{"gene":"PPP1R3C","run_date":"2026-06-10T06:43:35","timeline":{"discoveries":[{"year":1997,"finding":"PTG (PPP1R3C) was identified as a glycogen-targeting subunit of PP1 that acts as a molecular scaffold: it binds PP1C, localizes it to glycogen, and also forms complexes with phosphorylase kinase, phosphorylase a, and glycogen synthase. Overexpression of PTG in CHO cells markedly increased basal and insulin-stimulated glycogen synthesis.","method":"Cloning from 3T3-L1 adipocytes, co-immunoprecipitation/pulldown of PTG with PP1C and glycogen metabolism enzymes, overexpression in CHO cells with insulin receptor","journal":"Science","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal binding assays, functional overexpression with defined phenotype, replicated across multiple subsequent studies","pmids":["9045612"],"is_preprint":false},{"year":1997,"finding":"PTG increases PP1 activity against phosphorylase a by decreasing the Km of PP1 for this substrate 5-fold without affecting Vmax; PTG did not affect PP1 activity against hormone-sensitive lipase. PTG was not phosphorylated in vivo or in vitro by insulin- or forskolin-activated kinases. PTG decreased the ability of DARPP-32 to inhibit PP1 activity.","method":"GST-PTG pulldown from 3T3-L1 lysates, in vitro phosphatase activity assay with 32P-labeled phosphorylase a, in vivo and in vitro kinase assays, PP1 inhibitor (DARPP-32) competition assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro enzymatic reconstitution with multiple substrates, mutagenesis-independent but multiple orthogonal methods in one study","pmids":["9242697"],"is_preprint":false},{"year":1998,"finding":"Adenovirus-mediated overexpression of PTG in primary rat hepatocytes potently activates glycogen synthesis even in the absence of carbohydrates or insulin, increases glycogen synthase activation state 3.6-fold, and decreases glycogen phosphorylase activity 40%. Glycogenolytic agents (forskolin, glucagon) are largely ineffective at activating glycogen degradation in PTG-overexpressing hepatocytes despite large cAMP increases.","method":"Recombinant adenovirus-mediated PTG overexpression in primary rat hepatocytes; glycogen synthase activity assay; glycogen phosphorylase activity assay; cAMP measurement","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean gain-of-function in primary cells with multiple enzymatic readouts, consistent with founding paper","pmids":["9756875"],"is_preprint":false},{"year":2003,"finding":"PTG (PPP1R3C) knockout mice (heterozygous deletion) have reduced glycogen stores in adipose tissue, liver, heart, and skeletal muscle, with decreased glycogen synthase activity and glycogen synthesis rate, demonstrating PTG is required for normal glycogen synthesis in vivo.","method":"Heterozygous PTG gene deletion in mice; tissue glycogen measurement; glycogen synthase activity assay; metabolic phenotyping including glucose tolerance and insulin resistance","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic knockout with defined enzymatic and metabolic phenotype, multiple tissues analyzed","pmids":["12727934"],"is_preprint":false},{"year":2003,"finding":"Laforin interacts with the glycogen-targeting regulatory subunit R5/PTG. The interaction requires full-length laforin, and a minimal central region of R5 (amino acids 116-238) including the glycogen and glycogen synthase binding sites is sufficient. Point mutagenesis of the glycogen synthase-binding site of R5 completely blocks interaction with laforin. Lafora disease-associated laforin mutation G240S disrupts the interaction with R5 without affecting phosphatase or glycogen binding activities.","method":"Pulldown assays (GST-fusion proteins), co-localization experiments, point mutagenesis of R5 and laforin","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal pulldown and co-localization with mutagenesis mapping of interaction domain, single lab but orthogonal methods","pmids":["14532330"],"is_preprint":false},{"year":2007,"finding":"Malin (E3 ubiquitin ligase) ubiquitinates PTG in a laforin-dependent manner both in vivo and in vitro, targeting PTG for proteasome-dependent degradation. Co-expression of malin and laforin abolished PTG-stimulated glycogen accumulation in tissue culture cells.","method":"Co-expression of PTG, malin, and laforin in tissue culture cells; in vitro and in vivo ubiquitination assays; proteasome inhibitor rescue experiments; glycogen accumulation assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro ubiquitination reconstitution plus in vivo validation plus functional glycogen accumulation readout","pmids":["18070875"],"is_preprint":false},{"year":2009,"finding":"AMPK physically interacts with R5/PTG and phosphorylates it at Ser-8 and Ser-268 (mapped by mass spectrometry). Phosphorylation of Ser-8 by AMPK accelerates laforin/malin-dependent ubiquitination and proteasomal degradation of R5/PTG, resulting in decreased glycogenic activity.","method":"Co-immunoprecipitation of AMPK with R5/PTG; mass spectrometry phosphorylation site mapping; in vitro AMPK kinase assay; ubiquitination and proteasome-dependent degradation assays; glycogenic activity measurement","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro kinase assay with mass spectrometry site mapping plus functional degradation assay, multiple orthogonal methods single lab","pmids":["19171932"],"is_preprint":false},{"year":2009,"finding":"PTG (PP1 regulatory subunit) associates physically with PP1γ, and high NaCl reduces PTG-PP1γ association and remaining PTG-associated PP1γ activity. PTG and PP1γ bind to SHP-1, and knockdown of PTG or PP1γ increases high NaCl-induced phosphorylation of SHP-1-S591 (inhibitory), which in turn reduces SHP-1's inhibitory effect on NFAT5. Thus PTG/PP1γ dephosphorylates SHP-1 to dampen NFAT5 activity under high NaCl.","method":"Co-immunoprecipitation of PTG with PP1γ and SHP-1; siRNA knockdown of PTG and PP1γ; phospho-specific Western blot for SHP-1-S591; mutation of SHP-1-S591 to alanine; NFAT5 transcriptional activity assay","journal":"American journal of physiology. Renal physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP plus knockdown plus mutagenesis, but single lab and novel non-glycogenic function","pmids":["23720348"],"is_preprint":false},{"year":2010,"finding":"HIF1 directly regulates PPP1R3C expression through a functional hypoxia response element 229 bp upstream of the PPP1R3C gene. PPP1R3C induction by hypoxia correlates with glycogen accumulation in MCF7 cells; knockdown of either HIF1α or PPP1R3C attenuates hypoxia-induced glycogen accumulation.","method":"Mutation analysis of hypoxia response element by luciferase reporter assay; siRNA knockdown of HIF1α, HIF2α, and PPP1R3C; glycogen content measurement under hypoxia","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — HRE mutagenesis plus functional siRNA knockdown with glycogen readout, two orthogonal methods, single lab","pmids":["20888814"],"is_preprint":false},{"year":2011,"finding":"Genetic removal of PTG from Lafora disease mice (laforin- or malin-deficient) results in near-complete disappearance of polyglucosan (Lafora body) accumulation and resolution of neurodegeneration and myoclonic epilepsy, demonstrating that PTG-driven PP1 activation of glycogen synthase is the proximal cause of Lafora body formation.","method":"Genetic cross of PTG-knockout mice with Lafora disease (laforin-deficient) mice; histological analysis of polyglucosan accumulation; EEG/behavioral assessment of myoclonic epilepsy","journal":"PLoS genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis in mouse disease model with multiple phenotypic readouts (histology, EEG, behavior), replicated in malin-deficient model","pmids":["21552327"],"is_preprint":false},{"year":2011,"finding":"A PTG variant (N249S, c.746A>G) results in decreased capacity to induce glycogen synthesis and reduced interaction with glycogen phosphorylase and laforin, establishing that the glycogen phosphorylase and laforin binding region of PTG is required for full glycogenic activity.","method":"Identification of N249S mutation; functional assay of glycogen synthesis; interaction assays with glycogen phosphorylase and laforin","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — natural variant with functional characterization using multiple interaction readouts, single lab","pmids":["21738631"],"is_preprint":false},{"year":2014,"finding":"Genetic reduction of PTG in malin-deficient Lafora disease mice nearly completely eliminates Lafora bodies and rescues neurodegeneration, myoclonus, seizure susceptibility, and behavioral abnormality, confirming that PTG-mediated glycogen synthesis activation is the key pathogenic mechanism downstream of malin.","method":"Genetic cross of PTG-knockout mice with malin-deficient mice; histological Lafora body quantification; seizure susceptibility and behavioral testing","journal":"Annals of neurology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis in second Lafora disease mouse model, multiple phenotypic readouts, replicates laforin-model findings","pmids":["24419970"],"is_preprint":false},{"year":2019,"finding":"PPP1R3C overexpression in primary mouse hepatocytes and mouse liver promotes hepatic glucose production and gluconeogenic gene expression. Knockdown of PPP1R3C suppresses cAMP-stimulated gluconeogenic gene expression and blocks TORC2 dephosphorylation (nuclear localization). AMPK activation (by metformin) suppresses Ppp1r3c mRNA expression. PPP1R3C-mediated TORC2 dephosphorylation links PPP1R3C to gluconeogenic transcription.","method":"Adenovirus-mediated overexpression and knockdown of PPP1R3C in primary hepatocytes and mouse liver in vivo; Western blot and immunofluorescence for TORC2 phosphorylation/localization; hepatic glucose production assay; gluconeogenic gene expression","journal":"Metabolism: clinical and experimental","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — gain- and loss-of-function in vivo plus mechanistic TORC2 localization readout, single lab","pmids":["31181215"],"is_preprint":false},{"year":2020,"finding":"PPP1R3C knockout reduces skeletal muscle polyglucosan bodies in an APBD (GBE-deficient) mouse model and improves lifespan, morphology, and neuromuscular function, confirming PTG's role in activating glycogen synthase (GYS1) in muscle in vivo.","method":"PPP1R3C knockout crossed into APBD mouse model; histological polyglucosan body quantification; lifespan and behavioral assays; brain and muscle glycogen quantification","journal":"Annals of clinical and translational neurology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis in disease model, multiple phenotypic readouts, single study","pmids":["33034425"],"is_preprint":false},{"year":2020,"finding":"IRF4 in skeletal muscle regulates glycogen metabolism via transcriptional control of PTG. Skeletal muscle-specific IRF4 knockout increases glycogen content and exercise capacity; IRF4 overexpression decreases both. Knockdown of PTG reverses the phenotype of IRF4 knockout, placing PTG downstream of IRF4 in a glycogen regulatory pathway.","method":"Skeletal muscle-specific IRF4 knockout and overexpression mice; glycogen content measurement; exercise capacity testing; adenovirus-mediated PTG knockdown as epistasis test","journal":"Advanced science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis with gain- and loss-of-function and rescue experiment, single lab","pmids":["33042761"],"is_preprint":false},{"year":2022,"finding":"Crystal structure of the ternary PP1/PTG/carbohydrate complex was determined, revealing an unusual combination of PP1-recruitment sites on PTG. PTG uses multiple binding interfaces to recruit PP1 to glycogen granules. In-solution SAXS analyses revealed conformational heterogeneity of the complex. Individual contributions of recruitment sites to overall binding affinity were characterized.","method":"X-ray crystallography of PP1/PTG/carbohydrate ternary complex; SAXS (small-angle X-ray scattering) in solution analysis; binding affinity measurements of individual recruitment sites","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure of ternary complex plus SAXS plus binding affinity measurements, multiple orthogonal structural and biophysical methods","pmids":["36261419"],"is_preprint":false},{"year":2000,"finding":"Among glycogen-targeting PP1 subunits expressed in hepatocytes, PTG overexpression retains dose-dependent regulation of glycogen synthesis and glycogen synthase activity by insulin, whereas PTG-overexpressing cells show reduced glycogenolytic response to forskolin compared to GL- or GM/RGl-overexpressing cells. This is partly explained by lesser forskolin-induced increase in glycogen phosphorylase activity in PTG cells.","method":"Adenovirus-mediated overexpression of PTG, GL, and GM/RGl in hepatocytes; glycogen synthase activity ratio measurement; glycogen phosphorylase activity assay; glycogenolytic response to forskolin","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — comparative gain-of-function with multiple enzymatic readouts, single lab","pmids":["10862764"],"is_preprint":false},{"year":2006,"finding":"The PTG promoter contains functional FoxA2 binding sites. FoxA2 transactivates the PTG promoter in H4IIE hepatoma cells. FoxA2 binds the PTG promoter in vivo (shown by ChIP). cAMP analog treatment activates the PTG promoter and increases PTG protein levels in H4IIE cells.","method":"Luciferase reporter assays with PTG promoter constructs; electrophoretic mobility shift assay with nuclear extracts; chromatin immunoprecipitation (ChIP); Western blot of PTG levels after cAMP treatment","journal":"Endocrinology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP plus reporter plus EMSA, multiple orthogonal methods, single lab","pmids":["16627590"],"is_preprint":false},{"year":2011,"finding":"PPP1R3C/PTG overexpression in skeletal muscle myotubes activates glycogen synthase (reduces phosphorylation at Ser-641/0), increases glycogen content, and produces larger glycogen particles (mean diameter 36.9 nm) compared to PPP1R6 (14.4 nm) or GM (28.3 nm). PTG-derived glycogen is found in membrane- and organelle-devoid cytosolic glycogen-rich areas.","method":"Overexpression in skeletal muscle myotubes; glycogen synthase activity and phosphorylation assay; glycogen content measurement; electron microscopy of glycogen particle size and subcellular localization","journal":"BMC biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct comparison by overexpression with EM localization and enzymatic readouts, single lab","pmids":["22054094"],"is_preprint":false},{"year":2013,"finding":"PER2 promotes expression of PTG (and GL) by binding to genomic regions of PTG in liver. Per2-deficient mice show reduced hepatic glycogen content, altered rhythms of glycogen accumulation, and altered glycogen phosphorylase activity. These effects are at least partly mediated through PER2's transcriptional control of PTG.","method":"Chromatin immunoprecipitation (ChIP) of PER2 at PTG genomic regions; Per2 mutant mice phenotyped for glycogen content, glycogen synthase protein levels, and glycogen phosphorylase activity under fasting/refeeding","journal":"Molecular metabolism","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP plus genetic mouse model with multiple metabolic readouts, single lab","pmids":["24049741"],"is_preprint":false},{"year":2026,"finding":"PPP1R3C acts as a tumor suppressor in endometrial cancer cells through promotion of glycogen synthesis: ectopic PPP1R3C expression induces cell cycle arrest and apoptosis in UCEC-derived cells (HEC1A, HEC1B) and inhibits xenograft tumor growth. Inhibition of glycogen synthase abrogates the growth inhibitory effect of PPP1R3C, establishing that glycogen synthesis activation is required for its tumor suppressor function.","method":"Ectopic expression of PPP1R3C in UCEC cell lines; glycogen synthase inhibition rescue experiment; xenograft tumor growth in BALB/c nude mice; cell cycle and apoptosis assays","journal":"BMB reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — gain-of-function with mechanistic rescue (glycogen synthase inhibition) plus in vivo xenograft, single lab","pmids":["41781186"],"is_preprint":false},{"year":2026,"finding":"PTG overexpression in inguinal white adipose tissue restores glycogen metabolism, thermogenesis, and mitochondrial function impaired by PM2.5 exposure. Mechanistically, PTG negatively regulates VEGFB, and VEGFB knockdown rescues browning. ADRB3 activation restores PTG and normalizes VEGFB, defining an ADRB3-PTG-VEGFB axis.","method":"PTG overexpression in iWAT via adenovirus/AAV in PM2.5-exposed mice; VEGFB knockdown rescue experiment; ADRB3 agonist treatment; thermogenesis and mitochondrial function assays; glycogen content measurement","journal":"Advanced science","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single study with novel non-canonical PTG function (VEGFB regulation), mechanistic chain not fully established in abstracts alone","pmids":["41514494"],"is_preprint":false}],"current_model":"PPP1R3C/PTG is a glycogen-targeting scaffolding subunit of protein phosphatase 1 (PP1) that binds PP1C and directs it to glycogen granules, where it assembles with glycogen synthase, phosphorylase kinase, phosphorylase a, and laforin into a multiprotein complex; by decreasing the Km of PP1 for glycogen-bound substrates, PTG activates glycogen synthase and inactivates glycogen phosphorylase to promote glycogen synthesis. Its activity is regulated by AMPK-mediated phosphorylation at Ser-8 (and Ser-268), which accelerates laforin/malin-dependent ubiquitination and proteasomal degradation of PTG, while its expression is transcriptionally induced by HIF1 (via a proximal HRE) and FoxA2/cAMP in liver. Structural studies reveal an unusual combination of PP1-recruitment sites in the ternary PP1/PTG/carbohydrate complex. Genetic loss of PTG eliminates Lafora body formation and rescues fatal epilepsy in Lafora disease mouse models, and PTG also functions in hepatic gluconeogenesis (via TORC2 dephosphorylation), osmotic stress signaling (via PP1γ-mediated dephosphorylation of SHP-1 to regulate NFAT5), and as a tumor suppressor in endometrial cancer through glycogen synthesis activation."},"narrative":{"mechanistic_narrative":"PPP1R3C (PTG/R5) is a glycogen-targeting scaffolding subunit of protein phosphatase 1 (PP1) that drives glycogen synthesis by spatially organizing PP1 with the enzymes of glycogen metabolism [PMID:9045612]. It binds PP1C and recruits it to glycogen granules, while simultaneously assembling phosphorylase kinase, phosphorylase a, and glycogen synthase into a multiprotein complex; the crystal structure of the PP1/PTG/carbohydrate ternary complex shows that PTG uses an unusual combination of PP1-recruitment sites to capture the phosphatase at the glycogen particle [PMID:9045612, PMID:36261419]. Mechanistically PTG acts by lowering the Km of PP1 for glycogen-bound substrates rather than altering Vmax, thereby net-activating glycogen synthase and inactivating glycogen phosphorylase to promote glycogen accumulation [PMID:9242697, PMID:9756875]. Heterozygous deletion in mice reduces glycogen synthase activity and glycogen stores across adipose, liver, heart, and skeletal muscle, establishing PTG as required for normal in vivo glycogen synthesis [PMID:12727934]. PTG abundance is controlled by a laforin/malin axis: laforin binds PTG through its central glycogen/glycogen-synthase-binding region and recruits the E3 ligase malin to ubiquitinate PTG for proteasomal degradation, a step accelerated by AMPK phosphorylation at Ser-8 [PMID:14532330, PMID:18070875, PMID:19171932]. Transcriptionally, PTG is induced by HIF1 through a proximal hypoxia response element and by FoxA2/cAMP, PER2, and IRF4 in liver and muscle [PMID:20888814, PMID:16627590, PMID:24049741, PMID:33042761]. Genetic removal of PTG eliminates pathogenic polyglucosan (Lafora body) formation and rescues neurodegeneration and myoclonic epilepsy in both laforin- and malin-deficient Lafora disease models, identifying PTG-driven glycogen synthesis as the proximal cause of disease [PMID:21552327, PMID:24419970]. Beyond glycogen storage, PTG contributes to hepatic gluconeogenesis via TORC2 dephosphorylation [PMID:31181215], to osmotic-stress signaling through PP1γ-mediated dephosphorylation of SHP-1 to dampen NFAT5 [PMID:23720348], and acts as a tumor suppressor in endometrial cancer through glycogen-synthesis-dependent cell cycle arrest and apoptosis [PMID:41781186].","teleology":[{"year":1997,"claim":"Established what PTG is at the molecular level: a scaffolding PP1 subunit that physically links the phosphatase to glycogen and to glycogen-metabolizing enzymes, defining a mechanism for spatially coordinated regulation.","evidence":"Cloning from 3T3-L1 adipocytes, co-IP/pulldown with PP1C and metabolic enzymes, and overexpression in CHO cells","pmids":["9045612"],"confidence":"High","gaps":["Stoichiometry and architecture of the multienzyme complex not resolved","Did not show how scaffolding alters catalytic kinetics"]},{"year":1997,"claim":"Defined the catalytic basis of PTG action, showing it activates PP1 against phosphorylase a by lowering substrate Km rather than altering Vmax, with substrate selectivity (no effect on hormone-sensitive lipase).","evidence":"In vitro phosphatase activity assays with 32P-phosphorylase a, kinase assays, and DARPP-32 competition","pmids":["9242697"],"confidence":"High","gaps":["Whether PTG itself is regulated by phosphorylation left open (none detected here)","Kinetics measured for one substrate only"]},{"year":1998,"claim":"Showed PTG is sufficient to drive glycogen synthesis and to suppress glycogenolysis in primary hepatocytes even without insulin or carbohydrate, demonstrating dominant control over glycogen flux.","evidence":"Adenoviral PTG overexpression in primary rat hepatocytes with glycogen synthase/phosphorylase activity and cAMP measurements","pmids":["9756875"],"confidence":"High","gaps":["Did not establish physiological requirement (gain-of-function only)","Mechanism of resistance to glycogenolytic agents not fully defined"]},{"year":2000,"claim":"Distinguished PTG from other glycogen-targeting PP1 subunits, showing it retains insulin responsiveness but blunts the glycogenolytic response to forskolin relative to GL and GM.","evidence":"Comparative adenoviral overexpression of PTG, GL, and GM in hepatocytes with enzymatic readouts","pmids":["10862764"],"confidence":"Medium","gaps":["Mechanistic basis for differential glycogenolysis control only partly explained","Single-lab comparative study"]},{"year":2003,"claim":"Provided the in vivo requirement for PTG, showing genetic loss reduces glycogen synthase activity and glycogen stores across multiple tissues.","evidence":"Heterozygous PTG knockout mice with tissue glycogen and enzymatic phenotyping","pmids":["12727934"],"confidence":"High","gaps":["Homozygous null phenotype not reported here","Tissue-specific contributions not dissected"]},{"year":2003,"claim":"Connected PTG to Lafora disease biology by showing laforin binds PTG via its central glycogen/GS-binding region, and that a disease-causing laforin mutation selectively disrupts this interaction.","evidence":"GST pulldowns, co-localization, and point mutagenesis of R5 and laforin","pmids":["14532330"],"confidence":"High","gaps":["Functional consequence of the interaction not yet established here","In vivo relevance not tested"]},{"year":2007,"claim":"Defined the functional output of the laforin interaction: laforin enables malin to ubiquitinate PTG for proteasomal degradation, providing a mechanism to limit glycogen accumulation.","evidence":"Co-expression with in vitro/in vivo ubiquitination assays, proteasome inhibitor rescue, and glycogen accumulation readout","pmids":["18070875"],"confidence":"High","gaps":["Upstream signals triggering this degradation not identified here","Ubiquitination site mapping not reported"]},{"year":2009,"claim":"Identified AMPK as the upstream regulator coupling energy status to PTG turnover, phosphorylating Ser-8/Ser-268 to accelerate laforin/malin-dependent degradation.","evidence":"Co-IP, MS site mapping, in vitro kinase assay, and degradation/glycogenic activity assays","pmids":["19171932"],"confidence":"High","gaps":["Relative contributions of Ser-8 vs Ser-268 not fully resolved","In vivo physiological context of this regulation not tested"]},{"year":2013,"claim":"Showed PTG/PP1γ has a non-glycogenic signaling role, dephosphorylating SHP-1 to dampen NFAT5 transcriptional activity under osmotic stress.","evidence":"Reciprocal Co-IP, siRNA knockdown, phospho-specific Western, SHP-1 S591A mutagenesis, and NFAT5 reporter","pmids":["23720348"],"confidence":"Medium","gaps":["Single-lab finding for a novel non-glycogenic function","Physiological/in vivo relevance not established"]},{"year":2010,"claim":"Identified hypoxic transcriptional control of PTG, with HIF1 driving glycogen accumulation through a proximal hypoxia response element.","evidence":"HRE luciferase mutagenesis, siRNA knockdown of HIF1α/HIF2α/PPP1R3C, and glycogen measurement under hypoxia","pmids":["20888814"],"confidence":"Medium","gaps":["Direct HIF1 occupancy not shown by ChIP here","Tissue specificity of this axis unclear"]},{"year":2006,"claim":"Defined hepatic transcriptional regulation by showing FoxA2 directly transactivates the PTG promoter and cAMP induces PTG protein.","evidence":"Reporter assays, EMSA, ChIP, and Western blot after cAMP treatment","pmids":["16627590"],"confidence":"Medium","gaps":["Integration with insulin/glucagon signaling not resolved","Single cell-line context"]},{"year":2011,"claim":"Confirmed PTG-mediated glycogen synthesis activation as the proximal cause of Lafora body formation through genetic epistasis in laforin-deficient mice.","evidence":"PTG-knockout crossed into laforin-deficient Lafora mice, with polyglucosan histology, EEG, and behavior","pmids":["21552327"],"confidence":"High","gaps":["Did not address whether residual glycogen synthase activity contributes","Therapeutic translatability not addressed"]},{"year":2011,"claim":"Mapped a functionally required region of PTG by characterizing the N249S variant, which reduces glycogenic activity and binding to glycogen phosphorylase and laforin.","evidence":"Functional glycogen synthesis assays and interaction assays of the natural variant","pmids":["21738631"],"confidence":"Medium","gaps":["Clinical significance of the variant not established","Structural basis defined only later"]},{"year":2011,"claim":"Characterized the glycogen product driven by PTG, showing it activates glycogen synthase and produces enlarged cytosolic glycogen particles distinct from other PP1 subunits.","evidence":"Myotube overexpression with GS phosphorylation, glycogen content, and EM particle-size/localization analyses","pmids":["22054094"],"confidence":"Medium","gaps":["Determinants of particle morphology unknown","Single-lab descriptive comparison"]},{"year":2013,"claim":"Placed PTG within circadian metabolic control, showing PER2 binds PTG genomic regions and contributes to rhythmic hepatic glycogen accumulation.","evidence":"PER2 ChIP and Per2-mutant mouse glycogen/enzymatic phenotyping","pmids":["24049741"],"confidence":"Medium","gaps":["Direct vs indirect transcriptional effect not fully separated","Mechanism of PER2 recruitment unclear"]},{"year":2014,"claim":"Replicated and extended the Lafora epistasis to malin-deficient mice, confirming PTG-mediated glycogen synthesis as the key pathogenic mechanism downstream of malin.","evidence":"PTG-knockout crossed into malin-deficient mice with Lafora body, seizure, and behavioral readouts","pmids":["24419970"],"confidence":"High","gaps":["Did not test partial PTG inhibition as a therapeutic strategy directly","Neuronal vs astrocytic contributions not dissected"]},{"year":2019,"claim":"Identified a gluconeogenic role for PTG, linking it to hepatic glucose production via TORC2 dephosphorylation and nuclear localization.","evidence":"Adenoviral gain/loss-of-function in hepatocytes and mouse liver with TORC2 phospho/localization and glucose production assays","pmids":["31181215"],"confidence":"Medium","gaps":["Whether PP1 catalytic activity mediates TORC2 dephosphorylation not directly shown","Single-lab finding"]},{"year":2020,"claim":"Generalized PTG's pathogenic glycogen-synthesis role to a second polyglucosan disease, showing PTG knockout reduces muscle polyglucosan bodies and improves outcomes in an APBD model.","evidence":"PTG knockout crossed into GBE-deficient APBD mice with histology, lifespan, and neuromuscular testing","pmids":["33034425"],"confidence":"Medium","gaps":["Brain vs muscle relative benefit not fully resolved","Single study"]},{"year":2020,"claim":"Defined IRF4 as a transcriptional regulator acting through PTG to control muscle glycogen and exercise capacity, demonstrated by epistatic rescue.","evidence":"Muscle-specific IRF4 knockout/overexpression with adenoviral PTG knockdown rescue","pmids":["33042761"],"confidence":"Medium","gaps":["Direct IRF4 binding to PTG promoter not detailed","Single-lab finding"]},{"year":2022,"claim":"Provided the structural basis of PTG function, revealing how multiple PP1-recruitment sites assemble the PP1/PTG/carbohydrate ternary complex.","evidence":"X-ray crystallography, in-solution SAXS, and per-site binding affinity measurements","pmids":["36261419"],"confidence":"High","gaps":["Substrate enzymes not captured in the structure","Conformational heterogeneity not mechanistically resolved"]},{"year":2026,"claim":"Established PTG as a glycogen-synthesis-dependent tumor suppressor in endometrial cancer, with glycogen synthase activity required for its growth-inhibitory effect.","evidence":"Ectopic expression in UCEC cell lines, glycogen synthase inhibition rescue, xenografts, and cell cycle/apoptosis assays","pmids":["41781186"],"confidence":"Medium","gaps":["Link between glycogen accumulation and apoptosis mechanism unclear","Single-lab finding"]},{"year":2026,"claim":"Proposed a non-canonical adipose role for PTG in browning via an ADRB3-PTG-VEGFB axis, linking glycogen metabolism to thermogenesis.","evidence":"PTG overexpression in iWAT, VEGFB knockdown rescue, and ADRB3 agonist treatment in PM2.5-exposed mice","pmids":["41514494"],"confidence":"Low","gaps":["Mechanistic chain from PTG to VEGFB not established","Novel function reported in a single study"]},{"year":null,"claim":"It remains unresolved how PTG's diverse non-glycogenic functions (TORC2 dephosphorylation, SHP-1/NFAT5, VEGFB regulation) mechanistically depend on PP1 catalytic activity and how they are coordinated with its canonical glycogenic role across tissues.","evidence":"No timeline study reconstitutes these non-glycogenic activities with defined PP1 substrate-targeting mechanisms","pmids":[],"confidence":"Low","gaps":["Direct PP1 substrate identification for non-glycogenic roles missing","Tissue-specific regulatory integration not defined","Structural basis for substrate enzyme recruitment unresolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,1,2]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,15]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[0,18]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[18]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[0,2,3,12]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[9,11,13,20]}],"complexes":["PP1/PTG/glycogen complex"],"partners":["PPP1CC","GYS1","PYGL","PHKB","EPM2A (LAFORIN)","NHLRC1 (MALIN)","PRKAA (AMPK)","PTPN6 (SHP-1)"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9UQK1","full_name":"Protein phosphatase 1 regulatory subunit 3C","aliases":["Protein phosphatase 1 regulatory subunit 5","PP1 subunit R5","Protein targeting to glycogen","PTG"],"length_aa":317,"mass_kda":36.4,"function":"Acts as a glycogen-targeting subunit for PP1 and regulates its activity. Activates glycogen synthase, reduces glycogen phosphorylase activity and limits glycogen breakdown. Dramatically increases basal and insulin-stimulated glycogen synthesis upon overexpression in a variety of cell types","subcellular_location":"","url":"https://www.uniprot.org/uniprotkb/Q9UQK1/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PPP1R3C","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/PPP1R3C","total_profiled":1310},"omim":[{"mim_id":"619540","title":"PROTEIN PHOSPHATASE 1, REGULATORY SUBUNIT 3E; PPP1R3E","url":"https://www.omim.org/entry/619540"},{"mim_id":"616328","title":"LONG INTERGENIC NONCODING RNA PINKY","url":"https://www.omim.org/entry/616328"},{"mim_id":"608072","title":"NHL REPEAT-CONTAINING PROTEIN 1; 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Overexpression of PTG in CHO cells markedly increased basal and insulin-stimulated glycogen synthesis.\",\n      \"method\": \"Cloning from 3T3-L1 adipocytes, co-immunoprecipitation/pulldown of PTG with PP1C and glycogen metabolism enzymes, overexpression in CHO cells with insulin receptor\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal binding assays, functional overexpression with defined phenotype, replicated across multiple subsequent studies\",\n      \"pmids\": [\"9045612\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"PTG increases PP1 activity against phosphorylase a by decreasing the Km of PP1 for this substrate 5-fold without affecting Vmax; PTG did not affect PP1 activity against hormone-sensitive lipase. PTG was not phosphorylated in vivo or in vitro by insulin- or forskolin-activated kinases. PTG decreased the ability of DARPP-32 to inhibit PP1 activity.\",\n      \"method\": \"GST-PTG pulldown from 3T3-L1 lysates, in vitro phosphatase activity assay with 32P-labeled phosphorylase a, in vivo and in vitro kinase assays, PP1 inhibitor (DARPP-32) competition assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro enzymatic reconstitution with multiple substrates, mutagenesis-independent but multiple orthogonal methods in one study\",\n      \"pmids\": [\"9242697\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Adenovirus-mediated overexpression of PTG in primary rat hepatocytes potently activates glycogen synthesis even in the absence of carbohydrates or insulin, increases glycogen synthase activation state 3.6-fold, and decreases glycogen phosphorylase activity 40%. Glycogenolytic agents (forskolin, glucagon) are largely ineffective at activating glycogen degradation in PTG-overexpressing hepatocytes despite large cAMP increases.\",\n      \"method\": \"Recombinant adenovirus-mediated PTG overexpression in primary rat hepatocytes; glycogen synthase activity assay; glycogen phosphorylase activity assay; cAMP measurement\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean gain-of-function in primary cells with multiple enzymatic readouts, consistent with founding paper\",\n      \"pmids\": [\"9756875\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"PTG (PPP1R3C) knockout mice (heterozygous deletion) have reduced glycogen stores in adipose tissue, liver, heart, and skeletal muscle, with decreased glycogen synthase activity and glycogen synthesis rate, demonstrating PTG is required for normal glycogen synthesis in vivo.\",\n      \"method\": \"Heterozygous PTG gene deletion in mice; tissue glycogen measurement; glycogen synthase activity assay; metabolic phenotyping including glucose tolerance and insulin resistance\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic knockout with defined enzymatic and metabolic phenotype, multiple tissues analyzed\",\n      \"pmids\": [\"12727934\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Laforin interacts with the glycogen-targeting regulatory subunit R5/PTG. The interaction requires full-length laforin, and a minimal central region of R5 (amino acids 116-238) including the glycogen and glycogen synthase binding sites is sufficient. Point mutagenesis of the glycogen synthase-binding site of R5 completely blocks interaction with laforin. Lafora disease-associated laforin mutation G240S disrupts the interaction with R5 without affecting phosphatase or glycogen binding activities.\",\n      \"method\": \"Pulldown assays (GST-fusion proteins), co-localization experiments, point mutagenesis of R5 and laforin\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal pulldown and co-localization with mutagenesis mapping of interaction domain, single lab but orthogonal methods\",\n      \"pmids\": [\"14532330\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Malin (E3 ubiquitin ligase) ubiquitinates PTG in a laforin-dependent manner both in vivo and in vitro, targeting PTG for proteasome-dependent degradation. Co-expression of malin and laforin abolished PTG-stimulated glycogen accumulation in tissue culture cells.\",\n      \"method\": \"Co-expression of PTG, malin, and laforin in tissue culture cells; in vitro and in vivo ubiquitination assays; proteasome inhibitor rescue experiments; glycogen accumulation assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro ubiquitination reconstitution plus in vivo validation plus functional glycogen accumulation readout\",\n      \"pmids\": [\"18070875\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"AMPK physically interacts with R5/PTG and phosphorylates it at Ser-8 and Ser-268 (mapped by mass spectrometry). Phosphorylation of Ser-8 by AMPK accelerates laforin/malin-dependent ubiquitination and proteasomal degradation of R5/PTG, resulting in decreased glycogenic activity.\",\n      \"method\": \"Co-immunoprecipitation of AMPK with R5/PTG; mass spectrometry phosphorylation site mapping; in vitro AMPK kinase assay; ubiquitination and proteasome-dependent degradation assays; glycogenic activity measurement\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro kinase assay with mass spectrometry site mapping plus functional degradation assay, multiple orthogonal methods single lab\",\n      \"pmids\": [\"19171932\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"PTG (PP1 regulatory subunit) associates physically with PP1γ, and high NaCl reduces PTG-PP1γ association and remaining PTG-associated PP1γ activity. PTG and PP1γ bind to SHP-1, and knockdown of PTG or PP1γ increases high NaCl-induced phosphorylation of SHP-1-S591 (inhibitory), which in turn reduces SHP-1's inhibitory effect on NFAT5. Thus PTG/PP1γ dephosphorylates SHP-1 to dampen NFAT5 activity under high NaCl.\",\n      \"method\": \"Co-immunoprecipitation of PTG with PP1γ and SHP-1; siRNA knockdown of PTG and PP1γ; phospho-specific Western blot for SHP-1-S591; mutation of SHP-1-S591 to alanine; NFAT5 transcriptional activity assay\",\n      \"journal\": \"American journal of physiology. Renal physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP plus knockdown plus mutagenesis, but single lab and novel non-glycogenic function\",\n      \"pmids\": [\"23720348\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"HIF1 directly regulates PPP1R3C expression through a functional hypoxia response element 229 bp upstream of the PPP1R3C gene. PPP1R3C induction by hypoxia correlates with glycogen accumulation in MCF7 cells; knockdown of either HIF1α or PPP1R3C attenuates hypoxia-induced glycogen accumulation.\",\n      \"method\": \"Mutation analysis of hypoxia response element by luciferase reporter assay; siRNA knockdown of HIF1α, HIF2α, and PPP1R3C; glycogen content measurement under hypoxia\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — HRE mutagenesis plus functional siRNA knockdown with glycogen readout, two orthogonal methods, single lab\",\n      \"pmids\": [\"20888814\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Genetic removal of PTG from Lafora disease mice (laforin- or malin-deficient) results in near-complete disappearance of polyglucosan (Lafora body) accumulation and resolution of neurodegeneration and myoclonic epilepsy, demonstrating that PTG-driven PP1 activation of glycogen synthase is the proximal cause of Lafora body formation.\",\n      \"method\": \"Genetic cross of PTG-knockout mice with Lafora disease (laforin-deficient) mice; histological analysis of polyglucosan accumulation; EEG/behavioral assessment of myoclonic epilepsy\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis in mouse disease model with multiple phenotypic readouts (histology, EEG, behavior), replicated in malin-deficient model\",\n      \"pmids\": [\"21552327\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"A PTG variant (N249S, c.746A>G) results in decreased capacity to induce glycogen synthesis and reduced interaction with glycogen phosphorylase and laforin, establishing that the glycogen phosphorylase and laforin binding region of PTG is required for full glycogenic activity.\",\n      \"method\": \"Identification of N249S mutation; functional assay of glycogen synthesis; interaction assays with glycogen phosphorylase and laforin\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — natural variant with functional characterization using multiple interaction readouts, single lab\",\n      \"pmids\": [\"21738631\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Genetic reduction of PTG in malin-deficient Lafora disease mice nearly completely eliminates Lafora bodies and rescues neurodegeneration, myoclonus, seizure susceptibility, and behavioral abnormality, confirming that PTG-mediated glycogen synthesis activation is the key pathogenic mechanism downstream of malin.\",\n      \"method\": \"Genetic cross of PTG-knockout mice with malin-deficient mice; histological Lafora body quantification; seizure susceptibility and behavioral testing\",\n      \"journal\": \"Annals of neurology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis in second Lafora disease mouse model, multiple phenotypic readouts, replicates laforin-model findings\",\n      \"pmids\": [\"24419970\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PPP1R3C overexpression in primary mouse hepatocytes and mouse liver promotes hepatic glucose production and gluconeogenic gene expression. Knockdown of PPP1R3C suppresses cAMP-stimulated gluconeogenic gene expression and blocks TORC2 dephosphorylation (nuclear localization). AMPK activation (by metformin) suppresses Ppp1r3c mRNA expression. PPP1R3C-mediated TORC2 dephosphorylation links PPP1R3C to gluconeogenic transcription.\",\n      \"method\": \"Adenovirus-mediated overexpression and knockdown of PPP1R3C in primary hepatocytes and mouse liver in vivo; Western blot and immunofluorescence for TORC2 phosphorylation/localization; hepatic glucose production assay; gluconeogenic gene expression\",\n      \"journal\": \"Metabolism: clinical and experimental\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — gain- and loss-of-function in vivo plus mechanistic TORC2 localization readout, single lab\",\n      \"pmids\": [\"31181215\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"PPP1R3C knockout reduces skeletal muscle polyglucosan bodies in an APBD (GBE-deficient) mouse model and improves lifespan, morphology, and neuromuscular function, confirming PTG's role in activating glycogen synthase (GYS1) in muscle in vivo.\",\n      \"method\": \"PPP1R3C knockout crossed into APBD mouse model; histological polyglucosan body quantification; lifespan and behavioral assays; brain and muscle glycogen quantification\",\n      \"journal\": \"Annals of clinical and translational neurology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis in disease model, multiple phenotypic readouts, single study\",\n      \"pmids\": [\"33034425\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"IRF4 in skeletal muscle regulates glycogen metabolism via transcriptional control of PTG. Skeletal muscle-specific IRF4 knockout increases glycogen content and exercise capacity; IRF4 overexpression decreases both. Knockdown of PTG reverses the phenotype of IRF4 knockout, placing PTG downstream of IRF4 in a glycogen regulatory pathway.\",\n      \"method\": \"Skeletal muscle-specific IRF4 knockout and overexpression mice; glycogen content measurement; exercise capacity testing; adenovirus-mediated PTG knockdown as epistasis test\",\n      \"journal\": \"Advanced science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis with gain- and loss-of-function and rescue experiment, single lab\",\n      \"pmids\": [\"33042761\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Crystal structure of the ternary PP1/PTG/carbohydrate complex was determined, revealing an unusual combination of PP1-recruitment sites on PTG. PTG uses multiple binding interfaces to recruit PP1 to glycogen granules. In-solution SAXS analyses revealed conformational heterogeneity of the complex. Individual contributions of recruitment sites to overall binding affinity were characterized.\",\n      \"method\": \"X-ray crystallography of PP1/PTG/carbohydrate ternary complex; SAXS (small-angle X-ray scattering) in solution analysis; binding affinity measurements of individual recruitment sites\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure of ternary complex plus SAXS plus binding affinity measurements, multiple orthogonal structural and biophysical methods\",\n      \"pmids\": [\"36261419\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Among glycogen-targeting PP1 subunits expressed in hepatocytes, PTG overexpression retains dose-dependent regulation of glycogen synthesis and glycogen synthase activity by insulin, whereas PTG-overexpressing cells show reduced glycogenolytic response to forskolin compared to GL- or GM/RGl-overexpressing cells. This is partly explained by lesser forskolin-induced increase in glycogen phosphorylase activity in PTG cells.\",\n      \"method\": \"Adenovirus-mediated overexpression of PTG, GL, and GM/RGl in hepatocytes; glycogen synthase activity ratio measurement; glycogen phosphorylase activity assay; glycogenolytic response to forskolin\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — comparative gain-of-function with multiple enzymatic readouts, single lab\",\n      \"pmids\": [\"10862764\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"The PTG promoter contains functional FoxA2 binding sites. FoxA2 transactivates the PTG promoter in H4IIE hepatoma cells. FoxA2 binds the PTG promoter in vivo (shown by ChIP). cAMP analog treatment activates the PTG promoter and increases PTG protein levels in H4IIE cells.\",\n      \"method\": \"Luciferase reporter assays with PTG promoter constructs; electrophoretic mobility shift assay with nuclear extracts; chromatin immunoprecipitation (ChIP); Western blot of PTG levels after cAMP treatment\",\n      \"journal\": \"Endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP plus reporter plus EMSA, multiple orthogonal methods, single lab\",\n      \"pmids\": [\"16627590\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"PPP1R3C/PTG overexpression in skeletal muscle myotubes activates glycogen synthase (reduces phosphorylation at Ser-641/0), increases glycogen content, and produces larger glycogen particles (mean diameter 36.9 nm) compared to PPP1R6 (14.4 nm) or GM (28.3 nm). PTG-derived glycogen is found in membrane- and organelle-devoid cytosolic glycogen-rich areas.\",\n      \"method\": \"Overexpression in skeletal muscle myotubes; glycogen synthase activity and phosphorylation assay; glycogen content measurement; electron microscopy of glycogen particle size and subcellular localization\",\n      \"journal\": \"BMC biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct comparison by overexpression with EM localization and enzymatic readouts, single lab\",\n      \"pmids\": [\"22054094\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"PER2 promotes expression of PTG (and GL) by binding to genomic regions of PTG in liver. Per2-deficient mice show reduced hepatic glycogen content, altered rhythms of glycogen accumulation, and altered glycogen phosphorylase activity. These effects are at least partly mediated through PER2's transcriptional control of PTG.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP) of PER2 at PTG genomic regions; Per2 mutant mice phenotyped for glycogen content, glycogen synthase protein levels, and glycogen phosphorylase activity under fasting/refeeding\",\n      \"journal\": \"Molecular metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP plus genetic mouse model with multiple metabolic readouts, single lab\",\n      \"pmids\": [\"24049741\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"PPP1R3C acts as a tumor suppressor in endometrial cancer cells through promotion of glycogen synthesis: ectopic PPP1R3C expression induces cell cycle arrest and apoptosis in UCEC-derived cells (HEC1A, HEC1B) and inhibits xenograft tumor growth. Inhibition of glycogen synthase abrogates the growth inhibitory effect of PPP1R3C, establishing that glycogen synthesis activation is required for its tumor suppressor function.\",\n      \"method\": \"Ectopic expression of PPP1R3C in UCEC cell lines; glycogen synthase inhibition rescue experiment; xenograft tumor growth in BALB/c nude mice; cell cycle and apoptosis assays\",\n      \"journal\": \"BMB reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — gain-of-function with mechanistic rescue (glycogen synthase inhibition) plus in vivo xenograft, single lab\",\n      \"pmids\": [\"41781186\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"PTG overexpression in inguinal white adipose tissue restores glycogen metabolism, thermogenesis, and mitochondrial function impaired by PM2.5 exposure. Mechanistically, PTG negatively regulates VEGFB, and VEGFB knockdown rescues browning. ADRB3 activation restores PTG and normalizes VEGFB, defining an ADRB3-PTG-VEGFB axis.\",\n      \"method\": \"PTG overexpression in iWAT via adenovirus/AAV in PM2.5-exposed mice; VEGFB knockdown rescue experiment; ADRB3 agonist treatment; thermogenesis and mitochondrial function assays; glycogen content measurement\",\n      \"journal\": \"Advanced science\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single study with novel non-canonical PTG function (VEGFB regulation), mechanistic chain not fully established in abstracts alone\",\n      \"pmids\": [\"41514494\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PPP1R3C/PTG is a glycogen-targeting scaffolding subunit of protein phosphatase 1 (PP1) that binds PP1C and directs it to glycogen granules, where it assembles with glycogen synthase, phosphorylase kinase, phosphorylase a, and laforin into a multiprotein complex; by decreasing the Km of PP1 for glycogen-bound substrates, PTG activates glycogen synthase and inactivates glycogen phosphorylase to promote glycogen synthesis. Its activity is regulated by AMPK-mediated phosphorylation at Ser-8 (and Ser-268), which accelerates laforin/malin-dependent ubiquitination and proteasomal degradation of PTG, while its expression is transcriptionally induced by HIF1 (via a proximal HRE) and FoxA2/cAMP in liver. Structural studies reveal an unusual combination of PP1-recruitment sites in the ternary PP1/PTG/carbohydrate complex. Genetic loss of PTG eliminates Lafora body formation and rescues fatal epilepsy in Lafora disease mouse models, and PTG also functions in hepatic gluconeogenesis (via TORC2 dephosphorylation), osmotic stress signaling (via PP1γ-mediated dephosphorylation of SHP-1 to regulate NFAT5), and as a tumor suppressor in endometrial cancer through glycogen synthesis activation.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PPP1R3C (PTG/R5) is a glycogen-targeting scaffolding subunit of protein phosphatase 1 (PP1) that drives glycogen synthesis by spatially organizing PP1 with the enzymes of glycogen metabolism [#0]. It binds PP1C and recruits it to glycogen granules, while simultaneously assembling phosphorylase kinase, phosphorylase a, and glycogen synthase into a multiprotein complex; the crystal structure of the PP1/PTG/carbohydrate ternary complex shows that PTG uses an unusual combination of PP1-recruitment sites to capture the phosphatase at the glycogen particle [#0, #15]. Mechanistically PTG acts by lowering the Km of PP1 for glycogen-bound substrates rather than altering Vmax, thereby net-activating glycogen synthase and inactivating glycogen phosphorylase to promote glycogen accumulation [#1, #2]. Heterozygous deletion in mice reduces glycogen synthase activity and glycogen stores across adipose, liver, heart, and skeletal muscle, establishing PTG as required for normal in vivo glycogen synthesis [#3]. PTG abundance is controlled by a laforin/malin axis: laforin binds PTG through its central glycogen/glycogen-synthase-binding region and recruits the E3 ligase malin to ubiquitinate PTG for proteasomal degradation, a step accelerated by AMPK phosphorylation at Ser-8 [#4, #5, #6]. Transcriptionally, PTG is induced by HIF1 through a proximal hypoxia response element and by FoxA2/cAMP, PER2, and IRF4 in liver and muscle [#8, #17, #19, #14]. Genetic removal of PTG eliminates pathogenic polyglucosan (Lafora body) formation and rescues neurodegeneration and myoclonic epilepsy in both laforin- and malin-deficient Lafora disease models, identifying PTG-driven glycogen synthesis as the proximal cause of disease [#9, #11]. Beyond glycogen storage, PTG contributes to hepatic gluconeogenesis via TORC2 dephosphorylation [#12], to osmotic-stress signaling through PP1\\u03b3-mediated dephosphorylation of SHP-1 to dampen NFAT5 [#7], and acts as a tumor suppressor in endometrial cancer through glycogen-synthesis-dependent cell cycle arrest and apoptosis [#20].\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"Established what PTG is at the molecular level: a scaffolding PP1 subunit that physically links the phosphatase to glycogen and to glycogen-metabolizing enzymes, defining a mechanism for spatially coordinated regulation.\",\n      \"evidence\": \"Cloning from 3T3-L1 adipocytes, co-IP/pulldown with PP1C and metabolic enzymes, and overexpression in CHO cells\",\n      \"pmids\": [\"9045612\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and architecture of the multienzyme complex not resolved\", \"Did not show how scaffolding alters catalytic kinetics\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Defined the catalytic basis of PTG action, showing it activates PP1 against phosphorylase a by lowering substrate Km rather than altering Vmax, with substrate selectivity (no effect on hormone-sensitive lipase).\",\n      \"evidence\": \"In vitro phosphatase activity assays with 32P-phosphorylase a, kinase assays, and DARPP-32 competition\",\n      \"pmids\": [\"9242697\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PTG itself is regulated by phosphorylation left open (none detected here)\", \"Kinetics measured for one substrate only\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Showed PTG is sufficient to drive glycogen synthesis and to suppress glycogenolysis in primary hepatocytes even without insulin or carbohydrate, demonstrating dominant control over glycogen flux.\",\n      \"evidence\": \"Adenoviral PTG overexpression in primary rat hepatocytes with glycogen synthase/phosphorylase activity and cAMP measurements\",\n      \"pmids\": [\"9756875\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish physiological requirement (gain-of-function only)\", \"Mechanism of resistance to glycogenolytic agents not fully defined\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Distinguished PTG from other glycogen-targeting PP1 subunits, showing it retains insulin responsiveness but blunts the glycogenolytic response to forskolin relative to GL and GM.\",\n      \"evidence\": \"Comparative adenoviral overexpression of PTG, GL, and GM in hepatocytes with enzymatic readouts\",\n      \"pmids\": [\"10862764\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanistic basis for differential glycogenolysis control only partly explained\", \"Single-lab comparative study\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Provided the in vivo requirement for PTG, showing genetic loss reduces glycogen synthase activity and glycogen stores across multiple tissues.\",\n      \"evidence\": \"Heterozygous PTG knockout mice with tissue glycogen and enzymatic phenotyping\",\n      \"pmids\": [\"12727934\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Homozygous null phenotype not reported here\", \"Tissue-specific contributions not dissected\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Connected PTG to Lafora disease biology by showing laforin binds PTG via its central glycogen/GS-binding region, and that a disease-causing laforin mutation selectively disrupts this interaction.\",\n      \"evidence\": \"GST pulldowns, co-localization, and point mutagenesis of R5 and laforin\",\n      \"pmids\": [\"14532330\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of the interaction not yet established here\", \"In vivo relevance not tested\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Defined the functional output of the laforin interaction: laforin enables malin to ubiquitinate PTG for proteasomal degradation, providing a mechanism to limit glycogen accumulation.\",\n      \"evidence\": \"Co-expression with in vitro/in vivo ubiquitination assays, proteasome inhibitor rescue, and glycogen accumulation readout\",\n      \"pmids\": [\"18070875\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Upstream signals triggering this degradation not identified here\", \"Ubiquitination site mapping not reported\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Identified AMPK as the upstream regulator coupling energy status to PTG turnover, phosphorylating Ser-8/Ser-268 to accelerate laforin/malin-dependent degradation.\",\n      \"evidence\": \"Co-IP, MS site mapping, in vitro kinase assay, and degradation/glycogenic activity assays\",\n      \"pmids\": [\"19171932\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contributions of Ser-8 vs Ser-268 not fully resolved\", \"In vivo physiological context of this regulation not tested\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Showed PTG/PP1\\u03b3 has a non-glycogenic signaling role, dephosphorylating SHP-1 to dampen NFAT5 transcriptional activity under osmotic stress.\",\n      \"evidence\": \"Reciprocal Co-IP, siRNA knockdown, phospho-specific Western, SHP-1 S591A mutagenesis, and NFAT5 reporter\",\n      \"pmids\": [\"23720348\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab finding for a novel non-glycogenic function\", \"Physiological/in vivo relevance not established\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Identified hypoxic transcriptional control of PTG, with HIF1 driving glycogen accumulation through a proximal hypoxia response element.\",\n      \"evidence\": \"HRE luciferase mutagenesis, siRNA knockdown of HIF1\\u03b1/HIF2\\u03b1/PPP1R3C, and glycogen measurement under hypoxia\",\n      \"pmids\": [\"20888814\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct HIF1 occupancy not shown by ChIP here\", \"Tissue specificity of this axis unclear\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Defined hepatic transcriptional regulation by showing FoxA2 directly transactivates the PTG promoter and cAMP induces PTG protein.\",\n      \"evidence\": \"Reporter assays, EMSA, ChIP, and Western blot after cAMP treatment\",\n      \"pmids\": [\"16627590\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Integration with insulin/glucagon signaling not resolved\", \"Single cell-line context\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Confirmed PTG-mediated glycogen synthesis activation as the proximal cause of Lafora body formation through genetic epistasis in laforin-deficient mice.\",\n      \"evidence\": \"PTG-knockout crossed into laforin-deficient Lafora mice, with polyglucosan histology, EEG, and behavior\",\n      \"pmids\": [\"21552327\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not address whether residual glycogen synthase activity contributes\", \"Therapeutic translatability not addressed\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Mapped a functionally required region of PTG by characterizing the N249S variant, which reduces glycogenic activity and binding to glycogen phosphorylase and laforin.\",\n      \"evidence\": \"Functional glycogen synthesis assays and interaction assays of the natural variant\",\n      \"pmids\": [\"21738631\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Clinical significance of the variant not established\", \"Structural basis defined only later\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Characterized the glycogen product driven by PTG, showing it activates glycogen synthase and produces enlarged cytosolic glycogen particles distinct from other PP1 subunits.\",\n      \"evidence\": \"Myotube overexpression with GS phosphorylation, glycogen content, and EM particle-size/localization analyses\",\n      \"pmids\": [\"22054094\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Determinants of particle morphology unknown\", \"Single-lab descriptive comparison\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Placed PTG within circadian metabolic control, showing PER2 binds PTG genomic regions and contributes to rhythmic hepatic glycogen accumulation.\",\n      \"evidence\": \"PER2 ChIP and Per2-mutant mouse glycogen/enzymatic phenotyping\",\n      \"pmids\": [\"24049741\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct vs indirect transcriptional effect not fully separated\", \"Mechanism of PER2 recruitment unclear\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Replicated and extended the Lafora epistasis to malin-deficient mice, confirming PTG-mediated glycogen synthesis as the key pathogenic mechanism downstream of malin.\",\n      \"evidence\": \"PTG-knockout crossed into malin-deficient mice with Lafora body, seizure, and behavioral readouts\",\n      \"pmids\": [\"24419970\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not test partial PTG inhibition as a therapeutic strategy directly\", \"Neuronal vs astrocytic contributions not dissected\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identified a gluconeogenic role for PTG, linking it to hepatic glucose production via TORC2 dephosphorylation and nuclear localization.\",\n      \"evidence\": \"Adenoviral gain/loss-of-function in hepatocytes and mouse liver with TORC2 phospho/localization and glucose production assays\",\n      \"pmids\": [\"31181215\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether PP1 catalytic activity mediates TORC2 dephosphorylation not directly shown\", \"Single-lab finding\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Generalized PTG's pathogenic glycogen-synthesis role to a second polyglucosan disease, showing PTG knockout reduces muscle polyglucosan bodies and improves outcomes in an APBD model.\",\n      \"evidence\": \"PTG knockout crossed into GBE-deficient APBD mice with histology, lifespan, and neuromuscular testing\",\n      \"pmids\": [\"33034425\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Brain vs muscle relative benefit not fully resolved\", \"Single study\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Defined IRF4 as a transcriptional regulator acting through PTG to control muscle glycogen and exercise capacity, demonstrated by epistatic rescue.\",\n      \"evidence\": \"Muscle-specific IRF4 knockout/overexpression with adenoviral PTG knockdown rescue\",\n      \"pmids\": [\"33042761\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct IRF4 binding to PTG promoter not detailed\", \"Single-lab finding\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Provided the structural basis of PTG function, revealing how multiple PP1-recruitment sites assemble the PP1/PTG/carbohydrate ternary complex.\",\n      \"evidence\": \"X-ray crystallography, in-solution SAXS, and per-site binding affinity measurements\",\n      \"pmids\": [\"36261419\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Substrate enzymes not captured in the structure\", \"Conformational heterogeneity not mechanistically resolved\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Established PTG as a glycogen-synthesis-dependent tumor suppressor in endometrial cancer, with glycogen synthase activity required for its growth-inhibitory effect.\",\n      \"evidence\": \"Ectopic expression in UCEC cell lines, glycogen synthase inhibition rescue, xenografts, and cell cycle/apoptosis assays\",\n      \"pmids\": [\"41781186\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Link between glycogen accumulation and apoptosis mechanism unclear\", \"Single-lab finding\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Proposed a non-canonical adipose role for PTG in browning via an ADRB3-PTG-VEGFB axis, linking glycogen metabolism to thermogenesis.\",\n      \"evidence\": \"PTG overexpression in iWAT, VEGFB knockdown rescue, and ADRB3 agonist treatment in PM2.5-exposed mice\",\n      \"pmids\": [\"41514494\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Mechanistic chain from PTG to VEGFB not established\", \"Novel function reported in a single study\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved how PTG's diverse non-glycogenic functions (TORC2 dephosphorylation, SHP-1/NFAT5, VEGFB regulation) mechanistically depend on PP1 catalytic activity and how they are coordinated with its canonical glycogenic role across tissues.\",\n      \"evidence\": \"No timeline study reconstitutes these non-glycogenic activities with defined PP1 substrate-targeting mechanisms\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Direct PP1 substrate identification for non-glycogenic roles missing\", \"Tissue-specific regulatory integration not defined\", \"Structural basis for substrate enzyme recruitment unresolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 1, 2]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 15]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [0, 18]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [18]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [0, 2, 3, 12]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [9, 11, 13, 20]}\n    ],\n    \"complexes\": [\n      \"PP1/PTG/glycogen complex\"\n    ],\n    \"partners\": [\n      \"PPP1CC\",\n      \"GYS1\",\n      \"PYGL\",\n      \"PHKB\",\n      \"EPM2A (laforin)\",\n      \"NHLRC1 (malin)\",\n      \"PRKAA (AMPK)\",\n      \"PTPN6 (SHP-1)\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}