{"gene":"CHEK1","run_date":"2026-06-09T22:57:18","timeline":{"discoveries":[{"year":1993,"finding":"Fission yeast Chk1 is a protein kinase that links the DNA damage checkpoint pathway (rad1-dependent) to cell-cycle regulatory kinase p34cdc2, coupling DNA damage sensing to cell cycle arrest.","method":"Genetic screen (multicopy suppressor of cdc2 mutant), sensitivity assays with rad mutants","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 / Strong — foundational genetic epistasis experiment replicated across multiple organisms, establishing Chk1's position in the checkpoint-to-Cdc2 axis","pmids":["8497322"],"is_preprint":false},{"year":1995,"finding":"In fission yeast, a Chk1-dependent pathway prevents mitosis when passage through 'start' (G1 commitment point) is compromised, identifying a third mitotic control checkpoint distinct from S-M and DNA-damage checkpoints.","method":"Genetic epistasis in S. pombe (chk1 deletion, rad17 deletion, cell cycle analysis with 1C DNA content)","journal":"Current biology : CB","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean genetic epistasis in yeast with defined phenotypic readout, single lab","pmids":["8548290"],"is_preprint":false},{"year":1999,"finding":"Human Chk1 (hChk1) is expressed specifically at S-to-M phase of the cell cycle, localizes to the nucleus during this window, and phosphorylates Cdc25C at serine 216 in the absence of DNA damage, in an ATM-independent manner.","method":"Cell cycle synchronization, kinase assay (Cdc25C phosphorylation), subcellular fractionation/localization, ATM-deficient patient cells","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct kinase assay plus localization with ATM-deficient cells as genetic control, single lab","pmids":["10391675"],"is_preprint":false},{"year":2000,"finding":"Chk1 is required for the G2/M checkpoint in mammals; Chk1-null mouse embryos fail to arrest the cell cycle before mitosis in response to DNA replication block or DNA damage and die of apoptosis at the blastocyst stage.","method":"Targeted gene disruption in mice (Chk1−/− knockout), morphological analysis, cell cycle analysis of embryos","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 / Strong — definitive loss-of-function in whole animal with clear cellular phenotype, independently cited widely","pmids":["10859163"],"is_preprint":false},{"year":2001,"finding":"p53 transcriptionally represses CHK1 through a pathway requiring p21 and the retinoblastoma protein (pRB), suggesting E2F-dependent regulation; this establishes a feedback loop where p53 reduces CHK1 protein levels.","method":"Tetracycline-inducible p53 expression, p21-null cells, pRB-null cells, Northern blot/RT-PCR for CHK1 mRNA","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis with multiple cell lines (p21-null, pRB-null), single lab, two orthogonal readouts (mRNA and protein)","pmids":["11158294"],"is_preprint":false},{"year":2003,"finding":"p73α is a direct substrate of Chk1; Chk1 phosphorylates p73α at serine 47 in vitro and in vivo upon DNA damage, and this phosphorylation is required for the apoptotic function of p73α. Chk2 does not phosphorylate p73α in vitro.","method":"Co-immunoprecipitation of endogenous proteins, in vitro kinase assay, site-directed mutagenesis (S47A), in vivo phosphorylation assay","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro kinase assay with mutagenesis plus in vivo co-IP and phosphorylation validation, single lab with multiple orthogonal methods","pmids":["14585975"],"is_preprint":false},{"year":2004,"finding":"ATR-mediated phosphorylation of the C-terminal regulatory domain of Chk1 relieves an autoinhibitory intramolecular interaction between the C-terminal autoinhibitory region (AIR) and the kinase domain, converting Chk1 to an active conformation.","method":"Domain truncation and coexpression in Xenopus oocytes/embryos, phospho-mimic mutations, interaction assays","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 1 / Moderate — reconstitution in Xenopus system with domain mapping and phospho-mimic mutagenesis, multiple orthogonal assays in one study","pmids":["14767054"],"is_preprint":false},{"year":2004,"finding":"In fission yeast, 14-3-3 proteins (Rad24/Rad25) interact with phosphorylated Chk1 after DNA damage; a leucine-rich domain mediates this interaction. 14-3-3 binding is required for Chk1 phosphorylation, nuclear accumulation upon DNA damage, and checkpoint function.","method":"Co-immunoprecipitation, site-directed mutagenesis (leucine-to-alanine), nuclear localization imaging, UV sensitivity assays","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal interaction and functional mutagenesis in S. pombe, single lab, multiple orthogonal readouts","pmids":["15585577"],"is_preprint":false},{"year":2005,"finding":"PPM1D (Wip1) phosphatase directly binds Chk1 and dephosphorylates the ATR-targeted pSer345 site, decreasing Chk1 kinase activity and abrogating intra-S and G2/M checkpoint responses to DNA damage.","method":"Co-immunoprecipitation, in vitro phosphatase assay, kinase activity assay, checkpoint abrogation assays after UV/IR","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro phosphatase assay with defined substrate site plus Co-IP and checkpoint functional readout, multiple orthogonal methods in one study","pmids":["15870257"],"is_preprint":false},{"year":2005,"finding":"DNA-dependent phosphorylation of Chk1 by ATR/ATM in human cells requires Claspin, which binds Chk1 through phosphorylated residues Thr916 and Ser945 within its Chk1-binding domain. A phosphopeptide from this motif competitively inhibits the Claspin-Chk1 interaction and blocks ATR/ATM-dependent Chk1 phosphorylation.","method":"Human cell-free biochemical system, double-stranded DNA oligonucleotide-induced phosphorylation, phosphopeptide competition, kinase inhibitor panel","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1 / Moderate — reconstituted human cell-free system with phosphopeptide competition and defined interaction residues, multiple orthogonal methods","pmids":["15707391"],"is_preprint":false},{"year":2007,"finding":"Chk1 is required for spindle checkpoint function; Chk1-deficient vertebrate cells show decreased Aurora-B kinase activity and impaired BubR1 phosphorylation and kinetochore localization. Chk1 directly phosphorylates Aurora-B and enhances its catalytic activity in vitro.","method":"Chk1−/− DT40 cells, RNAi knockdown, in vitro kinase assay (Chk1 phosphorylates Aurora-B), taxol/nocodazole treatment, BubR1 kinetochore localization by immunofluorescence","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro kinase assay plus genetic knockout with defined molecular phenotype (Aurora-B activity, BubR1 localization), multiple orthogonal methods","pmids":["17276342"],"is_preprint":false},{"year":2007,"finding":"Chk1 phosphorylation at S345 is required for cytoplasmic localization and prevention of mitotic catastrophe, while S317 phosphorylation is required for chromatin release upon genotoxic stress and checkpoint activation; both sites contribute distinctly to Chk1 function. Forced centrosomal immobilization of Chk1 prevents apoptosis.","method":"Knockout-knockin system with phosphorylation-site mutants (S317A, S345A), subcellular fractionation, localization imaging, centrosomal targeting construct","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — knock-in of separation-of-function mutants in null cell background with multiple phenotypic readouts, single lab, multiple orthogonal methods","pmids":["17242188"],"is_preprint":false},{"year":2007,"finding":"DNA damage induces Chk1-dependent centrosome amplification (not fragmentation); kinase-dead Chk1 and the non-phosphorylatable Chk1-S345A mutant fail to restore centrosome amplification, demonstrating that both ATR signaling to Chk1 and Chk1 catalytic activity are required.","method":"Chk1−/− DT40 cells, transgenic rescue with kinase-dead and S345A mutants, light and electron microscopy, RNAi knockdown, caffeine treatment","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 2 / Moderate — genetic knockout with defined rescue by wild-type vs. mutant transgenes, multiple orthogonal methods, single lab","pmids":["17468739"],"is_preprint":false},{"year":2008,"finding":"Chk1 regulates DNA damage-induced PCNA ubiquitination by stabilizing Claspin, which in turn controls Rad18 ubiquitin ligase binding to chromatin; this function requires Claspin but not ATR, revealing an ATR-independent arm of Chk1 activity at stressed forks.","method":"RNAi knockdown (Chk1, Claspin, Timeless), PCNA ubiquitination assay, chromatin fractionation, Rad18-chromatin binding assay","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 / Moderate — epistasis by siRNA with molecular mechanistic readout (PCNA ubiquitination, Rad18 chromatin binding), multiple orthogonal methods, single lab","pmids":["18451105"],"is_preprint":false},{"year":2008,"finding":"Chk1 is cleaved by caspases during apoptosis at Asp-299 (chicken) and Asp-299/Asp-351 (human); the N-terminal cleavage fragment (residues 1–299) has elevated kinase activity and induces abnormal nuclear morphology and H2AX phosphorylation when ectopically expressed.","method":"Caspase inhibitor experiments, mapping of cleavage sites, truncated Chk1 expression (residues 1–299), kinase assay, immunofluorescence of H2AX","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro and in vivo cleavage mapping with defined truncation expressing elevated kinase activity, single lab","pmids":["18550533"],"is_preprint":false},{"year":2008,"finding":"The C-terminal domain of Chk1 (S. pombe) does not simply autoinhibit the kinase; it is also required for adopting an active configuration. Intragenic suppressor mutations cluster to the substrate-binding face of the catalytic domain, suggesting the C-terminus interacts with this region.","method":"Truncation analysis, activating mutations in C-terminal domain, intragenic suppressor screen, temperature-sensitive alleles expressed from endogenous locus","journal":"Molecular biology of the cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic suppressor screen plus in vivo expression from endogenous locus, single lab, multiple alleles","pmids":["18716058"],"is_preprint":false},{"year":2009,"finding":"The SCF E3 ubiquitin ligase containing F-box protein Fbx6 mediates ubiquitination and proteasomal degradation of Chk1 after DNA damage, exposing a C-terminal degron; this terminates checkpoint signaling. Low Fbx6 levels correlate inversely with Chk1 levels and with cancer cell resistance to camptothecin.","method":"Co-immunoprecipitation, ubiquitination assay in vitro and in vivo, siRNA knockdown, proteasome inhibitor experiments, immunohistochemistry in tumor tissues","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro ubiquitination reconstitution plus in vivo Co-IP with defined degron, multiple orthogonal methods, single lab","pmids":["19716789"],"is_preprint":false},{"year":2009,"finding":"DNA polymerase alpha (Polα) associates with Chk1 in native cell extracts; following replication stress, Polα-associated Chk1 is phosphorylated at Ser345 in a TopBP1- and ATR-dependent manner, and this association is required for efficient intra-S checkpoint activation.","method":"Co-immunoprecipitation from native cell extracts, siRNA depletion of Polα, ATR/TopBP1 epistasis, γH2AX measurement","journal":"Cell cycle (Georgetown, Tex.)","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — Co-IP plus siRNA epistasis, single lab, two orthogonal methods","pmids":["19177015"],"is_preprint":false},{"year":2009,"finding":"Chk1 signaling causes centrosome amplification after ionizing radiation by upregulating Cdk2 activity through activating T160 phosphorylation of Cdk2; Cdk1 can substitute for Cdk2 in this pathway.","method":"Chk1−/− DT40 cells, Cdk2−/− cells, Cdk2 T160A mutant rescue, IR treatment, centrosome counting","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — epistatic genetic knockouts with site-specific mutant rescue, single lab","pmids":["19838212"],"is_preprint":false},{"year":2010,"finding":"NEK11, a NIMA-related kinase, is activated by CHK1-mediated phosphorylation at Ser273 and is the critical kinase that directly phosphorylates CDC25A to trigger its beta-TrCP-mediated polyubiquitylation and degradation, linking CHK1 to CDC25A destruction.","method":"In vitro kinase assay (CHK1 phosphorylates NEK11 Ser273), CDC25A ubiquitination assay, RNAi knockdown, checkpoint rescue experiments","journal":"Cell cycle (Georgetown, Tex.)","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro kinase assay defining the phosphorylation event, plus functional epistasis, single lab","pmids":["20090422"],"is_preprint":false},{"year":2012,"finding":"CHK1 is a novel substrate of the CRL4(CDT2) E3 ubiquitin ligase; CRL4(CDT2) ubiquitinates the activated form of CHK1 in the nucleoplasm in a PCNA-independent manner, targeting it for degradation. CHK1 activity maintains G2 arrest in CDT2-depleted cells.","method":"Co-immunoprecipitation, ubiquitination assay, subcellular fractionation, siRNA knockdown of CDT2, G2 arrest rescue experiments","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus ubiquitination assay with subcellular localization distinction, single lab, two orthogonal methods","pmids":["23109433"],"is_preprint":false},{"year":2012,"finding":"Chk1 promotes replication fork progression after UV irradiation through a kinase-independent mechanism that requires its PCNA-interacting motif and chromatin release; this function is independent of Claspin and is required for efficient recruitment of DNA polymerase η (pol η) to replication foci for translesion synthesis.","method":"Kinase-dead Chk1 mutant, PCNA-interaction motif mutant, histone H2B-Chk1 chromatin-tethering chimera, pol η foci by immunofluorescence, DNA fiber assay","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple separation-of-function mutants (kinase-dead, PIP-mutant, chromatin-tethered) with defined molecular phenotype, single lab, multiple orthogonal methods","pmids":["22529391"],"is_preprint":false},{"year":2013,"finding":"Chk1 protects vertebrate cells against merotelic kinetochore attachments; Chk1 phosphorylates Aurora-B at Ser331 in prometaphase, which is required for optimal kinetochore localization of MCAK, Kif2b, and Mps1 and for Hec1 phosphorylation, enabling error correction.","method":"Chk1 inhibitor/knockdown, in vitro kinase assay (Chk1 phosphorylates Aurora-B Ser331), immunofluorescence of MCAK/Kif2b/Mps1/Hec1 at kinetochores, lagging chromosome analysis","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro kinase assay defining substrate site plus genetic/pharmacological loss-of-function with multiple molecular readouts, single lab","pmids":["23321637"],"is_preprint":false},{"year":2014,"finding":"ATM phosphorylates and stabilizes ZEB1 after DNA damage; ZEB1 then interacts with USP7 deubiquitylase and enhances USP7's ability to deubiquitylate and stabilize CHK1, promoting homologous recombination-dependent DNA repair and radioresistance.","method":"Co-immunoprecipitation (ZEB1-USP7-CHK1), ubiquitination assay, in vitro deubiquitination assay, ATM kinase assay, siRNA knockdown, clonogenic survival after radiation","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro deubiquitination assay plus Co-IP and functional rescue, multiple orthogonal methods in one study","pmids":["25086746"],"is_preprint":false},{"year":2014,"finding":"USP7 deubiquitylase directly stabilizes Chk1 protein levels by removing ubiquitin chains: wild-type but not catalytic-mutant USP7 deubiquitinates Chk1 in vivo and in vitro, prolongs Chk1 half-life, and this effect is independent of USP7's known effect on Claspin.","method":"Co-immunoprecipitation, in vitro and in vivo deubiquitination assay, USP7 catalytic mutant, Chk1 half-life measurement (cycloheximide chase), siRNA knockdown","journal":"Cell cycle (Georgetown, Tex.)","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro and in vivo deubiquitination assay with catalytic mutant control plus half-life measurement, single lab, multiple orthogonal methods","pmids":["25483066"],"is_preprint":false},{"year":2014,"finding":"Chk1 phosphorylates Smurf1 E3 ubiquitin ligase after DNA damage (UV/MMS), enhancing Smurf1 self-degradation, which leads to RhoB accumulation and apoptosis, defining an ATR/Chk1/Smurf1/RhoB cell fate pathway.","method":"In vitro kinase assay (Chk1 phosphorylates Smurf1), co-immunoprecipitation, ubiquitination assay, siRNA knockdown, apoptosis assay","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro kinase assay with defined substrate plus Co-IP and functional epistasis, single lab","pmids":["25249323"],"is_preprint":false},{"year":2016,"finding":"Human Chk1 maintains a closed, autoinhibited conformation through an intramolecular interaction between residues 31–87 of the N-terminal kinase domain and the distal C-terminus (critical residue Leu-449). DNA damage-induced ATR-dependent phosphorylation, or Leu-449→Arg mutation, disrupts this interaction and opens Chk1 to an active conformation.","method":"FRET, bimolecular fluorescence complementation (BiFC), site-directed mutagenesis (L449R), phospho-mimic mutations, ATR-dependent DNA damage induction","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — structural/FRET approach with mutagenesis and DNA-damage activation in cells, multiple orthogonal methods in one study","pmids":["27129240"],"is_preprint":false},{"year":2016,"finding":"PERK kinase (UPR effector) inhibits DNA replication via Claspin phosphorylation and subsequent CHK1 activation in the absence of genotoxic DNA damage; depletion of Claspin or CHK1 rescues thapsigargin-induced replication inhibition by allowing increased origin firing.","method":"Thapsigargin-induced UPR (non-genotoxic), Claspin/Chk1 siRNA knockdown, DNA synthesis assay, Chk1 phosphorylation assay, replication origin firing analysis","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — epistasis via siRNA of two pathway components with mechanistic molecular readouts, single lab","pmids":["27375025"],"is_preprint":false},{"year":2017,"finding":"Ataxin-3 (ATX3) interacts with Chk1 under basal and DNA damage conditions, protecting it from DDB1/CUL4A- and FBXO6/CUL1-mediated polyubiquitination and degradation. ATX3 is a deubiquitinase of Chk1; under prolonged replication stress ATX3 dissociates from Chk1, allowing its degradation.","method":"Co-immunoprecipitation (ATX3-Chk1), in vivo and in vitro ubiquitination/deubiquitination assay, siRNA of ATX3, ectopic ATX3 expression, G2/M checkpoint assay","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro and in vivo deubiquitination assay plus Co-IP and epistatic rescue with ectopic ATX3, single lab, multiple orthogonal methods","pmids":["28180282"],"is_preprint":false},{"year":2018,"finding":"K63-linked ubiquitination of CHK1 at K132 (active site residue) by TRAF4 promotes CHK1 chromatin association and is required for ATR-mediated CHK1 phosphorylation and activation after DNA damage; USP3 deubiquitinase removes this K63 chain, releasing CHK1 from chromatin and restoring kinase active-site accessibility.","method":"Co-immunoprecipitation, ubiquitination assay (in vitro and in vivo), site-directed mutagenesis (K132), USP3 knockdown/mutants, CHK1 chromatin fractionation","journal":"Proceedings of the National Academy of Sciences of the United States of America / Journal of hematology & oncology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro ubiquitination/deubiquitination assay with defined site mutagenesis and functional rescue, two independent studies (PMID 29735693 and 32357935), multiple orthogonal methods","pmids":["29735693","32357935"],"is_preprint":false},{"year":2019,"finding":"CHK1 stability under unperturbed proliferation is maintained by basal ATR/ETAA1-driven CHK1 autophosphorylation at S296; this autoactivatory loop opposes ubiquitylation and proteasomal degradation, thereby preserving intrinsic S-phase checkpoint functions.","method":"siRNA depletion of ATR/ETAA1, S296 phospho-mutants, cycloheximide half-life assay, ubiquitylation assay, S-phase checkpoint functional assay","journal":"The Journal of cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — phospho-mutant analysis with half-life and ubiquitylation readouts, single lab, two orthogonal methods","pmids":["31366665"],"is_preprint":false},{"year":2019,"finding":"ATR and CHK1 kinase signaling during unperturbed S phase suppresses CDK1 activity, which stabilizes a RIF1–PP1 phosphatase interaction; this PP1 activity dephosphorylates CDC7 and CDK2 substrates to inhibit helicase assembly/activation and limit dormant origin firing.","method":"ATR/CHK1 inhibitor treatment during unperturbed replication, RIF1 Ser2205 phosphorylation assay, RIF1–PP1 co-immunoprecipitation, CDK1-dependence (CDK1 inhibitor), origin firing analysis by DNA fiber","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological epistasis with defined molecular interaction (RIF1-PP1) and substrate dephosphorylation readout, single lab, multiple orthogonal methods","pmids":["31209037"],"is_preprint":false},{"year":2019,"finding":"HUWE1 (HECT E3 ubiquitin ligase) directly ubiquitinates multiple lysine residues within the Chk1 kinase domain in vitro and controls Chk1 protein stability independently of ATM, ATR, and p53; HUWE1 knockdown prolongs Chk1 half-life and rescues Chk1 loss during prolonged replication stress.","method":"In vitro ubiquitination assay with mass spectrometry site mapping, cycloheximide half-life assay, siRNA knockdown of HUWE1 vs. Cul4A, replication stress (HU/CPT) treatment","journal":"The FEBS journal","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro ubiquitination with MS-identified sites plus in vivo half-life analysis, single lab","pmids":["31713291"],"is_preprint":false},{"year":2020,"finding":"CHK1 directly phosphorylates FAM122A/PABIR1, leading to activation of PP2A-B55α phosphatase; in CHK1-inhibited cells, loss of FAM122A phosphorylation allows PP2A-B55α to dephosphorylate and stabilize WEE1, increasing WEE1 expression, reducing replication stress, and conferring resistance to CHK1 inhibitors.","method":"CRISPR knockout screen (FAM122A), kinase assay (CHK1 phosphorylates FAM122A), PP2A-B55α activity assay, WEE1 stability assay, rescue by WEE1 inhibitor combination","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct kinase assay with CRISPR knockout and defined mechanistic pathway rescue, multiple orthogonal methods in one study","pmids":["33108758"],"is_preprint":false},{"year":2021,"finding":"In Drosophila sensory neurons and mammalian neurons, the Atr-Chek1-Cdc25 axis acts downstream of Piezo mechanosensitive ion channel and NO signaling (independent of DNA damage) to inhibit axon regeneration; removing Atr or Chek1, or overexpressing Cdc25, promotes regeneration.","method":"Drosophila genetic epistasis (Atr/Chek1/Cdc25 overexpression and knockdown), Piezo channel genetics, NO signaling pathway analysis, mammalian neuron pharmacological inhibition, behavioral recovery assay","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis in Drosophila with parallel pharmacological validation in mammalian neurons, single lab, multiple orthogonal methods","pmids":["34158506"],"is_preprint":false},{"year":2022,"finding":"CHK1 directly phosphorylates PRIMPOL to promote repriming activity and replication stress tolerance; this phosphorylation is important for cellular resistance to DNA damage but promotes single-strand gap formation and reduces cell fitness when constitutively active.","method":"In vitro CHK1 kinase assay on PRIMPOL, CLASPIN overexpression to increase CHK1 activation, PRIMPOL repriming assay, DNA fiber analysis, cell viability assays","journal":"Science advances","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct in vitro kinase assay with defined substrate plus functional repriming assay and cellular validation, multiple orthogonal methods, single lab","pmids":["35353580"],"is_preprint":false},{"year":2021,"finding":"CHEK1 promotes chromosomal instability in multiple myeloma partly by phosphorylating CEP170; CHEK1 also promotes osteoclast differentiation by upregulating NFATc1 expression.","method":"CHEK1 overexpression/knockdown, Giemsa staining/exon sequencing for CIN, immunofluorescence, TRAP staining for osteoclast differentiation, xenograft model","journal":"Molecular cancer","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — defined substrate (CEP170) phosphorylation plus functional osteoclast assay, single lab","pmids":["34090465"],"is_preprint":false},{"year":2008,"finding":"BCL6 transcriptional repressor directly binds a consensus element in the CHEK1 promoter and represses CHEK1 expression in normal and malignant B-cells; BCL6 peptide inhibitor (BPI) reactivates CHEK1 in DLBCL cells.","method":"Chromatin immunoprecipitation (BCL6 binds CHEK1 promoter), reporter assay, BPI treatment with CHEK1 re-expression measurement","journal":"Blood cells, molecules & diseases","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct ChIP demonstrating promoter binding with pharmacological reactivation, single lab","pmids":["18346918"],"is_preprint":false},{"year":2011,"finding":"Nuclear localization of Chk1 (not centrosomal) is the critical determinant for preventing premature mitotic entry; a Chk1 mutant forced to the nucleus delays mitotic entry, while centrosome-immobilized Chk1 has little impact on mitotic timing.","method":"Conditional Chk1 knockout in MEFs, Chk1+/myc knock-in (DLD-1 cells), nuclear-targeted vs. centrosome-targeted Chk1 constructs, antibody specificity validation, live-cell mitotic entry assay","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — targeted localization constructs in knock-in and conditional KO cells with mitotic entry functional readout, single lab","pmids":["21628425"],"is_preprint":false}],"current_model":"CHK1 (CHEK1) is a serine/threonine kinase that is activated by ATR-mediated phosphorylation at Ser317/Ser345 within its C-terminal regulatory domain, which relieves an intramolecular autoinhibitory interaction between the C-terminus and kinase domain (Leu-449 critical); its stability is controlled by multiple E3 ubiquitin ligases (SCF-Fbx6/CRL4-CDT2/HUWE1) targeting it for proteasomal degradation, counterbalanced by deubiquitylases USP7 and Ataxin-3, and by K63-linked ubiquitination at K132 (by TRAF4) that promotes chromatin association and ATR-mediated activation before being removed by USP3; activated CHK1 enforces cell cycle checkpoints (G2/M, intra-S, spindle) by phosphorylating downstream targets including Cdc25A/B/C, Aurora-B (Ser331), NEK11 (Ser273), p73α (Ser47), Smurf1, PRIMPOL, and FAM122A, and also promotes replication fork stability through kinase-independent interaction with PCNA, all together preserving genomic integrity during both perturbed and unperturbed cell proliferation."},"narrative":{"mechanistic_narrative":"CHEK1 (CHK1) is a serine/threonine protein kinase that couples DNA damage and replication-stress sensing to cell-cycle control, enforcing checkpoints that preserve genomic integrity during both perturbed and unperturbed proliferation [PMID:8497322, PMID:10859163]. CHK1 is held in a closed, autoinhibited state by an intramolecular interaction between its N-terminal kinase domain and its distal C-terminus (critical residue Leu-449); ATR-mediated phosphorylation of the C-terminal regulatory domain, or an L449R mutation, disrupts this contact and converts CHK1 to its active conformation [PMID:14767054, PMID:27129240]. Activation requires the Claspin adaptor, which binds CHK1 through phosphorylated Thr916/Ser945 to permit ATR/ATM-dependent phosphorylation at Ser317/Ser345; these sites direct distinct outputs, with Ser345 controlling cytoplasmic localization and survival and Ser317 controlling chromatin release [PMID:15707391, PMID:17242188], and the activating signal is reversed by the PPM1D (Wip1) phosphatase acting on pSer345 [PMID:15870257]. Once active, CHK1 enforces the G2/M, intra-S, and spindle checkpoints by phosphorylating a broad substrate set: Cdc25C (Ser216) and the NEK11 kinase (Ser273), which drives Cdc25A degradation; Aurora-B (Ser331), promoting kinetochore error correction; p73α (Ser47) for apoptosis; and FAM122A, PRIMPOL, and Smurf1 to modulate replication-stress tolerance and cell fate [PMID:10391675, PMID:20090422, PMID:17276342, PMID:23321637, PMID:14585975, PMID:33108758, PMID:35353580, PMID:25249323]. Beyond its catalytic checkpoint role, CHK1 stabilizes replication forks through a kinase-independent, PCNA-interaction-motif-dependent mechanism that promotes translesion polymerase η recruitment and PCNA ubiquitination via Claspin/Rad18 [PMID:18451105, PMID:22529391]. CHK1 abundance is tightly set by competing ubiquitin systems: the SCF-Fbx6, CRL4(CDT2), and HUWE1 E3 ligases target it for proteasomal degradation, opposed by the deubiquitylases USP7 (enhanced by ZEB1) and Ataxin-3, while K63-linked ubiquitination at K132 by TRAF4 promotes chromatin association and ATR-mediated activation before removal by USP3 [PMID:19716789, PMID:23109433, PMID:31713291, PMID:25483066, PMID:25086746, PMID:28180282, PMID:29735693, PMID:32357935]. CHK1 expression is itself constrained by transcriptional repressors p53/p21/pRB and BCL6 [PMID:11158294, PMID:18346918].","teleology":[{"year":1993,"claim":"Established CHK1's foundational role by placing it as a kinase linking DNA damage sensing to the cell-cycle engine, defining the entire checkpoint-to-Cdc2 axis.","evidence":"Genetic suppressor screen and rad-mutant epistasis in fission yeast","pmids":["8497322"],"confidence":"High","gaps":["Did not define mammalian substrates or the activating upstream kinase","Molecular mechanism of Cdc2 inhibition not resolved"]},{"year":1999,"claim":"Showed human CHK1 acts during S-to-M phase to phosphorylate Cdc25C at Ser216 independently of ATM, identifying its first direct mammalian substrate and decoupling it from the ATM arm.","evidence":"Kinase assay, cell-cycle synchronization and localization in ATM-deficient cells","pmids":["10391675"],"confidence":"Medium","gaps":["Did not identify the ATM-independent activating kinase (later ATR)","Single substrate; broader target set unknown"]},{"year":2000,"claim":"Defined CHK1 as essential for the mammalian G2/M checkpoint and for embryonic viability, converting yeast genetics into a whole-animal loss-of-function requirement.","evidence":"Chk1-null mouse knockout with embryo cell-cycle and apoptosis analysis","pmids":["10859163"],"confidence":"High","gaps":["Embryonic lethality precluded analysis of adult/tissue-specific roles","Did not separate catalytic from non-catalytic functions"]},{"year":2003,"claim":"Identified p73α (Ser47) as a CHK1-specific substrate required for apoptosis, extending CHK1 output beyond cell-cycle arrest into cell-fate decisions.","evidence":"In vitro kinase assay, S47A mutagenesis, co-IP and in vivo phosphorylation; Chk2 negative control","pmids":["14585975"],"confidence":"High","gaps":["Physiological contexts where CHK1 favors apoptosis vs. arrest not defined"]},{"year":2004,"claim":"Resolved the activation mechanism: ATR phosphorylation of the C-terminus relieves an autoinhibitory interaction with the kinase domain, explaining how upstream signaling switches CHK1 on.","evidence":"Domain truncation, phospho-mimic mutants and interaction assays in Xenopus; 14-3-3/Rad24-Rad25 binding to phospho-CHK1 in fission yeast","pmids":["14767054","15585577"],"confidence":"High","gaps":["Precise intramolecular contact residues not yet mapped (resolved 2016)","Structural basis of C-terminus/kinase-domain contact unknown at this stage"]},{"year":2005,"claim":"Defined the activation interface and its reversal: Claspin (via pThr916/pSer945) is required for ATR/ATM-dependent CHK1 phosphorylation, while PPM1D/Wip1 dephosphorylates pSer345 to terminate signaling.","evidence":"Human cell-free reconstitution with phosphopeptide competition; in vitro phosphatase assay, co-IP and checkpoint abrogation","pmids":["15707391","15870257"],"confidence":"High","gaps":["Did not address how Claspin loading is regulated at forks","Other phosphatases acting on CHK1 not excluded"]},{"year":2007,"claim":"Assigned phospho-site-specific outputs (Ser345 cytoplasmic/survival, Ser317 chromatin release) and extended CHK1 into spindle/centrosome control via Aurora-B activation and Cdk-dependent centrosome amplification.","evidence":"Knock-in S317A/S345A separation-of-function mutants, subcellular fractionation; Chk1-/- DT40 cells with kinase-dead/S345A rescue and in vitro Aurora-B kinase assay","pmids":["17242188","17276342","17468739"],"confidence":"High","gaps":["How a single kinase coordinates nuclear, cytoplasmic and centrosomal pools not fully resolved","Direct Aurora-B site not yet mapped (resolved 2013)"]},{"year":2008,"claim":"Uncovered a kinase-independent, Claspin-dependent arm at stressed forks where CHK1 controls PCNA ubiquitination via Rad18, and revealed CHK1 is a caspase substrate during apoptosis.","evidence":"siRNA epistasis with PCNA ubiquitination and Rad18 chromatin-binding readouts; caspase cleavage-site mapping and truncated-kinase expression","pmids":["18451105","18550533"],"confidence":"High","gaps":["Mechanism by which CHK1 stabilizes Claspin not detailed","Physiological significance of the hyperactive cleavage fragment unclear"]},{"year":2008,"claim":"Established transcriptional control of CHEK1 by BCL6, complementing the earlier p53/p21/pRB repression circuit and showing CHK1 dosage is set at the promoter level.","evidence":"ChIP of BCL6 on the CHEK1 promoter, reporter assay and pharmacological reactivation in DLBCL","pmids":["18346918"],"confidence":"Medium","gaps":["Direct relevance to checkpoint output not measured","Interplay with p53-axis repression not addressed"]},{"year":2009,"claim":"Defined the first dedicated E3 ligase (SCF-Fbx6) terminating checkpoint signaling by degrading CHK1, and linked the pathway to Polα-associated fork-localized activation.","evidence":"In vitro/in vivo ubiquitination with degron mapping, tumor IHC; co-IP of Polα-CHK1 with TopBP1/ATR epistasis","pmids":["19716789","19177015"],"confidence":"High","gaps":["Whether multiple ligases act redundantly was unresolved (later: CRL4-CDT2, HUWE1)","Spatial coupling of Polα-CHK1 to ATR not fully defined"]},{"year":2010,"claim":"Connected CHK1 to Cdc25A destruction through an intermediate kinase, showing CHK1 phosphorylates NEK11 (Ser273), which in turn phosphorylates Cdc25A for beta-TrCP-mediated degradation.","evidence":"In vitro kinase assay, Cdc25A ubiquitination assay and checkpoint rescue with RNAi","pmids":["20090422"],"confidence":"Medium","gaps":["Relative contribution of direct vs. NEK11-mediated Cdc25A control not quantified"]},{"year":2012,"claim":"Separated CHK1's catalytic checkpoint role from a structural fork-protection role: a kinase-independent, PCNA-interaction-motif-dependent function promotes pol η recruitment and fork progression; CRL4(CDT2) was added as a second degradation route.","evidence":"Kinase-dead/PIP-mutant and chromatin-tethered chimeras, DNA fiber and pol η foci assays; co-IP and ubiquitination with CDT2 depletion","pmids":["22529391","23109433"],"confidence":"High","gaps":["How the kinase-independent function is regulated relative to catalytic activation unclear","Substrate-independent fork role mechanism only partially defined"]},{"year":2013,"claim":"Mapped the CHK1→Aurora-B activating site (Ser331) and showed CHK1 protects against merotelic attachments by enabling kinetochore loading of error-correction factors.","evidence":"In vitro kinase assay on Aurora-B Ser331 plus loss-of-function with MCAK/Kif2b/Mps1/Hec1 immunofluorescence","pmids":["23321637"],"confidence":"Medium","gaps":["How CHK1 accesses kinetochores spatially not resolved"]},{"year":2014,"claim":"Defined the deubiquitylase axis stabilizing CHK1—USP7 (enhanced by ATM-stabilized ZEB1) and the Smurf1/RhoB apoptotic output—balancing the degradation machinery and tuning DNA-repair/radioresistance.","evidence":"In vitro/in vivo deubiquitination assays, co-IP, half-life measurement, clonogenic survival; in vitro CHK1 kinase assay on Smurf1","pmids":["25086746","25483066","25249323"],"confidence":"High","gaps":["How DUB vs. E3 competition is dynamically resolved during stress not defined","Cell-type specificity of the ZEB1-USP7-CHK1 axis unclear"]},{"year":2016,"claim":"Pinned the autoinhibitory contact to residues 31–87 of the kinase domain and Leu-449 of the C-terminus, providing the structural logic for how ATR phosphorylation opens CHK1.","evidence":"FRET, BiFC, L449R and phospho-mimic mutagenesis with DNA-damage activation in cells","pmids":["27129240"],"confidence":"High","gaps":["High-resolution structure of the full-length closed state not provided"]},{"year":2016,"claim":"Showed CHK1 can be activated by non-genotoxic signals: PERK/UPR triggers Claspin-dependent CHK1 activation to inhibit replication origin firing, broadening CHK1's role beyond DNA damage.","evidence":"Thapsigargin UPR induction with Claspin/CHK1 siDNA rescue and origin-firing analysis","pmids":["27375025"],"confidence":"Medium","gaps":["Direct PERK-Claspin biochemical link not fully defined"]},{"year":2017,"claim":"Added Ataxin-3 as a stress-regulated CHK1 deubiquitinase that protects against CRL4A and FBXO6/CUL1 degradation and dissociates under prolonged replication stress, providing a timer for CHK1 turnover.","evidence":"Co-IP, in vitro/in vivo (de)ubiquitination, ATX3 depletion/overexpression and G2/M checkpoint assays","pmids":["28180282"],"confidence":"High","gaps":["Signal triggering ATX3 dissociation under prolonged stress unknown"]},{"year":2018,"claim":"Defined a non-degradative ubiquitin code: TRAF4-mediated K63 ubiquitination at the active-site K132 promotes chromatin association and ATR-dependent activation, reversed by USP3, distinguishing activation-linked from degradation-linked ubiquitination.","evidence":"In vitro/in vivo ubiquitination, K132 mutagenesis, USP3 knockdown and chromatin fractionation across two studies","pmids":["29735693","32357935"],"confidence":"High","gaps":["How K63 chromatin signal is coordinated with ATR/Claspin recruitment not fully mapped"]},{"year":2019,"claim":"Established CHK1 functions during unperturbed S phase: basal ATR/ETAA1-driven S296 autophosphorylation stabilizes CHK1, and ATR/CHK1 signaling restrains CDK1 to maintain RIF1-PP1 activity that limits dormant origin firing.","evidence":"S296 phospho-mutants with half-life/ubiquitylation assays; pharmacological ATR/CHK1 epistasis with RIF1-PP1 co-IP, substrate dephosphorylation and DNA fiber origin analysis; HUWE1 added as ATM/ATR/p53-independent E3","pmids":["31366665","31209037","31713291"],"confidence":"Medium","gaps":["How basal vs. damage-induced CHK1 activity are discriminated mechanistically","Redundancy among Fbx6/CRL4-CDT2/HUWE1 in vivo not resolved"]},{"year":2020,"claim":"Linked CHK1 to phosphatase regulation and drug resistance: CHK1 phosphorylates FAM122A to activate PP2A-B55α, and loss of this control stabilizes WEE1, conferring resistance to CHK1 inhibitors.","evidence":"CRISPR knockout screen, in vitro CHK1 kinase assay on FAM122A, PP2A-B55α activity and WEE1 stability assays with WEE1-inhibitor rescue","pmids":["33108758"],"confidence":"High","gaps":["Generality of the resistance mechanism across tumor types not established"]},{"year":2021,"claim":"Extended CHK1 functions beyond replication into tissue and disease contexts: a DNA-damage-independent Atr-Chek1-Cdc25 axis downstream of Piezo/NO inhibits axon regeneration, and CHEK1 drives chromosomal instability (via CEP170) and osteoclast differentiation in myeloma.","evidence":"Drosophila/mammalian neuron genetics and pharmacology; CHEK1 over/under-expression with CEP170 phosphorylation, CIN scoring, osteoclast assays and xenografts","pmids":["34158506","34090465"],"confidence":"Medium","gaps":["Direct CHK1 substrates in the neuronal axis not defined","Mechanism coupling CHK1 to NFATc1 not biochemically resolved"]},{"year":2022,"claim":"Identified PRIMPOL as a CHK1 substrate whose phosphorylation promotes repriming and replication-stress tolerance but generates fitness-reducing single-strand gaps when constitutive, illustrating the cost-benefit of CHK1 fork signaling.","evidence":"In vitro CHK1 kinase assay on PRIMPOL, repriming and DNA fiber assays, viability assays with Claspin-driven CHK1 activation","pmids":["35353580"],"confidence":"High","gaps":["In vivo PRIMPOL phospho-site usage and regulation not fully mapped"]},{"year":null,"claim":"How the multiple, partly redundant ubiquitin ligase/DUB systems and phospho-codes are integrated in real time to set CHK1 abundance, conformation, and localization for the correct checkpoint vs. fork vs. apoptotic output remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified quantitative model of CHK1 activation/turnover dynamics","Relative in vivo contributions of Fbx6, CRL4-CDT2, and HUWE1 not dissected","Spatial coordination of nuclear, cytoplasmic, centrosomal and chromatin pools not integrated"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[2,5,10,19,22,25,33,35,36]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[2,5,10,19,33,35]},{"term_id":"GO:0140657","term_label":"ATP-dependent activity","supporting_discovery_ids":[6,26]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[2,38]},{"term_id":"GO:0005654","term_label":"nucleoplasm","supporting_discovery_ids":[20]},{"term_id":"GO:0000228","term_label":"nuclear chromosome","supporting_discovery_ids":[11,13,29]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[11]},{"term_id":"GO:0005815","term_label":"microtubule organizing center","supporting_discovery_ids":[11,12,18,38]}],"pathway":[{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[0,2,3,10,19,38]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[13,21,23,35]},{"term_id":"R-HSA-69306","term_label":"DNA Replication","supporting_discovery_ids":[17,21,30,31,35]},{"term_id":"R-HSA-8953897","term_label":"Cellular responses to stimuli","supporting_discovery_ids":[6,8,27]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[5,25]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[16,20,24,28,29,32]}],"complexes":[],"partners":["CLASPIN","ATR","PCNA","USP7","ATXN3","TRAF4","PPM1D","FBXO6"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O14757","full_name":"Serine/threonine-protein kinase Chk1","aliases":["CHK1 checkpoint homolog","Cell cycle checkpoint kinase","Checkpoint kinase-1"],"length_aa":476,"mass_kda":54.4,"function":"Serine/threonine-protein kinase which is required for checkpoint-mediated cell cycle arrest and activation of DNA repair in response to the presence of DNA damage or unreplicated DNA (PubMed:11535615, PubMed:12399544, PubMed:12446774, PubMed:14559997, PubMed:14988723, PubMed:15311285, PubMed:15650047, PubMed:15665856, PubMed:32357935). May also negatively regulate cell cycle progression during unperturbed cell cycles (PubMed:11535615, PubMed:12399544, PubMed:12446774, PubMed:14559997, PubMed:14988723, PubMed:15311285, PubMed:15650047, PubMed:15665856). This regulation is achieved by a number of mechanisms that together help to preserve the integrity of the genome (PubMed:11535615, PubMed:12399544, PubMed:12446774, PubMed:14559997, PubMed:14988723, PubMed:15311285, PubMed:15650047, PubMed:15665856). Recognizes the substrate consensus sequence [R-X-X-S/T] (PubMed:11535615, PubMed:12399544, PubMed:12446774, PubMed:14559997, PubMed:14988723, PubMed:15311285, PubMed:15650047, PubMed:15665856). Binds to and phosphorylates CDC25A, CDC25B and CDC25C (PubMed:12676583, PubMed:12676925, PubMed:12759351, PubMed:14559997, PubMed:14681206, PubMed:19734889, PubMed:9278511). Phosphorylation of CDC25A at 'Ser-178' and 'Thr-507' and phosphorylation of CDC25C at 'Ser-216' creates binding sites for 14-3-3 proteins which inhibit CDC25A and CDC25C (PubMed:9278511). Phosphorylation of CDC25A at 'Ser-76', 'Ser-124', 'Ser-178', 'Ser-279' and 'Ser-293' promotes proteolysis of CDC25A (PubMed:12676583, PubMed:12676925, PubMed:12759351, PubMed:14681206, PubMed:19734889, PubMed:9278511). Phosphorylation of CDC25A at 'Ser-76' primes the protein for subsequent phosphorylation at 'Ser-79', 'Ser-82' and 'Ser-88' by NEK11, which is required for polyubiquitination and degradation of CDCD25A (PubMed:19734889, PubMed:20090422, PubMed:9278511). Inhibition of CDC25 leads to increased inhibitory tyrosine phosphorylation of CDK-cyclin complexes and blocks cell cycle progression (PubMed:9278511). Also phosphorylates NEK6 (PubMed:18728393). Binds to and phosphorylates RAD51 at 'Thr-309', which promotes the release of RAD51 from BRCA2 and enhances the association of RAD51 with chromatin, thereby promoting DNA repair by homologous recombination (PubMed:15665856). Phosphorylates multiple sites within the C-terminus of TP53, which promotes activation of TP53 by acetylation and promotes cell cycle arrest and suppression of cellular proliferation (PubMed:10673501, PubMed:15659650, PubMed:16511572). Also promotes repair of DNA cross-links through phosphorylation of FANCE (PubMed:17296736). Binds to and phosphorylates TLK1 at 'Ser-743', which prevents the TLK1-dependent phosphorylation of the chromatin assembly factor ASF1A (PubMed:12660173, PubMed:12955071). This may enhance chromatin assembly both in the presence or absence of DNA damage (PubMed:12660173, PubMed:12955071). May also play a role in replication fork maintenance through regulation of PCNA (PubMed:18451105). May regulate the transcription of genes that regulate cell-cycle progression through the phosphorylation of histones (By similarity). Phosphorylates histone H3.1 (to form H3T11ph), which leads to epigenetic inhibition of a subset of genes (By similarity). May also phosphorylate RB1 to promote its interaction with the E2F family of transcription factors and subsequent cell cycle arrest (PubMed:17380128). Phosphorylates SPRTN, promoting SPRTN recruitment to chromatin (PubMed:31316063). Reduces replication stress and activates the G2/M checkpoint, by phosphorylating and inactivating PABIR1/FAM122A and promoting the serine/threonine-protein phosphatase 2A-mediated dephosphorylation and stabilization of WEE1 levels and activity (PubMed:33108758) Endogenous repressor of isoform 1, interacts with, and antagonizes CHK1 to promote the S to G2/M phase transition","subcellular_location":"Nucleus; Chromosome; Cytoplasm; Cytoplasm, cytoskeleton, microtubule organizing center, centrosome","url":"https://www.uniprot.org/uniprotkb/O14757/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/CHEK1","classification":"Common Essential","n_dependent_lines":1207,"n_total_lines":1208,"dependency_fraction":0.9991721854304636},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000149554","cell_line_id":"CID000518","localizations":[{"compartment":"nucleoplasm","grade":3},{"compartment":"cytoplasmic","grade":1}],"interactors":[{"gene":"CAPZB","stoichiometry":0.2},{"gene":"RNF13","stoichiometry":0.2},{"gene":"PARP1","stoichiometry":0.2},{"gene":"H1FX","stoichiometry":0.2},{"gene":"HIST1H2BN;HIST1H2BM;HIST1H2BH;HIST2H2BF;HIST1H2BC;HIST1H2BD;HIST1H2BK;H2BFS","stoichiometry":0.2},{"gene":"RPS27A;UBC;UBB;UBA52","stoichiometry":0.2},{"gene":"CDC37","stoichiometry":0.2},{"gene":"HIST2H2AA3;HIST2H2AC","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID000518","total_profiled":1310},"omim":[{"mim_id":"621421","title":"RAMOND-ELLIOTT NEURODEVELOPMENTAL SYNDROME; RAMELN","url":"https://www.omim.org/entry/621421"},{"mim_id":"620610","title":"OOCYTE/ZYGOTE/EMBRYO MATURATION ARREST 21; OZEMA21","url":"https://www.omim.org/entry/620610"},{"mim_id":"620291","title":"WD REPEAT-CONTAINING PROTEIN 18; WDR18","url":"https://www.omim.org/entry/620291"},{"mim_id":"619309","title":"PROTEIN PHOSPHATASE, MAGNESIUM/MANGANESE-DEPENDENT, 1F; PPM1F","url":"https://www.omim.org/entry/619309"},{"mim_id":"618740","title":"COILED-COIL DOMAIN-CONTAINING PROTEIN 154; CCDC154","url":"https://www.omim.org/entry/618740"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Vesicles","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"bone marrow","ntpm":24.9},{"tissue":"lymphoid tissue","ntpm":19.5},{"tissue":"seminal vesicle","ntpm":28.7}],"url":"https://www.proteinatlas.org/search/CHEK1"},"hgnc":{"alias_symbol":["CHK1"],"prev_symbol":[]},"alphafold":{"accession":"O14757","domains":[{"cath_id":"3.30.200.20","chopping":"4-87","consensus_level":"high","plddt":87.3825,"start":4,"end":87},{"cath_id":"1.10.510.10","chopping":"92-261","consensus_level":"high","plddt":95.6042,"start":92,"end":261},{"cath_id":"3.30.310.80","chopping":"378-463","consensus_level":"high","plddt":87.3552,"start":378,"end":463}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O14757","model_url":"https://alphafold.ebi.ac.uk/files/AF-O14757-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O14757-F1-predicted_aligned_error_v6.png","plddt_mean":76.12},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CHEK1","jax_strain_url":"https://www.jax.org/strain/search?query=CHEK1"},"sequence":{"accession":"O14757","fasta_url":"https://rest.uniprot.org/uniprotkb/O14757.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O14757/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O14757"}},"corpus_meta":[{"pmid":"12781359","id":"PMC_12781359","title":"Chk1 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is a protein kinase that links the DNA damage checkpoint pathway (rad1-dependent) to cell-cycle regulatory kinase p34cdc2, coupling DNA damage sensing to cell cycle arrest.\",\n      \"method\": \"Genetic screen (multicopy suppressor of cdc2 mutant), sensitivity assays with rad mutants\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — foundational genetic epistasis experiment replicated across multiple organisms, establishing Chk1's position in the checkpoint-to-Cdc2 axis\",\n      \"pmids\": [\"8497322\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"In fission yeast, a Chk1-dependent pathway prevents mitosis when passage through 'start' (G1 commitment point) is compromised, identifying a third mitotic control checkpoint distinct from S-M and DNA-damage checkpoints.\",\n      \"method\": \"Genetic epistasis in S. pombe (chk1 deletion, rad17 deletion, cell cycle analysis with 1C DNA content)\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean genetic epistasis in yeast with defined phenotypic readout, single lab\",\n      \"pmids\": [\"8548290\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Human Chk1 (hChk1) is expressed specifically at S-to-M phase of the cell cycle, localizes to the nucleus during this window, and phosphorylates Cdc25C at serine 216 in the absence of DNA damage, in an ATM-independent manner.\",\n      \"method\": \"Cell cycle synchronization, kinase assay (Cdc25C phosphorylation), subcellular fractionation/localization, ATM-deficient patient cells\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct kinase assay plus localization with ATM-deficient cells as genetic control, single lab\",\n      \"pmids\": [\"10391675\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Chk1 is required for the G2/M checkpoint in mammals; Chk1-null mouse embryos fail to arrest the cell cycle before mitosis in response to DNA replication block or DNA damage and die of apoptosis at the blastocyst stage.\",\n      \"method\": \"Targeted gene disruption in mice (Chk1−/− knockout), morphological analysis, cell cycle analysis of embryos\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — definitive loss-of-function in whole animal with clear cellular phenotype, independently cited widely\",\n      \"pmids\": [\"10859163\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"p53 transcriptionally represses CHK1 through a pathway requiring p21 and the retinoblastoma protein (pRB), suggesting E2F-dependent regulation; this establishes a feedback loop where p53 reduces CHK1 protein levels.\",\n      \"method\": \"Tetracycline-inducible p53 expression, p21-null cells, pRB-null cells, Northern blot/RT-PCR for CHK1 mRNA\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis with multiple cell lines (p21-null, pRB-null), single lab, two orthogonal readouts (mRNA and protein)\",\n      \"pmids\": [\"11158294\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"p73α is a direct substrate of Chk1; Chk1 phosphorylates p73α at serine 47 in vitro and in vivo upon DNA damage, and this phosphorylation is required for the apoptotic function of p73α. Chk2 does not phosphorylate p73α in vitro.\",\n      \"method\": \"Co-immunoprecipitation of endogenous proteins, in vitro kinase assay, site-directed mutagenesis (S47A), in vivo phosphorylation assay\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro kinase assay with mutagenesis plus in vivo co-IP and phosphorylation validation, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"14585975\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"ATR-mediated phosphorylation of the C-terminal regulatory domain of Chk1 relieves an autoinhibitory intramolecular interaction between the C-terminal autoinhibitory region (AIR) and the kinase domain, converting Chk1 to an active conformation.\",\n      \"method\": \"Domain truncation and coexpression in Xenopus oocytes/embryos, phospho-mimic mutations, interaction assays\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstitution in Xenopus system with domain mapping and phospho-mimic mutagenesis, multiple orthogonal assays in one study\",\n      \"pmids\": [\"14767054\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"In fission yeast, 14-3-3 proteins (Rad24/Rad25) interact with phosphorylated Chk1 after DNA damage; a leucine-rich domain mediates this interaction. 14-3-3 binding is required for Chk1 phosphorylation, nuclear accumulation upon DNA damage, and checkpoint function.\",\n      \"method\": \"Co-immunoprecipitation, site-directed mutagenesis (leucine-to-alanine), nuclear localization imaging, UV sensitivity assays\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal interaction and functional mutagenesis in S. pombe, single lab, multiple orthogonal readouts\",\n      \"pmids\": [\"15585577\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"PPM1D (Wip1) phosphatase directly binds Chk1 and dephosphorylates the ATR-targeted pSer345 site, decreasing Chk1 kinase activity and abrogating intra-S and G2/M checkpoint responses to DNA damage.\",\n      \"method\": \"Co-immunoprecipitation, in vitro phosphatase assay, kinase activity assay, checkpoint abrogation assays after UV/IR\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro phosphatase assay with defined substrate site plus Co-IP and checkpoint functional readout, multiple orthogonal methods in one study\",\n      \"pmids\": [\"15870257\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"DNA-dependent phosphorylation of Chk1 by ATR/ATM in human cells requires Claspin, which binds Chk1 through phosphorylated residues Thr916 and Ser945 within its Chk1-binding domain. A phosphopeptide from this motif competitively inhibits the Claspin-Chk1 interaction and blocks ATR/ATM-dependent Chk1 phosphorylation.\",\n      \"method\": \"Human cell-free biochemical system, double-stranded DNA oligonucleotide-induced phosphorylation, phosphopeptide competition, kinase inhibitor panel\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstituted human cell-free system with phosphopeptide competition and defined interaction residues, multiple orthogonal methods\",\n      \"pmids\": [\"15707391\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Chk1 is required for spindle checkpoint function; Chk1-deficient vertebrate cells show decreased Aurora-B kinase activity and impaired BubR1 phosphorylation and kinetochore localization. Chk1 directly phosphorylates Aurora-B and enhances its catalytic activity in vitro.\",\n      \"method\": \"Chk1−/− DT40 cells, RNAi knockdown, in vitro kinase assay (Chk1 phosphorylates Aurora-B), taxol/nocodazole treatment, BubR1 kinetochore localization by immunofluorescence\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro kinase assay plus genetic knockout with defined molecular phenotype (Aurora-B activity, BubR1 localization), multiple orthogonal methods\",\n      \"pmids\": [\"17276342\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Chk1 phosphorylation at S345 is required for cytoplasmic localization and prevention of mitotic catastrophe, while S317 phosphorylation is required for chromatin release upon genotoxic stress and checkpoint activation; both sites contribute distinctly to Chk1 function. Forced centrosomal immobilization of Chk1 prevents apoptosis.\",\n      \"method\": \"Knockout-knockin system with phosphorylation-site mutants (S317A, S345A), subcellular fractionation, localization imaging, centrosomal targeting construct\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — knock-in of separation-of-function mutants in null cell background with multiple phenotypic readouts, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"17242188\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"DNA damage induces Chk1-dependent centrosome amplification (not fragmentation); kinase-dead Chk1 and the non-phosphorylatable Chk1-S345A mutant fail to restore centrosome amplification, demonstrating that both ATR signaling to Chk1 and Chk1 catalytic activity are required.\",\n      \"method\": \"Chk1−/− DT40 cells, transgenic rescue with kinase-dead and S345A mutants, light and electron microscopy, RNAi knockdown, caffeine treatment\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic knockout with defined rescue by wild-type vs. mutant transgenes, multiple orthogonal methods, single lab\",\n      \"pmids\": [\"17468739\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Chk1 regulates DNA damage-induced PCNA ubiquitination by stabilizing Claspin, which in turn controls Rad18 ubiquitin ligase binding to chromatin; this function requires Claspin but not ATR, revealing an ATR-independent arm of Chk1 activity at stressed forks.\",\n      \"method\": \"RNAi knockdown (Chk1, Claspin, Timeless), PCNA ubiquitination assay, chromatin fractionation, Rad18-chromatin binding assay\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis by siRNA with molecular mechanistic readout (PCNA ubiquitination, Rad18 chromatin binding), multiple orthogonal methods, single lab\",\n      \"pmids\": [\"18451105\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Chk1 is cleaved by caspases during apoptosis at Asp-299 (chicken) and Asp-299/Asp-351 (human); the N-terminal cleavage fragment (residues 1–299) has elevated kinase activity and induces abnormal nuclear morphology and H2AX phosphorylation when ectopically expressed.\",\n      \"method\": \"Caspase inhibitor experiments, mapping of cleavage sites, truncated Chk1 expression (residues 1–299), kinase assay, immunofluorescence of H2AX\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro and in vivo cleavage mapping with defined truncation expressing elevated kinase activity, single lab\",\n      \"pmids\": [\"18550533\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The C-terminal domain of Chk1 (S. pombe) does not simply autoinhibit the kinase; it is also required for adopting an active configuration. Intragenic suppressor mutations cluster to the substrate-binding face of the catalytic domain, suggesting the C-terminus interacts with this region.\",\n      \"method\": \"Truncation analysis, activating mutations in C-terminal domain, intragenic suppressor screen, temperature-sensitive alleles expressed from endogenous locus\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic suppressor screen plus in vivo expression from endogenous locus, single lab, multiple alleles\",\n      \"pmids\": [\"18716058\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"The SCF E3 ubiquitin ligase containing F-box protein Fbx6 mediates ubiquitination and proteasomal degradation of Chk1 after DNA damage, exposing a C-terminal degron; this terminates checkpoint signaling. Low Fbx6 levels correlate inversely with Chk1 levels and with cancer cell resistance to camptothecin.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay in vitro and in vivo, siRNA knockdown, proteasome inhibitor experiments, immunohistochemistry in tumor tissues\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro ubiquitination reconstitution plus in vivo Co-IP with defined degron, multiple orthogonal methods, single lab\",\n      \"pmids\": [\"19716789\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"DNA polymerase alpha (Polα) associates with Chk1 in native cell extracts; following replication stress, Polα-associated Chk1 is phosphorylated at Ser345 in a TopBP1- and ATR-dependent manner, and this association is required for efficient intra-S checkpoint activation.\",\n      \"method\": \"Co-immunoprecipitation from native cell extracts, siRNA depletion of Polα, ATR/TopBP1 epistasis, γH2AX measurement\",\n      \"journal\": \"Cell cycle (Georgetown, Tex.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — Co-IP plus siRNA epistasis, single lab, two orthogonal methods\",\n      \"pmids\": [\"19177015\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Chk1 signaling causes centrosome amplification after ionizing radiation by upregulating Cdk2 activity through activating T160 phosphorylation of Cdk2; Cdk1 can substitute for Cdk2 in this pathway.\",\n      \"method\": \"Chk1−/− DT40 cells, Cdk2−/− cells, Cdk2 T160A mutant rescue, IR treatment, centrosome counting\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistatic genetic knockouts with site-specific mutant rescue, single lab\",\n      \"pmids\": [\"19838212\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"NEK11, a NIMA-related kinase, is activated by CHK1-mediated phosphorylation at Ser273 and is the critical kinase that directly phosphorylates CDC25A to trigger its beta-TrCP-mediated polyubiquitylation and degradation, linking CHK1 to CDC25A destruction.\",\n      \"method\": \"In vitro kinase assay (CHK1 phosphorylates NEK11 Ser273), CDC25A ubiquitination assay, RNAi knockdown, checkpoint rescue experiments\",\n      \"journal\": \"Cell cycle (Georgetown, Tex.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro kinase assay defining the phosphorylation event, plus functional epistasis, single lab\",\n      \"pmids\": [\"20090422\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"CHK1 is a novel substrate of the CRL4(CDT2) E3 ubiquitin ligase; CRL4(CDT2) ubiquitinates the activated form of CHK1 in the nucleoplasm in a PCNA-independent manner, targeting it for degradation. CHK1 activity maintains G2 arrest in CDT2-depleted cells.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, subcellular fractionation, siRNA knockdown of CDT2, G2 arrest rescue experiments\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus ubiquitination assay with subcellular localization distinction, single lab, two orthogonal methods\",\n      \"pmids\": [\"23109433\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Chk1 promotes replication fork progression after UV irradiation through a kinase-independent mechanism that requires its PCNA-interacting motif and chromatin release; this function is independent of Claspin and is required for efficient recruitment of DNA polymerase η (pol η) to replication foci for translesion synthesis.\",\n      \"method\": \"Kinase-dead Chk1 mutant, PCNA-interaction motif mutant, histone H2B-Chk1 chromatin-tethering chimera, pol η foci by immunofluorescence, DNA fiber assay\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple separation-of-function mutants (kinase-dead, PIP-mutant, chromatin-tethered) with defined molecular phenotype, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"22529391\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Chk1 protects vertebrate cells against merotelic kinetochore attachments; Chk1 phosphorylates Aurora-B at Ser331 in prometaphase, which is required for optimal kinetochore localization of MCAK, Kif2b, and Mps1 and for Hec1 phosphorylation, enabling error correction.\",\n      \"method\": \"Chk1 inhibitor/knockdown, in vitro kinase assay (Chk1 phosphorylates Aurora-B Ser331), immunofluorescence of MCAK/Kif2b/Mps1/Hec1 at kinetochores, lagging chromosome analysis\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro kinase assay defining substrate site plus genetic/pharmacological loss-of-function with multiple molecular readouts, single lab\",\n      \"pmids\": [\"23321637\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"ATM phosphorylates and stabilizes ZEB1 after DNA damage; ZEB1 then interacts with USP7 deubiquitylase and enhances USP7's ability to deubiquitylate and stabilize CHK1, promoting homologous recombination-dependent DNA repair and radioresistance.\",\n      \"method\": \"Co-immunoprecipitation (ZEB1-USP7-CHK1), ubiquitination assay, in vitro deubiquitination assay, ATM kinase assay, siRNA knockdown, clonogenic survival after radiation\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro deubiquitination assay plus Co-IP and functional rescue, multiple orthogonal methods in one study\",\n      \"pmids\": [\"25086746\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"USP7 deubiquitylase directly stabilizes Chk1 protein levels by removing ubiquitin chains: wild-type but not catalytic-mutant USP7 deubiquitinates Chk1 in vivo and in vitro, prolongs Chk1 half-life, and this effect is independent of USP7's known effect on Claspin.\",\n      \"method\": \"Co-immunoprecipitation, in vitro and in vivo deubiquitination assay, USP7 catalytic mutant, Chk1 half-life measurement (cycloheximide chase), siRNA knockdown\",\n      \"journal\": \"Cell cycle (Georgetown, Tex.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro and in vivo deubiquitination assay with catalytic mutant control plus half-life measurement, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"25483066\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Chk1 phosphorylates Smurf1 E3 ubiquitin ligase after DNA damage (UV/MMS), enhancing Smurf1 self-degradation, which leads to RhoB accumulation and apoptosis, defining an ATR/Chk1/Smurf1/RhoB cell fate pathway.\",\n      \"method\": \"In vitro kinase assay (Chk1 phosphorylates Smurf1), co-immunoprecipitation, ubiquitination assay, siRNA knockdown, apoptosis assay\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro kinase assay with defined substrate plus Co-IP and functional epistasis, single lab\",\n      \"pmids\": [\"25249323\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Human Chk1 maintains a closed, autoinhibited conformation through an intramolecular interaction between residues 31–87 of the N-terminal kinase domain and the distal C-terminus (critical residue Leu-449). DNA damage-induced ATR-dependent phosphorylation, or Leu-449→Arg mutation, disrupts this interaction and opens Chk1 to an active conformation.\",\n      \"method\": \"FRET, bimolecular fluorescence complementation (BiFC), site-directed mutagenesis (L449R), phospho-mimic mutations, ATR-dependent DNA damage induction\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — structural/FRET approach with mutagenesis and DNA-damage activation in cells, multiple orthogonal methods in one study\",\n      \"pmids\": [\"27129240\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"PERK kinase (UPR effector) inhibits DNA replication via Claspin phosphorylation and subsequent CHK1 activation in the absence of genotoxic DNA damage; depletion of Claspin or CHK1 rescues thapsigargin-induced replication inhibition by allowing increased origin firing.\",\n      \"method\": \"Thapsigargin-induced UPR (non-genotoxic), Claspin/Chk1 siRNA knockdown, DNA synthesis assay, Chk1 phosphorylation assay, replication origin firing analysis\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis via siRNA of two pathway components with mechanistic molecular readouts, single lab\",\n      \"pmids\": [\"27375025\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Ataxin-3 (ATX3) interacts with Chk1 under basal and DNA damage conditions, protecting it from DDB1/CUL4A- and FBXO6/CUL1-mediated polyubiquitination and degradation. ATX3 is a deubiquitinase of Chk1; under prolonged replication stress ATX3 dissociates from Chk1, allowing its degradation.\",\n      \"method\": \"Co-immunoprecipitation (ATX3-Chk1), in vivo and in vitro ubiquitination/deubiquitination assay, siRNA of ATX3, ectopic ATX3 expression, G2/M checkpoint assay\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro and in vivo deubiquitination assay plus Co-IP and epistatic rescue with ectopic ATX3, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"28180282\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"K63-linked ubiquitination of CHK1 at K132 (active site residue) by TRAF4 promotes CHK1 chromatin association and is required for ATR-mediated CHK1 phosphorylation and activation after DNA damage; USP3 deubiquitinase removes this K63 chain, releasing CHK1 from chromatin and restoring kinase active-site accessibility.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay (in vitro and in vivo), site-directed mutagenesis (K132), USP3 knockdown/mutants, CHK1 chromatin fractionation\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America / Journal of hematology & oncology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro ubiquitination/deubiquitination assay with defined site mutagenesis and functional rescue, two independent studies (PMID 29735693 and 32357935), multiple orthogonal methods\",\n      \"pmids\": [\"29735693\", \"32357935\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"CHK1 stability under unperturbed proliferation is maintained by basal ATR/ETAA1-driven CHK1 autophosphorylation at S296; this autoactivatory loop opposes ubiquitylation and proteasomal degradation, thereby preserving intrinsic S-phase checkpoint functions.\",\n      \"method\": \"siRNA depletion of ATR/ETAA1, S296 phospho-mutants, cycloheximide half-life assay, ubiquitylation assay, S-phase checkpoint functional assay\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — phospho-mutant analysis with half-life and ubiquitylation readouts, single lab, two orthogonal methods\",\n      \"pmids\": [\"31366665\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"ATR and CHK1 kinase signaling during unperturbed S phase suppresses CDK1 activity, which stabilizes a RIF1–PP1 phosphatase interaction; this PP1 activity dephosphorylates CDC7 and CDK2 substrates to inhibit helicase assembly/activation and limit dormant origin firing.\",\n      \"method\": \"ATR/CHK1 inhibitor treatment during unperturbed replication, RIF1 Ser2205 phosphorylation assay, RIF1–PP1 co-immunoprecipitation, CDK1-dependence (CDK1 inhibitor), origin firing analysis by DNA fiber\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological epistasis with defined molecular interaction (RIF1-PP1) and substrate dephosphorylation readout, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"31209037\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"HUWE1 (HECT E3 ubiquitin ligase) directly ubiquitinates multiple lysine residues within the Chk1 kinase domain in vitro and controls Chk1 protein stability independently of ATM, ATR, and p53; HUWE1 knockdown prolongs Chk1 half-life and rescues Chk1 loss during prolonged replication stress.\",\n      \"method\": \"In vitro ubiquitination assay with mass spectrometry site mapping, cycloheximide half-life assay, siRNA knockdown of HUWE1 vs. Cul4A, replication stress (HU/CPT) treatment\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro ubiquitination with MS-identified sites plus in vivo half-life analysis, single lab\",\n      \"pmids\": [\"31713291\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CHK1 directly phosphorylates FAM122A/PABIR1, leading to activation of PP2A-B55α phosphatase; in CHK1-inhibited cells, loss of FAM122A phosphorylation allows PP2A-B55α to dephosphorylate and stabilize WEE1, increasing WEE1 expression, reducing replication stress, and conferring resistance to CHK1 inhibitors.\",\n      \"method\": \"CRISPR knockout screen (FAM122A), kinase assay (CHK1 phosphorylates FAM122A), PP2A-B55α activity assay, WEE1 stability assay, rescue by WEE1 inhibitor combination\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct kinase assay with CRISPR knockout and defined mechanistic pathway rescue, multiple orthogonal methods in one study\",\n      \"pmids\": [\"33108758\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"In Drosophila sensory neurons and mammalian neurons, the Atr-Chek1-Cdc25 axis acts downstream of Piezo mechanosensitive ion channel and NO signaling (independent of DNA damage) to inhibit axon regeneration; removing Atr or Chek1, or overexpressing Cdc25, promotes regeneration.\",\n      \"method\": \"Drosophila genetic epistasis (Atr/Chek1/Cdc25 overexpression and knockdown), Piezo channel genetics, NO signaling pathway analysis, mammalian neuron pharmacological inhibition, behavioral recovery assay\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis in Drosophila with parallel pharmacological validation in mammalian neurons, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"34158506\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CHK1 directly phosphorylates PRIMPOL to promote repriming activity and replication stress tolerance; this phosphorylation is important for cellular resistance to DNA damage but promotes single-strand gap formation and reduces cell fitness when constitutively active.\",\n      \"method\": \"In vitro CHK1 kinase assay on PRIMPOL, CLASPIN overexpression to increase CHK1 activation, PRIMPOL repriming assay, DNA fiber analysis, cell viability assays\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct in vitro kinase assay with defined substrate plus functional repriming assay and cellular validation, multiple orthogonal methods, single lab\",\n      \"pmids\": [\"35353580\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CHEK1 promotes chromosomal instability in multiple myeloma partly by phosphorylating CEP170; CHEK1 also promotes osteoclast differentiation by upregulating NFATc1 expression.\",\n      \"method\": \"CHEK1 overexpression/knockdown, Giemsa staining/exon sequencing for CIN, immunofluorescence, TRAP staining for osteoclast differentiation, xenograft model\",\n      \"journal\": \"Molecular cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — defined substrate (CEP170) phosphorylation plus functional osteoclast assay, single lab\",\n      \"pmids\": [\"34090465\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"BCL6 transcriptional repressor directly binds a consensus element in the CHEK1 promoter and represses CHEK1 expression in normal and malignant B-cells; BCL6 peptide inhibitor (BPI) reactivates CHEK1 in DLBCL cells.\",\n      \"method\": \"Chromatin immunoprecipitation (BCL6 binds CHEK1 promoter), reporter assay, BPI treatment with CHEK1 re-expression measurement\",\n      \"journal\": \"Blood cells, molecules & diseases\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct ChIP demonstrating promoter binding with pharmacological reactivation, single lab\",\n      \"pmids\": [\"18346918\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Nuclear localization of Chk1 (not centrosomal) is the critical determinant for preventing premature mitotic entry; a Chk1 mutant forced to the nucleus delays mitotic entry, while centrosome-immobilized Chk1 has little impact on mitotic timing.\",\n      \"method\": \"Conditional Chk1 knockout in MEFs, Chk1+/myc knock-in (DLD-1 cells), nuclear-targeted vs. centrosome-targeted Chk1 constructs, antibody specificity validation, live-cell mitotic entry assay\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — targeted localization constructs in knock-in and conditional KO cells with mitotic entry functional readout, single lab\",\n      \"pmids\": [\"21628425\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CHK1 (CHEK1) is a serine/threonine kinase that is activated by ATR-mediated phosphorylation at Ser317/Ser345 within its C-terminal regulatory domain, which relieves an intramolecular autoinhibitory interaction between the C-terminus and kinase domain (Leu-449 critical); its stability is controlled by multiple E3 ubiquitin ligases (SCF-Fbx6/CRL4-CDT2/HUWE1) targeting it for proteasomal degradation, counterbalanced by deubiquitylases USP7 and Ataxin-3, and by K63-linked ubiquitination at K132 (by TRAF4) that promotes chromatin association and ATR-mediated activation before being removed by USP3; activated CHK1 enforces cell cycle checkpoints (G2/M, intra-S, spindle) by phosphorylating downstream targets including Cdc25A/B/C, Aurora-B (Ser331), NEK11 (Ser273), p73α (Ser47), Smurf1, PRIMPOL, and FAM122A, and also promotes replication fork stability through kinase-independent interaction with PCNA, all together preserving genomic integrity during both perturbed and unperturbed cell proliferation.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"CHEK1 (CHK1) is a serine/threonine protein kinase that couples DNA damage and replication-stress sensing to cell-cycle control, enforcing checkpoints that preserve genomic integrity during both perturbed and unperturbed proliferation [#0, #3]. CHK1 is held in a closed, autoinhibited state by an intramolecular interaction between its N-terminal kinase domain and its distal C-terminus (critical residue Leu-449); ATR-mediated phosphorylation of the C-terminal regulatory domain, or an L449R mutation, disrupts this contact and converts CHK1 to its active conformation [#6, #26]. Activation requires the Claspin adaptor, which binds CHK1 through phosphorylated Thr916/Ser945 to permit ATR/ATM-dependent phosphorylation at Ser317/Ser345; these sites direct distinct outputs, with Ser345 controlling cytoplasmic localization and survival and Ser317 controlling chromatin release [#9, #11], and the activating signal is reversed by the PPM1D (Wip1) phosphatase acting on pSer345 [#8]. Once active, CHK1 enforces the G2/M, intra-S, and spindle checkpoints by phosphorylating a broad substrate set: Cdc25C (Ser216) and the NEK11 kinase (Ser273), which drives Cdc25A degradation; Aurora-B (Ser331), promoting kinetochore error correction; p73\\u03b1 (Ser47) for apoptosis; and FAM122A, PRIMPOL, and Smurf1 to modulate replication-stress tolerance and cell fate [#2, #19, #10, #22, #5, #33, #35, #25]. Beyond its catalytic checkpoint role, CHK1 stabilizes replication forks through a kinase-independent, PCNA-interaction-motif-dependent mechanism that promotes translesion polymerase \\u03b7 recruitment and PCNA ubiquitination via Claspin/Rad18 [#13, #21]. CHK1 abundance is tightly set by competing ubiquitin systems: the SCF-Fbx6, CRL4(CDT2), and HUWE1 E3 ligases target it for proteasomal degradation, opposed by the deubiquitylases USP7 (enhanced by ZEB1) and Ataxin-3, while K63-linked ubiquitination at K132 by TRAF4 promotes chromatin association and ATR-mediated activation before removal by USP3 [#16, #20, #32, #24, #23, #28, #29]. CHK1 expression is itself constrained by transcriptional repressors p53/p21/pRB and BCL6 [#4, #37].\",\n  \"teleology\": [\n    {\n      \"year\": 1993,\n      \"claim\": \"Established CHK1's foundational role by placing it as a kinase linking DNA damage sensing to the cell-cycle engine, defining the entire checkpoint-to-Cdc2 axis.\",\n      \"evidence\": \"Genetic suppressor screen and rad-mutant epistasis in fission yeast\",\n      \"pmids\": [\"8497322\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define mammalian substrates or the activating upstream kinase\", \"Molecular mechanism of Cdc2 inhibition not resolved\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Showed human CHK1 acts during S-to-M phase to phosphorylate Cdc25C at Ser216 independently of ATM, identifying its first direct mammalian substrate and decoupling it from the ATM arm.\",\n      \"evidence\": \"Kinase assay, cell-cycle synchronization and localization in ATM-deficient cells\",\n      \"pmids\": [\"10391675\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Did not identify the ATM-independent activating kinase (later ATR)\", \"Single substrate; broader target set unknown\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Defined CHK1 as essential for the mammalian G2/M checkpoint and for embryonic viability, converting yeast genetics into a whole-animal loss-of-function requirement.\",\n      \"evidence\": \"Chk1-null mouse knockout with embryo cell-cycle and apoptosis analysis\",\n      \"pmids\": [\"10859163\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Embryonic lethality precluded analysis of adult/tissue-specific roles\", \"Did not separate catalytic from non-catalytic functions\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Identified p73\\u03b1 (Ser47) as a CHK1-specific substrate required for apoptosis, extending CHK1 output beyond cell-cycle arrest into cell-fate decisions.\",\n      \"evidence\": \"In vitro kinase assay, S47A mutagenesis, co-IP and in vivo phosphorylation; Chk2 negative control\",\n      \"pmids\": [\"14585975\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological contexts where CHK1 favors apoptosis vs. arrest not defined\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Resolved the activation mechanism: ATR phosphorylation of the C-terminus relieves an autoinhibitory interaction with the kinase domain, explaining how upstream signaling switches CHK1 on.\",\n      \"evidence\": \"Domain truncation, phospho-mimic mutants and interaction assays in Xenopus; 14-3-3/Rad24-Rad25 binding to phospho-CHK1 in fission yeast\",\n      \"pmids\": [\"14767054\", \"15585577\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Precise intramolecular contact residues not yet mapped (resolved 2016)\", \"Structural basis of C-terminus/kinase-domain contact unknown at this stage\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Defined the activation interface and its reversal: Claspin (via pThr916/pSer945) is required for ATR/ATM-dependent CHK1 phosphorylation, while PPM1D/Wip1 dephosphorylates pSer345 to terminate signaling.\",\n      \"evidence\": \"Human cell-free reconstitution with phosphopeptide competition; in vitro phosphatase assay, co-IP and checkpoint abrogation\",\n      \"pmids\": [\"15707391\", \"15870257\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not address how Claspin loading is regulated at forks\", \"Other phosphatases acting on CHK1 not excluded\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Assigned phospho-site-specific outputs (Ser345 cytoplasmic/survival, Ser317 chromatin release) and extended CHK1 into spindle/centrosome control via Aurora-B activation and Cdk-dependent centrosome amplification.\",\n      \"evidence\": \"Knock-in S317A/S345A separation-of-function mutants, subcellular fractionation; Chk1-/- DT40 cells with kinase-dead/S345A rescue and in vitro Aurora-B kinase assay\",\n      \"pmids\": [\"17242188\", \"17276342\", \"17468739\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How a single kinase coordinates nuclear, cytoplasmic and centrosomal pools not fully resolved\", \"Direct Aurora-B site not yet mapped (resolved 2013)\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Uncovered a kinase-independent, Claspin-dependent arm at stressed forks where CHK1 controls PCNA ubiquitination via Rad18, and revealed CHK1 is a caspase substrate during apoptosis.\",\n      \"evidence\": \"siRNA epistasis with PCNA ubiquitination and Rad18 chromatin-binding readouts; caspase cleavage-site mapping and truncated-kinase expression\",\n      \"pmids\": [\"18451105\", \"18550533\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which CHK1 stabilizes Claspin not detailed\", \"Physiological significance of the hyperactive cleavage fragment unclear\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Established transcriptional control of CHEK1 by BCL6, complementing the earlier p53/p21/pRB repression circuit and showing CHK1 dosage is set at the promoter level.\",\n      \"evidence\": \"ChIP of BCL6 on the CHEK1 promoter, reporter assay and pharmacological reactivation in DLBCL\",\n      \"pmids\": [\"18346918\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct relevance to checkpoint output not measured\", \"Interplay with p53-axis repression not addressed\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Defined the first dedicated E3 ligase (SCF-Fbx6) terminating checkpoint signaling by degrading CHK1, and linked the pathway to Pol\\u03b1-associated fork-localized activation.\",\n      \"evidence\": \"In vitro/in vivo ubiquitination with degron mapping, tumor IHC; co-IP of Pol\\u03b1-CHK1 with TopBP1/ATR epistasis\",\n      \"pmids\": [\"19716789\", \"19177015\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether multiple ligases act redundantly was unresolved (later: CRL4-CDT2, HUWE1)\", \"Spatial coupling of Pol\\u03b1-CHK1 to ATR not fully defined\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Connected CHK1 to Cdc25A destruction through an intermediate kinase, showing CHK1 phosphorylates NEK11 (Ser273), which in turn phosphorylates Cdc25A for beta-TrCP-mediated degradation.\",\n      \"evidence\": \"In vitro kinase assay, Cdc25A ubiquitination assay and checkpoint rescue with RNAi\",\n      \"pmids\": [\"20090422\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relative contribution of direct vs. NEK11-mediated Cdc25A control not quantified\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Separated CHK1's catalytic checkpoint role from a structural fork-protection role: a kinase-independent, PCNA-interaction-motif-dependent function promotes pol \\u03b7 recruitment and fork progression; CRL4(CDT2) was added as a second degradation route.\",\n      \"evidence\": \"Kinase-dead/PIP-mutant and chromatin-tethered chimeras, DNA fiber and pol \\u03b7 foci assays; co-IP and ubiquitination with CDT2 depletion\",\n      \"pmids\": [\"22529391\", \"23109433\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How the kinase-independent function is regulated relative to catalytic activation unclear\", \"Substrate-independent fork role mechanism only partially defined\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Mapped the CHK1\\u2192Aurora-B activating site (Ser331) and showed CHK1 protects against merotelic attachments by enabling kinetochore loading of error-correction factors.\",\n      \"evidence\": \"In vitro kinase assay on Aurora-B Ser331 plus loss-of-function with MCAK/Kif2b/Mps1/Hec1 immunofluorescence\",\n      \"pmids\": [\"23321637\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How CHK1 accesses kinetochores spatially not resolved\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Defined the deubiquitylase axis stabilizing CHK1\\u2014USP7 (enhanced by ATM-stabilized ZEB1) and the Smurf1/RhoB apoptotic output\\u2014balancing the degradation machinery and tuning DNA-repair/radioresistance.\",\n      \"evidence\": \"In vitro/in vivo deubiquitination assays, co-IP, half-life measurement, clonogenic survival; in vitro CHK1 kinase assay on Smurf1\",\n      \"pmids\": [\"25086746\", \"25483066\", \"25249323\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How DUB vs. E3 competition is dynamically resolved during stress not defined\", \"Cell-type specificity of the ZEB1-USP7-CHK1 axis unclear\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Pinned the autoinhibitory contact to residues 31\\u201387 of the kinase domain and Leu-449 of the C-terminus, providing the structural logic for how ATR phosphorylation opens CHK1.\",\n      \"evidence\": \"FRET, BiFC, L449R and phospho-mimic mutagenesis with DNA-damage activation in cells\",\n      \"pmids\": [\"27129240\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"High-resolution structure of the full-length closed state not provided\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Showed CHK1 can be activated by non-genotoxic signals: PERK/UPR triggers Claspin-dependent CHK1 activation to inhibit replication origin firing, broadening CHK1's role beyond DNA damage.\",\n      \"evidence\": \"Thapsigargin UPR induction with Claspin/CHK1 siDNA rescue and origin-firing analysis\",\n      \"pmids\": [\"27375025\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct PERK-Claspin biochemical link not fully defined\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Added Ataxin-3 as a stress-regulated CHK1 deubiquitinase that protects against CRL4A and FBXO6/CUL1 degradation and dissociates under prolonged replication stress, providing a timer for CHK1 turnover.\",\n      \"evidence\": \"Co-IP, in vitro/in vivo (de)ubiquitination, ATX3 depletion/overexpression and G2/M checkpoint assays\",\n      \"pmids\": [\"28180282\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Signal triggering ATX3 dissociation under prolonged stress unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Defined a non-degradative ubiquitin code: TRAF4-mediated K63 ubiquitination at the active-site K132 promotes chromatin association and ATR-dependent activation, reversed by USP3, distinguishing activation-linked from degradation-linked ubiquitination.\",\n      \"evidence\": \"In vitro/in vivo ubiquitination, K132 mutagenesis, USP3 knockdown and chromatin fractionation across two studies\",\n      \"pmids\": [\"29735693\", \"32357935\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How K63 chromatin signal is coordinated with ATR/Claspin recruitment not fully mapped\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Established CHK1 functions during unperturbed S phase: basal ATR/ETAA1-driven S296 autophosphorylation stabilizes CHK1, and ATR/CHK1 signaling restrains CDK1 to maintain RIF1-PP1 activity that limits dormant origin firing.\",\n      \"evidence\": \"S296 phospho-mutants with half-life/ubiquitylation assays; pharmacological ATR/CHK1 epistasis with RIF1-PP1 co-IP, substrate dephosphorylation and DNA fiber origin analysis; HUWE1 added as ATM/ATR/p53-independent E3\",\n      \"pmids\": [\"31366665\", \"31209037\", \"31713291\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How basal vs. damage-induced CHK1 activity are discriminated mechanistically\", \"Redundancy among Fbx6/CRL4-CDT2/HUWE1 in vivo not resolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Linked CHK1 to phosphatase regulation and drug resistance: CHK1 phosphorylates FAM122A to activate PP2A-B55\\u03b1, and loss of this control stabilizes WEE1, conferring resistance to CHK1 inhibitors.\",\n      \"evidence\": \"CRISPR knockout screen, in vitro CHK1 kinase assay on FAM122A, PP2A-B55\\u03b1 activity and WEE1 stability assays with WEE1-inhibitor rescue\",\n      \"pmids\": [\"33108758\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Generality of the resistance mechanism across tumor types not established\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Extended CHK1 functions beyond replication into tissue and disease contexts: a DNA-damage-independent Atr-Chek1-Cdc25 axis downstream of Piezo/NO inhibits axon regeneration, and CHEK1 drives chromosomal instability (via CEP170) and osteoclast differentiation in myeloma.\",\n      \"evidence\": \"Drosophila/mammalian neuron genetics and pharmacology; CHEK1 over/under-expression with CEP170 phosphorylation, CIN scoring, osteoclast assays and xenografts\",\n      \"pmids\": [\"34158506\", \"34090465\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct CHK1 substrates in the neuronal axis not defined\", \"Mechanism coupling CHK1 to NFATc1 not biochemically resolved\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identified PRIMPOL as a CHK1 substrate whose phosphorylation promotes repriming and replication-stress tolerance but generates fitness-reducing single-strand gaps when constitutive, illustrating the cost-benefit of CHK1 fork signaling.\",\n      \"evidence\": \"In vitro CHK1 kinase assay on PRIMPOL, repriming and DNA fiber assays, viability assays with Claspin-driven CHK1 activation\",\n      \"pmids\": [\"35353580\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo PRIMPOL phospho-site usage and regulation not fully mapped\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the multiple, partly redundant ubiquitin ligase/DUB systems and phospho-codes are integrated in real time to set CHK1 abundance, conformation, and localization for the correct checkpoint vs. fork vs. apoptotic output remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified quantitative model of CHK1 activation/turnover dynamics\", \"Relative in vivo contributions of Fbx6, CRL4-CDT2, and HUWE1 not dissected\", \"Spatial coordination of nuclear, cytoplasmic, centrosomal and chromatin pools not integrated\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [2, 5, 10, 19, 22, 25, 33, 35, 36]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [2, 5, 10, 19, 33, 35]},\n      {\"term_id\": \"GO:0140657\", \"supporting_discovery_ids\": [6, 26]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [2, 38]},\n      {\"term_id\": \"GO:0005654\", \"supporting_discovery_ids\": [20]},\n      {\"term_id\": \"GO:0000228\", \"supporting_discovery_ids\": [11, 13, 29]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [11]},\n      {\"term_id\": \"GO:0005815\", \"supporting_discovery_ids\": [11, 12, 18, 38]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [0, 2, 3, 10, 19, 38]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [13, 21, 23, 35]},\n      {\"term_id\": \"R-HSA-69306\", \"supporting_discovery_ids\": [17, 21, 30, 31, 35]},\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [6, 8, 27]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [5, 25]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [16, 20, 24, 28, 29, 32]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"Claspin\", \"ATR\", \"PCNA\", \"USP7\", \"ATXN3\", \"TRAF4\", \"PPM1D\", \"FBXO6\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}