{"gene":"PBK","run_date":"2026-04-29T11:37:58","timeline":{"discoveries":[{"year":2004,"finding":"TOPK/PBK is phosphorylated at Thr-9 by cdk1/cyclin B during mitosis, associates with mitotic spindles, and is required for formation of the spindle midzone and cytokinesis; knockdown of TOPK disrupts spindle midzone formation and cytokinesis.","method":"Immunofluorescence, Western blot, kinase assay, siRNA knockdown with phenotypic readout","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 2 — direct phosphorylation site identified, localization tied to functional consequence, replicated by multiple subsequent studies","pmids":["15541388"],"is_preprint":false},{"year":2007,"finding":"TOPK and ERK2 form a positive feedback loop: TOPK phosphorylates ERK2 and ERK2 phosphorylates TOPK; knockdown of either reduces phosphorylation of the other and downstream ERK2 substrates in HCT116 colorectal cancer cells.","method":"In vitro kinase assay, siRNA knockdown, EGF-stimulation Western blot, transient transfection","journal":"Gastroenterology","confidence":"High","confidence_rationale":"Tier 1–2 — bidirectional kinase assay with epistatic knockdown experiments, high citation count indicating replication","pmids":["17631144"],"is_preprint":false},{"year":2007,"finding":"TOPK enhances cdk1/cyclin B1-dependent phosphorylation of the microtubule-bundling protein PRC1 at T481 during mitosis by forming a ternary complex with cdk1/cyclin B1 and PRC1 on microtubules; TOPK enzymatic activity and its association with PRC1 are both required, but TOPK cannot phosphorylate PRC1 directly in vitro without cdk1/cyclin B1.","method":"In vitro kinase assay, Co-IP, in vivo phosphorylation assay, dominant-negative constructs","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 — reconstitution in vitro with multiple orthogonal methods (kinase assay, Co-IP, mutagenesis)","pmids":["17512944"],"is_preprint":false},{"year":2005,"finding":"PBK/TOPK phosphorylates p38 MAPK and is required for appropriate p38 activation by growth factors; PBK knockdown impairs p38 activation, reduces cell motility, and impairs DNA damage response (reduced γ-H2AX, increased DNA damage).","method":"siRNA knockdown, Western blot, kinase assay, soft agar growth assay","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 2 — siRNA knockdown with multiple orthogonal readouts, highly cited","pmids":["17160018"],"is_preprint":false},{"year":2005,"finding":"PBK/TOPK is expressed in proliferating neural progenitor cells and phosphorylates p38 MAPK in a cell-cycle-dependent manner; inhibition of the PBK/TOPK–p38 pathway disrupts neural progenitor proliferation and self-renewal in vitro and in vivo.","method":"Microarray profiling, in vitro kinase assay, pharmacological inhibition, transgenic ablation/lineage tracing in mice","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods including in vivo genetic approach, high citation count","pmids":["16291951"],"is_preprint":false},{"year":2005,"finding":"TOPK is expressed in spermatocytes and spermatids; TOPK-Thr-9 is specifically phosphorylated by cdk1/cyclin B during both mitotic and meiotic phases, while Thr-198 (ATP pocket) is constitutively phosphorylated, indicating a role in cytokinesis/chromosomal segregation during spermatogenesis.","method":"Immunofluorescence in situ, phospho-specific antibodies, Western blot","journal":"Development, growth & differentiation","confidence":"Medium","confidence_rationale":"Tier 2 — direct localization and phospho-site data but single lab, single method approach","pmids":["16316408"],"is_preprint":false},{"year":2010,"finding":"PBK/TOPK physically interacts with the DNA-binding domain (DBD) of tumor suppressor p53 in HCT116 cells; this interaction suppresses p53 transactivation function, reducing expression of p21 and other p53 target genes; PBK knockdown upregulates p21 particularly after genotoxic damage.","method":"Co-immunoprecipitation, yeast two-hybrid, gene knockdown with microarray analysis","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP and orthogonal yeast two-hybrid, multiple downstream readouts, highly cited","pmids":["20622899"],"is_preprint":false},{"year":2010,"finding":"PBK/TOPK phosphorylates LGN/GPSM2 at Thr450 during mitosis; overexpression of a T450A phosphorylation-deficient mutant causes aberrant chromosomal segregation and growth suppression in breast cancer cells.","method":"In vitro kinase assay, Western blot (G2/M-enriched lysates), siRNA, mutant overexpression with phenotypic readout","journal":"Genes, chromosomes & cancer","confidence":"High","confidence_rationale":"Tier 1–2 — direct kinase assay with phosphorylation site identification plus functional mutagenesis","pmids":["20589935"],"is_preprint":false},{"year":2010,"finding":"TOPK binds peroxiredoxin 1 (Prx1) and phosphorylates it at Ser-32, altering Prx1's secondary structure and enhancing its peroxidase activity; this phosphorylation prevents UVB-induced H2O2 accumulation and apoptosis in melanoma cells.","method":"LC-MS/MS binding identification, in vitro kinase assay, CD spectroscopy, immunofluorescence, siRNA/stable mutant lines, flow cytometry","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — reconstitution with MS identification, structural analysis, and functional validation in multiple cell models","pmids":["20647304"],"is_preprint":false},{"year":2012,"finding":"HI-TOPK-032 directly inhibits TOPK kinase activity in vitro with selectivity over ERK1, JNK1, and p38; in cells it reduces ERK-RSK phosphorylation and increases apoptosis via p53, cleaved caspase-7, and cleaved PARP; suppresses tumor growth in colon cancer xenograft in vivo.","method":"In vitro kinase assay screen, Western blot, xenograft model","journal":"Cancer research","confidence":"High","confidence_rationale":"Tier 1–2 — in vitro kinase assay with specificity profiling plus in vivo validation, widely cited","pmids":["22523035"],"is_preprint":false},{"year":2013,"finding":"CHFR (E3 ubiquitin ligase) ubiquitinates TOPK and regulates its protein levels; TOPK in turn phosphorylates and inactivates PTEN, leading to Akt activation and G2/M progression; this CHFR–TOPK–PTEN–Akt axis regulates the mitotic checkpoint.","method":"Co-IP, in vitro kinase/ubiquitination assay, siRNA epistasis, phospho-Western blot","journal":"Cellular signalling","confidence":"High","confidence_rationale":"Tier 1–2 — reconstitution of ubiquitination and kinase activity with epistasis in the same study","pmids":["24012691"],"is_preprint":false},{"year":2015,"finding":"TOPK/PBK is the master mitotic kinase that phosphorylates the conserved linker motif of C2H2 zinc finger proteins (ZFPs), driving their coordinate dissociation from condensing chromatin during mitosis; TOPK is activated by Cdk1 with precise temporal correlation to ZFP linker phosphorylation.","method":"Biotinylated kinase inhibitor (K252a) affinity purification, in vitro kinase assay with ZFP substrates, pharmacological and genetic inhibition","journal":"Oncotarget","confidence":"High","confidence_rationale":"Tier 1 — biochemical purification followed by in vitro kinase assay confirming substrate identity, mechanistic timing validated","pmids":["25575812"],"is_preprint":false},{"year":2016,"finding":"Src kinase directly binds and phosphorylates TOPK at Tyr74 and Tyr272; these phosphorylations increase TOPK stability by reducing its ubiquitination, elevate TOPK kinase activity toward histone H3 (Ser10), and promote colon cancer tumorigenesis.","method":"In vitro kinase assay, phospho-specific antibody generation, Co-IP, pulse-chase stability assay, Src KO MEF comparison, xenograft model","journal":"Oncotarget","confidence":"High","confidence_rationale":"Tier 1–2 — in vitro kinase assay, validated endogenous phosphorylation, genetic Src KO model, multiple orthogonal readouts","pmids":["27016416"],"is_preprint":false},{"year":2016,"finding":"TOPK directly binds and phosphorylates c-Jun, activating AP-1 transcription of CCND1 and CDC2, thereby conferring resistance of NSCLC cells to EGFR-TKI gefitinib.","method":"Co-IP, in vitro kinase assay, reporter assay, siRNA knockdown, xenograft model","journal":"Oncotarget","confidence":"High","confidence_rationale":"Tier 1–2 — direct binding and kinase assay combined with functional rescue experiments","pmids":["26745678"],"is_preprint":false},{"year":2017,"finding":"CDK1 phosphorylates PBK at Thr-9, Thr-24, Ser-32, and Ser-59 during mitosis in vitro and in cells; phosphorylation of Thr-9 is specifically involved in cytokinesis, and the non-phosphorylatable PBK-T9A mutant exhibits greater tumor-promoting activity than wild-type PBK, indicating CDK1-mediated phosphorylation inhibits PBK's oncogenic function.","method":"In vitro kinase assay, phosphomapping, mutant overexpression, tumorigenesis assays in breast cancer cells","journal":"Cellular signalling","confidence":"High","confidence_rationale":"Tier 1 — in vitro kinase assay with multiple phosphorylation sites mapped, functional consequences of phospho-mutants demonstrated","pmids":["28780319"],"is_preprint":false},{"year":2018,"finding":"TOPK promotes microglia/macrophage M2 polarization by binding to HDAC1 and HDAC2 and promoting their phosphorylation; TOPK overexpression increases M2 markers (CD206, Arg1) and reduces M1 inflammatory cytokines; effects are reversed by HDAC1/2 inhibitor FK228, placing TOPK upstream of HDAC1/2 in anti-inflammatory signaling after cerebral ischemia.","method":"Co-IP (in vivo binding), Western blot, siRNA/overexpression in BV2 cells, MCAO mouse model","journal":"Aging and disease","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP and in vivo co-localization with pharmacological epistasis, single lab","pmids":["29896413"],"is_preprint":false},{"year":2018,"finding":"TOPK is phosphorylated and activated by solar UV; it directly phosphorylates c-Jun at Ser63 and Ser73 in a JNK-independent manner, activating AP-1 and promoting skin carcinogenesis.","method":"In vitro kinase assay, phospho-specific Western blot, siRNA knockdown, mouse skin carcinogenesis model","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 1–2 — direct in vitro kinase assay with phospho-site identification, confirmed in vivo","pmids":["32277233"],"is_preprint":false},{"year":2018,"finding":"TOPK phosphorylates PRPK (p53-related protein kinase); knockdown of TOPK inhibits PRPK phosphorylation and confers resistance to solar UV-induced skin carcinogenesis in mouse models.","method":"In vitro/cell kinase assay, siRNA knockdown, mouse skin carcinogenesis model, FDA-approved drug PRPK inhibitors","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 — kinase assay plus in vivo validation, single lab","pmids":["29904102"],"is_preprint":false},{"year":2019,"finding":"TOPK directly binds and phosphorylates ULK1 at Ser469, Ser495, and Ser533, decreasing ULK1 activity and stability, thereby inhibiting autophagy initiation in glioma cells and contributing to temozolomide resistance.","method":"Co-IP, in vitro kinase assay, phospho-site mapping, Western blot, autophagy flux assay, drug sensitivity assay","journal":"Cell death & disease","confidence":"High","confidence_rationale":"Tier 1 — direct in vitro kinase assay with three phosphorylation sites identified, functional autophagy readouts","pmids":["31378785"],"is_preprint":false},{"year":2019,"finding":"PBK promotes HCC metastasis via the ETV4–uPAR signaling pathway: PBK enhances binding of transcription factor ETV4 to the uPAR promoter (shown by ChIP assay), increasing uPAR expression; uPAR overexpression rescues the metastasis suppressed by PBK knockdown.","method":"Chromatin immunoprecipitation (ChIP), luciferase promoter assay, gain/loss-of-function, orthotopic mouse model","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP and epistasis rescue experiment, single lab","pmids":["30914208"],"is_preprint":false},{"year":2019,"finding":"MET tyrosine kinase phosphorylates TOPK at Tyr74, preventing apoptosis in gefitinib-resistant NSCLC cells; this is downstream of the COX2-TXA2 pathway regulating MET via AP-1.","method":"Western blot, phospho-antibody detection, Co-IP, cell viability assays, in vitro and ex vivo validation","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 — phosphorylation site identified and functionally linked, single lab","pmids":["31611604"],"is_preprint":false},{"year":2020,"finding":"PBK/TOPK mediates paclitaxel resistance in H460 NSCLC cells by promoting p53 nuclear export and ubiquitination, thereby suppressing p53-dependent autophagic cell death.","method":"siRNA knockdown, Western blot for nuclear/cytoplasmic fractionation, ubiquitination assay, LC3 puncta imaging, flow cytometry","journal":"FEBS open bio","confidence":"Medium","confidence_rationale":"Tier 2 — fractionation and ubiquitination assay linking PBK to p53 regulation, single lab","pmids":["32237067"],"is_preprint":false},{"year":2021,"finding":"PBK phosphorylates MSL1 and enhances the interaction of MSL1 with MSL2, MSL3, and KAT8 (components of the MSL complex), promoting MSL complex enrichment on the CD276 promoter, leading to increased histone H4 K16 acetylation and CD276 transcription in nasopharyngeal carcinoma.","method":"Co-IP, in vitro kinase assay, ChIP, reporter assay, siRNA knockdown","journal":"Oncogenesis","confidence":"High","confidence_rationale":"Tier 1–2 — direct kinase assay, Co-IP with multiple complex partners, ChIP for chromatin occupancy","pmids":["33431797"],"is_preprint":false},{"year":2021,"finding":"Menin/JunD/HDAC3 complex represses PBK expression by reducing histone H3 acetylation at the PBK promoter; menin inhibitor disrupts the menin-JunD interaction, derepresses PBK, and promotes beta cell proliferation in HFD-induced diabetic mice; Pbk kinase activity (knock-in deficiency model) is required for menin-inhibitor-induced beta cell proliferation.","method":"Pbk kinase-deficiency knock-in mouse model, ChIP, Co-IP, menin inhibitor pharmacology, HFD mouse model","journal":"EMBO molecular medicine","confidence":"High","confidence_rationale":"Tier 2 — genetic knock-in model with ChIP and Co-IP, in vivo validation","pmids":["33821572"],"is_preprint":false},{"year":2022,"finding":"ERK2 phosphorylates TOPK at Ser32 (a novel site in addition to Thr9); pTOPK(S32) is associated with sorafenib resistance in renal cell carcinoma; HGF/c-Met signaling activates p-TOPK(S32) during resistance development.","method":"In vitro kinase assay, phospho-specific antibody, Western blot, drug resistance cell models","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 — novel phosphorylation site validated by specific antibody and kinase assay, single lab","pmids":["35546143"],"is_preprint":false},{"year":2022,"finding":"PBK directly interacts with TRIM37 and promotes its phosphorylation and nuclear translocation, activating the NFκB pathway and conferring PARP inhibitor resistance in ovarian cancer.","method":"Co-IP, Western blot for phosphorylation and nuclear translocation, siRNA/overexpression, in vitro and in vivo drug resistance assays","journal":"Experimental & molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP with functional rescue, single lab","pmids":["35859118"],"is_preprint":false},{"year":2022,"finding":"PBK directly phosphorylates histone H3 (in vitro reconstitution) and promotes CDH1 phosphorylation at S840/S846/S847 in cells (indirectly, as PBK failed to phosphorylate CDH1 directly in vitro), stabilizing CDH1 and suppressing Wnt/β-catenin signaling to inhibit CRC cell migration and invasion.","method":"In vitro kinase assay with recombinant PBK and HH3, phospho-CDH1 Western blot, siRNA/overexpression, migration/invasion assays","journal":"Frontiers in pharmacology","confidence":"Medium","confidence_rationale":"Tier 1–3 — direct H3 phosphorylation confirmed in vitro; CDH1 phosphorylation indirect, single lab","pmids":["35115926"],"is_preprint":false},{"year":2023,"finding":"FYN tyrosine kinase directly binds and phosphorylates TOPK at Y272; the TOPK-272F mutation abolishes this phosphorylation and interaction; FYN–TOPK axis promotes gastric cancer progression by phosphorylating HSPB1 at Ser15 as identified by phosphoproteomics in TOPK-knockout mice.","method":"Co-IP, pull-down assay, in vitro kinase assay with 32P isotope, phospho-specific antibody generation, phosphoproteomics, TOPK knockout mice, immunofluorescence co-localization","journal":"Journal of experimental & clinical cancer research","confidence":"High","confidence_rationale":"Tier 1 — reconstituted kinase assay, genetic KO mouse, phosphoproteomics, multiple orthogonal methods","pmids":["37016377"],"is_preprint":false},{"year":2023,"finding":"TOPK phosphorylates YB1 at Thr89 and Ser209; phosphorylated YB1 binds the eEF1A1 promoter to activate its transcription, leading to AKT/mTOR signaling activation and esophageal cancer cell proliferation.","method":"In vitro kinase assay, ChIP, reporter assay, TOPK KO, rescue experiments, xenograft model","journal":"Cell death & disease","confidence":"High","confidence_rationale":"Tier 1–2 — direct kinase assay with phospho-site identification, ChIP, and rescue experiments","pmids":["37328464"],"is_preprint":false},{"year":2020,"finding":"TOPK directly interacts with CHK1 and Cdc25c; TOPK depletion increases fork stalling and collapse under replication stress, impairs recovery from replication fork stalling, and increases replication-associated single-stranded DNA foci, placing TOPK in the S-phase checkpoint signaling pathway.","method":"Co-IP, siRNA knockdown, DNA fiber assay, ssDNA immunofluorescence, cancer cell xenograft with fractionated irradiation","journal":"Cell death and differentiation","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP with functional replication assays, single lab","pmids":["33168956"],"is_preprint":false},{"year":2014,"finding":"TOPK promotes NF-κB-dependent iNOS gene expression and nitric oxide production in response to LPS: TOPK interacts with IκBα and phosphorylates it, promoting NF-κB transcriptional activity; knockdown abolishes LPS-induced iNOS and NF-κB promoter activity.","method":"Co-IP, in vitro kinase assay for IκBα, reporter assay, siRNA knockdown, NOS expression Western blot","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2 — kinase assay for IκBα plus epistasis, single lab","pmids":["24440499"],"is_preprint":false},{"year":2015,"finding":"PBK/TOPK enhances aggressive phenotype in prostate cancer through β-catenin–TCF/LEF-mediated upregulation of MMP-2 and MMP-9 transcription; gain- and loss-of-function studies show PBK modulates invasive ability causally.","method":"siRNA/overexpression, promoter reporter assay, invasion assay, tissue array","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2 — promoter reporter assay with epistasis, single lab","pmids":["25909225"],"is_preprint":false},{"year":2015,"finding":"Geranylgeranylation regulates PBK expression in breast cancer cells via YAP (Yes-associated protein) as mediator; atorvastatin or GGTI-298 downregulates PBK through YAP inactivation, identifying PBK as a downstream target of the Hippo-YAP pathway.","method":"shRNA knockdown, Western blot, cell proliferation assay, pharmacological inhibition","journal":"Cancer cell international","confidence":"Medium","confidence_rationale":"Tier 2–3 — shRNA epistasis linking YAP to PBK expression, single lab","pmids":["25745361"],"is_preprint":false},{"year":2012,"finding":"c-Myc regulates PBK expression through E2F1 in high-grade lymphomas; inhibition of c-Myc or E2F1 decreases PBK expression and cell growth, establishing a c-Myc–E2F1–PBK transcriptional axis.","method":"ChIP (implied), Western blot, siRNA knockdown, cell viability assay","journal":"Leukemia research","confidence":"Medium","confidence_rationale":"Tier 3 — transcriptional pathway established by knockdown experiments, correlation data, single lab","pmids":["23237560"],"is_preprint":false}],"current_model":"PBK/TOPK is a MAPKK-like serine/threonine kinase that is activated by CDK1-mediated phosphorylation (Thr9, Thr24, Ser32, Ser59) and by Src-mediated tyrosine phosphorylation (Y74, Y272) during mitosis; it phosphorylates multiple substrates including p38 MAPK, ERK2 (bidirectional loop), PRC1 (cooperatively with CDK1/cyclin B1), LGN/GPSM2 (Thr450), histone H3, C2H2 zinc finger protein linkers, Prx1 (Ser32), ULK1 (Ser469/495/533), IκBα, c-Jun (Ser63/73), YB1 (Thr89/Ser209), PTEN, TRIM37, MSL1, and PRPK; through these substrates it regulates mitotic spindle/cytokinesis integrity, the DNA damage and replication stress checkpoints, p53 transcriptional suppression, autophagy inhibition, NF-κB activation, and AP-1-driven gene expression, collectively promoting cancer cell proliferation, survival, and metastasis."},"narrative":{"teleology":[{"year":2004,"claim":"Establishing PBK as a CDK1-activated mitotic kinase required for cytokinesis resolved its cell-cycle phase of action and placed it at the spindle midzone, a critical structure for cell division.","evidence":"Phospho-site mapping (Thr9 by CDK1/cyclin B), immunofluorescence at spindle midzone, siRNA knockdown causing cytokinesis failure in HeLa cells","pmids":["15541388"],"confidence":"High","gaps":["Mechanism by which PBK promotes midzone assembly not defined","Other CDK1 phosphorylation sites on PBK not yet mapped at this time"]},{"year":2005,"claim":"Identification of p38 MAPK as a direct PBK substrate linked PBK to DNA damage signaling and demonstrated its role in neural progenitor proliferation, extending PBK function beyond cancer cells to normal stem cell biology.","evidence":"In vitro kinase assay, siRNA knockdown reducing p38 activation and γ-H2AX, pharmacological inhibition and transgenic ablation in mouse neural progenitors","pmids":["17160018","16291951"],"confidence":"High","gaps":["Phosphorylation sites on p38 targeted by PBK not mapped","Relative contribution of PBK versus canonical MKKs to p38 activation unclear"]},{"year":2007,"claim":"Discovery of the PBK–ERK2 positive feedback loop and the PBK–CDK1–PRC1 ternary complex established PBK as a signaling hub that both amplifies MAPK cascades and cooperatively regulates mitotic microtubule bundling.","evidence":"Bidirectional in vitro kinase assays between PBK and ERK2 with epistatic knockdowns; ternary complex reconstitution showing PBK enhances CDK1-dependent PRC1-T481 phosphorylation","pmids":["17631144","17512944"],"confidence":"High","gaps":["Direct PBK phosphorylation sites on ERK2 not mapped","Structural basis of ternary PBK–CDK1–PRC1 complex unknown"]},{"year":2010,"claim":"Three new direct substrates—LGN/GPSM2 (Thr450), Prx1 (Ser32), and the p53 DNA-binding domain interaction—expanded PBK's roles to spindle orientation, antioxidant defense, and tumor suppressor antagonism, respectively.","evidence":"In vitro kinase assays with phospho-site identification for LGN and Prx1; reciprocal Co-IP and yeast two-hybrid for p53-DBD binding; CD spectroscopy for Prx1 structural change; p21 upregulation upon PBK knockdown","pmids":["20589935","20647304","20622899"],"confidence":"High","gaps":["Whether PBK directly phosphorylates p53 or only binds it was not resolved","In vivo relevance of Prx1-S32 phosphorylation beyond melanoma not tested"]},{"year":2012,"claim":"Development of HI-TOPK-032 as a selective PBK inhibitor provided a pharmacological tool confirming that PBK kinase activity drives ERK-RSK signaling and survival in colon cancer, validating PBK as a druggable target.","evidence":"In vitro kinase assay showing selectivity over ERK1/JNK1/p38, xenograft tumor suppression, apoptosis markers","pmids":["22523035"],"confidence":"High","gaps":["Off-target effects of HI-TOPK-032 not comprehensively profiled","Clinical translation not addressed"]},{"year":2013,"claim":"The CHFR–PBK–PTEN–Akt axis revealed that PBK is both regulated by E3-ligase-mediated ubiquitination and itself inactivates PTEN by phosphorylation, connecting PBK to PI3K/Akt signaling and mitotic checkpoint control.","evidence":"In vitro ubiquitination and kinase assays, siRNA epistasis linking CHFR to PBK levels and PBK to PTEN phosphorylation","pmids":["24012691"],"confidence":"High","gaps":["PTEN phosphorylation sites by PBK not mapped","Whether CHFR ubiquitinates PBK via K48 or K63 chains not determined"]},{"year":2014,"claim":"Demonstration that PBK phosphorylates IκBα to activate NF-κB-dependent iNOS expression established PBK as a pro-inflammatory kinase operating outside its canonical mitotic context.","evidence":"Co-IP, in vitro kinase assay for IκBα, NF-κB reporter assay, siRNA abolishing LPS-induced iNOS","pmids":["24440499"],"confidence":"Medium","gaps":["IκBα phosphorylation sites by PBK not identified","Whether PBK activates NF-κB independently of IKK complex not resolved","Single-lab finding"]},{"year":2015,"claim":"Identification of PBK as the master kinase phosphorylating C2H2 zinc-finger protein linkers during mitosis explained the coordinate chromatin dissociation of hundreds of ZFPs, revealing a major role in mitotic chromatin reorganization.","evidence":"Biotinylated kinase-inhibitor affinity purification identifying PBK, in vitro kinase assay with ZFP substrates, temporal correlation with CDK1 activation","pmids":["25575812"],"confidence":"High","gaps":["Functional consequence of ZFP chromatin dissociation for gene bookmarking or re-activation post-mitosis not determined","Full spectrum of ZFP substrates not catalogued"]},{"year":2016,"claim":"Src-mediated tyrosine phosphorylation of PBK at Y74 and Y272 was shown to stabilize PBK protein and enhance its histone H3 kinase activity, while PBK was found to directly phosphorylate c-Jun at Ser63/73 to activate AP-1, linking upstream tyrosine kinase input to downstream transcriptional output.","evidence":"In vitro kinase assays, Src KO MEFs, pulse-chase stability, Co-IP of PBK–c-Jun, AP-1 reporter, xenograft models","pmids":["27016416","26745678"],"confidence":"High","gaps":["Relative contributions of Src versus FYN to PBK Y74/Y272 phosphorylation in different tissues not compared","Structural basis of Src–PBK interaction unknown"]},{"year":2017,"claim":"Comprehensive CDK1 phospho-mapping of PBK (Thr9, Thr24, Ser32, Ser59) revealed that CDK1-mediated phosphorylation paradoxically restrains PBK's oncogenic function, with the non-phosphorylatable T9A mutant being more tumorigenic than wild-type.","evidence":"In vitro kinase assay, phospho-mapping, mutant overexpression with tumorigenesis assays in breast cancer cells","pmids":["28780319"],"confidence":"High","gaps":["Mechanism by which T9 phosphorylation suppresses oncogenic activity not elucidated","Whether CDK1 phosphorylation affects PBK substrate selectivity untested"]},{"year":2019,"claim":"PBK was shown to directly phosphorylate ULK1 at three sites (S469/S495/S533) to inhibit autophagy initiation, establishing PBK as a negative regulator of autophagy and explaining its role in temozolomide resistance in glioma.","evidence":"In vitro kinase assay with phospho-site mapping, autophagy flux assays, drug sensitivity assays in glioma cells","pmids":["31378785"],"confidence":"High","gaps":["Whether PBK inhibits autophagy through ULK1 in non-cancer contexts not tested","Relative importance of each ULK1 phospho-site not dissected"]},{"year":2020,"claim":"PBK was placed in the replication stress checkpoint through its interaction with CHK1 and Cdc25c, with PBK depletion causing replication fork collapse, extending PBK's roles from mitosis into S-phase DNA integrity.","evidence":"Co-IP of PBK with CHK1/Cdc25c, DNA fiber assays showing increased fork stalling upon PBK siRNA, ssDNA foci, xenograft with fractionated irradiation","pmids":["33168956"],"confidence":"Medium","gaps":["Whether PBK directly phosphorylates CHK1 or Cdc25c not determined","Mechanism of PBK recruitment to stalled forks unknown","Single-lab finding"]},{"year":2021,"claim":"PBK was shown to phosphorylate MSL1, enhancing MSL complex assembly and H4K16 acetylation at target promoters such as CD276, revealing an epigenetic effector role; separately, a Pbk kinase-dead knock-in mouse demonstrated that PBK kinase activity is required for menin-inhibitor-induced pancreatic beta cell proliferation.","evidence":"In vitro kinase assay and ChIP for MSL1/CD276; Pbk kinase-deficiency knock-in mouse with HFD model and menin inhibitor pharmacology","pmids":["33431797","33821572"],"confidence":"High","gaps":["MSL1 phosphorylation sites not mapped","Whether PBK-MSL1 axis operates outside nasopharyngeal carcinoma not tested","Downstream mediators of PBK in beta cell proliferation beyond kinase requirement not identified"]},{"year":2022,"claim":"Identification of ERK2 phosphorylation of PBK at Ser32 (in addition to CDK1-mediated Thr9) linked PBK activation to drug resistance signaling via HGF/c-Met, while PBK was shown to phosphorylate TRIM37 to activate NF-κB and confer PARP inhibitor resistance.","evidence":"In vitro kinase assay for ERK2→PBK-S32, phospho-specific antibody in sorafenib-resistant RCC; Co-IP of PBK–TRIM37 with nuclear translocation and drug resistance assays in ovarian cancer","pmids":["35546143","35859118"],"confidence":"Medium","gaps":["Whether ERK2- and CDK1-mediated S32 phosphorylation are functionally redundant untested","TRIM37 phosphorylation sites not mapped","Clinical relevance of PBK in PARP inhibitor resistance needs validation"]},{"year":2023,"claim":"FYN kinase was identified as a second Src-family kinase phosphorylating PBK at Y272, and phosphoproteomics in TOPK-knockout mice identified HSPB1-Ser15 as a downstream substrate; separately, PBK was shown to phosphorylate YB1 at Thr89/Ser209 to drive eEF1A1 transcription and AKT/mTOR activation.","evidence":"Isotope kinase assay for FYN→PBK-Y272, phosphoproteomics in KO mice identifying HSPB1; in vitro kinase assay for PBK→YB1 with ChIP and rescue experiments","pmids":["37016377","37328464"],"confidence":"High","gaps":["Full phosphoproteomic landscape of PBK-dependent substrates in vivo not yet catalogued beyond HSPB1","Structural basis for PBK's broad substrate recognition unknown"]},{"year":null,"claim":"Despite extensive substrate identification, the structural basis for PBK's unusually broad substrate specificity, its consensus phosphorylation motif, and the tissue-specific regulatory logic that selects among its many substrates remain unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No crystal or cryo-EM structure of PBK available","No defined consensus phosphorylation motif","Systematic comparison of substrate selectivity across tissues not performed"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,1,2,3,7,8,10,11,12,13,16,17,18,22,25,26,27,28,30]}],"localization":[{"term_id":"GO:0005694","term_label":"chromosome","supporting_discovery_ids":[0,11]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[0,2]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[6,22]}],"pathway":[{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[0,2,5,7,10,11,14]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[1,3,4,10,13,16,28,30]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[8,9,21]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[18,21]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[3,29]},{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[11,22,26]}],"complexes":[],"partners":["CDK1","ERK2","PRC1","TP53","PRKWNK1","ULK1","SRC","FYN"],"other_free_text":[]},"mechanistic_narrative":"PBK (also called TOPK) is a mitotic serine/threonine kinase that integrates cell-cycle progression, checkpoint signaling, and chromatin regulation by phosphorylating a broad array of substrates downstream of CDK1/cyclin B1 activation. CDK1 phosphorylates PBK at Thr9, Thr24, Ser32, and Ser59 during mitosis, and Src/FYN phosphorylate it at Tyr74 and Tyr272 to increase its stability and activity; once active, PBK phosphorylates p38 MAPK, ERK2 (forming a positive feedback loop), PRC1, LGN/GPSM2, histone H3, C2H2 zinc-finger protein linkers, c-Jun, IκBα, ULK1, Prx1, YB1, MSL1, PTEN, TRIM37, and PRPK, thereby controlling spindle midzone formation, cytokinesis, the DNA replication stress checkpoint, NF-κB and AP-1 transcriptional programs, autophagy suppression, and antioxidant defense [PMID:15541388, PMID:17631144, PMID:17512944, PMID:17160018, PMID:25575812, PMID:18, PMID:33431797, PMID:24012691, PMID:31378785, PMID:37016377]. PBK also binds the DNA-binding domain of p53 and suppresses its transactivation function, linking PBK to p53-dependent tumor suppression and drug resistance [PMID:20622899, PMID:32237067]. Through these activities PBK is essential for proliferation of neural progenitor cells and spermatocytes and drives tumorigenesis, metastasis, and multi-drug resistance across diverse cancer types [PMID:16291951, PMID:16316408, PMID:26745678, PMID:35859118]."},"prefetch_data":{"uniprot":{"accession":"Q96KB5","full_name":"Lymphokine-activated killer T-cell-originated protein kinase","aliases":["Cancer/testis antigen 84","CT84","MAPKK-like protein kinase","Nori-3","PDZ-binding kinase","Spermatogenesis-related protein kinase","SPK","T-LAK cell-originated protein kinase"],"length_aa":322,"mass_kda":36.1,"function":"Phosphorylates MAP kinase p38. Seems to be active only in mitosis. May also play a role in the activation of lymphoid cells. When phosphorylated, forms a complex with TP53, leading to TP53 destabilization and attenuation of G2/M checkpoint during doxorubicin-induced DNA damage","subcellular_location":"","url":"https://www.uniprot.org/uniprotkb/Q96KB5/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PBK","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000168078","cell_line_id":"CID001232","localizations":[{"compartment":"cytoplasmic","grade":3},{"compartment":"nucleoplasm","grade":3}],"interactors":[{"gene":"KAT8","stoichiometry":0.2},{"gene":"RBM25","stoichiometry":0.2},{"gene":"KIAA1429","stoichiometry":0.2},{"gene":"PRPF40A","stoichiometry":0.2},{"gene":"XRCC1","stoichiometry":0.2},{"gene":"SUB1","stoichiometry":0.2},{"gene":"MSL1","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID001232","total_profiled":1310},"omim":[{"mim_id":"611210","title":"PDZ-BINDING KINASE; PBK","url":"https://www.omim.org/entry/611210"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Cytosol","reliability":"Approved"}],"tissue_specificity":"Group enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"lymphoid tissue","ntpm":21.3},{"tissue":"testis","ntpm":65.7}],"url":"https://www.proteinatlas.org/search/PBK"},"hgnc":{"alias_symbol":["TOPK","FLJ14385","Nori-3","SPK","CT84"],"prev_symbol":[]},"alphafold":{"accession":"Q96KB5","domains":[{"cath_id":"3.30.200.20","chopping":"34-115","consensus_level":"high","plddt":82.86,"start":34,"end":115},{"cath_id":"1.10.510.10","chopping":"120-252_265-319","consensus_level":"high","plddt":95.1247,"start":120,"end":319}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96KB5","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q96KB5-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q96KB5-F1-predicted_aligned_error_v6.png","plddt_mean":84.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PBK","jax_strain_url":"https://www.jax.org/strain/search?query=PBK"},"sequence":{"accession":"Q96KB5","fasta_url":"https://rest.uniprot.org/uniprotkb/Q96KB5.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q96KB5/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96KB5"}},"corpus_meta":[{"pmid":"17631144","id":"PMC_17631144","title":"Bidirectional 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an official journal of the Society of Toxicology","url":"https://pubmed.ncbi.nlm.nih.gov/28498972","citation_count":19,"is_preprint":false},{"pmid":"33168956","id":"PMC_33168956","title":"Targeting TOPK sensitises tumour cells to radiation-induced damage by enhancing replication stress.","date":"2020","source":"Cell death and differentiation","url":"https://pubmed.ncbi.nlm.nih.gov/33168956","citation_count":18,"is_preprint":false},{"pmid":"25550851","id":"PMC_25550851","title":"Expression of PBK/TOPK in cervical cancer and cervical intraepithelial neoplasia.","date":"2014","source":"International journal of clinical and experimental pathology","url":"https://pubmed.ncbi.nlm.nih.gov/25550851","citation_count":17,"is_preprint":false},{"pmid":"33772548","id":"PMC_33772548","title":"PBK/TOPK promotes chemoresistance to oxaliplatin in hepatocellular carcinoma cells by regulating PTEN.","date":"2021","source":"Acta biochimica et biophysica Sinica","url":"https://pubmed.ncbi.nlm.nih.gov/33772548","citation_count":17,"is_preprint":false},{"pmid":"33848589","id":"PMC_33848589","title":"Next generation risk assessment (NGRA): Bridging in vitro points-of-departure to human safety assessment using physiologically-based kinetic (PBK) modelling - A case study of doxorubicin with dose metrics considerations.","date":"2021","source":"Toxicology in vitro : an international journal published in association with BIBRA","url":"https://pubmed.ncbi.nlm.nih.gov/33848589","citation_count":17,"is_preprint":false},{"pmid":"29543705","id":"PMC_29543705","title":"Glycycoumarin Sensitizes Liver Cancer Cells to ABT-737 by Targeting De Novo Lipogenesis and TOPK-Survivin Axis.","date":"2018","source":"Nutrients","url":"https://pubmed.ncbi.nlm.nih.gov/29543705","citation_count":16,"is_preprint":false},{"pmid":"30453248","id":"PMC_30453248","title":"Design, synthesis and biological evaluation of novel 1-phenyl phenanthridin-6(5H)-one derivatives as anti-tumor agents targeting TOPK.","date":"2018","source":"European journal of medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/30453248","citation_count":16,"is_preprint":false},{"pmid":"37148702","id":"PMC_37148702","title":"TOPK inhibits TNF-α-induced granulosa cell apoptosis via regulation of SIRT1/p53.","date":"2023","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/37148702","citation_count":15,"is_preprint":false},{"pmid":"37328464","id":"PMC_37328464","title":"TOPK promotes the growth of esophageal cancer in vitro and in vivo by enhancing YB1/eEF1A1 signal pathway.","date":"2023","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/37328464","citation_count":15,"is_preprint":false},{"pmid":"31714026","id":"PMC_31714026","title":"Potent anti-myeloma activity of the TOPK inhibitor OTS514 in pre-clinical models.","date":"2019","source":"Cancer medicine","url":"https://pubmed.ncbi.nlm.nih.gov/31714026","citation_count":14,"is_preprint":false},{"pmid":"35115926","id":"PMC_35115926","title":"PBK Enhances Cellular Proliferation With Histone H3 Phosphorylation and Suppresses Migration and Invasion With CDH1 Stabilization in Colorectal Cancer.","date":"2022","source":"Frontiers in pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/35115926","citation_count":14,"is_preprint":false},{"pmid":"29271010","id":"PMC_29271010","title":"Impact of a novel biomarker, T-LAK cell-originating protein kinase (TOPK) expression on outcome in malignant glioma.","date":"2017","source":"Neuropathology : official journal of the Japanese Society of Neuropathology","url":"https://pubmed.ncbi.nlm.nih.gov/29271010","citation_count":14,"is_preprint":false},{"pmid":"22940854","id":"PMC_22940854","title":"In silico structural and functional analysis of the human TOPK protein by structure modeling and molecular dynamics studies.","date":"2012","source":"Journal of molecular modeling","url":"https://pubmed.ncbi.nlm.nih.gov/22940854","citation_count":14,"is_preprint":false},{"pmid":"33821572","id":"PMC_33821572","title":"Menin-regulated Pbk controls high fat diet-induced compensatory beta cell proliferation.","date":"2021","source":"EMBO molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/33821572","citation_count":13,"is_preprint":false},{"pmid":"24561179","id":"PMC_24561179","title":"A physiologically based kinetic (PBK) model describing plasma concentrations of quercetin and its metabolites in rats.","date":"2014","source":"Biochemical pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/24561179","citation_count":13,"is_preprint":false},{"pmid":"15356337","id":"PMC_15356337","title":"A rice antisense SPK transformant that lacks the accumulation of seed storage substances shows no correlation between sucrose concentration in phloem sap and demand for carbon sources in the sink organs.","date":"2004","source":"Plant & cell physiology","url":"https://pubmed.ncbi.nlm.nih.gov/15356337","citation_count":13,"is_preprint":false},{"pmid":"35135547","id":"PMC_35135547","title":"PBK/TOPK inhibitor OTS964 resistance is mediated by ABCB1-dependent transport function in cancer: in vitro and in vivo study.","date":"2022","source":"Molecular cancer","url":"https://pubmed.ncbi.nlm.nih.gov/35135547","citation_count":12,"is_preprint":false},{"pmid":"33658942","id":"PMC_33658942","title":"OTS964, a TOPK Inhibitor, Is Susceptible to ABCG2-Mediated Drug Resistance.","date":"2021","source":"Frontiers in pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/33658942","citation_count":12,"is_preprint":false},{"pmid":"21245325","id":"PMC_21245325","title":"SPK-1, an SR protein kinase, inhibits programmed cell death in Caenorhabditis elegans.","date":"2011","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/21245325","citation_count":12,"is_preprint":false},{"pmid":"30864683","id":"PMC_30864683","title":"TOPK is regulated by PP2A and BCR/ABL in leukemia and enhances cell proliferation.","date":"2019","source":"International journal of oncology","url":"https://pubmed.ncbi.nlm.nih.gov/30864683","citation_count":12,"is_preprint":false},{"pmid":"35756488","id":"PMC_35756488","title":"TOPK Affects Autophagy of Skin Squamous Cell Carcinoma by Regulating NF-KB Pathway through HDAC1.","date":"2022","source":"Disease markers","url":"https://pubmed.ncbi.nlm.nih.gov/35756488","citation_count":11,"is_preprint":false},{"pmid":"33158479","id":"PMC_33158479","title":"TOPK mediates hypoxia-induced epithelial-mesenchymal transition and the invasion of nonsmall-cell lung cancer cells via the HIF-1α/snail axis.","date":"2020","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/33158479","citation_count":10,"is_preprint":false},{"pmid":"34859049","id":"PMC_34859049","title":"An Integrative Pan-Cancer Analysis of PBK in Human Tumors.","date":"2021","source":"Frontiers in molecular biosciences","url":"https://pubmed.ncbi.nlm.nih.gov/34859049","citation_count":10,"is_preprint":false},{"pmid":"30357568","id":"PMC_30357568","title":"[18F]FE-OTS964: a Small Molecule Targeting TOPK for In Vivo PET Imaging in a Glioblastoma Xenograft Model.","date":"2019","source":"Molecular imaging and biology","url":"https://pubmed.ncbi.nlm.nih.gov/30357568","citation_count":10,"is_preprint":false},{"pmid":"37341142","id":"PMC_37341142","title":"The LIN28B-let-7-PBK pathway is essential for group 3 medulloblastoma tumor growth and survival.","date":"2023","source":"Molecular oncology","url":"https://pubmed.ncbi.nlm.nih.gov/37341142","citation_count":10,"is_preprint":false},{"pmid":"30827262","id":"PMC_30827262","title":"Gossypetin Inhibits Solar-UV Induced Cutaneous Basal Cell Carcinoma Through Direct Inhibiting PBK/TOPK Protein Kinase.","date":"2019","source":"Anti-cancer agents in medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/30827262","citation_count":10,"is_preprint":false},{"pmid":"37226642","id":"PMC_37226642","title":"KRASG12C mutation-induced TOPK overexpression contributes to tumour progression in non-small cell lung cancer.","date":"2023","source":"Journal of cellular and molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/37226642","citation_count":9,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":50191,"output_tokens":7447,"usd":0.131139},"stage2":{"model":"claude-opus-4-6","input_tokens":11291,"output_tokens":4340,"usd":0.247432},"total_usd":0.378571,"stage1_batch_id":"msgbatch_012ZiiCUBfB62NCTQd4Bk1Jo","stage2_batch_id":"msgbatch_01Xuqq9aUHoQouS7UVGZNStZ","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2004,\n      \"finding\": \"TOPK/PBK is phosphorylated at Thr-9 by cdk1/cyclin B during mitosis, associates with mitotic spindles, and is required for formation of the spindle midzone and cytokinesis; knockdown of TOPK disrupts spindle midzone formation and cytokinesis.\",\n      \"method\": \"Immunofluorescence, Western blot, kinase assay, siRNA knockdown with phenotypic readout\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct phosphorylation site identified, localization tied to functional consequence, replicated by multiple subsequent studies\",\n      \"pmids\": [\"15541388\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"TOPK and ERK2 form a positive feedback loop: TOPK phosphorylates ERK2 and ERK2 phosphorylates TOPK; knockdown of either reduces phosphorylation of the other and downstream ERK2 substrates in HCT116 colorectal cancer cells.\",\n      \"method\": \"In vitro kinase assay, siRNA knockdown, EGF-stimulation Western blot, transient transfection\",\n      \"journal\": \"Gastroenterology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — bidirectional kinase assay with epistatic knockdown experiments, high citation count indicating replication\",\n      \"pmids\": [\"17631144\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"TOPK enhances cdk1/cyclin B1-dependent phosphorylation of the microtubule-bundling protein PRC1 at T481 during mitosis by forming a ternary complex with cdk1/cyclin B1 and PRC1 on microtubules; TOPK enzymatic activity and its association with PRC1 are both required, but TOPK cannot phosphorylate PRC1 directly in vitro without cdk1/cyclin B1.\",\n      \"method\": \"In vitro kinase assay, Co-IP, in vivo phosphorylation assay, dominant-negative constructs\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution in vitro with multiple orthogonal methods (kinase assay, Co-IP, mutagenesis)\",\n      \"pmids\": [\"17512944\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"PBK/TOPK phosphorylates p38 MAPK and is required for appropriate p38 activation by growth factors; PBK knockdown impairs p38 activation, reduces cell motility, and impairs DNA damage response (reduced γ-H2AX, increased DNA damage).\",\n      \"method\": \"siRNA knockdown, Western blot, kinase assay, soft agar growth assay\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — siRNA knockdown with multiple orthogonal readouts, highly cited\",\n      \"pmids\": [\"17160018\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"PBK/TOPK is expressed in proliferating neural progenitor cells and phosphorylates p38 MAPK in a cell-cycle-dependent manner; inhibition of the PBK/TOPK–p38 pathway disrupts neural progenitor proliferation and self-renewal in vitro and in vivo.\",\n      \"method\": \"Microarray profiling, in vitro kinase assay, pharmacological inhibition, transgenic ablation/lineage tracing in mice\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods including in vivo genetic approach, high citation count\",\n      \"pmids\": [\"16291951\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"TOPK is expressed in spermatocytes and spermatids; TOPK-Thr-9 is specifically phosphorylated by cdk1/cyclin B during both mitotic and meiotic phases, while Thr-198 (ATP pocket) is constitutively phosphorylated, indicating a role in cytokinesis/chromosomal segregation during spermatogenesis.\",\n      \"method\": \"Immunofluorescence in situ, phospho-specific antibodies, Western blot\",\n      \"journal\": \"Development, growth & differentiation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct localization and phospho-site data but single lab, single method approach\",\n      \"pmids\": [\"16316408\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PBK/TOPK physically interacts with the DNA-binding domain (DBD) of tumor suppressor p53 in HCT116 cells; this interaction suppresses p53 transactivation function, reducing expression of p21 and other p53 target genes; PBK knockdown upregulates p21 particularly after genotoxic damage.\",\n      \"method\": \"Co-immunoprecipitation, yeast two-hybrid, gene knockdown with microarray analysis\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP and orthogonal yeast two-hybrid, multiple downstream readouts, highly cited\",\n      \"pmids\": [\"20622899\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PBK/TOPK phosphorylates LGN/GPSM2 at Thr450 during mitosis; overexpression of a T450A phosphorylation-deficient mutant causes aberrant chromosomal segregation and growth suppression in breast cancer cells.\",\n      \"method\": \"In vitro kinase assay, Western blot (G2/M-enriched lysates), siRNA, mutant overexpression with phenotypic readout\",\n      \"journal\": \"Genes, chromosomes & cancer\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — direct kinase assay with phosphorylation site identification plus functional mutagenesis\",\n      \"pmids\": [\"20589935\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"TOPK binds peroxiredoxin 1 (Prx1) and phosphorylates it at Ser-32, altering Prx1's secondary structure and enhancing its peroxidase activity; this phosphorylation prevents UVB-induced H2O2 accumulation and apoptosis in melanoma cells.\",\n      \"method\": \"LC-MS/MS binding identification, in vitro kinase assay, CD spectroscopy, immunofluorescence, siRNA/stable mutant lines, flow cytometry\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution with MS identification, structural analysis, and functional validation in multiple cell models\",\n      \"pmids\": [\"20647304\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"HI-TOPK-032 directly inhibits TOPK kinase activity in vitro with selectivity over ERK1, JNK1, and p38; in cells it reduces ERK-RSK phosphorylation and increases apoptosis via p53, cleaved caspase-7, and cleaved PARP; suppresses tumor growth in colon cancer xenograft in vivo.\",\n      \"method\": \"In vitro kinase assay screen, Western blot, xenograft model\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro kinase assay with specificity profiling plus in vivo validation, widely cited\",\n      \"pmids\": [\"22523035\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"CHFR (E3 ubiquitin ligase) ubiquitinates TOPK and regulates its protein levels; TOPK in turn phosphorylates and inactivates PTEN, leading to Akt activation and G2/M progression; this CHFR–TOPK–PTEN–Akt axis regulates the mitotic checkpoint.\",\n      \"method\": \"Co-IP, in vitro kinase/ubiquitination assay, siRNA epistasis, phospho-Western blot\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — reconstitution of ubiquitination and kinase activity with epistasis in the same study\",\n      \"pmids\": [\"24012691\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"TOPK/PBK is the master mitotic kinase that phosphorylates the conserved linker motif of C2H2 zinc finger proteins (ZFPs), driving their coordinate dissociation from condensing chromatin during mitosis; TOPK is activated by Cdk1 with precise temporal correlation to ZFP linker phosphorylation.\",\n      \"method\": \"Biotinylated kinase inhibitor (K252a) affinity purification, in vitro kinase assay with ZFP substrates, pharmacological and genetic inhibition\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — biochemical purification followed by in vitro kinase assay confirming substrate identity, mechanistic timing validated\",\n      \"pmids\": [\"25575812\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Src kinase directly binds and phosphorylates TOPK at Tyr74 and Tyr272; these phosphorylations increase TOPK stability by reducing its ubiquitination, elevate TOPK kinase activity toward histone H3 (Ser10), and promote colon cancer tumorigenesis.\",\n      \"method\": \"In vitro kinase assay, phospho-specific antibody generation, Co-IP, pulse-chase stability assay, Src KO MEF comparison, xenograft model\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro kinase assay, validated endogenous phosphorylation, genetic Src KO model, multiple orthogonal readouts\",\n      \"pmids\": [\"27016416\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"TOPK directly binds and phosphorylates c-Jun, activating AP-1 transcription of CCND1 and CDC2, thereby conferring resistance of NSCLC cells to EGFR-TKI gefitinib.\",\n      \"method\": \"Co-IP, in vitro kinase assay, reporter assay, siRNA knockdown, xenograft model\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — direct binding and kinase assay combined with functional rescue experiments\",\n      \"pmids\": [\"26745678\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"CDK1 phosphorylates PBK at Thr-9, Thr-24, Ser-32, and Ser-59 during mitosis in vitro and in cells; phosphorylation of Thr-9 is specifically involved in cytokinesis, and the non-phosphorylatable PBK-T9A mutant exhibits greater tumor-promoting activity than wild-type PBK, indicating CDK1-mediated phosphorylation inhibits PBK's oncogenic function.\",\n      \"method\": \"In vitro kinase assay, phosphomapping, mutant overexpression, tumorigenesis assays in breast cancer cells\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro kinase assay with multiple phosphorylation sites mapped, functional consequences of phospho-mutants demonstrated\",\n      \"pmids\": [\"28780319\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"TOPK promotes microglia/macrophage M2 polarization by binding to HDAC1 and HDAC2 and promoting their phosphorylation; TOPK overexpression increases M2 markers (CD206, Arg1) and reduces M1 inflammatory cytokines; effects are reversed by HDAC1/2 inhibitor FK228, placing TOPK upstream of HDAC1/2 in anti-inflammatory signaling after cerebral ischemia.\",\n      \"method\": \"Co-IP (in vivo binding), Western blot, siRNA/overexpression in BV2 cells, MCAO mouse model\",\n      \"journal\": \"Aging and disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP and in vivo co-localization with pharmacological epistasis, single lab\",\n      \"pmids\": [\"29896413\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"TOPK is phosphorylated and activated by solar UV; it directly phosphorylates c-Jun at Ser63 and Ser73 in a JNK-independent manner, activating AP-1 and promoting skin carcinogenesis.\",\n      \"method\": \"In vitro kinase assay, phospho-specific Western blot, siRNA knockdown, mouse skin carcinogenesis model\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — direct in vitro kinase assay with phospho-site identification, confirmed in vivo\",\n      \"pmids\": [\"32277233\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"TOPK phosphorylates PRPK (p53-related protein kinase); knockdown of TOPK inhibits PRPK phosphorylation and confers resistance to solar UV-induced skin carcinogenesis in mouse models.\",\n      \"method\": \"In vitro/cell kinase assay, siRNA knockdown, mouse skin carcinogenesis model, FDA-approved drug PRPK inhibitors\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — kinase assay plus in vivo validation, single lab\",\n      \"pmids\": [\"29904102\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"TOPK directly binds and phosphorylates ULK1 at Ser469, Ser495, and Ser533, decreasing ULK1 activity and stability, thereby inhibiting autophagy initiation in glioma cells and contributing to temozolomide resistance.\",\n      \"method\": \"Co-IP, in vitro kinase assay, phospho-site mapping, Western blot, autophagy flux assay, drug sensitivity assay\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct in vitro kinase assay with three phosphorylation sites identified, functional autophagy readouts\",\n      \"pmids\": [\"31378785\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PBK promotes HCC metastasis via the ETV4–uPAR signaling pathway: PBK enhances binding of transcription factor ETV4 to the uPAR promoter (shown by ChIP assay), increasing uPAR expression; uPAR overexpression rescues the metastasis suppressed by PBK knockdown.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP), luciferase promoter assay, gain/loss-of-function, orthotopic mouse model\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP and epistasis rescue experiment, single lab\",\n      \"pmids\": [\"30914208\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"MET tyrosine kinase phosphorylates TOPK at Tyr74, preventing apoptosis in gefitinib-resistant NSCLC cells; this is downstream of the COX2-TXA2 pathway regulating MET via AP-1.\",\n      \"method\": \"Western blot, phospho-antibody detection, Co-IP, cell viability assays, in vitro and ex vivo validation\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — phosphorylation site identified and functionally linked, single lab\",\n      \"pmids\": [\"31611604\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"PBK/TOPK mediates paclitaxel resistance in H460 NSCLC cells by promoting p53 nuclear export and ubiquitination, thereby suppressing p53-dependent autophagic cell death.\",\n      \"method\": \"siRNA knockdown, Western blot for nuclear/cytoplasmic fractionation, ubiquitination assay, LC3 puncta imaging, flow cytometry\",\n      \"journal\": \"FEBS open bio\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — fractionation and ubiquitination assay linking PBK to p53 regulation, single lab\",\n      \"pmids\": [\"32237067\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PBK phosphorylates MSL1 and enhances the interaction of MSL1 with MSL2, MSL3, and KAT8 (components of the MSL complex), promoting MSL complex enrichment on the CD276 promoter, leading to increased histone H4 K16 acetylation and CD276 transcription in nasopharyngeal carcinoma.\",\n      \"method\": \"Co-IP, in vitro kinase assay, ChIP, reporter assay, siRNA knockdown\",\n      \"journal\": \"Oncogenesis\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — direct kinase assay, Co-IP with multiple complex partners, ChIP for chromatin occupancy\",\n      \"pmids\": [\"33431797\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Menin/JunD/HDAC3 complex represses PBK expression by reducing histone H3 acetylation at the PBK promoter; menin inhibitor disrupts the menin-JunD interaction, derepresses PBK, and promotes beta cell proliferation in HFD-induced diabetic mice; Pbk kinase activity (knock-in deficiency model) is required for menin-inhibitor-induced beta cell proliferation.\",\n      \"method\": \"Pbk kinase-deficiency knock-in mouse model, ChIP, Co-IP, menin inhibitor pharmacology, HFD mouse model\",\n      \"journal\": \"EMBO molecular medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic knock-in model with ChIP and Co-IP, in vivo validation\",\n      \"pmids\": [\"33821572\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"ERK2 phosphorylates TOPK at Ser32 (a novel site in addition to Thr9); pTOPK(S32) is associated with sorafenib resistance in renal cell carcinoma; HGF/c-Met signaling activates p-TOPK(S32) during resistance development.\",\n      \"method\": \"In vitro kinase assay, phospho-specific antibody, Western blot, drug resistance cell models\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — novel phosphorylation site validated by specific antibody and kinase assay, single lab\",\n      \"pmids\": [\"35546143\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"PBK directly interacts with TRIM37 and promotes its phosphorylation and nuclear translocation, activating the NFκB pathway and conferring PARP inhibitor resistance in ovarian cancer.\",\n      \"method\": \"Co-IP, Western blot for phosphorylation and nuclear translocation, siRNA/overexpression, in vitro and in vivo drug resistance assays\",\n      \"journal\": \"Experimental & molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP with functional rescue, single lab\",\n      \"pmids\": [\"35859118\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"PBK directly phosphorylates histone H3 (in vitro reconstitution) and promotes CDH1 phosphorylation at S840/S846/S847 in cells (indirectly, as PBK failed to phosphorylate CDH1 directly in vitro), stabilizing CDH1 and suppressing Wnt/β-catenin signaling to inhibit CRC cell migration and invasion.\",\n      \"method\": \"In vitro kinase assay with recombinant PBK and HH3, phospho-CDH1 Western blot, siRNA/overexpression, migration/invasion assays\",\n      \"journal\": \"Frontiers in pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–3 — direct H3 phosphorylation confirmed in vitro; CDH1 phosphorylation indirect, single lab\",\n      \"pmids\": [\"35115926\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"FYN tyrosine kinase directly binds and phosphorylates TOPK at Y272; the TOPK-272F mutation abolishes this phosphorylation and interaction; FYN–TOPK axis promotes gastric cancer progression by phosphorylating HSPB1 at Ser15 as identified by phosphoproteomics in TOPK-knockout mice.\",\n      \"method\": \"Co-IP, pull-down assay, in vitro kinase assay with 32P isotope, phospho-specific antibody generation, phosphoproteomics, TOPK knockout mice, immunofluorescence co-localization\",\n      \"journal\": \"Journal of experimental & clinical cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted kinase assay, genetic KO mouse, phosphoproteomics, multiple orthogonal methods\",\n      \"pmids\": [\"37016377\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"TOPK phosphorylates YB1 at Thr89 and Ser209; phosphorylated YB1 binds the eEF1A1 promoter to activate its transcription, leading to AKT/mTOR signaling activation and esophageal cancer cell proliferation.\",\n      \"method\": \"In vitro kinase assay, ChIP, reporter assay, TOPK KO, rescue experiments, xenograft model\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — direct kinase assay with phospho-site identification, ChIP, and rescue experiments\",\n      \"pmids\": [\"37328464\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"TOPK directly interacts with CHK1 and Cdc25c; TOPK depletion increases fork stalling and collapse under replication stress, impairs recovery from replication fork stalling, and increases replication-associated single-stranded DNA foci, placing TOPK in the S-phase checkpoint signaling pathway.\",\n      \"method\": \"Co-IP, siRNA knockdown, DNA fiber assay, ssDNA immunofluorescence, cancer cell xenograft with fractionated irradiation\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP with functional replication assays, single lab\",\n      \"pmids\": [\"33168956\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"TOPK promotes NF-κB-dependent iNOS gene expression and nitric oxide production in response to LPS: TOPK interacts with IκBα and phosphorylates it, promoting NF-κB transcriptional activity; knockdown abolishes LPS-induced iNOS and NF-κB promoter activity.\",\n      \"method\": \"Co-IP, in vitro kinase assay for IκBα, reporter assay, siRNA knockdown, NOS expression Western blot\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — kinase assay for IκBα plus epistasis, single lab\",\n      \"pmids\": [\"24440499\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"PBK/TOPK enhances aggressive phenotype in prostate cancer through β-catenin–TCF/LEF-mediated upregulation of MMP-2 and MMP-9 transcription; gain- and loss-of-function studies show PBK modulates invasive ability causally.\",\n      \"method\": \"siRNA/overexpression, promoter reporter assay, invasion assay, tissue array\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — promoter reporter assay with epistasis, single lab\",\n      \"pmids\": [\"25909225\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Geranylgeranylation regulates PBK expression in breast cancer cells via YAP (Yes-associated protein) as mediator; atorvastatin or GGTI-298 downregulates PBK through YAP inactivation, identifying PBK as a downstream target of the Hippo-YAP pathway.\",\n      \"method\": \"shRNA knockdown, Western blot, cell proliferation assay, pharmacological inhibition\",\n      \"journal\": \"Cancer cell international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — shRNA epistasis linking YAP to PBK expression, single lab\",\n      \"pmids\": [\"25745361\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"c-Myc regulates PBK expression through E2F1 in high-grade lymphomas; inhibition of c-Myc or E2F1 decreases PBK expression and cell growth, establishing a c-Myc–E2F1–PBK transcriptional axis.\",\n      \"method\": \"ChIP (implied), Western blot, siRNA knockdown, cell viability assay\",\n      \"journal\": \"Leukemia research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — transcriptional pathway established by knockdown experiments, correlation data, single lab\",\n      \"pmids\": [\"23237560\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PBK/TOPK is a MAPKK-like serine/threonine kinase that is activated by CDK1-mediated phosphorylation (Thr9, Thr24, Ser32, Ser59) and by Src-mediated tyrosine phosphorylation (Y74, Y272) during mitosis; it phosphorylates multiple substrates including p38 MAPK, ERK2 (bidirectional loop), PRC1 (cooperatively with CDK1/cyclin B1), LGN/GPSM2 (Thr450), histone H3, C2H2 zinc finger protein linkers, Prx1 (Ser32), ULK1 (Ser469/495/533), IκBα, c-Jun (Ser63/73), YB1 (Thr89/Ser209), PTEN, TRIM37, MSL1, and PRPK; through these substrates it regulates mitotic spindle/cytokinesis integrity, the DNA damage and replication stress checkpoints, p53 transcriptional suppression, autophagy inhibition, NF-κB activation, and AP-1-driven gene expression, collectively promoting cancer cell proliferation, survival, and metastasis.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"PBK (also called TOPK) is a mitotic serine/threonine kinase that integrates cell-cycle progression, checkpoint signaling, and chromatin regulation by phosphorylating a broad array of substrates downstream of CDK1/cyclin B1 activation. CDK1 phosphorylates PBK at Thr9, Thr24, Ser32, and Ser59 during mitosis, and Src/FYN phosphorylate it at Tyr74 and Tyr272 to increase its stability and activity; once active, PBK phosphorylates p38 MAPK, ERK2 (forming a positive feedback loop), PRC1, LGN/GPSM2, histone H3, C2H2 zinc-finger protein linkers, c-Jun, IκBα, ULK1, Prx1, YB1, MSL1, PTEN, TRIM37, and PRPK, thereby controlling spindle midzone formation, cytokinesis, the DNA replication stress checkpoint, NF-κB and AP-1 transcriptional programs, autophagy suppression, and antioxidant defense [PMID:15541388, PMID:17631144, PMID:17512944, PMID:17160018, PMID:25575812, PMID:18, PMID:33431797, PMID:24012691, PMID:31378785, PMID:37016377]. PBK also binds the DNA-binding domain of p53 and suppresses its transactivation function, linking PBK to p53-dependent tumor suppression and drug resistance [PMID:20622899, PMID:32237067]. Through these activities PBK is essential for proliferation of neural progenitor cells and spermatocytes and drives tumorigenesis, metastasis, and multi-drug resistance across diverse cancer types [PMID:16291951, PMID:16316408, PMID:26745678, PMID:35859118].\",\n  \"teleology\": [\n    {\n      \"year\": 2004,\n      \"claim\": \"Establishing PBK as a CDK1-activated mitotic kinase required for cytokinesis resolved its cell-cycle phase of action and placed it at the spindle midzone, a critical structure for cell division.\",\n      \"evidence\": \"Phospho-site mapping (Thr9 by CDK1/cyclin B), immunofluorescence at spindle midzone, siRNA knockdown causing cytokinesis failure in HeLa cells\",\n      \"pmids\": [\"15541388\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which PBK promotes midzone assembly not defined\", \"Other CDK1 phosphorylation sites on PBK not yet mapped at this time\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Identification of p38 MAPK as a direct PBK substrate linked PBK to DNA damage signaling and demonstrated its role in neural progenitor proliferation, extending PBK function beyond cancer cells to normal stem cell biology.\",\n      \"evidence\": \"In vitro kinase assay, siRNA knockdown reducing p38 activation and γ-H2AX, pharmacological inhibition and transgenic ablation in mouse neural progenitors\",\n      \"pmids\": [\"17160018\", \"16291951\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Phosphorylation sites on p38 targeted by PBK not mapped\", \"Relative contribution of PBK versus canonical MKKs to p38 activation unclear\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Discovery of the PBK–ERK2 positive feedback loop and the PBK–CDK1–PRC1 ternary complex established PBK as a signaling hub that both amplifies MAPK cascades and cooperatively regulates mitotic microtubule bundling.\",\n      \"evidence\": \"Bidirectional in vitro kinase assays between PBK and ERK2 with epistatic knockdowns; ternary complex reconstitution showing PBK enhances CDK1-dependent PRC1-T481 phosphorylation\",\n      \"pmids\": [\"17631144\", \"17512944\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct PBK phosphorylation sites on ERK2 not mapped\", \"Structural basis of ternary PBK–CDK1–PRC1 complex unknown\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Three new direct substrates—LGN/GPSM2 (Thr450), Prx1 (Ser32), and the p53 DNA-binding domain interaction—expanded PBK's roles to spindle orientation, antioxidant defense, and tumor suppressor antagonism, respectively.\",\n      \"evidence\": \"In vitro kinase assays with phospho-site identification for LGN and Prx1; reciprocal Co-IP and yeast two-hybrid for p53-DBD binding; CD spectroscopy for Prx1 structural change; p21 upregulation upon PBK knockdown\",\n      \"pmids\": [\"20589935\", \"20647304\", \"20622899\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PBK directly phosphorylates p53 or only binds it was not resolved\", \"In vivo relevance of Prx1-S32 phosphorylation beyond melanoma not tested\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Development of HI-TOPK-032 as a selective PBK inhibitor provided a pharmacological tool confirming that PBK kinase activity drives ERK-RSK signaling and survival in colon cancer, validating PBK as a druggable target.\",\n      \"evidence\": \"In vitro kinase assay showing selectivity over ERK1/JNK1/p38, xenograft tumor suppression, apoptosis markers\",\n      \"pmids\": [\"22523035\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Off-target effects of HI-TOPK-032 not comprehensively profiled\", \"Clinical translation not addressed\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"The CHFR–PBK–PTEN–Akt axis revealed that PBK is both regulated by E3-ligase-mediated ubiquitination and itself inactivates PTEN by phosphorylation, connecting PBK to PI3K/Akt signaling and mitotic checkpoint control.\",\n      \"evidence\": \"In vitro ubiquitination and kinase assays, siRNA epistasis linking CHFR to PBK levels and PBK to PTEN phosphorylation\",\n      \"pmids\": [\"24012691\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"PTEN phosphorylation sites by PBK not mapped\", \"Whether CHFR ubiquitinates PBK via K48 or K63 chains not determined\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Demonstration that PBK phosphorylates IκBα to activate NF-κB-dependent iNOS expression established PBK as a pro-inflammatory kinase operating outside its canonical mitotic context.\",\n      \"evidence\": \"Co-IP, in vitro kinase assay for IκBα, NF-κB reporter assay, siRNA abolishing LPS-induced iNOS\",\n      \"pmids\": [\"24440499\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"IκBα phosphorylation sites by PBK not identified\", \"Whether PBK activates NF-κB independently of IKK complex not resolved\", \"Single-lab finding\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Identification of PBK as the master kinase phosphorylating C2H2 zinc-finger protein linkers during mitosis explained the coordinate chromatin dissociation of hundreds of ZFPs, revealing a major role in mitotic chromatin reorganization.\",\n      \"evidence\": \"Biotinylated kinase-inhibitor affinity purification identifying PBK, in vitro kinase assay with ZFP substrates, temporal correlation with CDK1 activation\",\n      \"pmids\": [\"25575812\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of ZFP chromatin dissociation for gene bookmarking or re-activation post-mitosis not determined\", \"Full spectrum of ZFP substrates not catalogued\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Src-mediated tyrosine phosphorylation of PBK at Y74 and Y272 was shown to stabilize PBK protein and enhance its histone H3 kinase activity, while PBK was found to directly phosphorylate c-Jun at Ser63/73 to activate AP-1, linking upstream tyrosine kinase input to downstream transcriptional output.\",\n      \"evidence\": \"In vitro kinase assays, Src KO MEFs, pulse-chase stability, Co-IP of PBK–c-Jun, AP-1 reporter, xenograft models\",\n      \"pmids\": [\"27016416\", \"26745678\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contributions of Src versus FYN to PBK Y74/Y272 phosphorylation in different tissues not compared\", \"Structural basis of Src–PBK interaction unknown\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Comprehensive CDK1 phospho-mapping of PBK (Thr9, Thr24, Ser32, Ser59) revealed that CDK1-mediated phosphorylation paradoxically restrains PBK's oncogenic function, with the non-phosphorylatable T9A mutant being more tumorigenic than wild-type.\",\n      \"evidence\": \"In vitro kinase assay, phospho-mapping, mutant overexpression with tumorigenesis assays in breast cancer cells\",\n      \"pmids\": [\"28780319\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which T9 phosphorylation suppresses oncogenic activity not elucidated\", \"Whether CDK1 phosphorylation affects PBK substrate selectivity untested\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"PBK was shown to directly phosphorylate ULK1 at three sites (S469/S495/S533) to inhibit autophagy initiation, establishing PBK as a negative regulator of autophagy and explaining its role in temozolomide resistance in glioma.\",\n      \"evidence\": \"In vitro kinase assay with phospho-site mapping, autophagy flux assays, drug sensitivity assays in glioma cells\",\n      \"pmids\": [\"31378785\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PBK inhibits autophagy through ULK1 in non-cancer contexts not tested\", \"Relative importance of each ULK1 phospho-site not dissected\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"PBK was placed in the replication stress checkpoint through its interaction with CHK1 and Cdc25c, with PBK depletion causing replication fork collapse, extending PBK's roles from mitosis into S-phase DNA integrity.\",\n      \"evidence\": \"Co-IP of PBK with CHK1/Cdc25c, DNA fiber assays showing increased fork stalling upon PBK siRNA, ssDNA foci, xenograft with fractionated irradiation\",\n      \"pmids\": [\"33168956\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether PBK directly phosphorylates CHK1 or Cdc25c not determined\", \"Mechanism of PBK recruitment to stalled forks unknown\", \"Single-lab finding\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"PBK was shown to phosphorylate MSL1, enhancing MSL complex assembly and H4K16 acetylation at target promoters such as CD276, revealing an epigenetic effector role; separately, a Pbk kinase-dead knock-in mouse demonstrated that PBK kinase activity is required for menin-inhibitor-induced pancreatic beta cell proliferation.\",\n      \"evidence\": \"In vitro kinase assay and ChIP for MSL1/CD276; Pbk kinase-deficiency knock-in mouse with HFD model and menin inhibitor pharmacology\",\n      \"pmids\": [\"33431797\", \"33821572\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"MSL1 phosphorylation sites not mapped\", \"Whether PBK-MSL1 axis operates outside nasopharyngeal carcinoma not tested\", \"Downstream mediators of PBK in beta cell proliferation beyond kinase requirement not identified\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identification of ERK2 phosphorylation of PBK at Ser32 (in addition to CDK1-mediated Thr9) linked PBK activation to drug resistance signaling via HGF/c-Met, while PBK was shown to phosphorylate TRIM37 to activate NF-κB and confer PARP inhibitor resistance.\",\n      \"evidence\": \"In vitro kinase assay for ERK2→PBK-S32, phospho-specific antibody in sorafenib-resistant RCC; Co-IP of PBK–TRIM37 with nuclear translocation and drug resistance assays in ovarian cancer\",\n      \"pmids\": [\"35546143\", \"35859118\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether ERK2- and CDK1-mediated S32 phosphorylation are functionally redundant untested\", \"TRIM37 phosphorylation sites not mapped\", \"Clinical relevance of PBK in PARP inhibitor resistance needs validation\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"FYN kinase was identified as a second Src-family kinase phosphorylating PBK at Y272, and phosphoproteomics in TOPK-knockout mice identified HSPB1-Ser15 as a downstream substrate; separately, PBK was shown to phosphorylate YB1 at Thr89/Ser209 to drive eEF1A1 transcription and AKT/mTOR activation.\",\n      \"evidence\": \"Isotope kinase assay for FYN→PBK-Y272, phosphoproteomics in KO mice identifying HSPB1; in vitro kinase assay for PBK→YB1 with ChIP and rescue experiments\",\n      \"pmids\": [\"37016377\", \"37328464\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full phosphoproteomic landscape of PBK-dependent substrates in vivo not yet catalogued beyond HSPB1\", \"Structural basis for PBK's broad substrate recognition unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Despite extensive substrate identification, the structural basis for PBK's unusually broad substrate specificity, its consensus phosphorylation motif, and the tissue-specific regulatory logic that selects among its many substrates remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No crystal or cryo-EM structure of PBK available\", \"No defined consensus phosphorylation motif\", \"Systematic comparison of substrate selectivity across tissues not performed\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1, 2, 3, 7, 8, 10, 11, 12, 13, 16, 17, 18, 22, 25, 26, 27, 28, 30]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005694\", \"supporting_discovery_ids\": [0, 11]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [6, 22]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [0, 2, 5, 7, 10, 11, 14]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 3, 4, 10, 13, 16, 28, 30]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [8, 9, 21]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [18, 21]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [3, 29]},\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [11, 22, 26]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"CDK1\",\n      \"ERK2\",\n      \"PRC1\",\n      \"TP53\",\n      \"PRKWNK1\",\n      \"ULK1\",\n      \"SRC\",\n      \"FYN\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}