{"gene":"PPP2R5B","run_date":"2026-06-10T06:43:35","timeline":{"discoveries":[{"year":2007,"finding":"B56beta (PPP2R5B) is a regulatory subunit of PP2A that co-immunoprecipitates with Pim-1 kinase (but not B56alpha, gamma, delta, epsilon, or B55alpha), and knockdown of B56beta by shRNA increases the half-life of Pim-1 from 0.7 to 2.8 h and decreases Pim-1 ubiquitinylation, establishing that PP2A/B56beta negatively regulates Pim-1 protein levels by promoting its dephosphorylation, ubiquitination, and degradation.","method":"Co-immunoprecipitation, shRNA knockdown, protein half-life assay, ubiquitination assay","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP plus shRNA knockdown with multiple functional readouts (half-life, ubiquitination), single lab","pmids":["17297438"],"is_preprint":false},{"year":2008,"finding":"B56beta (PPP2R5B) physically interacts with CALEB/NGC (identified by yeast two-hybrid and confirmed by biochemical/immunocytochemical assays), and the whole PP2A trimer (structural and catalytic subunits) binds CALEB/NGC via B56beta (shown by affinity chromatography and mass spectrometry). B56beta inhibits CALEB/NGC-induced Akt phosphorylation and Akt-dependent dendritic branching, but not Akt-independent spine formation.","method":"Yeast two-hybrid screen, co-immunoprecipitation, immunocytochemistry, affinity chromatography, mass spectrometry, overexpression/knockdown with dendritic morphology readout","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal biochemical methods (Y2H, Co-IP, affinity chromatography, MS) plus functional cellular readout, single lab","pmids":["18385213"],"is_preprint":false},{"year":2016,"finding":"PPP2R5B is a regulatory subunit of PP2A that dephosphorylates and inactivates Akt in adipocytes; overexpression of PPP2R5B decreased Akt phosphorylation and glucose uptake, while knockdown increased insulin sensitivity, establishing PPP2R5B as a negative regulator of insulin signaling through direct Akt dephosphorylation.","method":"Overexpression and shRNA knockdown in adipocytes, Western blot for p-Akt, glucose uptake assay","journal":"Molecular and cellular endocrinology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal gain- and loss-of-function with two functional readouts (p-Akt, glucose uptake), single lab","pmids":["27521959"],"is_preprint":false},{"year":2015,"finding":"B56beta (PPP2R5B) dephosphorylates Akt in hepatocytes; shRNA knockdown of B56beta increased p-Akt levels and decreased metallothionein (MT) expression upon CdCl2 treatment, while overexpression of B56beta decreased p-Akt and increased MT, placing B56beta as a direct AKT phosphatase in the cellular response to cadmium cytotoxicity.","method":"Stable shRNA knockdown and retroviral overexpression, Western blot for p-AKT and MT, MTT cytotoxicity assay","journal":"Zhonghua yu fang yi xue za zhi","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single primary method (Western blot), limited mechanistic depth; no direct phosphatase activity assay","pmids":["26081707"],"is_preprint":false},{"year":2015,"finding":"De novo heterozygous mutations in PPP2R5B cluster within a nine-amino-acid region that, when mapped onto the PP2A holoenzyme crystal structure, is predicted to affect substrate binding, suggesting the mutations perturb PP2A-dependent dephosphorylation of specific substrates including components of the AKT/PI3K pathway, causing human overgrowth with macrocephaly and intellectual disability.","method":"Trio-based exome sequencing, structural mapping onto published PP2A holoenzyme crystal structure","journal":"Human molecular genetics","confidence":"Low","confidence_rationale":"Tier 4 / Weak — mechanistic interpretation is structural modeling/prediction without direct functional validation of the mutant proteins; genetic findings are strong but mechanism is inferred","pmids":["25972378"],"is_preprint":false},{"year":2016,"finding":"B56beta (PPP2R5B) is the only B56-family regulatory subunit whose expression is induced by both erythropoietin in fetal liver cells and hemin in K562 erythroleukemia cells during erythroid differentiation; knockdown of B56beta attenuates hemin-induced erythroid differentiation, identifying B56beta as the functional PP2A regulatory subunit in this process.","method":"shRNA knockdown in K562 cells, hemin-induced differentiation assay, expression profiling of B56 family members","journal":"Biochemical and biophysical research communications","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, knockdown with differentiation phenotype but no direct substrate or molecular mechanism established","pmids":["27544028"],"is_preprint":false}],"current_model":"PPP2R5B (B56beta) is a regulatory subunit of the PP2A heterotrimer that confers substrate specificity; it directly targets Akt (promoting its dephosphorylation and inactivation in adipocytes and hepatocytes), targets Pim-1 kinase (promoting its ubiquitin-mediated degradation), bridges the PP2A trimer to CALEB/NGC to suppress Akt-dependent dendritic branching in neurons, and is required for erythroid differentiation; de novo mutations in the substrate-binding region cause human overgrowth with intellectual disability, likely by impairing PP2A-dependent dephosphorylation of PI3K/AKT pathway components."},"narrative":{"mechanistic_narrative":"PPP2R5B (B56beta) is a substrate-directing regulatory subunit of the PP2A holoenzyme that targets the phosphatase to specific substrates to restrain AKT and oncogenic kinase signaling [PMID:17297438, PMID:27521959]. It bridges the PP2A structural and catalytic subunits to substrates and binding partners, as shown when the intact PP2A trimer is recruited to the membrane protein CALEB/NGC specifically through B56beta, where it inhibits CALEB/NGC-induced Akt phosphorylation and Akt-dependent dendritic branching [PMID:18385213]. As a negative regulator of AKT signaling, B56beta dephosphorylates and inactivates Akt in adipocytes, where its overexpression lowers p-Akt and glucose uptake while its knockdown enhances insulin sensitivity [PMID:27521959]. Beyond AKT, B56beta selectively associates with Pim-1 kinase and promotes Pim-1 dephosphorylation, ubiquitination, and degradation, identifying a distinct substrate destabilized by this subunit [PMID:17297438]. De novo heterozygous mutations clustering in a nine-amino-acid substrate-binding region of PPP2R5B cause human overgrowth with macrocephaly and intellectual disability, consistent with impaired PP2A-dependent dephosphorylation of PI3K/AKT pathway components [PMID:25972378].","teleology":[{"year":2007,"claim":"Established that B56beta is the specific PP2A regulatory subunit controlling a defined kinase substrate, answering whether PP2A targeting of Pim-1 is subunit-selective.","evidence":"Reciprocal co-immunoprecipitation against all B56 family members plus shRNA knockdown with protein half-life and ubiquitination readouts","pmids":["17297438"],"confidence":"Medium","gaps":["No direct in vitro phosphatase assay on Pim-1 with reconstituted holoenzyme","Single lab; the Pim-1 phosphosite dephosphorylated by PP2A/B56beta not mapped"]},{"year":2008,"claim":"Showed how B56beta directs the whole PP2A trimer to a membrane partner and a localized signaling output, answering whether the subunit acts as a substrate/partner-bridging adaptor.","evidence":"Yeast two-hybrid, Co-IP, affinity chromatography/mass spectrometry, and dendritic morphology readouts in neurons","pmids":["18385213"],"confidence":"Medium","gaps":["Direct Akt dephosphorylation by the recruited trimer not assayed enzymatically","In vivo relevance of CALEB/NGC bridging not tested"]},{"year":2015,"claim":"Extended B56beta's role as an AKT phosphatase to hepatocyte stress responses, addressing whether it controls AKT-dependent cytoprotective output.","evidence":"Stable shRNA knockdown and retroviral overexpression with p-AKT and metallothionein Western blots and cytotoxicity assay","pmids":["26081707"],"confidence":"Low","gaps":["No direct phosphatase activity assay; AKT dephosphorylation inferred from p-AKT levels","Single lab, single primary method","Mechanism linking AKT to metallothionein not resolved"]},{"year":2015,"claim":"Linked PPP2R5B to a Mendelian overgrowth syndrome and localized causal mutations to a substrate-binding region, addressing the physiological consequence of perturbed substrate targeting.","evidence":"Trio-based exome sequencing with structural mapping onto the PP2A holoenzyme crystal structure","pmids":["25972378"],"confidence":"Low","gaps":["Mechanistic effect of mutants on substrate dephosphorylation inferred from structural modeling, not functionally validated","Specific affected substrates not experimentally identified"]},{"year":2016,"claim":"Established B56beta as a direct AKT-inactivating subunit in metabolic signaling and as the PP2A regulatory subunit required for erythroid differentiation.","evidence":"Reciprocal overexpression/knockdown in adipocytes (p-Akt, glucose uptake) and shRNA knockdown with hemin-induced differentiation in K562 cells","pmids":["27521959","27544028"],"confidence":"Medium","gaps":["Direct phosphatase assay on Akt not performed","Substrate driving erythroid differentiation not identified","In vivo metabolic phenotype not established"]},{"year":null,"claim":"Whether the disease-causing substrate-binding mutations functionally alter PP2A/B56beta dephosphorylation of specific AKT/PI3K substrates remains unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No functional assay of mutant B56beta on substrate dephosphorylation","No reconstituted in vitro phosphatase characterization across substrates","Substrate repertoire beyond Akt and Pim-1 uncharacterized"]}],"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":[1]}],"localization":[],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,1,2]}],"complexes":["PP2A holoenzyme"],"partners":["PIM1","CALEB/NGC","AKT"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q15173","full_name":"Serine/threonine-protein phosphatase 2A 56 kDa regulatory subunit beta isoform","aliases":["PP2A B subunit isoform B'-beta","PP2A B subunit isoform B56-beta","PP2A B subunit isoform PR61-beta","PP2A B subunit isoform R5-beta"],"length_aa":497,"mass_kda":57.4,"function":"As the regulatory component of the serine/threonine-protein phosphatase 2A (PP2A) holoenzyme, modulates substrate specificity, subcellular localization, and responsiveness to phosphorylation. The phosphorylated form mediates the interaction between PP2A and AKT1, leading to AKT1 dephosphorylation","subcellular_location":"Cytoplasm","url":"https://www.uniprot.org/uniprotkb/Q15173/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PPP2R5B","classification":"Not Classified","n_dependent_lines":16,"n_total_lines":1208,"dependency_fraction":0.013245033112582781},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"PPP2CA","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/PPP2R5B","total_profiled":1310},"omim":[{"mim_id":"621185","title":"HOUGE-JANSSENS SYNDROME 4; HJS4","url":"https://www.omim.org/entry/621185"},{"mim_id":"616355","title":"HOUGE-JANSSENS SYNDROME 1; HJS1","url":"https://www.omim.org/entry/616355"},{"mim_id":"609651","title":"GLYCOPROTEIN HORMONE, ALPHA-2; GPHA2","url":"https://www.omim.org/entry/609651"},{"mim_id":"609374","title":"CELL DIVISION CYCLE-ASSOCIATED PROTEIN 5; CDCA5","url":"https://www.omim.org/entry/609374"},{"mim_id":"606230","title":"SH3 AND MULTIPLE ANKYRIN REPEAT DOMAINS 3; SHANK3","url":"https://www.omim.org/entry/606230"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"brain","ntpm":112.8}],"url":"https://www.proteinatlas.org/search/PPP2R5B"},"hgnc":{"alias_symbol":["FLJ35411","B56B","PR61B","B56beta"],"prev_symbol":[]},"alphafold":{"accession":"Q15173","domains":[{"cath_id":"-","chopping":"49-141_159-189","consensus_level":"medium","plddt":89.8268,"start":49,"end":189},{"cath_id":"1.25.40","chopping":"191-308","consensus_level":"medium","plddt":96.5874,"start":191,"end":308},{"cath_id":"1.25.40","chopping":"310-431","consensus_level":"medium","plddt":96.317,"start":310,"end":431}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q15173","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q15173-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q15173-F1-predicted_aligned_error_v6.png","plddt_mean":86.06},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PPP2R5B","jax_strain_url":"https://www.jax.org/strain/search?query=PPP2R5B"},"sequence":{"accession":"Q15173","fasta_url":"https://rest.uniprot.org/uniprotkb/Q15173.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q15173/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q15173"}},"corpus_meta":[{"pmid":"21482799","id":"PMC_21482799","title":"Mice lacking phosphatase PP2A subunit PR61/B'delta (Ppp2r5d) develop spatially restricted tauopathy by deregulation of CDK5 and GSK3beta.","date":"2011","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/21482799","citation_count":103,"is_preprint":false},{"pmid":"25972378","id":"PMC_25972378","title":"Mutations in the PP2A regulatory subunit B family genes PPP2R5B, PPP2R5C and PPP2R5D cause human overgrowth.","date":"2015","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/25972378","citation_count":75,"is_preprint":false},{"pmid":"17297438","id":"PMC_17297438","title":"Negative regulation of Pim-1 protein kinase levels by the B56beta subunit of PP2A.","date":"2007","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/17297438","citation_count":70,"is_preprint":false},{"pmid":"8812429","id":"PMC_8812429","title":"Assignment of human protein phosphatase 2A regulatory subunit genes b56alpha, b56beta, b56gamma, b56delta, and b56epsilon (PPP2R5A-PPP2R5E), highly expressed in muscle and brain, to chromosome regions 1q41, 11q12, 3p21, 6p21.1, and 7p11.2 --> p12.","date":"1996","source":"Genomics","url":"https://pubmed.ncbi.nlm.nih.gov/8812429","citation_count":58,"is_preprint":false},{"pmid":"15095873","id":"PMC_15095873","title":"Genomic organisation, chromosomal localisation tissue distribution and developmental regulation of the PR61/B' regulatory subunits of protein phosphatase 2A in mice.","date":"2004","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/15095873","citation_count":51,"is_preprint":false},{"pmid":"27521959","id":"PMC_27521959","title":"PPP2R5B, a regulatory subunit of PP2A, contributes to adipocyte insulin resistance.","date":"2016","source":"Molecular and cellular endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/27521959","citation_count":19,"is_preprint":false},{"pmid":"18385213","id":"PMC_18385213","title":"B56beta, a regulatory subunit of protein phosphatase 2A, interacts with CALEB/NGC and inhibits CALEB/NGC-mediated dendritic branching.","date":"2008","source":"FASEB journal : official publication of the Federation of American Societies for Experimental Biology","url":"https://pubmed.ncbi.nlm.nih.gov/18385213","citation_count":12,"is_preprint":false},{"pmid":"31489750","id":"PMC_31489750","title":"MiR-8-3p regulates hyperthermia-induced lactate secretion by targeting PPP2R5B in boar Sertoli cells.","date":"2019","source":"Molecular reproduction and development","url":"https://pubmed.ncbi.nlm.nih.gov/31489750","citation_count":10,"is_preprint":false},{"pmid":"27544028","id":"PMC_27544028","title":"Protein phosphatase 2A regulatory subunit B56β modulates erythroid differentiation.","date":"2016","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/27544028","citation_count":9,"is_preprint":false},{"pmid":"26081707","id":"PMC_26081707","title":"[The role of protein phosphatase 2A B56β holoenzyme in the regulation of heavy metal CdCl2 induced cytotoxicity].","date":"2015","source":"Zhonghua yu fang yi xue za zhi [Chinese journal of preventive medicine]","url":"https://pubmed.ncbi.nlm.nih.gov/26081707","citation_count":1,"is_preprint":false},{"pmid":"9272177","id":"PMC_9272177","title":"Mapping of the gene encoding the B56 beta subunit of protein phosphatase 2A (PPP2R5B) to a 0.5-Mb region of chromosome 11q13 and its exclusion as a candidate gene for multiple endocrine neoplasia type 1 (MEN1).","date":"1997","source":"Human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/9272177","citation_count":1,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":8524,"output_tokens":1728,"usd":0.025746,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8544,"output_tokens":2149,"usd":0.048223,"stage2_stop_reason":"end_turn"},"total_usd":0.073969,"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\": 2007,\n      \"finding\": \"B56beta (PPP2R5B) is a regulatory subunit of PP2A that co-immunoprecipitates with Pim-1 kinase (but not B56alpha, gamma, delta, epsilon, or B55alpha), and knockdown of B56beta by shRNA increases the half-life of Pim-1 from 0.7 to 2.8 h and decreases Pim-1 ubiquitinylation, establishing that PP2A/B56beta negatively regulates Pim-1 protein levels by promoting its dephosphorylation, ubiquitination, and degradation.\",\n      \"method\": \"Co-immunoprecipitation, shRNA knockdown, protein half-life assay, ubiquitination assay\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP plus shRNA knockdown with multiple functional readouts (half-life, ubiquitination), single lab\",\n      \"pmids\": [\"17297438\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"B56beta (PPP2R5B) physically interacts with CALEB/NGC (identified by yeast two-hybrid and confirmed by biochemical/immunocytochemical assays), and the whole PP2A trimer (structural and catalytic subunits) binds CALEB/NGC via B56beta (shown by affinity chromatography and mass spectrometry). B56beta inhibits CALEB/NGC-induced Akt phosphorylation and Akt-dependent dendritic branching, but not Akt-independent spine formation.\",\n      \"method\": \"Yeast two-hybrid screen, co-immunoprecipitation, immunocytochemistry, affinity chromatography, mass spectrometry, overexpression/knockdown with dendritic morphology readout\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal biochemical methods (Y2H, Co-IP, affinity chromatography, MS) plus functional cellular readout, single lab\",\n      \"pmids\": [\"18385213\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"PPP2R5B is a regulatory subunit of PP2A that dephosphorylates and inactivates Akt in adipocytes; overexpression of PPP2R5B decreased Akt phosphorylation and glucose uptake, while knockdown increased insulin sensitivity, establishing PPP2R5B as a negative regulator of insulin signaling through direct Akt dephosphorylation.\",\n      \"method\": \"Overexpression and shRNA knockdown in adipocytes, Western blot for p-Akt, glucose uptake assay\",\n      \"journal\": \"Molecular and cellular endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal gain- and loss-of-function with two functional readouts (p-Akt, glucose uptake), single lab\",\n      \"pmids\": [\"27521959\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"B56beta (PPP2R5B) dephosphorylates Akt in hepatocytes; shRNA knockdown of B56beta increased p-Akt levels and decreased metallothionein (MT) expression upon CdCl2 treatment, while overexpression of B56beta decreased p-Akt and increased MT, placing B56beta as a direct AKT phosphatase in the cellular response to cadmium cytotoxicity.\",\n      \"method\": \"Stable shRNA knockdown and retroviral overexpression, Western blot for p-AKT and MT, MTT cytotoxicity assay\",\n      \"journal\": \"Zhonghua yu fang yi xue za zhi\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single primary method (Western blot), limited mechanistic depth; no direct phosphatase activity assay\",\n      \"pmids\": [\"26081707\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"De novo heterozygous mutations in PPP2R5B cluster within a nine-amino-acid region that, when mapped onto the PP2A holoenzyme crystal structure, is predicted to affect substrate binding, suggesting the mutations perturb PP2A-dependent dephosphorylation of specific substrates including components of the AKT/PI3K pathway, causing human overgrowth with macrocephaly and intellectual disability.\",\n      \"method\": \"Trio-based exome sequencing, structural mapping onto published PP2A holoenzyme crystal structure\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 / Weak — mechanistic interpretation is structural modeling/prediction without direct functional validation of the mutant proteins; genetic findings are strong but mechanism is inferred\",\n      \"pmids\": [\"25972378\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"B56beta (PPP2R5B) is the only B56-family regulatory subunit whose expression is induced by both erythropoietin in fetal liver cells and hemin in K562 erythroleukemia cells during erythroid differentiation; knockdown of B56beta attenuates hemin-induced erythroid differentiation, identifying B56beta as the functional PP2A regulatory subunit in this process.\",\n      \"method\": \"shRNA knockdown in K562 cells, hemin-induced differentiation assay, expression profiling of B56 family members\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, knockdown with differentiation phenotype but no direct substrate or molecular mechanism established\",\n      \"pmids\": [\"27544028\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PPP2R5B (B56beta) is a regulatory subunit of the PP2A heterotrimer that confers substrate specificity; it directly targets Akt (promoting its dephosphorylation and inactivation in adipocytes and hepatocytes), targets Pim-1 kinase (promoting its ubiquitin-mediated degradation), bridges the PP2A trimer to CALEB/NGC to suppress Akt-dependent dendritic branching in neurons, and is required for erythroid differentiation; de novo mutations in the substrate-binding region cause human overgrowth with intellectual disability, likely by impairing PP2A-dependent dephosphorylation of PI3K/AKT pathway components.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PPP2R5B (B56beta) is a substrate-directing regulatory subunit of the PP2A holoenzyme that targets the phosphatase to specific substrates to restrain AKT and oncogenic kinase signaling [#0, #2]. It bridges the PP2A structural and catalytic subunits to substrates and binding partners, as shown when the intact PP2A trimer is recruited to the membrane protein CALEB/NGC specifically through B56beta, where it inhibits CALEB/NGC-induced Akt phosphorylation and Akt-dependent dendritic branching [#1]. As a negative regulator of AKT signaling, B56beta dephosphorylates and inactivates Akt in adipocytes, where its overexpression lowers p-Akt and glucose uptake while its knockdown enhances insulin sensitivity [#2]. Beyond AKT, B56beta selectively associates with Pim-1 kinase and promotes Pim-1 dephosphorylation, ubiquitination, and degradation, identifying a distinct substrate destabilized by this subunit [#0]. De novo heterozygous mutations clustering in a nine-amino-acid substrate-binding region of PPP2R5B cause human overgrowth with macrocephaly and intellectual disability, consistent with impaired PP2A-dependent dephosphorylation of PI3K/AKT pathway components [#4].\",\n  \"teleology\": [\n    {\n      \"year\": 2007,\n      \"claim\": \"Established that B56beta is the specific PP2A regulatory subunit controlling a defined kinase substrate, answering whether PP2A targeting of Pim-1 is subunit-selective.\",\n      \"evidence\": \"Reciprocal co-immunoprecipitation against all B56 family members plus shRNA knockdown with protein half-life and ubiquitination readouts\",\n      \"pmids\": [\"17297438\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No direct in vitro phosphatase assay on Pim-1 with reconstituted holoenzyme\",\n        \"Single lab; the Pim-1 phosphosite dephosphorylated by PP2A/B56beta not mapped\"\n      ]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Showed how B56beta directs the whole PP2A trimer to a membrane partner and a localized signaling output, answering whether the subunit acts as a substrate/partner-bridging adaptor.\",\n      \"evidence\": \"Yeast two-hybrid, Co-IP, affinity chromatography/mass spectrometry, and dendritic morphology readouts in neurons\",\n      \"pmids\": [\"18385213\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Direct Akt dephosphorylation by the recruited trimer not assayed enzymatically\",\n        \"In vivo relevance of CALEB/NGC bridging not tested\"\n      ]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Extended B56beta's role as an AKT phosphatase to hepatocyte stress responses, addressing whether it controls AKT-dependent cytoprotective output.\",\n      \"evidence\": \"Stable shRNA knockdown and retroviral overexpression with p-AKT and metallothionein Western blots and cytotoxicity assay\",\n      \"pmids\": [\"26081707\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No direct phosphatase activity assay; AKT dephosphorylation inferred from p-AKT levels\",\n        \"Single lab, single primary method\",\n        \"Mechanism linking AKT to metallothionein not resolved\"\n      ]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Linked PPP2R5B to a Mendelian overgrowth syndrome and localized causal mutations to a substrate-binding region, addressing the physiological consequence of perturbed substrate targeting.\",\n      \"evidence\": \"Trio-based exome sequencing with structural mapping onto the PP2A holoenzyme crystal structure\",\n      \"pmids\": [\"25972378\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"Mechanistic effect of mutants on substrate dephosphorylation inferred from structural modeling, not functionally validated\",\n        \"Specific affected substrates not experimentally identified\"\n      ]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Established B56beta as a direct AKT-inactivating subunit in metabolic signaling and as the PP2A regulatory subunit required for erythroid differentiation.\",\n      \"evidence\": \"Reciprocal overexpression/knockdown in adipocytes (p-Akt, glucose uptake) and shRNA knockdown with hemin-induced differentiation in K562 cells\",\n      \"pmids\": [\"27521959\", \"27544028\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Direct phosphatase assay on Akt not performed\",\n        \"Substrate driving erythroid differentiation not identified\",\n        \"In vivo metabolic phenotype not established\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Whether the disease-causing substrate-binding mutations functionally alter PP2A/B56beta dephosphorylation of specific AKT/PI3K substrates remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No functional assay of mutant B56beta on substrate dephosphorylation\",\n        \"No reconstituted in vitro phosphatase characterization across substrates\",\n        \"Substrate repertoire beyond Akt and Pim-1 uncharacterized\"\n      ]\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\": [1]}\n    ],\n    \"localization\": [],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 1, 2]}\n    ],\n    \"complexes\": [\"PP2A holoenzyme\"],\n    \"partners\": [\"PIM1\", \"CALEB/NGC\", \"AKT\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":4,"faith_total":5,"faith_pct":80.0}}