{"gene":"C2CD5","run_date":"2026-06-09T22:02:45","timeline":{"discoveries":[{"year":2011,"finding":"CDP138 (C2CD5) is a substrate for Akt2 (PKBβ); the purified C2 domain binds Ca²⁺ and lipid membranes; Akt2 phosphorylates CDP138 at S197; CDP138 is dynamically associated with the plasma membrane and GLUT4-containing vesicles in response to insulin; mutants lacking Ca²⁺-binding sites or the S197 phosphorylation site inhibit insulin-stimulated GLUT4 insertion into the plasma membrane; CDP138 is required for fusion of GLUT4 vesicles with the plasma membrane in live adipocytes.","method":"Quantitative phosphoproteomics, RNAi knockdown, purified C2 domain lipid/Ca²⁺ binding assays, site-directed mutagenesis, live-cell GLUT4 vesicle fusion imaging in adipocytes","journal":"Cell Metabolism","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods including in vitro biochemical assays, mutagenesis of active site (S197 and Ca²⁺-binding sites), live-cell imaging, and RNAi knockdown with defined functional readout","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 the assembly and stability of this CDK5 complex; depletion of any of the three components impairs breast cancer cell proliferation and migration.","method":"Proteomic affinity purification/mass spectrometry, modified SAINT analysis, co-immunoprecipitation, RNAi knockdown with proliferation and migration assays","journal":"Molecular & Cellular Proteomics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP and MS in two cell lines, functional knockdown with defined readouts, single lab","pmids":["25096995"],"is_preprint":false},{"year":2017,"finding":"CDP138 positively modulates TGF-β/Smad signaling through upregulation of GDF15; CDP138 silencing reduces GDF15 expression, attenuates TGF-β/Smad pathway activation, and the phenotypes (reduced migration, invasion, radioresistance) caused by CDP138 knockdown are partially rescued by GDF15.","method":"RNAi knockdown, rescue experiments with GDF15, Smad signaling assays, migration/invasion assays, radiosensitivity assays in lung cancer cells","journal":"Cell Death & Disease","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — functional epistasis via rescue experiment with GDF15, multiple phenotypic readouts, single lab","pmids":["28880265"],"is_preprint":false},{"year":2018,"finding":"CDP138 (C2CD5) is a calcium- and lipid-binding membrane trafficking protein exclusively expressed in adrenal medulla and sympathetic nervous terminals in inguinal fat; CDP138 knockout mice show altered catecholamine levels and impaired cold-induced adrenergic signaling (reduced cAMP and HSL phosphorylation), indicating CDP138 regulates catecholamine secretion from sympathetic neurons and adrenal gland, which in turn controls fat browning and insulin sensitivity.","method":"CDP138 whole-body knockout mice, catecholamine measurement, adrenergic signaling assays (cAMP, HSL phosphorylation), cold-challenge experiments, colocalization with tyrosine hydroxylase","journal":"Molecular and Cellular Biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — whole-body KO mouse model with multiple orthogonal phenotypic and biochemical readouts; mechanistic pathway (catecholamine secretion → adrenergic signaling → browning) established with rescue-equivalent specificity controls","pmids":["29378832"],"is_preprint":false},{"year":2019,"finding":"C2CD5 (KIAA0528) acts as a CDK5 cofactor that, together with CDK5 and 14-3-3ε, promotes NudEL phosphorylation, thereby increasing the dynein–NudEL interaction and enabling force adaptation (increased dynein force production) for lipid droplet, lysosome, and mitochondria transport in vivo.","method":"Single-molecule dynein force measurements in COS-1 cells, RNAi knockdown of KIAA0528/CDK5/14-3-3ε, NudEL phosphorylation assays, lipid droplet/lysosome/mitochondria transport assays","journal":"Nature Communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — quantitative single-molecule force measurements combined with RNAi epistasis across multiple organelle systems, mechanistic pathway clearly established","pmids":["30651536"],"is_preprint":false},{"year":2019,"finding":"Hypothalamic C2CD5 is involved in MC4R endocytosis; loss of functional C2CD5 (lacking the C2 domain) blunts MC4R endocytosis in vitro and increases MC4R at the cell surface, which then fails to respond to MC4R ligand; C2CD5 interacts with endocytosis machinery in the hypothalamus; C2CD5KO mice exhibit decreased acute responses to MC4R agonist MTII injected into the paraventricular hypothalamus.","method":"C2CD5 whole-body KO mice, antibody feeding endocytosis assay in N2A cells stably expressing HA-MC4R-GFP, flow cytometry, in vivo MTII injection, electron microscopy, in situ hybridization/RNAscope","journal":"Metabolism: Clinical and Experimental","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — in vitro endocytosis assay with domain-deletion mutant and in vivo KO with agonist challenge; single lab, two orthogonal approaches","pmids":["31666192"],"is_preprint":false},{"year":2021,"finding":"C2CD5 is necessary for proper mitochondrial trafficking, ultrastructure, and function (oxygen consumption) in hypothalamic neurons; loss of C2CD5 alters mitochondrial morphology (electron microscopy), localization (live imaging), and activity; impaired mitochondrial function in C2CD5 KO neurons is linked to reduced MC4R endocytosis/trafficking.","method":"C2CD5 whole-body KO primary hypothalamic neuronal cultures, electron microscopy, live-cell imaging, oxygen consumption assay","journal":"Neuroendocrinology","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — multiple orthogonal methods (EM, live imaging, oxygen consumption) in primary neurons, single lab","pmids":["34034255"],"is_preprint":false},{"year":2025,"finding":"USP5 deubiquitinase stabilizes C2CD5 through deubiquitination; USP5 interacts with a complex containing C2CD5, FIBP, and CDK5; stabilization of C2CD5 by USP5 activates the PI3K/AKT/mTOR signaling pathway and enhances glycolytic flux via HIF-1α to drive AML progression.","method":"Co-immunoprecipitation coupled with mass spectrometry, USP5 knockdown, deubiquitination assays, PI3K/AKT/mTOR pathway readouts, in vivo AML mouse model","journal":"Biochemical Pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP/MS identification of complex, deubiquitination assay, pathway activation readouts, in vivo model; single lab","pmids":["41344512"],"is_preprint":false},{"year":2026,"finding":"C2CD5 is expressed in dopamine β-hydroxylase (DBH)-positive sympathetic neurons; conditional knockout of C2CD5 in DBH+ neurons reduces norepinephrine (NE) secretion, impairs thermogenesis, lowers energy expenditure, and promotes adiposity; supplementation with NE mitigates these effects, placing C2CD5 upstream of NE secretion in sympathetic regulation of thermogenesis.","method":"Conditional KO mice (C2CD5 deleted in DBH+ neurons), NE secretion measurements, metabolic cage analysis, NE supplementation rescue experiment","journal":"iScience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cell-type-specific conditional KO with NE rescue, multiple metabolic readouts; single lab, extends prior whole-body KO findings","pmids":["42006349"],"is_preprint":false}],"current_model":"C2CD5 (CDP138) is a calcium- and lipid-binding C2-domain protein that functions as a membrane trafficking regulator: it is phosphorylated by Akt2 at S197 to promote GLUT4 vesicle fusion with the plasma membrane in adipocytes; it forms a stable complex with CDK5 and FIBP to enable CDK5-mediated NudEL phosphorylation and dynein force adaptation for intracellular organelle transport; it is stabilized by the deubiquitinase USP5 (which activates PI3K/AKT/mTOR/HIF-1α–driven glycolysis); it regulates MC4R endocytosis and mitochondrial trafficking/function in hypothalamic neurons; and, in DBH+ sympathetic neurons, it controls norepinephrine secretion to govern thermogenesis and energy balance."},"narrative":{"mechanistic_narrative":"C2CD5 (CDP138/KIAA0528) is a calcium- and lipid-binding C2-domain protein that regulates regulated membrane trafficking and vesicle fusion across metabolic and neuronal tissues [PMID:21907143, PMID:29378832]. In adipocytes it acts as a direct Akt2 substrate: its purified C2 domain binds Ca²⁺ and lipid membranes, Akt2 phosphorylates it at S197, and both Ca²⁺-binding and S197 phosphorylation are required for insulin-stimulated fusion of GLUT4 vesicles with the plasma membrane [PMID:21907143]. A second mechanistic role centers on intracellular organelle transport, where C2CD5 forms a stable complex with CDK5 and FIBP and, together with 14-3-3ε, promotes CDK5-mediated NudEL phosphorylation to increase dynein–NudEL interaction and dynein force production for movement of lipid droplets, lysosomes, and mitochondria [PMID:25096995, PMID:30651536]. In the nervous system C2CD5 governs sympathetic catecholamine output: it is expressed in adrenal medulla and DBH⁺ sympathetic neurons, and its loss reduces norepinephrine secretion and impairs cold-induced adrenergic signaling, fat browning, energy expenditure, and insulin sensitivity, defects mitigated by norepinephrine supplementation [PMID:29378832, PMID:42006349]. In hypothalamic neurons C2CD5 promotes MC4R endocytosis through its C2 domain and is required for proper mitochondrial trafficking, ultrastructure, and respiration [PMID:31666192, PMID:34034255]. C2CD5 is stabilized by the deubiquitinase USP5, which acts on a C2CD5–FIBP–CDK5 complex to activate PI3K/AKT/mTOR signaling and HIF-1α–driven glycolysis in acute myeloid leukemia [PMID:41344512].","teleology":[{"year":2011,"claim":"Established C2CD5 as an Akt2 effector linking insulin signaling to vesicle fusion, answering how phosphoinositide-3-kinase output is converted into membrane fusion of glucose transporter vesicles.","evidence":"Quantitative phosphoproteomics, purified C2-domain Ca²⁺/lipid binding assays, S197 and Ca²⁺-site mutagenesis, RNAi, and live-cell GLUT4 fusion imaging in adipocytes","pmids":["21907143"],"confidence":"High","gaps":["Identity of the fusion machinery (SNAREs/tethers) C2CD5 engages not defined","Structural basis of Ca²⁺/lipid binding by the C2 domain not resolved"]},{"year":2014,"claim":"Defined C2CD5 as a structural component of a CDK5 complex, showing it is not solely an adipocyte trafficking protein but an assembly factor for a kinase complex relevant to cell proliferation and migration.","evidence":"Affinity purification/MS with SAINT analysis, reciprocal co-IP, and RNAi proliferation/migration assays in breast cancer cells","pmids":["25096995"],"confidence":"Medium","gaps":["Molecular role of C2CD5 within the complex (scaffold vs. cofactor) not mechanistically dissected here","Substrates downstream of the complex not identified at this stage"]},{"year":2017,"claim":"Connected C2CD5 to TGF-β/Smad signaling via GDF15, extending its functional reach to a transcriptional/secreted-factor axis controlling cancer cell phenotypes.","evidence":"RNAi knockdown, GDF15 rescue, Smad signaling, migration/invasion, and radiosensitivity assays in lung cancer cells","pmids":["28880265"],"confidence":"Medium","gaps":["Direct mechanism by which C2CD5 upregulates GDF15 unknown","Rescue was only partial, leaving additional effectors unaccounted for"]},{"year":2018,"claim":"Established an in vivo physiological role for C2CD5 in sympathetic/adrenal catecholamine secretion controlling fat browning and insulin sensitivity, moving beyond cell-based trafficking assays.","evidence":"Whole-body knockout mice, catecholamine measurement, cAMP/HSL phosphorylation readouts, cold challenge, and tyrosine hydroxylase colocalization","pmids":["29378832"],"confidence":"High","gaps":["Molecular step in catecholamine vesicle secretion controlled by C2CD5 not pinpointed","Whole-body KO cannot exclude contributions from non-neuronal tissues"]},{"year":2019,"claim":"Mechanistically resolved the CDK5 complex function, showing C2CD5 acts as a CDK5 cofactor driving NudEL phosphorylation and dynein force adaptation for organelle transport.","evidence":"Single-molecule dynein force measurements, RNAi epistasis of C2CD5/CDK5/14-3-3ε, NudEL phosphorylation, and lipid droplet/lysosome/mitochondria transport assays in COS-1 cells","pmids":["30651536"],"confidence":"High","gaps":["How C2CD5's C2/lipid-binding activity contributes to this cytosolic kinase function not clarified","Direct contact between C2CD5 and CDK5 active site not structurally defined"]},{"year":2019,"claim":"Identified a hypothalamic neuronal role in MC4R endocytosis, linking C2CD5 trafficking activity to central melanocortin signaling and energy balance.","evidence":"Whole-body KO mice, antibody-feeding endocytosis assay with C2-domain deletion mutant, flow cytometry, EM, in vivo MTII injection, and RNAscope","pmids":["31666192"],"confidence":"Medium","gaps":["Specific endocytic machinery components C2CD5 binds not named","Whether MC4R endocytosis defect is direct or secondary to broader trafficking loss unresolved"]},{"year":2021,"claim":"Showed C2CD5 is required for mitochondrial trafficking, morphology, and respiration in hypothalamic neurons, tying its transport function to neuronal bioenergetics.","evidence":"Primary hypothalamic neuron cultures from KO mice, EM, live-cell imaging, and oxygen consumption assays","pmids":["34034255"],"confidence":"Medium","gaps":["Causal ordering between mitochondrial dysfunction and MC4R trafficking defect not established","Whether mitochondrial phenotype reflects the dynein/CDK5 transport pathway not tested directly"]},{"year":2025,"claim":"Revealed post-translational control of C2CD5 by USP5 deubiquitination, coupling C2CD5 stability to PI3K/AKT/mTOR and HIF-1α–driven glycolysis in leukemia.","evidence":"Co-IP/MS, USP5 knockdown, deubiquitination assays, pathway readouts, and an in vivo AML mouse model","pmids":["41344512"],"confidence":"Medium","gaps":["Ubiquitin ligase opposing USP5 on C2CD5 not identified","Direct mechanism by which stabilized C2CD5 activates PI3K/AKT/mTOR not defined"]},{"year":2026,"claim":"Refined the sympathetic role using cell-type-specific deletion, placing C2CD5 upstream of norepinephrine secretion in DBH⁺ neurons to control thermogenesis and adiposity.","evidence":"DBH-specific conditional KO mice, NE secretion measurements, metabolic cage analysis, and NE supplementation rescue","pmids":["42006349"],"confidence":"Medium","gaps":["Molecular step in NE vesicle secretion governed by C2CD5 not defined","Connection to the C2CD5 GLUT4/dynein mechanisms in this neuronal context not established"]},{"year":null,"claim":"How a single C2-domain trafficking protein mechanistically unifies Akt2-dependent GLUT4 fusion, CDK5-dependent dynein force adaptation, and regulated catecholamine secretion remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of C2CD5 or its complexes","Whether the C2/Ca²⁺-lipid module is used in all these contexts is untested","The direct fusion/secretion machinery C2CD5 engages is not identified"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[0,3]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[1,4]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[4]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[0]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[4]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[0,5]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,7]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[4,6]}],"complexes":["C2CD5-CDK5-FIBP complex"],"partners":["CDK5","FIBP","AKT2","YWHAE","USP5"],"other_free_text":[]}},"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":56,"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":46,"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":21,"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":15,"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":7,"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":9627,"output_tokens":2669,"usd":0.034458,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":10010,"output_tokens":3705,"usd":0.071337,"stage2_stop_reason":"end_turn"},"total_usd":0.105795,"stage1_batch_id":"msgbatch_0179Z2pxRYBsXi2xADneafRw","stage2_batch_id":"msgbatch_01LaY9ZaVdgjWArcZo9eqQE5","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); the purified C2 domain binds Ca²⁺ and lipid membranes; Akt2 phosphorylates CDP138 at S197; CDP138 is dynamically associated with the plasma membrane and GLUT4-containing vesicles in response to insulin; mutants lacking Ca²⁺-binding sites or the S197 phosphorylation site inhibit insulin-stimulated GLUT4 insertion into the plasma membrane; CDP138 is required for fusion of GLUT4 vesicles with the plasma membrane in live adipocytes.\",\n      \"method\": \"Quantitative phosphoproteomics, RNAi knockdown, purified C2 domain lipid/Ca²⁺ binding assays, site-directed mutagenesis, live-cell GLUT4 vesicle fusion imaging in adipocytes\",\n      \"journal\": \"Cell Metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods including in vitro biochemical assays, mutagenesis of active site (S197 and Ca²⁺-binding sites), live-cell imaging, and RNAi knockdown with defined functional readout\",\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 the assembly and stability of this CDK5 complex; depletion of any of the three components impairs breast cancer cell proliferation and migration.\",\n      \"method\": \"Proteomic affinity purification/mass spectrometry, modified SAINT analysis, co-immunoprecipitation, RNAi knockdown with proliferation and migration assays\",\n      \"journal\": \"Molecular & Cellular Proteomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP and MS in two cell lines, functional knockdown with defined readouts, single lab\",\n      \"pmids\": [\"25096995\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"CDP138 positively modulates TGF-β/Smad signaling through upregulation of GDF15; CDP138 silencing reduces GDF15 expression, attenuates TGF-β/Smad pathway activation, and the phenotypes (reduced migration, invasion, radioresistance) caused by CDP138 knockdown are partially rescued by GDF15.\",\n      \"method\": \"RNAi knockdown, rescue experiments with GDF15, Smad signaling assays, migration/invasion assays, radiosensitivity assays in lung cancer cells\",\n      \"journal\": \"Cell Death & Disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — functional epistasis via rescue experiment with GDF15, multiple phenotypic readouts, single lab\",\n      \"pmids\": [\"28880265\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"CDP138 (C2CD5) is a calcium- and lipid-binding membrane trafficking protein exclusively expressed in adrenal medulla and sympathetic nervous terminals in inguinal fat; CDP138 knockout mice show altered catecholamine levels and impaired cold-induced adrenergic signaling (reduced cAMP and HSL phosphorylation), indicating CDP138 regulates catecholamine secretion from sympathetic neurons and adrenal gland, which in turn controls fat browning and insulin sensitivity.\",\n      \"method\": \"CDP138 whole-body knockout mice, catecholamine measurement, adrenergic signaling assays (cAMP, HSL phosphorylation), cold-challenge experiments, colocalization with tyrosine hydroxylase\",\n      \"journal\": \"Molecular and Cellular Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — whole-body KO mouse model with multiple orthogonal phenotypic and biochemical readouts; mechanistic pathway (catecholamine secretion → adrenergic signaling → browning) established with rescue-equivalent specificity controls\",\n      \"pmids\": [\"29378832\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"C2CD5 (KIAA0528) acts as a CDK5 cofactor that, together with CDK5 and 14-3-3ε, promotes NudEL phosphorylation, thereby increasing the dynein–NudEL interaction and enabling force adaptation (increased dynein force production) for lipid droplet, lysosome, and mitochondria transport in vivo.\",\n      \"method\": \"Single-molecule dynein force measurements in COS-1 cells, RNAi knockdown of KIAA0528/CDK5/14-3-3ε, NudEL phosphorylation assays, lipid droplet/lysosome/mitochondria transport assays\",\n      \"journal\": \"Nature Communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — quantitative single-molecule force measurements combined with RNAi epistasis across multiple organelle systems, mechanistic pathway clearly established\",\n      \"pmids\": [\"30651536\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Hypothalamic C2CD5 is involved in MC4R endocytosis; loss of functional C2CD5 (lacking the C2 domain) blunts MC4R endocytosis in vitro and increases MC4R at the cell surface, which then fails to respond to MC4R ligand; C2CD5 interacts with endocytosis machinery in the hypothalamus; C2CD5KO mice exhibit decreased acute responses to MC4R agonist MTII injected into the paraventricular hypothalamus.\",\n      \"method\": \"C2CD5 whole-body KO mice, antibody feeding endocytosis assay in N2A cells stably expressing HA-MC4R-GFP, flow cytometry, in vivo MTII injection, electron microscopy, in situ hybridization/RNAscope\",\n      \"journal\": \"Metabolism: Clinical and Experimental\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — in vitro endocytosis assay with domain-deletion mutant and in vivo KO with agonist challenge; single lab, two orthogonal approaches\",\n      \"pmids\": [\"31666192\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"C2CD5 is necessary for proper mitochondrial trafficking, ultrastructure, and function (oxygen consumption) in hypothalamic neurons; loss of C2CD5 alters mitochondrial morphology (electron microscopy), localization (live imaging), and activity; impaired mitochondrial function in C2CD5 KO neurons is linked to reduced MC4R endocytosis/trafficking.\",\n      \"method\": \"C2CD5 whole-body KO primary hypothalamic neuronal cultures, electron microscopy, live-cell imaging, oxygen consumption assay\",\n      \"journal\": \"Neuroendocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — multiple orthogonal methods (EM, live imaging, oxygen consumption) in primary neurons, single lab\",\n      \"pmids\": [\"34034255\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"USP5 deubiquitinase stabilizes C2CD5 through deubiquitination; USP5 interacts with a complex containing C2CD5, FIBP, and CDK5; stabilization of C2CD5 by USP5 activates the PI3K/AKT/mTOR signaling pathway and enhances glycolytic flux via HIF-1α to drive AML progression.\",\n      \"method\": \"Co-immunoprecipitation coupled with mass spectrometry, USP5 knockdown, deubiquitination assays, PI3K/AKT/mTOR pathway readouts, in vivo AML mouse model\",\n      \"journal\": \"Biochemical Pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP/MS identification of complex, deubiquitination assay, pathway activation readouts, in vivo model; single lab\",\n      \"pmids\": [\"41344512\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"C2CD5 is expressed in dopamine β-hydroxylase (DBH)-positive sympathetic neurons; conditional knockout of C2CD5 in DBH+ neurons reduces norepinephrine (NE) secretion, impairs thermogenesis, lowers energy expenditure, and promotes adiposity; supplementation with NE mitigates these effects, placing C2CD5 upstream of NE secretion in sympathetic regulation of thermogenesis.\",\n      \"method\": \"Conditional KO mice (C2CD5 deleted in DBH+ neurons), NE secretion measurements, metabolic cage analysis, NE supplementation rescue experiment\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cell-type-specific conditional KO with NE rescue, multiple metabolic readouts; single lab, extends prior whole-body KO findings\",\n      \"pmids\": [\"42006349\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"C2CD5 (CDP138) is a calcium- and lipid-binding C2-domain protein that functions as a membrane trafficking regulator: it is phosphorylated by Akt2 at S197 to promote GLUT4 vesicle fusion with the plasma membrane in adipocytes; it forms a stable complex with CDK5 and FIBP to enable CDK5-mediated NudEL phosphorylation and dynein force adaptation for intracellular organelle transport; it is stabilized by the deubiquitinase USP5 (which activates PI3K/AKT/mTOR/HIF-1α–driven glycolysis); it regulates MC4R endocytosis and mitochondrial trafficking/function in hypothalamic neurons; and, in DBH+ sympathetic neurons, it controls norepinephrine secretion to govern thermogenesis and energy balance.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"C2CD5 (CDP138/KIAA0528) is a calcium- and lipid-binding C2-domain protein that regulates regulated membrane trafficking and vesicle fusion across metabolic and neuronal tissues [#0, #3]. In adipocytes it acts as a direct Akt2 substrate: its purified C2 domain binds Ca\\u00b2\\u207a and lipid membranes, Akt2 phosphorylates it at S197, and both Ca\\u00b2\\u207a-binding and S197 phosphorylation are required for insulin-stimulated fusion of GLUT4 vesicles with the plasma membrane [#0]. A second mechanistic role centers on intracellular organelle transport, where C2CD5 forms a stable complex with CDK5 and FIBP and, together with 14-3-3\\u03b5, promotes CDK5-mediated NudEL phosphorylation to increase dynein\\u2013NudEL interaction and dynein force production for movement of lipid droplets, lysosomes, and mitochondria [#1, #4]. In the nervous system C2CD5 governs sympathetic catecholamine output: it is expressed in adrenal medulla and DBH\\u207a sympathetic neurons, and its loss reduces norepinephrine secretion and impairs cold-induced adrenergic signaling, fat browning, energy expenditure, and insulin sensitivity, defects mitigated by norepinephrine supplementation [#3, #8]. In hypothalamic neurons C2CD5 promotes MC4R endocytosis through its C2 domain and is required for proper mitochondrial trafficking, ultrastructure, and respiration [#5, #6]. C2CD5 is stabilized by the deubiquitinase USP5, which acts on a C2CD5\\u2013FIBP\\u2013CDK5 complex to activate PI3K/AKT/mTOR signaling and HIF-1\\u03b1\\u2013driven glycolysis in acute myeloid leukemia [#7].\",\n  \"teleology\": [\n    {\n      \"year\": 2011,\n      \"claim\": \"Established C2CD5 as an Akt2 effector linking insulin signaling to vesicle fusion, answering how phosphoinositide-3-kinase output is converted into membrane fusion of glucose transporter vesicles.\",\n      \"evidence\": \"Quantitative phosphoproteomics, purified C2-domain Ca\\u00b2\\u207a/lipid binding assays, S197 and Ca\\u00b2\\u207a-site mutagenesis, RNAi, and live-cell GLUT4 fusion imaging in adipocytes\",\n      \"pmids\": [\"21907143\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the fusion machinery (SNAREs/tethers) C2CD5 engages not defined\", \"Structural basis of Ca\\u00b2\\u207a/lipid binding by the C2 domain not resolved\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Defined C2CD5 as a structural component of a CDK5 complex, showing it is not solely an adipocyte trafficking protein but an assembly factor for a kinase complex relevant to cell proliferation and migration.\",\n      \"evidence\": \"Affinity purification/MS with SAINT analysis, reciprocal co-IP, and RNAi proliferation/migration assays in breast cancer cells\",\n      \"pmids\": [\"25096995\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular role of C2CD5 within the complex (scaffold vs. cofactor) not mechanistically dissected here\", \"Substrates downstream of the complex not identified at this stage\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Connected C2CD5 to TGF-\\u03b2/Smad signaling via GDF15, extending its functional reach to a transcriptional/secreted-factor axis controlling cancer cell phenotypes.\",\n      \"evidence\": \"RNAi knockdown, GDF15 rescue, Smad signaling, migration/invasion, and radiosensitivity assays in lung cancer cells\",\n      \"pmids\": [\"28880265\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct mechanism by which C2CD5 upregulates GDF15 unknown\", \"Rescue was only partial, leaving additional effectors unaccounted for\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Established an in vivo physiological role for C2CD5 in sympathetic/adrenal catecholamine secretion controlling fat browning and insulin sensitivity, moving beyond cell-based trafficking assays.\",\n      \"evidence\": \"Whole-body knockout mice, catecholamine measurement, cAMP/HSL phosphorylation readouts, cold challenge, and tyrosine hydroxylase colocalization\",\n      \"pmids\": [\"29378832\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular step in catecholamine vesicle secretion controlled by C2CD5 not pinpointed\", \"Whole-body KO cannot exclude contributions from non-neuronal tissues\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Mechanistically resolved the CDK5 complex function, showing C2CD5 acts as a CDK5 cofactor driving NudEL phosphorylation and dynein force adaptation for organelle transport.\",\n      \"evidence\": \"Single-molecule dynein force measurements, RNAi epistasis of C2CD5/CDK5/14-3-3\\u03b5, NudEL phosphorylation, and lipid droplet/lysosome/mitochondria transport assays in COS-1 cells\",\n      \"pmids\": [\"30651536\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How C2CD5's C2/lipid-binding activity contributes to this cytosolic kinase function not clarified\", \"Direct contact between C2CD5 and CDK5 active site not structurally defined\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identified a hypothalamic neuronal role in MC4R endocytosis, linking C2CD5 trafficking activity to central melanocortin signaling and energy balance.\",\n      \"evidence\": \"Whole-body KO mice, antibody-feeding endocytosis assay with C2-domain deletion mutant, flow cytometry, EM, in vivo MTII injection, and RNAscope\",\n      \"pmids\": [\"31666192\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific endocytic machinery components C2CD5 binds not named\", \"Whether MC4R endocytosis defect is direct or secondary to broader trafficking loss unresolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Showed C2CD5 is required for mitochondrial trafficking, morphology, and respiration in hypothalamic neurons, tying its transport function to neuronal bioenergetics.\",\n      \"evidence\": \"Primary hypothalamic neuron cultures from KO mice, EM, live-cell imaging, and oxygen consumption assays\",\n      \"pmids\": [\"34034255\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causal ordering between mitochondrial dysfunction and MC4R trafficking defect not established\", \"Whether mitochondrial phenotype reflects the dynein/CDK5 transport pathway not tested directly\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Revealed post-translational control of C2CD5 by USP5 deubiquitination, coupling C2CD5 stability to PI3K/AKT/mTOR and HIF-1\\u03b1\\u2013driven glycolysis in leukemia.\",\n      \"evidence\": \"Co-IP/MS, USP5 knockdown, deubiquitination assays, pathway readouts, and an in vivo AML mouse model\",\n      \"pmids\": [\"41344512\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Ubiquitin ligase opposing USP5 on C2CD5 not identified\", \"Direct mechanism by which stabilized C2CD5 activates PI3K/AKT/mTOR not defined\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Refined the sympathetic role using cell-type-specific deletion, placing C2CD5 upstream of norepinephrine secretion in DBH\\u207a neurons to control thermogenesis and adiposity.\",\n      \"evidence\": \"DBH-specific conditional KO mice, NE secretion measurements, metabolic cage analysis, and NE supplementation rescue\",\n      \"pmids\": [\"42006349\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular step in NE vesicle secretion governed by C2CD5 not defined\", \"Connection to the C2CD5 GLUT4/dynein mechanisms in this neuronal context not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How a single C2-domain trafficking protein mechanistically unifies Akt2-dependent GLUT4 fusion, CDK5-dependent dynein force adaptation, and regulated catecholamine secretion remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of C2CD5 or its complexes\", \"Whether the C2/Ca\\u00b2\\u207a-lipid module is used in all these contexts is untested\", \"The direct fusion/secretion machinery C2CD5 engages is not identified\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [0, 3]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [1, 4]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [0, 5]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 7]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [4, 6]}\n    ],\n    \"complexes\": [\n      \"C2CD5-CDK5-FIBP complex\"\n    ],\n    \"partners\": [\n      \"CDK5\",\n      \"FIBP\",\n      \"AKT2\",\n      \"YWHAE\",\n      \"USP5\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}