{"gene":"PPP1R1A","run_date":"2026-04-28T19:45:44","timeline":{"discoveries":[{"year":2017,"finding":"PPP1R1A functions as a potent inhibitor of protein phosphatase 1 (PP1) in Ewing sarcoma; PKA phosphorylation of PPP1R1A at Thr35 is required for its activation, subsequent PP1 binding and inhibition, and PPP1R1A-mediated tumorigenesis and metastasis. A constitutively active PPP1R1A rescued PKA inhibitor-induced suppression of ES proliferation, establishing the PKA/PPP1R1A/PP1 pathway.","method":"Loss-of-function (siRNA/shRNA depletion), rescue with constitutively active PPP1R1A mutant, PKA inhibitor treatment, in vitro cell migration/proliferation assays, orthotopic xenograft mouse model, RNA-seq","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal methods including mutagenesis, rescue experiments, in vivo model, and RNA-seq in a single rigorous study","pmids":["29059150"],"is_preprint":false},{"year":2023,"finding":"PPP1R1A (inhibitory subunit 1, I1) acts as a negative regulator of PP1A (Ppp1Ca) in the kidney distal tubule; high dietary potassium suppresses Ppp1r1a expression and dephosphorylates I1, thereby activating PP1A to directly bind and dephosphorylate NCC (NaCl cotransporter), reducing blood pressure. This was confirmed using genetically engineered mice with constitutively active SPAK.","method":"Transcriptomics screen, genetically engineered constitutively active SPAK mice, dietary potassium manipulation, Western blotting for phospho-NCC and phospho-I1, BP measurements","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis in engineered mice plus biochemical phosphorylation assays; multiple orthogonal approaches in a single study","pmids":["37676724"],"is_preprint":false},{"year":2021,"finding":"In pancreatic β-cells, PPP1R1A expression is driven by the transcription factor MafA; silencing PPP1R1A in INS-1 (832/13) cells impaired GLP1R-mediated amplification of glucose-stimulated insulin secretion (GSIS), reduced PKA-target protein phosphorylation, and impaired mitochondrial coupling efficiency, while also downregulating β-cell identity genes (MafA, Pdx1, NeuroD1, Pax6).","method":"siRNA silencing in INS-1 cells, acute MafA knockdown, GSIS assay, phospho-Western blotting of PKA targets, mitochondrial coupling efficiency measurement, mRNA expression analysis","journal":"Metabolism: clinical and experimental","confidence":"High","confidence_rationale":"Tier 2 — clean KD with multiple orthogonal functional readouts (secretion, phosphorylation, mitochondrial function, gene expression) in a single study","pmids":["33631146"],"is_preprint":false},{"year":2020,"finding":"PPP1R1A regulates G1/S cell cycle progression in Ewing sarcoma cells by downregulating cell cycle inhibitors p21Cip1 and p27Kip1, leading to Rb protein hyperphosphorylation. PPP1R1A depletion also impaired histone gene transcription during the cell cycle. Combined targeting of PPP1R1A and IGF-1R showed synergistic/additive effects on reducing ES cell proliferation and tumor growth.","method":"Loss-of-function depletion, cell cycle analysis, Western blotting for p21, p27, phospho-Rb, IGF-1R inhibitor combination, in vitro proliferation/migration assays, xenograft tumor model","journal":"Oncotarget","confidence":"High","confidence_rationale":"Tier 2 — clean KD with defined molecular readouts (p21, p27, Rb phosphorylation) and in vivo validation","pmids":["32477459"],"is_preprint":false},{"year":2013,"finding":"PPP1R1A protein is highly abundant and relatively selective in pancreatic β-cells; upon chemical injury or streptozotocin treatment, PPP1R1A is discharged from β-cell cytoplasm into extracellular space/blood proportionate to the extent of β-cell death, demonstrating its cytoplasmic localization and release upon cell destruction.","method":"LC-MS/MS proteomics of FACS-purified β-cells, Western blotting of tissues, immunohistochemistry, affinity-capture measurement of plasma PPP1R1A in STZ-treated rats and islet transplant patients","journal":"Diabetes","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal methods (proteomics, WB, IHC, in vivo model) establishing subcellular localization and release mechanism; single lab","pmids":["23557701"],"is_preprint":false},{"year":2014,"finding":"siRNA silencing of PPP1R1A in INS-1 832/13 β-cells reduced insulin secretion, establishing a functional role for PPP1R1A in regulated insulin secretion.","method":"siRNA knockdown in INS-1 832/13 cells, insulin secretion assay","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 — clean KD with defined secretion phenotype; moderate evidence from single lab with corroborating human islet expression correlation","pmids":["25489054"],"is_preprint":false},{"year":2024,"finding":"PPP1R1A is a target gene of the β-cell transcription factor PDX1: silencing Pdx1 in INS-1 cells altered PPP1R1A expression. Overexpression of PPP1R1A in human islets augmented insulin secretion and upregulated MAFA, PDX1, and GLUT1 protein levels, while silencing PPP1R1A reduced these proteins and impaired glucose uptake without affecting cell viability or apoptosis.","method":"siRNA knockdown of Ppp1r1a and Pdx1 in INS-1 cells, PPP1R1A overexpression in human islets, insulin secretion assay, Western blotting, RNA-seq of human islets, glucose uptake assay","journal":"Life sciences","confidence":"Medium","confidence_rationale":"Tier 2 — gain- and loss-of-function with multiple molecular readouts; single lab","pmids":["38574885"],"is_preprint":false},{"year":2025,"finding":"Proteomic profiling after Ppp1r1a silencing in INS-1 cells identified ~2846 proteins with >2-fold change; key downregulated proteins included INS2, Cacna1a, PCSK2, SNAP25, SYT5, and VAMP7 (involved in insulin biosynthesis, vesicle exocytosis). Pathway analysis showed disruption of insulin secretion and mTOR signaling, confirmed by reduced phospho-AKT levels.","method":"siRNA knockdown, label-free DIA mass spectrometry (Orbitrap Exploris 480), pathway enrichment analysis, Western blotting for phospho-AKT","journal":"Journal of proteome research","confidence":"Medium","confidence_rationale":"Tier 2 — unbiased proteomics with biochemical validation of AKT phosphorylation; single lab, single study","pmids":["41359828"],"is_preprint":false},{"year":2017,"finding":"In zebrafish kidney distal tubule, functional knockdown of the PPP1R1A homologue ppp1r1b reduced NCC phosphorylation in the pronephros, consistent with Ppp1r1a acting as a negative regulator of PP1-mediated NCC dephosphorylation in mammals.","method":"Transgenic zebrafish DCT isolation, RNA-seq, functional knockdown of ppp1r1b, immunofluorescence for phospho-NCC","journal":"Pflugers Archiv : European journal of physiology","confidence":"Low","confidence_rationale":"Tier 3 — ortholog study (zebrafish ppp1r1b, not direct PPP1R1A), single method for functional readout","pmids":["28656378"],"is_preprint":false},{"year":2019,"finding":"PPP1R1A mRNA/protein is upregulated by the lncRNA HOXC-AS3 acting as a sponge for miR-3922-5p in breast cancer cells, establishing PPP1R1A as a downstream target of the HOXC-AS3/miR-3922-5p axis that promotes breast cancer cell migration and invasion.","method":"Luciferase reporter assay (miRNA target validation), Western blotting for PPP1R1A protein, TCGA expression analysis, in vitro migration/invasion assays, in vivo xenograft","journal":"Cancer investigation","confidence":"Low","confidence_rationale":"Tier 3 — miRNA sponge mechanism validated by reporter assay and WB; PPP1R1A mechanistic role not further characterized beyond being a target","pmids":["31797701"],"is_preprint":false}],"current_model":"PPP1R1A is a cAMP/PKA-responsive inhibitor of protein phosphatase 1 (PP1): upon phosphorylation at Thr35 by PKA, PPP1R1A binds and inhibits PP1, thereby elevating phosphorylation of PP1 substrates including NCC (in kidney, regulating salt reabsorption and blood pressure) and multiple signaling proteins in β-cells (promoting insulin secretion downstream of GLP1R/PKA) and Ewing sarcoma cells (driving cell cycle progression via Rb hyperphosphorylation and suppression of p21/p27); its expression in β-cells is transcriptionally controlled by MafA and PDX1, and loss of PPP1R1A broadly disrupts insulin biosynthesis, exocytosis machinery, and mTOR/AKT signaling."},"narrative":{"teleology":[{"year":2013,"claim":"Establishing that PPP1R1A protein is highly abundant and cytoplasmic in pancreatic β-cells provided the first evidence that this PP1 inhibitor has a tissue-selective role in islet biology.","evidence":"LC-MS/MS proteomics of FACS-purified β-cells, Western blotting across tissues, IHC, and plasma PPP1R1A measurement after STZ-induced β-cell destruction in rats","pmids":["23557701"],"confidence":"Medium","gaps":["No functional assay for PP1 inhibition in β-cells was performed","Release mechanism not linked to any signaling role"]},{"year":2014,"claim":"Demonstrating that PPP1R1A knockdown impairs insulin secretion in β-cells established a functional requirement beyond expression, linking PP1 inhibition to secretory output.","evidence":"siRNA knockdown in INS-1 832/13 cells with insulin secretion assay","pmids":["25489054"],"confidence":"Medium","gaps":["Mechanism by which PPP1R1A promotes secretion not defined","No rescue or in vivo confirmation"]},{"year":2017,"claim":"Identifying that PKA phosphorylation of PPP1R1A at Thr35 is required for PP1 binding, inhibition, and downstream oncogenic activity in Ewing sarcoma resolved the activation mechanism and placed PPP1R1A in a defined PKA→PP1 signaling axis.","evidence":"siRNA/shRNA depletion, constitutively active PPP1R1A mutant rescue of PKA inhibitor effects, in vitro proliferation/migration, orthotopic xenograft mouse model, RNA-seq in Ewing sarcoma cells","pmids":["29059150"],"confidence":"High","gaps":["Direct PP1 substrates mediating oncogenic phenotype not identified","Whether Thr35 is the sole activating phosphosite was not addressed"]},{"year":2020,"claim":"Showing that PPP1R1A depletion upregulates p21 and p27 and reduces Rb phosphorylation clarified the cell cycle mechanism downstream of PP1 inhibition in Ewing sarcoma.","evidence":"Loss-of-function depletion, cell cycle analysis, Western blotting for p21/p27/phospho-Rb, IGF-1R inhibitor combination, xenograft tumor model","pmids":["32477459"],"confidence":"High","gaps":["Whether PP1 directly dephosphorylates Rb or acts indirectly through CDK-inhibitor regulation is unresolved","Histone gene transcription link not mechanistically defined"]},{"year":2021,"claim":"Demonstrating that MafA drives PPP1R1A expression and that PPP1R1A is required for GLP1R/PKA-mediated GSIS amplification, PKA-target phosphorylation, and mitochondrial coupling connected PPP1R1A to incretin signaling and β-cell identity.","evidence":"siRNA knockdown of PPP1R1A and MafA in INS-1 cells, GSIS assay, phospho-Western blotting, mitochondrial coupling measurement, mRNA analysis","pmids":["33631146"],"confidence":"High","gaps":["Specific PP1 substrates mediating GSIS amplification not identified","No in vivo β-cell-specific knockout model"]},{"year":2023,"claim":"Genetic and dietary experiments in mice established that PPP1R1A/I1 controls NCC phosphorylation and blood pressure in the kidney distal tubule by gating PP1A activity, revealing a physiological role in potassium-dependent salt reabsorption.","evidence":"Constitutively active SPAK knock-in mice, dietary potassium manipulation, Western blotting for phospho-NCC and phospho-I1, blood pressure measurements","pmids":["37676724"],"confidence":"High","gaps":["Direct physical interaction between PP1A and NCC not demonstrated biochemically in this study","Kidney-specific PPP1R1A knockout not performed"]},{"year":2024,"claim":"Identifying PDX1 as a second transcriptional regulator of PPP1R1A and showing that PPP1R1A overexpression in human islets augments insulin secretion and upregulates MAFA, PDX1, and GLUT1 established a positive feedback loop maintaining β-cell function.","evidence":"Pdx1 and Ppp1r1a siRNA in INS-1 cells, PPP1R1A overexpression in human islets, insulin secretion assay, Western blotting, RNA-seq, glucose uptake assay","pmids":["38574885"],"confidence":"Medium","gaps":["Whether PPP1R1A acts on PP1 to stabilize these transcription factors or through a parallel mechanism is unknown","No ChIP confirmation of PDX1 binding at the PPP1R1A promoter reported"]},{"year":2025,"claim":"Unbiased proteomics after PPP1R1A silencing revealed broad disruption of insulin biosynthesis and exocytosis machinery proteins and reduced phospho-AKT/mTOR signaling, expanding the downstream landscape of PPP1R1A-mediated PP1 inhibition in β-cells.","evidence":"siRNA knockdown in INS-1 cells, label-free DIA mass spectrometry, pathway enrichment analysis, Western blotting for phospho-AKT","pmids":["41359828"],"confidence":"Medium","gaps":["Proteomic changes are correlative; direct PP1 substrate identification not performed","No validation in primary human β-cells or in vivo models"]},{"year":null,"claim":"The direct PP1 substrates through which PPP1R1A mediates its tissue-specific effects — GSIS amplification in β-cells, NCC regulation in kidney, and cell cycle control in Ewing sarcoma — remain unidentified, and no β-cell- or kidney-specific conditional knockout model has been reported.","evidence":"","pmids":[],"confidence":"High","gaps":["No substrate-trapping or phosphoproteomics to identify direct PP1 targets downstream of PPP1R1A","No conditional tissue-specific knockout in vivo","Structural basis of PPP1R1A–PP1 interaction beyond Thr35 phosphosite not resolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,1,2,3]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[4]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,1,2,3]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[2,6,7]},{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[1]}],"complexes":[],"partners":["PPP1CA","SLC12A3","MAFA","PDX1"],"other_free_text":[]},"mechanistic_narrative":"PPP1R1A is a cAMP/PKA-responsive inhibitor of protein phosphatase 1 (PP1) that, upon phosphorylation at Thr35 by PKA, binds and inhibits PP1 catalytic activity, thereby amplifying phosphorylation-dependent signaling in multiple tissues [PMID:29059150, PMID:37676724]. In pancreatic β-cells, PPP1R1A is transcriptionally controlled by MafA and PDX1 and is required for GLP1R/PKA-mediated amplification of glucose-stimulated insulin secretion, maintenance of β-cell identity gene expression, mitochondrial coupling efficiency, and mTOR/AKT signaling; its loss broadly disrupts insulin biosynthesis and exocytosis machinery [PMID:33631146, PMID:38574885, PMID:41359828]. In the kidney distal tubule, dietary potassium suppresses PPP1R1A expression and dephosphorylates Thr35, relieving PP1 inhibition to promote NCC dephosphorylation and lower blood pressure [PMID:37676724]. In Ewing sarcoma, PPP1R1A drives G1/S cell cycle progression through PP1 inhibition–dependent downregulation of p21 and p27 and consequent Rb hyperphosphorylation, promoting tumorigenesis and metastasis [PMID:29059150, PMID:32477459]."},"prefetch_data":{"uniprot":{"accession":"Q13522","full_name":"Protein phosphatase 1 regulatory subunit 1A","aliases":["Protein phosphatase inhibitor 1","I-1","IPP-1"],"length_aa":171,"mass_kda":18.9,"function":"Inhibitor of protein-phosphatase 1. This protein may be important in hormonal control of glycogen metabolism. Hormones that elevate intracellular cAMP increase I-1 activity in many tissues. I-1 activation may impose cAMP control over proteins that are not directly phosphorylated by PKA. Following a rise in intracellular calcium, I-1 is inactivated by calcineurin (or PP2B). Does not inhibit type-2 phosphatases","subcellular_location":"","url":"https://www.uniprot.org/uniprotkb/Q13522/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PPP1R1A","classification":"Not Classified","n_dependent_lines":91,"n_total_lines":1208,"dependency_fraction":0.07533112582781457},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/PPP1R1A","total_profiled":1310},"omim":[{"mim_id":"613246","title":"PROTEIN PHOSPHATASE 1, REGULATORY SUBUNIT 1A; PPP1R1A","url":"https://www.omim.org/entry/613246"},{"mim_id":"601792","title":"PROTEIN PHOSPHATASE 1, REGULATORY SUBUNIT 2; PPP1R2","url":"https://www.omim.org/entry/601792"},{"mim_id":"176875","title":"PROTEIN PHOSPHATASE 1, CATALYTIC SUBUNIT, ALPHA ISOFORM; PPP1CA","url":"https://www.omim.org/entry/176875"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"skeletal muscle","ntpm":779.6},{"tissue":"tongue","ntpm":253.3}],"url":"https://www.proteinatlas.org/search/PPP1R1A"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"Q13522","domains":[{"cath_id":"-","chopping":"59-92","consensus_level":"medium","plddt":78.8591,"start":59,"end":92}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q13522","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q13522-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q13522-F1-predicted_aligned_error_v6.png","plddt_mean":66.5},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PPP1R1A","jax_strain_url":"https://www.jax.org/strain/search?query=PPP1R1A"},"sequence":{"accession":"Q13522","fasta_url":"https://rest.uniprot.org/uniprotkb/Q13522.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q13522/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q13522"}},"corpus_meta":[{"pmid":"29185012","id":"PMC_29185012","title":"Systems biology of the IMIDIA biobank from organ donors and pancreatectomised patients defines a novel transcriptomic signature of islets from individuals with type 2 diabetes.","date":"2017","source":"Diabetologia","url":"https://pubmed.ncbi.nlm.nih.gov/29185012","citation_count":130,"is_preprint":false},{"pmid":"25489054","id":"PMC_25489054","title":"Identification of novel genes for glucose metabolism based upon expression pattern in human islets and effect on insulin secretion and glycemia.","date":"2014","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/25489054","citation_count":91,"is_preprint":false},{"pmid":"11836553","id":"PMC_11836553","title":"Expression analysis of pediatric solid tumor cell lines using oligonucleotide microarrays.","date":"2002","source":"International journal of oncology","url":"https://pubmed.ncbi.nlm.nih.gov/11836553","citation_count":59,"is_preprint":false},{"pmid":"29059150","id":"PMC_29059150","title":"Protein phosphatase 1 regulatory subunit 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A constitutively active PPP1R1A rescued PKA inhibitor-induced suppression of ES proliferation, establishing the PKA/PPP1R1A/PP1 pathway.\",\n      \"method\": \"Loss-of-function (siRNA/shRNA depletion), rescue with constitutively active PPP1R1A mutant, PKA inhibitor treatment, in vitro cell migration/proliferation assays, orthotopic xenograft mouse model, RNA-seq\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal methods including mutagenesis, rescue experiments, in vivo model, and RNA-seq in a single rigorous study\",\n      \"pmids\": [\"29059150\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PPP1R1A (inhibitory subunit 1, I1) acts as a negative regulator of PP1A (Ppp1Ca) in the kidney distal tubule; high dietary potassium suppresses Ppp1r1a expression and dephosphorylates I1, thereby activating PP1A to directly bind and dephosphorylate NCC (NaCl cotransporter), reducing blood pressure. This was confirmed using genetically engineered mice with constitutively active SPAK.\",\n      \"method\": \"Transcriptomics screen, genetically engineered constitutively active SPAK mice, dietary potassium manipulation, Western blotting for phospho-NCC and phospho-I1, BP measurements\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis in engineered mice plus biochemical phosphorylation assays; multiple orthogonal approaches in a single study\",\n      \"pmids\": [\"37676724\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"In pancreatic β-cells, PPP1R1A expression is driven by the transcription factor MafA; silencing PPP1R1A in INS-1 (832/13) cells impaired GLP1R-mediated amplification of glucose-stimulated insulin secretion (GSIS), reduced PKA-target protein phosphorylation, and impaired mitochondrial coupling efficiency, while also downregulating β-cell identity genes (MafA, Pdx1, NeuroD1, Pax6).\",\n      \"method\": \"siRNA silencing in INS-1 cells, acute MafA knockdown, GSIS assay, phospho-Western blotting of PKA targets, mitochondrial coupling efficiency measurement, mRNA expression analysis\",\n      \"journal\": \"Metabolism: clinical and experimental\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KD with multiple orthogonal functional readouts (secretion, phosphorylation, mitochondrial function, gene expression) in a single study\",\n      \"pmids\": [\"33631146\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"PPP1R1A regulates G1/S cell cycle progression in Ewing sarcoma cells by downregulating cell cycle inhibitors p21Cip1 and p27Kip1, leading to Rb protein hyperphosphorylation. PPP1R1A depletion also impaired histone gene transcription during the cell cycle. Combined targeting of PPP1R1A and IGF-1R showed synergistic/additive effects on reducing ES cell proliferation and tumor growth.\",\n      \"method\": \"Loss-of-function depletion, cell cycle analysis, Western blotting for p21, p27, phospho-Rb, IGF-1R inhibitor combination, in vitro proliferation/migration assays, xenograft tumor model\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KD with defined molecular readouts (p21, p27, Rb phosphorylation) and in vivo validation\",\n      \"pmids\": [\"32477459\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"PPP1R1A protein is highly abundant and relatively selective in pancreatic β-cells; upon chemical injury or streptozotocin treatment, PPP1R1A is discharged from β-cell cytoplasm into extracellular space/blood proportionate to the extent of β-cell death, demonstrating its cytoplasmic localization and release upon cell destruction.\",\n      \"method\": \"LC-MS/MS proteomics of FACS-purified β-cells, Western blotting of tissues, immunohistochemistry, affinity-capture measurement of plasma PPP1R1A in STZ-treated rats and islet transplant patients\",\n      \"journal\": \"Diabetes\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (proteomics, WB, IHC, in vivo model) establishing subcellular localization and release mechanism; single lab\",\n      \"pmids\": [\"23557701\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"siRNA silencing of PPP1R1A in INS-1 832/13 β-cells reduced insulin secretion, establishing a functional role for PPP1R1A in regulated insulin secretion.\",\n      \"method\": \"siRNA knockdown in INS-1 832/13 cells, insulin secretion assay\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KD with defined secretion phenotype; moderate evidence from single lab with corroborating human islet expression correlation\",\n      \"pmids\": [\"25489054\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"PPP1R1A is a target gene of the β-cell transcription factor PDX1: silencing Pdx1 in INS-1 cells altered PPP1R1A expression. Overexpression of PPP1R1A in human islets augmented insulin secretion and upregulated MAFA, PDX1, and GLUT1 protein levels, while silencing PPP1R1A reduced these proteins and impaired glucose uptake without affecting cell viability or apoptosis.\",\n      \"method\": \"siRNA knockdown of Ppp1r1a and Pdx1 in INS-1 cells, PPP1R1A overexpression in human islets, insulin secretion assay, Western blotting, RNA-seq of human islets, glucose uptake assay\",\n      \"journal\": \"Life sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — gain- and loss-of-function with multiple molecular readouts; single lab\",\n      \"pmids\": [\"38574885\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Proteomic profiling after Ppp1r1a silencing in INS-1 cells identified ~2846 proteins with >2-fold change; key downregulated proteins included INS2, Cacna1a, PCSK2, SNAP25, SYT5, and VAMP7 (involved in insulin biosynthesis, vesicle exocytosis). Pathway analysis showed disruption of insulin secretion and mTOR signaling, confirmed by reduced phospho-AKT levels.\",\n      \"method\": \"siRNA knockdown, label-free DIA mass spectrometry (Orbitrap Exploris 480), pathway enrichment analysis, Western blotting for phospho-AKT\",\n      \"journal\": \"Journal of proteome research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — unbiased proteomics with biochemical validation of AKT phosphorylation; single lab, single study\",\n      \"pmids\": [\"41359828\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"In zebrafish kidney distal tubule, functional knockdown of the PPP1R1A homologue ppp1r1b reduced NCC phosphorylation in the pronephros, consistent with Ppp1r1a acting as a negative regulator of PP1-mediated NCC dephosphorylation in mammals.\",\n      \"method\": \"Transgenic zebrafish DCT isolation, RNA-seq, functional knockdown of ppp1r1b, immunofluorescence for phospho-NCC\",\n      \"journal\": \"Pflugers Archiv : European journal of physiology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — ortholog study (zebrafish ppp1r1b, not direct PPP1R1A), single method for functional readout\",\n      \"pmids\": [\"28656378\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PPP1R1A mRNA/protein is upregulated by the lncRNA HOXC-AS3 acting as a sponge for miR-3922-5p in breast cancer cells, establishing PPP1R1A as a downstream target of the HOXC-AS3/miR-3922-5p axis that promotes breast cancer cell migration and invasion.\",\n      \"method\": \"Luciferase reporter assay (miRNA target validation), Western blotting for PPP1R1A protein, TCGA expression analysis, in vitro migration/invasion assays, in vivo xenograft\",\n      \"journal\": \"Cancer investigation\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — miRNA sponge mechanism validated by reporter assay and WB; PPP1R1A mechanistic role not further characterized beyond being a target\",\n      \"pmids\": [\"31797701\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PPP1R1A is a cAMP/PKA-responsive inhibitor of protein phosphatase 1 (PP1): upon phosphorylation at Thr35 by PKA, PPP1R1A binds and inhibits PP1, thereby elevating phosphorylation of PP1 substrates including NCC (in kidney, regulating salt reabsorption and blood pressure) and multiple signaling proteins in β-cells (promoting insulin secretion downstream of GLP1R/PKA) and Ewing sarcoma cells (driving cell cycle progression via Rb hyperphosphorylation and suppression of p21/p27); its expression in β-cells is transcriptionally controlled by MafA and PDX1, and loss of PPP1R1A broadly disrupts insulin biosynthesis, exocytosis machinery, and mTOR/AKT signaling.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"PPP1R1A is a cAMP/PKA-responsive inhibitor of protein phosphatase 1 (PP1) that, upon phosphorylation at Thr35 by PKA, binds and inhibits PP1 catalytic activity, thereby amplifying phosphorylation-dependent signaling in multiple tissues [PMID:29059150, PMID:37676724]. In pancreatic β-cells, PPP1R1A is transcriptionally controlled by MafA and PDX1 and is required for GLP1R/PKA-mediated amplification of glucose-stimulated insulin secretion, maintenance of β-cell identity gene expression, mitochondrial coupling efficiency, and mTOR/AKT signaling; its loss broadly disrupts insulin biosynthesis and exocytosis machinery [PMID:33631146, PMID:38574885, PMID:41359828]. In the kidney distal tubule, dietary potassium suppresses PPP1R1A expression and dephosphorylates Thr35, relieving PP1 inhibition to promote NCC dephosphorylation and lower blood pressure [PMID:37676724]. In Ewing sarcoma, PPP1R1A drives G1/S cell cycle progression through PP1 inhibition–dependent downregulation of p21 and p27 and consequent Rb hyperphosphorylation, promoting tumorigenesis and metastasis [PMID:29059150, PMID:32477459].\",\n  \"teleology\": [\n    {\n      \"year\": 2013,\n      \"claim\": \"Establishing that PPP1R1A protein is highly abundant and cytoplasmic in pancreatic β-cells provided the first evidence that this PP1 inhibitor has a tissue-selective role in islet biology.\",\n      \"evidence\": \"LC-MS/MS proteomics of FACS-purified β-cells, Western blotting across tissues, IHC, and plasma PPP1R1A measurement after STZ-induced β-cell destruction in rats\",\n      \"pmids\": [\"23557701\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No functional assay for PP1 inhibition in β-cells was performed\", \"Release mechanism not linked to any signaling role\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Demonstrating that PPP1R1A knockdown impairs insulin secretion in β-cells established a functional requirement beyond expression, linking PP1 inhibition to secretory output.\",\n      \"evidence\": \"siRNA knockdown in INS-1 832/13 cells with insulin secretion assay\",\n      \"pmids\": [\"25489054\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which PPP1R1A promotes secretion not defined\", \"No rescue or in vivo confirmation\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Identifying that PKA phosphorylation of PPP1R1A at Thr35 is required for PP1 binding, inhibition, and downstream oncogenic activity in Ewing sarcoma resolved the activation mechanism and placed PPP1R1A in a defined PKA→PP1 signaling axis.\",\n      \"evidence\": \"siRNA/shRNA depletion, constitutively active PPP1R1A mutant rescue of PKA inhibitor effects, in vitro proliferation/migration, orthotopic xenograft mouse model, RNA-seq in Ewing sarcoma cells\",\n      \"pmids\": [\"29059150\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct PP1 substrates mediating oncogenic phenotype not identified\", \"Whether Thr35 is the sole activating phosphosite was not addressed\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Showing that PPP1R1A depletion upregulates p21 and p27 and reduces Rb phosphorylation clarified the cell cycle mechanism downstream of PP1 inhibition in Ewing sarcoma.\",\n      \"evidence\": \"Loss-of-function depletion, cell cycle analysis, Western blotting for p21/p27/phospho-Rb, IGF-1R inhibitor combination, xenograft tumor model\",\n      \"pmids\": [\"32477459\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PP1 directly dephosphorylates Rb or acts indirectly through CDK-inhibitor regulation is unresolved\", \"Histone gene transcription link not mechanistically defined\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Demonstrating that MafA drives PPP1R1A expression and that PPP1R1A is required for GLP1R/PKA-mediated GSIS amplification, PKA-target phosphorylation, and mitochondrial coupling connected PPP1R1A to incretin signaling and β-cell identity.\",\n      \"evidence\": \"siRNA knockdown of PPP1R1A and MafA in INS-1 cells, GSIS assay, phospho-Western blotting, mitochondrial coupling measurement, mRNA analysis\",\n      \"pmids\": [\"33631146\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific PP1 substrates mediating GSIS amplification not identified\", \"No in vivo β-cell-specific knockout model\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Genetic and dietary experiments in mice established that PPP1R1A/I1 controls NCC phosphorylation and blood pressure in the kidney distal tubule by gating PP1A activity, revealing a physiological role in potassium-dependent salt reabsorption.\",\n      \"evidence\": \"Constitutively active SPAK knock-in mice, dietary potassium manipulation, Western blotting for phospho-NCC and phospho-I1, blood pressure measurements\",\n      \"pmids\": [\"37676724\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct physical interaction between PP1A and NCC not demonstrated biochemically in this study\", \"Kidney-specific PPP1R1A knockout not performed\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identifying PDX1 as a second transcriptional regulator of PPP1R1A and showing that PPP1R1A overexpression in human islets augments insulin secretion and upregulates MAFA, PDX1, and GLUT1 established a positive feedback loop maintaining β-cell function.\",\n      \"evidence\": \"Pdx1 and Ppp1r1a siRNA in INS-1 cells, PPP1R1A overexpression in human islets, insulin secretion assay, Western blotting, RNA-seq, glucose uptake assay\",\n      \"pmids\": [\"38574885\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether PPP1R1A acts on PP1 to stabilize these transcription factors or through a parallel mechanism is unknown\", \"No ChIP confirmation of PDX1 binding at the PPP1R1A promoter reported\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Unbiased proteomics after PPP1R1A silencing revealed broad disruption of insulin biosynthesis and exocytosis machinery proteins and reduced phospho-AKT/mTOR signaling, expanding the downstream landscape of PPP1R1A-mediated PP1 inhibition in β-cells.\",\n      \"evidence\": \"siRNA knockdown in INS-1 cells, label-free DIA mass spectrometry, pathway enrichment analysis, Western blotting for phospho-AKT\",\n      \"pmids\": [\"41359828\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Proteomic changes are correlative; direct PP1 substrate identification not performed\", \"No validation in primary human β-cells or in vivo models\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The direct PP1 substrates through which PPP1R1A mediates its tissue-specific effects — GSIS amplification in β-cells, NCC regulation in kidney, and cell cycle control in Ewing sarcoma — remain unidentified, and no β-cell- or kidney-specific conditional knockout model has been reported.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No substrate-trapping or phosphoproteomics to identify direct PP1 targets downstream of PPP1R1A\", \"No conditional tissue-specific knockout in vivo\", \"Structural basis of PPP1R1A–PP1 interaction beyond Thr35 phosphosite not resolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 1, 2, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0162582\", \"supporting_discovery_ids\": [0, 1, 2, 3]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 1, 2, 3]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [2, 6, 7]},\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"PPP1CA\",\n      \"SLC12A3\",\n      \"MAFA\",\n      \"PDX1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}