{"gene":"STK36","run_date":"2026-06-10T10:51:54","timeline":{"discoveries":[{"year":1996,"finding":"Drosophila fused (fu) is required to transmit the Hedgehog (Hh) signal in imaginal discs; fu mutations rescue phenotypes caused by ectopic hh expression or loss of patched (ptc) activity, placing fu genetically downstream of hh and ptc in the pathway controlling dpp expression. fu is also required for engrailed activation downstream of Hh, but fu mutations do not rescue phenotypes caused by abnormal ci, cos-2, or pkA activity, indicating fu acts in the same pathway as these components but is not epistatic to them.","method":"Genetic epistasis analysis using Drosophila imaginal disc mutations and ectopic Hh expression","journal":"Mechanisms of development","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean genetic epistasis across multiple allele combinations, replicated across several pathway components in a single rigorous study","pmids":["8861096"],"is_preprint":false},{"year":2004,"finding":"The human FU gene (STK36) encodes at least two protein isoforms arising from alternative splicing, including a long form and a shorter isoform. The long FU isoform enhances GLI2-induced transcriptional activity but does not affect GLI1-induced transcription. FU did not reverse SUFU-mediated inhibition of GLI.","method":"RT-PCR/nested PCR to characterize splice isoforms; transient overexpression with luciferase transcriptional reporter assays for GLI1 and GLI2 activity","journal":"BMC genomics","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — transient overexpression reporter assay, single lab, two isoforms tested with two GLI targets","pmids":["15268766"],"is_preprint":false},{"year":2007,"finding":"Mouse Fu (Stk36) can enhance Gli-induced transcription in transient overexpression assays similarly to human FU. In one cell line where mFu expression was reduced by RNAi, Hedgehog signaling was severely impaired, indicating mFu may have a role in Hedgehog signaling and Gli regulation in certain cellular contexts.","method":"cDNA cloning of mouse Fu; transient overexpression with Gli transcriptional reporter; RNAi knockdown with Hedgehog signaling readout","journal":"Journal of cell communication and signaling","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single RNAi experiment in one cell line, overexpression reporter assay without mutagenesis","pmids":["18600476"],"is_preprint":false},{"year":2013,"finding":"Mouse Fused (Stk36) is required for central pair (CP) apparatus assembly and proper cilia orientation in motile cilia of the oviductal epithelium. Fu-deficient mouse oviducts show defects in CP construction and cilia orientation. Fu protein localizes to motile cilia and physically associates with kinesin Kif27 at the cilium base and with known central pair components Spag16 and Pcdp1.","method":"Conditional knockout mouse analysis (Fu-deficient); transmission electron microscopy of oviductal cilia ultrastructure; immunofluorescence localization; co-immunoprecipitation of Fu with Kif27, Spag16, and Pcdp1","journal":"Developmental dynamics : an official publication of the American Association of Anatomists","confidence":"High","confidence_rationale":"Tier 2 / Strong — knockout phenotype with ultrastructural readout, direct localization by immunofluorescence, and reciprocal Co-IP with multiple binding partners in a single study","pmids":["23907739"],"is_preprint":false},{"year":2014,"finding":"The E3 ubiquitin ligase MID1 catalyzes ubiquitination and proteasomal cleavage of Fu (STK36). MID1-mediated ubiquitination and cleavage of Fu is identified as a key element connecting the MID1-PP2A protein complex to GLI3 activity control in SHH-GLI signaling.","method":"Biochemical ubiquitination assays; proteasomal cleavage assays; interaction studies between MID1 and Fu in cancer cell lines with autonomous SHH signaling","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro/cell-based ubiquitination and cleavage assays with defined enzymatic reaction, single lab but multiple biochemical methods","pmids":["25278022"],"is_preprint":false},{"year":2017,"finding":"Homozygous loss-of-function mutations in STK36 cause primary ciliary dyskinesia (PCD) with a central pair defect in a human patient with situs solitus. Transmission electron microscopy of respiratory epithelial cells from the affected individual demonstrates that STK36 is required for cilia orientation, with a probable localization of STK36 between the radial spokes and central pair of the ciliary axoneme.","method":"Whole-exome/gene sequencing identifying homozygous STK36 mutations; transmission electron microscopy of respiratory epithelial cilia ultrastructure","journal":"Human mutation","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — human loss-of-function (natural mutation) with ultrastructural ciliary phenotype, single patient/family, no functional rescue experiment","pmids":["28543983"],"is_preprint":false}],"current_model":"STK36 (Fused) is a serine-threonine kinase that functions as a positive regulator of Hedgehog signaling — acting downstream of Patched and upstream of or parallel to Costal-2/Cubitus interruptus in Drosophila — and in mammals serves as a critical component of motile cilia biogenesis, where it physically associates with kinesin Kif27 and central pair proteins Spag16/Pcdp1 to assemble the central pair apparatus and orient cilia; its activity is regulated by the E3 ligase MID1, which ubiquitinates and cleaves Fu to modulate GLI3 transcriptional output, and loss-of-function mutations in humans cause primary ciliary dyskinesia with central pair defects."},"narrative":{"mechanistic_narrative":"STK36, the mammalian ortholog of Drosophila Fused, is a serine-threonine kinase with dual roles spanning Hedgehog signal transduction and motile cilia assembly [PMID:8861096, PMID:23907739]. In Drosophila, fused acts genetically downstream of Hedgehog and Patched to transmit the Hh signal controlling dpp and engrailed expression, operating within the same pathway as Costal-2, Cubitus interruptus, and PKA without being epistatic to them [PMID:8861096]. In mammals, STK36 enhances GLI-induced transcription, with the long human isoform selectively potentiating GLI2 activity, and its loss impairs Hedgehog signaling output [PMID:15268766]. Its transcriptional contribution is controlled by the E3 ubiquitin ligase MID1, which ubiquitinates and proteasomally cleaves Fu to couple the MID1-PP2A complex to GLI3 regulation [PMID:25278022]. Independently of its signaling role, STK36 is required for assembly of the central pair apparatus and orientation of motile cilia, localizing to motile cilia where it physically associates with the kinesin Kif27 at the cilium base and with central pair components Spag16 and Pcdp1 [PMID:23907739]. Homozygous loss-of-function mutations in STK36 cause primary ciliary dyskinesia with a central pair defect, with the protein localizing between the radial spokes and central pair of the axoneme [PMID:28543983].","teleology":[{"year":1996,"claim":"Established that Fused operates within the Hedgehog pathway to transmit the signal, fixing its genetic position downstream of Hh and Patched and clarifying its relationship to Costal-2, Ci, and PKA.","evidence":"Genetic epistasis using Drosophila imaginal disc mutations and ectopic Hh expression","pmids":["8861096"],"confidence":"High","gaps":["Does not identify direct biochemical substrates of the kinase","Pathway position relative to Ci/Cos-2 left unresolved (same pathway but not epistatic)","No mammalian generalization addressed"]},{"year":2004,"claim":"Showed the human ortholog STK36 retains a transcriptional function, with isoform-specific potentiation of GLI2 but not GLI1, indicating the Drosophila signaling role extends to mammals at the level of GLI effectors.","evidence":"Splice isoform characterization by RT-PCR and luciferase reporter assays for GLI1/GLI2 in transient overexpression","pmids":["15268766"],"confidence":"Medium","gaps":["Overexpression reporter assay only, no endogenous validation","Mechanism of GLI2-selective enhancement unknown","Did not reverse SUFU-mediated GLI inhibition, leaving the regulatory node undefined"]},{"year":2007,"claim":"Extended GLI-enhancing activity to mouse Fu and provided loss-of-function support for a Hedgehog role in a cellular context.","evidence":"Mouse Fu cDNA cloning, Gli reporter overexpression, and RNAi knockdown in one cell line","pmids":["18600476"],"confidence":"Low","gaps":["Single RNAi experiment in one cell line without rescue or mutagenesis","Context-dependence of the Hedgehog requirement not delineated","No biochemical mechanism established"]},{"year":2013,"claim":"Revealed a Hedgehog-independent function for Fu in motile cilia, identifying it as essential for central pair assembly and cilia orientation and naming its direct structural partners.","evidence":"Conditional knockout mouse oviduct analysis, TEM of ciliary ultrastructure, immunofluorescence, and reciprocal Co-IP with Kif27, Spag16, and Pcdp1","pmids":["23907739"],"confidence":"High","gaps":["Whether kinase catalytic activity is required for central pair assembly not tested","Order of recruitment of Kif27/Spag16/Pcdp1 unresolved","Relationship between ciliary and Hedgehog roles not reconciled"]},{"year":2014,"claim":"Defined how Fu protein levels are controlled, showing MID1 ubiquitinates and cleaves Fu to link the MID1-PP2A complex to GLI3 transcriptional output.","evidence":"Biochemical ubiquitination and proteasomal cleavage assays and MID1-Fu interaction studies in SHH-active cancer cells","pmids":["25278022"],"confidence":"High","gaps":["Functional consequence of Fu cleavage products not characterized","Whether this regulation operates in cilia as well as signaling unknown","In vivo relevance of MID1-Fu axis not established"]},{"year":2017,"claim":"Connected STK36 loss directly to human disease, demonstrating that loss-of-function mutations cause primary ciliary dyskinesia with a central pair defect.","evidence":"Gene sequencing identifying homozygous STK36 mutations and TEM of respiratory epithelial cilia in an affected individual","pmids":["28543983"],"confidence":"Medium","gaps":["Single patient/family with no functional rescue experiment","Precise axonemal position inferred, not directly mapped","Genotype-phenotype spectrum across patients undefined"]},{"year":null,"claim":"The catalytic substrates of STK36 kinase activity in both Hedgehog signaling and central pair assembly remain unidentified, leaving the mechanistic link between its enzymatic function and its two cellular roles open.","evidence":"No direct substrate identification in the available corpus","pmids":[],"confidence":"Low","gaps":["No phosphorylation substrate identified","Whether kinase activity is required for ciliary versus signaling functions untested","Structural basis of partner binding unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,3]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[1,2]}],"localization":[{"term_id":"GO:0005929","term_label":"cilium","supporting_discovery_ids":[3,5]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,1,4]},{"term_id":"R-HSA-1852241","term_label":"Organelle biogenesis and maintenance","supporting_discovery_ids":[3,5]}],"complexes":["central pair apparatus"],"partners":["KIF27","SPAG16","PCDP1","MID1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9NRP7","full_name":"Serine/threonine-protein kinase 36","aliases":["Fused homolog"],"length_aa":1315,"mass_kda":144.0,"function":"Serine/threonine protein kinase which plays an important role in the sonic hedgehog (Shh) pathway by regulating the activity of GLI transcription factors (PubMed:10806483). Controls the activity of the transcriptional regulators GLI1, GLI2 and GLI3 by opposing the effect of SUFU and promoting their nuclear localization (PubMed:10806483). GLI2 requires an additional function of STK36 to become transcriptionally active, but the enzyme does not need to possess an active kinase catalytic site for this to occur (PubMed:10806483). Required for postnatal development, possibly by regulating the homeostasis of cerebral spinal fluid or ciliary function. Essential for construction of the central pair apparatus of motile cilia","subcellular_location":"Cytoplasm; Nucleus; Cytoplasm, cytoskeleton, cilium axoneme","url":"https://www.uniprot.org/uniprotkb/Q9NRP7/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/STK36","classification":"Not Classified","n_dependent_lines":3,"n_total_lines":1208,"dependency_fraction":0.0024834437086092716},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/STK36","total_profiled":1310},"omim":[{"mim_id":"619436","title":"CILIARY DYSKINESIA, PRIMARY, 46; CILD46","url":"https://www.omim.org/entry/619436"},{"mim_id":"613472","title":"UNC51-LIKE KINASE 3; ULK3","url":"https://www.omim.org/entry/613472"},{"mim_id":"607652","title":"SERINE/THREONINE PROTEIN KINASE 36; STK36","url":"https://www.omim.org/entry/607652"},{"mim_id":"244400","title":"CILIARY DYSKINESIA, PRIMARY, 1; CILD1","url":"https://www.omim.org/entry/244400"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Cytosol","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/STK36"},"hgnc":{"alias_symbol":["KIAA1278","FU"],"prev_symbol":[]},"alphafold":{"accession":"Q9NRP7","domains":[{"cath_id":"3.30.200.20","chopping":"5-82","consensus_level":"high","plddt":88.1782,"start":5,"end":82},{"cath_id":"1.10.510.10","chopping":"85-293","consensus_level":"medium","plddt":88.8223,"start":85,"end":293}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NRP7","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9NRP7-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9NRP7-F1-predicted_aligned_error_v6.png","plddt_mean":80.88},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=STK36","jax_strain_url":"https://www.jax.org/strain/search?query=STK36"},"sequence":{"accession":"Q9NRP7","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9NRP7.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9NRP7/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NRP7"}},"corpus_meta":[{"pmid":"16709241","id":"PMC_16709241","title":"Cellular 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treatment with 5-FU and cooperates with vitamin D analogue PRI-2191 in the downregulation of expression of stemness-related genes in 5-FU refractory cells.","date":"2019","source":"The Journal of steroid biochemistry and molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/30772447","citation_count":16,"is_preprint":false},{"pmid":"33860796","id":"PMC_33860796","title":"HDAC6 inhibitor WT161 performs anti-tumor effect on osteosarcoma and synergistically interacts with 5-FU.","date":"2021","source":"Bioscience reports","url":"https://pubmed.ncbi.nlm.nih.gov/33860796","citation_count":16,"is_preprint":false},{"pmid":"35670088","id":"PMC_35670088","title":"Effects of Fu's subcutaneous needling on mitochondrial structure and function in rats with sciatica.","date":"2022","source":"Molecular pain","url":"https://pubmed.ncbi.nlm.nih.gov/35670088","citation_count":15,"is_preprint":false},{"pmid":"32742490","id":"PMC_32742490","title":"Combinational inhibition of EGFR and YAP reverses 5-Fu resistance in colorectal cancer.","date":"2020","source":"Journal of Cancer","url":"https://pubmed.ncbi.nlm.nih.gov/32742490","citation_count":15,"is_preprint":false},{"pmid":"19714313","id":"PMC_19714313","title":"Enhanced cytotoxicity of 5-FU by bFGF through up-regulation of uridine phosphorylase 1.","date":"2009","source":"Molecules and cells","url":"https://pubmed.ncbi.nlm.nih.gov/19714313","citation_count":15,"is_preprint":false},{"pmid":"27648358","id":"PMC_27648358","title":"Targeting PCDH20 gene by microRNA-122 confers 5-FU resistance in hepatic carcinoma.","date":"2016","source":"American journal of cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/27648358","citation_count":15,"is_preprint":false},{"pmid":"38215891","id":"PMC_38215891","title":"5-FU promotes HBV replication through oxidative stress-induced autophagy dysfunction.","date":"2024","source":"Free radical biology & 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screening for DPD-deficiency in patients treated with 5-FU, capecitabine (and tegafur).","date":"2021","source":"Acta clinica Belgica","url":"https://pubmed.ncbi.nlm.nih.gov/33423619","citation_count":14,"is_preprint":false},{"pmid":"31799650","id":"PMC_31799650","title":"MiR-335 promotes cell proliferation by inhibiting MEF2D and sensitizes cells to 5-Fu treatment in gallbladder carcinoma.","date":"2019","source":"European review for medical and pharmacological sciences","url":"https://pubmed.ncbi.nlm.nih.gov/31799650","citation_count":14,"is_preprint":false},{"pmid":"40414047","id":"PMC_40414047","title":"Pectolinarigenin mitigates 5-FU-induced intestinal mucositis via suppressing ferroptosis through activating PPARγ/GPX4 signaling.","date":"2025","source":"Phytomedicine : international journal of phytotherapy and phytopharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/40414047","citation_count":13,"is_preprint":false},{"pmid":"40487654","id":"PMC_40487654","title":"Targeting the JAK2-STAT3-UCHL3-ENO1 axis suppresses glycolysis and enhances the sensitivity to 5-FU chemotherapy in TP53-mutant colorectal cancer.","date":"2025","source":"Acta pharmaceutica Sinica. B","url":"https://pubmed.ncbi.nlm.nih.gov/40487654","citation_count":13,"is_preprint":false},{"pmid":"40082673","id":"PMC_40082673","title":"KLF6-mediated recruitment of the p300 complex enhances H3K23su and cooperatively upregulates SEMA3C with FOSL2 to drive 5-FU resistance in colon cancer cells.","date":"2025","source":"Experimental & molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/40082673","citation_count":13,"is_preprint":false},{"pmid":"36297411","id":"PMC_36297411","title":"Synthesis and Chemopreventive Potential of 5-FU/Genistein Hybrids on Colorectal Cancer Cells.","date":"2022","source":"Pharmaceuticals (Basel, Switzerland)","url":"https://pubmed.ncbi.nlm.nih.gov/36297411","citation_count":13,"is_preprint":false},{"pmid":"15268766","id":"PMC_15268766","title":"The FU gene and its possible protein isoforms.","date":"2004","source":"BMC genomics","url":"https://pubmed.ncbi.nlm.nih.gov/15268766","citation_count":13,"is_preprint":false},{"pmid":"9726093","id":"PMC_9726093","title":"Irinotecan plus 5-FU and leucovorin in advanced colorectal cancer: North American trials.","date":"1998","source":"Oncology (Williston Park, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/9726093","citation_count":13,"is_preprint":false},{"pmid":"23125179","id":"PMC_23125179","title":"TFPI-2 downregulates multidrug resistance protein in 5-FU-resistant human hepatocellular carcinoma BEL-7402/5-FU cells.","date":"2012","source":"Anatomical record (Hoboken, N.J. : 2007)","url":"https://pubmed.ncbi.nlm.nih.gov/23125179","citation_count":13,"is_preprint":false},{"pmid":"35903686","id":"PMC_35903686","title":"Genome-wide CRISPR Screening Reveals Pyrimidine Metabolic Reprogramming in 5-FU Chronochemotherapy of Colorectal Cancer.","date":"2022","source":"Frontiers in oncology","url":"https://pubmed.ncbi.nlm.nih.gov/35903686","citation_count":13,"is_preprint":false},{"pmid":"31582208","id":"PMC_31582208","title":"H1, a derivative of tetrandrine, enhances the efficacy of 5-FU in Bel7402/5-FU cells via suppressing STAT3/MCL-1 and inducing PUMA.","date":"2019","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/31582208","citation_count":12,"is_preprint":false},{"pmid":"31708100","id":"PMC_31708100","title":"BET inhibitor bromosporine enhances 5-FU effect in colorectal cancer cells.","date":"2019","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/31708100","citation_count":11,"is_preprint":false},{"pmid":"37740873","id":"PMC_37740873","title":"Vactosertib potently improves anti-tumor properties of 5-FU for colon cancer.","date":"2023","source":"Daru : journal of Faculty of Pharmacy, Tehran University of Medical Sciences","url":"https://pubmed.ncbi.nlm.nih.gov/37740873","citation_count":11,"is_preprint":false},{"pmid":"35933584","id":"PMC_35933584","title":"Development of 5-FU-modified tumor suppressor microRNAs as a platform for novel microRNA-based cancer therapeutics.","date":"2022","source":"Molecular therapy : the journal of the American Society of Gene Therapy","url":"https://pubmed.ncbi.nlm.nih.gov/35933584","citation_count":11,"is_preprint":false},{"pmid":"37477870","id":"PMC_37477870","title":"Hungatella hathewayi impairs the sensitivity of colorectal cancer cells to 5-FU through decreasing CDX2 expression.","date":"2023","source":"Human cell","url":"https://pubmed.ncbi.nlm.nih.gov/37477870","citation_count":11,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":53321,"output_tokens":1947,"usd":0.094584,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8533,"output_tokens":2526,"usd":0.052908,"stage2_stop_reason":"end_turn"},"total_usd":0.147492,"stage1_batch_id":"msgbatch_017qqVz33Ga63SCDwzb35XPb","stage2_batch_id":"msgbatch_01Scr2Ei9x4HJMiRGxwrmvLK","note":"batch pricing = 50% of standard"},"stage1_raw":"Looking through the abstracts, I need to identify papers about STK36 (also known as FU, KIAA1278) - the serine/threonine kinase involved in Hedgehog signaling and cilia biology. Most papers in this corpus are about 5-fluorouracil (5-FU) chemotherapy, which is completely unrelated to STK36. Let me identify the relevant papers:\n\n- [16] Drosophila *fu* (fused) gene - ortholog, Hedgehog pathway\n- [18] STK36 mutations in primary ciliary dyskinesia\n- [27] Drosophila Su(fu)/Ci - related pathway\n- [35] Mouse Fused (Stk36) in oviduct cilia\n- [55] MID1 ubiquitinates Fu (STK36)\n- [67] Mouse Fu (STK36) in Hedgehog/Gli signaling\n- [92] Human FU gene structure and Gli regulation\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1996,\n      \"finding\": \"Drosophila fused (fu) is required to transmit the Hedgehog (Hh) signal in imaginal discs; fu mutations rescue phenotypes caused by ectopic hh expression or loss of patched (ptc) activity, placing fu genetically downstream of hh and ptc in the pathway controlling dpp expression. fu is also required for engrailed activation downstream of Hh, but fu mutations do not rescue phenotypes caused by abnormal ci, cos-2, or pkA activity, indicating fu acts in the same pathway as these components but is not epistatic to them.\",\n      \"method\": \"Genetic epistasis analysis using Drosophila imaginal disc mutations and ectopic Hh expression\",\n      \"journal\": \"Mechanisms of development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean genetic epistasis across multiple allele combinations, replicated across several pathway components in a single rigorous study\",\n      \"pmids\": [\"8861096\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"The human FU gene (STK36) encodes at least two protein isoforms arising from alternative splicing, including a long form and a shorter isoform. The long FU isoform enhances GLI2-induced transcriptional activity but does not affect GLI1-induced transcription. FU did not reverse SUFU-mediated inhibition of GLI.\",\n      \"method\": \"RT-PCR/nested PCR to characterize splice isoforms; transient overexpression with luciferase transcriptional reporter assays for GLI1 and GLI2 activity\",\n      \"journal\": \"BMC genomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — transient overexpression reporter assay, single lab, two isoforms tested with two GLI targets\",\n      \"pmids\": [\"15268766\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Mouse Fu (Stk36) can enhance Gli-induced transcription in transient overexpression assays similarly to human FU. In one cell line where mFu expression was reduced by RNAi, Hedgehog signaling was severely impaired, indicating mFu may have a role in Hedgehog signaling and Gli regulation in certain cellular contexts.\",\n      \"method\": \"cDNA cloning of mouse Fu; transient overexpression with Gli transcriptional reporter; RNAi knockdown with Hedgehog signaling readout\",\n      \"journal\": \"Journal of cell communication and signaling\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single RNAi experiment in one cell line, overexpression reporter assay without mutagenesis\",\n      \"pmids\": [\"18600476\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Mouse Fused (Stk36) is required for central pair (CP) apparatus assembly and proper cilia orientation in motile cilia of the oviductal epithelium. Fu-deficient mouse oviducts show defects in CP construction and cilia orientation. Fu protein localizes to motile cilia and physically associates with kinesin Kif27 at the cilium base and with known central pair components Spag16 and Pcdp1.\",\n      \"method\": \"Conditional knockout mouse analysis (Fu-deficient); transmission electron microscopy of oviductal cilia ultrastructure; immunofluorescence localization; co-immunoprecipitation of Fu with Kif27, Spag16, and Pcdp1\",\n      \"journal\": \"Developmental dynamics : an official publication of the American Association of Anatomists\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — knockout phenotype with ultrastructural readout, direct localization by immunofluorescence, and reciprocal Co-IP with multiple binding partners in a single study\",\n      \"pmids\": [\"23907739\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The E3 ubiquitin ligase MID1 catalyzes ubiquitination and proteasomal cleavage of Fu (STK36). MID1-mediated ubiquitination and cleavage of Fu is identified as a key element connecting the MID1-PP2A protein complex to GLI3 activity control in SHH-GLI signaling.\",\n      \"method\": \"Biochemical ubiquitination assays; proteasomal cleavage assays; interaction studies between MID1 and Fu in cancer cell lines with autonomous SHH signaling\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro/cell-based ubiquitination and cleavage assays with defined enzymatic reaction, single lab but multiple biochemical methods\",\n      \"pmids\": [\"25278022\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Homozygous loss-of-function mutations in STK36 cause primary ciliary dyskinesia (PCD) with a central pair defect in a human patient with situs solitus. Transmission electron microscopy of respiratory epithelial cells from the affected individual demonstrates that STK36 is required for cilia orientation, with a probable localization of STK36 between the radial spokes and central pair of the ciliary axoneme.\",\n      \"method\": \"Whole-exome/gene sequencing identifying homozygous STK36 mutations; transmission electron microscopy of respiratory epithelial cilia ultrastructure\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — human loss-of-function (natural mutation) with ultrastructural ciliary phenotype, single patient/family, no functional rescue experiment\",\n      \"pmids\": [\"28543983\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"STK36 (Fused) is a serine-threonine kinase that functions as a positive regulator of Hedgehog signaling — acting downstream of Patched and upstream of or parallel to Costal-2/Cubitus interruptus in Drosophila — and in mammals serves as a critical component of motile cilia biogenesis, where it physically associates with kinesin Kif27 and central pair proteins Spag16/Pcdp1 to assemble the central pair apparatus and orient cilia; its activity is regulated by the E3 ligase MID1, which ubiquitinates and cleaves Fu to modulate GLI3 transcriptional output, and loss-of-function mutations in humans cause primary ciliary dyskinesia with central pair defects.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"STK36, the mammalian ortholog of Drosophila Fused, is a serine-threonine kinase with dual roles spanning Hedgehog signal transduction and motile cilia assembly [#0, #3]. In Drosophila, fused acts genetically downstream of Hedgehog and Patched to transmit the Hh signal controlling dpp and engrailed expression, operating within the same pathway as Costal-2, Cubitus interruptus, and PKA without being epistatic to them [#0]. In mammals, STK36 enhances GLI-induced transcription, with the long human isoform selectively potentiating GLI2 activity, and its loss impairs Hedgehog signaling output [#1]. Its transcriptional contribution is controlled by the E3 ubiquitin ligase MID1, which ubiquitinates and proteasomally cleaves Fu to couple the MID1-PP2A complex to GLI3 regulation [#4]. Independently of its signaling role, STK36 is required for assembly of the central pair apparatus and orientation of motile cilia, localizing to motile cilia where it physically associates with the kinesin Kif27 at the cilium base and with central pair components Spag16 and Pcdp1 [#3]. Homozygous loss-of-function mutations in STK36 cause primary ciliary dyskinesia with a central pair defect, with the protein localizing between the radial spokes and central pair of the axoneme [#5].\",\n  \"teleology\": [\n    {\n      \"year\": 1996,\n      \"claim\": \"Established that Fused operates within the Hedgehog pathway to transmit the signal, fixing its genetic position downstream of Hh and Patched and clarifying its relationship to Costal-2, Ci, and PKA.\",\n      \"evidence\": \"Genetic epistasis using Drosophila imaginal disc mutations and ectopic Hh expression\",\n      \"pmids\": [\"8861096\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Does not identify direct biochemical substrates of the kinase\",\n        \"Pathway position relative to Ci/Cos-2 left unresolved (same pathway but not epistatic)\",\n        \"No mammalian generalization addressed\"\n      ]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Showed the human ortholog STK36 retains a transcriptional function, with isoform-specific potentiation of GLI2 but not GLI1, indicating the Drosophila signaling role extends to mammals at the level of GLI effectors.\",\n      \"evidence\": \"Splice isoform characterization by RT-PCR and luciferase reporter assays for GLI1/GLI2 in transient overexpression\",\n      \"pmids\": [\"15268766\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Overexpression reporter assay only, no endogenous validation\",\n        \"Mechanism of GLI2-selective enhancement unknown\",\n        \"Did not reverse SUFU-mediated GLI inhibition, leaving the regulatory node undefined\"\n      ]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Extended GLI-enhancing activity to mouse Fu and provided loss-of-function support for a Hedgehog role in a cellular context.\",\n      \"evidence\": \"Mouse Fu cDNA cloning, Gli reporter overexpression, and RNAi knockdown in one cell line\",\n      \"pmids\": [\"18600476\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"Single RNAi experiment in one cell line without rescue or mutagenesis\",\n        \"Context-dependence of the Hedgehog requirement not delineated\",\n        \"No biochemical mechanism established\"\n      ]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Revealed a Hedgehog-independent function for Fu in motile cilia, identifying it as essential for central pair assembly and cilia orientation and naming its direct structural partners.\",\n      \"evidence\": \"Conditional knockout mouse oviduct analysis, TEM of ciliary ultrastructure, immunofluorescence, and reciprocal Co-IP with Kif27, Spag16, and Pcdp1\",\n      \"pmids\": [\"23907739\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether kinase catalytic activity is required for central pair assembly not tested\",\n        \"Order of recruitment of Kif27/Spag16/Pcdp1 unresolved\",\n        \"Relationship between ciliary and Hedgehog roles not reconciled\"\n      ]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Defined how Fu protein levels are controlled, showing MID1 ubiquitinates and cleaves Fu to link the MID1-PP2A complex to GLI3 transcriptional output.\",\n      \"evidence\": \"Biochemical ubiquitination and proteasomal cleavage assays and MID1-Fu interaction studies in SHH-active cancer cells\",\n      \"pmids\": [\"25278022\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Functional consequence of Fu cleavage products not characterized\",\n        \"Whether this regulation operates in cilia as well as signaling unknown\",\n        \"In vivo relevance of MID1-Fu axis not established\"\n      ]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Connected STK36 loss directly to human disease, demonstrating that loss-of-function mutations cause primary ciliary dyskinesia with a central pair defect.\",\n      \"evidence\": \"Gene sequencing identifying homozygous STK36 mutations and TEM of respiratory epithelial cilia in an affected individual\",\n      \"pmids\": [\"28543983\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single patient/family with no functional rescue experiment\",\n        \"Precise axonemal position inferred, not directly mapped\",\n        \"Genotype-phenotype spectrum across patients undefined\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The catalytic substrates of STK36 kinase activity in both Hedgehog signaling and central pair assembly remain unidentified, leaving the mechanistic link between its enzymatic function and its two cellular roles open.\",\n      \"evidence\": \"No direct substrate identification in the available corpus\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No phosphorylation substrate identified\",\n        \"Whether kinase activity is required for ciliary versus signaling functions untested\",\n        \"Structural basis of partner binding unknown\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 3]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [1, 2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005929\", \"supporting_discovery_ids\": [3, 5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 1, 4]},\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [3, 5]}\n    ],\n    \"complexes\": [\"central pair apparatus\"],\n    \"partners\": [\"KIF27\", \"SPAG16\", \"PCDP1\", \"MID1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":6,"faith_pct":83.33333333333333}}