{"gene":"STK33","run_date":"2026-06-10T10:51:54","timeline":{"discoveries":[{"year":2009,"finding":"STK33 promotes cancer cell viability in a kinase activity-dependent manner by regulating suppression of mitochondrial apoptosis through S6K1-induced inactivation of the death agonist BAD, selectively in mutant KRAS-dependent cells.","method":"High-throughput RNAi screen, knockdown with viability readout, pathway analysis","journal":"Cell","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — single lab, RNAi screen with pathway analysis but no direct in vitro reconstitution; subsequently contradicted by multiple independent labs","pmids":["19490892"],"is_preprint":false},{"year":2011,"finding":"STK33 kinase activity is NOT required for survival of KRAS-dependent cancer cells: STK33 knockdown, dominant mutant overexpression, and small-molecule kinase inhibitors all failed to affect KRAS signaling or cell survival, refuting the proposed synthetic lethal interaction.","method":"RNAi, dominant mutant overexpression, small-molecule inhibitors, synthetic lethal siRNA screen across broad panel","journal":"Cancer research","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (RNAi, dominant mutants, small molecules), replicated by independent labs (PMID 22323609, 23256033)","pmids":["21742770","22323609","23256033"],"is_preprint":false},{"year":2001,"finding":"STK33 was identified as a novel serine/threonine protein kinase encoded on human chromosome 11p15.3, with phylogenetic analysis placing it in the calcium/calmodulin-dependent protein kinase (CAMK) group, though lacking the canonical calcium/calmodulin binding domain.","method":"Comparative genome analysis, cDNA sequencing, phylogenetic analysis, RT-PCR","journal":"Gene","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — sequence-based classification replicated by subsequent expression studies (PMID 16176263); no direct enzymatic validation in this paper","pmids":["11738831"],"is_preprint":false},{"year":2005,"finding":"STK33/Stk33 protein is highly expressed in testis (particularly in spermatogenic epithelial cells), lung epithelia, alveolar macrophages, retinal horizontal cells, and embryonic organs, establishing a non-ubiquitous expression pattern consistent with roles in spermatogenesis and organ ontogenesis.","method":"Immunofluorescence, Western blot, RNA analysis across tissues","journal":"The FEBS journal","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — direct protein localization by immunofluorescence, replicated in subsequent studies (PMID 29155043, 34155512)","pmids":["16176263"],"is_preprint":false},{"year":2008,"finding":"Stk33 directly binds to vimentin and phosphorylates the non-alpha-helical amino-terminal domain of vimentin in vitro; co-immunoprecipitation from cultured cell extracts confirmed in vivo association, and co-sedimentation assay showed direct binding without additional mediating proteins.","method":"In vitro kinase assay with recombinant vimentin, co-immunoprecipitation, co-sedimentation assay, immunofluorescence colocalization","journal":"BMC biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro kinase assay with mutagenesis (truncation), reciprocal Co-IP, direct co-sedimentation; multiple orthogonal methods in one study","pmids":["18811945"],"is_preprint":false},{"year":2012,"finding":"The HSP90/CDC37 chaperone complex binds to and stabilizes STK33 protein in human cancer cells; pharmacologic HSP90 inhibition induces proteasome-mediated degradation of STK33, triggering apoptosis preferentially in KRAS mutant cells in an STK33-dependent manner.","method":"Mass spectrometry-based protein interaction screen, co-immunoprecipitation, pharmacologic HSP90 inhibition, in vitro and in vivo tumor models","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 / Moderate — MS-based interaction screen, Co-IP validation, pharmacologic and genetic rescue in vitro and in vivo, multiple structurally divergent HSP90 inhibitors tested","pmids":["22451720"],"is_preprint":false},{"year":2013,"finding":"Stk33 co-localizes with vimentin in hypothalamic tanycytes in rodent and higher mammalian brains, and Stk33 expression in tanycytes is regulated by photoperiod, mirroring vimentin regulation, suggesting involvement in photoperiodic endocrine regulation.","method":"Immunofluorescence, double-immunostaining, co-immunoprecipitation, Western blot across photoperiod conditions","journal":"Cell and tissue research","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — direct immunofluorescence localization with functional context (photoperiod regulation), builds on prior Co-IP evidence (PMID 18811945)","pmids":["24057876"],"is_preprint":false},{"year":2014,"finding":"STK33 directly binds to c-Myc and increases its transcriptional activity, promoting hepatocellular carcinoma cell proliferation; the C-terminus of STK33 blocks this STK33/c-Myc association and downregulates HCC cell proliferation.","method":"Co-immunoprecipitation, domain-mapping with C-terminus constructs, in vitro and in vivo HCC proliferation assays, TAM-inducible transgenic and knockout mouse models","journal":"Gut","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP with domain mapping, validated in transgenic/KO mouse models and in vitro; single lab","pmids":["25398772"],"is_preprint":false},{"year":2017,"finding":"Stk33 is essential for spermatid differentiation: constitutive Stk33 deletion in mice results in severely malformed and immotile spermatozoa with disordered structural tail elements; Stk33 protein localizes to the cytoplasm and partially co-localizes with the caudal end of the manchette in elongating spermatids, and its loss leads to an abnormal tight, straight, elongated manchette.","method":"Constitutive and conditional knockout mice, immunofluorescence localization, histological analysis of spermatogenesis","journal":"Developmental biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — constitutive and germ-cell-specific conditional KO both replicate the phenotype; direct subcellular localization linked to functional consequence; replicated by human mutation data (PMID 34155512, 37146716)","pmids":["29155043"],"is_preprint":false},{"year":2017,"finding":"HSP90-stabilized STK33 interacts with and regulates hypoxia-driven accumulation and activation of HIF-1α, as well as secretion of VEGF-A in hypoxic cancer cells, promoting tumor angiogenesis; ectopic STK33 restored blood vessel formation in vivo after HSP90 inhibition.","method":"Co-immunoprecipitation, genetic STK33 abrogation/overexpression, tumor xenograft vascularization assay, VEGF-A secretion assay","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, in vitro and in vivo rescue experiments; single lab","pmids":["29100402"],"is_preprint":false},{"year":2017,"finding":"HIF-1α directly transcriptionally upregulates STK33 by binding to a hypoxia response element in its promoter, establishing STK33 as a downstream mediator of HIF1α in pancreatic ductal adenocarcinoma.","method":"Chromatin immunoprecipitation (ChIP), reporter assay, knockdown/overexpression in PDAC cells and xenografts","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP showing direct HIF1α binding to STK33 promoter HRE, functional rescue in vitro and in vivo; single lab","pmids":["29038348"],"is_preprint":false},{"year":2019,"finding":"TTC36 binds HPD and reduces STK33 binding to HPD, thereby inhibiting STK33-mediated phosphorylation of HPD at T382; this phosphorylation recruits PELI1, which polyubiquitylates HPD leading to its degradation. Deficiency of TTC36 enhances STK33-mediated HPD T382 phosphorylation and PELI1-mediated HPD downregulation, causing tyrosinemia and neurological damage in Ttc36-/- mice.","method":"Co-immunoprecipitation, in vitro kinase assay (identifying T382 phosphorylation site), ubiquitylation assay, Ttc36 knockout mouse model with biochemical and behavioral phenotyping","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro kinase assay identifying specific substrate site, Co-IP, ubiquitylation assay, and in vivo KO model with multi-level phenotypic validation; multiple orthogonal methods","pmids":["31537781"],"is_preprint":false},{"year":2019,"finding":"STK33 phosphorylates ERK2 in vitro, binds ERK2 in cells, and acts as an upstream kinase to increase ERK2 activity, promoting tumorigenesis of colorectal cancer cells.","method":"In vitro kinase assay, co-immunoprecipitation, knockdown/overexpression in HCT15 cells, in vivo xenograft","journal":"Bioscience reports","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single paper; note PMID 31272359 is a withdrawn paper from the same authors, reducing confidence","pmids":["30760631"],"is_preprint":false},{"year":2019,"finding":"STK33 promotes growth and progression of pancreatic neuroendocrine tumors via activation of the PI3K/AKT/mTOR pathway, as demonstrated by knockdown and overexpression experiments.","method":"siRNA knockdown, overexpression, Western blot for PI3K/AKT/mTOR pathway components, in vitro proliferation/invasion assays, in vivo xenograft","journal":"Neuroendocrinology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KD and OE with pathway readout in vitro and in vivo; single lab","pmids":["31261148"],"is_preprint":false},{"year":2021,"finding":"A homozygous frameshift mutation (c.1235del, p.T412Kfs*14) in STK33 causes MMAF (multiple morphological abnormalities of the flagella) phenotype in humans, establishing STK33 as an MMAF-related gene required for normal sperm flagellar structure and motility.","method":"Whole-exome sequencing, mRNA analysis, sperm morphology and ultrastructure analysis (electron microscopy)","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — human loss-of-function mutation with detailed sperm ultrastructural phenotyping; consistent with mouse KO data (PMID 29155043)","pmids":["34155512"],"is_preprint":false},{"year":2021,"finding":"NFYB transcription factor binds to the STK33 promoter and promotes STK33 expression, which in turn activates the Hedgehog signaling pathway to promote cisplatin resistance in diffuse large B-cell lymphoma.","method":"Chromatin immunoprecipitation, promoter binding assay, knockdown of STK33 and NFYB, Hedgehog pathway inhibitor experiments","journal":"Leukemia research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP for NFYB-STK33 promoter interaction, pathway rescue experiments; single lab","pmids":["34536775"],"is_preprint":false},{"year":2023,"finding":"STK33 phosphorylates fibrous sheath components AKAP3 and AKAP4 (A-kinase anchoring proteins 3 and 4) in vitro; STK33 deletion in mice results in defects in mitochondrial sheath, fibrous sheath, outer dense fiber, and axoneme assembly, with AKAP3/4 expression decreased in testis. Loss-of-function mutations in STK33 in humans cause non-obstructive azoospermia.","method":"Differential phosphoproteomic analysis, in vitro kinase assay, Stk33 knockout and knockin mouse models, human mutation identification, sperm structural analysis","journal":"Molecular & cellular proteomics","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro kinase assay identifying specific substrates, phosphoproteomics, mouse KO/KI models with detailed structural phenotype, human genetic validation; multiple orthogonal methods","pmids":["37146716"],"is_preprint":false},{"year":2023,"finding":"STK33 affects autophagy in renal cell carcinoma cells by activating the mTOR/ULK1 pathway: STK33 knockdown leads to decreased p-mTOR and P62 and increased Beclin1, LC3, and p-ULK1, promoting autophagy and inhibiting cell proliferation and migration.","method":"siRNA knockdown, Western blot for mTOR/ULK1 pathway components, LC3 fluorescence assay, proliferation and migration assays","journal":"Molecular biology reports","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single method per readout, no direct kinase activity measurement","pmids":["37101009"],"is_preprint":false},{"year":2023,"finding":"KLHDC2 (CUL2 diGly receptor) was identified as an efficient E3 ubiquitin ligase capable of degrading STK33 via proximity-induced degradation (AdPROM system), demonstrating that STK33 can be targeted for proteasomal degradation by KLHDC2-recruiting molecules.","method":"AdPROM E3 ligase screen with GFP-tagged endogenous STK33, Western blot for degradation, peptide-based PROTAC proof-of-concept","journal":"Cell chemical biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — systematic E3 ligase screen with endogenously tagged target, functional PROTAC proof-of-concept; single lab","pmids":["37591251"],"is_preprint":false},{"year":2025,"finding":"STK33 is identified as a binding partner of TSKS (Testis Specific Serine Kinase Substrate) in testicular germ cells by co-immunoprecipitation; STK33 is recruited to TSKS foci through this interaction. STK33 was unable to phosphorylate TSKS or YBX2 in vitro, suggesting a non-catalytic scaffolding role in this context.","method":"Immunoprecipitation/mass spectrometry, co-immunoprecipitation, proximity ligation assay, in vitro phosphorylation assay (negative result for TSKS and YBX2)","journal":"Reproductive sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP and PLA for interaction, in vitro kinase assay (negative for these substrates); single lab, 2025","pmids":["39909973"],"is_preprint":false},{"year":2026,"finding":"STK33 promotes glycolysis and PanNET growth via the mTORC1/S6K1/HIF-1α signaling axis: STK33 knockdown reduces S6K1 phosphorylation and S6K1 inhibition reverses STK33-driven glycolysis; HIF-1α transcriptionally upregulates STK33 while STK33 promotes HIF-1α protein levels via mTORC1/S6K1, enhancing LDHA expression.","method":"shRNA knockdown, overexpression, S6K1 pharmacologic inhibition, Western blot for pathway components, glucose/lactate/ATP assays, in vivo xenograft, immunochemistry in patient specimens","journal":"Journal of translational medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic and pharmacologic modulation with pathway rescue in vitro and in vivo; single lab, builds on prior PNET work (PMID 31261148)","pmids":["42157211"],"is_preprint":false},{"year":2025,"finding":"STK33 is implicated as a novel kinase in acrosomal exocytosis during sperm maturation, identified through phosphoproteomic analysis of epididymal sperm maturation; knockout mouse model validation confirmed functional relevance for sperm motility and fertilization capacity.","method":"High-resolution mass spectrometry phosphoproteomics, knockout mouse model, sperm motility and fertilization assays","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 2 / Weak — preprint, phosphoproteomic identification with KO validation but STK33-specific mechanistic details are limited in abstract; single study","pmids":[],"is_preprint":true}],"current_model":"STK33 is a CAMK-family serine/threonine kinase that is essential for spermiogenesis by phosphorylating fibrous sheath components AKAP3/4 and localizing to the manchette during spermatid elongation; it stabilizes the intermediate filament protein vimentin through direct phosphorylation of its N-terminal domain; it is stabilized by the HSP90/CDC37 chaperone complex and degraded via the proteasome upon HSP90 inhibition; it phosphorylates HPD at T382 to regulate tyrosine metabolism via a TTC36-STK33-PELI1 signaling axis; it interacts with c-Myc to promote transcriptional activity in liver cancer; and it modulates HIF-1α/VEGF signaling and mTORC1/S6K1 pathways in tumor contexts, while its originally proposed synthetic lethal kinase activity requirement in KRAS-mutant cancer has been refuted by multiple independent studies."},"narrative":{"mechanistic_narrative":"STK33 is a CAMK-group serine/threonine protein kinase whose best-established physiological role is in male germ cell differentiation, where it is required for spermatid elongation and assembly of the sperm tail [PMID:29155043, PMID:37146716]. STK33 protein localizes to the spermatid cytoplasm and the caudal end of the manchette during spermatid elongation, and its loss produces malformed, immotile spermatozoa with disordered tail structures including defective mitochondrial sheath, fibrous sheath, outer dense fiber, and axoneme [PMID:29155043, PMID:37146716]. Mechanistically it phosphorylates the fibrous sheath A-kinase anchoring proteins AKAP3 and AKAP4 in vitro, and loss-of-function mutations in STK33 cause non-obstructive azoospermia and multiple morphological abnormalities of the flagella (MMAF) in humans [PMID:34155512, PMID:37146716]. Beyond the testis, STK33 directly binds and phosphorylates the non-alpha-helical amino-terminal domain of the intermediate filament vimentin [PMID:18811945]. STK33 also phosphorylates the tyrosine-metabolic enzyme HPD at T382, a mark that recruits the E3 ligase PELI1 to drive HPD polyubiquitylation and degradation; this STK33 activity is restrained by TTC36, defining a TTC36–STK33–PELI1 axis controlling tyrosine catabolism [PMID:31537781]. STK33 protein is held stable by the HSP90/CDC37 chaperone complex and is degraded via the proteasome upon HSP90 inhibition [PMID:22451720]. In tumor contexts STK33 binds c-Myc to enhance its transcriptional activity and modulates HIF-1α/VEGF and mTORC1/S6K1 signaling [PMID:25398772, PMID:29100402, PMID:42157211]. The early proposal that STK33 kinase activity is selectively required for survival of KRAS-mutant cancer cells was refuted by multiple orthogonal approaches across independent laboratories [PMID:21742770, PMID:22323609, PMID:23256033].","teleology":[{"year":2001,"claim":"Established STK33 as a distinct gene product by identifying it as a novel serine/threonine kinase and placing it phylogenetically in the CAMK group, framing expectations for its catalytic class.","evidence":"Comparative genome analysis, cDNA sequencing and phylogenetic classification","pmids":["11738831"],"confidence":"Medium","gaps":["No direct enzymatic activity demonstrated","Lacks the canonical calcium/calmodulin binding domain, leaving regulation unknown","No substrate identified at this stage"]},{"year":2005,"claim":"Defined a non-ubiquitous expression pattern enriched in testis and other epithelia, pointing toward specialized roles in spermatogenesis and organ development rather than a housekeeping function.","evidence":"Immunofluorescence, Western blot and RNA analysis across tissues","pmids":["16176263"],"confidence":"Medium","gaps":["Expression pattern does not establish molecular function","No causal link to a cellular process yet"]},{"year":2008,"claim":"Provided the first direct substrate by showing STK33 binds and phosphorylates the amino-terminal domain of vimentin, the first concrete biochemical activity assigned to the kinase.","evidence":"In vitro kinase assay with recombinant vimentin, reciprocal Co-IP, co-sedimentation and colocalization","pmids":["18811945"],"confidence":"High","gaps":["Functional consequence of vimentin phosphorylation not defined","Phosphosite on vimentin not mapped"]},{"year":2009,"claim":"Proposed a synthetic lethal role in which STK33 kinase activity sustains KRAS-mutant cancer cell viability via S6K1/BAD, motivating it as a drug target.","evidence":"High-throughput RNAi screen with viability readout and pathway analysis","pmids":["19490892"],"confidence":"Medium","gaps":["No in vitro reconstitution of the proposed kinase activity","Subsequently contradicted by independent labs"]},{"year":2011,"claim":"Refuted the KRAS synthetic-lethality model by showing STK33 kinase activity is dispensable for KRAS-dependent survival, correcting the field's target rationale.","evidence":"RNAi, dominant-mutant overexpression, small-molecule inhibitors and synthetic-lethal siRNA screening across a broad cell panel, replicated by independent labs","pmids":["21742770","22323609","23256033"],"confidence":"High","gaps":["Does not address whether STK33 has KRAS-independent oncogenic roles","Leaves the physiological substrate question open"]},{"year":2012,"claim":"Identified the mechanism controlling STK33 protein stability, showing HSP90/CDC37 chaperones STK33 and that HSP90 inhibition drives its proteasomal degradation.","evidence":"MS-based interaction screen, Co-IP, pharmacologic HSP90 inhibition with in vitro and in vivo rescue","pmids":["22451720"],"confidence":"High","gaps":["Does not resolve the contested KRAS dependency mechanism","Phosphorylation targets downstream of stabilized STK33 not defined here"]},{"year":2017,"claim":"Established STK33 as essential for spermatid differentiation, linking its manchette localization to a defined structural sperm phenotype upon knockout.","evidence":"Constitutive and germ-cell conditional knockout mice with immunofluorescence localization and histology","pmids":["29155043"],"confidence":"High","gaps":["Substrates driving the manchette/tail phenotype not yet identified","Whether kinase activity is required in vivo not tested here"]},{"year":2017,"claim":"Connected STK33 to tumor angiogenesis and a hypoxia transcriptional circuit, showing it regulates HIF-1α/VEGF-A and is itself a direct HIF-1α target gene.","evidence":"Co-IP and rescue for HIF-1α/VEGF; ChIP and reporter assays for HIF-1α binding to the STK33 promoter in PDAC","pmids":["29100402","29038348"],"confidence":"Medium","gaps":["Direct kinase substrate within the HIF axis not defined","Single-lab findings for each arm"]},{"year":2019,"claim":"Defined a physiological substrate and signaling axis outside the testis: STK33 phosphorylates HPD at T382 to trigger PELI1-mediated degradation, with TTC36 as a negative regulator controlling tyrosine metabolism.","evidence":"Co-IP, in vitro kinase assay mapping T382, ubiquitylation assay, and Ttc36 knockout mouse with biochemical/behavioral phenotyping","pmids":["31537781"],"confidence":"High","gaps":["Tissue scope of the TTC36-STK33-PELI1 axis beyond the KO model not defined","How STK33 activity is regulated in this context unknown"]},{"year":2019,"claim":"Extended STK33's oncogenic interactome with reports that it binds and activates ERK2 and drives PI3K/AKT/mTOR signaling in tumor cells.","evidence":"In vitro kinase assay and Co-IP for ERK2 in colorectal cells; knockdown/overexpression with pathway readout in PanNET cells","pmids":["30760631","31261148"],"confidence":"Low","gaps":["ERK2 finding is from a single lab with a related withdrawn paper, not independently confirmed","Direct kinase activity on pathway components in the PI3K/AKT/mTOR arm not measured"]},{"year":2021,"claim":"Validated the spermatogenic role in humans and added a transcriptional regulator, showing STK33 loss-of-function causes MMAF and that NFYB drives STK33 expression in lymphoma.","evidence":"Whole-exome sequencing with sperm ultrastructure analysis; ChIP and pathway rescue for NFYB/Hedgehog in DLBCL","pmids":["34155512","34536775"],"confidence":"Medium","gaps":["MMAF mutation effect on kinase activity not dissected","NFYB-Hedgehog link is single-lab"]},{"year":2023,"claim":"Pinpointed AKAP3/AKAP4 as fibrous sheath substrates explaining the sperm tail defect and confirmed STK33 loss causes human non-obstructive azoospermia, unifying the spermiogenesis mechanism.","evidence":"Differential phosphoproteomics, in vitro kinase assays, mouse KO/KI models, human mutation identification and sperm structural analysis","pmids":["37146716"],"confidence":"High","gaps":["Direct in vivo demonstration that AKAP3/4 phosphorylation alone drives the phenotype not isolated","Full set of germ-cell substrates not enumerated"]},{"year":2023,"claim":"Added chemical-biology tractability and a renal autophagy role, showing STK33 can be degraded by KLHDC2-recruiting PROTACs and that its knockdown activates mTOR/ULK1-dependent autophagy.","evidence":"AdPROM E3 ligase screen with endogenously tagged STK33 and PROTAC proof-of-concept; siRNA knockdown with autophagy markers in RCC","pmids":["37591251","37101009"],"confidence":"Medium","gaps":["Autophagy finding is low-confidence single-lab without direct kinase measurement","Whether degrader-based STK33 loss phenocopies genetic loss in vivo untested"]},{"year":2025,"claim":"Revealed a potential non-catalytic scaffolding role in germ cells, where STK33 is recruited to TSKS foci but does not phosphorylate TSKS or YBX2 in vitro.","evidence":"IP/MS, reciprocal Co-IP, proximity ligation assay and in vitro kinase assay (negative for TSKS/YBX2)","pmids":["39909973"],"confidence":"Medium","gaps":["Functional role of the STK33-TSKS interaction not established","Whether TSKS recruitment is kinase-independent in vivo unknown"]},{"year":null,"claim":"How STK33 kinase activity is regulated in the absence of a canonical calcium/calmodulin binding domain, and which subset of substrates and scaffolding interactions account for its distinct roles across spermiogenesis, tyrosine metabolism, and tumors, remains unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structural model of activation defined in the corpus","Catalytic versus scaffolding contributions not separated across contexts","Mechanism integrating mTORC1/S6K1, HIF-1α, and c-Myc effects not unified"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[4,11,16]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[4,11,16]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[8]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[4,6]}],"pathway":[{"term_id":"R-HSA-1474165","term_label":"Reproduction","supporting_discovery_ids":[8,16]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[11]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[5,11]}],"complexes":[],"partners":["VIM","AKAP3","AKAP4","HPD","MYC","HSP90","CDC37","TSKS"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9BYT3","full_name":"Serine/threonine-protein kinase 33","aliases":[],"length_aa":514,"mass_kda":57.8,"function":"Serine/threonine protein kinase required for spermatid differentiation and male fertility (PubMed:37146716, PubMed:38781365). Promotes sperm flagella assembly during spermatogenesis by mediating phosphorylation of fibrous sheath proteins AKAP3 and AKAP4 (By similarity). Also phosphorylates vimentin/VIM, thereby regulating the dynamic behavior of the intermediate filament cytoskeleton (By similarity)","subcellular_location":"Cytoplasm; Cytoplasm, cytoskeleton; Cytoplasm, perinuclear region","url":"https://www.uniprot.org/uniprotkb/Q9BYT3/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/STK33","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/STK33","total_profiled":1310},"omim":[{"mim_id":"620849","title":"SPERMATOGENIC FAILURE 93; SPGF93","url":"https://www.omim.org/entry/620849"},{"mim_id":"610785","title":"PDLIM1-INTERACTING KINASE 1-LIKE; PDIK1L","url":"https://www.omim.org/entry/610785"},{"mim_id":"607670","title":"SERINE/THREONINE PROTEIN KINASE 33; STK33","url":"https://www.omim.org/entry/607670"},{"mim_id":"258150","title":"SPERMATOGENIC FAILURE 1; SPGF1","url":"https://www.omim.org/entry/258150"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"},{"location":"Flagellar centriole","reliability":"Approved"},{"location":"Nucleoli","reliability":"Additional"},{"location":"Cytosol","reliability":"Additional"},{"location":"Mid piece","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"choroid plexus","ntpm":38.3},{"tissue":"testis","ntpm":45.2}],"url":"https://www.proteinatlas.org/search/STK33"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"Q9BYT3","domains":[{"cath_id":"3.30.200.20","chopping":"101-195","consensus_level":"medium","plddt":90.9135,"start":101,"end":195},{"cath_id":"1.10.510.10","chopping":"196-274_286-388","consensus_level":"medium","plddt":90.7913,"start":196,"end":388}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9BYT3","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9BYT3-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9BYT3-F1-predicted_aligned_error_v6.png","plddt_mean":67.19},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=STK33","jax_strain_url":"https://www.jax.org/strain/search?query=STK33"},"sequence":{"accession":"Q9BYT3","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9BYT3.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9BYT3/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9BYT3"}},"corpus_meta":[{"pmid":"19490892","id":"PMC_19490892","title":"Synthetic lethal interaction between oncogenic KRAS dependency and STK33 suppression in human cancer cells.","date":"2009","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/19490892","citation_count":461,"is_preprint":false},{"pmid":"21742770","id":"PMC_21742770","title":"STK33 kinase activity is nonessential in KRAS-dependent cancer cells.","date":"2011","source":"Cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/21742770","citation_count":98,"is_preprint":false},{"pmid":"22323609","id":"PMC_22323609","title":"STK33 kinase inhibitor BRD-8899 has no effect on KRAS-dependent cancer cell viability.","date":"2012","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/22323609","citation_count":64,"is_preprint":false},{"pmid":"22451720","id":"PMC_22451720","title":"Targeting of KRAS mutant tumors by HSP90 inhibitors involves degradation of STK33.","date":"2012","source":"The Journal of experimental medicine","url":"https://pubmed.ncbi.nlm.nih.gov/22451720","citation_count":58,"is_preprint":false},{"pmid":"23256033","id":"PMC_23256033","title":"A Potent and Selective Quinoxalinone-Based STK33 Inhibitor Does Not Show Synthetic Lethality in KRAS-Dependent Cells.","date":"2012","source":"ACS medicinal chemistry letters","url":"https://pubmed.ncbi.nlm.nih.gov/23256033","citation_count":58,"is_preprint":false},{"pmid":"11738831","id":"PMC_11738831","title":"A novel serine/threonine kinase gene, STK33, on human chromosome 11p15.3.","date":"2001","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/11738831","citation_count":39,"is_preprint":false},{"pmid":"16176263","id":"PMC_16176263","title":"Differential expression pattern of the novel serine/threonine kinase, STK33, in mice and men.","date":"2005","source":"The FEBS journal","url":"https://pubmed.ncbi.nlm.nih.gov/16176263","citation_count":33,"is_preprint":false},{"pmid":"25398772","id":"PMC_25398772","title":"STK33 promotes hepatocellular carcinoma through binding to c-Myc.","date":"2014","source":"Gut","url":"https://pubmed.ncbi.nlm.nih.gov/25398772","citation_count":33,"is_preprint":false},{"pmid":"29038348","id":"PMC_29038348","title":"STK33 Promotes Growth and Progression of Pancreatic Cancer as a Critical Downstream Mediator of HIF1α.","date":"2017","source":"Cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/29038348","citation_count":32,"is_preprint":false},{"pmid":"31537781","id":"PMC_31537781","title":"HPD degradation regulated by the TTC36-STK33-PELI1 signaling axis induces tyrosinemia and neurological damage.","date":"2019","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/31537781","citation_count":29,"is_preprint":false},{"pmid":"34155512","id":"PMC_34155512","title":"Novel frameshift mutation in STK33 is associated with asthenozoospermia and multiple morphological abnormalities of the flagella.","date":"2021","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/34155512","citation_count":28,"is_preprint":false},{"pmid":"18811945","id":"PMC_18811945","title":"The Serine/threonine kinase Stk33 exhibits autophosphorylation and phosphorylates the intermediate filament protein Vimentin.","date":"2008","source":"BMC biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/18811945","citation_count":27,"is_preprint":false},{"pmid":"29155043","id":"PMC_29155043","title":"Stk33 is required for spermatid differentiation and male fertility in mice.","date":"2017","source":"Developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/29155043","citation_count":25,"is_preprint":false},{"pmid":"37591251","id":"PMC_37591251","title":"Identification of KLHDC2 as an efficient proximity-induced degrader of K-RAS, STK33, β-catenin, and FoxP3.","date":"2023","source":"Cell chemical biology","url":"https://pubmed.ncbi.nlm.nih.gov/37591251","citation_count":23,"is_preprint":false},{"pmid":"25603720","id":"PMC_25603720","title":"STK33 overexpression in hypopharyngeal squamous cell carcinoma: possible role in tumorigenesis.","date":"2015","source":"BMC cancer","url":"https://pubmed.ncbi.nlm.nih.gov/25603720","citation_count":20,"is_preprint":false},{"pmid":"30256516","id":"PMC_30256516","title":"STK33 alleviates gentamicin-induced ototoxicity in cochlear hair cells and House Ear Institute-Organ of Corti 1 cells.","date":"2018","source":"Journal of cellular and molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/30256516","citation_count":19,"is_preprint":false},{"pmid":"25662617","id":"PMC_25662617","title":"STK33 plays an important positive role in the development of human large cell lung cancers with variable metastatic potential.","date":"2015","source":"Acta biochimica et biophysica Sinica","url":"https://pubmed.ncbi.nlm.nih.gov/25662617","citation_count":19,"is_preprint":false},{"pmid":"29100402","id":"PMC_29100402","title":"STK33 participates to HSP90-supported angiogenic program in hypoxic tumors by regulating HIF-1α/VEGF signaling pathway.","date":"2017","source":"Oncotarget","url":"https://pubmed.ncbi.nlm.nih.gov/29100402","citation_count":17,"is_preprint":false},{"pmid":"34536775","id":"PMC_34536775","title":"NFYB potentiates STK33 activation to promote cisplatin resistance in diffuse large B-cell lymphoma.","date":"2021","source":"Leukemia research","url":"https://pubmed.ncbi.nlm.nih.gov/34536775","citation_count":15,"is_preprint":false},{"pmid":"38824700","id":"PMC_38824700","title":"Click-chemistry mediated synthesis of OTBN-1,2,3-Triazole derivatives exhibiting STK33 inhibition with diverse anti-cancer activities.","date":"2024","source":"Bioorganic chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/38824700","citation_count":15,"is_preprint":false},{"pmid":"37146716","id":"PMC_37146716","title":"STK33 Phosphorylates Fibrous Sheath Protein AKAP3/4 to Regulate Sperm Flagella Assembly in Spermiogenesis.","date":"2023","source":"Molecular & cellular proteomics : MCP","url":"https://pubmed.ncbi.nlm.nih.gov/37146716","citation_count":13,"is_preprint":false},{"pmid":"30760631","id":"PMC_30760631","title":"STK33/ERK2 signal pathway contribute the tumorigenesis of colorectal cancer HCT15 cells.","date":"2019","source":"Bioscience reports","url":"https://pubmed.ncbi.nlm.nih.gov/30760631","citation_count":13,"is_preprint":false},{"pmid":"32395291","id":"PMC_32395291","title":"miR-107 inhibited malignant biological behavior of non-small cell lung cancer cells by regulating the STK33/ERK signaling pathway in vivo and vitro.","date":"2020","source":"Journal of thoracic disease","url":"https://pubmed.ncbi.nlm.nih.gov/32395291","citation_count":13,"is_preprint":false},{"pmid":"31261148","id":"PMC_31261148","title":"STK33 Promotes the Growth and Progression of Human Pancreatic Neuroendocrine Tumour via Activation of the PI3K/AKT/mTOR Pathway.","date":"2019","source":"Neuroendocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/31261148","citation_count":12,"is_preprint":false},{"pmid":"24057876","id":"PMC_24057876","title":"Co-localization of serine/threonine kinase 33 (Stk33) and vimentin in the hypothalamus.","date":"2013","source":"Cell and tissue research","url":"https://pubmed.ncbi.nlm.nih.gov/24057876","citation_count":11,"is_preprint":false},{"pmid":"27414193","id":"PMC_27414193","title":"STK33 potentiates the malignancy of hypopharyngeal squamous carcinoma: Possible relation to calcium.","date":"2016","source":"Cancer biology & therapy","url":"https://pubmed.ncbi.nlm.nih.gov/27414193","citation_count":8,"is_preprint":false},{"pmid":"37101009","id":"PMC_37101009","title":"Interaction between STK33 and autophagy promoted renal cell carcinoma metastasis by regulating mTOR/ULK1 signaling pathway.","date":"2023","source":"Molecular biology reports","url":"https://pubmed.ncbi.nlm.nih.gov/37101009","citation_count":6,"is_preprint":false},{"pmid":"27840186","id":"PMC_27840186","title":"Serine/threonine-kinase 33 (Stk33) - Component of the neuroendocrine network?","date":"2016","source":"Brain research","url":"https://pubmed.ncbi.nlm.nih.gov/27840186","citation_count":6,"is_preprint":false},{"pmid":"23967198","id":"PMC_23967198","title":"The STK33-linked SNP rs4929949 is associated with obesity and BMI in two independent cohorts of Swedish and Greek children.","date":"2013","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/23967198","citation_count":6,"is_preprint":false},{"pmid":"39515612","id":"PMC_39515612","title":"STK33 as the functional substrate of miR-454-3p for suppression and apoptosis in neuroblastoma.","date":"2024","source":"Molecules and cells","url":"https://pubmed.ncbi.nlm.nih.gov/39515612","citation_count":1,"is_preprint":false},{"pmid":"39909973","id":"PMC_39909973","title":"Identification of YBX2 and TSKS As STK33 Interacting Proteins in Testicular Germ Cells.","date":"2025","source":"Reproductive sciences (Thousand Oaks, Calif.)","url":"https://pubmed.ncbi.nlm.nih.gov/39909973","citation_count":0,"is_preprint":false},{"pmid":"42157211","id":"PMC_42157211","title":"The STK33/mTORC1/S6K1/HIF-1α signalling axis drives glycolysis and progression in pancreatic neuroendocrine tumours.","date":"2026","source":"Journal of translational medicine","url":"https://pubmed.ncbi.nlm.nih.gov/42157211","citation_count":0,"is_preprint":false},{"pmid":"42265708","id":"PMC_42265708","title":"Piceatannol attenuates thoracic aortic aneurysm progression by targeting STK33.","date":"2026","source":"Biology direct","url":"https://pubmed.ncbi.nlm.nih.gov/42265708","citation_count":0,"is_preprint":false},{"pmid":"31272359","id":"PMC_31272359","title":"WITHDRAWN: STK33/ERK2 signal pathway contribute the tumorigenesis of colorectal cancer HCT15 cells.","date":"2019","source":"Anti-cancer agents in medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/31272359","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.09.18.677062","title":"The functional maturation of mouse spermatozoa is underpinned by global remodeling of the cellular phosphoproteome","date":"2025-09-21","source":"bioRxiv","url":"https://doi.org/10.1101/2025.09.18.677062","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2024.11.15.623822","title":"Pan-Cancer Genetic Profiles of Mitotic DNA Integrity Checkpoint Protein Kinases","date":"2024-11-15","source":"bioRxiv","url":"https://doi.org/10.1101/2024.11.15.623822","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":18801,"output_tokens":5268,"usd":0.067711,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":13641,"output_tokens":4469,"usd":0.089965,"stage2_stop_reason":"end_turn"},"total_usd":0.157676,"stage1_batch_id":"msgbatch_017qqVz33Ga63SCDwzb35XPb","stage2_batch_id":"msgbatch_01Scr2Ei9x4HJMiRGxwrmvLK","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2009,\n      \"finding\": \"STK33 promotes cancer cell viability in a kinase activity-dependent manner by regulating suppression of mitochondrial apoptosis through S6K1-induced inactivation of the death agonist BAD, selectively in mutant KRAS-dependent cells.\",\n      \"method\": \"High-throughput RNAi screen, knockdown with viability readout, pathway analysis\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — single lab, RNAi screen with pathway analysis but no direct in vitro reconstitution; subsequently contradicted by multiple independent labs\",\n      \"pmids\": [\"19490892\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"STK33 kinase activity is NOT required for survival of KRAS-dependent cancer cells: STK33 knockdown, dominant mutant overexpression, and small-molecule kinase inhibitors all failed to affect KRAS signaling or cell survival, refuting the proposed synthetic lethal interaction.\",\n      \"method\": \"RNAi, dominant mutant overexpression, small-molecule inhibitors, synthetic lethal siRNA screen across broad panel\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (RNAi, dominant mutants, small molecules), replicated by independent labs (PMID 22323609, 23256033)\",\n      \"pmids\": [\"21742770\", \"22323609\", \"23256033\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"STK33 was identified as a novel serine/threonine protein kinase encoded on human chromosome 11p15.3, with phylogenetic analysis placing it in the calcium/calmodulin-dependent protein kinase (CAMK) group, though lacking the canonical calcium/calmodulin binding domain.\",\n      \"method\": \"Comparative genome analysis, cDNA sequencing, phylogenetic analysis, RT-PCR\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — sequence-based classification replicated by subsequent expression studies (PMID 16176263); no direct enzymatic validation in this paper\",\n      \"pmids\": [\"11738831\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"STK33/Stk33 protein is highly expressed in testis (particularly in spermatogenic epithelial cells), lung epithelia, alveolar macrophages, retinal horizontal cells, and embryonic organs, establishing a non-ubiquitous expression pattern consistent with roles in spermatogenesis and organ ontogenesis.\",\n      \"method\": \"Immunofluorescence, Western blot, RNA analysis across tissues\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — direct protein localization by immunofluorescence, replicated in subsequent studies (PMID 29155043, 34155512)\",\n      \"pmids\": [\"16176263\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Stk33 directly binds to vimentin and phosphorylates the non-alpha-helical amino-terminal domain of vimentin in vitro; co-immunoprecipitation from cultured cell extracts confirmed in vivo association, and co-sedimentation assay showed direct binding without additional mediating proteins.\",\n      \"method\": \"In vitro kinase assay with recombinant vimentin, co-immunoprecipitation, co-sedimentation assay, immunofluorescence colocalization\",\n      \"journal\": \"BMC biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro kinase assay with mutagenesis (truncation), reciprocal Co-IP, direct co-sedimentation; multiple orthogonal methods in one study\",\n      \"pmids\": [\"18811945\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"The HSP90/CDC37 chaperone complex binds to and stabilizes STK33 protein in human cancer cells; pharmacologic HSP90 inhibition induces proteasome-mediated degradation of STK33, triggering apoptosis preferentially in KRAS mutant cells in an STK33-dependent manner.\",\n      \"method\": \"Mass spectrometry-based protein interaction screen, co-immunoprecipitation, pharmacologic HSP90 inhibition, in vitro and in vivo tumor models\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — MS-based interaction screen, Co-IP validation, pharmacologic and genetic rescue in vitro and in vivo, multiple structurally divergent HSP90 inhibitors tested\",\n      \"pmids\": [\"22451720\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Stk33 co-localizes with vimentin in hypothalamic tanycytes in rodent and higher mammalian brains, and Stk33 expression in tanycytes is regulated by photoperiod, mirroring vimentin regulation, suggesting involvement in photoperiodic endocrine regulation.\",\n      \"method\": \"Immunofluorescence, double-immunostaining, co-immunoprecipitation, Western blot across photoperiod conditions\",\n      \"journal\": \"Cell and tissue research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — direct immunofluorescence localization with functional context (photoperiod regulation), builds on prior Co-IP evidence (PMID 18811945)\",\n      \"pmids\": [\"24057876\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"STK33 directly binds to c-Myc and increases its transcriptional activity, promoting hepatocellular carcinoma cell proliferation; the C-terminus of STK33 blocks this STK33/c-Myc association and downregulates HCC cell proliferation.\",\n      \"method\": \"Co-immunoprecipitation, domain-mapping with C-terminus constructs, in vitro and in vivo HCC proliferation assays, TAM-inducible transgenic and knockout mouse models\",\n      \"journal\": \"Gut\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP with domain mapping, validated in transgenic/KO mouse models and in vitro; single lab\",\n      \"pmids\": [\"25398772\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Stk33 is essential for spermatid differentiation: constitutive Stk33 deletion in mice results in severely malformed and immotile spermatozoa with disordered structural tail elements; Stk33 protein localizes to the cytoplasm and partially co-localizes with the caudal end of the manchette in elongating spermatids, and its loss leads to an abnormal tight, straight, elongated manchette.\",\n      \"method\": \"Constitutive and conditional knockout mice, immunofluorescence localization, histological analysis of spermatogenesis\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — constitutive and germ-cell-specific conditional KO both replicate the phenotype; direct subcellular localization linked to functional consequence; replicated by human mutation data (PMID 34155512, 37146716)\",\n      \"pmids\": [\"29155043\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"HSP90-stabilized STK33 interacts with and regulates hypoxia-driven accumulation and activation of HIF-1α, as well as secretion of VEGF-A in hypoxic cancer cells, promoting tumor angiogenesis; ectopic STK33 restored blood vessel formation in vivo after HSP90 inhibition.\",\n      \"method\": \"Co-immunoprecipitation, genetic STK33 abrogation/overexpression, tumor xenograft vascularization assay, VEGF-A secretion assay\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, in vitro and in vivo rescue experiments; single lab\",\n      \"pmids\": [\"29100402\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"HIF-1α directly transcriptionally upregulates STK33 by binding to a hypoxia response element in its promoter, establishing STK33 as a downstream mediator of HIF1α in pancreatic ductal adenocarcinoma.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP), reporter assay, knockdown/overexpression in PDAC cells and xenografts\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP showing direct HIF1α binding to STK33 promoter HRE, functional rescue in vitro and in vivo; single lab\",\n      \"pmids\": [\"29038348\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"TTC36 binds HPD and reduces STK33 binding to HPD, thereby inhibiting STK33-mediated phosphorylation of HPD at T382; this phosphorylation recruits PELI1, which polyubiquitylates HPD leading to its degradation. Deficiency of TTC36 enhances STK33-mediated HPD T382 phosphorylation and PELI1-mediated HPD downregulation, causing tyrosinemia and neurological damage in Ttc36-/- mice.\",\n      \"method\": \"Co-immunoprecipitation, in vitro kinase assay (identifying T382 phosphorylation site), ubiquitylation assay, Ttc36 knockout mouse model with biochemical and behavioral phenotyping\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro kinase assay identifying specific substrate site, Co-IP, ubiquitylation assay, and in vivo KO model with multi-level phenotypic validation; multiple orthogonal methods\",\n      \"pmids\": [\"31537781\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"STK33 phosphorylates ERK2 in vitro, binds ERK2 in cells, and acts as an upstream kinase to increase ERK2 activity, promoting tumorigenesis of colorectal cancer cells.\",\n      \"method\": \"In vitro kinase assay, co-immunoprecipitation, knockdown/overexpression in HCT15 cells, in vivo xenograft\",\n      \"journal\": \"Bioscience reports\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single paper; note PMID 31272359 is a withdrawn paper from the same authors, reducing confidence\",\n      \"pmids\": [\"30760631\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"STK33 promotes growth and progression of pancreatic neuroendocrine tumors via activation of the PI3K/AKT/mTOR pathway, as demonstrated by knockdown and overexpression experiments.\",\n      \"method\": \"siRNA knockdown, overexpression, Western blot for PI3K/AKT/mTOR pathway components, in vitro proliferation/invasion assays, in vivo xenograft\",\n      \"journal\": \"Neuroendocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KD and OE with pathway readout in vitro and in vivo; single lab\",\n      \"pmids\": [\"31261148\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"A homozygous frameshift mutation (c.1235del, p.T412Kfs*14) in STK33 causes MMAF (multiple morphological abnormalities of the flagella) phenotype in humans, establishing STK33 as an MMAF-related gene required for normal sperm flagellar structure and motility.\",\n      \"method\": \"Whole-exome sequencing, mRNA analysis, sperm morphology and ultrastructure analysis (electron microscopy)\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — human loss-of-function mutation with detailed sperm ultrastructural phenotyping; consistent with mouse KO data (PMID 29155043)\",\n      \"pmids\": [\"34155512\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"NFYB transcription factor binds to the STK33 promoter and promotes STK33 expression, which in turn activates the Hedgehog signaling pathway to promote cisplatin resistance in diffuse large B-cell lymphoma.\",\n      \"method\": \"Chromatin immunoprecipitation, promoter binding assay, knockdown of STK33 and NFYB, Hedgehog pathway inhibitor experiments\",\n      \"journal\": \"Leukemia research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP for NFYB-STK33 promoter interaction, pathway rescue experiments; single lab\",\n      \"pmids\": [\"34536775\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"STK33 phosphorylates fibrous sheath components AKAP3 and AKAP4 (A-kinase anchoring proteins 3 and 4) in vitro; STK33 deletion in mice results in defects in mitochondrial sheath, fibrous sheath, outer dense fiber, and axoneme assembly, with AKAP3/4 expression decreased in testis. Loss-of-function mutations in STK33 in humans cause non-obstructive azoospermia.\",\n      \"method\": \"Differential phosphoproteomic analysis, in vitro kinase assay, Stk33 knockout and knockin mouse models, human mutation identification, sperm structural analysis\",\n      \"journal\": \"Molecular & cellular proteomics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro kinase assay identifying specific substrates, phosphoproteomics, mouse KO/KI models with detailed structural phenotype, human genetic validation; multiple orthogonal methods\",\n      \"pmids\": [\"37146716\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"STK33 affects autophagy in renal cell carcinoma cells by activating the mTOR/ULK1 pathway: STK33 knockdown leads to decreased p-mTOR and P62 and increased Beclin1, LC3, and p-ULK1, promoting autophagy and inhibiting cell proliferation and migration.\",\n      \"method\": \"siRNA knockdown, Western blot for mTOR/ULK1 pathway components, LC3 fluorescence assay, proliferation and migration assays\",\n      \"journal\": \"Molecular biology reports\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single method per readout, no direct kinase activity measurement\",\n      \"pmids\": [\"37101009\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"KLHDC2 (CUL2 diGly receptor) was identified as an efficient E3 ubiquitin ligase capable of degrading STK33 via proximity-induced degradation (AdPROM system), demonstrating that STK33 can be targeted for proteasomal degradation by KLHDC2-recruiting molecules.\",\n      \"method\": \"AdPROM E3 ligase screen with GFP-tagged endogenous STK33, Western blot for degradation, peptide-based PROTAC proof-of-concept\",\n      \"journal\": \"Cell chemical biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — systematic E3 ligase screen with endogenously tagged target, functional PROTAC proof-of-concept; single lab\",\n      \"pmids\": [\"37591251\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"STK33 is identified as a binding partner of TSKS (Testis Specific Serine Kinase Substrate) in testicular germ cells by co-immunoprecipitation; STK33 is recruited to TSKS foci through this interaction. STK33 was unable to phosphorylate TSKS or YBX2 in vitro, suggesting a non-catalytic scaffolding role in this context.\",\n      \"method\": \"Immunoprecipitation/mass spectrometry, co-immunoprecipitation, proximity ligation assay, in vitro phosphorylation assay (negative result for TSKS and YBX2)\",\n      \"journal\": \"Reproductive sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP and PLA for interaction, in vitro kinase assay (negative for these substrates); single lab, 2025\",\n      \"pmids\": [\"39909973\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"STK33 promotes glycolysis and PanNET growth via the mTORC1/S6K1/HIF-1α signaling axis: STK33 knockdown reduces S6K1 phosphorylation and S6K1 inhibition reverses STK33-driven glycolysis; HIF-1α transcriptionally upregulates STK33 while STK33 promotes HIF-1α protein levels via mTORC1/S6K1, enhancing LDHA expression.\",\n      \"method\": \"shRNA knockdown, overexpression, S6K1 pharmacologic inhibition, Western blot for pathway components, glucose/lactate/ATP assays, in vivo xenograft, immunochemistry in patient specimens\",\n      \"journal\": \"Journal of translational medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic and pharmacologic modulation with pathway rescue in vitro and in vivo; single lab, builds on prior PNET work (PMID 31261148)\",\n      \"pmids\": [\"42157211\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"STK33 is implicated as a novel kinase in acrosomal exocytosis during sperm maturation, identified through phosphoproteomic analysis of epididymal sperm maturation; knockout mouse model validation confirmed functional relevance for sperm motility and fertilization capacity.\",\n      \"method\": \"High-resolution mass spectrometry phosphoproteomics, knockout mouse model, sperm motility and fertilization assays\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 2 / Weak — preprint, phosphoproteomic identification with KO validation but STK33-specific mechanistic details are limited in abstract; single study\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"STK33 is a CAMK-family serine/threonine kinase that is essential for spermiogenesis by phosphorylating fibrous sheath components AKAP3/4 and localizing to the manchette during spermatid elongation; it stabilizes the intermediate filament protein vimentin through direct phosphorylation of its N-terminal domain; it is stabilized by the HSP90/CDC37 chaperone complex and degraded via the proteasome upon HSP90 inhibition; it phosphorylates HPD at T382 to regulate tyrosine metabolism via a TTC36-STK33-PELI1 signaling axis; it interacts with c-Myc to promote transcriptional activity in liver cancer; and it modulates HIF-1α/VEGF signaling and mTORC1/S6K1 pathways in tumor contexts, while its originally proposed synthetic lethal kinase activity requirement in KRAS-mutant cancer has been refuted by multiple independent studies.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"STK33 is a CAMK-group serine/threonine protein kinase whose best-established physiological role is in male germ cell differentiation, where it is required for spermatid elongation and assembly of the sperm tail [#8, #16]. STK33 protein localizes to the spermatid cytoplasm and the caudal end of the manchette during spermatid elongation, and its loss produces malformed, immotile spermatozoa with disordered tail structures including defective mitochondrial sheath, fibrous sheath, outer dense fiber, and axoneme [#8, #16]. Mechanistically it phosphorylates the fibrous sheath A-kinase anchoring proteins AKAP3 and AKAP4 in vitro, and loss-of-function mutations in STK33 cause non-obstructive azoospermia and multiple morphological abnormalities of the flagella (MMAF) in humans [#14, #16]. Beyond the testis, STK33 directly binds and phosphorylates the non-alpha-helical amino-terminal domain of the intermediate filament vimentin [#4]. STK33 also phosphorylates the tyrosine-metabolic enzyme HPD at T382, a mark that recruits the E3 ligase PELI1 to drive HPD polyubiquitylation and degradation; this STK33 activity is restrained by TTC36, defining a TTC36–STK33–PELI1 axis controlling tyrosine catabolism [#11]. STK33 protein is held stable by the HSP90/CDC37 chaperone complex and is degraded via the proteasome upon HSP90 inhibition [#5]. In tumor contexts STK33 binds c-Myc to enhance its transcriptional activity and modulates HIF-1α/VEGF and mTORC1/S6K1 signaling [#7, #9, #20]. The early proposal that STK33 kinase activity is selectively required for survival of KRAS-mutant cancer cells was refuted by multiple orthogonal approaches across independent laboratories [#1].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Established STK33 as a distinct gene product by identifying it as a novel serine/threonine kinase and placing it phylogenetically in the CAMK group, framing expectations for its catalytic class.\",\n      \"evidence\": \"Comparative genome analysis, cDNA sequencing and phylogenetic classification\",\n      \"pmids\": [\"11738831\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No direct enzymatic activity demonstrated\", \"Lacks the canonical calcium/calmodulin binding domain, leaving regulation unknown\", \"No substrate identified at this stage\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Defined a non-ubiquitous expression pattern enriched in testis and other epithelia, pointing toward specialized roles in spermatogenesis and organ development rather than a housekeeping function.\",\n      \"evidence\": \"Immunofluorescence, Western blot and RNA analysis across tissues\",\n      \"pmids\": [\"16176263\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Expression pattern does not establish molecular function\", \"No causal link to a cellular process yet\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Provided the first direct substrate by showing STK33 binds and phosphorylates the amino-terminal domain of vimentin, the first concrete biochemical activity assigned to the kinase.\",\n      \"evidence\": \"In vitro kinase assay with recombinant vimentin, reciprocal Co-IP, co-sedimentation and colocalization\",\n      \"pmids\": [\"18811945\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of vimentin phosphorylation not defined\", \"Phosphosite on vimentin not mapped\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Proposed a synthetic lethal role in which STK33 kinase activity sustains KRAS-mutant cancer cell viability via S6K1/BAD, motivating it as a drug target.\",\n      \"evidence\": \"High-throughput RNAi screen with viability readout and pathway analysis\",\n      \"pmids\": [\"19490892\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No in vitro reconstitution of the proposed kinase activity\", \"Subsequently contradicted by independent labs\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Refuted the KRAS synthetic-lethality model by showing STK33 kinase activity is dispensable for KRAS-dependent survival, correcting the field's target rationale.\",\n      \"evidence\": \"RNAi, dominant-mutant overexpression, small-molecule inhibitors and synthetic-lethal siRNA screening across a broad cell panel, replicated by independent labs\",\n      \"pmids\": [\"21742770\", \"22323609\", \"23256033\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not address whether STK33 has KRAS-independent oncogenic roles\", \"Leaves the physiological substrate question open\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Identified the mechanism controlling STK33 protein stability, showing HSP90/CDC37 chaperones STK33 and that HSP90 inhibition drives its proteasomal degradation.\",\n      \"evidence\": \"MS-based interaction screen, Co-IP, pharmacologic HSP90 inhibition with in vitro and in vivo rescue\",\n      \"pmids\": [\"22451720\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not resolve the contested KRAS dependency mechanism\", \"Phosphorylation targets downstream of stabilized STK33 not defined here\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Established STK33 as essential for spermatid differentiation, linking its manchette localization to a defined structural sperm phenotype upon knockout.\",\n      \"evidence\": \"Constitutive and germ-cell conditional knockout mice with immunofluorescence localization and histology\",\n      \"pmids\": [\"29155043\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Substrates driving the manchette/tail phenotype not yet identified\", \"Whether kinase activity is required in vivo not tested here\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Connected STK33 to tumor angiogenesis and a hypoxia transcriptional circuit, showing it regulates HIF-1α/VEGF-A and is itself a direct HIF-1α target gene.\",\n      \"evidence\": \"Co-IP and rescue for HIF-1α/VEGF; ChIP and reporter assays for HIF-1α binding to the STK33 promoter in PDAC\",\n      \"pmids\": [\"29100402\", \"29038348\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct kinase substrate within the HIF axis not defined\", \"Single-lab findings for each arm\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Defined a physiological substrate and signaling axis outside the testis: STK33 phosphorylates HPD at T382 to trigger PELI1-mediated degradation, with TTC36 as a negative regulator controlling tyrosine metabolism.\",\n      \"evidence\": \"Co-IP, in vitro kinase assay mapping T382, ubiquitylation assay, and Ttc36 knockout mouse with biochemical/behavioral phenotyping\",\n      \"pmids\": [\"31537781\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Tissue scope of the TTC36-STK33-PELI1 axis beyond the KO model not defined\", \"How STK33 activity is regulated in this context unknown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Extended STK33's oncogenic interactome with reports that it binds and activates ERK2 and drives PI3K/AKT/mTOR signaling in tumor cells.\",\n      \"evidence\": \"In vitro kinase assay and Co-IP for ERK2 in colorectal cells; knockdown/overexpression with pathway readout in PanNET cells\",\n      \"pmids\": [\"30760631\", \"31261148\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"ERK2 finding is from a single lab with a related withdrawn paper, not independently confirmed\", \"Direct kinase activity on pathway components in the PI3K/AKT/mTOR arm not measured\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Validated the spermatogenic role in humans and added a transcriptional regulator, showing STK33 loss-of-function causes MMAF and that NFYB drives STK33 expression in lymphoma.\",\n      \"evidence\": \"Whole-exome sequencing with sperm ultrastructure analysis; ChIP and pathway rescue for NFYB/Hedgehog in DLBCL\",\n      \"pmids\": [\"34155512\", \"34536775\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"MMAF mutation effect on kinase activity not dissected\", \"NFYB-Hedgehog link is single-lab\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Pinpointed AKAP3/AKAP4 as fibrous sheath substrates explaining the sperm tail defect and confirmed STK33 loss causes human non-obstructive azoospermia, unifying the spermiogenesis mechanism.\",\n      \"evidence\": \"Differential phosphoproteomics, in vitro kinase assays, mouse KO/KI models, human mutation identification and sperm structural analysis\",\n      \"pmids\": [\"37146716\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct in vivo demonstration that AKAP3/4 phosphorylation alone drives the phenotype not isolated\", \"Full set of germ-cell substrates not enumerated\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Added chemical-biology tractability and a renal autophagy role, showing STK33 can be degraded by KLHDC2-recruiting PROTACs and that its knockdown activates mTOR/ULK1-dependent autophagy.\",\n      \"evidence\": \"AdPROM E3 ligase screen with endogenously tagged STK33 and PROTAC proof-of-concept; siRNA knockdown with autophagy markers in RCC\",\n      \"pmids\": [\"37591251\", \"37101009\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Autophagy finding is low-confidence single-lab without direct kinase measurement\", \"Whether degrader-based STK33 loss phenocopies genetic loss in vivo untested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Revealed a potential non-catalytic scaffolding role in germ cells, where STK33 is recruited to TSKS foci but does not phosphorylate TSKS or YBX2 in vitro.\",\n      \"evidence\": \"IP/MS, reciprocal Co-IP, proximity ligation assay and in vitro kinase assay (negative for TSKS/YBX2)\",\n      \"pmids\": [\"39909973\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional role of the STK33-TSKS interaction not established\", \"Whether TSKS recruitment is kinase-independent in vivo unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How STK33 kinase activity is regulated in the absence of a canonical calcium/calmodulin binding domain, and which subset of substrates and scaffolding interactions account for its distinct roles across spermiogenesis, tyrosine metabolism, and tumors, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No structural model of activation defined in the corpus\", \"Catalytic versus scaffolding contributions not separated across contexts\", \"Mechanism integrating mTORC1/S6K1, HIF-1α, and c-Myc effects not unified\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [4, 11, 16]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [4, 11, 16]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [8]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [4, 6]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1474165\", \"supporting_discovery_ids\": [8, 16]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [11]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [5, 11]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"VIM\", \"AKAP3\", \"AKAP4\", \"HPD\", \"MYC\", \"HSP90\", \"CDC37\", \"TSKS\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}