{"gene":"CLCC1","run_date":"2026-04-28T17:28:52","timeline":{"discoveries":[{"year":2015,"finding":"Loss-of-function mutation in Clcc1 (retrotransposon insertion) in mice causes progressive cerebellar granule cell death and peripheral motor axon degeneration. Acute knockdown of Clcc1 in cultured cells increases sensitivity to ER stress, GRP78 is upregulated in Clcc1-deficient neurons in vivo, and ubiquitinated proteins accumulate prior to neurodegeneration, establishing that CLCC1 is required for ER protein-folding homeostasis.","method":"Positional cloning, retrotransposon insertion mouse model, siRNA knockdown in cultured cells, immunohistochemistry for GRP78 and ubiquitinated proteins","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 — in vivo loss-of-function mouse model with defined molecular phenotype (ER stress markers, ubiquitinated protein accumulation) plus in vitro knockdown replicated findings","pmids":["25698737"],"is_preprint":false},{"year":2018,"finding":"CLCC1 functions as an intracellular chloride channel highly expressed in the retina; a missense variant p.D25E decreases CLCC1 channel function and causes mutant protein to accumulate in granules within the ER lumen. siRNA knockdown of CLCC1 induces apoptosis in ARPE-19 cells, and loss of CLCC1 in zebrafish impairs cone ERG response, retinal thickness, and opsin expression — all rescued by wild-type CLCC1 mRNA injection.","method":"Electrophysiology (channel function assay), immunofluorescence/EM for protein localization, siRNA knockdown, TALEN knockout zebrafish with rescue by mRNA injection, ERG recordings, Clcc1+/- mouse phenotyping","journal":"PLoS genetics","confidence":"High","confidence_rationale":"Tier 1-2 — channel function directly measured, multiple orthogonal methods including KO rescue in zebrafish and heterozygous mouse phenotyping","pmids":["30157172"],"is_preprint":false},{"year":2019,"finding":"CLCC1 interacts with the mitochondrial outer membrane microprotein PIGBOS at ER-mitochondria contact sites (MAMs). Loss of PIGBOS (the interacting partner) leads to heightened UPR and increased cell death, placing CLCC1 at the ER-mitochondria interface as part of inter-organelle UPR regulation.","method":"Co-localization microscopy, proximity interaction (BioID), functional loss-of-function studies of PIGBOS with UPR readouts","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 3 — interaction identified and localization confirmed, but functional link was demonstrated via PIGBOS KO rather than direct CLCC1 manipulation in this study","pmids":["31653868"],"is_preprint":false},{"year":2023,"finding":"CLCC1 is a pore-forming component of an ER anion channel that forms homomultimers. Channel activity is inhibited by luminal Ca2+ (binding mediated by conserved residues D25 and D181 in the N-terminus) and facilitated by PIP2 (sensed by K298 in the intraluminal loop). CLCC1 maintains steady-state [Cl-]ER, [K+]ER, and ER morphology, and regulates ER Ca2+ homeostasis including internal Ca2+ release and steady-state [Ca2+]ER. ALS-associated mutations increase steady-state [Cl-]ER and impair ER Ca2+ homeostasis. Conditional knockout of Clcc1 cell-autonomously causes motor neuron loss, ER stress, misfolded protein accumulation, and ALS-like pathologies.","method":"Electrophysiology (patch-clamp of ER-derived vesicles), site-directed mutagenesis of Ca2+-binding and PIP2-sensing residues, ion imaging ([Cl-]ER, [K+]ER, [Ca2+]ER), co-IP for homomultimerization, conditional Clcc1 knockout mouse, phenotypic comparison of multiple loss-of-function alleles","journal":"Cell research","confidence":"High","confidence_rationale":"Tier 1 — direct electrophysiological demonstration of pore-forming activity, mutagenesis of functional residues, multiple orthogonal methods, in vivo conditional KO with defined phenotype","pmids":["37142673"],"is_preprint":false},{"year":2023,"finding":"SARS-CoV-2 ORF3A co-localizes with and co-immunoprecipitates with CLCC1. ORF3A expression triggers a UPR similar to CLCC1 knockdown; cells with CLCC1 knockdown are partially protected from ORF3A-mediated cell death, and pre-upregulation of UPR targets (HSPA6, spliced XBP1) by CLCC1 knockdown prevents further induction by ORF3A, placing CLCC1 in the same pathway as ORF3A-induced UPR.","method":"Co-immunoprecipitation, co-localization microscopy, siRNA knockdown, transcriptional UPR reporter assays, cell death assays with chemical chaperone rescue","journal":"PeerJ","confidence":"Medium","confidence_rationale":"Tier 2-3 — reciprocal co-IP plus epistatic relationship demonstrated by knockdown/overexpression with defined molecular readouts","pmids":["37033725"],"is_preprint":false},{"year":2024,"finding":"The CLCC1 interactome (identified by LC-MS) is substantially composed of ER-localized proteins. The pathogenic p.Asp25Glu variant causes a notable loss and gain of specific protein interactors, with increased association with cytoplasmic proteins. Two novel interactors, Calnexin and SigmaR1, were validated by co-localization microscopy, and CLCC1 was shown to co-localize with SigmaR1 not only at the ER but also at mitochondria-associated ER membranes (MAMs).","method":"Liquid chromatography-mass spectrometry (LC-MS) interactome, co-localization microscopy","journal":"Neuroscience letters","confidence":"Medium","confidence_rationale":"Tier 3 — MS-based interactome with microscopy validation of selected interactors; single lab, no reciprocal Co-IP","pmids":["38621504"],"is_preprint":false},{"year":2025,"finding":"CLCC1 is required for the fusion stage of herpes simplex virus 1 nuclear egress (identified by whole-genome CRISPR screen). Loss of CLCC1 causes accumulation of capsid-containing perinuclear vesicles and a drop in viral titers. In uninfected cells, loss of CLCC1 causes nuclear blebbing, implicating CLCC1 in host nuclear envelope membrane fusion. Herpesviruses infecting mollusks and fish encode viral CLCC1 homologs acquired by horizontal gene transfer, suggesting CLCC1 mediates an ancient membrane fusion mechanism hijacked by herpesviruses.","method":"Whole-genome CRISPR screen, CLCC1 knockout cells with viral titer and capsid localization assays, nuclear morphology imaging, phylogenetic analysis","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — genome-wide unbiased screen plus functional validation with defined molecular and viral phenotypes, supported by evolutionary evidence","pmids":["41271665"],"is_preprint":false},{"year":2025,"finding":"CLCC1 regulates trans-bilayer equilibration of phospholipids at the ER by partnering with the phospholipid scramblase TMEM41B to recognize imbalanced ER bilayers and promote lipid scrambling. Loss of CLCC1 leads to emergence of giant lumenal lipid droplets enclosed by imbalanced ER bilayers and accelerates metabolic-dysfunction-associated liver steatohepatitis (MASH), establishing CLCC1 as a regulator of lipoprotein biogenesis and systemic lipid homeostasis.","method":"CRISPR-Cas9 knockout (cells and mice), co-immunoprecipitation/interaction with TMEM41B, lipid droplet and ER morphology imaging, lipoprotein secretion assays, liver steatosis pathology in mouse KO","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods (KO in cells and mice, partner identification, organelle morphology, functional lipid flux assays) in a high-rigor study","pmids":["41741642"],"is_preprint":false},{"year":2025,"finding":"Senkyunolide A (SenA) binds CLCC1 and promotes its ubiquitination, thereby inhibiting CLCC1 activity and ER Ca2+ release in cholangiocytes. Inhibiting CLCC1 prevents Ca2+-mediated cholangiocyte proliferation and ductular reaction in cholestatic liver disease; si-CLCC1-loaded liposomes targeting cholangiocytes enhanced anti-ductular reaction effects.","method":"Molecular docking/binding assay (SenA-CLCC1 interaction), ubiquitination assay, siRNA knockdown, Ca2+ imaging, BDL animal model, primary cholangiocyte and human intrahepatic biliary epithelial cell experiments","journal":"Acta pharmacologica Sinica","confidence":"Medium","confidence_rationale":"Tier 2-3 — direct binding and ubiquitination demonstrated with functional Ca2+ and proliferation readouts in multiple systems; single lab","pmids":["40664817"],"is_preprint":false},{"year":2025,"finding":"CLCC1 is identified as the human functional homolog of yeast Brl1p/Brr6p nuclear pore complex (NPC) assembly factors. Loss of CLCC1 in human cells causes extensive nuclear membrane herniations consistent with impaired NPC assembly. In Drosophila, loss of dClcc1 phenocopies Torsin-loss nuclear membrane fusion defects at NPC assembly sites; CLCC1/dClcc1 overexpression rescues NPC biogenesis and developmental defects caused by Torsin loss-of-function. Proximity labeling identified CLCC1 as a Torsin1A binding partner.","method":"Proximity labeling (BioTurboID), CRISPR-Cas9 KO in human cells, Drosophila genetic loss-of-function and rescue experiments, nuclear morphology EM/fluorescence imaging, remote homology/phylogenetic analysis","journal":"bioRxiv (preprint)","confidence":"Medium","confidence_rationale":"Tier 2 — genetic epistasis in two model systems with defined NPC phenotype; functional rescue by overexpression; preprint not yet peer-reviewed","pmids":[],"is_preprint":true},{"year":2024,"finding":"CRISPR-Cas9 chemical-genetic interaction screens identified CLCC1 as a critical regulator of hepatic neutral lipid flux. Loss of CLCC1 results in large lumenal ER lipid droplets with lipoprotein properties, and knockout in mice causes liver steatosis. Remote homology analysis identified a domain in CLCC1 homologous to yeast Brl1p/Brr6p, and loss of CLCC1 leads to extensive nuclear membrane herniations, consistent with impaired NPC assembly.","method":"Genome-wide CRISPR-Cas9 chemical-genetic screens, KO mouse liver histology, EM of ER lipid droplets, remote homology search, nuclear morphology analysis","journal":"bioRxiv (preprint)","confidence":"Medium","confidence_rationale":"Tier 2 — unbiased CRISPR screen plus in vivo KO phenotype and organelle morphology; preprint","pmids":[],"is_preprint":true}],"current_model":"CLCC1 is an ER-resident, pore-forming anion channel that forms homomultimers and whose activity is regulated by luminal Ca2+ (via D25/D181) and PIP2 (via K298); it maintains ER ion homeostasis ([Cl-]ER, [K+]ER), ER Ca2+ homeostasis, ER morphology, and protein-folding capacity (UPR), and also promotes trans-bilayer phospholipid scrambling by partnering with TMEM41B to support lipoprotein biogenesis and systemic lipid homeostasis, while additionally functioning as a membrane fusogen required for nuclear pore complex biogenesis and herpesviral nuclear egress—with disruption of any of these functions leading to ER stress, neurodegeneration, ALS-like pathologies, retinal degeneration, or liver steatohepatitis."},"narrative":{"teleology":[{"year":2015,"claim":"Establishing CLCC1 as essential for ER protein-folding homeostasis resolved the molecular basis of a progressive neurodegenerative phenotype in mice and linked the gene's loss to ER stress and ubiquitinated-protein accumulation.","evidence":"Positional cloning of a retrotransposon insertion in Clcc1 in a mouse model, supplemented by siRNA knockdown in cultured cells with GRP78 and ubiquitin readouts","pmids":["25698737"],"confidence":"High","gaps":["Molecular mechanism (channel vs. other activity) was unknown","Whether CLCC1 loss in other tissues caused similar pathology was untested","Direct biochemical activity of the protein was not demonstrated"]},{"year":2018,"claim":"Demonstrating that CLCC1 functions as an intracellular chloride channel and that the disease-associated D25E variant impairs channel activity connected the ER-stress phenotype to a specific ion-conduction defect and extended pathology to the retina.","evidence":"Electrophysiology of CLCC1 channel function, siRNA knockdown-induced apoptosis in ARPE-19 cells, TALEN-knockout zebrafish with wild-type mRNA rescue, ERG recordings, heterozygous mouse retinal phenotyping","pmids":["30157172"],"confidence":"High","gaps":["Whether CLCC1 itself forms the pore or requires auxiliary subunits was unresolved","Selectivity profile and gating mechanism were not fully characterized","Downstream signaling between ion flux and UPR induction was unclear"]},{"year":2019,"claim":"Identification of CLCC1 as an interactor of mitochondrial microprotein PIGBOS at ER–mitochondria contact sites placed the channel at inter-organelle signaling hubs involved in UPR regulation.","evidence":"BioID proximity labeling and co-localization microscopy at MAMs; UPR and cell death readouts upon PIGBOS loss","pmids":["31653868"],"confidence":"Medium","gaps":["Functional consequence was shown via PIGBOS KO, not direct CLCC1 manipulation in this study","Whether CLCC1 channel activity is modulated at MAMs was not tested","Stoichiometry and directness of the CLCC1–PIGBOS interaction were not established"]},{"year":2023,"claim":"Direct electrophysiology of ER-derived vesicles established CLCC1 as a pore-forming homomultimeric anion channel gated by luminal Ca²⁺ (D25/D181) and PIP₂ (K298), and conditional knockout demonstrated cell-autonomous motor neuron loss with ALS-like features, unifying ion homeostasis and neurodegeneration.","evidence":"Patch-clamp of ER vesicles, site-directed mutagenesis, ion imaging for [Cl⁻]ER/[K⁺]ER/[Ca²⁺]ER, co-IP for homomultimerization, conditional Clcc1 KO mouse","pmids":["37142673"],"confidence":"High","gaps":["High-resolution structure of the channel pore is lacking","Precise stoichiometry of the homomultimer is not defined","Causal link between specific ion imbalance (Cl⁻ vs. K⁺ vs. Ca²⁺) and neurodegeneration has not been dissected"]},{"year":2023,"claim":"Identification of SARS-CoV-2 ORF3A as a CLCC1 interactor that phenocopies CLCC1 knockdown-induced UPR suggested that viral proteins can co-opt or disrupt CLCC1-dependent ER homeostasis.","evidence":"Co-immunoprecipitation, co-localization, siRNA knockdown epistasis with ORF3A expression, UPR reporter and cell death assays","pmids":["37033725"],"confidence":"Medium","gaps":["Direct effect of ORF3A on CLCC1 channel activity was not measured","Physiological relevance during live SARS-CoV-2 infection was not demonstrated","Mechanism of protection from ORF3A-mediated death upon CLCC1 knockdown is unclear"]},{"year":2024,"claim":"Proteomic mapping of the CLCC1 interactome confirmed its ER-centric interaction network, identified calnexin and SigmaR1 as novel partners (including at MAMs), and showed that the D25E pathogenic variant remodels the interactome.","evidence":"LC-MS interactome of wild-type and D25E CLCC1, co-localization microscopy for calnexin and SigmaR1","pmids":["38621504"],"confidence":"Medium","gaps":["Interactions validated only by co-localization, not reciprocal co-IP","Functional consequences of altered interactome for the D25E variant were not tested","Whether calnexin or SigmaR1 modulate channel activity is unknown"]},{"year":2025,"claim":"A genome-wide CRISPR screen revealed that CLCC1 is required for herpesviral nuclear egress at the membrane fusion step, and its loss in uninfected cells causes nuclear blebbing, establishing CLCC1 as a host membrane fusogen with an ancient evolutionary role hijacked by herpesviruses.","evidence":"Whole-genome CRISPR screen, CLCC1 KO cells with viral titer and capsid localization assays, nuclear morphology imaging, phylogenetic analysis of viral CLCC1 homologs","pmids":["41271665"],"confidence":"High","gaps":["Mechanism by which CLCC1 mediates membrane fusion is uncharacterized at the biochemical level","Whether the fusogenic activity depends on channel function is unknown","Relationship between nuclear blebbing phenotype and NPC biogenesis was not dissected in this study"]},{"year":2025,"claim":"Discovery that CLCC1 partners with TMEM41B to promote ER phospholipid scrambling and lipoprotein biogenesis revealed a lipid-homeostatic function; loss causes giant lumenal lipid droplets and accelerates steatohepatitis, linking CLCC1 to systemic metabolic disease.","evidence":"CRISPR KO in cells and mice, co-IP with TMEM41B, lipid droplet/ER morphology imaging, lipoprotein secretion assays, liver histopathology","pmids":["41741642"],"confidence":"High","gaps":["Whether CLCC1 ion-channel activity is required for its scramblase-partnering role is not determined","Structural basis of the CLCC1–TMEM41B interaction is unknown","Relative contribution of lipid vs. ion homeostasis defects to liver pathology is unclear"]},{"year":2025,"claim":"Pharmacological targeting of CLCC1 by Senkyunolide A, which promotes CLCC1 ubiquitination and inhibits ER Ca²⁺ release, demonstrated that CLCC1 activity drives cholangiocyte proliferation in cholestatic liver disease, providing proof-of-concept for therapeutic modulation.","evidence":"SenA binding assay, ubiquitination assay, Ca²⁺ imaging, siRNA in primary cholangiocytes and human biliary epithelial cells, bile-duct-ligation mouse model","pmids":["40664817"],"confidence":"Medium","gaps":["Direct binding site of SenA on CLCC1 relies on molecular docking and needs structural confirmation","Specificity of SenA for CLCC1 vs. off-target effects was not comprehensively assessed","Whether ubiquitination-mediated degradation or direct channel block is the primary inhibitory mechanism is unresolved"]},{"year":null,"claim":"Key open questions include the high-resolution structure of the CLCC1 channel, whether ion-channel and membrane-fusion/scramblase-partnering activities are mechanistically separable, and how disruption of distinct CLCC1 functions (ion homeostasis, lipid scrambling, NPC assembly) leads to tissue-specific disease outcomes.","evidence":"","pmids":[],"confidence":"High","gaps":["No high-resolution structure exists","Separation-of-function mutants distinguishing channel, fusogenic, and scramblase-partnering roles have not been generated","Tissue-specific phenotype determinants (neuronal vs. retinal vs. hepatic) are not understood"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[1,3]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[3,7]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[0,1,3,5,7]},{"term_id":"GO:0005635","term_label":"nuclear envelope","supporting_discovery_ids":[6,9]}],"pathway":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[1,3]},{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[1,3]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[7]},{"term_id":"R-HSA-8953897","term_label":"Cellular responses to stimuli","supporting_discovery_ids":[0,3]},{"term_id":"R-HSA-1852241","term_label":"Organelle biogenesis and maintenance","supporting_discovery_ids":[6,9]}],"complexes":["CLCC1 homomultimer","CLCC1–TMEM41B complex"],"partners":["TMEM41B","PIGBOS","SIGMAR1","CANX","TOR1A"],"other_free_text":[]},"mechanistic_narrative":"CLCC1 is an ER-resident, pore-forming anion channel that maintains ER ion and Ca²⁺ homeostasis, ER morphology, protein-folding capacity, lipid bilayer symmetry, and nuclear envelope membrane fusion. It forms homomultimers whose channel activity is inhibited by luminal Ca²⁺ (via D25 and D181) and facilitated by PIP₂ (via K298), and it sustains steady-state [Cl⁻]ER, [K⁺]ER, and [Ca²⁺]ER; loss-of-function mutations cause ER stress, misfolded protein accumulation, and ALS-like motor neuron degeneration in conditional knockout mice [PMID:37142673], while a D25E variant impairs channel function and causes retinal degeneration in zebrafish and mice [PMID:30157172]. CLCC1 partners with the phospholipid scramblase TMEM41B to promote trans-bilayer phospholipid equilibration at the ER, and its loss produces giant lumenal lipid droplets and accelerates metabolic-dysfunction-associated steatohepatitis [PMID:41741642]. CLCC1 also functions as a membrane fusogen required for nuclear pore complex biogenesis and herpesviral nuclear egress, with loss causing nuclear membrane herniations and blebbing [PMID:41271665]."},"prefetch_data":{"uniprot":{"accession":"Q96S66","full_name":"Chloride channel CLIC-like protein 1","aliases":["ER anion channel 1","ERAC1","Mid-1-related chloride channel protein"],"length_aa":551,"mass_kda":62.0,"function":"Anion-selective channel with Ca(2+)-dependent and voltage-independent gating. Permeable to small monovalent anions with selectivity for bromide > chloride > nitrate > fluoride (By similarity). Operates in the endoplasmic reticulum (ER) membrane where it mediates chloride efflux to compensate for the loss of positive charges from the ER lumen upon Ca(2+) release. Contributes to the maintenance of ER Ca(2+) pools and activation of unfolded protein response to prevent accumulation of misfolded proteins in the ER lumen. Particularly involved in ER homeostasis mechanisms underlying motor neurons and retinal photoreceptors survival (By similarity) (PubMed:25698737, PubMed:30157172, PubMed:37142673)","subcellular_location":"Endoplasmic reticulum membrane","url":"https://www.uniprot.org/uniprotkb/Q96S66/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CLCC1","classification":"Not Classified","n_dependent_lines":303,"n_total_lines":1208,"dependency_fraction":0.2508278145695364},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"CANX","stoichiometry":0.2},{"gene":"CCDC47","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/CLCC1","total_profiled":1310},"omim":[{"mim_id":"618809","title":"PIGB OPPOSITE STRAND 1; PIGBOS1","url":"https://www.omim.org/entry/618809"},{"mim_id":"617539","title":"CHLORIDE CHANNEL CLIC-LIKE 1; CLCC1","url":"https://www.omim.org/entry/617539"},{"mim_id":"609913","title":"RETINITIS PIGMENTOSA 32; RP32","url":"https://www.omim.org/entry/609913"},{"mim_id":"268000","title":"RETINITIS PIGMENTOSA; RP","url":"https://www.omim.org/entry/268000"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Endoplasmic reticulum","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/CLCC1"},"hgnc":{"alias_symbol":["MCLC"],"prev_symbol":[]},"alphafold":{"accession":"Q96S66","domains":[{"cath_id":"-","chopping":"94-163","consensus_level":"medium","plddt":74.5551,"start":94,"end":163},{"cath_id":"-","chopping":"187-330","consensus_level":"medium","plddt":75.0936,"start":187,"end":330}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96S66","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q96S66-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q96S66-F1-predicted_aligned_error_v6.png","plddt_mean":60.41},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CLCC1","jax_strain_url":"https://www.jax.org/strain/search?query=CLCC1"},"sequence":{"accession":"Q96S66","fasta_url":"https://rest.uniprot.org/uniprotkb/Q96S66.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q96S66/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96S66"}},"corpus_meta":[{"pmid":"25698737","id":"PMC_25698737","title":"Loss of Clcc1 results in ER stress, misfolded protein accumulation, and neurodegeneration.","date":"2015","source":"The Journal of neuroscience : the official journal of the Society for Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/25698737","citation_count":35,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"30157172","id":"PMC_30157172","title":"Mutation in the intracellular chloride channel CLCC1 associated with autosomal recessive retinitis pigmentosa.","date":"2018","source":"PLoS genetics","url":"https://pubmed.ncbi.nlm.nih.gov/30157172","citation_count":32,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"37142673","id":"PMC_37142673","title":"Disruption of ER ion homeostasis maintained by an ER anion channel CLCC1 contributes to ALS-like pathologies.","date":"2023","source":"Cell 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acute knockdown in cultured cells increases sensitivity to ER stress, establishing that CLCC1 is required for ER protein-folding homeostasis.\",\n      \"method\": \"Positional cloning of spontaneous mouse mutation, in vivo immunohistochemistry for GRP78 and ubiquitin, siRNA knockdown in cultured cells with ER stress sensitivity assay\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal in vivo and in vitro methods, replicated across mouse model and cell culture\",\n      \"pmids\": [\"25698737\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"CLCC1 functions as an intracellular chloride channel; the disease-associated p.D25E missense variant decreases CLCC1 channel function and causes mutant protein to accumulate in granules within the ER lumen; siRNA knockdown of CLCC1 induces apoptosis in retinal pigment epithelial cells; TALEN knockout in zebrafish causes retinal degeneration rescuable by wild-type CLCC1 mRNA injection.\",\n      \"method\": \"Electrophysiology (channel function assay), fluorescence microscopy of mutant protein localization, siRNA knockdown + apoptosis assay, TALEN KO zebrafish rescue experiment\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — electrophysiology for channel activity, mutagenesis, multiple model organisms with rescue experiment\",\n      \"pmids\": [\"30157172\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CLCC1 is a pore-forming component of an ER anion channel that forms homomultimers; its channel activity is inhibited by luminal Ca2+ binding at conserved residues D25 and D181 and facilitated by PIP2 sensed at residue K298 in the intraluminal loop; CLCC1 maintains steady-state [Cl-]ER, [K+]ER, ER morphology, and ER Ca2+ homeostasis including internal Ca2+ release and steady-state [Ca2+]ER; ALS-associated mutations impair channel conductance and increase [Cl-]ER.\",\n      \"method\": \"Electrophysiology, site-directed mutagenesis of D25, D181, K298, ion concentration measurements, Ca2+ imaging, conditional knockout of Clcc1 in motor neurons, multiple Clcc1 loss-of-function allele comparisons\",\n      \"journal\": \"Cell research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted channel activity, mutagenesis of key residues, multiple orthogonal assays in vivo and in vitro\",\n      \"pmids\": [\"37142673\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SARS-CoV-2 ORF3A physically interacts with CLCC1 (co-immunoprecipitation and co-localization); ORF3A expression triggers a transcriptional UPR similar to CLCC1 knockdown; CLCC1 knockdown partially protects cells from ORF3A-mediated cell death and pre-activates homeostatic UPR targets (HSPA6, spliced XBP1) that are not further induced by ORF3A.\",\n      \"method\": \"Co-immunoprecipitation, co-localization microscopy, siRNA knockdown, transcriptional UPR assay, cell death quantification\",\n      \"journal\": \"PeerJ\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — reciprocal co-IP and functional epistasis but single lab, single study\",\n      \"pmids\": [\"37033725\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"The CLCC1 interactome, identified by LC-MS, is substantially composed of ER-compartment proteins; the p.D25E variant causes loss and gain of specific protein interactors, with the mutant showing increased interactions with cytoplasmic proteins; CLCC1 co-localizes with calnexin and SigmaR1 at the ER, and also co-localizes with SigmaR1 at mitochondria-associated ER membranes (MAMs).\",\n      \"method\": \"LC-MS interactome profiling, co-localization microscopy, validation of calnexin and SigmaR1 interactions\",\n      \"journal\": \"Neuroscience letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — MS interactome with microscopy validation, single lab\",\n      \"pmids\": [\"38621504\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CLCC1 is required for the membrane fusion step during herpes simplex virus 1 nuclear egress; loss of CLCC1 causes accumulation of capsid-containing perinuclear vesicles and reduced viral titers; in uninfected cells, CLCC1 loss causes nuclear blebbing consistent with a role in host nuclear export/NPC insertion; CLCC1 homologs were acquired from host genomes by horizontal gene transfer in Herpesvirales of mollusks and fish.\",\n      \"method\": \"Whole-genome CRISPR screen, electron microscopy of nuclear egress defects, viral titer assay, nuclear blebbing phenotyping in uninfected cells\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genome-wide CRISPR screen, multiple orthogonal phenotypic assays, published in high-impact peer-reviewed journal\",\n      \"pmids\": [\"41271665\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"CLCC1 regulates cellular lipid partition and systemic lipid homeostasis by participating in trans-bilayer equilibration (scrambling) of phospholipids at the ER; CLCC1 partners with the phospholipid scramblase TMEM41B to recognize imbalanced bilayers and promote lipid scrambling, thereby supporting lipoprotein biogenesis and bulk lipid transport; loss of CLCC1 causes giant lumenal lipid droplets enclosed by imbalanced ER bilayers and accelerated metabolic liver disease.\",\n      \"method\": \"CRISPR-Cas9 knockout, lipid droplet imaging, phospholipid asymmetry assays, Co-IP/interaction studies with TMEM41B, mouse knockout with hepatic phenotyping\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal biochemical and cell biological methods, published in Nature, replicated in preprint\",\n      \"pmids\": [\"41741642\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CLCC1 is required for nuclear pore complex (NPC) biogenesis; loss of CLCC1 causes nuclear membrane herniations and impaired NPC assembly; CLCC1 is the human homolog of yeast Brl1p/Brr6p, identified by remote homology; Torsins (Tor1A) interact with CLCC1 and regulate its activity at NPC assembly sites, and CLCC1 overexpression rescues NPC biogenesis and developmental defects caused by Torsin loss-of-function.\",\n      \"method\": \"Proximity labeling (BioID) of Torsin1A, CRISPR knockout, nuclear membrane herniation imaging, CLCC1 overexpression rescue, phylogenetic analysis, Drosophila genetic experiments\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — proximity labeling, genetic rescue, multiple model systems, but preprint not yet peer-reviewed\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SenA (senkyunolide A) binds CLCC1 and promotes its ubiquitination, thereby inhibiting CLCC1 channel activity and ER Ca2+ release; si-CLCC1 in cholangiocytes phenocopies SenA effects on ER Ca2+ release and cholangiocyte proliferation, establishing CLCC1 as a regulator of ER Ca2+ release in cholangiocytes.\",\n      \"method\": \"Molecular binding assay, ubiquitination assay, siRNA knockdown, Ca2+ imaging, BDL mouse model\",\n      \"journal\": \"Acta pharmacologica Sinica\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — multiple biochemical methods with functional readout, single lab\",\n      \"pmids\": [\"40664817\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CLCC1 is an ER-resident anion channel that forms homomultimers and whose conductance is regulated by luminal Ca2+ (binding residues D25/D181) and PIP2 (sensing residue K298); it maintains ER ion homeostasis (Cl⁻, K⁺) and ER Ca2+ homeostasis, supports protein folding capacity (UPR regulation), participates in trans-bilayer phospholipid scrambling together with TMEM41B to support lipoprotein biogenesis, and acts as a membrane fusogen at the nuclear envelope required for nuclear pore complex assembly—roles disrupted by disease-associated mutations causing neurodegeneration, retinitis pigmentosa, and ALS-like pathologies.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2015,\n      \"finding\": \"Loss-of-function mutation in Clcc1 (retrotransposon insertion) in mice causes progressive cerebellar granule cell death and peripheral motor axon degeneration. Acute knockdown of Clcc1 in cultured cells increases sensitivity to ER stress, GRP78 is upregulated in Clcc1-deficient neurons in vivo, and ubiquitinated proteins accumulate prior to neurodegeneration, establishing that CLCC1 is required for ER protein-folding homeostasis.\",\n      \"method\": \"Positional cloning, retrotransposon insertion mouse model, siRNA knockdown in cultured cells, immunohistochemistry for GRP78 and ubiquitinated proteins\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo loss-of-function mouse model with defined molecular phenotype (ER stress markers, ubiquitinated protein accumulation) plus in vitro knockdown replicated findings\",\n      \"pmids\": [\"25698737\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"CLCC1 functions as an intracellular chloride channel highly expressed in the retina; a missense variant p.D25E decreases CLCC1 channel function and causes mutant protein to accumulate in granules within the ER lumen. siRNA knockdown of CLCC1 induces apoptosis in ARPE-19 cells, and loss of CLCC1 in zebrafish impairs cone ERG response, retinal thickness, and opsin expression — all rescued by wild-type CLCC1 mRNA injection.\",\n      \"method\": \"Electrophysiology (channel function assay), immunofluorescence/EM for protein localization, siRNA knockdown, TALEN knockout zebrafish with rescue by mRNA injection, ERG recordings, Clcc1+/- mouse phenotyping\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — channel function directly measured, multiple orthogonal methods including KO rescue in zebrafish and heterozygous mouse phenotyping\",\n      \"pmids\": [\"30157172\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"CLCC1 interacts with the mitochondrial outer membrane microprotein PIGBOS at ER-mitochondria contact sites (MAMs). Loss of PIGBOS (the interacting partner) leads to heightened UPR and increased cell death, placing CLCC1 at the ER-mitochondria interface as part of inter-organelle UPR regulation.\",\n      \"method\": \"Co-localization microscopy, proximity interaction (BioID), functional loss-of-function studies of PIGBOS with UPR readouts\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — interaction identified and localization confirmed, but functional link was demonstrated via PIGBOS KO rather than direct CLCC1 manipulation in this study\",\n      \"pmids\": [\"31653868\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CLCC1 is a pore-forming component of an ER anion channel that forms homomultimers. Channel activity is inhibited by luminal Ca2+ (binding mediated by conserved residues D25 and D181 in the N-terminus) and facilitated by PIP2 (sensed by K298 in the intraluminal loop). CLCC1 maintains steady-state [Cl-]ER, [K+]ER, and ER morphology, and regulates ER Ca2+ homeostasis including internal Ca2+ release and steady-state [Ca2+]ER. ALS-associated mutations increase steady-state [Cl-]ER and impair ER Ca2+ homeostasis. Conditional knockout of Clcc1 cell-autonomously causes motor neuron loss, ER stress, misfolded protein accumulation, and ALS-like pathologies.\",\n      \"method\": \"Electrophysiology (patch-clamp of ER-derived vesicles), site-directed mutagenesis of Ca2+-binding and PIP2-sensing residues, ion imaging ([Cl-]ER, [K+]ER, [Ca2+]ER), co-IP for homomultimerization, conditional Clcc1 knockout mouse, phenotypic comparison of multiple loss-of-function alleles\",\n      \"journal\": \"Cell research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct electrophysiological demonstration of pore-forming activity, mutagenesis of functional residues, multiple orthogonal methods, in vivo conditional KO with defined phenotype\",\n      \"pmids\": [\"37142673\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SARS-CoV-2 ORF3A co-localizes with and co-immunoprecipitates with CLCC1. ORF3A expression triggers a UPR similar to CLCC1 knockdown; cells with CLCC1 knockdown are partially protected from ORF3A-mediated cell death, and pre-upregulation of UPR targets (HSPA6, spliced XBP1) by CLCC1 knockdown prevents further induction by ORF3A, placing CLCC1 in the same pathway as ORF3A-induced UPR.\",\n      \"method\": \"Co-immunoprecipitation, co-localization microscopy, siRNA knockdown, transcriptional UPR reporter assays, cell death assays with chemical chaperone rescue\",\n      \"journal\": \"PeerJ\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — reciprocal co-IP plus epistatic relationship demonstrated by knockdown/overexpression with defined molecular readouts\",\n      \"pmids\": [\"37033725\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"The CLCC1 interactome (identified by LC-MS) is substantially composed of ER-localized proteins. The pathogenic p.Asp25Glu variant causes a notable loss and gain of specific protein interactors, with increased association with cytoplasmic proteins. Two novel interactors, Calnexin and SigmaR1, were validated by co-localization microscopy, and CLCC1 was shown to co-localize with SigmaR1 not only at the ER but also at mitochondria-associated ER membranes (MAMs).\",\n      \"method\": \"Liquid chromatography-mass spectrometry (LC-MS) interactome, co-localization microscopy\",\n      \"journal\": \"Neuroscience letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — MS-based interactome with microscopy validation of selected interactors; single lab, no reciprocal Co-IP\",\n      \"pmids\": [\"38621504\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CLCC1 is required for the fusion stage of herpes simplex virus 1 nuclear egress (identified by whole-genome CRISPR screen). Loss of CLCC1 causes accumulation of capsid-containing perinuclear vesicles and a drop in viral titers. In uninfected cells, loss of CLCC1 causes nuclear blebbing, implicating CLCC1 in host nuclear envelope membrane fusion. Herpesviruses infecting mollusks and fish encode viral CLCC1 homologs acquired by horizontal gene transfer, suggesting CLCC1 mediates an ancient membrane fusion mechanism hijacked by herpesviruses.\",\n      \"method\": \"Whole-genome CRISPR screen, CLCC1 knockout cells with viral titer and capsid localization assays, nuclear morphology imaging, phylogenetic analysis\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genome-wide unbiased screen plus functional validation with defined molecular and viral phenotypes, supported by evolutionary evidence\",\n      \"pmids\": [\"41271665\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CLCC1 regulates trans-bilayer equilibration of phospholipids at the ER by partnering with the phospholipid scramblase TMEM41B to recognize imbalanced ER bilayers and promote lipid scrambling. Loss of CLCC1 leads to emergence of giant lumenal lipid droplets enclosed by imbalanced ER bilayers and accelerates metabolic-dysfunction-associated liver steatohepatitis (MASH), establishing CLCC1 as a regulator of lipoprotein biogenesis and systemic lipid homeostasis.\",\n      \"method\": \"CRISPR-Cas9 knockout (cells and mice), co-immunoprecipitation/interaction with TMEM41B, lipid droplet and ER morphology imaging, lipoprotein secretion assays, liver steatosis pathology in mouse KO\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods (KO in cells and mice, partner identification, organelle morphology, functional lipid flux assays) in a high-rigor study\",\n      \"pmids\": [\"41741642\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Senkyunolide A (SenA) binds CLCC1 and promotes its ubiquitination, thereby inhibiting CLCC1 activity and ER Ca2+ release in cholangiocytes. Inhibiting CLCC1 prevents Ca2+-mediated cholangiocyte proliferation and ductular reaction in cholestatic liver disease; si-CLCC1-loaded liposomes targeting cholangiocytes enhanced anti-ductular reaction effects.\",\n      \"method\": \"Molecular docking/binding assay (SenA-CLCC1 interaction), ubiquitination assay, siRNA knockdown, Ca2+ imaging, BDL animal model, primary cholangiocyte and human intrahepatic biliary epithelial cell experiments\",\n      \"journal\": \"Acta pharmacologica Sinica\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — direct binding and ubiquitination demonstrated with functional Ca2+ and proliferation readouts in multiple systems; single lab\",\n      \"pmids\": [\"40664817\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CLCC1 is identified as the human functional homolog of yeast Brl1p/Brr6p nuclear pore complex (NPC) assembly factors. Loss of CLCC1 in human cells causes extensive nuclear membrane herniations consistent with impaired NPC assembly. In Drosophila, loss of dClcc1 phenocopies Torsin-loss nuclear membrane fusion defects at NPC assembly sites; CLCC1/dClcc1 overexpression rescues NPC biogenesis and developmental defects caused by Torsin loss-of-function. Proximity labeling identified CLCC1 as a Torsin1A binding partner.\",\n      \"method\": \"Proximity labeling (BioTurboID), CRISPR-Cas9 KO in human cells, Drosophila genetic loss-of-function and rescue experiments, nuclear morphology EM/fluorescence imaging, remote homology/phylogenetic analysis\",\n      \"journal\": \"bioRxiv (preprint)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis in two model systems with defined NPC phenotype; functional rescue by overexpression; preprint not yet peer-reviewed\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CRISPR-Cas9 chemical-genetic interaction screens identified CLCC1 as a critical regulator of hepatic neutral lipid flux. Loss of CLCC1 results in large lumenal ER lipid droplets with lipoprotein properties, and knockout in mice causes liver steatosis. Remote homology analysis identified a domain in CLCC1 homologous to yeast Brl1p/Brr6p, and loss of CLCC1 leads to extensive nuclear membrane herniations, consistent with impaired NPC assembly.\",\n      \"method\": \"Genome-wide CRISPR-Cas9 chemical-genetic screens, KO mouse liver histology, EM of ER lipid droplets, remote homology search, nuclear morphology analysis\",\n      \"journal\": \"bioRxiv (preprint)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — unbiased CRISPR screen plus in vivo KO phenotype and organelle morphology; preprint\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"CLCC1 is an ER-resident, pore-forming anion channel that forms homomultimers and whose activity is regulated by luminal Ca2+ (via D25/D181) and PIP2 (via K298); it maintains ER ion homeostasis ([Cl-]ER, [K+]ER), ER Ca2+ homeostasis, ER morphology, and protein-folding capacity (UPR), and also promotes trans-bilayer phospholipid scrambling by partnering with TMEM41B to support lipoprotein biogenesis and systemic lipid homeostasis, while additionally functioning as a membrane fusogen required for nuclear pore complex biogenesis and herpesviral nuclear egress—with disruption of any of these functions leading to ER stress, neurodegeneration, ALS-like pathologies, retinal degeneration, or liver steatohepatitis.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"CLCC1 is an ER-resident anion channel that maintains ER ion and protein-folding homeostasis, participates in phospholipid scrambling for lipoprotein biogenesis, and functions as a membrane fusogen required for nuclear pore complex assembly. CLCC1 forms homomultimers whose pore conductance is inhibited by luminal Ca²⁺ binding at conserved residues D25 and D181 and facilitated by PIP2 sensed at K298; it maintains steady-state ER Cl⁻, K⁺, and Ca²⁺ concentrations, and its loss triggers ER stress, UPR activation, and neurodegeneration [PMID:37142673, PMID:25698737]. CLCC1 partners with the phospholipid scramblase TMEM41B to recognize and correct trans-bilayer phospholipid imbalance at the ER, supporting lipoprotein biogenesis; hepatic loss causes giant luminal lipid droplets and accelerated metabolic liver disease [PMID:41741642]. Disease-associated mutations in CLCC1 impair channel conductance and cause retinitis pigmentosa and ALS-like motor neuron degeneration [PMID:30157172, PMID:37142673].\",\n  \"teleology\": [\n    {\n      \"year\": 2015,\n      \"claim\": \"Establishing that CLCC1 is essential for ER protein-folding homeostasis resolved why its loss causes neurodegeneration: CLCC1 deficiency triggers ER stress, GRP78 upregulation, and ubiquitinated protein accumulation in vivo.\",\n      \"evidence\": \"Positional cloning of spontaneous mouse mutation, immunohistochemistry, siRNA knockdown with ER stress sensitivity assay\",\n      \"pmids\": [\"25698737\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Channel mechanism and ion selectivity not yet determined\", \"Whether ER stress is the proximal cause of neuronal death or a secondary effect was unresolved\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Demonstrating that CLCC1 functions as an intracellular chloride channel and that the disease-associated D25E variant impairs this activity linked a specific molecular defect to retinal degeneration, confirmed by zebrafish rescue.\",\n      \"evidence\": \"Electrophysiology, fluorescence microscopy of mutant protein, TALEN KO zebrafish with mRNA rescue\",\n      \"pmids\": [\"30157172\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Pore-forming topology and multimerization state unknown\", \"Regulatory mechanisms of channel gating uncharacterized\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Reconstituting CLCC1 as a pore-forming homomultimeric ER anion channel gated by luminal Ca²⁺ (D25/D181) and PIP2 (K298) established its biophysical mechanism and showed that ALS-associated mutations impair conductance and elevate ER Cl⁻.\",\n      \"evidence\": \"Electrophysiology with site-directed mutagenesis, ER ion concentration measurements, Ca²⁺ imaging, conditional motor neuron knockout\",\n      \"pmids\": [\"37142673\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"High-resolution structure of the channel pore not available\", \"How ER Cl⁻ elevation mechanistically drives motor neuron degeneration was unclear\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"The finding that SARS-CoV-2 ORF3A physically interacts with CLCC1 and triggers a UPR phenocopying CLCC1 loss revealed a viral strategy to co-opt ER ion homeostasis.\",\n      \"evidence\": \"Co-immunoprecipitation, co-localization microscopy, siRNA epistasis with UPR transcriptional readout\",\n      \"pmids\": [\"37033725\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether ORF3A directly blocks CLCC1 channel conductance was not tested\", \"Relevance during authentic SARS-CoV-2 infection not demonstrated\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Interactome profiling placed CLCC1 in a network of ER-resident proteins including calnexin and SigmaR1 and showed that the D25E mutation aberrantly shifts interactions toward cytoplasmic partners, suggesting mislocalization contributes to pathogenesis.\",\n      \"evidence\": \"LC-MS interactome of wild-type vs. D25E CLCC1, co-localization microscopy at MAMs\",\n      \"pmids\": [\"38621504\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequences of altered interactome not tested\", \"MAM localization functional significance uncharacterized\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"A genome-wide CRISPR screen identified CLCC1 as required for the membrane fusion step of herpes simplex virus 1 nuclear egress, and nuclear blebbing in uninfected knockout cells revealed an intrinsic role in nuclear envelope membrane dynamics.\",\n      \"evidence\": \"Whole-genome CRISPR screen, electron microscopy of perinuclear vesicle accumulation, nuclear blebbing in uninfected cells\",\n      \"pmids\": [\"41271665\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CLCC1 acts as a direct fusogen or facilitates fusion indirectly was not resolved\", \"Relationship to NPC assembly not established in this study\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identification of CLCC1 as a Torsin-regulated fusogen required for NPC biogenesis — the human ortholog of yeast Brl1p/Brr6p — unified the nuclear blebbing phenotype with a specific molecular function at nuclear pore insertion sites.\",\n      \"evidence\": \"BioID proximity labeling of Torsin1A, CRISPR KO, CLCC1 overexpression rescue of Torsin loss, phylogenetic analysis, Drosophila genetics (preprint)\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Not yet peer-reviewed\", \"Biochemical reconstitution of CLCC1-mediated membrane fusion not performed\", \"Whether channel activity and fusogenic activity are separable functions is unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Demonstrating that SenA promotes CLCC1 ubiquitination and inhibits ER Ca²⁺ release in cholangiocytes provided pharmacological evidence that CLCC1 channel activity controls ER Ca²⁺ release in a therapeutically targetable manner.\",\n      \"evidence\": \"Molecular binding assay, ubiquitination assay, siRNA phenocopy, Ca²⁺ imaging in cholangiocytes, BDL mouse model\",\n      \"pmids\": [\"40664817\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct binding site of SenA on CLCC1 not mapped\", \"Whether ubiquitination degrades CLCC1 or allosterically modulates channel gating is unclear\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Establishing that CLCC1 partners with TMEM41B to scramble phospholipids at the ER expanded its function beyond ion transport and explained how its loss causes giant luminal lipid droplets and metabolic liver disease.\",\n      \"evidence\": \"CRISPR KO, phospholipid asymmetry assays, Co-IP with TMEM41B, mouse hepatic phenotyping\",\n      \"pmids\": [\"41741642\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CLCC1 itself has intrinsic scramblase activity or solely activates TMEM41B is unresolved\", \"Structural basis of CLCC1–TMEM41B complex formation unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A high-resolution structure of CLCC1 — alone and in complex with TMEM41B or Torsins — is needed to determine how ion channel, scramblase, and fusogenic activities are structurally integrated or segregated.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No atomic structure of CLCC1 available\", \"Whether channel and fusogen functions use the same or distinct protein surfaces is unknown\", \"Tissue-specific regulation of CLCC1's diverse activities is uncharacterized\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [1, 2]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [0, 1, 2, 4]},\n      {\"term_id\": \"GO:0005635\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": []},\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [1, 2]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [6]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"complexes\": [\n      \"CLCC1 homomultimer\",\n      \"CLCC1–TMEM41B complex\"\n    ],\n    \"partners\": [\n      \"TMEM41B\",\n      \"TOR1A\",\n      \"SIGMAR1\",\n      \"CANX\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"CLCC1 is an ER-resident, pore-forming anion channel that maintains ER ion and Ca²⁺ homeostasis, ER morphology, protein-folding capacity, lipid bilayer symmetry, and nuclear envelope membrane fusion. It forms homomultimers whose channel activity is inhibited by luminal Ca²⁺ (via D25 and D181) and facilitated by PIP₂ (via K298), and it sustains steady-state [Cl⁻]ER, [K⁺]ER, and [Ca²⁺]ER; loss-of-function mutations cause ER stress, misfolded protein accumulation, and ALS-like motor neuron degeneration in conditional knockout mice [PMID:37142673], while a D25E variant impairs channel function and causes retinal degeneration in zebrafish and mice [PMID:30157172]. CLCC1 partners with the phospholipid scramblase TMEM41B to promote trans-bilayer phospholipid equilibration at the ER, and its loss produces giant lumenal lipid droplets and accelerates metabolic-dysfunction-associated steatohepatitis [PMID:41741642]. CLCC1 also functions as a membrane fusogen required for nuclear pore complex biogenesis and herpesviral nuclear egress, with loss causing nuclear membrane herniations and blebbing [PMID:41271665].\",\n  \"teleology\": [\n    {\n      \"year\": 2015,\n      \"claim\": \"Establishing CLCC1 as essential for ER protein-folding homeostasis resolved the molecular basis of a progressive neurodegenerative phenotype in mice and linked the gene's loss to ER stress and ubiquitinated-protein accumulation.\",\n      \"evidence\": \"Positional cloning of a retrotransposon insertion in Clcc1 in a mouse model, supplemented by siRNA knockdown in cultured cells with GRP78 and ubiquitin readouts\",\n      \"pmids\": [\"25698737\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Molecular mechanism (channel vs. other activity) was unknown\",\n        \"Whether CLCC1 loss in other tissues caused similar pathology was untested\",\n        \"Direct biochemical activity of the protein was not demonstrated\"\n      ]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Demonstrating that CLCC1 functions as an intracellular chloride channel and that the disease-associated D25E variant impairs channel activity connected the ER-stress phenotype to a specific ion-conduction defect and extended pathology to the retina.\",\n      \"evidence\": \"Electrophysiology of CLCC1 channel function, siRNA knockdown-induced apoptosis in ARPE-19 cells, TALEN-knockout zebrafish with wild-type mRNA rescue, ERG recordings, heterozygous mouse retinal phenotyping\",\n      \"pmids\": [\"30157172\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether CLCC1 itself forms the pore or requires auxiliary subunits was unresolved\",\n        \"Selectivity profile and gating mechanism were not fully characterized\",\n        \"Downstream signaling between ion flux and UPR induction was unclear\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identification of CLCC1 as an interactor of mitochondrial microprotein PIGBOS at ER–mitochondria contact sites placed the channel at inter-organelle signaling hubs involved in UPR regulation.\",\n      \"evidence\": \"BioID proximity labeling and co-localization microscopy at MAMs; UPR and cell death readouts upon PIGBOS loss\",\n      \"pmids\": [\"31653868\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Functional consequence was shown via PIGBOS KO, not direct CLCC1 manipulation in this study\",\n        \"Whether CLCC1 channel activity is modulated at MAMs was not tested\",\n        \"Stoichiometry and directness of the CLCC1–PIGBOS interaction were not established\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Direct electrophysiology of ER-derived vesicles established CLCC1 as a pore-forming homomultimeric anion channel gated by luminal Ca²⁺ (D25/D181) and PIP₂ (K298), and conditional knockout demonstrated cell-autonomous motor neuron loss with ALS-like features, unifying ion homeostasis and neurodegeneration.\",\n      \"evidence\": \"Patch-clamp of ER vesicles, site-directed mutagenesis, ion imaging for [Cl⁻]ER/[K⁺]ER/[Ca²⁺]ER, co-IP for homomultimerization, conditional Clcc1 KO mouse\",\n      \"pmids\": [\"37142673\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"High-resolution structure of the channel pore is lacking\",\n        \"Precise stoichiometry of the homomultimer is not defined\",\n        \"Causal link between specific ion imbalance (Cl⁻ vs. K⁺ vs. Ca²⁺) and neurodegeneration has not been dissected\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Identification of SARS-CoV-2 ORF3A as a CLCC1 interactor that phenocopies CLCC1 knockdown-induced UPR suggested that viral proteins can co-opt or disrupt CLCC1-dependent ER homeostasis.\",\n      \"evidence\": \"Co-immunoprecipitation, co-localization, siRNA knockdown epistasis with ORF3A expression, UPR reporter and cell death assays\",\n      \"pmids\": [\"37033725\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Direct effect of ORF3A on CLCC1 channel activity was not measured\",\n        \"Physiological relevance during live SARS-CoV-2 infection was not demonstrated\",\n        \"Mechanism of protection from ORF3A-mediated death upon CLCC1 knockdown is unclear\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Proteomic mapping of the CLCC1 interactome confirmed its ER-centric interaction network, identified calnexin and SigmaR1 as novel partners (including at MAMs), and showed that the D25E pathogenic variant remodels the interactome.\",\n      \"evidence\": \"LC-MS interactome of wild-type and D25E CLCC1, co-localization microscopy for calnexin and SigmaR1\",\n      \"pmids\": [\"38621504\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Interactions validated only by co-localization, not reciprocal co-IP\",\n        \"Functional consequences of altered interactome for the D25E variant were not tested\",\n        \"Whether calnexin or SigmaR1 modulate channel activity is unknown\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"A genome-wide CRISPR screen revealed that CLCC1 is required for herpesviral nuclear egress at the membrane fusion step, and its loss in uninfected cells causes nuclear blebbing, establishing CLCC1 as a host membrane fusogen with an ancient evolutionary role hijacked by herpesviruses.\",\n      \"evidence\": \"Whole-genome CRISPR screen, CLCC1 KO cells with viral titer and capsid localization assays, nuclear morphology imaging, phylogenetic analysis of viral CLCC1 homologs\",\n      \"pmids\": [\"41271665\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Mechanism by which CLCC1 mediates membrane fusion is uncharacterized at the biochemical level\",\n        \"Whether the fusogenic activity depends on channel function is unknown\",\n        \"Relationship between nuclear blebbing phenotype and NPC biogenesis was not dissected in this study\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Discovery that CLCC1 partners with TMEM41B to promote ER phospholipid scrambling and lipoprotein biogenesis revealed a lipid-homeostatic function; loss causes giant lumenal lipid droplets and accelerates steatohepatitis, linking CLCC1 to systemic metabolic disease.\",\n      \"evidence\": \"CRISPR KO in cells and mice, co-IP with TMEM41B, lipid droplet/ER morphology imaging, lipoprotein secretion assays, liver histopathology\",\n      \"pmids\": [\"41741642\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether CLCC1 ion-channel activity is required for its scramblase-partnering role is not determined\",\n        \"Structural basis of the CLCC1–TMEM41B interaction is unknown\",\n        \"Relative contribution of lipid vs. ion homeostasis defects to liver pathology is unclear\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Pharmacological targeting of CLCC1 by Senkyunolide A, which promotes CLCC1 ubiquitination and inhibits ER Ca²⁺ release, demonstrated that CLCC1 activity drives cholangiocyte proliferation in cholestatic liver disease, providing proof-of-concept for therapeutic modulation.\",\n      \"evidence\": \"SenA binding assay, ubiquitination assay, Ca²⁺ imaging, siRNA in primary cholangiocytes and human biliary epithelial cells, bile-duct-ligation mouse model\",\n      \"pmids\": [\"40664817\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Direct binding site of SenA on CLCC1 relies on molecular docking and needs structural confirmation\",\n        \"Specificity of SenA for CLCC1 vs. off-target effects was not comprehensively assessed\",\n        \"Whether ubiquitination-mediated degradation or direct channel block is the primary inhibitory mechanism is unresolved\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key open questions include the high-resolution structure of the CLCC1 channel, whether ion-channel and membrane-fusion/scramblase-partnering activities are mechanistically separable, and how disruption of distinct CLCC1 functions (ion homeostasis, lipid scrambling, NPC assembly) leads to tissue-specific disease outcomes.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No high-resolution structure exists\",\n        \"Separation-of-function mutants distinguishing channel, fusogenic, and scramblase-partnering roles have not been generated\",\n        \"Tissue-specific phenotype determinants (neuronal vs. retinal vs. hepatic) are not understood\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [1, 3]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [3, 7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [0, 1, 3, 5, 7]},\n      {\"term_id\": \"GO:0005635\", \"supporting_discovery_ids\": [6, 9]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [1, 3]},\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [1, 3]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [7]},\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [0, 3]},\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [6, 9]}\n    ],\n    \"complexes\": [\n      \"CLCC1 homomultimer\",\n      \"CLCC1–TMEM41B complex\"\n    ],\n    \"partners\": [\n      \"TMEM41B\",\n      \"PIGBOS\",\n      \"SIGMAR1\",\n      \"CANX\",\n      \"TOR1A\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}