{"gene":"C2CD5","run_date":"2026-04-28T17:12:38","timeline":{"discoveries":[{"year":2011,"finding":"CDP138 (C2CD5) is a substrate for Akt2 (PKBβ); its C2 domain binds Ca²⁺ and lipid membranes; phosphorylation at S197 by Akt2 and intact Ca²⁺-binding sites in the C2 domain are required for insulin-stimulated GLUT4 vesicle insertion into the plasma membrane in adipocytes; CDP138 dynamically associates with the plasma membrane and GLUT4-containing vesicles in response to insulin.","method":"Quantitative phosphoproteomics, RNAi knockdown, live-cell imaging of GLUT4 fusion, purified C2 domain lipid/Ca²⁺-binding assay, Akt2 phosphorylation site mutagenesis (S197A), Ca²⁺-binding site mutants","journal":"Cell metabolism","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal methods including in vitro binding assay, site-directed mutagenesis, and live-cell functional readout in a single study","pmids":["21907143"],"is_preprint":false},{"year":2014,"finding":"C2CD5 (KIAA0528) forms a stable complex with CDK5 and FIBP in non-neuronal cells; KIAA0528 and FIBP are required for assembly and stability of this CDK5 complex; depletion of any component impairs cell proliferation and migration.","method":"Proteomic AP-MS (modified SAINT analysis), co-immunoprecipitation, RNAi knockdown with proliferation and migration assays","journal":"Molecular & cellular proteomics : MCP","confidence":"High","confidence_rationale":"Tier 2 — reciprocal co-IP/AP-MS with functional KD validation across two cell lines","pmids":["25096995"],"is_preprint":false},{"year":2017,"finding":"CDP138 (C2CD5) physically interacts with CDK5 and modulates TGF-β/Smad signaling in lung cancer cells through upregulation of GDF15; knockdown of CDP138 attenuates GDF15 expression and downstream Smad signaling, reducing radioresistance and invasive migration.","method":"RNAi knockdown, GDF15 rescue experiments, TGF-β/Smad pathway reporter/western blot, migration/invasion assays","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2–3 — functional epistasis via rescue but mechanistic linkage to CDK5 complex is primarily by co-IP without deep structural validation","pmids":["28880265"],"is_preprint":false},{"year":2018,"finding":"CDP138 (C2CD5) is a Ca²⁺- and lipid-binding membrane trafficking protein exclusively expressed in adrenal medulla and sympathetic nerve terminals in fat; its loss impairs catecholamine (epinephrine/norepinephrine) secretion, reducing cAMP formation and HSL phosphorylation in adipose tissue and impairing cold-induced beige fat browning and thermogenesis; knockout mice develop obesity and HFD-induced insulin resistance.","method":"CDP138 whole-body KO mice, immunolocalization (co-staining with tyrosine hydroxylase), catecholamine ELISA, cAMP and HSL phosphorylation assays, metabolic cage measurements, glucose/insulin tolerance tests","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — KO mouse model with multiple orthogonal biochemical readouts linking C2CD5 to catecholamine secretion pathway","pmids":["29378832"],"is_preprint":false},{"year":2019,"finding":"C2CD5 (KIAA0528) acts together with CDK5 and 14-3-3ε to promote NudEL phosphorylation, which increases the dynein–NudEL interaction and enables dynein force adaptation (increasing force production duration and magnitude) for intracellular transport of lipid droplets, lysosomes, and mitochondria.","method":"Single-molecule in vivo force measurements on lipid droplets, RNAi depletion of each component, epistasis analysis in COS-1 cells (lacking Tau), extended to lysosomes/mitochondria","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1–2 — quantitative single-molecule force assay combined with genetic epistasis across multiple cargo types","pmids":["30651536"],"is_preprint":false},{"year":2019,"finding":"C2CD5 is expressed in hypothalamic neurons and interacts with endocytosis machinery; loss of functional C2CD5 (lacking its C2 domain) blunts MC4R endocytosis, increases MC4R surface levels that fail to respond to ligand, and reduces acute anorectic responses to MTII injection; C2CD5 KO mice exhibit increased food intake and obesity.","method":"In situ hybridization/RNAscope + EM, antibody-feeding endocytosis assay in HA-MC4R-GFP Neuro2A cells, flow cytometry, C2CD5 KO mice with PVH MTII injection, TSE metabolic cages","journal":"Metabolism: clinical and experimental","confidence":"High","confidence_rationale":"Tier 2 — domain deletion mutant combined with in vitro endocytosis assay and in vivo KO phenotype with defined molecular target","pmids":["31666192"],"is_preprint":false},{"year":2021,"finding":"C2CD5 is required for proper mitochondrial trafficking, ultrastructure, and oxidative function in hypothalamic neurons; loss of C2CD5 alters mitochondrial localization and activity, and impaired mitochondrial function correlates with defective MC4R endocytosis/trafficking.","method":"C2CD5 KO primary hypothalamic neuronal cultures and cell lines, electron microscopy, live-cell imaging, oxygen consumption assay","journal":"Neuroendocrinology","confidence":"Medium","confidence_rationale":"Tier 2 — KO with multiple cellular assays but mechanistic link between mitochondrial function and MC4R trafficking is correlative","pmids":["34034255"],"is_preprint":false},{"year":2025,"finding":"USP5 deubiquitinase stabilizes C2CD5 protein by removing ubiquitin modifications (deubiquitination); C2CD5 stability activates the PI3K/AKT/mTOR signaling pathway and enhances glycolytic flux via HIF-1α; USP5, C2CD5, FIBP, and CDK5 form a protein complex identified by co-immunoprecipitation coupled with mass spectrometry.","method":"Co-immunoprecipitation + mass spectrometry, ubiquitination assay, USP5 knockdown/overexpression, PI3K/AKT/mTOR/HIF-1α pathway western blots, AML mouse model","journal":"Biochemical pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 — co-IP/MS identifies complex; deubiquitination and downstream pathway activation shown by biochemical assays in single study","pmids":["41344512"],"is_preprint":false},{"year":2026,"finding":"C2CD5 expressed in DBH+ noradrenergic sympathetic neurons regulates norepinephrine secretion; conditional KO of C2CD5 in DBH+ neurons reduces NE secretion, impairs thermogenesis, lowers energy expenditure, and promotes adiposity; NE supplementation rescues these metabolic defects.","method":"Conditional KO mice (DBH-Cre × C2CD5-flox), NE secretion measurements, metabolic phenotyping (energy expenditure, body composition, thermogenesis), NE rescue experiment","journal":"iScience","confidence":"High","confidence_rationale":"Tier 2 — cell-type-specific KO with NE rescue providing clean mechanistic evidence for C2CD5 role in NE secretion","pmids":["42006349"],"is_preprint":false}],"current_model":"C2CD5 (CDP138) is a Ca²⁺- and lipid-binding C2-domain phosphoprotein that functions as a membrane trafficking regulator: it is phosphorylated by Akt2 at S197 to drive GLUT4 vesicle fusion with the plasma membrane in adipocytes, acts in a stable complex with CDK5 and FIBP to regulate dynein force adaptation and intracellular organelle transport via NudEL phosphorylation, controls MC4R endocytosis in hypothalamic neurons through its C2 domain, regulates catecholamine/norepinephrine secretion from sympathetic neurons to govern thermogenesis and energy balance, and is itself stabilized post-translationally by the USP5 deubiquitinase, which links C2CD5 to PI3K/AKT/mTOR/HIF-1α-driven glycolysis."},"narrative":{"teleology":[{"year":2011,"claim":"Identification of C2CD5 as an Akt2 substrate with Ca²⁺/lipid-binding capacity established it as a regulated membrane-trafficking effector in the insulin-GLUT4 pathway, answering how post-insulin signaling is coupled to vesicle fusion at the plasma membrane.","evidence":"Quantitative phosphoproteomics, S197A mutagenesis, C2-domain lipid/Ca²⁺ binding assays, and live-cell GLUT4 fusion imaging in 3T3-L1 adipocytes","pmids":["21907143"],"confidence":"High","gaps":["Identity of the SNARE or tethering machinery engaged by phospho-C2CD5 at the plasma membrane is unknown","Whether C2CD5 acts catalytically or as a scaffold/adaptor during vesicle fusion is unresolved"]},{"year":2014,"claim":"Discovery that C2CD5 forms a stable trimeric complex with CDK5 and FIBP revealed it as a scaffold required for CDK5 complex integrity, broadening its role beyond adipocyte GLUT4 trafficking to a general cell-biological function.","evidence":"Reciprocal AP-MS (SAINT analysis) and co-IP in non-neuronal cells; RNAi depletion showing interdependent complex stability and effects on proliferation/migration","pmids":["25096995"],"confidence":"High","gaps":["Structural basis for the C2CD5–CDK5–FIBP interaction is unknown","Whether C2CD5 modulates CDK5 kinase activity directly or only mediates substrate access is unresolved"]},{"year":2017,"claim":"Linking the C2CD5–CDK5 axis to TGF-β/Smad signaling via GDF15 upregulation showed a route through which this complex modulates radioresistance and invasion in lung cancer cells.","evidence":"RNAi knockdown with GDF15 rescue, Smad pathway reporters, and invasion assays in lung cancer cell lines","pmids":["28880265"],"confidence":"Medium","gaps":["How C2CD5–CDK5 upregulates GDF15 transcriptionally is not defined","Relevance beyond lung cancer cell lines not tested","No direct kinase-substrate relationship between CDK5 and GDF15 or Smad components demonstrated"]},{"year":2018,"claim":"Whole-body KO mice demonstrated that C2CD5 is selectively expressed in catecholaminergic cells (adrenal medulla and sympathetic nerve terminals in fat) and is required for catecholamine secretion, establishing C2CD5 as a neuroendocrine exocytosis regulator governing thermogenesis and energy balance.","evidence":"C2CD5 KO mice with catecholamine ELISA, HSL phosphorylation, metabolic phenotyping, and glucose/insulin tolerance tests","pmids":["29378832"],"confidence":"High","gaps":["Molecular step at which C2CD5 acts in catecholamine vesicle exocytosis is undefined","Relative contribution of adrenal medulla versus sympathetic nerve terminals not dissected"]},{"year":2019,"claim":"Demonstration that the C2CD5–CDK5–14-3-3ε axis phosphorylates NudEL to enhance dynein force adaptation provided a defined molecular mechanism for C2CD5's role in intracellular organelle transport across lipid droplets, lysosomes, and mitochondria.","evidence":"Single-molecule in vivo force measurements on lipid droplets in COS-1 cells, RNAi epistasis, extension to lysosomes and mitochondria","pmids":["30651536"],"confidence":"High","gaps":["Whether C2CD5's C2 domain or its CDK5-scaffolding function is the critical determinant for cargo-specific transport is unresolved","Force adaptation measured only in COS-1 cells; relevance in neurons and adipocytes not directly tested"]},{"year":2019,"claim":"Showing that C2CD5's C2 domain is required for MC4R endocytosis in hypothalamic neurons connected C2CD5's membrane-trafficking function to central appetite regulation, explaining the obesity phenotype of KO mice through impaired receptor internalization.","evidence":"Antibody-feeding endocytosis assay in HA-MC4R-GFP Neuro2A cells, C2-domain deletion mutant, C2CD5 KO mice with PVH MTII injection and metabolic phenotyping","pmids":["31666192"],"confidence":"High","gaps":["Direct binding between C2CD5 and MC4R or its endocytic adaptor not demonstrated","Whether C2CD5 facilitates clathrin-dependent or -independent endocytosis of MC4R is unknown"]},{"year":2021,"claim":"Linking C2CD5 loss to defective mitochondrial trafficking and oxidative function in hypothalamic neurons provided a potential explanation for how impaired organelle transport secondary to C2CD5 deficiency might compound MC4R trafficking defects.","evidence":"C2CD5 KO primary hypothalamic neurons and cell lines with electron microscopy, live-cell imaging, and oxygen consumption assays","pmids":["34034255"],"confidence":"Medium","gaps":["Causal direction between mitochondrial dysfunction and MC4R trafficking defect not established","Whether mitochondrial phenotype is dynein/NudEL-dependent is untested"]},{"year":2025,"claim":"Identification of USP5 as a deubiquitinase that stabilizes C2CD5 protein, coupled with evidence that C2CD5 stability activates PI3K/AKT/mTOR/HIF-1α-driven glycolysis, revealed a post-translational control layer for C2CD5 abundance with implications in AML.","evidence":"Co-IP/MS identifying USP5–C2CD5–FIBP–CDK5 complex, ubiquitination assays, USP5 knockdown/overexpression, pathway western blots in AML model","pmids":["41344512"],"confidence":"Medium","gaps":["Ubiquitin chain type and specific lysine residues on C2CD5 targeted by USP5 not identified","Whether PI3K/AKT/mTOR activation is a direct consequence of C2CD5 scaffolding or indirect through CDK5 is unresolved","Single study; independent confirmation in non-AML contexts needed"]},{"year":2026,"claim":"Cell-type-specific conditional KO in DBH+ noradrenergic neurons, with NE rescue of metabolic defects, provided definitive evidence that C2CD5 functions cell-autonomously in sympathetic neurons to control norepinephrine secretion and systemic energy homeostasis.","evidence":"DBH-Cre × C2CD5-flox conditional KO mice with NE secretion measurements, metabolic phenotyping, and NE supplementation rescue","pmids":["42006349"],"confidence":"High","gaps":["Step in the NE vesicle cycle (docking, priming, or fusion) at which C2CD5 acts is not pinpointed","Whether the CDK5–NudEL force adaptation mechanism operates in NE secretory vesicle transport is unknown"]},{"year":null,"claim":"The precise molecular mechanism by which C2CD5 promotes vesicle exocytosis — whether through Ca²⁺-dependent membrane docking, CDK5-dependent cytoskeletal force generation, or both — remains to be resolved, as does the structural basis for its multivalent scaffolding of CDK5, FIBP, and 14-3-3ε.","evidence":"","pmids":[],"confidence":"Low","gaps":["No high-resolution structure of C2CD5 or its complexes exists","Relative contribution of C2 domain membrane binding versus CDK5 scaffolding to each trafficking function is unresolved","Whether C2CD5 possesses any intrinsic catalytic activity is unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[0]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,1,4]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,5]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[0,3,8]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[1,4]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,7]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[0,3,5,8]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[3,8]}],"complexes":["CDK5–C2CD5–FIBP complex"],"partners":["CDK5","FIBP","YWHAE","NDEL1","USP5","AKT2"],"other_free_text":[]},"mechanistic_narrative":"C2CD5 is a Ca²⁺- and lipid-binding C2-domain protein that controls vesicle fusion, endocytosis, and organelle transport across multiple cell types, linking membrane trafficking to metabolic homeostasis. Its C2 domain mediates Ca²⁺-dependent membrane association; phosphorylation at S197 by Akt2 drives insulin-stimulated GLUT4 vesicle insertion at the plasma membrane in adipocytes, while the same domain is required for MC4R endocytosis in hypothalamic neurons [PMID:21907143, PMID:31666192]. C2CD5 forms a stable complex with CDK5 and FIBP that promotes NudEL phosphorylation, enabling dynein force adaptation for intracellular transport of lipid droplets, lysosomes, and mitochondria [PMID:25096995, PMID:30651536]. In sympathetic neurons, C2CD5 is essential for catecholamine and norepinephrine secretion; its loss impairs thermogenesis and energy expenditure, producing obesity in knockout mice that is rescued by norepinephrine supplementation [PMID:29378832, PMID:42006349]."},"prefetch_data":{"uniprot":{"accession":"Q86YS7","full_name":"C2 domain-containing protein 5","aliases":["C2 domain-containing phosphoprotein of 138 kDa"],"length_aa":1000,"mass_kda":110.4,"function":"Required for insulin-stimulated glucose transport and glucose transporter SLC2A4/GLUT4 translocation from intracellular glucose storage vesicle (GSV) to the plasma membrane (PM) in adipocytes. Binds phospholipid membranes in a calcium-dependent manner and is necessary for the optimal membrane fusion between SLC2A4/GLUT4 GSV and the PM","subcellular_location":"Cytoplasmic vesicle membrane; Cytoplasm, cell cortex; Cell membrane; Cell projection, ruffle","url":"https://www.uniprot.org/uniprotkb/Q86YS7/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/C2CD5","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/C2CD5","total_profiled":1310},"omim":[{"mim_id":"618044","title":"C2 CALCIUM-DEPENDENT DOMAIN-CONTAINING PROTEIN 5; C2CD5","url":"https://www.omim.org/entry/618044"},{"mim_id":"607844","title":"LEM DOMAIN-CONTAINING PROTEIN 3; LEMD3","url":"https://www.omim.org/entry/607844"},{"mim_id":"166700","title":"BUSCHKE-OLLENDORFF SYNDROME; BOS","url":"https://www.omim.org/entry/166700"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Cytosol","reliability":"Supported"},{"location":"Centriolar satellite","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/C2CD5"},"hgnc":{"alias_symbol":["CDP138"],"prev_symbol":["KIAA0528"]},"alphafold":{"accession":"Q86YS7","domains":[{"cath_id":"2.60.40.150","chopping":"2-136","consensus_level":"medium","plddt":89.8825,"start":2,"end":136},{"cath_id":"3.30.110.70","chopping":"145-250","consensus_level":"medium","plddt":87.9875,"start":145,"end":250},{"cath_id":"-","chopping":"349-443_462-633_678-797","consensus_level":"medium","plddt":86.0353,"start":349,"end":797}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q86YS7","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q86YS7-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q86YS7-F1-predicted_aligned_error_v6.png","plddt_mean":74.06},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=C2CD5","jax_strain_url":"https://www.jax.org/strain/search?query=C2CD5"},"sequence":{"accession":"Q86YS7","fasta_url":"https://rest.uniprot.org/uniprotkb/Q86YS7.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q86YS7/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q86YS7"}},"corpus_meta":[{"pmid":"21907143","id":"PMC_21907143","title":"C2 domain-containing phosphoprotein CDP138 regulates GLUT4 insertion into the plasma membrane.","date":"2011","source":"Cell metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/21907143","citation_count":55,"is_preprint":false},{"pmid":"28880265","id":"PMC_28880265","title":"CDP138 silencing inhibits TGF-β/Smad signaling to impair radioresistance and metastasis via GDF15 in lung cancer.","date":"2017","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/28880265","citation_count":45,"is_preprint":false},{"pmid":"25096995","id":"PMC_25096995","title":"Proteomic analysis of the human cyclin-dependent kinase family reveals a novel CDK5 complex involved in cell growth and migration.","date":"2014","source":"Molecular & cellular proteomics : MCP","url":"https://pubmed.ncbi.nlm.nih.gov/25096995","citation_count":37,"is_preprint":false},{"pmid":"31666192","id":"PMC_31666192","title":"Hypothalamic C2-domain protein involved in MC4R trafficking and control of energy balance.","date":"2019","source":"Metabolism: clinical and experimental","url":"https://pubmed.ncbi.nlm.nih.gov/31666192","citation_count":20,"is_preprint":false},{"pmid":"30651536","id":"PMC_30651536","title":"Regulation of in vivo dynein force production by CDK5 and 14-3-3ε and KIAA0528.","date":"2019","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/30651536","citation_count":16,"is_preprint":false},{"pmid":"29378832","id":"PMC_29378832","title":"Membrane Trafficking Protein CDP138 Regulates Fat Browning and Insulin Sensitivity through Controlling Catecholamine Release.","date":"2018","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/29378832","citation_count":14,"is_preprint":false},{"pmid":"34034255","id":"PMC_34034255","title":"Loss of C2 Domain Protein (C2CD5) Alters Hypothalamic Mitochondrial Trafficking, Structure, and Function.","date":"2021","source":"Neuroendocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/34034255","citation_count":6,"is_preprint":false},{"pmid":"37679009","id":"PMC_37679009","title":"Mosaicism for a 12p12.1p12.2 microdeletion with a normal euploid cell line at amniocentesis in a pregnancy with a favorable outcome and postnatal decrease of the aneuploid cell line with microdeletion.","date":"2023","source":"Taiwanese journal of obstetrics & gynecology","url":"https://pubmed.ncbi.nlm.nih.gov/37679009","citation_count":5,"is_preprint":false},{"pmid":"39127651","id":"PMC_39127651","title":"Core biomarkers analysis benefit for diagnosis on human intrahepatic cholestasis of pregnancy.","date":"2024","source":"BMC pregnancy and childbirth","url":"https://pubmed.ncbi.nlm.nih.gov/39127651","citation_count":2,"is_preprint":false},{"pmid":"41344512","id":"PMC_41344512","title":"Deubiquitinase USP5 promotes acute myeloid leukemia through C2CD5 stabilization and PI3K/AKT/mTOR/HIF-1α-driven glycolysis.","date":"2025","source":"Biochemical pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/41344512","citation_count":0,"is_preprint":false},{"pmid":"42006349","id":"PMC_42006349","title":"C2CD5 in noradrenergic neurons regulates thermogenesis and lipid homeostasis via norepinephrine secretion.","date":"2026","source":"iScience","url":"https://pubmed.ncbi.nlm.nih.gov/42006349","citation_count":0,"is_preprint":false},{"pmid":"40049403","id":"PMC_40049403","title":"Genetic parameters and identification of genomic regions and candidate genes associated with vaginal discharge score in Holstein cattle based on genomic and transcriptomic analyses.","date":"2025","source":"Journal of dairy science","url":"https://pubmed.ncbi.nlm.nih.gov/40049403","citation_count":0,"is_preprint":false},{"pmid":"41880302","id":"PMC_41880302","title":"Composite selection signal analysis: Uncovering candidate genes and quantitative trait loci in Indian sheep breeds.","date":"2026","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/41880302","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":8865,"output_tokens":2495,"usd":0.03201},"stage2":{"model":"claude-opus-4-6","input_tokens":5855,"output_tokens":2909,"usd":0.153},"total_usd":0.18501,"stage1_batch_id":"msgbatch_01TqNM6p6FsoMBT2jzQTwKBr","stage2_batch_id":"msgbatch_01Ya473eco8sTHbvRymQaU8o","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2011,\n      \"finding\": \"CDP138 (C2CD5) is a substrate for Akt2 (PKBβ); its C2 domain binds Ca²⁺ and lipid membranes; phosphorylation at S197 by Akt2 and intact Ca²⁺-binding sites in the C2 domain are required for insulin-stimulated GLUT4 vesicle insertion into the plasma membrane in adipocytes; CDP138 dynamically associates with the plasma membrane and GLUT4-containing vesicles in response to insulin.\",\n      \"method\": \"Quantitative phosphoproteomics, RNAi knockdown, live-cell imaging of GLUT4 fusion, purified C2 domain lipid/Ca²⁺-binding assay, Akt2 phosphorylation site mutagenesis (S197A), Ca²⁺-binding site mutants\",\n      \"journal\": \"Cell metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal methods including in vitro binding assay, site-directed mutagenesis, and live-cell functional readout in a single study\",\n      \"pmids\": [\"21907143\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"C2CD5 (KIAA0528) forms a stable complex with CDK5 and FIBP in non-neuronal cells; KIAA0528 and FIBP are required for assembly and stability of this CDK5 complex; depletion of any component impairs cell proliferation and migration.\",\n      \"method\": \"Proteomic AP-MS (modified SAINT analysis), co-immunoprecipitation, RNAi knockdown with proliferation and migration assays\",\n      \"journal\": \"Molecular & cellular proteomics : MCP\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP/AP-MS with functional KD validation across two cell lines\",\n      \"pmids\": [\"25096995\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"CDP138 (C2CD5) physically interacts with CDK5 and modulates TGF-β/Smad signaling in lung cancer cells through upregulation of GDF15; knockdown of CDP138 attenuates GDF15 expression and downstream Smad signaling, reducing radioresistance and invasive migration.\",\n      \"method\": \"RNAi knockdown, GDF15 rescue experiments, TGF-β/Smad pathway reporter/western blot, migration/invasion assays\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — functional epistasis via rescue but mechanistic linkage to CDK5 complex is primarily by co-IP without deep structural validation\",\n      \"pmids\": [\"28880265\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"CDP138 (C2CD5) is a Ca²⁺- and lipid-binding membrane trafficking protein exclusively expressed in adrenal medulla and sympathetic nerve terminals in fat; its loss impairs catecholamine (epinephrine/norepinephrine) secretion, reducing cAMP formation and HSL phosphorylation in adipose tissue and impairing cold-induced beige fat browning and thermogenesis; knockout mice develop obesity and HFD-induced insulin resistance.\",\n      \"method\": \"CDP138 whole-body KO mice, immunolocalization (co-staining with tyrosine hydroxylase), catecholamine ELISA, cAMP and HSL phosphorylation assays, metabolic cage measurements, glucose/insulin tolerance tests\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — KO mouse model with multiple orthogonal biochemical readouts linking C2CD5 to catecholamine secretion pathway\",\n      \"pmids\": [\"29378832\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"C2CD5 (KIAA0528) acts together with CDK5 and 14-3-3ε to promote NudEL phosphorylation, which increases the dynein–NudEL interaction and enables dynein force adaptation (increasing force production duration and magnitude) for intracellular transport of lipid droplets, lysosomes, and mitochondria.\",\n      \"method\": \"Single-molecule in vivo force measurements on lipid droplets, RNAi depletion of each component, epistasis analysis in COS-1 cells (lacking Tau), extended to lysosomes/mitochondria\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — quantitative single-molecule force assay combined with genetic epistasis across multiple cargo types\",\n      \"pmids\": [\"30651536\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"C2CD5 is expressed in hypothalamic neurons and interacts with endocytosis machinery; loss of functional C2CD5 (lacking its C2 domain) blunts MC4R endocytosis, increases MC4R surface levels that fail to respond to ligand, and reduces acute anorectic responses to MTII injection; C2CD5 KO mice exhibit increased food intake and obesity.\",\n      \"method\": \"In situ hybridization/RNAscope + EM, antibody-feeding endocytosis assay in HA-MC4R-GFP Neuro2A cells, flow cytometry, C2CD5 KO mice with PVH MTII injection, TSE metabolic cages\",\n      \"journal\": \"Metabolism: clinical and experimental\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — domain deletion mutant combined with in vitro endocytosis assay and in vivo KO phenotype with defined molecular target\",\n      \"pmids\": [\"31666192\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"C2CD5 is required for proper mitochondrial trafficking, ultrastructure, and oxidative function in hypothalamic neurons; loss of C2CD5 alters mitochondrial localization and activity, and impaired mitochondrial function correlates with defective MC4R endocytosis/trafficking.\",\n      \"method\": \"C2CD5 KO primary hypothalamic neuronal cultures and cell lines, electron microscopy, live-cell imaging, oxygen consumption assay\",\n      \"journal\": \"Neuroendocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO with multiple cellular assays but mechanistic link between mitochondrial function and MC4R trafficking is correlative\",\n      \"pmids\": [\"34034255\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"USP5 deubiquitinase stabilizes C2CD5 protein by removing ubiquitin modifications (deubiquitination); C2CD5 stability activates the PI3K/AKT/mTOR signaling pathway and enhances glycolytic flux via HIF-1α; USP5, C2CD5, FIBP, and CDK5 form a protein complex identified by co-immunoprecipitation coupled with mass spectrometry.\",\n      \"method\": \"Co-immunoprecipitation + mass spectrometry, ubiquitination assay, USP5 knockdown/overexpression, PI3K/AKT/mTOR/HIF-1α pathway western blots, AML mouse model\",\n      \"journal\": \"Biochemical pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — co-IP/MS identifies complex; deubiquitination and downstream pathway activation shown by biochemical assays in single study\",\n      \"pmids\": [\"41344512\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"C2CD5 expressed in DBH+ noradrenergic sympathetic neurons regulates norepinephrine secretion; conditional KO of C2CD5 in DBH+ neurons reduces NE secretion, impairs thermogenesis, lowers energy expenditure, and promotes adiposity; NE supplementation rescues these metabolic defects.\",\n      \"method\": \"Conditional KO mice (DBH-Cre × C2CD5-flox), NE secretion measurements, metabolic phenotyping (energy expenditure, body composition, thermogenesis), NE rescue experiment\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — cell-type-specific KO with NE rescue providing clean mechanistic evidence for C2CD5 role in NE secretion\",\n      \"pmids\": [\"42006349\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"C2CD5 (CDP138) is a Ca²⁺- and lipid-binding C2-domain phosphoprotein that functions as a membrane trafficking regulator: it is phosphorylated by Akt2 at S197 to drive GLUT4 vesicle fusion with the plasma membrane in adipocytes, acts in a stable complex with CDK5 and FIBP to regulate dynein force adaptation and intracellular organelle transport via NudEL phosphorylation, controls MC4R endocytosis in hypothalamic neurons through its C2 domain, regulates catecholamine/norepinephrine secretion from sympathetic neurons to govern thermogenesis and energy balance, and is itself stabilized post-translationally by the USP5 deubiquitinase, which links C2CD5 to PI3K/AKT/mTOR/HIF-1α-driven glycolysis.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"C2CD5 is a Ca²⁺- and lipid-binding C2-domain protein that controls vesicle fusion, endocytosis, and organelle transport across multiple cell types, linking membrane trafficking to metabolic homeostasis. Its C2 domain mediates Ca²⁺-dependent membrane association; phosphorylation at S197 by Akt2 drives insulin-stimulated GLUT4 vesicle insertion at the plasma membrane in adipocytes, while the same domain is required for MC4R endocytosis in hypothalamic neurons [PMID:21907143, PMID:31666192]. C2CD5 forms a stable complex with CDK5 and FIBP that promotes NudEL phosphorylation, enabling dynein force adaptation for intracellular transport of lipid droplets, lysosomes, and mitochondria [PMID:25096995, PMID:30651536]. In sympathetic neurons, C2CD5 is essential for catecholamine and norepinephrine secretion; its loss impairs thermogenesis and energy expenditure, producing obesity in knockout mice that is rescued by norepinephrine supplementation [PMID:29378832, PMID:42006349].\",\n  \"teleology\": [\n    {\n      \"year\": 2011,\n      \"claim\": \"Identification of C2CD5 as an Akt2 substrate with Ca²⁺/lipid-binding capacity established it as a regulated membrane-trafficking effector in the insulin-GLUT4 pathway, answering how post-insulin signaling is coupled to vesicle fusion at the plasma membrane.\",\n      \"evidence\": \"Quantitative phosphoproteomics, S197A mutagenesis, C2-domain lipid/Ca²⁺ binding assays, and live-cell GLUT4 fusion imaging in 3T3-L1 adipocytes\",\n      \"pmids\": [\"21907143\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Identity of the SNARE or tethering machinery engaged by phospho-C2CD5 at the plasma membrane is unknown\",\n        \"Whether C2CD5 acts catalytically or as a scaffold/adaptor during vesicle fusion is unresolved\"\n      ]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Discovery that C2CD5 forms a stable trimeric complex with CDK5 and FIBP revealed it as a scaffold required for CDK5 complex integrity, broadening its role beyond adipocyte GLUT4 trafficking to a general cell-biological function.\",\n      \"evidence\": \"Reciprocal AP-MS (SAINT analysis) and co-IP in non-neuronal cells; RNAi depletion showing interdependent complex stability and effects on proliferation/migration\",\n      \"pmids\": [\"25096995\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis for the C2CD5–CDK5–FIBP interaction is unknown\",\n        \"Whether C2CD5 modulates CDK5 kinase activity directly or only mediates substrate access is unresolved\"\n      ]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Linking the C2CD5–CDK5 axis to TGF-β/Smad signaling via GDF15 upregulation showed a route through which this complex modulates radioresistance and invasion in lung cancer cells.\",\n      \"evidence\": \"RNAi knockdown with GDF15 rescue, Smad pathway reporters, and invasion assays in lung cancer cell lines\",\n      \"pmids\": [\"28880265\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"How C2CD5–CDK5 upregulates GDF15 transcriptionally is not defined\",\n        \"Relevance beyond lung cancer cell lines not tested\",\n        \"No direct kinase-substrate relationship between CDK5 and GDF15 or Smad components demonstrated\"\n      ]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Whole-body KO mice demonstrated that C2CD5 is selectively expressed in catecholaminergic cells (adrenal medulla and sympathetic nerve terminals in fat) and is required for catecholamine secretion, establishing C2CD5 as a neuroendocrine exocytosis regulator governing thermogenesis and energy balance.\",\n      \"evidence\": \"C2CD5 KO mice with catecholamine ELISA, HSL phosphorylation, metabolic phenotyping, and glucose/insulin tolerance tests\",\n      \"pmids\": [\"29378832\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Molecular step at which C2CD5 acts in catecholamine vesicle exocytosis is undefined\",\n        \"Relative contribution of adrenal medulla versus sympathetic nerve terminals not dissected\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Demonstration that the C2CD5–CDK5–14-3-3ε axis phosphorylates NudEL to enhance dynein force adaptation provided a defined molecular mechanism for C2CD5's role in intracellular organelle transport across lipid droplets, lysosomes, and mitochondria.\",\n      \"evidence\": \"Single-molecule in vivo force measurements on lipid droplets in COS-1 cells, RNAi epistasis, extension to lysosomes and mitochondria\",\n      \"pmids\": [\"30651536\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether C2CD5's C2 domain or its CDK5-scaffolding function is the critical determinant for cargo-specific transport is unresolved\",\n        \"Force adaptation measured only in COS-1 cells; relevance in neurons and adipocytes not directly tested\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Showing that C2CD5's C2 domain is required for MC4R endocytosis in hypothalamic neurons connected C2CD5's membrane-trafficking function to central appetite regulation, explaining the obesity phenotype of KO mice through impaired receptor internalization.\",\n      \"evidence\": \"Antibody-feeding endocytosis assay in HA-MC4R-GFP Neuro2A cells, C2-domain deletion mutant, C2CD5 KO mice with PVH MTII injection and metabolic phenotyping\",\n      \"pmids\": [\"31666192\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Direct binding between C2CD5 and MC4R or its endocytic adaptor not demonstrated\",\n        \"Whether C2CD5 facilitates clathrin-dependent or -independent endocytosis of MC4R is unknown\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Linking C2CD5 loss to defective mitochondrial trafficking and oxidative function in hypothalamic neurons provided a potential explanation for how impaired organelle transport secondary to C2CD5 deficiency might compound MC4R trafficking defects.\",\n      \"evidence\": \"C2CD5 KO primary hypothalamic neurons and cell lines with electron microscopy, live-cell imaging, and oxygen consumption assays\",\n      \"pmids\": [\"34034255\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Causal direction between mitochondrial dysfunction and MC4R trafficking defect not established\",\n        \"Whether mitochondrial phenotype is dynein/NudEL-dependent is untested\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identification of USP5 as a deubiquitinase that stabilizes C2CD5 protein, coupled with evidence that C2CD5 stability activates PI3K/AKT/mTOR/HIF-1α-driven glycolysis, revealed a post-translational control layer for C2CD5 abundance with implications in AML.\",\n      \"evidence\": \"Co-IP/MS identifying USP5–C2CD5–FIBP–CDK5 complex, ubiquitination assays, USP5 knockdown/overexpression, pathway western blots in AML model\",\n      \"pmids\": [\"41344512\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Ubiquitin chain type and specific lysine residues on C2CD5 targeted by USP5 not identified\",\n        \"Whether PI3K/AKT/mTOR activation is a direct consequence of C2CD5 scaffolding or indirect through CDK5 is unresolved\",\n        \"Single study; independent confirmation in non-AML contexts needed\"\n      ]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Cell-type-specific conditional KO in DBH+ noradrenergic neurons, with NE rescue of metabolic defects, provided definitive evidence that C2CD5 functions cell-autonomously in sympathetic neurons to control norepinephrine secretion and systemic energy homeostasis.\",\n      \"evidence\": \"DBH-Cre × C2CD5-flox conditional KO mice with NE secretion measurements, metabolic phenotyping, and NE supplementation rescue\",\n      \"pmids\": [\"42006349\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Step in the NE vesicle cycle (docking, priming, or fusion) at which C2CD5 acts is not pinpointed\",\n        \"Whether the CDK5–NudEL force adaptation mechanism operates in NE secretory vesicle transport is unknown\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The precise molecular mechanism by which C2CD5 promotes vesicle exocytosis — whether through Ca²⁺-dependent membrane docking, CDK5-dependent cytoskeletal force generation, or both — remains to be resolved, as does the structural basis for its multivalent scaffolding of CDK5, FIBP, and 14-3-3ε.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No high-resolution structure of C2CD5 or its complexes exists\",\n        \"Relative contribution of C2 domain membrane binding versus CDK5 scaffolding to each trafficking function is unresolved\",\n        \"Whether C2CD5 possesses any intrinsic catalytic activity is unknown\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 1, 4]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 5]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [0, 3, 8]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [1, 4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 7]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [0, 3, 5, 8]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [3, 8]}\n    ],\n    \"complexes\": [\n      \"CDK5–C2CD5–FIBP complex\"\n    ],\n    \"partners\": [\n      \"CDK5\",\n      \"FIBP\",\n      \"YWHAE\",\n      \"NDEL1\",\n      \"USP5\",\n      \"AKT2\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}