{"gene":"MYL6B","run_date":"2026-06-10T05:19:52","timeline":{"discoveries":[{"year":1990,"finding":"MLC1sa (MYL6B) is a myosin alkali light chain isoform that arose by gene duplication from MLC3nm (nonmuscle isoform), is expressed at the onset of myogenesis in vitro, is detectable in nonmuscle cells, and is functionally distinct from other alkali myosin light chain isoforms.","method":"cDNA cloning, nucleotide sequencing, isoform-specific probes, Northern/Western blotting across species and tissues","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — sequence analysis with expression profiling across multiple species and tissues in one focused study; functional distinctiveness inferred from sequence divergence rather than direct biochemical assay","pmids":["2304459"],"is_preprint":false},{"year":1996,"finding":"MLC1sa (MYL6B) shows weak but detectable sarcomeric sorting in cardiomyocytes when co-expressed with MLC3nm, but is distributed throughout the cytoplasm when co-expressed with fast or slow isoforms MLC1f, MLC3f, or MLC1sb. The N-terminal lobe of each MLC isoprotein is responsible for isoform-specific sarcomeric sorting.","method":"Double epitope-tagging competition assay with VSV and mT tags, co-expression in adult and neonatal rat cardiomyocytes, confocal microscopy, chimeric cDNA expression","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct localization experiments with chimeric constructs to map functional domain, replicated across multiple isoform combinations in two cardiomyocyte cell types","pmids":["8856505"],"is_preprint":false},{"year":2006,"finding":"MLC1Sa (MYL6B) expression level in pig diaphragm slow fibers is inversely related to maximal shortening velocity (Vmax), and fibers expressing MLC1Sa without MLC1Sb generate greater maximal isometric force per cross-sectional area. MLC1Sa level is reciprocally related to levels of MLC1Sb and MLC1F.","method":"Single-fiber mechanics (maximal shortening velocity, isometric force) correlated with MLC isoform composition measured by gel electrophoresis","journal":"Archives of biochemistry and biophysics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct single-fiber functional measurements correlated with isoform identity; single lab, single species","pmids":["16884681"],"is_preprint":false},{"year":2008,"finding":"Mlc1sa (MYL6B) binds specifically to the first IQ motif (IQ1) of human IQGAP1, as demonstrated by native gel electrophoresis with synthetic IQ-motif peptides.","method":"Native gel electrophoresis using synthetic peptides corresponding to each of the four IQ motifs of IQGAP1 with purified Mlc1sa protein","journal":"Molecular and cellular biochemistry","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — direct binding mapped to specific IQ motif, replicated in a follow-up study (PMID:21299499); single method (native gel)","pmids":["18587628"],"is_preprint":false},{"year":2011,"finding":"Mlc1sa (MYL6B) forms a transient interaction with the first IQ motif of IQGAP3, and also with the first IQ motif of IQGAP2 (transient). The interaction with IQGAP1 IQ1 was confirmed. None of these IQ motifs interacted with S100B.","method":"Native gel electrophoresis with synthetic IQ-motif peptides from IQGAP2 and IQGAP3, molecular modelling","journal":"Bioscience reports","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — binding specificity mapped across three IQGAP family members by consistent method; single lab but replication of IQ1-MYL6B interaction established across multiple IQGAPs","pmids":["21299499"],"is_preprint":false},{"year":2018,"finding":"MYL6B binds both MDM2 and p53 (identified by immunoprecipitation and mass spectrometry), facilitates MDM2-p53 interaction, and promotes MDM2-mediated ubiquitination and degradation of p53. This effect requires MYL6B to be incorporated into non-muscle myosin II (NMII) holoenzymes, as inhibiting myosin II heavy chain ATPase activity largely blocks the p53-suppressing effect. Knockout of MYL6B suppresses clonogenic ability and increases apoptosis in HCC cell lines.","method":"Immunoprecipitation, mass spectrometry, ubiquitination assay, myosin II ATPase inhibitor treatment, CRISPR knockout, clone formation assay, flow cytometry for apoptosis","journal":"Journal of experimental & clinical cancer research : CR","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (Co-IP/MS for binding, ubiquitination assay for mechanism, ATPase inhibition for context-dependence, KO for cellular phenotype) in a single focused study","pmids":["29439719"],"is_preprint":false},{"year":2020,"finding":"MYL6B knockdown in rectal adenocarcinoma cells inhibits proliferation, migration, and invasion while promoting apoptosis. Knockdown increases E-cadherin and decreases N-cadherin and Vimentin, indicating MYL6B drives EMT in these cancer cells.","method":"siRNA knockdown, CCK-8 proliferation assay, Transwell migration/invasion assay, flow cytometry (apoptosis), Western blot for EMT markers","journal":"Open life sciences","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — clean KD with defined cellular phenotypes and molecular markers; single lab, multiple functional readouts but no mechanistic pathway placement beyond EMT markers","pmids":["33817240"],"is_preprint":false},{"year":1999,"finding":"The MLC1Sa/MLC1Sb ratio in rat soleus slow-twitch muscle increases during ageing in parallel with age-related decreases in shortening velocity, consistent with MLC1Sa (MYL6B) modulating contractile velocity. Thyroid hormone treatment altered MLC1Sa and MLC1Sb expression in a complex manner not parallel to changes in shortening velocity.","method":"Two-dimensional gel electrophoresis for MLC isoform quantification, thyroid hormone treatment of rats, correlation with published contractile velocity data","journal":"Acta physiologica Scandinavica","confidence":"Low","confidence_rationale":"Tier 3 / Weak — correlative single-lab study; no direct functional measurement of shortening velocity in the same fibers, velocity modulation by MLC1Sa is inferred not directly demonstrated","pmids":["10632633"],"is_preprint":false}],"current_model":"MYL6B (MLC1sa) is a myosin alkali essential light chain that incorporates into non-muscle myosin II (NMII) holoenzymes; its N-terminal lobe governs isoform-specific sorting to sarcomeric A-bands, its expression level inversely modulates maximal shortening velocity and affects force generation in slow muscle fibers, it binds the first IQ motif of IQGAP1/2/3, and as part of NMII it facilitates MDM2 binding to p53, promoting p53 ubiquitination and degradation—a mechanism that drives proliferation and suppresses apoptosis in cancer cells and is linked to EMT regulation."},"narrative":{"mechanistic_narrative":"MYL6B (MLC1sa) is a myosin alkali essential light chain that arose by gene duplication from a nonmuscle light chain isoform and is expressed at the onset of myogenesis while remaining detectable in nonmuscle cells [PMID:2304459]. It is functionally distinguished from other alkali light chains by its N-terminal lobe, which governs isoform-specific sorting: MYL6B shows only weak sarcomeric targeting in cardiomyocytes and is otherwise distributed throughout the cytoplasm, and chimeric mapping localizes this sorting determinant to the N-terminal lobe [PMID:8856505]. In slow muscle fibers its expression level is inversely related to maximal shortening velocity, and fibers carrying MYL6B without the MLC1Sb isoform generate greater isometric force, marking it as a modulator of contractile mechanics [PMID:16884681]. Beyond muscle, MYL6B binds the first IQ motif of IQGAP1, with transient interactions to the first IQ motifs of IQGAP2 and IQGAP3 [PMID:18587628, PMID:21299499]. As a light-chain subunit of non-muscle myosin II holoenzymes, MYL6B binds both MDM2 and p53 and facilitates MDM2-mediated ubiquitination and degradation of p53; this requires its incorporation into functional NMII, since inhibiting myosin II heavy-chain ATPase blocks the effect, and MYL6B loss reduces clonogenicity and increases apoptosis in hepatocellular carcinoma cells [PMID:29439719]. Consistent with a pro-tumorigenic role, MYL6B knockdown in rectal adenocarcinoma cells suppresses proliferation, migration, and invasion and reverses EMT marker patterns [PMID:33817240].","teleology":[{"year":1990,"claim":"Established MYL6B as a distinct myosin alkali light chain isoform of duplication origin, defining the gene's molecular identity and expression breadth across muscle and nonmuscle cells.","evidence":"cDNA cloning, sequencing, and isoform-specific expression profiling across species and tissues","pmids":["2304459"],"confidence":"Medium","gaps":["Functional distinctiveness inferred from sequence rather than biochemical assay","No direct demonstration of light-chain binding to a myosin heavy chain at this stage"]},{"year":1996,"claim":"Resolved how isoform-specific localization is encoded, showing MYL6B sorts only weakly to sarcomeres and that the N-terminal lobe carries the sorting determinant.","evidence":"Double epitope-tagging competition and chimeric cDNA expression in rat cardiomyocytes with confocal microscopy","pmids":["8856505"],"confidence":"High","gaps":["Molecular partner mediating N-terminal lobe sorting not identified","Behavior in nonmuscle cell types not addressed"]},{"year":1999,"claim":"Correlated MYL6B abundance with declining contractile velocity during aging, supporting a role in tuning slow-fiber mechanics.","evidence":"2D gel quantification of MLC isoform ratios in aging rat soleus with thyroid hormone treatment, correlated to published velocity data","pmids":["10632633"],"confidence":"Low","gaps":["Correlative only; velocity not measured in the same fibers, so velocity modulation is inferred not demonstrated","Thyroid hormone effects did not parallel velocity changes"]},{"year":2006,"claim":"Provided direct functional evidence that MYL6B level inversely sets maximal shortening velocity and raises isometric force in slow fibers.","evidence":"Single-fiber mechanics correlated with MLC isoform composition by gel electrophoresis in pig diaphragm","pmids":["16884681"],"confidence":"Medium","gaps":["Single species and lab","Mechanism by which the light chain alters velocity/force not resolved"]},{"year":2011,"claim":"Mapped MYL6B binding specificity to the first IQ motif across the IQGAP family, defining a scaffold-interaction interface beyond myosin.","evidence":"Native gel electrophoresis with synthetic IQ-motif peptides from IQGAP1/2/3 and molecular modelling","pmids":["18587628","21299499"],"confidence":"Medium","gaps":["Interactions with IQGAP2/3 are transient and shown by a single method","Functional consequence of IQGAP binding not established"]},{"year":2018,"claim":"Connected MYL6B to tumor cell survival by showing it facilitates MDM2-p53 binding and p53 degradation in an NMII-dependent manner.","evidence":"Co-IP/MS, ubiquitination assay, myosin II ATPase inhibition, CRISPR knockout, clonogenic and apoptosis assays in HCC cells","pmids":["29439719"],"confidence":"High","gaps":["Structural basis of the MYL6B-MDM2-p53 ternary arrangement unknown","How NMII enzymatic activity couples to p53 ubiquitination mechanistically unresolved"]},{"year":2020,"claim":"Extended the pro-tumorigenic role to EMT, showing MYL6B promotes proliferation, invasion, and mesenchymal marker expression.","evidence":"siRNA knockdown with proliferation, migration/invasion, apoptosis assays and EMT marker Western blots in rectal adenocarcinoma cells","pmids":["33817240"],"confidence":"Medium","gaps":["No mechanistic pathway placement beyond EMT markers","Link to the p53 axis in this cancer context not tested"]},{"year":null,"claim":"How MYL6B's distinct biophysical contribution to myosin mechanics relates to its scaffolding (IQGAP) and tumor-survival (NMII-MDM2-p53) functions remains unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structural model of MYL6B within NMII or bound to MDM2/p53","Whether IQGAP binding and p53 regulation share a common cellular pathway is untested"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,1,2]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[3,4]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[1]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[1,2]}],"pathway":[{"term_id":"R-HSA-397014","term_label":"Muscle contraction","supporting_discovery_ids":[2]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[5,6]}],"complexes":["non-muscle myosin II"],"partners":["IQGAP1","IQGAP2","IQGAP3","MDM2","TP53"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P14649","full_name":"Myosin light chain 6B","aliases":["Myosin light chain 1 slow-twitch muscle A isoform","MLC1sa","Smooth muscle and nonmuscle myosin light chain alkali 6B"],"length_aa":208,"mass_kda":22.8,"function":"Regulatory light chain of myosin. Does not bind calcium","subcellular_location":"","url":"https://www.uniprot.org/uniprotkb/P14649/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MYL6B","classification":"Not Classified","n_dependent_lines":13,"n_total_lines":1208,"dependency_fraction":0.01076158940397351},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000196465","cell_line_id":"CID001438","localizations":[{"compartment":"cytoplasmic","grade":3},{"compartment":"cytoskeleton","grade":3},{"compartment":"membrane","grade":2}],"interactors":[{"gene":"MYL6","stoichiometry":10.0},{"gene":"MYH9","stoichiometry":4.0},{"gene":"CALM1","stoichiometry":0.2},{"gene":"CALM2","stoichiometry":0.2},{"gene":"CALM3","stoichiometry":0.2},{"gene":"CDC42","stoichiometry":0.2},{"gene":"MYH10","stoichiometry":0.2},{"gene":"MYL12A","stoichiometry":0.2},{"gene":"MYL12B","stoichiometry":0.2},{"gene":"MYO9B","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID001438","total_profiled":1310},"omim":[{"mim_id":"621092","title":"IQ MOTIF-CONTAINING GTPase-ACTIVATING PROTEIN 3; IQGAP3","url":"https://www.omim.org/entry/621092"},{"mim_id":"609930","title":"MYOSIN, LIGHT CHAIN 6B, ALKALI, SMOOTH MUSCLE AND NONMUSCLE, SLOW; MYL6B","url":"https://www.omim.org/entry/609930"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"skeletal muscle","ntpm":639.5},{"tissue":"tongue","ntpm":611.1}],"url":"https://www.proteinatlas.org/search/MYL6B"},"hgnc":{"alias_symbol":["MLC1SA"],"prev_symbol":[]},"alphafold":{"accession":"P14649","domains":[{"cath_id":"1.10.238.10","chopping":"55-135","consensus_level":"high","plddt":94.2386,"start":55,"end":135},{"cath_id":"1.10.238.10","chopping":"142-205","consensus_level":"high","plddt":94.8059,"start":142,"end":205}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P14649","model_url":"https://alphafold.ebi.ac.uk/files/AF-P14649-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P14649-F1-predicted_aligned_error_v6.png","plddt_mean":81.94},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=MYL6B","jax_strain_url":"https://www.jax.org/strain/search?query=MYL6B"},"sequence":{"accession":"P14649","fasta_url":"https://rest.uniprot.org/uniprotkb/P14649.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P14649/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P14649"}},"corpus_meta":[{"pmid":"2304459","id":"PMC_2304459","title":"Characterization of human myosin light chains 1sa and 3nm: implications for isoform evolution and function.","date":"1990","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/2304459","citation_count":56,"is_preprint":false},{"pmid":"36871648","id":"PMC_36871648","title":"Towards the discovery of goat meat quality biomarkers using label-free proteomics.","date":"2023","source":"Journal of proteomics","url":"https://pubmed.ncbi.nlm.nih.gov/36871648","citation_count":31,"is_preprint":false},{"pmid":"29289712","id":"PMC_29289712","title":"Proteome changes of beef in Nellore cattle with different genotypes for tenderness.","date":"2017","source":"Meat science","url":"https://pubmed.ncbi.nlm.nih.gov/29289712","citation_count":30,"is_preprint":false},{"pmid":"21299499","id":"PMC_21299499","title":"IQ-motif selectivity in human IQGAP2 and IQGAP3: binding of calmodulin and myosin essential light chain.","date":"2011","source":"Bioscience 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transactions","url":"https://pubmed.ncbi.nlm.nih.gov/21428964","citation_count":18,"is_preprint":false},{"pmid":"18587628","id":"PMC_18587628","title":"IQ motif selectivity in human IQGAP1: binding of myosin essential light chain and S100B.","date":"2008","source":"Molecular and cellular biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/18587628","citation_count":18,"is_preprint":false},{"pmid":"36126390","id":"PMC_36126390","title":"Transcriptome-based analysis of early post-mortem formation of pale, soft, and exudative (PSE) pork.","date":"2022","source":"Meat science","url":"https://pubmed.ncbi.nlm.nih.gov/36126390","citation_count":14,"is_preprint":false},{"pmid":"30524470","id":"PMC_30524470","title":"A Novel 12q13.2-q13.3 Microdeletion Syndrome With Combined Features of Diamond Blackfan Anemia, Pierre Robin Sequence and Klippel Feil Deformity.","date":"2018","source":"Frontiers in 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Scandinavica","url":"https://pubmed.ncbi.nlm.nih.gov/10632633","citation_count":7,"is_preprint":false},{"pmid":"37128318","id":"PMC_37128318","title":"Breast cancer cell secretome analysis to decipher miRNA regulating the tumor microenvironment and discover potential biomarkers.","date":"2023","source":"Heliyon","url":"https://pubmed.ncbi.nlm.nih.gov/37128318","citation_count":6,"is_preprint":false},{"pmid":"35625411","id":"PMC_35625411","title":"Neuregulin (NRG-1β) Is Pro-Myogenic and Anti-Cachectic in Respiratory Muscles of Post-Myocardial Infarcted Swine.","date":"2022","source":"Biology","url":"https://pubmed.ncbi.nlm.nih.gov/35625411","citation_count":5,"is_preprint":false},{"pmid":"33817240","id":"PMC_33817240","title":"MYL6B drives the capabilities of proliferation, invasion, and migration in rectal adenocarcinoma through the EMT process.","date":"2020","source":"Open life 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X","url":"https://pubmed.ncbi.nlm.nih.gov/42028547","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":13039,"output_tokens":2158,"usd":0.035743,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9190,"output_tokens":2710,"usd":0.05685,"stage2_stop_reason":"end_turn"},"total_usd":0.092593,"stage1_batch_id":"msgbatch_013a8chtv3AWyTqv4z4sEF4C","stage2_batch_id":"msgbatch_01AHsuW63vinsvuTgzmQ3n62","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1990,\n      \"finding\": \"MLC1sa (MYL6B) is a myosin alkali light chain isoform that arose by gene duplication from MLC3nm (nonmuscle isoform), is expressed at the onset of myogenesis in vitro, is detectable in nonmuscle cells, and is functionally distinct from other alkali myosin light chain isoforms.\",\n      \"method\": \"cDNA cloning, nucleotide sequencing, isoform-specific probes, Northern/Western blotting across species and tissues\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — sequence analysis with expression profiling across multiple species and tissues in one focused study; functional distinctiveness inferred from sequence divergence rather than direct biochemical assay\",\n      \"pmids\": [\"2304459\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"MLC1sa (MYL6B) shows weak but detectable sarcomeric sorting in cardiomyocytes when co-expressed with MLC3nm, but is distributed throughout the cytoplasm when co-expressed with fast or slow isoforms MLC1f, MLC3f, or MLC1sb. The N-terminal lobe of each MLC isoprotein is responsible for isoform-specific sarcomeric sorting.\",\n      \"method\": \"Double epitope-tagging competition assay with VSV and mT tags, co-expression in adult and neonatal rat cardiomyocytes, confocal microscopy, chimeric cDNA expression\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct localization experiments with chimeric constructs to map functional domain, replicated across multiple isoform combinations in two cardiomyocyte cell types\",\n      \"pmids\": [\"8856505\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"MLC1Sa (MYL6B) expression level in pig diaphragm slow fibers is inversely related to maximal shortening velocity (Vmax), and fibers expressing MLC1Sa without MLC1Sb generate greater maximal isometric force per cross-sectional area. MLC1Sa level is reciprocally related to levels of MLC1Sb and MLC1F.\",\n      \"method\": \"Single-fiber mechanics (maximal shortening velocity, isometric force) correlated with MLC isoform composition measured by gel electrophoresis\",\n      \"journal\": \"Archives of biochemistry and biophysics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct single-fiber functional measurements correlated with isoform identity; single lab, single species\",\n      \"pmids\": [\"16884681\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Mlc1sa (MYL6B) binds specifically to the first IQ motif (IQ1) of human IQGAP1, as demonstrated by native gel electrophoresis with synthetic IQ-motif peptides.\",\n      \"method\": \"Native gel electrophoresis using synthetic peptides corresponding to each of the four IQ motifs of IQGAP1 with purified Mlc1sa protein\",\n      \"journal\": \"Molecular and cellular biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — direct binding mapped to specific IQ motif, replicated in a follow-up study (PMID:21299499); single method (native gel)\",\n      \"pmids\": [\"18587628\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Mlc1sa (MYL6B) forms a transient interaction with the first IQ motif of IQGAP3, and also with the first IQ motif of IQGAP2 (transient). The interaction with IQGAP1 IQ1 was confirmed. None of these IQ motifs interacted with S100B.\",\n      \"method\": \"Native gel electrophoresis with synthetic IQ-motif peptides from IQGAP2 and IQGAP3, molecular modelling\",\n      \"journal\": \"Bioscience reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — binding specificity mapped across three IQGAP family members by consistent method; single lab but replication of IQ1-MYL6B interaction established across multiple IQGAPs\",\n      \"pmids\": [\"21299499\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"MYL6B binds both MDM2 and p53 (identified by immunoprecipitation and mass spectrometry), facilitates MDM2-p53 interaction, and promotes MDM2-mediated ubiquitination and degradation of p53. This effect requires MYL6B to be incorporated into non-muscle myosin II (NMII) holoenzymes, as inhibiting myosin II heavy chain ATPase activity largely blocks the p53-suppressing effect. Knockout of MYL6B suppresses clonogenic ability and increases apoptosis in HCC cell lines.\",\n      \"method\": \"Immunoprecipitation, mass spectrometry, ubiquitination assay, myosin II ATPase inhibitor treatment, CRISPR knockout, clone formation assay, flow cytometry for apoptosis\",\n      \"journal\": \"Journal of experimental & clinical cancer research : CR\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (Co-IP/MS for binding, ubiquitination assay for mechanism, ATPase inhibition for context-dependence, KO for cellular phenotype) in a single focused study\",\n      \"pmids\": [\"29439719\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"MYL6B knockdown in rectal adenocarcinoma cells inhibits proliferation, migration, and invasion while promoting apoptosis. Knockdown increases E-cadherin and decreases N-cadherin and Vimentin, indicating MYL6B drives EMT in these cancer cells.\",\n      \"method\": \"siRNA knockdown, CCK-8 proliferation assay, Transwell migration/invasion assay, flow cytometry (apoptosis), Western blot for EMT markers\",\n      \"journal\": \"Open life sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — clean KD with defined cellular phenotypes and molecular markers; single lab, multiple functional readouts but no mechanistic pathway placement beyond EMT markers\",\n      \"pmids\": [\"33817240\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The MLC1Sa/MLC1Sb ratio in rat soleus slow-twitch muscle increases during ageing in parallel with age-related decreases in shortening velocity, consistent with MLC1Sa (MYL6B) modulating contractile velocity. Thyroid hormone treatment altered MLC1Sa and MLC1Sb expression in a complex manner not parallel to changes in shortening velocity.\",\n      \"method\": \"Two-dimensional gel electrophoresis for MLC isoform quantification, thyroid hormone treatment of rats, correlation with published contractile velocity data\",\n      \"journal\": \"Acta physiologica Scandinavica\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — correlative single-lab study; no direct functional measurement of shortening velocity in the same fibers, velocity modulation by MLC1Sa is inferred not directly demonstrated\",\n      \"pmids\": [\"10632633\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"MYL6B (MLC1sa) is a myosin alkali essential light chain that incorporates into non-muscle myosin II (NMII) holoenzymes; its N-terminal lobe governs isoform-specific sorting to sarcomeric A-bands, its expression level inversely modulates maximal shortening velocity and affects force generation in slow muscle fibers, it binds the first IQ motif of IQGAP1/2/3, and as part of NMII it facilitates MDM2 binding to p53, promoting p53 ubiquitination and degradation—a mechanism that drives proliferation and suppresses apoptosis in cancer cells and is linked to EMT regulation.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"MYL6B (MLC1sa) is a myosin alkali essential light chain that arose by gene duplication from a nonmuscle light chain isoform and is expressed at the onset of myogenesis while remaining detectable in nonmuscle cells [#0]. It is functionally distinguished from other alkali light chains by its N-terminal lobe, which governs isoform-specific sorting: MYL6B shows only weak sarcomeric targeting in cardiomyocytes and is otherwise distributed throughout the cytoplasm, and chimeric mapping localizes this sorting determinant to the N-terminal lobe [#1]. In slow muscle fibers its expression level is inversely related to maximal shortening velocity, and fibers carrying MYL6B without the MLC1Sb isoform generate greater isometric force, marking it as a modulator of contractile mechanics [#2]. Beyond muscle, MYL6B binds the first IQ motif of IQGAP1, with transient interactions to the first IQ motifs of IQGAP2 and IQGAP3 [#3, #4]. As a light-chain subunit of non-muscle myosin II holoenzymes, MYL6B binds both MDM2 and p53 and facilitates MDM2-mediated ubiquitination and degradation of p53; this requires its incorporation into functional NMII, since inhibiting myosin II heavy-chain ATPase blocks the effect, and MYL6B loss reduces clonogenicity and increases apoptosis in hepatocellular carcinoma cells [#5]. Consistent with a pro-tumorigenic role, MYL6B knockdown in rectal adenocarcinoma cells suppresses proliferation, migration, and invasion and reverses EMT marker patterns [#6].\",\n  \"teleology\": [\n    {\n      \"year\": 1990,\n      \"claim\": \"Established MYL6B as a distinct myosin alkali light chain isoform of duplication origin, defining the gene's molecular identity and expression breadth across muscle and nonmuscle cells.\",\n      \"evidence\": \"cDNA cloning, sequencing, and isoform-specific expression profiling across species and tissues\",\n      \"pmids\": [\"2304459\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Functional distinctiveness inferred from sequence rather than biochemical assay\",\n        \"No direct demonstration of light-chain binding to a myosin heavy chain at this stage\"\n      ]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Resolved how isoform-specific localization is encoded, showing MYL6B sorts only weakly to sarcomeres and that the N-terminal lobe carries the sorting determinant.\",\n      \"evidence\": \"Double epitope-tagging competition and chimeric cDNA expression in rat cardiomyocytes with confocal microscopy\",\n      \"pmids\": [\"8856505\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Molecular partner mediating N-terminal lobe sorting not identified\",\n        \"Behavior in nonmuscle cell types not addressed\"\n      ]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Correlated MYL6B abundance with declining contractile velocity during aging, supporting a role in tuning slow-fiber mechanics.\",\n      \"evidence\": \"2D gel quantification of MLC isoform ratios in aging rat soleus with thyroid hormone treatment, correlated to published velocity data\",\n      \"pmids\": [\"10632633\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"Correlative only; velocity not measured in the same fibers, so velocity modulation is inferred not demonstrated\",\n        \"Thyroid hormone effects did not parallel velocity changes\"\n      ]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Provided direct functional evidence that MYL6B level inversely sets maximal shortening velocity and raises isometric force in slow fibers.\",\n      \"evidence\": \"Single-fiber mechanics correlated with MLC isoform composition by gel electrophoresis in pig diaphragm\",\n      \"pmids\": [\"16884681\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single species and lab\",\n        \"Mechanism by which the light chain alters velocity/force not resolved\"\n      ]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Mapped MYL6B binding specificity to the first IQ motif across the IQGAP family, defining a scaffold-interaction interface beyond myosin.\",\n      \"evidence\": \"Native gel electrophoresis with synthetic IQ-motif peptides from IQGAP1/2/3 and molecular modelling\",\n      \"pmids\": [\"18587628\", \"21299499\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Interactions with IQGAP2/3 are transient and shown by a single method\",\n        \"Functional consequence of IQGAP binding not established\"\n      ]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Connected MYL6B to tumor cell survival by showing it facilitates MDM2-p53 binding and p53 degradation in an NMII-dependent manner.\",\n      \"evidence\": \"Co-IP/MS, ubiquitination assay, myosin II ATPase inhibition, CRISPR knockout, clonogenic and apoptosis assays in HCC cells\",\n      \"pmids\": [\"29439719\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis of the MYL6B-MDM2-p53 ternary arrangement unknown\",\n        \"How NMII enzymatic activity couples to p53 ubiquitination mechanistically unresolved\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Extended the pro-tumorigenic role to EMT, showing MYL6B promotes proliferation, invasion, and mesenchymal marker expression.\",\n      \"evidence\": \"siRNA knockdown with proliferation, migration/invasion, apoptosis assays and EMT marker Western blots in rectal adenocarcinoma cells\",\n      \"pmids\": [\"33817240\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No mechanistic pathway placement beyond EMT markers\",\n        \"Link to the p53 axis in this cancer context not tested\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How MYL6B's distinct biophysical contribution to myosin mechanics relates to its scaffolding (IQGAP) and tumor-survival (NMII-MDM2-p53) functions remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No structural model of MYL6B within NMII or bound to MDM2/p53\",\n        \"Whether IQGAP binding and p53 regulation share a common cellular pathway is untested\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 1, 2]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [3, 4]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [1, 2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-397014\", \"supporting_discovery_ids\": [2]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [5, 6]}\n    ],\n    \"complexes\": [\n      \"non-muscle myosin II\"\n    ],\n    \"partners\": [\n      \"IQGAP1\",\n      \"IQGAP2\",\n      \"IQGAP3\",\n      \"MDM2\",\n      \"TP53\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"faith_supported":5,"faith_total":6,"faith_pct":83.33333333333333}}