{"gene":"PPM1E","run_date":"2026-06-10T06:43:35","timeline":{"discoveries":[{"year":2002,"finding":"PPM1E (POPX1) was isolated as a binding partner for the PAK-interacting guanine nucleotide exchange factor PIX, and was shown to dephosphorylate and inactivate PAK (p21-activated kinase) in vitro and in vivo; its dephosphorylating activity correlated with blockade of active PAK effects, and it inhibited actin stress fiber breakdown and morphological changes driven by active Cdc42(V12).","method":"Co-immunoprecipitation (PIX binding), in vitro phosphatase assay, cell-based overexpression with PAK/Cdc42 activity readouts","journal":"Current biology : CB","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal binding demonstrated, in vitro dephosphorylation assay, and in vivo phenotypic rescue experiments; independently foundational paper with multiple orthogonal methods","pmids":["11864573"],"is_preprint":false},{"year":2001,"finding":"CaMKP-N (PPM1E) was identified as a nuclear Ser/Thr phosphatase that dephosphorylates CaMKIV; its activity requires Mn2+ ions and is stimulated by polycations; when transiently expressed in COS-7 cells it localizes to the nucleus, suggesting it dephosphorylates nuclear CaMKIV and nuclear CaMKII.","method":"Recombinant protein expression, in vitro phosphatase assay with CaMKIV substrate, transient transfection with subcellular localization imaging","journal":"Journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — in vitro enzymatic activity with defined substrate plus direct localization experiment; single lab but multiple orthogonal methods","pmids":["11726284"],"is_preprint":false},{"year":2010,"finding":"Stable lentiviral knockdown of Ppm1E (but not Ppm1A) in HEK293 cells increased AMPKα-Thr172 phosphorylation approximately 3-fold; Ppm1E and Ppm1F interact weakly with AMPK, identifying Ppm1E as an in-cellulo AMPK phosphatase; phenformin treatment decreased Ppm1E phosphatase activity, connecting Ppm1E inhibition to biguanide-induced AMPK activation.","method":"Stable lentiviral shRNA knockdown, phospho-AMPKα-Thr172 western blot, co-immunoprecipitation of AMPK with Ppm1E, phosphatase activity assay with specific antibodies","journal":"Cellular signalling","confidence":"High","confidence_rationale":"Tier 2 / Moderate — stable KD with defined phosphorylation readout, weak Co-IP, and phosphatase activity assay in single lab with multiple orthogonal methods","pmids":["20801214"],"is_preprint":false},{"year":2004,"finding":"CaMKP-N (PPM1E) contains two independent nuclear localization signals (NLS1 and NLS2) at its C-terminus; a cluster of basic residues in the NLSs is required for nuclear targeting; NLS1 and NLS2 function independently but mutagenesis suggests they interact with each other.","method":"Deletion and point mutagenesis of NLS sequences, subcellular localization assay by fluorescence microscopy","journal":"Journal of biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct mutagenesis of NLS residues with localization readout; single lab, single paper","pmids":["15496589"],"is_preprint":false},{"year":2007,"finding":"Evans Blue and Chicago Sky Blue 6B were identified as inhibitors of CaMKP-N (PPM1E) and CaMKP; the minimum inhibitory structure is 1-amino-8-naphthol-4-sulfonic acid; in Neuro2a cells co-transfected with CaMKIV and CaMKP-N, these compounds suppressed CaMKIV dephosphorylation, demonstrating in-cell inhibitory activity.","method":"In vitro phosphatase assay with inhibitor compounds, cell-based dephosphorylation assay in Neuro2a cells","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro enzymatic inhibition plus cellular validation; single lab, two methods","pmids":["17897624"],"is_preprint":false},{"year":2011,"finding":"Zebrafish CaMKP-N (PPM1E ortholog) undergoes proteolytic processing via the ubiquitin-proteasome pathway in brain and Neuro2a cells; this processing relocates the protein from the nucleus to the cytosol, changes its substrate targeting, and markedly activates its catalytic activity by removal of the C-terminal domain.","method":"Proteasome inhibitor treatment (MG-132, Epoxomicin, Lactacystin), subcellular fractionation, substrate phosphorylation assays in Neuro2a cells","journal":"Archives of biochemistry and biophysics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological inhibition of proteasome with localization and activity readouts; single lab, multiple orthogonal methods","pmids":["22100705"],"is_preprint":false},{"year":2012,"finding":"CaMKI phosphorylates zebrafish CaMKP-N (PPM1E ortholog) at Ser-480; phosphorylation-mimic mutants (S480D/S480E) showed higher phosphatase activities than wild-type or non-phosphorylatable (S480A) mutants; in Neuro2a cells, phosphorylation-mimic CaMKP-N more strongly attenuated CaMKII autophosphorylation after ionomycin treatment, demonstrating that CaMKI-mediated phosphorylation activates CaMKP-N.","method":"In vitro phosphorylation assay with CaMKI, site-directed mutagenesis (S480A, S480D, S480E), solution-based phosphatase assay, cell-based CaMKII autophosphorylation assay in Neuro2a cells","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro phosphorylation reconstitution combined with mutagenesis and cellular functional validation; single lab but multiple rigorous orthogonal methods","pmids":["22627141"],"is_preprint":false},{"year":2013,"finding":"A C-terminally truncated form of human CaMKP-N/PPM1E (residues 1-559) exhibits much higher Vmax than full-length enzyme; it displays Mn2+/Mg2+-dependent phosphatase activity with preference for phospho-Thr residues, binds postsynaptic density, dephosphorylates autophosphorylated CaMKII, and is reversibly inactivated by H2O2 (oxidation), indicating redox regulation.","method":"Wheat-embryo cell-free protein expression, phosphopeptide phosphatase assay, postsynaptic density binding assay, CaMKII dephosphorylation assay, H2O2/DTT redox treatment","journal":"BioMed research international","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with multiple substrates and biochemical characterization; single lab, multiple orthogonal methods","pmids":["23991411"],"is_preprint":false}],"current_model":"PPM1E (CaMKP-N/POPX1) is a nuclear-localized PPM-family Ser/Thr phosphatase that directly dephosphorylates and inactivates CaMKI, CaMKII, and CaMKIV (nuclear isoforms), as well as AMPKα at Thr172; it is recruited to PAK complexes via PIX to inactivate PAK and suppress Cdc42/Rac-driven actin remodeling; its catalytic activity is activated by CaMKI-mediated phosphorylation at Ser-480 and by proteasomal C-terminal truncation, is reversibly inhibited by oxidation, and is subject to nuclear targeting through two C-terminal NLS elements."},"narrative":{"mechanistic_narrative":"PPM1E (CaMKP-N/POPX1) is a metal-dependent PPM-family Ser/Thr phosphatase that turns off Ca2+/calmodulin- and stress-responsive kinase signaling [PMID:11726284, PMID:11864573]. It dephosphorylates and inactivates members of the CaMK cascade, including nuclear CaMKIV and autophosphorylated CaMKII [PMID:11726284, PMID:23991411], and acts as an in-cellulo AMPKα phosphatase, with its knockdown elevating AMPKα-Thr172 phosphorylation [PMID:20801214]. In parallel, PPM1E is recruited through the exchange factor PIX to dephosphorylate and inactivate PAK, thereby suppressing Cdc42/Rac-driven actin stress-fiber remodeling [PMID:11864573]. The enzyme requires Mn2+/Mg2+ for catalysis, prefers phospho-Thr substrates, and is targeted to the nucleus by two independent C-terminal NLS elements [PMID:11726284, PMID:23991411, PMID:15496589]. Its catalytic output is tightly regulated: CaMKI-mediated phosphorylation at Ser-480 stimulates activity [PMID:22627141], ubiquitin-proteasome-dependent C-terminal truncation markedly activates the enzyme while relocating it from nucleus to cytosol and shifting substrate targeting [PMID:22100705, PMID:23991411], and oxidation by H2O2 reversibly inactivates it [PMID:23991411]. Evans Blue and Chicago Sky Blue 6B inhibit PPM1E in vitro and in cells [PMID:17897624].","teleology":[{"year":2001,"claim":"Established PPM1E as a nuclear Mn2+-dependent phosphatase acting on the CaMK cascade, defining its substrate class and compartment.","evidence":"recombinant protein, in vitro phosphatase assay with CaMKIV, transfection localization in COS-7 cells","pmids":["11726284"],"confidence":"High","gaps":["Direct dephosphorylation of nuclear CaMKII inferred from localization rather than measured","Physiological substrate selectivity in vivo not established"]},{"year":2002,"claim":"Showed PPM1E acts beyond the CaMK cascade by binding PIX and inactivating PAK, linking it to Cdc42/Rac actin-cytoskeleton control.","evidence":"Co-IP of PIX, in vitro phosphatase assay, cell-based PAK/Cdc42(V12) activity and actin readouts","pmids":["11864573"],"confidence":"High","gaps":["PAK residues dephosphorylated not mapped","How nuclear localization reconciles with cytoskeletal/PAK function unresolved"]},{"year":2004,"claim":"Defined the nuclear-targeting determinants, showing two independent C-terminal NLS elements drive nuclear localization.","evidence":"deletion/point mutagenesis of NLS basic residues with fluorescence localization","pmids":["15496589"],"confidence":"Medium","gaps":["Import receptors mediating NLS recognition unidentified","Single-lab characterization"]},{"year":2007,"claim":"Identified small-molecule inhibitors and the minimal pharmacophore, providing chemical tools and demonstrating in-cell inhibition.","evidence":"in vitro phosphatase inhibition assays and Neuro2a cell dephosphorylation assays","pmids":["17897624"],"confidence":"Medium","gaps":["Inhibitor selectivity across PPM-family phosphatases unknown","No structural basis of inhibition"]},{"year":2010,"claim":"Connected PPM1E to energy-sensing signaling by identifying it as an in-cellulo AMPKα-Thr172 phosphatase responsive to biguanides.","evidence":"stable shRNA knockdown, phospho-AMPKα western blot, AMPK Co-IP, phosphatase activity assay in HEK293","pmids":["20801214"],"confidence":"High","gaps":["AMPK-PPM1E interaction was weak","Mechanism by which phenformin lowers PPM1E activity not defined"]},{"year":2011,"claim":"Revealed proteasome-dependent C-terminal processing as a regulatory switch that relocalizes PPM1E, retargets substrates, and activates catalysis.","evidence":"proteasome inhibitors, subcellular fractionation, substrate phosphorylation assays in Neuro2a and brain (zebrafish ortholog)","pmids":["22100705"],"confidence":"Medium","gaps":["Protease/E3 machinery and cleavage site not identified in human enzyme","Demonstrated in zebrafish ortholog"]},{"year":2012,"claim":"Identified CaMKI phosphorylation at Ser-480 as an activating post-translational modification, establishing feedback regulation within the CaMK network.","evidence":"in vitro phosphorylation with CaMKI, S480A/D/E mutagenesis, phosphatase and cellular CaMKII autophosphorylation assays (zebrafish ortholog)","pmids":["22627141"],"confidence":"High","gaps":["Mechanism by which Ser-480 phosphorylation enhances activity unknown","Validation in human PPM1E pending"]},{"year":2013,"claim":"Characterized the activated truncated human enzyme biochemically, defining metal/substrate preferences, PSD binding, and reversible redox inactivation.","evidence":"cell-free expressed PPM1E(1-559), phosphopeptide and CaMKII dephosphorylation assays, PSD binding, H2O2/DTT redox treatment","pmids":["23991411"],"confidence":"Medium","gaps":["Oxidized residue(s) mediating redox control not mapped","Single-lab in vitro reconstitution"]},{"year":null,"claim":"How the distinct regulatory inputs (Ser-480 phosphorylation, proteasomal truncation, oxidation, localization) are integrated to govern substrate choice across CaMK, AMPK, and PAK pathways in vivo remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of the holoenzyme or substrate-bound state","Physiological contexts selecting each substrate not defined","No in vivo loss-of-function phenotype reported"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[1,0,7]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[1,0,2,7]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[1,3]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[5]}],"pathway":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[1,0]}],"complexes":[],"partners":["ARHGEF6","PAK1","PRKAA1","CAMK4","CAMK2A","CAMK1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q8WY54","full_name":"Protein phosphatase 1E","aliases":["Ca(2+)/calmodulin-dependent protein kinase phosphatase N","CaMKP-N","CaMKP-nucleus","CaMKN","Partner of PIX 1","Partner of PIX-alpha","Partner of PIXA"],"length_aa":755,"mass_kda":84.0,"function":"Protein phosphatase that inactivates multifunctional CaM kinases such as CAMK4 and CAMK2 (By similarity). Dephosphorylates and inactivates PAK. May play a role in the inhibition of actin fiber stress breakdown and in morphological changes driven by TNK2/CDC42. Dephosphorylates PRKAA2 (By similarity)","subcellular_location":"Nucleus; Cytoplasm","url":"https://www.uniprot.org/uniprotkb/Q8WY54/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PPM1E","classification":"Not Classified","n_dependent_lines":7,"n_total_lines":1208,"dependency_fraction":0.005794701986754967},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"PSME3","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/PPM1E","total_profiled":1310},"omim":[{"mim_id":"619309","title":"PROTEIN PHOSPHATASE, MAGNESIUM/MANGANESE-DEPENDENT, 1F; PPM1F","url":"https://www.omim.org/entry/619309"},{"mim_id":"619308","title":"PROTEIN PHOSPHATASE, MAGNESIUM/MANGANESE-DEPENDENT, 1E; PPM1E","url":"https://www.omim.org/entry/619308"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoli","reliability":"Approved"},{"location":"Nucleoplasm","reliability":"Additional"}],"tissue_specificity":"Group enriched","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"adrenal gland","ntpm":5.1},{"tissue":"brain","ntpm":11.7},{"tissue":"retina","ntpm":20.7},{"tissue":"testis","ntpm":6.2}],"url":"https://www.proteinatlas.org/search/PPM1E"},"hgnc":{"alias_symbol":["POPX1","KIAA1072","PP2CH","CaMKP-N"],"prev_symbol":[]},"alphafold":{"accession":"Q8WY54","domains":[{"cath_id":"-","chopping":"125-225","consensus_level":"medium","plddt":85.9297,"start":125,"end":225},{"cath_id":"3.60.40.10","chopping":"234-493","consensus_level":"high","plddt":95.838,"start":234,"end":493}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8WY54","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8WY54-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8WY54-F1-predicted_aligned_error_v6.png","plddt_mean":64.5},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PPM1E","jax_strain_url":"https://www.jax.org/strain/search?query=PPM1E"},"sequence":{"accession":"Q8WY54","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8WY54.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8WY54/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8WY54"}},"corpus_meta":[{"pmid":"11864573","id":"PMC_11864573","title":"The p21-activated kinase PAK is negatively regulated by POPX1 and POPX2, a pair of serine/threonine phosphatases of the PP2C family.","date":"2002","source":"Current biology : CB","url":"https://pubmed.ncbi.nlm.nih.gov/11864573","citation_count":110,"is_preprint":false},{"pmid":"20801214","id":"PMC_20801214","title":"Ppm1E is an in cellulo AMP-activated protein kinase phosphatase.","date":"2010","source":"Cellular signalling","url":"https://pubmed.ncbi.nlm.nih.gov/20801214","citation_count":81,"is_preprint":false},{"pmid":"27661114","id":"PMC_27661114","title":"miR-135b expression downregulates Ppm1e to activate AMPK signaling and protect osteoblastic cells from dexamethasone.","date":"2016","source":"Oncotarget","url":"https://pubmed.ncbi.nlm.nih.gov/27661114","citation_count":52,"is_preprint":false},{"pmid":"27793001","id":"PMC_27793001","title":"miR-135b-5p inhibits LPS-induced TNFα production via silencing AMPK phosphatase Ppm1e.","date":"2016","source":"Oncotarget","url":"https://pubmed.ncbi.nlm.nih.gov/27793001","citation_count":37,"is_preprint":false},{"pmid":"11726284","id":"PMC_11726284","title":"Identification and characterization of CaMKP-N, nuclear calmodulin-dependent protein kinase phosphatase.","date":"2001","source":"Journal of biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/11726284","citation_count":36,"is_preprint":false},{"pmid":"30439702","id":"PMC_30439702","title":"Long Non-Coding RNA MALAT1 Protects Human Osteoblasts from Dexamethasone-Induced Injury via Activation of PPM1E-AMPK Signaling.","date":"2018","source":"Cellular physiology and biochemistry : international journal of experimental cellular physiology, biochemistry, and pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/30439702","citation_count":31,"is_preprint":false},{"pmid":"17897624","id":"PMC_17897624","title":"Inhibitors of the Ca(2+)/calmodulin-dependent protein kinase phosphatase family (CaMKP and CaMKP-N).","date":"2007","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/17897624","citation_count":24,"is_preprint":false},{"pmid":"28423719","id":"PMC_28423719","title":"AMPKα phosphatase Ppm1E upregulation in human gastric cancer is required for cell proliferation.","date":"2017","source":"Oncotarget","url":"https://pubmed.ncbi.nlm.nih.gov/28423719","citation_count":23,"is_preprint":false},{"pmid":"29317228","id":"PMC_29317228","title":"Functions and dysfunctions of Ca2+/calmodulin-dependent protein kinase phosphatase (CaMKP/PPM1F) and CaMKP-N/PPM1E.","date":"2018","source":"Archives of biochemistry and biophysics","url":"https://pubmed.ncbi.nlm.nih.gov/29317228","citation_count":19,"is_preprint":false},{"pmid":"28460435","id":"PMC_28460435","title":"microRNA-135b expression silences Ppm1e to provoke AMPK activation and inhibit osteoblastoma cell proliferation.","date":"2017","source":"Oncotarget","url":"https://pubmed.ncbi.nlm.nih.gov/28460435","citation_count":12,"is_preprint":false},{"pmid":"34556632","id":"PMC_34556632","title":"CircHAS2 promotes the proliferation, migration, and invasion of gastric cancer cells by regulating PPM1E mediated by hsa-miR-944.","date":"2021","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/34556632","citation_count":12,"is_preprint":false},{"pmid":"15496589","id":"PMC_15496589","title":"Identification and characterization of nuclear localization signals of CaMKP-N.","date":"2004","source":"Journal of biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/15496589","citation_count":11,"is_preprint":false},{"pmid":"22627141","id":"PMC_22627141","title":"Phosphorylation and activation of nuclear Ca2+/calmodulin-dependent protein kinase phosphatase (CaMKP-N/PPM1E) by Ca2+/calmodulin-dependent protein kinase I (CaMKI).","date":"2012","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/22627141","citation_count":10,"is_preprint":false},{"pmid":"22100705","id":"PMC_22100705","title":"Functional processing of nuclear Ca2+/calmodulin-dependent protein kinase phosphatase (CaMKP-N): evidence for a critical role of proteolytic processing in the regulation of its catalytic activity, subcellular localization and substrate targeting in vivo.","date":"2011","source":"Archives of biochemistry and biophysics","url":"https://pubmed.ncbi.nlm.nih.gov/22100705","citation_count":9,"is_preprint":false},{"pmid":"40216985","id":"PMC_40216985","title":"The PP2CH- and PBL27-mediated phosphorylation switch of aluminium ion receptor PSKR1/ALR1 controls plant aluminum sensing ability.","date":"2025","source":"Nature plants","url":"https://pubmed.ncbi.nlm.nih.gov/40216985","citation_count":8,"is_preprint":false},{"pmid":"23991411","id":"PMC_23991411","title":"An active C-terminally truncated form of Ca (2+) /calmodulin-dependent protein kinase phosphatase-N (CaMKP-N/PPM1E).","date":"2013","source":"BioMed research international","url":"https://pubmed.ncbi.nlm.nih.gov/23991411","citation_count":6,"is_preprint":false},{"pmid":"35368894","id":"PMC_35368894","title":"LINC01087 Promotes the Proliferation, Migration, and Invasion of Thyroid Cancer Cells by Upregulating PPM1E.","date":"2022","source":"Journal of oncology","url":"https://pubmed.ncbi.nlm.nih.gov/35368894","citation_count":5,"is_preprint":false},{"pmid":"38948282","id":"PMC_38948282","title":"[miR-342-3p Promotes the Proliferation, Migration, and Invasion of Clear Cell Renal Cell Carcinoma Cells by Targeted Inhibition of PPM1E].","date":"2024","source":"Sichuan da xue xue bao. Yi xue ban = Journal of Sichuan University. Medical science edition","url":"https://pubmed.ncbi.nlm.nih.gov/38948282","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.02.09.25321494","title":"Genetic-epigenetic interactions (meQTLs) in orofacial clefts etiology","date":"2025-02-12","source":"bioRxiv","url":"https://doi.org/10.1101/2025.02.09.25321494","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":12073,"output_tokens":2327,"usd":0.035562,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9358,"output_tokens":2707,"usd":0.057232,"stage2_stop_reason":"end_turn"},"total_usd":0.092794,"stage1_batch_id":"msgbatch_01CNoDbkChHEkgrJnL7BwtGJ","stage2_batch_id":"msgbatch_016Y4x9E9Wg5VQDANj9quSQD","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2002,\n      \"finding\": \"PPM1E (POPX1) was isolated as a binding partner for the PAK-interacting guanine nucleotide exchange factor PIX, and was shown to dephosphorylate and inactivate PAK (p21-activated kinase) in vitro and in vivo; its dephosphorylating activity correlated with blockade of active PAK effects, and it inhibited actin stress fiber breakdown and morphological changes driven by active Cdc42(V12).\",\n      \"method\": \"Co-immunoprecipitation (PIX binding), in vitro phosphatase assay, cell-based overexpression with PAK/Cdc42 activity readouts\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal binding demonstrated, in vitro dephosphorylation assay, and in vivo phenotypic rescue experiments; independently foundational paper with multiple orthogonal methods\",\n      \"pmids\": [\"11864573\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"CaMKP-N (PPM1E) was identified as a nuclear Ser/Thr phosphatase that dephosphorylates CaMKIV; its activity requires Mn2+ ions and is stimulated by polycations; when transiently expressed in COS-7 cells it localizes to the nucleus, suggesting it dephosphorylates nuclear CaMKIV and nuclear CaMKII.\",\n      \"method\": \"Recombinant protein expression, in vitro phosphatase assay with CaMKIV substrate, transient transfection with subcellular localization imaging\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro enzymatic activity with defined substrate plus direct localization experiment; single lab but multiple orthogonal methods\",\n      \"pmids\": [\"11726284\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Stable lentiviral knockdown of Ppm1E (but not Ppm1A) in HEK293 cells increased AMPKα-Thr172 phosphorylation approximately 3-fold; Ppm1E and Ppm1F interact weakly with AMPK, identifying Ppm1E as an in-cellulo AMPK phosphatase; phenformin treatment decreased Ppm1E phosphatase activity, connecting Ppm1E inhibition to biguanide-induced AMPK activation.\",\n      \"method\": \"Stable lentiviral shRNA knockdown, phospho-AMPKα-Thr172 western blot, co-immunoprecipitation of AMPK with Ppm1E, phosphatase activity assay with specific antibodies\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — stable KD with defined phosphorylation readout, weak Co-IP, and phosphatase activity assay in single lab with multiple orthogonal methods\",\n      \"pmids\": [\"20801214\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"CaMKP-N (PPM1E) contains two independent nuclear localization signals (NLS1 and NLS2) at its C-terminus; a cluster of basic residues in the NLSs is required for nuclear targeting; NLS1 and NLS2 function independently but mutagenesis suggests they interact with each other.\",\n      \"method\": \"Deletion and point mutagenesis of NLS sequences, subcellular localization assay by fluorescence microscopy\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct mutagenesis of NLS residues with localization readout; single lab, single paper\",\n      \"pmids\": [\"15496589\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Evans Blue and Chicago Sky Blue 6B were identified as inhibitors of CaMKP-N (PPM1E) and CaMKP; the minimum inhibitory structure is 1-amino-8-naphthol-4-sulfonic acid; in Neuro2a cells co-transfected with CaMKIV and CaMKP-N, these compounds suppressed CaMKIV dephosphorylation, demonstrating in-cell inhibitory activity.\",\n      \"method\": \"In vitro phosphatase assay with inhibitor compounds, cell-based dephosphorylation assay in Neuro2a cells\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro enzymatic inhibition plus cellular validation; single lab, two methods\",\n      \"pmids\": [\"17897624\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Zebrafish CaMKP-N (PPM1E ortholog) undergoes proteolytic processing via the ubiquitin-proteasome pathway in brain and Neuro2a cells; this processing relocates the protein from the nucleus to the cytosol, changes its substrate targeting, and markedly activates its catalytic activity by removal of the C-terminal domain.\",\n      \"method\": \"Proteasome inhibitor treatment (MG-132, Epoxomicin, Lactacystin), subcellular fractionation, substrate phosphorylation assays in Neuro2a cells\",\n      \"journal\": \"Archives of biochemistry and biophysics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological inhibition of proteasome with localization and activity readouts; single lab, multiple orthogonal methods\",\n      \"pmids\": [\"22100705\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"CaMKI phosphorylates zebrafish CaMKP-N (PPM1E ortholog) at Ser-480; phosphorylation-mimic mutants (S480D/S480E) showed higher phosphatase activities than wild-type or non-phosphorylatable (S480A) mutants; in Neuro2a cells, phosphorylation-mimic CaMKP-N more strongly attenuated CaMKII autophosphorylation after ionomycin treatment, demonstrating that CaMKI-mediated phosphorylation activates CaMKP-N.\",\n      \"method\": \"In vitro phosphorylation assay with CaMKI, site-directed mutagenesis (S480A, S480D, S480E), solution-based phosphatase assay, cell-based CaMKII autophosphorylation assay in Neuro2a cells\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro phosphorylation reconstitution combined with mutagenesis and cellular functional validation; single lab but multiple rigorous orthogonal methods\",\n      \"pmids\": [\"22627141\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"A C-terminally truncated form of human CaMKP-N/PPM1E (residues 1-559) exhibits much higher Vmax than full-length enzyme; it displays Mn2+/Mg2+-dependent phosphatase activity with preference for phospho-Thr residues, binds postsynaptic density, dephosphorylates autophosphorylated CaMKII, and is reversibly inactivated by H2O2 (oxidation), indicating redox regulation.\",\n      \"method\": \"Wheat-embryo cell-free protein expression, phosphopeptide phosphatase assay, postsynaptic density binding assay, CaMKII dephosphorylation assay, H2O2/DTT redox treatment\",\n      \"journal\": \"BioMed research international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with multiple substrates and biochemical characterization; single lab, multiple orthogonal methods\",\n      \"pmids\": [\"23991411\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PPM1E (CaMKP-N/POPX1) is a nuclear-localized PPM-family Ser/Thr phosphatase that directly dephosphorylates and inactivates CaMKI, CaMKII, and CaMKIV (nuclear isoforms), as well as AMPKα at Thr172; it is recruited to PAK complexes via PIX to inactivate PAK and suppress Cdc42/Rac-driven actin remodeling; its catalytic activity is activated by CaMKI-mediated phosphorylation at Ser-480 and by proteasomal C-terminal truncation, is reversibly inhibited by oxidation, and is subject to nuclear targeting through two C-terminal NLS elements.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PPM1E (CaMKP-N/POPX1) is a metal-dependent PPM-family Ser/Thr phosphatase that turns off Ca2+/calmodulin- and stress-responsive kinase signaling [#1, #0]. It dephosphorylates and inactivates members of the CaMK cascade, including nuclear CaMKIV and autophosphorylated CaMKII [#1, #7], and acts as an in-cellulo AMPKα phosphatase, with its knockdown elevating AMPKα-Thr172 phosphorylation [#2]. In parallel, PPM1E is recruited through the exchange factor PIX to dephosphorylate and inactivate PAK, thereby suppressing Cdc42/Rac-driven actin stress-fiber remodeling [#0]. The enzyme requires Mn2+/Mg2+ for catalysis, prefers phospho-Thr substrates, and is targeted to the nucleus by two independent C-terminal NLS elements [#1, #7, #3]. Its catalytic output is tightly regulated: CaMKI-mediated phosphorylation at Ser-480 stimulates activity [#6], ubiquitin-proteasome-dependent C-terminal truncation markedly activates the enzyme while relocating it from nucleus to cytosol and shifting substrate targeting [#5, #7], and oxidation by H2O2 reversibly inactivates it [#7]. Evans Blue and Chicago Sky Blue 6B inhibit PPM1E in vitro and in cells [#4].\"\n  ,\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Established PPM1E as a nuclear Mn2+-dependent phosphatase acting on the CaMK cascade, defining its substrate class and compartment.\",\n      \"evidence\": \"recombinant protein, in vitro phosphatase assay with CaMKIV, transfection localization in COS-7 cells\",\n      \"pmids\": [\"11726284\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct dephosphorylation of nuclear CaMKII inferred from localization rather than measured\", \"Physiological substrate selectivity in vivo not established\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Showed PPM1E acts beyond the CaMK cascade by binding PIX and inactivating PAK, linking it to Cdc42/Rac actin-cytoskeleton control.\",\n      \"evidence\": \"Co-IP of PIX, in vitro phosphatase assay, cell-based PAK/Cdc42(V12) activity and actin readouts\",\n      \"pmids\": [\"11864573\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"PAK residues dephosphorylated not mapped\", \"How nuclear localization reconciles with cytoskeletal/PAK function unresolved\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Defined the nuclear-targeting determinants, showing two independent C-terminal NLS elements drive nuclear localization.\",\n      \"evidence\": \"deletion/point mutagenesis of NLS basic residues with fluorescence localization\",\n      \"pmids\": [\"15496589\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Import receptors mediating NLS recognition unidentified\", \"Single-lab characterization\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Identified small-molecule inhibitors and the minimal pharmacophore, providing chemical tools and demonstrating in-cell inhibition.\",\n      \"evidence\": \"in vitro phosphatase inhibition assays and Neuro2a cell dephosphorylation assays\",\n      \"pmids\": [\"17897624\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Inhibitor selectivity across PPM-family phosphatases unknown\", \"No structural basis of inhibition\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Connected PPM1E to energy-sensing signaling by identifying it as an in-cellulo AMPKα-Thr172 phosphatase responsive to biguanides.\",\n      \"evidence\": \"stable shRNA knockdown, phospho-AMPKα western blot, AMPK Co-IP, phosphatase activity assay in HEK293\",\n      \"pmids\": [\"20801214\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"AMPK-PPM1E interaction was weak\", \"Mechanism by which phenformin lowers PPM1E activity not defined\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Revealed proteasome-dependent C-terminal processing as a regulatory switch that relocalizes PPM1E, retargets substrates, and activates catalysis.\",\n      \"evidence\": \"proteasome inhibitors, subcellular fractionation, substrate phosphorylation assays in Neuro2a and brain (zebrafish ortholog)\",\n      \"pmids\": [\"22100705\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Protease/E3 machinery and cleavage site not identified in human enzyme\", \"Demonstrated in zebrafish ortholog\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Identified CaMKI phosphorylation at Ser-480 as an activating post-translational modification, establishing feedback regulation within the CaMK network.\",\n      \"evidence\": \"in vitro phosphorylation with CaMKI, S480A/D/E mutagenesis, phosphatase and cellular CaMKII autophosphorylation assays (zebrafish ortholog)\",\n      \"pmids\": [\"22627141\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which Ser-480 phosphorylation enhances activity unknown\", \"Validation in human PPM1E pending\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Characterized the activated truncated human enzyme biochemically, defining metal/substrate preferences, PSD binding, and reversible redox inactivation.\",\n      \"evidence\": \"cell-free expressed PPM1E(1-559), phosphopeptide and CaMKII dephosphorylation assays, PSD binding, H2O2/DTT redox treatment\",\n      \"pmids\": [\"23991411\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Oxidized residue(s) mediating redox control not mapped\", \"Single-lab in vitro reconstitution\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the distinct regulatory inputs (Ser-480 phosphorylation, proteasomal truncation, oxidation, localization) are integrated to govern substrate choice across CaMK, AMPK, and PAK pathways in vivo remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of the holoenzyme or substrate-bound state\", \"Physiological contexts selecting each substrate not defined\", \"No in vivo loss-of-function phenotype reported\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [1, 0, 7]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [1, 0, 2, 7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [1, 3]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [1, 0]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"ARHGEF6\", \"PAK1\", \"PRKAA1\", \"CAMK4\", \"CAMK2A\", \"CAMK1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}