{"gene":"CLK4","run_date":"2026-06-09T22:57:18","timeline":{"discoveries":[{"year":2001,"finding":"Human CLK4, when fused to glutathione S-transferase, exhibits dual-specificity kinase activity: it autophosphorylates and phosphorylates myelin basic protein, but does not phosphorylate histone H2B as a substrate.","method":"GST-fusion protein in vitro kinase assay","journal":"Genomics","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro kinase assay with defined substrates, but single lab, single method, no mutagenesis validation","pmids":["11170754"],"is_preprint":false},{"year":2002,"finding":"A novel SR-rich-related protein, Clasp (Clk4-associating SR-related protein), specifically binds the kinase-dead Clk4 K189R mutant but not wild-type Clk4, as shown by two-hybrid screen and in vitro protein interaction assay; overexpression of the long form of Clasp (ClaspL) promotes accumulation of Clk4 K189R in nuclear dots and induces exon EB inclusion from Clk1 pre-mRNA, placing Clasp as a binding partner of inactive Clk4 in the regulation of alternative splicing.","method":"Yeast two-hybrid screen; in vitro protein interaction assay; overexpression with alternative splicing readout","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — two orthogonal methods (two-hybrid + in vitro binding + functional splicing assay), single lab","pmids":["12169693"],"is_preprint":false},{"year":2022,"finding":"Wild-type CLK4 (but not the kinase-dead K189R mutant) phosphorylates the transcription factor MITF at tyrosine Y360; this phosphorylation promotes MITF interaction with E3 ligase COP1 and K63-linked ubiquitination of MITF at K308/K372, leading to sequestosome 1-mediated autophagic degradation of MITF; the deubiquitinase ZRANB1 reverses this ubiquitination and rescues MITF from degradation.","method":"In vitro kinase assay; co-immunoprecipitation; GST pulldown; kinase-dead mutant (K189R); ubiquitination assay; luciferase reporter","journal":"Clinical and translational medicine","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — multiple orthogonal methods (in vitro kinase assay, Co-IP, GST pulldown, kinase-dead mutant), single lab","pmids":["35092699"],"is_preprint":false},{"year":2022,"finding":"CLK4 methionine oxidation at M307 impairs its kinase activity, which is associated with enhanced mitochondrial length and inhibited lipid peroxidation in ESCC cells, indicating CLK4 is a redox-sensitive kinase whose activity is regulated by oxidative modification.","method":"Mass spectrometry; gain/loss-of-function experiments; metabolic profiling","journal":"Clinical and translational medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — mass spectrometry identification of modification site with functional readout, single lab","pmids":["35092699"],"is_preprint":false},{"year":2022,"finding":"RNAi-mediated silencing of CLK4 in mesenchymal-like TNBC cells reduces expression of multiple EMT genes and suppresses TGF-β signaling-induced invasion and cancer stem cell properties, establishing CLK4 as a functional mediator of TGF-β-driven metastatic programs in TNBC.","method":"RNAi knockdown; in vitro invasion assay; mouse xenograft model; pharmacological CLK4 inhibition","journal":"Cancer gene therapy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function with defined cellular and in vivo phenotypes, two orthogonal approaches (RNAi and pharmacological inhibition), single lab","pmids":["35046528"],"is_preprint":false},{"year":2023,"finding":"CLK2 and CLK4 are essential regulators of DNA damage-induced NF-κB activation; small molecule inhibitors of CLK2/4 block signal transmission between ATM/PARP1 and IKKγ without directly inhibiting IKK itself, sensitizing cancer cells to DNA-damaging agents by increasing p53-induced apoptosis.","method":"Multi-kinase panel deconvolution; derivatization of lead compounds; in vitro kinase inhibition; NF-κB activation assays with DNA damage stimuli","journal":"Cell chemical biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — kinase target deconvolution with multiple orthogonal strategies and pathway placement, single lab","pmids":["37506701"],"is_preprint":false},{"year":2023,"finding":"A potent and selective inhibitor of CLK1, 2, and 4 (SGC-CLK-1/CAF-170) reduces serine/arginine-rich (SR) protein phosphorylation and reversibly alters SR protein and CLK2 subcellular localization in cells, directly linking CLK4 (and CLK1/2) activity to SR protein phosphorylation status and nuclear distribution.","method":"Chemical probe (selective inhibitor); phosphorylation assays; subcellular localization imaging; reversibility experiments","journal":"Current research in chemical biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — selective chemical probe with phosphorylation and localization readouts, single lab, CLK4 not fully separated from CLK1/2 effects","pmids":["38009092"],"is_preprint":false},{"year":2025,"finding":"A selective CLK4 inhibitor (compound 150441, IC50 = 21.4 nM) suppresses phosphorylation of splicing factors SRSF4 and SRSF6 in pancreatic cancer cells and induces G2/M cell cycle arrest and apoptosis, with RNA-seq confirming widespread changes in alternative splicing and RNA processing pathways.","method":"In vitro kinase assay; phosphorylation assay; cell viability assay; cell cycle analysis; RNA-seq; structure-based virtual screening","journal":"Advanced science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — selective inhibitor with multiple cellular readouts and transcriptome-wide splicing data, single lab","pmids":["40126184"],"is_preprint":false}],"current_model":"CLK4 is a dual-specificity kinase that phosphorylates SR-rich splicing factors (including SRSF4 and SRSF6) to regulate alternative splicing, phosphorylates MITF at Y360 to trigger its COP1-mediated K63-ubiquitination and autophagic degradation, mediates TGF-β-driven EMT and invasion in breast cancer, and acts as an essential node in DNA damage-induced NF-κB signaling upstream of IKKγ; its activity is modulated by redox-sensitive methionine oxidation (M307), and the SR-related protein Clasp binds specifically to its kinase-dead form to regulate Clk family alternative splicing."},"narrative":{"mechanistic_narrative":"CLK4 is a dual-specificity protein kinase that governs alternative splicing through phosphorylation of serine/arginine-rich (SR) splicing factors and also acts as a signaling node controlling transcription factor turnover and stress-responsive pathways [PMID:11170754, PMID:40126184]. Catalytically, it autophosphorylates and phosphorylates substrates such as myelin basic protein, with kinase activity strictly dependent on the K189 residue [PMID:11170754, PMID:35092699]. Its principal cellular function is the phosphorylation of SR proteins including SRSF4 and SRSF6; selective inhibition of CLK4 reduces SR-protein phosphorylation, alters their nuclear distribution, and produces widespread changes in alternative splicing and RNA processing, coupled to G2/M arrest and apoptosis [PMID:38009092, PMID:40126184]. Beyond splicing, active CLK4 phosphorylates the transcription factor MITF at Y360, promoting its interaction with the E3 ligase COP1, K63-linked ubiquitination, and sequestosome-1-mediated autophagic degradation, a modification reversed by the deubiquitinase ZRANB1 [PMID:35092699]. CLK4 also functions as an essential relay in DNA damage-induced NF-κB activation, transmitting signals between ATM/PARP1 and IKKγ, and it mediates TGF-β-driven EMT, invasion, and cancer stem cell properties in triple-negative breast cancer [PMID:37506701, PMID:35046528]. Its catalytic output is itself redox-tunable: methionine oxidation at M307 impairs kinase activity [PMID:35092699]. The SR-related protein Clasp binds specifically the kinase-dead form of CLK4, linking inactive kinase to regulation of Clk-family alternative splicing [PMID:12169693].","teleology":[{"year":2001,"claim":"Established that human CLK4 is an enzymatically active dual-specificity kinase, defining its basic catalytic capacity and substrate selectivity.","evidence":"GST-fusion in vitro kinase assay with myelin basic protein and histone H2B as candidate substrates","pmids":["11170754"],"confidence":"Medium","gaps":["No physiological substrate identified","Single method, no mutagenesis validation","Catalytic residues not mapped"]},{"year":2002,"claim":"Identified Clasp as a partner that selectively engages the inactive (kinase-dead) form of CLK4, suggesting kinase state controls splicing-regulatory complex assembly.","evidence":"Yeast two-hybrid screen plus in vitro binding and an overexpression alternative splicing readout on Clk1 pre-mRNA","pmids":["12169693"],"confidence":"Medium","gaps":["Mechanism of state-selective binding unknown","Functional consequence shown only on overexpression","Single lab"]},{"year":2022,"claim":"Defined a non-splicing substrate axis in which active CLK4 phosphorylates MITF at Y360 to drive its ubiquitin- and autophagy-dependent degradation, with redox modification tuning kinase output.","evidence":"In vitro kinase assay, Co-IP, GST pulldown, K189R kinase-dead mutant, ubiquitination assays, plus mass spectrometry of M307 oxidation with metabolic readouts in ESCC cells","pmids":["35092699"],"confidence":"High","gaps":["Single lab","Physiological trigger of M307 oxidation undefined","Direct kinase-substrate contact at Y360 not structurally resolved"]},{"year":2022,"claim":"Placed CLK4 functionally within TGF-β-driven metastatic programs, linking its activity to EMT and invasion in TNBC.","evidence":"RNAi knockdown, in vitro invasion assays, mouse xenograft, and pharmacological CLK4 inhibition","pmids":["35046528"],"confidence":"Medium","gaps":["Direct CLK4 substrates in the TGF-β pathway not identified","Mechanistic link between kinase activity and EMT gene expression unresolved"]},{"year":2023,"claim":"Positioned CLK2/CLK4 as essential transducers in DNA damage-induced NF-κB activation, identifying a signaling step between ATM/PARP1 and IKKγ.","evidence":"Multi-kinase panel deconvolution, inhibitor derivatization, in vitro kinase inhibition, and NF-κB activation assays under DNA damage","pmids":["37506701"],"confidence":"Medium","gaps":["Direct CLK4 substrate in the NF-κB relay not identified","CLK4 contribution not fully separated from CLK2"]},{"year":2023,"claim":"Used a selective chemical probe to causally link CLK4 (with CLK1/2) activity to SR-protein phosphorylation status and nuclear localization.","evidence":"Selective inhibitor (SGC-CLK-1/CAF-170), phosphorylation assays, subcellular localization imaging, reversibility tests","pmids":["38009092"],"confidence":"Medium","gaps":["CLK4 effects not separated from CLK1/2","Specific SR substrates of CLK4 not delineated here"]},{"year":2025,"claim":"Demonstrated with a CLK4-selective inhibitor that CLK4 phosphorylates SRSF4/SRSF6 to control alternative splicing, coupling its kinase activity to cell cycle and survival outcomes.","evidence":"Selective inhibitor (compound 150441), in vitro kinase and phosphorylation assays, cell cycle and viability analysis, RNA-seq in pancreatic cancer cells","pmids":["40126184"],"confidence":"Medium","gaps":["Direct phosphosites on SRSF4/SRSF6 not mapped","Single lab","Causal splicing events driving phenotype not isolated"]},{"year":null,"claim":"How CLK4's distinct functions — SR-protein-directed splicing, MITF degradation, TGF-β/EMT, and DNA-damage NF-κB signaling — are coordinated, and whether common direct substrates or regulatory inputs unify them, remains unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structural model of substrate engagement","Substrate repertoire incompletely defined","Cross-talk between splicing and signaling roles unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,2,6,7]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,2,7]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[1,6]}],"pathway":[{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[6,7]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[4,5]}],"complexes":[],"partners":["CLASP","MITF","COP1","ZRANB1","SRSF4","SRSF6"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9HAZ1","full_name":"Dual specificity protein kinase CLK4","aliases":["CDC-like kinase 4"],"length_aa":481,"mass_kda":57.5,"function":"Dual specificity kinase acting on both serine/threonine and tyrosine-containing substrates. Phosphorylates serine- and arginine-rich (SR) proteins of the spliceosomal complex and may be a constituent of a network of regulatory mechanisms that enable SR proteins to control RNA splicing. Phosphorylates SRSF1 and SRSF3. Required for the regulation of alternative splicing of MAPT/TAU. Regulates the alternative splicing of tissue factor (F3) pre-mRNA in endothelial cells","subcellular_location":"Nucleus","url":"https://www.uniprot.org/uniprotkb/Q9HAZ1/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CLK4","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/CLK4","total_profiled":1310},"omim":[{"mim_id":"618532","title":"CLK4-ASSOCIATING SERINE/ARGININE-RICH PROTEIN; CLASRP","url":"https://www.omim.org/entry/618532"},{"mim_id":"607969","title":"CDC-LIKE KINASE 4; CLK4","url":"https://www.omim.org/entry/607969"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Actin filaments","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/CLK4"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"Q9HAZ1","domains":[{"cath_id":"3.30.200.20","chopping":"141-239","consensus_level":"high","plddt":95.0831,"start":141,"end":239},{"cath_id":"1.10.510.10","chopping":"243-479","consensus_level":"high","plddt":96.2001,"start":243,"end":479}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9HAZ1","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9HAZ1-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9HAZ1-F1-predicted_aligned_error_v6.png","plddt_mean":79.06},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CLK4","jax_strain_url":"https://www.jax.org/strain/search?query=CLK4"},"sequence":{"accession":"Q9HAZ1","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9HAZ1.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9HAZ1/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9HAZ1"}},"corpus_meta":[{"pmid":"23496085","id":"PMC_23496085","title":"Pharmacophore and 3D-QSAR characterization of 6-arylquinazolin-4-amines as Cdc2-like kinase 4 (Clk4) and dual specificity tyrosine-phosphorylation-regulated kinase 1A (Dyrk1A) inhibitors.","date":"2013","source":"Journal of chemical information and modeling","url":"https://pubmed.ncbi.nlm.nih.gov/23496085","citation_count":25,"is_preprint":false},{"pmid":"35046528","id":"PMC_35046528","title":"Targeting CLK4 inhibits the metastasis and progression of breast cancer by inactivating TGF-β pathway.","date":"2022","source":"Cancer gene therapy","url":"https://pubmed.ncbi.nlm.nih.gov/35046528","citation_count":19,"is_preprint":false},{"pmid":"12169693","id":"PMC_12169693","title":"Novel SR-rich-related protein clasp specifically interacts with inactivated Clk4 and induces the exon EB inclusion of Clk.","date":"2002","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/12169693","citation_count":16,"is_preprint":false},{"pmid":"35424985","id":"PMC_35424985","title":"Discovery of new Cdc2-like kinase 4 (CLK4) inhibitors via pharmacophore exploration combined with flexible docking-based ligand/receptor contact fingerprints and machine learning.","date":"2022","source":"RSC advances","url":"https://pubmed.ncbi.nlm.nih.gov/35424985","citation_count":14,"is_preprint":false},{"pmid":"35092699","id":"PMC_35092699","title":"Methionine oxidation of CLK4 promotes the metabolic switch and redox homeostasis in esophageal carcinoma via inhibiting MITF selective autophagy.","date":"2022","source":"Clinical and translational medicine","url":"https://pubmed.ncbi.nlm.nih.gov/35092699","citation_count":13,"is_preprint":false},{"pmid":"37506701","id":"PMC_37506701","title":"CLK2 and CLK4 are regulators of DNA damage-induced NF-κB targeted by novel small molecule inhibitors.","date":"2023","source":"Cell chemical biology","url":"https://pubmed.ncbi.nlm.nih.gov/37506701","citation_count":9,"is_preprint":false},{"pmid":"11170754","id":"PMC_11170754","title":"Molecular characterization of a cDNA encoding functional human CLK4 kinase and localization to chromosome 5q35 [correction of 4q35].","date":"2001","source":"Genomics","url":"https://pubmed.ncbi.nlm.nih.gov/11170754","citation_count":9,"is_preprint":false},{"pmid":"40126184","id":"PMC_40126184","title":"Identification and Biological Evaluation of a Novel CLK4 Inhibitor Targeting Alternative Splicing in Pancreatic Cancer Using Structure-Based Virtual Screening.","date":"2025","source":"Advanced science (Weinheim, Baden-Wurttemberg, Germany)","url":"https://pubmed.ncbi.nlm.nih.gov/40126184","citation_count":7,"is_preprint":false},{"pmid":"38478964","id":"PMC_38478964","title":"N1-Benzoylated 5-(4-pyridinyl)indazole-based kinase inhibitors: Attaining haspin and Clk4 selectivity via modulation of the benzoyl substituents.","date":"2024","source":"Archiv der Pharmazie","url":"https://pubmed.ncbi.nlm.nih.gov/38478964","citation_count":4,"is_preprint":false},{"pmid":"38009092","id":"PMC_38009092","title":"SGC-CLK-1: A chemical probe for the Cdc2-like kinases CLK1, CLK2, and CLK4.","date":"2023","source":"Current research in chemical biology","url":"https://pubmed.ncbi.nlm.nih.gov/38009092","citation_count":4,"is_preprint":false},{"pmid":"39430953","id":"PMC_39430953","title":"Design, synthesis, and structure-activity relationship studies of 6H-benzo[b]indeno[1,2-d]thiophen-6-one derivatives as DYRK1A/CLK1/CLK4/haspin inhibitors.","date":"2024","source":"RSC medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/39430953","citation_count":2,"is_preprint":false},{"pmid":"40464177","id":"PMC_40464177","title":"Novel Pyrrolopyrimidines as Inhibitors of CLK4 and HER2: Targeting Promising Anticancer Pathways.","date":"2025","source":"Medicinal chemistry (Shariqah (United Arab Emirates))","url":"https://pubmed.ncbi.nlm.nih.gov/40464177","citation_count":1,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":7930,"output_tokens":2054,"usd":0.0273,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9041,"output_tokens":2847,"usd":0.05819,"stage2_stop_reason":"end_turn"},"total_usd":0.08549,"stage1_batch_id":"msgbatch_01ACAxJQabDsht39JXeWG22d","stage2_batch_id":"msgbatch_01QEU22A9U5sbPTgsMzTmvSf","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2001,\n      \"finding\": \"Human CLK4, when fused to glutathione S-transferase, exhibits dual-specificity kinase activity: it autophosphorylates and phosphorylates myelin basic protein, but does not phosphorylate histone H2B as a substrate.\",\n      \"method\": \"GST-fusion protein in vitro kinase assay\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro kinase assay with defined substrates, but single lab, single method, no mutagenesis validation\",\n      \"pmids\": [\"11170754\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"A novel SR-rich-related protein, Clasp (Clk4-associating SR-related protein), specifically binds the kinase-dead Clk4 K189R mutant but not wild-type Clk4, as shown by two-hybrid screen and in vitro protein interaction assay; overexpression of the long form of Clasp (ClaspL) promotes accumulation of Clk4 K189R in nuclear dots and induces exon EB inclusion from Clk1 pre-mRNA, placing Clasp as a binding partner of inactive Clk4 in the regulation of alternative splicing.\",\n      \"method\": \"Yeast two-hybrid screen; in vitro protein interaction assay; overexpression with alternative splicing readout\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two orthogonal methods (two-hybrid + in vitro binding + functional splicing assay), single lab\",\n      \"pmids\": [\"12169693\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Wild-type CLK4 (but not the kinase-dead K189R mutant) phosphorylates the transcription factor MITF at tyrosine Y360; this phosphorylation promotes MITF interaction with E3 ligase COP1 and K63-linked ubiquitination of MITF at K308/K372, leading to sequestosome 1-mediated autophagic degradation of MITF; the deubiquitinase ZRANB1 reverses this ubiquitination and rescues MITF from degradation.\",\n      \"method\": \"In vitro kinase assay; co-immunoprecipitation; GST pulldown; kinase-dead mutant (K189R); ubiquitination assay; luciferase reporter\",\n      \"journal\": \"Clinical and translational medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — multiple orthogonal methods (in vitro kinase assay, Co-IP, GST pulldown, kinase-dead mutant), single lab\",\n      \"pmids\": [\"35092699\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CLK4 methionine oxidation at M307 impairs its kinase activity, which is associated with enhanced mitochondrial length and inhibited lipid peroxidation in ESCC cells, indicating CLK4 is a redox-sensitive kinase whose activity is regulated by oxidative modification.\",\n      \"method\": \"Mass spectrometry; gain/loss-of-function experiments; metabolic profiling\",\n      \"journal\": \"Clinical and translational medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — mass spectrometry identification of modification site with functional readout, single lab\",\n      \"pmids\": [\"35092699\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"RNAi-mediated silencing of CLK4 in mesenchymal-like TNBC cells reduces expression of multiple EMT genes and suppresses TGF-β signaling-induced invasion and cancer stem cell properties, establishing CLK4 as a functional mediator of TGF-β-driven metastatic programs in TNBC.\",\n      \"method\": \"RNAi knockdown; in vitro invasion assay; mouse xenograft model; pharmacological CLK4 inhibition\",\n      \"journal\": \"Cancer gene therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function with defined cellular and in vivo phenotypes, two orthogonal approaches (RNAi and pharmacological inhibition), single lab\",\n      \"pmids\": [\"35046528\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CLK2 and CLK4 are essential regulators of DNA damage-induced NF-κB activation; small molecule inhibitors of CLK2/4 block signal transmission between ATM/PARP1 and IKKγ without directly inhibiting IKK itself, sensitizing cancer cells to DNA-damaging agents by increasing p53-induced apoptosis.\",\n      \"method\": \"Multi-kinase panel deconvolution; derivatization of lead compounds; in vitro kinase inhibition; NF-κB activation assays with DNA damage stimuli\",\n      \"journal\": \"Cell chemical biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — kinase target deconvolution with multiple orthogonal strategies and pathway placement, single lab\",\n      \"pmids\": [\"37506701\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"A potent and selective inhibitor of CLK1, 2, and 4 (SGC-CLK-1/CAF-170) reduces serine/arginine-rich (SR) protein phosphorylation and reversibly alters SR protein and CLK2 subcellular localization in cells, directly linking CLK4 (and CLK1/2) activity to SR protein phosphorylation status and nuclear distribution.\",\n      \"method\": \"Chemical probe (selective inhibitor); phosphorylation assays; subcellular localization imaging; reversibility experiments\",\n      \"journal\": \"Current research in chemical biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — selective chemical probe with phosphorylation and localization readouts, single lab, CLK4 not fully separated from CLK1/2 effects\",\n      \"pmids\": [\"38009092\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"A selective CLK4 inhibitor (compound 150441, IC50 = 21.4 nM) suppresses phosphorylation of splicing factors SRSF4 and SRSF6 in pancreatic cancer cells and induces G2/M cell cycle arrest and apoptosis, with RNA-seq confirming widespread changes in alternative splicing and RNA processing pathways.\",\n      \"method\": \"In vitro kinase assay; phosphorylation assay; cell viability assay; cell cycle analysis; RNA-seq; structure-based virtual screening\",\n      \"journal\": \"Advanced science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — selective inhibitor with multiple cellular readouts and transcriptome-wide splicing data, single lab\",\n      \"pmids\": [\"40126184\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CLK4 is a dual-specificity kinase that phosphorylates SR-rich splicing factors (including SRSF4 and SRSF6) to regulate alternative splicing, phosphorylates MITF at Y360 to trigger its COP1-mediated K63-ubiquitination and autophagic degradation, mediates TGF-β-driven EMT and invasion in breast cancer, and acts as an essential node in DNA damage-induced NF-κB signaling upstream of IKKγ; its activity is modulated by redox-sensitive methionine oxidation (M307), and the SR-related protein Clasp binds specifically to its kinase-dead form to regulate Clk family alternative splicing.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"CLK4 is a dual-specificity protein kinase that governs alternative splicing through phosphorylation of serine/arginine-rich (SR) splicing factors and also acts as a signaling node controlling transcription factor turnover and stress-responsive pathways [#0, #7]. Catalytically, it autophosphorylates and phosphorylates substrates such as myelin basic protein, with kinase activity strictly dependent on the K189 residue [#0, #2]. Its principal cellular function is the phosphorylation of SR proteins including SRSF4 and SRSF6; selective inhibition of CLK4 reduces SR-protein phosphorylation, alters their nuclear distribution, and produces widespread changes in alternative splicing and RNA processing, coupled to G2/M arrest and apoptosis [#6, #7]. Beyond splicing, active CLK4 phosphorylates the transcription factor MITF at Y360, promoting its interaction with the E3 ligase COP1, K63-linked ubiquitination, and sequestosome-1-mediated autophagic degradation, a modification reversed by the deubiquitinase ZRANB1 [#2]. CLK4 also functions as an essential relay in DNA damage-induced NF-\\u03baB activation, transmitting signals between ATM/PARP1 and IKK\\u03b3, and it mediates TGF-\\u03b2-driven EMT, invasion, and cancer stem cell properties in triple-negative breast cancer [#5, #4]. Its catalytic output is itself redox-tunable: methionine oxidation at M307 impairs kinase activity [#3]. The SR-related protein Clasp binds specifically the kinase-dead form of CLK4, linking inactive kinase to regulation of Clk-family alternative splicing [#1].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Established that human CLK4 is an enzymatically active dual-specificity kinase, defining its basic catalytic capacity and substrate selectivity.\",\n      \"evidence\": \"GST-fusion in vitro kinase assay with myelin basic protein and histone H2B as candidate substrates\",\n      \"pmids\": [\"11170754\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"No physiological substrate identified\", \"Single method, no mutagenesis validation\", \"Catalytic residues not mapped\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Identified Clasp as a partner that selectively engages the inactive (kinase-dead) form of CLK4, suggesting kinase state controls splicing-regulatory complex assembly.\",\n      \"evidence\": \"Yeast two-hybrid screen plus in vitro binding and an overexpression alternative splicing readout on Clk1 pre-mRNA\",\n      \"pmids\": [\"12169693\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Mechanism of state-selective binding unknown\", \"Functional consequence shown only on overexpression\", \"Single lab\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defined a non-splicing substrate axis in which active CLK4 phosphorylates MITF at Y360 to drive its ubiquitin- and autophagy-dependent degradation, with redox modification tuning kinase output.\",\n      \"evidence\": \"In vitro kinase assay, Co-IP, GST pulldown, K189R kinase-dead mutant, ubiquitination assays, plus mass spectrometry of M307 oxidation with metabolic readouts in ESCC cells\",\n      \"pmids\": [\"35092699\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Single lab\", \"Physiological trigger of M307 oxidation undefined\", \"Direct kinase-substrate contact at Y360 not structurally resolved\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Placed CLK4 functionally within TGF-\\u03b2-driven metastatic programs, linking its activity to EMT and invasion in TNBC.\",\n      \"evidence\": \"RNAi knockdown, in vitro invasion assays, mouse xenograft, and pharmacological CLK4 inhibition\",\n      \"pmids\": [\"35046528\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Direct CLK4 substrates in the TGF-\\u03b2 pathway not identified\", \"Mechanistic link between kinase activity and EMT gene expression unresolved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Positioned CLK2/CLK4 as essential transducers in DNA damage-induced NF-\\u03baB activation, identifying a signaling step between ATM/PARP1 and IKK\\u03b3.\",\n      \"evidence\": \"Multi-kinase panel deconvolution, inhibitor derivatization, in vitro kinase inhibition, and NF-\\u03baB activation assays under DNA damage\",\n      \"pmids\": [\"37506701\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Direct CLK4 substrate in the NF-\\u03baB relay not identified\", \"CLK4 contribution not fully separated from CLK2\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Used a selective chemical probe to causally link CLK4 (with CLK1/2) activity to SR-protein phosphorylation status and nuclear localization.\",\n      \"evidence\": \"Selective inhibitor (SGC-CLK-1/CAF-170), phosphorylation assays, subcellular localization imaging, reversibility tests\",\n      \"pmids\": [\"38009092\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"CLK4 effects not separated from CLK1/2\", \"Specific SR substrates of CLK4 not delineated here\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Demonstrated with a CLK4-selective inhibitor that CLK4 phosphorylates SRSF4/SRSF6 to control alternative splicing, coupling its kinase activity to cell cycle and survival outcomes.\",\n      \"evidence\": \"Selective inhibitor (compound 150441), in vitro kinase and phosphorylation assays, cell cycle and viability analysis, RNA-seq in pancreatic cancer cells\",\n      \"pmids\": [\"40126184\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Direct phosphosites on SRSF4/SRSF6 not mapped\", \"Single lab\", \"Causal splicing events driving phenotype not isolated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How CLK4's distinct functions \\u2014 SR-protein-directed splicing, MITF degradation, TGF-\\u03b2/EMT, and DNA-damage NF-\\u03baB signaling \\u2014 are coordinated, and whether common direct substrates or regulatory inputs unify them, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"No structural model of substrate engagement\", \"Substrate repertoire incompletely defined\", \"Cross-talk between splicing and signaling roles unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 2, 6, 7]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 2, 7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [1, 6]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [6, 7]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [4, 5]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"Clasp\", \"MITF\", \"COP1\", \"ZRANB1\", \"SRSF4\", \"SRSF6\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":7,"faith_pct":85.71428571428571}}