{"gene":"PPP1R3G","run_date":"2026-04-28T19:45:44","timeline":{"discoveries":[{"year":2013,"finding":"PPP1R3G functions as a glycogen-targeting subunit (G subunit) of protein phosphatase 1 (PP1) that activates glycogen synthase via dephosphorylation, promoting hepatic glycogen accumulation. The glycogen-binding domain of PPP1R3G is indispensable for its effects on glucose metabolism and triglyceride accumulation in liver.","method":"Liver-specific overexpression in transgenic mice, glycogen synthase activity assays, primary hepatocyte experiments, glycogen-binding domain deletion mutant analysis","journal":"Molecular endocrinology (Baltimore, Md.)","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal in vivo and in vitro methods, domain mutagenesis, replicated in primary hepatocytes","pmids":["24264575"],"is_preprint":false},{"year":2016,"finding":"PPP1R3G is required for glycogen synthesis in adipose tissue; whole-body knockout reduces glycogen deposition and links glycogen metabolism to fat accumulation. Overexpression in 3T3-L1 cells increases both glycogen and triglyceride levels.","method":"Whole-body PPP1R3G knockout mouse model on high-fat diet, metabolic rate measurements, overexpression in 3T3-L1 adipocytes","journal":"Molecular and cellular endocrinology","confidence":"High","confidence_rationale":"Tier 2 — genetic knockout with defined metabolic phenotype, confirmed in cell line overexpression","pmids":["27815211"],"is_preprint":false},{"year":2021,"finding":"PPP1R3G recruits its catalytic subunit PP1γ (protein phosphatase 1 gamma) to TNFR1 complex I to dephosphorylate inhibitory phosphorylation sites on RIPK1 (including serine 25), thereby activating RIPK1 kinase activity and promoting apoptosis and necroptosis. A PPP1R3G mutant unable to bind PP1γ fails to rescue RIPK1 activation and cell death. Ppp1r3g-/- mice are protected from TNF-induced systemic inflammatory response syndrome.","method":"CRISPR whole-genome knockout screen, co-immunoprecipitation, PP1γ-binding mutant rescue experiments, RIPK1 S25A mutation, Ppp1r3g knockout mice with TNF-SIRS model","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — genome-wide screen discovery, reciprocal biochemical validation, mutagenesis, in vivo knockout confirmation","pmids":["34862394"],"is_preprint":false},{"year":2023,"finding":"PPP1R3G knockdown in HTR-8/SVneo trophoblasts decreases p-Akt/Akt expression and inhibits trophoblast migration, invasion, and proliferation; PPP1R3G positively regulates MMP-9 expression, placing PPP1R3G upstream of an Akt/MMP-9 signaling axis controlling trophoblast invasion.","method":"Lentiviral knockdown, wound-healing assay, Transwell invasion assay, CCK-8 proliferation assay, western blotting for Akt pathway components","journal":"Experimental biology and medicine (Maywood, N.J.)","confidence":"Medium","confidence_rationale":"Tier 3 — single lab, multiple cell-based assays but no direct biochemical reconstitution of pathway","pmids":["37642261"],"is_preprint":false},{"year":2025,"finding":"PPP1R3G deletion in oligodendrocyte precursor cells (OPCs) impairs OPC differentiation and myelination in aged mice through disruption of AMPK-Drp1-dependent mitochondrial homeostasis; PPP1R3G promotes AMPK activity, which negatively regulates Drp1 phosphorylation to restrain mitochondrial fission, and AMPK activation rescues the fission defects caused by PPP1R3G knockout.","method":"Ppp1r3g knockout mice, primary OPC cultures, RNA-seq, immunohistochemistry, TEM, mitochondrial functional assays (membrane potential, ATP production), AMPK activation rescue experiment","journal":"International immunopharmacology","confidence":"Medium","confidence_rationale":"Tier 2 — genetic knockout with multiple orthogonal mechanistic assays and pathway rescue, but single lab","pmids":["40834529"],"is_preprint":false},{"year":2026,"finding":"In doxorubicin-induced cardiotoxicity, PPP1R3G dephosphorylates RIPK1 (removing p38-mediated inhibitory phosphorylation) to activate RIPK1, triggering early-stage apoptosis. Activated RIPK1 promotes cytosolic release of mitochondrial DNA, which induces ZBP1 expression via IFN-β signaling, amplifying late-stage necroptosis in a feed-forward loop. Genetic ablation of Ppp1r3g suppresses both apoptosis and necroptosis and protects mice from DOX-induced cardiac dysfunction.","method":"Ppp1r3g knockout mice, in vitro cardiomyocyte assays, cytokine measurement, mechanistic dissection of p38-RIPK1-mtDNA-IFN-β-ZBP1 axis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — genetic knockout with multiple orthogonal mechanistic assays confirming PPP1R3G-RIPK1-ZBP1 axis in vivo and in vitro","pmids":["41984837"],"is_preprint":false}],"current_model":"PPP1R3G is a regulatory subunit of protein phosphatase 1 (PP1) that acts through two major mechanisms: (1) as a glycogen-targeting G subunit, it recruits PP1 to dephosphorylate and activate glycogen synthase in liver and adipose tissue, regulating glycogen synthesis and linked lipid metabolism; and (2) it recruits the PP1γ catalytic subunit to TNFR1 complex I to remove inhibitory phosphorylations from RIPK1 (including Ser25), unleashing RIPK1 kinase activity to drive apoptosis and necroptosis, with downstream consequences including mtDNA release, IFN-β-mediated ZBP1 induction, and amplified necroptotic signaling."},"narrative":{"teleology":[{"year":2013,"claim":"Establishing PPP1R3G as a hepatic glycogen-targeting PP1 subunit resolved how this previously uncharacterized regulatory subunit participates in glucose and lipid metabolism — it dephosphorylates glycogen synthase via a glycogen-binding domain essential for both glycogen and triglyceride accumulation.","evidence":"Liver-specific transgenic overexpression in mice, glycogen synthase activity assays, glycogen-binding domain deletion mutants, and primary hepatocyte experiments","pmids":["24264575"],"confidence":"High","gaps":["No structural information on PPP1R3G–PP1–glycogen synthase complex","Mechanism linking glycogen accumulation to triglyceride metabolism not resolved"]},{"year":2016,"claim":"Extending PPP1R3G function to adipose tissue via whole-body knockout demonstrated that its glycogen-targeting role is not liver-restricted and established a genetic link between PPP1R3G-dependent glycogen metabolism and fat accumulation.","evidence":"Whole-body PPP1R3G knockout mice on high-fat diet, metabolic phenotyping, and 3T3-L1 adipocyte overexpression","pmids":["27815211"],"confidence":"High","gaps":["Direct PP1 substrates in adipocytes beyond glycogen synthase not identified","Whether PPP1R3G affects insulin signaling directly in adipose tissue is unknown"]},{"year":2021,"claim":"A genome-wide CRISPR screen revealed an entirely unexpected second function: PPP1R3G recruits PP1γ to TNFR1 complex I to dephosphorylate RIPK1 Ser25, converting PPP1R3G from a metabolic regulator to a critical enabler of TNF-driven apoptosis and necroptosis.","evidence":"CRISPR knockout screen, co-immunoprecipitation, PP1γ-binding mutant rescue, RIPK1 S25A mutant epistasis, and Ppp1r3g-knockout mice in TNF-SIRS model","pmids":["34862394"],"confidence":"High","gaps":["How PPP1R3G is recruited to TNFR1 complex I is mechanistically undefined","Whether glycogen-binding and TNFR1-targeting functions are coordinately regulated is unknown","RIPK1 phosphorylation sites beyond Ser25 targeted by PPP1R3G–PP1γ not fully mapped"]},{"year":2023,"claim":"PPP1R3G knockdown in trophoblasts implicated it upstream of Akt/MMP-9 signaling, suggesting a broader phosphatase-regulatory role beyond glycogen metabolism and RIPK1, though the direct mechanism is unresolved.","evidence":"Lentiviral knockdown in HTR-8/SVneo trophoblasts, western blotting for p-Akt, Transwell invasion and proliferation assays","pmids":["37642261"],"confidence":"Medium","gaps":["No direct biochemical evidence that PPP1R3G–PP1 dephosphorylates Akt pathway components","Single cell line without in vivo validation","Mechanism connecting PPP1R3G to MMP-9 transcription not established"]},{"year":2025,"claim":"Conditional deletion in oligodendrocyte precursor cells revealed that PPP1R3G maintains mitochondrial homeostasis via AMPK-Drp1 signaling, broadening its functional repertoire to include mitochondrial fission control and myelination.","evidence":"OPC-conditional Ppp1r3g knockout mice, primary OPC cultures, RNA-seq, TEM, mitochondrial functional assays, AMPK activation rescue","pmids":["40834529"],"confidence":"Medium","gaps":["Direct PP1 substrate linking PPP1R3G to AMPK activation not identified","Whether the mitochondrial phenotype is cell-type specific or generalizable is unclear","Single-lab finding not yet independently replicated"]},{"year":2026,"claim":"The RIPK1-activating function was extended to doxorubicin cardiotoxicity, where PPP1R3G removes p38-mediated inhibitory phosphorylation from RIPK1, establishing a feed-forward loop in which RIPK1 triggers mtDNA release, IFN-β signaling, ZBP1 induction, and amplified necroptosis.","evidence":"Ppp1r3g knockout mice treated with doxorubicin, cardiomyocyte assays, dissection of p38–RIPK1–mtDNA–IFN-β–ZBP1 signaling axis","pmids":["41984837"],"confidence":"High","gaps":["Specific phospho-sites on RIPK1 removed by PPP1R3G–PP1 in the cardiac context beyond Ser25 not mapped","Whether PPP1R3G contributes to cardiotoxicity from other chemotherapeutics is untested"]},{"year":null,"claim":"It remains unknown how PPP1R3G is partitioned between its glycogen-targeting and TNFR1 complex I death-signaling functions, whether these are tissue-specific or signal-regulated, and what structural determinants dictate substrate selectivity of the PPP1R3G–PP1 holoenzyme.","evidence":"","pmids":[],"confidence":"High","gaps":["No structural model of PPP1R3G–PP1γ holoenzyme exists","Signal-dependent regulation of PPP1R3G expression or post-translational modification is poorly characterized","Whether the AMPK–Drp1 and Akt/MMP-9 functions reflect direct PP1 substrate dephosphorylation or indirect effects is unresolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,1,2,5]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0,2]}],"pathway":[{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[2,5]}],"complexes":["PP1 holoenzyme","TNFR1 complex I"],"partners":["PPP1CC","RIPK1","ZBP1"],"other_free_text":[]},"mechanistic_narrative":"PPP1R3G is a regulatory subunit of protein phosphatase 1 (PP1) that functions in two distinct biological contexts: glycogen metabolism and cell death signaling. As a glycogen-targeting (G) subunit, PPP1R3G recruits PP1 to glycogen particles where it dephosphorylates and activates glycogen synthase, promoting glycogen accumulation in liver and adipose tissue, with downstream effects on triglyceride metabolism [PMID:24264575, PMID:27815211]. In TNF-driven cell death signaling, PPP1R3G recruits the PP1γ catalytic subunit to TNFR1 complex I to remove inhibitory phosphorylations from RIPK1 (including Ser25), thereby unleashing RIPK1 kinase activity to drive apoptosis and necroptosis; this mechanism extends to doxorubicin-induced cardiotoxicity, where RIPK1 activation triggers mitochondrial DNA release, IFN-β-mediated ZBP1 induction, and amplified necroptotic signaling [PMID:34862394, PMID:41984837]. PPP1R3G additionally promotes AMPK-Drp1-dependent mitochondrial homeostasis in oligodendrocyte precursor cells, supporting their differentiation and myelination [PMID:40834529]."},"prefetch_data":{"uniprot":{"accession":"B7ZBB8","full_name":"Protein phosphatase 1 regulatory subunit 3G","aliases":[],"length_aa":358,"mass_kda":38.0,"function":"Glycogen-targeting subunit for protein phosphatase 1 (PP1). Involved in the regulation of hepatic glycogenesis in a manner coupled to the fasting-feeding cycle and distinct from other glycogen-targeting subunits (By similarity)","subcellular_location":"","url":"https://www.uniprot.org/uniprotkb/B7ZBB8/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PPP1R3G","classification":"Not Classified","n_dependent_lines":5,"n_total_lines":1208,"dependency_fraction":0.0041390728476821195},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/PPP1R3G","total_profiled":1310},"omim":[{"mim_id":"619541","title":"PROTEIN PHOSPHATASE 1, REGULATORY SUBUNIT 3G; PPP1R3G","url":"https://www.omim.org/entry/619541"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"liver","ntpm":6.0}],"url":"https://www.proteinatlas.org/search/PPP1R3G"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"B7ZBB8","domains":[{"cath_id":"2.60.40.2440","chopping":"197-271_294-307_323-353","consensus_level":"high","plddt":90.3061,"start":197,"end":353}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/B7ZBB8","model_url":"https://alphafold.ebi.ac.uk/files/AF-B7ZBB8-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-B7ZBB8-F1-predicted_aligned_error_v6.png","plddt_mean":67.81},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PPP1R3G","jax_strain_url":"https://www.jax.org/strain/search?query=PPP1R3G"},"sequence":{"accession":"B7ZBB8","fasta_url":"https://rest.uniprot.org/uniprotkb/B7ZBB8.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/B7ZBB8/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/B7ZBB8"}},"corpus_meta":[{"pmid":"24264575","id":"PMC_24264575","title":"Regulation of glucose homeostasis and lipid metabolism by PPP1R3G-mediated hepatic glycogenesis.","date":"2013","source":"Molecular endocrinology (Baltimore, Md.)","url":"https://pubmed.ncbi.nlm.nih.gov/24264575","citation_count":41,"is_preprint":false},{"pmid":"34862394","id":"PMC_34862394","title":"RIPK1 dephosphorylation and kinase activation by PPP1R3G/PP1γ promote apoptosis and necroptosis.","date":"2021","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/34862394","citation_count":31,"is_preprint":false},{"pmid":"27815211","id":"PMC_27815211","title":"Ablation of PPP1R3G reduces glycogen deposition and mitigates high-fat diet induced obesity.","date":"2016","source":"Molecular and cellular endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/27815211","citation_count":18,"is_preprint":false},{"pmid":"37642261","id":"PMC_37642261","title":"Decreased PPP1R3G in pre-eclampsia impairs human trophoblast invasion and migration via Akt/MMP-9 signaling pathway.","date":"2023","source":"Experimental biology and medicine (Maywood, N.J.)","url":"https://pubmed.ncbi.nlm.nih.gov/37642261","citation_count":3,"is_preprint":false},{"pmid":"39790903","id":"PMC_39790903","title":"Corrigendum: Decreased PPP1R3G in pre-eclampsia impairs human trophoblast invasion and migration via Akt/MMP-9 signaling pathway.","date":"2024","source":"Experimental biology and medicine (Maywood, N.J.)","url":"https://pubmed.ncbi.nlm.nih.gov/39790903","citation_count":1,"is_preprint":false},{"pmid":"40834529","id":"PMC_40834529","title":"PPP1R3G inhibition impairs OPCs differentiation and myelination in aged mice.","date":"2025","source":"International immunopharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/40834529","citation_count":0,"is_preprint":false},{"pmid":"41040151","id":"PMC_41040151","title":"PPP1R3G Deletion Blocks RIPK1-Mediated Apoptosis and Necroptosis in Doxorubicin-Induced Cardiotoxicity.","date":"2025","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/41040151","citation_count":0,"is_preprint":false},{"pmid":"41984837","id":"PMC_41984837","title":"PPP1R3G-RIPK1-ZBP1 axis activates early-stage apoptosis and late-stage necroptosis to promote doxorubicin-induced cardiotoxicity.","date":"2026","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/41984837","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":5130,"output_tokens":1796,"usd":0.021165},"stage2":{"model":"claude-opus-4-6","input_tokens":5061,"output_tokens":2187,"usd":0.11997},"total_usd":0.141135,"stage1_batch_id":"msgbatch_01SUR8NDzVrNmyszWyJeCct7","stage2_batch_id":"msgbatch_01G7Yfutko3cDWzejrwH5AMx","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2013,\n      \"finding\": \"PPP1R3G functions as a glycogen-targeting subunit (G subunit) of protein phosphatase 1 (PP1) that activates glycogen synthase via dephosphorylation, promoting hepatic glycogen accumulation. The glycogen-binding domain of PPP1R3G is indispensable for its effects on glucose metabolism and triglyceride accumulation in liver.\",\n      \"method\": \"Liver-specific overexpression in transgenic mice, glycogen synthase activity assays, primary hepatocyte experiments, glycogen-binding domain deletion mutant analysis\",\n      \"journal\": \"Molecular endocrinology (Baltimore, Md.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal in vivo and in vitro methods, domain mutagenesis, replicated in primary hepatocytes\",\n      \"pmids\": [\"24264575\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"PPP1R3G is required for glycogen synthesis in adipose tissue; whole-body knockout reduces glycogen deposition and links glycogen metabolism to fat accumulation. Overexpression in 3T3-L1 cells increases both glycogen and triglyceride levels.\",\n      \"method\": \"Whole-body PPP1R3G knockout mouse model on high-fat diet, metabolic rate measurements, overexpression in 3T3-L1 adipocytes\",\n      \"journal\": \"Molecular and cellular endocrinology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic knockout with defined metabolic phenotype, confirmed in cell line overexpression\",\n      \"pmids\": [\"27815211\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PPP1R3G recruits its catalytic subunit PP1γ (protein phosphatase 1 gamma) to TNFR1 complex I to dephosphorylate inhibitory phosphorylation sites on RIPK1 (including serine 25), thereby activating RIPK1 kinase activity and promoting apoptosis and necroptosis. A PPP1R3G mutant unable to bind PP1γ fails to rescue RIPK1 activation and cell death. Ppp1r3g-/- mice are protected from TNF-induced systemic inflammatory response syndrome.\",\n      \"method\": \"CRISPR whole-genome knockout screen, co-immunoprecipitation, PP1γ-binding mutant rescue experiments, RIPK1 S25A mutation, Ppp1r3g knockout mice with TNF-SIRS model\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genome-wide screen discovery, reciprocal biochemical validation, mutagenesis, in vivo knockout confirmation\",\n      \"pmids\": [\"34862394\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PPP1R3G knockdown in HTR-8/SVneo trophoblasts decreases p-Akt/Akt expression and inhibits trophoblast migration, invasion, and proliferation; PPP1R3G positively regulates MMP-9 expression, placing PPP1R3G upstream of an Akt/MMP-9 signaling axis controlling trophoblast invasion.\",\n      \"method\": \"Lentiviral knockdown, wound-healing assay, Transwell invasion assay, CCK-8 proliferation assay, western blotting for Akt pathway components\",\n      \"journal\": \"Experimental biology and medicine (Maywood, N.J.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — single lab, multiple cell-based assays but no direct biochemical reconstitution of pathway\",\n      \"pmids\": [\"37642261\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"PPP1R3G deletion in oligodendrocyte precursor cells (OPCs) impairs OPC differentiation and myelination in aged mice through disruption of AMPK-Drp1-dependent mitochondrial homeostasis; PPP1R3G promotes AMPK activity, which negatively regulates Drp1 phosphorylation to restrain mitochondrial fission, and AMPK activation rescues the fission defects caused by PPP1R3G knockout.\",\n      \"method\": \"Ppp1r3g knockout mice, primary OPC cultures, RNA-seq, immunohistochemistry, TEM, mitochondrial functional assays (membrane potential, ATP production), AMPK activation rescue experiment\",\n      \"journal\": \"International immunopharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic knockout with multiple orthogonal mechanistic assays and pathway rescue, but single lab\",\n      \"pmids\": [\"40834529\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"In doxorubicin-induced cardiotoxicity, PPP1R3G dephosphorylates RIPK1 (removing p38-mediated inhibitory phosphorylation) to activate RIPK1, triggering early-stage apoptosis. Activated RIPK1 promotes cytosolic release of mitochondrial DNA, which induces ZBP1 expression via IFN-β signaling, amplifying late-stage necroptosis in a feed-forward loop. Genetic ablation of Ppp1r3g suppresses both apoptosis and necroptosis and protects mice from DOX-induced cardiac dysfunction.\",\n      \"method\": \"Ppp1r3g knockout mice, in vitro cardiomyocyte assays, cytokine measurement, mechanistic dissection of p38-RIPK1-mtDNA-IFN-β-ZBP1 axis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic knockout with multiple orthogonal mechanistic assays confirming PPP1R3G-RIPK1-ZBP1 axis in vivo and in vitro\",\n      \"pmids\": [\"41984837\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PPP1R3G is a regulatory subunit of protein phosphatase 1 (PP1) that acts through two major mechanisms: (1) as a glycogen-targeting G subunit, it recruits PP1 to dephosphorylate and activate glycogen synthase in liver and adipose tissue, regulating glycogen synthesis and linked lipid metabolism; and (2) it recruits the PP1γ catalytic subunit to TNFR1 complex I to remove inhibitory phosphorylations from RIPK1 (including Ser25), unleashing RIPK1 kinase activity to drive apoptosis and necroptosis, with downstream consequences including mtDNA release, IFN-β-mediated ZBP1 induction, and amplified necroptotic signaling.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"PPP1R3G is a regulatory subunit of protein phosphatase 1 (PP1) that functions in two distinct biological contexts: glycogen metabolism and cell death signaling. As a glycogen-targeting (G) subunit, PPP1R3G recruits PP1 to glycogen particles where it dephosphorylates and activates glycogen synthase, promoting glycogen accumulation in liver and adipose tissue, with downstream effects on triglyceride metabolism [PMID:24264575, PMID:27815211]. In TNF-driven cell death signaling, PPP1R3G recruits the PP1γ catalytic subunit to TNFR1 complex I to remove inhibitory phosphorylations from RIPK1 (including Ser25), thereby unleashing RIPK1 kinase activity to drive apoptosis and necroptosis; this mechanism extends to doxorubicin-induced cardiotoxicity, where RIPK1 activation triggers mitochondrial DNA release, IFN-β-mediated ZBP1 induction, and amplified necroptotic signaling [PMID:34862394, PMID:41984837]. PPP1R3G additionally promotes AMPK-Drp1-dependent mitochondrial homeostasis in oligodendrocyte precursor cells, supporting their differentiation and myelination [PMID:40834529].\",\n  \"teleology\": [\n    {\n      \"year\": 2013,\n      \"claim\": \"Establishing PPP1R3G as a hepatic glycogen-targeting PP1 subunit resolved how this previously uncharacterized regulatory subunit participates in glucose and lipid metabolism — it dephosphorylates glycogen synthase via a glycogen-binding domain essential for both glycogen and triglyceride accumulation.\",\n      \"evidence\": \"Liver-specific transgenic overexpression in mice, glycogen synthase activity assays, glycogen-binding domain deletion mutants, and primary hepatocyte experiments\",\n      \"pmids\": [\"24264575\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No structural information on PPP1R3G–PP1–glycogen synthase complex\",\n        \"Mechanism linking glycogen accumulation to triglyceride metabolism not resolved\"\n      ]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Extending PPP1R3G function to adipose tissue via whole-body knockout demonstrated that its glycogen-targeting role is not liver-restricted and established a genetic link between PPP1R3G-dependent glycogen metabolism and fat accumulation.\",\n      \"evidence\": \"Whole-body PPP1R3G knockout mice on high-fat diet, metabolic phenotyping, and 3T3-L1 adipocyte overexpression\",\n      \"pmids\": [\"27815211\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Direct PP1 substrates in adipocytes beyond glycogen synthase not identified\",\n        \"Whether PPP1R3G affects insulin signaling directly in adipose tissue is unknown\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"A genome-wide CRISPR screen revealed an entirely unexpected second function: PPP1R3G recruits PP1γ to TNFR1 complex I to dephosphorylate RIPK1 Ser25, converting PPP1R3G from a metabolic regulator to a critical enabler of TNF-driven apoptosis and necroptosis.\",\n      \"evidence\": \"CRISPR knockout screen, co-immunoprecipitation, PP1γ-binding mutant rescue, RIPK1 S25A mutant epistasis, and Ppp1r3g-knockout mice in TNF-SIRS model\",\n      \"pmids\": [\"34862394\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"How PPP1R3G is recruited to TNFR1 complex I is mechanistically undefined\",\n        \"Whether glycogen-binding and TNFR1-targeting functions are coordinately regulated is unknown\",\n        \"RIPK1 phosphorylation sites beyond Ser25 targeted by PPP1R3G–PP1γ not fully mapped\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"PPP1R3G knockdown in trophoblasts implicated it upstream of Akt/MMP-9 signaling, suggesting a broader phosphatase-regulatory role beyond glycogen metabolism and RIPK1, though the direct mechanism is unresolved.\",\n      \"evidence\": \"Lentiviral knockdown in HTR-8/SVneo trophoblasts, western blotting for p-Akt, Transwell invasion and proliferation assays\",\n      \"pmids\": [\"37642261\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No direct biochemical evidence that PPP1R3G–PP1 dephosphorylates Akt pathway components\",\n        \"Single cell line without in vivo validation\",\n        \"Mechanism connecting PPP1R3G to MMP-9 transcription not established\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Conditional deletion in oligodendrocyte precursor cells revealed that PPP1R3G maintains mitochondrial homeostasis via AMPK-Drp1 signaling, broadening its functional repertoire to include mitochondrial fission control and myelination.\",\n      \"evidence\": \"OPC-conditional Ppp1r3g knockout mice, primary OPC cultures, RNA-seq, TEM, mitochondrial functional assays, AMPK activation rescue\",\n      \"pmids\": [\"40834529\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Direct PP1 substrate linking PPP1R3G to AMPK activation not identified\",\n        \"Whether the mitochondrial phenotype is cell-type specific or generalizable is unclear\",\n        \"Single-lab finding not yet independently replicated\"\n      ]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"The RIPK1-activating function was extended to doxorubicin cardiotoxicity, where PPP1R3G removes p38-mediated inhibitory phosphorylation from RIPK1, establishing a feed-forward loop in which RIPK1 triggers mtDNA release, IFN-β signaling, ZBP1 induction, and amplified necroptosis.\",\n      \"evidence\": \"Ppp1r3g knockout mice treated with doxorubicin, cardiomyocyte assays, dissection of p38–RIPK1–mtDNA–IFN-β–ZBP1 signaling axis\",\n      \"pmids\": [\"41984837\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Specific phospho-sites on RIPK1 removed by PPP1R3G–PP1 in the cardiac context beyond Ser25 not mapped\",\n        \"Whether PPP1R3G contributes to cardiotoxicity from other chemotherapeutics is untested\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unknown how PPP1R3G is partitioned between its glycogen-targeting and TNFR1 complex I death-signaling functions, whether these are tissue-specific or signal-regulated, and what structural determinants dictate substrate selectivity of the PPP1R3G–PP1 holoenzyme.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No structural model of PPP1R3G–PP1γ holoenzyme exists\",\n        \"Signal-dependent regulation of PPP1R3G expression or post-translational modification is poorly characterized\",\n        \"Whether the AMPK–Drp1 and Akt/MMP-9 functions reflect direct PP1 substrate dephosphorylation or indirect effects is unresolved\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 1, 2, 5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:1430728\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [2, 5]}\n    ],\n    \"complexes\": [\n      \"PP1 holoenzyme\",\n      \"TNFR1 complex I\"\n    ],\n    \"partners\": [\n      \"PPP1CC\",\n      \"RIPK1\",\n      \"ZBP1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}