongation factor attenuation not structurally defined\", \"Single-lab\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Showed CstF-77 binding allosterically enhances CstF-64 RNA-binding activity by stabilizing the RRM, coupling complex assembly to affinity.\",\n      \"evidence\": \"NMR of RRM-Hinge with CstF-77 CTD, reverse genetics, binding assays, and IF localization\",\n      \"pmids\": [\"30257008\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Quantitative contribution of this enhancement to in vivo site selection not measured\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Provided a direct disease link, showing an RRM missense mutation that increases RNA-binding on-rate reduces processing efficiency and causes X-linked intellectual disability with genome-wide poly(A) site shifts.\",\n      \"evidence\": \"Reporter C/P assay, NMR of D50A RRM, and genome-wide poly(A) site analysis in knock-in mice\",\n      \"pmids\": [\"32816001\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How altered poly(A) site usage translates to neuronal dysfunction not resolved\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defined electrostatics as the dominant binding force and revealed a competition between fast high-affinity RNA binding and correct cleavage/polyadenylation, reframing the D50A defect mechanistically.\",\n      \"evidence\": \"Surface-charge mutagenesis, NMR, ITC/SPR, and in vivo C/P reporter\",\n      \"pmids\": [\"35090899\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural intermediate driving the affinity-vs-efficiency tradeoff not directly visualized\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Refined the binding mechanism to a multistep process involving ps-ns dynamics and C-terminal helix structural change, extending the dynamic recognition model.\",\n      \"evidence\": \"NMR titration, spin relaxation, paramagnetic relaxation enhancement, and rigid-body docking\",\n      \"pmids\": [\"39305233\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic-resolution bound-state structure not obtained\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Connected CSTF2-driven 3'UTR shortening to m6A biology and disease, showing it removes or remodels m6A sites recognized by reader proteins to control mRNA stability, glycolysis, and anti-tumor immunity.\",\n      \"evidence\": \"RIP/RIP-seq, m6A-seq, poly(A) tail length assays, reader co-IPs, KO mouse and xenograft models for CXCL10 and PGK1\",\n      \"pmids\": [\"37816727\", \"39972059\", \"39514400\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct causal chain from elongation modulation to specific m6A site loss not fully reconstituted\", \"Single-lab studies per target\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How CstF-64 abundance, post-translational state, and competition between high-affinity binding and efficient processing are integrated to control alternative poly(A) site choice genome-wide in different cell types remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No genome-wide model linking CstF-64 dosage to tissue-specific APA outcomes\", \"Regulation of CstF-64 levels in vivo poorly defined\", \"Atomic structure of the RNA-bound complex incomplete\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [3, 4, 11, 16, 18]},\n      {\"term_id\": \"GO:0140098\", \"supporting_discovery_ids\": [0, 5, 6, 7]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [6, 8, 13]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [6, 13]},\n      {\"term_id\": \"GO:0005654\", \"supporting_discovery_ids\": [2]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [13]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [0, 3, 6, 8]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [14, 17]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [15, 19, 20]}\n    ],\n    \"complexes\": [\n      \"CstF complex\"\n    ],\n    \"partners\": [\n      \"CSTF3\",\n      \"SYMPK\",\n      \"PCF11\",\n      \"PAPOLA\",\n      \"IGF2BP2\",\n      \"YTHDF2\",\n      \"YTHDC1\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}