{"gene":"SCN4B","run_date":"2026-04-28T20:42:07","timeline":{"discoveries":[{"year":2007,"finding":"The SCN4B-encoded β4 subunit associates with the SCN5A-encoded Nav1.5 α-subunit (hNav1.5) in cardiac cells; the disease-associated L179F missense mutation in β4 causes an ~8-fold increase in late sodium current compared with SCN5A alone, establishing that β4 regulates Nav1.5 gating and that loss-of-function/gain-of-function perturbations in β4 underlie LQT3-type long-QT syndrome.","method":"Site-directed mutagenesis of L179F in SCN4B; heterologous co-expression with stably expressed SCN5A in HEK293 cells; patch-clamp electrophysiology measuring late sodium current","journal":"Circulation","confidence":"High","confidence_rationale":"Tier 1 — in vitro functional reconstitution with mutagenesis and electrophysiological readout in a defined cell system","pmids":["17592081"],"is_preprint":false},{"year":2016,"finding":"SCN4B/β4 suppresses cancer cell migration and invasion by restraining RhoA activity; the intracellular C-terminus of β4 is sufficient to prevent hyperactivated migration, and this function is independent of voltage-gated sodium channel (NaV) activity. Loss of β4 promotes an amoeboid-mesenchymal hybrid invasive phenotype, primary tumour growth, and metastatic spreading.","method":"shRNA-mediated knockdown and overexpression of SCN4B in breast cancer cells; overexpression of isolated C-terminal domain; RhoA activity assay; in vitro invasion/migration assays; in vivo xenograft/metastasis models","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (KD, OE, domain mapping, RhoA assay, in vivo) in a single rigorous study","pmids":["27917859"],"is_preprint":false},{"year":2019,"finding":"Two SCN4B variants (p.Gly8Ser and p.Ala145Ser) associated with ventricular tachycardia significantly reduce the steady-state expression level of the Navβ4 protein, indicating a loss-of-function mechanism.","method":"Western blotting of variant proteins expressed in heterologous cells","journal":"Molecular genetics and genomics : MGG","confidence":"Medium","confidence_rationale":"Tier 3 — single functional assay (Western blot) without electrophysiological follow-up","pmids":["31020414"],"is_preprint":false},{"year":2019,"finding":"miR-424-5p directly targets the 3′-UTR of SCN4B mRNA in colorectal cancer cells, suppressing SCN4B expression and thereby promoting cell proliferation and metastasis.","method":"Luciferase reporter assay with SCN4B 3′-UTR; miR-424-5p mimic/inhibitor transfection; in vitro proliferation and invasion assays; in vivo xenograft model","journal":"Pathology, research and practice","confidence":"Medium","confidence_rationale":"Tier 2 — direct luciferase 3′-UTR reporter confirms targeting, supported by gain/loss-of-function phenotypes in vitro and in vivo","pmids":["31785995"],"is_preprint":false},{"year":2020,"finding":"miR-3175 directly targets the SCN4B mRNA 3′-UTR in prostate cancer cells; knockdown of miR-3175 increases SCN4B expression and suppresses cell proliferation, migration, and invasion, with associated upregulation of E-cadherin and downregulation of N-cadherin.","method":"Luciferase reporter assay; RT-qPCR and Western blotting of SCN4B after miR-3175 inhibitor transfection; proliferation (MTT/EdU) and invasion/migration (scratch, Transwell) assays","journal":"The Kaohsiung journal of medical sciences","confidence":"Medium","confidence_rationale":"Tier 2 — direct 3′-UTR reporter plus multiple phenotypic readouts, single lab","pmids":["32833340"],"is_preprint":false},{"year":2026,"finding":"SCN4B overexpression in lung adenocarcinoma (LUAD) cell lines suppresses epithelial-mesenchymal transition (EMT), as shown by upregulation of E-cadherin and downregulation of N-cadherin, Vimentin, and Snail, and reduces cell viability, migration, and invasion while promoting apoptosis.","method":"Stable SCN4B overexpression in A549 and H1299 cells; Western blotting for EMT markers; CCK-8, wound healing, Transwell, and flow cytometry assays","journal":"Oncology reports","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal functional assays in two cell lines, single lab, no in vivo confirmation","pmids":["41685607"],"is_preprint":false},{"year":2026,"finding":"Loss of Scn4b in wild-type mice recapitulates HD-associated motor and cognitive deficits and striatal gene expression signatures; conversely, Scn4b overexpression in an HD mouse model rescues these phenotypes and improves electrophysiological properties of striatal spiny projection neurons (SPNs), implicating Scn4b in regulation of SPN excitability and HD pathogenesis.","method":"Scn4b knockout and overexpression in mouse models; single-nucleus RNA sequencing (snRNA-seq); in vivo motor/cognitive behavioral assays; ex vivo SPN electrophysiology","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal methods (KO, OE, snRNA-seq, electrophysiology, behavior) but preprint, single lab","pmids":["41959367"],"is_preprint":true}],"current_model":"SCN4B encodes the voltage-gated sodium channel auxiliary β4 subunit (Navβ4) that co-assembles with the Nav1.5 α-subunit (SCN5A) to modulate cardiac sodium channel gating—disease mutations increase late sodium current causing long-QT syndrome—while in non-excitable cells its intracellular C-terminus independently restrains RhoA activity to suppress invasive cell migration, and in neurons it supports striatal spiny projection neuron excitability; its expression is also post-transcriptionally repressed by miR-424-5p and miR-3175, which target its 3′-UTR to promote cancer cell invasion."},"narrative":{"teleology":[{"year":2007,"claim":"Whether the β4 subunit functionally modulates cardiac Nav1.5 was unknown; co-expression and electrophysiology showed that β4 associates with Nav1.5 and that the L179F mutation dramatically increases late sodium current, establishing SCN4B as a cardiac arrhythmia gene causing LQT3-type long-QT syndrome.","evidence":"Site-directed mutagenesis, HEK293 co-expression with SCN5A, patch-clamp electrophysiology","pmids":["17592081"],"confidence":"High","gaps":["Structural basis for β4–Nav1.5 interaction not resolved","Whether other SCN4B variants cause arrhythmia through similar gating perturbations was untested","In vivo cardiac phenotype of L179F not established"]},{"year":2016,"claim":"Whether SCN4B had functions beyond ion channel modulation was unknown; domain mapping and RhoA assays demonstrated that the β4 intracellular C-terminus restrains RhoA activity to suppress invasive cell migration, independent of sodium channel conductance, establishing a non-canonical tumor-suppressive role.","evidence":"shRNA knockdown, overexpression of full-length and C-terminal domain constructs, RhoA activity assay, in vivo xenograft and metastasis models in breast cancer cells","pmids":["27917859"],"confidence":"High","gaps":["Direct molecular target connecting the β4 C-terminus to RhoA inhibition not identified","Whether this mechanism operates in non-cancer, non-excitable cells remains untested","Structural basis of C-terminus–RhoA pathway interaction unresolved"]},{"year":2019,"claim":"Two arrhythmia-associated SCN4B variants (p.Gly8Ser and p.Ala145Ser) were shown to reduce steady-state Navβ4 protein levels, suggesting that loss-of-function via impaired protein stability is an additional disease mechanism beyond gating perturbation.","evidence":"Western blotting of variant proteins expressed in heterologous cells","pmids":["31020414"],"confidence":"Medium","gaps":["No electrophysiological characterization of these variants was performed","Protein degradation pathway responsible for reduced expression not identified","Clinical phenotype–genotype correlation in families not reported"]},{"year":2019,"claim":"How SCN4B is silenced in cancer was unclear; luciferase reporter assays established that miR-424-5p directly targets the SCN4B 3′-UTR in colorectal cancer, providing a post-transcriptional mechanism for SCN4B downregulation that promotes proliferation and metastasis.","evidence":"Luciferase 3′-UTR reporter assay, miR-424-5p mimic/inhibitor transfection, in vitro and in vivo xenograft assays in colorectal cancer cells","pmids":["31785995"],"confidence":"Medium","gaps":["Whether miR-424-5p-mediated SCN4B repression operates through the RhoA pathway was not tested","Contribution of SCN4B suppression versus other miR-424-5p targets not deconvolved","Single lab finding without independent replication"]},{"year":2020,"claim":"A second miRNA, miR-3175, was shown to directly target the SCN4B 3′-UTR in prostate cancer, with miR-3175 inhibition upregulating SCN4B and E-cadherin while suppressing invasion, reinforcing that post-transcriptional SCN4B silencing is a recurring cancer mechanism linked to EMT.","evidence":"Luciferase 3′-UTR reporter assay, RT-qPCR, Western blotting, proliferation and invasion assays in prostate cancer cells","pmids":["32833340"],"confidence":"Medium","gaps":["Direct demonstration that SCN4B re-expression alone accounts for miR-3175 inhibitor phenotype is lacking","Mechanistic link between SCN4B levels and E-cadherin/N-cadherin regulation not established","Single lab without in vivo validation"]},{"year":2026,"claim":"SCN4B overexpression in lung adenocarcinoma cells suppressed EMT markers (E-cadherin up, N-cadherin/Vimentin/Snail down), reduced viability and invasion, and promoted apoptosis, extending the tumor-suppressive role of SCN4B across a third cancer type and directly linking it to EMT suppression.","evidence":"Stable SCN4B overexpression in A549 and H1299 cells, Western blotting for EMT markers, CCK-8, wound healing, Transwell, and flow cytometry assays","pmids":["41685607"],"confidence":"Medium","gaps":["Whether the anti-EMT effect depends on the C-terminus/RhoA mechanism was not tested","No in vivo tumor model confirmation","Downstream signaling pathway from SCN4B to Snail suppression not mapped"]},{"year":2026,"claim":"Whether SCN4B has a neuronal function was unclear; Scn4b knockout in mice recapitulated Huntington's disease-like motor and cognitive deficits and striatal transcriptomic changes, while Scn4b overexpression in an HD mouse model rescued these phenotypes and restored striatal spiny projection neuron electrophysiology, implicating SCN4B in SPN excitability and HD pathogenesis.","evidence":"(preprint) Scn4b KO and overexpression in mouse models, snRNA-seq, behavioral assays, ex vivo electrophysiology","pmids":["41959367"],"confidence":"Medium","gaps":["Preprint not yet peer-reviewed","Mechanism by which Scn4b loss alters SPN excitability (direct channel effect vs. transcriptomic cascade) not resolved","Relevance to human Huntington's disease patients not established"]},{"year":null,"claim":"The direct molecular mechanism by which the Navβ4 C-terminus inhibits RhoA, the structural basis of β4–Nav1.5 interaction, and whether the channel-dependent and channel-independent functions of SCN4B are coordinated in vivo remain unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No structural model of the β4 C-terminus–RhoA interface exists","In vivo cardiac phenotype of SCN4B mutations not characterized in animal models","Integration of ion channel modulation and tumor-suppressive functions in the same tissue context has not been examined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,2]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,1]}],"pathway":[{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[0,3,4]}],"complexes":["Voltage-gated sodium channel complex (Nav1.5/β4)"],"partners":["SCN5A","RHOA"],"other_free_text":[]},"mechanistic_narrative":"SCN4B encodes the voltage-gated sodium channel β4 subunit (Navβ4), which modulates cardiac sodium channel gating and independently suppresses invasive cell migration through a channel-independent mechanism. Navβ4 associates with the Nav1.5 α-subunit (SCN5A) in cardiac cells, and the disease-associated L179F mutation causes an ~8-fold increase in late sodium current, establishing SCN4B as a long-QT syndrome (LQT10) gene [PMID:17592081]. In non-excitable cells, the intracellular C-terminus of Navβ4 restrains RhoA activity, and loss of SCN4B promotes an amoeboid-mesenchymal hybrid invasive phenotype, tumor growth, and metastasis; this anti-invasive function is independent of sodium channel conductance and is accompanied by suppression of epithelial-mesenchymal transition [PMID:27917859, PMID:41685607]. SCN4B expression is post-transcriptionally repressed by miR-424-5p and miR-3175 via direct 3′-UTR targeting in colorectal and prostate cancer cells, respectively, linking its downregulation to enhanced proliferation and metastasis [PMID:31785995, PMID:32833340]."},"prefetch_data":{"uniprot":{"accession":"Q8IWT1","full_name":"Sodium channel regulatory subunit beta-4","aliases":[],"length_aa":228,"mass_kda":25.0,"function":"Regulatory subunit of multiple voltage-gated sodium (Nav) channels directly mediating the depolarization of excitable membranes. Navs, also called VGSCs (voltage-gated sodium channels) or VDSCs (voltage-dependent sodium channels), operate by switching between closed and open conformations depending on the voltage difference across the membrane. In the open conformation they allow Na(+) ions to selectively pass through the pore, along their electrochemical gradient. The influx of Na+ ions provokes membrane depolarization, initiating the propagation of electrical signals throughout cells and tissues. The accessory beta subunits participate in localization and functional modulation of the Nav channels (PubMed:24297919). Modulates the activity of SCN1A/Nav1.1 (PubMed:33712547). Modulates the activity of SCN2A/Nav1.2 (PubMed:24297919)","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/Q8IWT1/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SCN4B","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SCN4B","total_profiled":1310},"omim":[{"mim_id":"615378","title":"ATRIAL FIBRILLATION, FAMILIAL, 14; ATFB14","url":"https://www.omim.org/entry/615378"},{"mim_id":"615377","title":"ATRIAL FIBRILLATION, FAMILIAL, 13; ATFB13","url":"https://www.omim.org/entry/615377"},{"mim_id":"613120","title":"BRUGADA SYNDROME 7; BRGDA7","url":"https://www.omim.org/entry/613120"},{"mim_id":"611819","title":"LONG QT SYNDROME 10; LQT10","url":"https://www.omim.org/entry/611819"},{"mim_id":"608583","title":"ATRIAL FIBRILLATION, FAMILIAL, 1; ATFB1","url":"https://www.omim.org/entry/608583"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"brain","ntpm":28.4},{"tissue":"skeletal muscle","ntpm":28.5},{"tissue":"tongue","ntpm":53.0}],"url":"https://www.proteinatlas.org/search/SCN4B"},"hgnc":{"alias_symbol":["LQT10"],"prev_symbol":[]},"alphafold":{"accession":"Q8IWT1","domains":[{"cath_id":"2.60.40.10","chopping":"30-151","consensus_level":"high","plddt":94.8926,"start":30,"end":151},{"cath_id":"1.20.5","chopping":"158-192","consensus_level":"medium","plddt":94.0383,"start":158,"end":192}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8IWT1","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8IWT1-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8IWT1-F1-predicted_aligned_error_v6.png","plddt_mean":83.06},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SCN4B","jax_strain_url":"https://www.jax.org/strain/search?query=SCN4B"},"sequence":{"accession":"Q8IWT1","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8IWT1.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8IWT1/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8IWT1"}},"corpus_meta":[{"pmid":"17592081","id":"PMC_17592081","title":"SCN4B-encoded sodium channel beta4 subunit in congenital long-QT syndrome.","date":"2007","source":"Circulation","url":"https://pubmed.ncbi.nlm.nih.gov/17592081","citation_count":271,"is_preprint":false},{"pmid":"23604097","id":"PMC_23604097","title":"Mutations of the SCN4B-encoded sodium channel β4 subunit in familial atrial fibrillation.","date":"2013","source":"International journal of molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/23604097","citation_count":56,"is_preprint":false},{"pmid":"27917859","id":"PMC_27917859","title":"SCN4B acts as a metastasis-suppressor gene preventing hyperactivation of cell migration in breast cancer.","date":"2016","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/27917859","citation_count":54,"is_preprint":false},{"pmid":"31785995","id":"PMC_31785995","title":"miR-424-5p promotes the proliferation and metastasis of colorectal cancer by directly targeting SCN4B.","date":"2019","source":"Pathology, research and practice","url":"https://pubmed.ncbi.nlm.nih.gov/31785995","citation_count":42,"is_preprint":false},{"pmid":"30821358","id":"PMC_30821358","title":"Significant association of rare variant p.Gly8Ser in cardiac sodium channel β4-subunit SCN4B with atrial fibrillation.","date":"2019","source":"Annals of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/30821358","citation_count":23,"is_preprint":false},{"pmid":"29723302","id":"PMC_29723302","title":"Preserved SCN4B expression is an independent indicator of favorable recurrence-free survival in classical papillary thyroid cancer.","date":"2018","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/29723302","citation_count":22,"is_preprint":false},{"pmid":"31020414","id":"PMC_31020414","title":"Identification of rare variants in cardiac sodium channel β4-subunit gene SCN4B associated with ventricular tachycardia.","date":"2019","source":"Molecular genetics and genomics : MGG","url":"https://pubmed.ncbi.nlm.nih.gov/31020414","citation_count":8,"is_preprint":false},{"pmid":"32833340","id":"PMC_32833340","title":"Silencing of microRNA-3175 represses cell proliferation and invasion in prostate cancer by targeting the potential tumor-suppressor SCN4B.","date":"2020","source":"The Kaohsiung journal of medical sciences","url":"https://pubmed.ncbi.nlm.nih.gov/32833340","citation_count":7,"is_preprint":false},{"pmid":"20730464","id":"PMC_20730464","title":"Mutational analysis of SCN2B, SCN3B and SCN4B in a large Chinese Han family with generalized tonic-clonic seizure.","date":"2010","source":"Neurological sciences : official journal of the Italian Neurological Society and of the Italian Society of Clinical Neurophysiology","url":"https://pubmed.ncbi.nlm.nih.gov/20730464","citation_count":3,"is_preprint":false},{"pmid":"41685607","id":"PMC_41685607","title":"Suppressive role of SCN4B in the epithelial‑mesenchymal transition of lung adenocarcinoma.","date":"2026","source":"Oncology reports","url":"https://pubmed.ncbi.nlm.nih.gov/41685607","citation_count":0,"is_preprint":false},{"pmid":"41959367","id":"PMC_41959367","title":"Scn4b Modulates Huntington's Disease Phenotype Severity in vivo.","date":"2026","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/41959367","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":7005,"output_tokens":1862,"usd":0.024473},"stage2":{"model":"claude-opus-4-6","input_tokens":5173,"output_tokens":2372,"usd":0.127748},"total_usd":0.152221,"stage1_batch_id":"msgbatch_011rkcQdVV1RaFq9XhcG6df6","stage2_batch_id":"msgbatch_01RzgrJafdF4EWHhj5mNi6dh","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2007,\n      \"finding\": \"The SCN4B-encoded β4 subunit associates with the SCN5A-encoded Nav1.5 α-subunit (hNav1.5) in cardiac cells; the disease-associated L179F missense mutation in β4 causes an ~8-fold increase in late sodium current compared with SCN5A alone, establishing that β4 regulates Nav1.5 gating and that loss-of-function/gain-of-function perturbations in β4 underlie LQT3-type long-QT syndrome.\",\n      \"method\": \"Site-directed mutagenesis of L179F in SCN4B; heterologous co-expression with stably expressed SCN5A in HEK293 cells; patch-clamp electrophysiology measuring late sodium current\",\n      \"journal\": \"Circulation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro functional reconstitution with mutagenesis and electrophysiological readout in a defined cell system\",\n      \"pmids\": [\"17592081\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"SCN4B/β4 suppresses cancer cell migration and invasion by restraining RhoA activity; the intracellular C-terminus of β4 is sufficient to prevent hyperactivated migration, and this function is independent of voltage-gated sodium channel (NaV) activity. Loss of β4 promotes an amoeboid-mesenchymal hybrid invasive phenotype, primary tumour growth, and metastatic spreading.\",\n      \"method\": \"shRNA-mediated knockdown and overexpression of SCN4B in breast cancer cells; overexpression of isolated C-terminal domain; RhoA activity assay; in vitro invasion/migration assays; in vivo xenograft/metastasis models\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (KD, OE, domain mapping, RhoA assay, in vivo) in a single rigorous study\",\n      \"pmids\": [\"27917859\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Two SCN4B variants (p.Gly8Ser and p.Ala145Ser) associated with ventricular tachycardia significantly reduce the steady-state expression level of the Navβ4 protein, indicating a loss-of-function mechanism.\",\n      \"method\": \"Western blotting of variant proteins expressed in heterologous cells\",\n      \"journal\": \"Molecular genetics and genomics : MGG\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — single functional assay (Western blot) without electrophysiological follow-up\",\n      \"pmids\": [\"31020414\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"miR-424-5p directly targets the 3′-UTR of SCN4B mRNA in colorectal cancer cells, suppressing SCN4B expression and thereby promoting cell proliferation and metastasis.\",\n      \"method\": \"Luciferase reporter assay with SCN4B 3′-UTR; miR-424-5p mimic/inhibitor transfection; in vitro proliferation and invasion assays; in vivo xenograft model\",\n      \"journal\": \"Pathology, research and practice\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct luciferase 3′-UTR reporter confirms targeting, supported by gain/loss-of-function phenotypes in vitro and in vivo\",\n      \"pmids\": [\"31785995\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"miR-3175 directly targets the SCN4B mRNA 3′-UTR in prostate cancer cells; knockdown of miR-3175 increases SCN4B expression and suppresses cell proliferation, migration, and invasion, with associated upregulation of E-cadherin and downregulation of N-cadherin.\",\n      \"method\": \"Luciferase reporter assay; RT-qPCR and Western blotting of SCN4B after miR-3175 inhibitor transfection; proliferation (MTT/EdU) and invasion/migration (scratch, Transwell) assays\",\n      \"journal\": \"The Kaohsiung journal of medical sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct 3′-UTR reporter plus multiple phenotypic readouts, single lab\",\n      \"pmids\": [\"32833340\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"SCN4B overexpression in lung adenocarcinoma (LUAD) cell lines suppresses epithelial-mesenchymal transition (EMT), as shown by upregulation of E-cadherin and downregulation of N-cadherin, Vimentin, and Snail, and reduces cell viability, migration, and invasion while promoting apoptosis.\",\n      \"method\": \"Stable SCN4B overexpression in A549 and H1299 cells; Western blotting for EMT markers; CCK-8, wound healing, Transwell, and flow cytometry assays\",\n      \"journal\": \"Oncology reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal functional assays in two cell lines, single lab, no in vivo confirmation\",\n      \"pmids\": [\"41685607\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Loss of Scn4b in wild-type mice recapitulates HD-associated motor and cognitive deficits and striatal gene expression signatures; conversely, Scn4b overexpression in an HD mouse model rescues these phenotypes and improves electrophysiological properties of striatal spiny projection neurons (SPNs), implicating Scn4b in regulation of SPN excitability and HD pathogenesis.\",\n      \"method\": \"Scn4b knockout and overexpression in mouse models; single-nucleus RNA sequencing (snRNA-seq); in vivo motor/cognitive behavioral assays; ex vivo SPN electrophysiology\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (KO, OE, snRNA-seq, electrophysiology, behavior) but preprint, single lab\",\n      \"pmids\": [\"41959367\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"SCN4B encodes the voltage-gated sodium channel auxiliary β4 subunit (Navβ4) that co-assembles with the Nav1.5 α-subunit (SCN5A) to modulate cardiac sodium channel gating—disease mutations increase late sodium current causing long-QT syndrome—while in non-excitable cells its intracellular C-terminus independently restrains RhoA activity to suppress invasive cell migration, and in neurons it supports striatal spiny projection neuron excitability; its expression is also post-transcriptionally repressed by miR-424-5p and miR-3175, which target its 3′-UTR to promote cancer cell invasion.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"SCN4B encodes the voltage-gated sodium channel β4 subunit (Navβ4), which modulates cardiac sodium channel gating and independently suppresses invasive cell migration through a channel-independent mechanism. Navβ4 associates with the Nav1.5 α-subunit (SCN5A) in cardiac cells, and the disease-associated L179F mutation causes an ~8-fold increase in late sodium current, establishing SCN4B as a long-QT syndrome (LQT10) gene [PMID:17592081]. In non-excitable cells, the intracellular C-terminus of Navβ4 restrains RhoA activity, and loss of SCN4B promotes an amoeboid-mesenchymal hybrid invasive phenotype, tumor growth, and metastasis; this anti-invasive function is independent of sodium channel conductance and is accompanied by suppression of epithelial-mesenchymal transition [PMID:27917859, PMID:41685607]. SCN4B expression is post-transcriptionally repressed by miR-424-5p and miR-3175 via direct 3′-UTR targeting in colorectal and prostate cancer cells, respectively, linking its downregulation to enhanced proliferation and metastasis [PMID:31785995, PMID:32833340].\",\n  \"teleology\": [\n    {\n      \"year\": 2007,\n      \"claim\": \"Whether the β4 subunit functionally modulates cardiac Nav1.5 was unknown; co-expression and electrophysiology showed that β4 associates with Nav1.5 and that the L179F mutation dramatically increases late sodium current, establishing SCN4B as a cardiac arrhythmia gene causing LQT3-type long-QT syndrome.\",\n      \"evidence\": \"Site-directed mutagenesis, HEK293 co-expression with SCN5A, patch-clamp electrophysiology\",\n      \"pmids\": [\"17592081\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis for β4–Nav1.5 interaction not resolved\",\n        \"Whether other SCN4B variants cause arrhythmia through similar gating perturbations was untested\",\n        \"In vivo cardiac phenotype of L179F not established\"\n      ]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Whether SCN4B had functions beyond ion channel modulation was unknown; domain mapping and RhoA assays demonstrated that the β4 intracellular C-terminus restrains RhoA activity to suppress invasive cell migration, independent of sodium channel conductance, establishing a non-canonical tumor-suppressive role.\",\n      \"evidence\": \"shRNA knockdown, overexpression of full-length and C-terminal domain constructs, RhoA activity assay, in vivo xenograft and metastasis models in breast cancer cells\",\n      \"pmids\": [\"27917859\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Direct molecular target connecting the β4 C-terminus to RhoA inhibition not identified\",\n        \"Whether this mechanism operates in non-cancer, non-excitable cells remains untested\",\n        \"Structural basis of C-terminus–RhoA pathway interaction unresolved\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Two arrhythmia-associated SCN4B variants (p.Gly8Ser and p.Ala145Ser) were shown to reduce steady-state Navβ4 protein levels, suggesting that loss-of-function via impaired protein stability is an additional disease mechanism beyond gating perturbation.\",\n      \"evidence\": \"Western blotting of variant proteins expressed in heterologous cells\",\n      \"pmids\": [\"31020414\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No electrophysiological characterization of these variants was performed\",\n        \"Protein degradation pathway responsible for reduced expression not identified\",\n        \"Clinical phenotype–genotype correlation in families not reported\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"How SCN4B is silenced in cancer was unclear; luciferase reporter assays established that miR-424-5p directly targets the SCN4B 3′-UTR in colorectal cancer, providing a post-transcriptional mechanism for SCN4B downregulation that promotes proliferation and metastasis.\",\n      \"evidence\": \"Luciferase 3′-UTR reporter assay, miR-424-5p mimic/inhibitor transfection, in vitro and in vivo xenograft assays in colorectal cancer cells\",\n      \"pmids\": [\"31785995\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether miR-424-5p-mediated SCN4B repression operates through the RhoA pathway was not tested\",\n        \"Contribution of SCN4B suppression versus other miR-424-5p targets not deconvolved\",\n        \"Single lab finding without independent replication\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"A second miRNA, miR-3175, was shown to directly target the SCN4B 3′-UTR in prostate cancer, with miR-3175 inhibition upregulating SCN4B and E-cadherin while suppressing invasion, reinforcing that post-transcriptional SCN4B silencing is a recurring cancer mechanism linked to EMT.\",\n      \"evidence\": \"Luciferase 3′-UTR reporter assay, RT-qPCR, Western blotting, proliferation and invasion assays in prostate cancer cells\",\n      \"pmids\": [\"32833340\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Direct demonstration that SCN4B re-expression alone accounts for miR-3175 inhibitor phenotype is lacking\",\n        \"Mechanistic link between SCN4B levels and E-cadherin/N-cadherin regulation not established\",\n        \"Single lab without in vivo validation\"\n      ]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"SCN4B overexpression in lung adenocarcinoma cells suppressed EMT markers (E-cadherin up, N-cadherin/Vimentin/Snail down), reduced viability and invasion, and promoted apoptosis, extending the tumor-suppressive role of SCN4B across a third cancer type and directly linking it to EMT suppression.\",\n      \"evidence\": \"Stable SCN4B overexpression in A549 and H1299 cells, Western blotting for EMT markers, CCK-8, wound healing, Transwell, and flow cytometry assays\",\n      \"pmids\": [\"41685607\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether the anti-EMT effect depends on the C-terminus/RhoA mechanism was not tested\",\n        \"No in vivo tumor model confirmation\",\n        \"Downstream signaling pathway from SCN4B to Snail suppression not mapped\"\n      ]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Whether SCN4B has a neuronal function was unclear; Scn4b knockout in mice recapitulated Huntington's disease-like motor and cognitive deficits and striatal transcriptomic changes, while Scn4b overexpression in an HD mouse model rescued these phenotypes and restored striatal spiny projection neuron electrophysiology, implicating SCN4B in SPN excitability and HD pathogenesis.\",\n      \"evidence\": \"(preprint) Scn4b KO and overexpression in mouse models, snRNA-seq, behavioral assays, ex vivo electrophysiology\",\n      \"pmids\": [\"41959367\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Preprint not yet peer-reviewed\",\n        \"Mechanism by which Scn4b loss alters SPN excitability (direct channel effect vs. transcriptomic cascade) not resolved\",\n        \"Relevance to human Huntington's disease patients not established\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The direct molecular mechanism by which the Navβ4 C-terminus inhibits RhoA, the structural basis of β4–Nav1.5 interaction, and whether the channel-dependent and channel-independent functions of SCN4B are coordinated in vivo remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No structural model of the β4 C-terminus–RhoA interface exists\",\n        \"In vivo cardiac phenotype of SCN4B mutations not characterized in animal models\",\n        \"Integration of ion channel modulation and tumor-suppressive functions in the same tissue context has not been examined\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0162582\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [0, 3, 4]}\n    ],\n    \"complexes\": [\n      \"Voltage-gated sodium channel complex (Nav1.5/β4)\"\n    ],\n    \"partners\": [\n      \"SCN5A\",\n      \"RHOA\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}