{"gene":"PPP4C","run_date":"2026-06-10T06:43:35","timeline":{"discoveries":[{"year":1993,"finding":"PPX (PPP4C) was identified as a novel mammalian protein serine/threonine phosphatase with substrate specificity and sensitivity to okadaic acid and microcystin similar (but not identical) to PP2A catalytic subunit; unlike PP2A, PPX did not bind the 65 kDa regulatory subunit of PP2A.","method":"Baculovirus expression, in vitro phosphatase assays, inhibitor sensitivity assays, co-immunoprecipitation","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro enzymatic characterization with multiple substrates and inhibitors, replicated across labs as foundational paper","pmids":["8384557"],"is_preprint":false},{"year":1993,"finding":"PPX (PPP4C) localizes intensely to centrosomes at all stages of mitosis except telophase, while also distributed throughout cytoplasm and nucleus; centrosomal staining colocalizes with the human autoantibody #5051 marking pericentriolar material.","method":"Immunofluorescence microscopy with two independent antibodies (anti-bacterially expressed PPX and anti-PPX peptide)","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct localization by two independent antibodies, foundational paper replicated in subsequent studies","pmids":["8384557"],"is_preprint":false},{"year":2008,"finding":"A three-protein PP4 complex containing PP4C, PP4R2, and PP4R3beta specifically dephosphorylates ATR-mediated gamma-H2AX generated during DNA replication; PP4 efficiently dephosphorylates gamma-H2AX within mononucleosomes in vitro without directly altering ATR or checkpoint kinase activity.","method":"Co-immunoprecipitation, siRNA knockdown, in vitro dephosphorylation assay with mononucleosomes, cell hypersensitivity assays","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with mononucleosome substrate, reciprocal co-IP defining complex, replicated by independent lab in same year","pmids":["18614045"],"is_preprint":false},{"year":2008,"finding":"PP4C contributes to dephosphorylation of gamma-H2AX both at sites of DNA damage and in undamaged chromatin in human cells; depletion of PP4C results in prolonged checkpoint arrest due to persistence of MDC1 at DNA lesion sites.","method":"siRNA knockdown, immunofluorescence, checkpoint assays, gamma-H2AX foci analysis","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KD with defined cellular phenotype (MDC1 persistence, checkpoint arrest), replicated by independent lab in same year","pmids":["18758438"],"is_preprint":false},{"year":2008,"finding":"Drosophila PP4 (ortholog of PPP4C) dephosphorylates Smoothened (Smo) to regulate Hedgehog signaling; RNAi knockdown of PP4 elevates Smo phosphorylation and accumulation, leading to increased Hh signaling. PP4 interaction with Smo is mediated by Cos2, and Hh signaling downregulates the Smo-PP4 interaction.","method":"In vivo RNAi screen, epistasis analysis, Co-IP, phosphorylation assays, deletion mapping (aa 626-678 of Smo)","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal functional epistasis, direct interaction mapping, multiple orthogonal approaches in single study","pmids":["19088085"],"is_preprint":false},{"year":2010,"finding":"A PP4 phosphatase complex dephosphorylates RPA2 (replication protein A subunit 2) to regulate its role in DSB response; PP4R2 mediates the DNA damage-dependent association between RPA2 and PP4C; PP4 efficiently dephosphorylates phospho-RPA2 in vitro; PP4-mediated dephosphorylation of RPA2 is required for efficient RAD51 loading and homologous recombination.","method":"Co-immunoprecipitation, in vitro dephosphorylation assay, siRNA knockdown, HR reporter assay, RAD51 foci analysis, phosphomimetic mutant analysis","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution, reciprocal Co-IP, phosphomimetic mutants with defined HR phenotype, multiple orthogonal methods","pmids":["20154705"],"is_preprint":false},{"year":2010,"finding":"Yeast PP4 (Pph3/Psy2) mediates centromere pairing during meiotic prophase by dephosphorylating Zip1 at serine 75, a consensus Mec1 (ATR) site; loss of PP4 leads to persistent Zip1-S75 phosphorylation and blocked centromere pairing; centromere pairing is restored in mec1 mutants, establishing genetic epistasis between Mec1 and PP4 at this step.","method":"Genetic epistasis (double mutant analysis), phosphorylation site mutagenesis, chromatin immunofluorescence for centromere pairing","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis with mechanistic substrate identification, multiple orthogonal approaches","pmids":["20951350"],"is_preprint":false},{"year":2010,"finding":"PP4C dephosphorylates the NCC (Na+-Cl- cotransporter) to inhibit its intrinsic transport activity (but not surface trafficking) through a mechanism requiring phosphatase activity and the conserved N-terminal threonine 58 of NCC; PP4 is selectively expressed in the distal nephron including distal convoluted tubule cells.","method":"Xenopus oocyte expression system, transport activity assays, phosphatase-dead mutant, NCC Thr58 mutagenesis, immunofluorescence of mouse kidney sections","journal":"Canadian journal of physiology and pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional assay in oocyte expression system with mutagenesis, single lab with two orthogonal approaches","pmids":["20962898"],"is_preprint":false},{"year":2012,"finding":"PP4C/R3beta complex dephosphorylates KAP-1 at S824 (phosphorylated by ATM) and S473 (phosphorylated by CHK2) after ionizing radiation; a PP4C/R3beta complex interacts with KAP-1; phosphorylation of KAP-1 S473 by CHK2 impacts the G2/M checkpoint; PP4-mediated dephosphorylation of KAP-1 S824 is required for repair of heterochromatic DNA lesions.","method":"Phosphoproteomic substrate identification screen, Co-IP, siRNA knockdown, phosphomimetic mutants, G2/M checkpoint assays, chromatin remodeling analysis","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — systematic phosphoproteomic substrate identification plus mechanistic follow-up with phosphomimetics and co-IP, multiple orthogonal methods","pmids":["22491012"],"is_preprint":false},{"year":2012,"finding":"PP4C and regulatory subunit PP4R2 physically interact with KAP1 and dephosphorylate pKAP1-S824 in vitro; PP4C depletion compromises NHEJ-mediated DSB repair; PP4C and KAP1 function in the same epistasis group for NHEJ.","method":"Co-IP, in vitro dephosphorylation assay, siRNA knockdown, I-SceI NHEJ reporter assay, epistasis analysis (co-depletion)","journal":"Cell cycle (Georgetown, Tex.)","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro dephosphorylation confirmed, reciprocal Co-IP, genetic epistasis via co-depletion","pmids":["22732494"],"is_preprint":false},{"year":2012,"finding":"PP4 complex (catalytic subunit Pph3, scaffold Psy2, regulatory subunits Rrd1 and Tip41) is the main Maf1 phosphatase in yeast, required for Maf1 dephosphorylation, nuclear localization, and rapid repression of RNA Pol III; purified PP4 dephosphorylates Maf1 in vitro and PP4 co-precipitates with Maf1.","method":"In vitro dephosphorylation assay, co-precipitation, genetic analysis of PP4 subunit mutants, nuclear localization assays, Pol III transcription assays","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro dephosphorylation plus co-precipitation plus genetic dissection of subunit requirements, multiple orthogonal methods","pmids":["22333918"],"is_preprint":false},{"year":2012,"finding":"PP4 (via PP4R1 regulatory subunit) forms a holoenzyme that bridges the IKK complex and PP4c, directing PP4c to dephosphorylate and inactivate the IKK complex, thereby negatively regulating NF-κB signaling in T lymphocytes.","method":"RNAi screen, Co-IP, kinase activity assays, NF-κB reporter assays, T cell activation assays","journal":"Immunity","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP establishing bridging mechanism, functional NF-κB/IKK assays, confirmed in primary cells","pmids":["23084358"],"is_preprint":false},{"year":2014,"finding":"Yeast PP4 (Pph3) physically interacts with the ATR homolog Mec1-Ddc2 complex, mediated by cofactors Psy2 and Ddc2; this interaction was demonstrated biochemically and by FRET in subnuclear repair foci; phosphoproteomic analysis showed 94% of mec1-100-compromised phosphorylation targets on HU are PP4 regulated; PP4 also dephosphorylates a phosphoacceptor site within Mec1 itself.","method":"Genetic suppressor screen, E-MAP screen, biochemical interaction assays, FRET microscopy in living cells, phosphoproteomic analysis","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — FRET imaging plus biochemical interaction plus phosphoproteomics, multiple orthogonal approaches, direct physical interaction demonstrated","pmids":["25533186"],"is_preprint":false},{"year":2014,"finding":"PP4R1 subunit of PP4 interacts with TRAF2 and TRAF6 in a RING finger domain-dependent manner (identified by yeast two-hybrid with TRAF2 as bait); PP4R1 mediates dephosphorylation of TRAF2 Ser11 and inhibits TRAF6 polyubiquitination, thereby inhibiting NF-κB activation.","method":"Yeast two-hybrid screen, Co-IP, phosphorylation assays, ubiquitination assays, NF-κB reporter assays, siRNA knockdown","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — yeast two-hybrid plus Co-IP plus functional assays, single lab, multiple orthogonal approaches","pmids":["25134449"],"is_preprint":false},{"year":2015,"finding":"PP4C dephosphorylates TBK1 at Ser172 upon RNA virus infection, inhibiting TBK1 activation and subsequent IRF3 activation, thereby suppressing type I IFN production; a phosphatase-dead PP4C mutant abolished inhibitory effects; PP4C directly binds TBK1 upon virus infection.","method":"Co-IP, in vitro/cellular dephosphorylation assays, phosphatase-dead mutant, siRNA knockdown in macrophages and DCs, viral infection assays, in vivo peritoneal macrophage assays","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct binding demonstrated by Co-IP, phosphatase-dead mutant controls, in vitro dephosphorylation, in vivo validation","pmids":["26363053"],"is_preprint":false},{"year":2016,"finding":"LCMT-1 is the major carboxyl methyltransferase for PP4C (as well as PP2A and PP6) in mouse embryonic fibroblasts; LCMT-1-dependent methylation differentially regulates PP4 holoenzyme formation, with the PP4R1-containing complex being most dramatically affected by LCMT-1 loss; LCMT-1 knockout MEFs show hyperphosphorylation of HDAC3, a target of the methylation-dependent PP4R1-PP4c complex.","method":"Methylation-specific antibodies, BN-PAGE holoenzyme analysis, LCMT-1 knockout MEFs, HDAC3 phosphorylation assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic knockout plus biochemical holoenzyme analysis plus substrate phosphorylation readout, multiple orthogonal methods","pmids":["27507813"],"is_preprint":false},{"year":2019,"finding":"PP4 (via regulatory subunit PPP4R3) recognizes substrates through a conserved FxxP consensus binding motif; X-ray crystallography revealed that FxxP motifs bind to a conserved pocket in PPP4R3; the FxxP motif in cohesin release factor WAPL regulates WAPL phosphorylation and is required for efficient cohesin release.","method":"X-ray crystallography, proteomic analysis of PP4 interacting proteins, in silico FxxP motif searches, functional WAPL phosphorylation and cohesin release assays","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure plus proteomic validation plus functional mutagenesis of motif, multiple orthogonal methods in single study","pmids":["31585692"],"is_preprint":false},{"year":2019,"finding":"PP4C dephosphorylates AMPK in a Ca2+-dependent manner downstream of mitochondrial Ca2+ (MCU); elevated cytosolic Ca2+ (when MCU is deleted) activates PP4 activity, which dephosphorylates AMPK, leading to increased hepatic lipid accumulation; PP4 knockdown or AMPK reconstitution restores lipid clearance in MCU-deleted hepatocytes.","method":"Mcu liver-specific knockout mice, CRISPR/Cas9 zebrafish knockout, Ca2+ measurements, PP4 activity assays, AMPK phosphorylation assays, siRNA knockdown, lipid accumulation measurements","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic knockout in two organisms, direct PP4 activity measurement, rescue experiments with PP4 knockdown and active AMPK reconstitution","pmids":["30917323"],"is_preprint":false},{"year":2019,"finding":"PP4C dephosphorylates HDAC3 following peripheral nerve injury, impairing HDAC3 activity and enhancing histone acetylation to promote a regenerative gene expression program; this PP4 activation is calcium-dependent (triggered by peripheral but not central injury); PP4-dependent HDAC3 dephosphorylation discriminates between axonal regeneration competence and failure.","method":"Pharmacological screen, in vivo injury models (DRG), calcium imaging, ChIP-seq (H3K9ac), RNA-seq, genetic and pharmacological HDAC3 inhibition, PP4 activity assays","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo genetic/pharmacological manipulation with H3K9ac ChIP-seq readout, multiple orthogonal approaches","pmids":["31268609"],"is_preprint":false},{"year":2019,"finding":"CDK5 directly phosphorylates PP4R3β (the PP4 regulatory subunit that recognizes 53BP1) in late mitotic phases in non-neuronal cells; CDK5-mediated phosphorylation of PP4R3β is required for PP4R3β to recognize and dephosphorylate 53BP1; without CDK5 activity in mitosis, 53BP1 fails to localize to damaged chromatin in G1.","method":"In vitro kinase assays, specific CDK5 inhibition in mitosis, Co-IP of PP4R3β-53BP1, 53BP1 foci assays in G1, phosphomimetic/phosphodeficient mutants","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro kinase reconstitution, phosphomimetic mutant analysis, specific inhibitor controls, defined cellular phenotype","pmids":["31534152"],"is_preprint":false},{"year":2019,"finding":"Drosophila PP4 (Falafel/R3 subunit) EVH1 domain recognizes FxxP and MxPP short linear motifs through a conserved leucine residue (replacing the invariant phenylalanine of canonical EVH1 domains) rather than canonical proline-rich sequences; the Smk-1 domain of Falafel also participates in target-binding.","method":"Binding studies, mass spectrometry identification of interactors, site-directed mutagenesis of EVH1 domain residues, structural analysis","journal":"Open biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mutagenesis plus MS-based interaction mapping, single lab, consistent with crystallography data from PPP4R3 paper","pmids":["33352067"],"is_preprint":false},{"year":2021,"finding":"C-terminal leucine methylation of PP4C (catalytic subunit) by LCMT-1 is required for PP4R1-containing and PP4R3β-containing holoenzyme assembly; deletion of the C-terminal leucine faithfully recapitulates loss of methylation; loss of methylation reduces PP4R1 and PP4R3β binding.","method":"Mass spectrometry-based proteomics, C-terminal leucine deletion mutants, genome editing, BN-PAGE holoenzyme analysis","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 1 / Strong — mass spectrometry proteomics with genome editing plus mutant analysis, multiple orthogonal methods, extends prior LCMT-1 findings","pmids":["34845248"],"is_preprint":false},{"year":2021,"finding":"PP4C dephosphorylates the sNASP phosphoprotein to terminate TLR4-induced TRAF6 activation; PP4 is directly recruited by phosphorylated sNASP; this PP4-mediated negative regulation reduces pro-inflammatory cytokine production; in vivo PP4 overexpression improves survival in a sepsis model.","method":"Co-IP, ectopic expression of PP4, siRNA knockdown, cytokine production assays, in vivo adenovirus-mediated PP4 expression in sepsis model","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct recruitment demonstrated by Co-IP, in vitro and in vivo validation, phosphatase-dead mutant controls used","pmids":["34789577"],"is_preprint":false},{"year":2021,"finding":"Deletion of PPP4C in mouse causes male-specific infertility characterized by oligoasthenoteratospermia (OAT): sperm tail bending, low sperm count, poor motility, and defective cytoplasm removal during spermiogenesis.","method":"Conditional knockout mouse model, light microscopy, transmission electron microscopy of spermiogenesis","journal":"Molecular human reproduction","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — clean knockout with defined morphological phenotype, single lab, phenotype described but direct substrate not identified","pmids":["33543287"],"is_preprint":false},{"year":2022,"finding":"PPP4C dephosphorylates PLK1 at Ser137, negatively regulating PLK1 activity during DNA DSB response in early embryos; PPP4C depletion causes sustained PLK1 activity, inhibits CHK2, upregulates CDK1 activation, and results in inefficient RAD51 loading, impairing homologous recombination.","method":"PPP4C conditional knockout in oocytes/embryos, in vitro dephosphorylation assay, PLK1 inhibition experiments, RAD51 foci analysis, CDK1/CHK2 activity assays","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro dephosphorylation of PLK1-S137, genetic knockout with defined molecular phenotype, epistatic rescue by PLK1 inhibition","pmids":["35546066"],"is_preprint":false},{"year":2022,"finding":"CCDC6 (when un-phosphorylated at T427) forms a complex with PP4c that sequesters PP4c activity; the CCDC6-PP4 interaction and PP4 regulation of gamma-H2AX is mediated via PP4R3α; functional or physical loss of CCDC6 enhances PP4c complex activity, causing BRCAness and PARP inhibitor sensitivity in ovarian cancer cells.","method":"Co-IP, phosphomimetic mutants (T427D), siRNA knockdown of CCDC6 and PP4R3α, gamma-H2AX assays, HR reporter assays, PARP inhibitor sensitivity assays","journal":"Journal of experimental & clinical cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus phosphomimetic analysis plus functional HR assays, single lab, multiple methods","pmids":["35964058"],"is_preprint":false},{"year":2023,"finding":"SIRT1 interacts with PP4c and promotes its inhibition by deacetylating the WH1 domain of regulatory subunits PP4R3α/β upon DNA damage; SIRT1-mediated inhibition of PP4 regulates gamma-H2AX and RPA2 phosphorylation; SIRT1-deficient cells show decreased gamma-H2AX levels consistent with unopposed PP4 activity.","method":"Co-IP of SIRT1 with PP4c, deacetylation assays, gamma-H2AX and RPA2 phosphorylation analysis in SIRT1-deficient cells","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP demonstrating SIRT1-PP4c interaction, functional assays linking SIRT1 deacetylase activity to PP4 substrate phosphorylation, single lab","pmids":["37309898"],"is_preprint":false},{"year":2026,"finding":"FBXO42 ubiquitinates the PP4 complex to govern the assembly of regulatory and catalytic subunits, with the net effect of restraining PP4 phosphatase activity; FBXO42 depletion unleashes PP4 activity with broad cellular effects on cell cycle, DNA damage response, and glioma stem cell survival.","method":"Mass spectrometry proteomics, ubiquitination assays, PP4 complex assembly analysis, FBXO42 depletion functional assays","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — MS-based proteomics, direct ubiquitination assays, holoenzyme assembly analysis, functional rescue experiments","pmids":["41484364"],"is_preprint":false},{"year":2026,"finding":"PP4 directly dephosphorylates TBK1 in macrophages, inactivating IRF3 and suppressing macrophage-derived CCL5 production during sepsis; wild-type PP4 (but not phosphatase-dead mutant) reduces LPS-mediated CCR5 expression in neutrophils, limiting ROS production and NETs formation; myeloid-specific PP4 KO mice show increased sepsis susceptibility.","method":"Myeloid-specific PP4 knockout mice (CLP model), in vitro dephosphorylation assay (TBK1), phosphatase-dead mutant, cytokine assays, NETosis assays","journal":"Redox biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — myeloid-specific KO with defined phenotype, phosphatase-dead mutant controls, single lab with in vitro and in vivo approaches","pmids":["41723906"],"is_preprint":false},{"year":2026,"finding":"PPP4C interacts with MST4 kinase and reduces its activity, thereby enabling YAP1 dephosphorylation and nuclear accumulation; PPP4C-mediated MST4 degradation promotes NSCLC cell growth and immunosuppression by restoring YAP1 activity through the MAP4K2-LATS1/2 cascade.","method":"Co-IP of PPP4C with MST4, gain/loss-of-function experiments, YAP1 phosphorylation assays, NK cell co-culture assays, in vivo syngeneic tumor models","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus functional pathway assays plus in vivo validation, single lab, mechanism involves PPP4C-MST4 direct interaction","pmids":["41690452"],"is_preprint":false},{"year":2026,"finding":"AAV Rep proteins engage the SMEK1 regulatory subunit of the PP4:SMEK1 complex to interfere with substrate recruitment, preventing KAP1-S824 and RPA2-S4/8/33 dephosphorylation; KAP1 interaction with SMEK1 is mediated by a MAPP short linear motif binding the SMEK1 EVH1 domain.","method":"Binding studies, Co-IP, substrate phosphorylation assays (KAP1-S824, RPA2), SLiM motif mapping, AAV replication assays","journal":"PLoS pathogens","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct binding studies plus functional substrate phosphorylation assays plus SLiM motif validation, single lab","pmids":["41805761"],"is_preprint":false},{"year":2013,"finding":"Targeted suppression of PP4C (but not PP1C, PP2AC, or PP5C) alone is sufficient to mimic many cellular actions of fostriecin, inducing apoptosis in tetraploid cells following mitotic slippage; PP4C is specifically required to prevent mitotic slippage/apoptosis.","method":"Antisense oligonucleotides specifically targeting PP4C, high-content time-lapse live imaging, comparison with fostriecin treatment","journal":"Molecular cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — specific antisense knockdown of individual phosphatases with live imaging readout, defines PP4C-specific mitotic role","pmids":["23671329"],"is_preprint":false},{"year":2014,"finding":"PP4 is required for pro-B cell development and immunoglobulin VDJ recombination; PP4-deficient pro-B cells show impaired Ig DJ(H) recombination, increased DNA double-strand breaks at Ig loci, and accumulate in G1 with excessive DNA damage; normal B cell development is rescued by transgenic Ig expression.","method":"B cell-specific pp4 knockout mice, flow cytometry, V(D)J recombination analysis, gamma-H2AX foci, cell cycle analysis, transgenic rescue","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean B cell-specific KO with defined developmental phenotype and transgenic rescue, single lab","pmids":["23874770"],"is_preprint":false},{"year":2014,"finding":"PP4 is required for germinal center formation and class switch recombination in B cells; PP4-deficient mature B cells show impaired proliferation, reduced Ig class switching efficiency, failure to form germinal centers in vivo, impaired CD40-mediated MAPK activation, and abnormal IgM-mediated NF-κB activation.","method":"CD23-cre conditional PP4 knockout mice, antigen immunization, flow cytometry for GC B cells, CSR assays in vitro, MAPK/NF-κB activation assays","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional KO with defined immunological phenotype and signaling readouts, single lab","pmids":["25215539"],"is_preprint":false},{"year":2005,"finding":"Co-transfection of PP4 with JNK-1 in prostate cancer cell lines PC-3 and LNCaP significantly increases JNK-1 activity following EGF or cisplatin stimulation, and this is associated with increased c-Jun/AP-1 and EGR-1 activities; PP4 appears to positively regulate JNK-1 stability/activity.","method":"Co-transfection assays, JNK-1 activity assays, AP-1/EGR-1 reporter assays","journal":"Biological research","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single co-transfection approach, no direct dephosphorylation assay; mechanism of PP4 effect on JNK-1 is indirect/unclear","pmids":["16238095"],"is_preprint":false},{"year":2017,"finding":"Fission yeast PP4 co-immunoprecipitates with Wpl1 and cohesin; PP4-dependent dephosphorylation of Rad21 (cohesin kleisin) promotes cohesin release from DNA by Wpl1; phosphomimetic alleles of Rad21 at the identified PP4-regulated sites dampen Wpl1 anti-cohesion activity.","method":"Genetic screen, Co-IP of PP4 with Wpl1 and cohesin, phosphomimetic/alanine Rad21 mutants, cohesion assays","journal":"The EMBO journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus phosphomimetic analysis plus genetic screen, single lab, defines PP4 role in cohesin regulation via Rad21 dephosphorylation","pmids":["28438891"],"is_preprint":false},{"year":2019,"finding":"PP4 phosphatase (via Psy2 subunit) dephosphorylates Rad53 during DSB repair to relieve Rad9-mediated inhibition of the Sgs1/Dna2 exonuclease complex, thereby stimulating DNA end resection; PP4-dependent Rad53 dephosphorylation is required for efficient single-strand annealing repair.","method":"Yeast genetics, Rad53 phosphorylation assays, resection assays, SSA repair assay, epistasis via Rad53 hyperphosphorylation mutants","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — yeast genetic epistasis with defined molecular mechanism (Rad53→Rad9→Sgs1/Dna2), functional resection assays, single lab","pmids":["31544936"],"is_preprint":false},{"year":2025,"finding":"CYB5R4 is an evolutionarily conserved activator of PP4 (and PP6 but not PP2A); heme binding is essential for CYB5R4 function; CYB5R4 activates PP4 by reducing the metal ions in the PP4 active site; CYB5R4-mediated activation of PP4 is critical for cell viability during DNA damage-inducing oxidative stress conditions.","method":"Genome-wide CRISPR KO and base editor screens, biochemical PP4 activity assays, heme-binding mutant analysis, cell viability assays under DNA damage/oxidative stress","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — systematic CRISPR screen plus direct activity assays plus mechanistic follow-up with heme-binding mutants; preprint, not yet peer-reviewed","pmids":[],"is_preprint":true},{"year":2025,"finding":"FBXO42 binds PPP4C, promotes its ubiquitination, and negatively regulates PPP4C expression; aberrant PPP4C expression is a major driver of cell death in FBXO42-essential neuroblastoma cells; CCDC6 independently interacts with PPP4C without affecting its ubiquitination; PPP4C knockdown reduces FBXO42-CCDC6 interactions.","method":"Mass spectrometry proteomics, ubiquitination assays, CRISPR KO screen (synthetic lethality), gene knockdown rescue experiments, Co-IP","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — MS-based proteomics plus ubiquitination assays plus functional rescue, preprint extending peer-reviewed FBXO42 paper","pmids":[],"is_preprint":true},{"year":2025,"finding":"Drosophila PP4 (Pp4) is required for centrosome asymmetry establishment in neural stem cells; Pp4 loss causes two inactive centrioles in interphase and failure to correctly transfer Centrobin (Cnb) from mother to daughter centriole in mitosis; phosphomimetic Centrobin fails to relocalize correctly; PP4 may dephosphorylate both Centrobin and gamma-Tubulin.","method":"In vivo live cell imaging, superresolution imaging, Pp4 mutant analysis, phosphomimetic Centrobin constructs, centrosome asymmetry assays","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo live imaging with defined centrosome phenotype plus phosphomimetic validation, preprint not yet peer-reviewed","pmids":[],"is_preprint":true}],"current_model":"PPP4C (PP4, PPX) is an evolutionarily conserved serine/threonine phosphatase that functions as the catalytic core of trimeric holoenzymes (assembled via C-terminal leucine methylation by LCMT-1 and regulatory subunits including PP4R1, PP4R2, PP4R3α/β/SMEK1), which achieve substrate specificity through FxxP/MxPP short linear motif recognition by the R3 subunit EVH1 domain; PP4C dephosphorylates key substrates including gamma-H2AX, RPA2, KAP1, 53BP1, PLK1, TBK1, AMPK, Maf1, Smo, NCC, and HDAC3, positioning it as a master regulator of the DNA damage response (controlling checkpoint recovery, homologous recombination, and NHEJ), innate immune signaling (negatively regulating TBK1/IFN and IKK/NF-κB pathways), centrosome biology, RNA Pol III transcription repression, and lipid/energy metabolism; PP4C activity is itself regulated by SIRT1-mediated deacetylation of its regulatory subunits, CDK5-mediated phosphorylation of PP4R3β, FBXO42-mediated ubiquitination of the holoenzyme, CYB5R4-mediated reduction of active-site metal ions, and CCDC6-dependent sequestration."},"narrative":{"mechanistic_narrative":"PPP4C (PP4, PPX) is an evolutionarily conserved okadaic-acid/microcystin-sensitive serine/threonine phosphatase, distinct from PP2A in that it does not bind the PP2A 65 kDa regulatory subunit, that acts as the catalytic core of multimeric holoenzymes to control the DNA damage response, innate immune signaling, and cell-cycle/developmental processes [PMID:8384557]. Holoenzyme assembly and substrate selection are coupled: C-terminal leucine methylation of the catalytic subunit by LCMT-1 is required to build PP4R1- and PP4R3β-containing complexes [PMID:27507813, PMID:34845248], and the R3-type regulatory subunits recognize substrates through FxxP/MxPP short linear motifs that dock into a conserved pocket of the regulatory subunit's EVH1/WH1 domain [PMID:31585692, PMID:33352067]. As a master phosphatase in the DNA damage response, PP4 dephosphorylates γ-H2AX within nucleosomes via a PP4C–PP4R2–PP4R3β complex to permit checkpoint recovery [PMID:18614045, PMID:18758438], dephosphorylates RPA2 to license RAD51 loading and homologous recombination [PMID:20154705], removes ATM/CHK2 marks from KAP-1 (S824/S473) to enable NHEJ and heterochromatic repair [PMID:22491012, PMID:22732494], and dephosphorylates PLK1-S137 to coordinate the DSB response in early embryos [PMID:35546066]. In innate immunity PP4 acts as a negative regulator, directly dephosphorylating TBK1-Ser172 to limit IRF3/type I IFN output [PMID:26363053, PMID:41723906] and inactivating the IKK complex and TRAF/NF-κB signaling through its PP4R1 subunit [PMID:23084358, PMID:25134449]. PP4 additionally functions at centrosomes [PMID:8384557], represses RNA Pol III transcription by dephosphorylating Maf1 [PMID:22333918], controls cohesin release via FxxP-dependent dephosphorylation of WAPL/Rad21 [PMID:31585692, PMID:28438891], and regulates metabolic and chromatin signaling through dephosphorylation of AMPK [PMID:30917323] and HDAC3 [PMID:27507813, PMID:31268609]. PP4 activity is held in check by multiple inputs: LCMT-1 methylation and CDK5 phosphorylation of PP4R3β gate holoenzyme function [PMID:31534152, PMID:34845248], FBXO42-mediated ubiquitination restrains complex assembly [PMID:41484364], SIRT1 deacetylation of the R3 WH1 domain inhibits the phosphatase after DNA damage [PMID:37309898], and CCDC6 sequesters the complex [PMID:35964058]. Loss of PPP4C causes male-specific oligoasthenoteratospermia in mice and is required for B-cell V(D)J and class-switch recombination [PMID:33543287, PMID:23874770, PMID:25215539].","teleology":[{"year":1993,"claim":"Established PPP4C as a distinct catalytic phosphatase: it shares PP2A-like substrate and inhibitor profiles yet does not bind the PP2A regulatory subunit, defining it as a separate enzyme, and localized it to centrosomes throughout mitosis.","evidence":"Baculovirus expression with in vitro phosphatase and inhibitor assays, plus dual-antibody immunofluorescence","pmids":["8384557"],"confidence":"High","gaps":["No regulatory subunits or physiological substrates identified at this stage","Functional role of centrosomal localization not defined"]},{"year":2008,"claim":"Resolved how PP4 acts in the DNA damage response by showing a defined PP4C–PP4R2–PP4R3β complex dephosphorylates γ-H2AX in nucleosomes to drive checkpoint recovery.","evidence":"Reciprocal Co-IP, siRNA knockdown, in vitro mononucleosome dephosphorylation, and γ-H2AX/MDC1 foci and checkpoint assays in human cells","pmids":["18614045","18758438"],"confidence":"High","gaps":["Did not establish how the complex is targeted to specific chromatin sites","Other DDR substrates not yet defined"]},{"year":2010,"claim":"Expanded PP4's DDR role to homologous recombination and uncovered conserved substrate logic across kingdoms, including RPA2, yeast Zip1, and the NCC cotransporter.","evidence":"In vitro dephosphorylation, HR reporter and RAD51 foci assays, genetic epistasis in yeast meiosis, and Xenopus oocyte transport assays","pmids":["20154705","20951350","20962898"],"confidence":"High","gaps":["NCC regulation rests on a single lab and oocyte system","How PP4R2 confers damage-dependent RPA2 recognition not structurally defined"]},{"year":2012,"claim":"Defined PP4 as both a DDR effector on KAP-1 and a negative regulator of innate immune/NF-κB signaling, showing regulatory subunits direct catalytic activity to distinct pathways.","evidence":"Phosphoproteomic substrate screen, in vitro dephosphorylation, NHEJ reporter epistasis, and PP4R1-bridged IKK/TRAF NF-κB assays in T and other cells; plus yeast Maf1/Pol III repression","pmids":["22491012","22732494","23084358","22333918","25134449"],"confidence":"High","gaps":["TRAF2/TRAF6 axis from single lab","How a single catalytic subunit is partitioned between immune and DDR roles not resolved"]},{"year":2014,"claim":"Connected PP4 directly to the apical ATR/Mec1 machinery and to lymphocyte development, showing PP4 governs both the kinase signal and the biological programs that depend on it.","evidence":"FRET and biochemical interaction with Mec1-Ddc2 plus phosphoproteomics in yeast; B-cell-specific knockouts with V(D)J/CSR and germinal center phenotypes","pmids":["25533186","23874770","25215539"],"confidence":"Medium","gaps":["Mammalian PP4–ATR physical interaction not directly demonstrated","B-cell phenotypes not tied to a single PP4 substrate"]},{"year":2015,"claim":"Pinpointed TBK1-Ser172 as a direct PP4C substrate, mechanistically explaining PP4's suppression of type I IFN during viral infection.","evidence":"Co-IP, in vitro/cellular dephosphorylation, phosphatase-dead mutant, and viral infection assays in macrophages/DCs with in vivo validation","pmids":["26363053"],"confidence":"High","gaps":["Which regulatory subunit recruits PP4C to TBK1 not defined here"]},{"year":2016,"claim":"Identified LCMT-1 carboxyl methylation as the switch controlling PP4 holoenzyme composition and revealed HDAC3 as a methylation-dependent PP4R1 substrate.","evidence":"LCMT-1 knockout MEFs, methylation-specific antibodies, BN-PAGE holoenzyme analysis, and HDAC3 phosphorylation readout","pmids":["27507813"],"confidence":"High","gaps":["Quantitative contribution of methylation to each holoenzyme not fully mapped"]},{"year":2019,"claim":"Established the structural basis of PP4 substrate selectivity (FxxP/MxPP SLiM recognition by the R3 EVH1 domain) and added cohesin regulation, AMPK/metabolism, HDAC3-driven axon regeneration, and CDK5-gated 53BP1 recruitment to its functional repertoire.","evidence":"X-ray crystallography and proteomics of FxxP recognition; WAPL/cohesin, AMPK (MCU knockout mice/zebrafish), HDAC3 ChIP-seq in nerve injury, and CDK5 kinase/phosphomimetic 53BP1 assays","pmids":["31585692","33352067","30917323","31268609","31534152","31544936"],"confidence":"High","gaps":["How a single SLiM pocket discriminates among hundreds of FxxP-bearing proteins unclear","Drosophila EVH1 leucine-substitution finding is Medium confidence/single lab"]},{"year":2021,"claim":"Confirmed the C-terminal leucine as the methylation site governing PP4R1/PP4R3β holoenzyme assembly and added sNASP-directed termination of TLR4/TRAF6 signaling and a spermiogenesis requirement.","evidence":"MS proteomics with C-terminal leucine deletion mutants and BN-PAGE; sNASP Co-IP with in vivo sepsis model; conditional knockout mouse spermiogenesis analysis","pmids":["34845248","34789577","33543287"],"confidence":"High","gaps":["Direct PP4 substrate underlying the infertility phenotype not identified","sNASP recruitment mechanism rests on single lab"]},{"year":2022,"claim":"Identified PLK1-Ser137 as a PP4C substrate coordinating the embryonic DSB response and revealed CCDC6 as a sequestering inhibitor whose loss confers BRCAness.","evidence":"Conditional knockout in oocytes/embryos with in vitro PLK1 dephosphorylation and CHK2/CDK1 readouts; CCDC6 Co-IP, phosphomimetics, and PARP-inhibitor sensitivity assays","pmids":["35546066","35964058"],"confidence":"High","gaps":["CCDC6 sequestration mechanism from single lab","Whether PLK1-S137 regulation generalizes beyond early embryos untested"]},{"year":2023,"claim":"Added a post-translational inhibitory input by showing SIRT1 deacetylates the R3 WH1 domain to restrain PP4 activity on γ-H2AX and RPA2 after DNA damage.","evidence":"Co-IP, deacetylation assays, and γ-H2AX/RPA2 phosphorylation analysis in SIRT1-deficient cells","pmids":["37309898"],"confidence":"Medium","gaps":["Single lab; specific acetyl-lysines and their direct effect on substrate docking not fully defined"]},{"year":2026,"claim":"Established FBXO42 ubiquitination as a regulator of PP4 holoenzyme assembly and extended PP4's roles to YAP1/Hippo signaling in cancer and macrophage/neutrophil control during sepsis.","evidence":"MS proteomics and ubiquitination assays (glioma); PPP4C–MST4 Co-IP and YAP1 assays with syngeneic tumors; myeloid-specific PP4 knockout sepsis models with TBK1 dephosphorylation","pmids":["41484364","41690452","41723906"],"confidence":"Medium","gaps":["MST4/YAP1 and FBXO42 axes each from single labs","Direct vs indirect PP4 effects on YAP1 not fully separated"]},{"year":null,"claim":"How a single catalytic subunit achieves pathway-specific substrate selection across DDR, immune, metabolic, and developmental programs in vivo, and how the converging regulatory inputs (methylation, ubiquitination, deacetylation, metal-ion reduction, sequestration) are integrated, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified structural model linking SLiM recognition to substrate-specific outcomes","CYB5R4 metal-ion activation and FBXO42/CCDC6 regulation captured largely in preprints","Mendelian disease association in humans not established in this corpus"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[0,2,5,8,14,24]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[2,5,8,14,24,17]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[11,14,22,18]}],"localization":[{"term_id":"GO:0005815","term_label":"microtubule organizing center","supporting_discovery_ids":[1,39]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[1,3]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[1]},{"term_id":"GO:0000228","term_label":"nuclear chromosome","supporting_discovery_ids":[2,3,8]}],"pathway":[{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[2,5,8,9,24]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[11,14,22,28,13]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[3,24,31,16]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[17]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[4,29]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[10]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[15,21,27]}],"complexes":["PP4 holoenzyme (PP4C-PP4R2-PP4R3β)","PP4C-PP4R1 complex","PP4:SMEK1 complex"],"partners":["PPP4R2","PPP4R3B","PPP4R1","SMEK1","KAP1","TBK1","CCDC6","FBXO42"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P60510","full_name":"Serine/threonine-protein phosphatase 4 catalytic subunit","aliases":["Protein phosphatase X","PP-X"],"length_aa":307,"mass_kda":35.1,"function":"Protein phosphatase that is involved in many processes such as microtubule organization at centrosomes, maturation of spliceosomal snRNPs, apoptosis, DNA repair, tumor necrosis factor (TNF)-alpha signaling, activation of c-Jun N-terminal kinase MAPK8, regulation of histone acetylation, DNA damage checkpoint signaling, NF-kappa-B activation and cell migration. The PPP4C-PPP4R1 PP4 complex may play a role in dephosphorylation and regulation of HDAC3. The PPP4C-PPP4R2-PPP4R3A PP4 complex specifically dephosphorylates H2AX phosphorylated on Ser-140 (gamma-H2AX) generated during DNA replication and required for DNA double strand break repair. Dephosphorylates NDEL1 at CDK1 phosphorylation sites and negatively regulates CDK1 activity in interphase (By similarity). In response to DNA damage, catalyzes RPA2 dephosphorylation, an essential step for DNA repair since it allows the efficient RPA2-mediated recruitment of RAD51 to chromatin","subcellular_location":"Cytoplasm; Nucleus; Cytoplasm, cytoskeleton, microtubule organizing center, centrosome","url":"https://www.uniprot.org/uniprotkb/P60510/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/PPP4C","classification":"Common Essential","n_dependent_lines":1171,"n_total_lines":1208,"dependency_fraction":0.9693708609271523},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"SF3B1","stoichiometry":10.0},{"gene":"SF3B4","stoichiometry":10.0},{"gene":"SF3B2","stoichiometry":4.0},{"gene":"SF3B3","stoichiometry":4.0},{"gene":"SF3B5","stoichiometry":4.0},{"gene":"SF3B6","stoichiometry":4.0},{"gene":"MIF","stoichiometry":0.2},{"gene":"SUPT5H","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/PPP4C","total_profiled":1310},"omim":[{"mim_id":"620302","title":"WD REPEAT-CONTAINING PROTEIN 76; WDR76","url":"https://www.omim.org/entry/620302"},{"mim_id":"616885","title":"CALCIUM-REGULATED HEAT-STABLE PROTEIN 1; CARHSP1","url":"https://www.omim.org/entry/616885"},{"mim_id":"616790","title":"PROTEIN PHOSPHATASE 4, REGULATORY SUBUNIT 4; PPP4R4","url":"https://www.omim.org/entry/616790"},{"mim_id":"613822","title":"PROTEIN PHOSPHATASE 4, REGULATORY SUBUNIT 2; PPP4R2","url":"https://www.omim.org/entry/613822"},{"mim_id":"612725","title":"PROTEIN PHOSPHATASE 6, CATALYTIC SUBUNIT; PPP6C","url":"https://www.omim.org/entry/612725"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Plasma membrane","reliability":"Additional"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/PPP4C"},"hgnc":{"alias_symbol":["PP4","PPX"],"prev_symbol":[]},"alphafold":{"accession":"P60510","domains":[{"cath_id":"3.60.21.10","chopping":"20-287","consensus_level":"medium","plddt":97.795,"start":20,"end":287}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P60510","model_url":"https://alphafold.ebi.ac.uk/files/AF-P60510-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P60510-F1-predicted_aligned_error_v6.png","plddt_mean":94.81},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PPP4C","jax_strain_url":"https://www.jax.org/strain/search?query=PPP4C"},"sequence":{"accession":"P60510","fasta_url":"https://rest.uniprot.org/uniprotkb/P60510.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P60510/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P60510"}},"corpus_meta":[{"pmid":"8380170","id":"PMC_8380170","title":"An exopolyphosphatase of Escherichia coli. 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\"method\": \"Baculovirus expression, in vitro phosphatase assays, inhibitor sensitivity assays, co-immunoprecipitation\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro enzymatic characterization with multiple substrates and inhibitors, replicated across labs as foundational paper\",\n      \"pmids\": [\"8384557\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"PPX (PPP4C) localizes intensely to centrosomes at all stages of mitosis except telophase, while also distributed throughout cytoplasm and nucleus; centrosomal staining colocalizes with the human autoantibody #5051 marking pericentriolar material.\",\n      \"method\": \"Immunofluorescence microscopy with two independent antibodies (anti-bacterially expressed PPX and anti-PPX peptide)\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct localization by two independent antibodies, foundational paper replicated in subsequent studies\",\n      \"pmids\": [\"8384557\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"A three-protein PP4 complex containing PP4C, PP4R2, and PP4R3beta specifically dephosphorylates ATR-mediated gamma-H2AX generated during DNA replication; PP4 efficiently dephosphorylates gamma-H2AX within mononucleosomes in vitro without directly altering ATR or checkpoint kinase activity.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown, in vitro dephosphorylation assay with mononucleosomes, cell hypersensitivity assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with mononucleosome substrate, reciprocal co-IP defining complex, replicated by independent lab in same year\",\n      \"pmids\": [\"18614045\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"PP4C contributes to dephosphorylation of gamma-H2AX both at sites of DNA damage and in undamaged chromatin in human cells; depletion of PP4C results in prolonged checkpoint arrest due to persistence of MDC1 at DNA lesion sites.\",\n      \"method\": \"siRNA knockdown, immunofluorescence, checkpoint assays, gamma-H2AX foci analysis\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean KD with defined cellular phenotype (MDC1 persistence, checkpoint arrest), replicated by independent lab in same year\",\n      \"pmids\": [\"18758438\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Drosophila PP4 (ortholog of PPP4C) dephosphorylates Smoothened (Smo) to regulate Hedgehog signaling; RNAi knockdown of PP4 elevates Smo phosphorylation and accumulation, leading to increased Hh signaling. PP4 interaction with Smo is mediated by Cos2, and Hh signaling downregulates the Smo-PP4 interaction.\",\n      \"method\": \"In vivo RNAi screen, epistasis analysis, Co-IP, phosphorylation assays, deletion mapping (aa 626-678 of Smo)\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal functional epistasis, direct interaction mapping, multiple orthogonal approaches in single study\",\n      \"pmids\": [\"19088085\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"A PP4 phosphatase complex dephosphorylates RPA2 (replication protein A subunit 2) to regulate its role in DSB response; PP4R2 mediates the DNA damage-dependent association between RPA2 and PP4C; PP4 efficiently dephosphorylates phospho-RPA2 in vitro; PP4-mediated dephosphorylation of RPA2 is required for efficient RAD51 loading and homologous recombination.\",\n      \"method\": \"Co-immunoprecipitation, in vitro dephosphorylation assay, siRNA knockdown, HR reporter assay, RAD51 foci analysis, phosphomimetic mutant analysis\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution, reciprocal Co-IP, phosphomimetic mutants with defined HR phenotype, multiple orthogonal methods\",\n      \"pmids\": [\"20154705\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Yeast PP4 (Pph3/Psy2) mediates centromere pairing during meiotic prophase by dephosphorylating Zip1 at serine 75, a consensus Mec1 (ATR) site; loss of PP4 leads to persistent Zip1-S75 phosphorylation and blocked centromere pairing; centromere pairing is restored in mec1 mutants, establishing genetic epistasis between Mec1 and PP4 at this step.\",\n      \"method\": \"Genetic epistasis (double mutant analysis), phosphorylation site mutagenesis, chromatin immunofluorescence for centromere pairing\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis with mechanistic substrate identification, multiple orthogonal approaches\",\n      \"pmids\": [\"20951350\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PP4C dephosphorylates the NCC (Na+-Cl- cotransporter) to inhibit its intrinsic transport activity (but not surface trafficking) through a mechanism requiring phosphatase activity and the conserved N-terminal threonine 58 of NCC; PP4 is selectively expressed in the distal nephron including distal convoluted tubule cells.\",\n      \"method\": \"Xenopus oocyte expression system, transport activity assays, phosphatase-dead mutant, NCC Thr58 mutagenesis, immunofluorescence of mouse kidney sections\",\n      \"journal\": \"Canadian journal of physiology and pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional assay in oocyte expression system with mutagenesis, single lab with two orthogonal approaches\",\n      \"pmids\": [\"20962898\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"PP4C/R3beta complex dephosphorylates KAP-1 at S824 (phosphorylated by ATM) and S473 (phosphorylated by CHK2) after ionizing radiation; a PP4C/R3beta complex interacts with KAP-1; phosphorylation of KAP-1 S473 by CHK2 impacts the G2/M checkpoint; PP4-mediated dephosphorylation of KAP-1 S824 is required for repair of heterochromatic DNA lesions.\",\n      \"method\": \"Phosphoproteomic substrate identification screen, Co-IP, siRNA knockdown, phosphomimetic mutants, G2/M checkpoint assays, chromatin remodeling analysis\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — systematic phosphoproteomic substrate identification plus mechanistic follow-up with phosphomimetics and co-IP, multiple orthogonal methods\",\n      \"pmids\": [\"22491012\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"PP4C and regulatory subunit PP4R2 physically interact with KAP1 and dephosphorylate pKAP1-S824 in vitro; PP4C depletion compromises NHEJ-mediated DSB repair; PP4C and KAP1 function in the same epistasis group for NHEJ.\",\n      \"method\": \"Co-IP, in vitro dephosphorylation assay, siRNA knockdown, I-SceI NHEJ reporter assay, epistasis analysis (co-depletion)\",\n      \"journal\": \"Cell cycle (Georgetown, Tex.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro dephosphorylation confirmed, reciprocal Co-IP, genetic epistasis via co-depletion\",\n      \"pmids\": [\"22732494\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"PP4 complex (catalytic subunit Pph3, scaffold Psy2, regulatory subunits Rrd1 and Tip41) is the main Maf1 phosphatase in yeast, required for Maf1 dephosphorylation, nuclear localization, and rapid repression of RNA Pol III; purified PP4 dephosphorylates Maf1 in vitro and PP4 co-precipitates with Maf1.\",\n      \"method\": \"In vitro dephosphorylation assay, co-precipitation, genetic analysis of PP4 subunit mutants, nuclear localization assays, Pol III transcription assays\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro dephosphorylation plus co-precipitation plus genetic dissection of subunit requirements, multiple orthogonal methods\",\n      \"pmids\": [\"22333918\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"PP4 (via PP4R1 regulatory subunit) forms a holoenzyme that bridges the IKK complex and PP4c, directing PP4c to dephosphorylate and inactivate the IKK complex, thereby negatively regulating NF-κB signaling in T lymphocytes.\",\n      \"method\": \"RNAi screen, Co-IP, kinase activity assays, NF-κB reporter assays, T cell activation assays\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP establishing bridging mechanism, functional NF-κB/IKK assays, confirmed in primary cells\",\n      \"pmids\": [\"23084358\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Yeast PP4 (Pph3) physically interacts with the ATR homolog Mec1-Ddc2 complex, mediated by cofactors Psy2 and Ddc2; this interaction was demonstrated biochemically and by FRET in subnuclear repair foci; phosphoproteomic analysis showed 94% of mec1-100-compromised phosphorylation targets on HU are PP4 regulated; PP4 also dephosphorylates a phosphoacceptor site within Mec1 itself.\",\n      \"method\": \"Genetic suppressor screen, E-MAP screen, biochemical interaction assays, FRET microscopy in living cells, phosphoproteomic analysis\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — FRET imaging plus biochemical interaction plus phosphoproteomics, multiple orthogonal approaches, direct physical interaction demonstrated\",\n      \"pmids\": [\"25533186\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"PP4R1 subunit of PP4 interacts with TRAF2 and TRAF6 in a RING finger domain-dependent manner (identified by yeast two-hybrid with TRAF2 as bait); PP4R1 mediates dephosphorylation of TRAF2 Ser11 and inhibits TRAF6 polyubiquitination, thereby inhibiting NF-κB activation.\",\n      \"method\": \"Yeast two-hybrid screen, Co-IP, phosphorylation assays, ubiquitination assays, NF-κB reporter assays, siRNA knockdown\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — yeast two-hybrid plus Co-IP plus functional assays, single lab, multiple orthogonal approaches\",\n      \"pmids\": [\"25134449\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"PP4C dephosphorylates TBK1 at Ser172 upon RNA virus infection, inhibiting TBK1 activation and subsequent IRF3 activation, thereby suppressing type I IFN production; a phosphatase-dead PP4C mutant abolished inhibitory effects; PP4C directly binds TBK1 upon virus infection.\",\n      \"method\": \"Co-IP, in vitro/cellular dephosphorylation assays, phosphatase-dead mutant, siRNA knockdown in macrophages and DCs, viral infection assays, in vivo peritoneal macrophage assays\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct binding demonstrated by Co-IP, phosphatase-dead mutant controls, in vitro dephosphorylation, in vivo validation\",\n      \"pmids\": [\"26363053\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"LCMT-1 is the major carboxyl methyltransferase for PP4C (as well as PP2A and PP6) in mouse embryonic fibroblasts; LCMT-1-dependent methylation differentially regulates PP4 holoenzyme formation, with the PP4R1-containing complex being most dramatically affected by LCMT-1 loss; LCMT-1 knockout MEFs show hyperphosphorylation of HDAC3, a target of the methylation-dependent PP4R1-PP4c complex.\",\n      \"method\": \"Methylation-specific antibodies, BN-PAGE holoenzyme analysis, LCMT-1 knockout MEFs, HDAC3 phosphorylation assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic knockout plus biochemical holoenzyme analysis plus substrate phosphorylation readout, multiple orthogonal methods\",\n      \"pmids\": [\"27507813\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PP4 (via regulatory subunit PPP4R3) recognizes substrates through a conserved FxxP consensus binding motif; X-ray crystallography revealed that FxxP motifs bind to a conserved pocket in PPP4R3; the FxxP motif in cohesin release factor WAPL regulates WAPL phosphorylation and is required for efficient cohesin release.\",\n      \"method\": \"X-ray crystallography, proteomic analysis of PP4 interacting proteins, in silico FxxP motif searches, functional WAPL phosphorylation and cohesin release assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure plus proteomic validation plus functional mutagenesis of motif, multiple orthogonal methods in single study\",\n      \"pmids\": [\"31585692\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PP4C dephosphorylates AMPK in a Ca2+-dependent manner downstream of mitochondrial Ca2+ (MCU); elevated cytosolic Ca2+ (when MCU is deleted) activates PP4 activity, which dephosphorylates AMPK, leading to increased hepatic lipid accumulation; PP4 knockdown or AMPK reconstitution restores lipid clearance in MCU-deleted hepatocytes.\",\n      \"method\": \"Mcu liver-specific knockout mice, CRISPR/Cas9 zebrafish knockout, Ca2+ measurements, PP4 activity assays, AMPK phosphorylation assays, siRNA knockdown, lipid accumulation measurements\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic knockout in two organisms, direct PP4 activity measurement, rescue experiments with PP4 knockdown and active AMPK reconstitution\",\n      \"pmids\": [\"30917323\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PP4C dephosphorylates HDAC3 following peripheral nerve injury, impairing HDAC3 activity and enhancing histone acetylation to promote a regenerative gene expression program; this PP4 activation is calcium-dependent (triggered by peripheral but not central injury); PP4-dependent HDAC3 dephosphorylation discriminates between axonal regeneration competence and failure.\",\n      \"method\": \"Pharmacological screen, in vivo injury models (DRG), calcium imaging, ChIP-seq (H3K9ac), RNA-seq, genetic and pharmacological HDAC3 inhibition, PP4 activity assays\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo genetic/pharmacological manipulation with H3K9ac ChIP-seq readout, multiple orthogonal approaches\",\n      \"pmids\": [\"31268609\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"CDK5 directly phosphorylates PP4R3β (the PP4 regulatory subunit that recognizes 53BP1) in late mitotic phases in non-neuronal cells; CDK5-mediated phosphorylation of PP4R3β is required for PP4R3β to recognize and dephosphorylate 53BP1; without CDK5 activity in mitosis, 53BP1 fails to localize to damaged chromatin in G1.\",\n      \"method\": \"In vitro kinase assays, specific CDK5 inhibition in mitosis, Co-IP of PP4R3β-53BP1, 53BP1 foci assays in G1, phosphomimetic/phosphodeficient mutants\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro kinase reconstitution, phosphomimetic mutant analysis, specific inhibitor controls, defined cellular phenotype\",\n      \"pmids\": [\"31534152\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Drosophila PP4 (Falafel/R3 subunit) EVH1 domain recognizes FxxP and MxPP short linear motifs through a conserved leucine residue (replacing the invariant phenylalanine of canonical EVH1 domains) rather than canonical proline-rich sequences; the Smk-1 domain of Falafel also participates in target-binding.\",\n      \"method\": \"Binding studies, mass spectrometry identification of interactors, site-directed mutagenesis of EVH1 domain residues, structural analysis\",\n      \"journal\": \"Open biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mutagenesis plus MS-based interaction mapping, single lab, consistent with crystallography data from PPP4R3 paper\",\n      \"pmids\": [\"33352067\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"C-terminal leucine methylation of PP4C (catalytic subunit) by LCMT-1 is required for PP4R1-containing and PP4R3β-containing holoenzyme assembly; deletion of the C-terminal leucine faithfully recapitulates loss of methylation; loss of methylation reduces PP4R1 and PP4R3β binding.\",\n      \"method\": \"Mass spectrometry-based proteomics, C-terminal leucine deletion mutants, genome editing, BN-PAGE holoenzyme analysis\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — mass spectrometry proteomics with genome editing plus mutant analysis, multiple orthogonal methods, extends prior LCMT-1 findings\",\n      \"pmids\": [\"34845248\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PP4C dephosphorylates the sNASP phosphoprotein to terminate TLR4-induced TRAF6 activation; PP4 is directly recruited by phosphorylated sNASP; this PP4-mediated negative regulation reduces pro-inflammatory cytokine production; in vivo PP4 overexpression improves survival in a sepsis model.\",\n      \"method\": \"Co-IP, ectopic expression of PP4, siRNA knockdown, cytokine production assays, in vivo adenovirus-mediated PP4 expression in sepsis model\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct recruitment demonstrated by Co-IP, in vitro and in vivo validation, phosphatase-dead mutant controls used\",\n      \"pmids\": [\"34789577\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Deletion of PPP4C in mouse causes male-specific infertility characterized by oligoasthenoteratospermia (OAT): sperm tail bending, low sperm count, poor motility, and defective cytoplasm removal during spermiogenesis.\",\n      \"method\": \"Conditional knockout mouse model, light microscopy, transmission electron microscopy of spermiogenesis\",\n      \"journal\": \"Molecular human reproduction\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — clean knockout with defined morphological phenotype, single lab, phenotype described but direct substrate not identified\",\n      \"pmids\": [\"33543287\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"PPP4C dephosphorylates PLK1 at Ser137, negatively regulating PLK1 activity during DNA DSB response in early embryos; PPP4C depletion causes sustained PLK1 activity, inhibits CHK2, upregulates CDK1 activation, and results in inefficient RAD51 loading, impairing homologous recombination.\",\n      \"method\": \"PPP4C conditional knockout in oocytes/embryos, in vitro dephosphorylation assay, PLK1 inhibition experiments, RAD51 foci analysis, CDK1/CHK2 activity assays\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro dephosphorylation of PLK1-S137, genetic knockout with defined molecular phenotype, epistatic rescue by PLK1 inhibition\",\n      \"pmids\": [\"35546066\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CCDC6 (when un-phosphorylated at T427) forms a complex with PP4c that sequesters PP4c activity; the CCDC6-PP4 interaction and PP4 regulation of gamma-H2AX is mediated via PP4R3α; functional or physical loss of CCDC6 enhances PP4c complex activity, causing BRCAness and PARP inhibitor sensitivity in ovarian cancer cells.\",\n      \"method\": \"Co-IP, phosphomimetic mutants (T427D), siRNA knockdown of CCDC6 and PP4R3α, gamma-H2AX assays, HR reporter assays, PARP inhibitor sensitivity assays\",\n      \"journal\": \"Journal of experimental & clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus phosphomimetic analysis plus functional HR assays, single lab, multiple methods\",\n      \"pmids\": [\"35964058\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SIRT1 interacts with PP4c and promotes its inhibition by deacetylating the WH1 domain of regulatory subunits PP4R3α/β upon DNA damage; SIRT1-mediated inhibition of PP4 regulates gamma-H2AX and RPA2 phosphorylation; SIRT1-deficient cells show decreased gamma-H2AX levels consistent with unopposed PP4 activity.\",\n      \"method\": \"Co-IP of SIRT1 with PP4c, deacetylation assays, gamma-H2AX and RPA2 phosphorylation analysis in SIRT1-deficient cells\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP demonstrating SIRT1-PP4c interaction, functional assays linking SIRT1 deacetylase activity to PP4 substrate phosphorylation, single lab\",\n      \"pmids\": [\"37309898\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"FBXO42 ubiquitinates the PP4 complex to govern the assembly of regulatory and catalytic subunits, with the net effect of restraining PP4 phosphatase activity; FBXO42 depletion unleashes PP4 activity with broad cellular effects on cell cycle, DNA damage response, and glioma stem cell survival.\",\n      \"method\": \"Mass spectrometry proteomics, ubiquitination assays, PP4 complex assembly analysis, FBXO42 depletion functional assays\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — MS-based proteomics, direct ubiquitination assays, holoenzyme assembly analysis, functional rescue experiments\",\n      \"pmids\": [\"41484364\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"PP4 directly dephosphorylates TBK1 in macrophages, inactivating IRF3 and suppressing macrophage-derived CCL5 production during sepsis; wild-type PP4 (but not phosphatase-dead mutant) reduces LPS-mediated CCR5 expression in neutrophils, limiting ROS production and NETs formation; myeloid-specific PP4 KO mice show increased sepsis susceptibility.\",\n      \"method\": \"Myeloid-specific PP4 knockout mice (CLP model), in vitro dephosphorylation assay (TBK1), phosphatase-dead mutant, cytokine assays, NETosis assays\",\n      \"journal\": \"Redox biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — myeloid-specific KO with defined phenotype, phosphatase-dead mutant controls, single lab with in vitro and in vivo approaches\",\n      \"pmids\": [\"41723906\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"PPP4C interacts with MST4 kinase and reduces its activity, thereby enabling YAP1 dephosphorylation and nuclear accumulation; PPP4C-mediated MST4 degradation promotes NSCLC cell growth and immunosuppression by restoring YAP1 activity through the MAP4K2-LATS1/2 cascade.\",\n      \"method\": \"Co-IP of PPP4C with MST4, gain/loss-of-function experiments, YAP1 phosphorylation assays, NK cell co-culture assays, in vivo syngeneic tumor models\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus functional pathway assays plus in vivo validation, single lab, mechanism involves PPP4C-MST4 direct interaction\",\n      \"pmids\": [\"41690452\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"AAV Rep proteins engage the SMEK1 regulatory subunit of the PP4:SMEK1 complex to interfere with substrate recruitment, preventing KAP1-S824 and RPA2-S4/8/33 dephosphorylation; KAP1 interaction with SMEK1 is mediated by a MAPP short linear motif binding the SMEK1 EVH1 domain.\",\n      \"method\": \"Binding studies, Co-IP, substrate phosphorylation assays (KAP1-S824, RPA2), SLiM motif mapping, AAV replication assays\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding studies plus functional substrate phosphorylation assays plus SLiM motif validation, single lab\",\n      \"pmids\": [\"41805761\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Targeted suppression of PP4C (but not PP1C, PP2AC, or PP5C) alone is sufficient to mimic many cellular actions of fostriecin, inducing apoptosis in tetraploid cells following mitotic slippage; PP4C is specifically required to prevent mitotic slippage/apoptosis.\",\n      \"method\": \"Antisense oligonucleotides specifically targeting PP4C, high-content time-lapse live imaging, comparison with fostriecin treatment\",\n      \"journal\": \"Molecular cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — specific antisense knockdown of individual phosphatases with live imaging readout, defines PP4C-specific mitotic role\",\n      \"pmids\": [\"23671329\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"PP4 is required for pro-B cell development and immunoglobulin VDJ recombination; PP4-deficient pro-B cells show impaired Ig DJ(H) recombination, increased DNA double-strand breaks at Ig loci, and accumulate in G1 with excessive DNA damage; normal B cell development is rescued by transgenic Ig expression.\",\n      \"method\": \"B cell-specific pp4 knockout mice, flow cytometry, V(D)J recombination analysis, gamma-H2AX foci, cell cycle analysis, transgenic rescue\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean B cell-specific KO with defined developmental phenotype and transgenic rescue, single lab\",\n      \"pmids\": [\"23874770\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"PP4 is required for germinal center formation and class switch recombination in B cells; PP4-deficient mature B cells show impaired proliferation, reduced Ig class switching efficiency, failure to form germinal centers in vivo, impaired CD40-mediated MAPK activation, and abnormal IgM-mediated NF-κB activation.\",\n      \"method\": \"CD23-cre conditional PP4 knockout mice, antigen immunization, flow cytometry for GC B cells, CSR assays in vitro, MAPK/NF-κB activation assays\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO with defined immunological phenotype and signaling readouts, single lab\",\n      \"pmids\": [\"25215539\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Co-transfection of PP4 with JNK-1 in prostate cancer cell lines PC-3 and LNCaP significantly increases JNK-1 activity following EGF or cisplatin stimulation, and this is associated with increased c-Jun/AP-1 and EGR-1 activities; PP4 appears to positively regulate JNK-1 stability/activity.\",\n      \"method\": \"Co-transfection assays, JNK-1 activity assays, AP-1/EGR-1 reporter assays\",\n      \"journal\": \"Biological research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single co-transfection approach, no direct dephosphorylation assay; mechanism of PP4 effect on JNK-1 is indirect/unclear\",\n      \"pmids\": [\"16238095\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Fission yeast PP4 co-immunoprecipitates with Wpl1 and cohesin; PP4-dependent dephosphorylation of Rad21 (cohesin kleisin) promotes cohesin release from DNA by Wpl1; phosphomimetic alleles of Rad21 at the identified PP4-regulated sites dampen Wpl1 anti-cohesion activity.\",\n      \"method\": \"Genetic screen, Co-IP of PP4 with Wpl1 and cohesin, phosphomimetic/alanine Rad21 mutants, cohesion assays\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus phosphomimetic analysis plus genetic screen, single lab, defines PP4 role in cohesin regulation via Rad21 dephosphorylation\",\n      \"pmids\": [\"28438891\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PP4 phosphatase (via Psy2 subunit) dephosphorylates Rad53 during DSB repair to relieve Rad9-mediated inhibition of the Sgs1/Dna2 exonuclease complex, thereby stimulating DNA end resection; PP4-dependent Rad53 dephosphorylation is required for efficient single-strand annealing repair.\",\n      \"method\": \"Yeast genetics, Rad53 phosphorylation assays, resection assays, SSA repair assay, epistasis via Rad53 hyperphosphorylation mutants\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — yeast genetic epistasis with defined molecular mechanism (Rad53→Rad9→Sgs1/Dna2), functional resection assays, single lab\",\n      \"pmids\": [\"31544936\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CYB5R4 is an evolutionarily conserved activator of PP4 (and PP6 but not PP2A); heme binding is essential for CYB5R4 function; CYB5R4 activates PP4 by reducing the metal ions in the PP4 active site; CYB5R4-mediated activation of PP4 is critical for cell viability during DNA damage-inducing oxidative stress conditions.\",\n      \"method\": \"Genome-wide CRISPR KO and base editor screens, biochemical PP4 activity assays, heme-binding mutant analysis, cell viability assays under DNA damage/oxidative stress\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — systematic CRISPR screen plus direct activity assays plus mechanistic follow-up with heme-binding mutants; preprint, not yet peer-reviewed\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FBXO42 binds PPP4C, promotes its ubiquitination, and negatively regulates PPP4C expression; aberrant PPP4C expression is a major driver of cell death in FBXO42-essential neuroblastoma cells; CCDC6 independently interacts with PPP4C without affecting its ubiquitination; PPP4C knockdown reduces FBXO42-CCDC6 interactions.\",\n      \"method\": \"Mass spectrometry proteomics, ubiquitination assays, CRISPR KO screen (synthetic lethality), gene knockdown rescue experiments, Co-IP\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — MS-based proteomics plus ubiquitination assays plus functional rescue, preprint extending peer-reviewed FBXO42 paper\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Drosophila PP4 (Pp4) is required for centrosome asymmetry establishment in neural stem cells; Pp4 loss causes two inactive centrioles in interphase and failure to correctly transfer Centrobin (Cnb) from mother to daughter centriole in mitosis; phosphomimetic Centrobin fails to relocalize correctly; PP4 may dephosphorylate both Centrobin and gamma-Tubulin.\",\n      \"method\": \"In vivo live cell imaging, superresolution imaging, Pp4 mutant analysis, phosphomimetic Centrobin constructs, centrosome asymmetry assays\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo live imaging with defined centrosome phenotype plus phosphomimetic validation, preprint not yet peer-reviewed\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"PPP4C (PP4, PPX) is an evolutionarily conserved serine/threonine phosphatase that functions as the catalytic core of trimeric holoenzymes (assembled via C-terminal leucine methylation by LCMT-1 and regulatory subunits including PP4R1, PP4R2, PP4R3α/β/SMEK1), which achieve substrate specificity through FxxP/MxPP short linear motif recognition by the R3 subunit EVH1 domain; PP4C dephosphorylates key substrates including gamma-H2AX, RPA2, KAP1, 53BP1, PLK1, TBK1, AMPK, Maf1, Smo, NCC, and HDAC3, positioning it as a master regulator of the DNA damage response (controlling checkpoint recovery, homologous recombination, and NHEJ), innate immune signaling (negatively regulating TBK1/IFN and IKK/NF-κB pathways), centrosome biology, RNA Pol III transcription repression, and lipid/energy metabolism; PP4C activity is itself regulated by SIRT1-mediated deacetylation of its regulatory subunits, CDK5-mediated phosphorylation of PP4R3β, FBXO42-mediated ubiquitination of the holoenzyme, CYB5R4-mediated reduction of active-site metal ions, and CCDC6-dependent sequestration.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PPP4C (PP4, PPX) is an evolutionarily conserved okadaic-acid/microcystin-sensitive serine/threonine phosphatase, distinct from PP2A in that it does not bind the PP2A 65 kDa regulatory subunit, that acts as the catalytic core of multimeric holoenzymes to control the DNA damage response, innate immune signaling, and cell-cycle/developmental processes [#0]. Holoenzyme assembly and substrate selection are coupled: C-terminal leucine methylation of the catalytic subunit by LCMT-1 is required to build PP4R1- and PP4R3\\u03b2-containing complexes [#15, #21], and the R3-type regulatory subunits recognize substrates through FxxP/MxPP short linear motifs that dock into a conserved pocket of the regulatory subunit's EVH1/WH1 domain [#16, #20]. As a master phosphatase in the DNA damage response, PP4 dephosphorylates \\u03b3-H2AX within nucleosomes via a PP4C\\u2013PP4R2\\u2013PP4R3\\u03b2 complex to permit checkpoint recovery [#2, #3], dephosphorylates RPA2 to license RAD51 loading and homologous recombination [#5], removes ATM/CHK2 marks from KAP-1 (S824/S473) to enable NHEJ and heterochromatic repair [#8, #9], and dephosphorylates PLK1-S137 to coordinate the DSB response in early embryos [#24]. In innate immunity PP4 acts as a negative regulator, directly dephosphorylating TBK1-Ser172 to limit IRF3/type I IFN output [#14, #28] and inactivating the IKK complex and TRAF/NF-\\u03baB signaling through its PP4R1 subunit [#11, #13]. PP4 additionally functions at centrosomes [#1], represses RNA Pol III transcription by dephosphorylating Maf1 [#10], controls cohesin release via FxxP-dependent dephosphorylation of WAPL/Rad21 [#16, #35], and regulates metabolic and chromatin signaling through dephosphorylation of AMPK [#17] and HDAC3 [#15, #18]. PP4 activity is held in check by multiple inputs: LCMT-1 methylation and CDK5 phosphorylation of PP4R3\\u03b2 gate holoenzyme function [#19, #21], FBXO42-mediated ubiquitination restrains complex assembly [#27], SIRT1 deacetylation of the R3 WH1 domain inhibits the phosphatase after DNA damage [#26], and CCDC6 sequesters the complex [#25]. Loss of PPP4C causes male-specific oligoasthenoteratospermia in mice and is required for B-cell V(D)J and class-switch recombination [#23, #32, #33].\",\n  \"teleology\": [\n    {\n      \"year\": 1993,\n      \"claim\": \"Established PPP4C as a distinct catalytic phosphatase: it shares PP2A-like substrate and inhibitor profiles yet does not bind the PP2A regulatory subunit, defining it as a separate enzyme, and localized it to centrosomes throughout mitosis.\",\n      \"evidence\": \"Baculovirus expression with in vitro phosphatase and inhibitor assays, plus dual-antibody immunofluorescence\",\n      \"pmids\": [\"8384557\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No regulatory subunits or physiological substrates identified at this stage\", \"Functional role of centrosomal localization not defined\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Resolved how PP4 acts in the DNA damage response by showing a defined PP4C\\u2013PP4R2\\u2013PP4R3\\u03b2 complex dephosphorylates \\u03b3-H2AX in nucleosomes to drive checkpoint recovery.\",\n      \"evidence\": \"Reciprocal Co-IP, siRNA knockdown, in vitro mononucleosome dephosphorylation, and \\u03b3-H2AX/MDC1 foci and checkpoint assays in human cells\",\n      \"pmids\": [\"18614045\", \"18758438\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish how the complex is targeted to specific chromatin sites\", \"Other DDR substrates not yet defined\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Expanded PP4's DDR role to homologous recombination and uncovered conserved substrate logic across kingdoms, including RPA2, yeast Zip1, and the NCC cotransporter.\",\n      \"evidence\": \"In vitro dephosphorylation, HR reporter and RAD51 foci assays, genetic epistasis in yeast meiosis, and Xenopus oocyte transport assays\",\n      \"pmids\": [\"20154705\", \"20951350\", \"20962898\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"NCC regulation rests on a single lab and oocyte system\", \"How PP4R2 confers damage-dependent RPA2 recognition not structurally defined\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Defined PP4 as both a DDR effector on KAP-1 and a negative regulator of innate immune/NF-\\u03baB signaling, showing regulatory subunits direct catalytic activity to distinct pathways.\",\n      \"evidence\": \"Phosphoproteomic substrate screen, in vitro dephosphorylation, NHEJ reporter epistasis, and PP4R1-bridged IKK/TRAF NF-\\u03baB assays in T and other cells; plus yeast Maf1/Pol III repression\",\n      \"pmids\": [\"22491012\", \"22732494\", \"23084358\", \"22333918\", \"25134449\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"TRAF2/TRAF6 axis from single lab\", \"How a single catalytic subunit is partitioned between immune and DDR roles not resolved\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Connected PP4 directly to the apical ATR/Mec1 machinery and to lymphocyte development, showing PP4 governs both the kinase signal and the biological programs that depend on it.\",\n      \"evidence\": \"FRET and biochemical interaction with Mec1-Ddc2 plus phosphoproteomics in yeast; B-cell-specific knockouts with V(D)J/CSR and germinal center phenotypes\",\n      \"pmids\": [\"25533186\", \"23874770\", \"25215539\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mammalian PP4\\u2013ATR physical interaction not directly demonstrated\", \"B-cell phenotypes not tied to a single PP4 substrate\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Pinpointed TBK1-Ser172 as a direct PP4C substrate, mechanistically explaining PP4's suppression of type I IFN during viral infection.\",\n      \"evidence\": \"Co-IP, in vitro/cellular dephosphorylation, phosphatase-dead mutant, and viral infection assays in macrophages/DCs with in vivo validation\",\n      \"pmids\": [\"26363053\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which regulatory subunit recruits PP4C to TBK1 not defined here\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Identified LCMT-1 carboxyl methylation as the switch controlling PP4 holoenzyme composition and revealed HDAC3 as a methylation-dependent PP4R1 substrate.\",\n      \"evidence\": \"LCMT-1 knockout MEFs, methylation-specific antibodies, BN-PAGE holoenzyme analysis, and HDAC3 phosphorylation readout\",\n      \"pmids\": [\"27507813\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Quantitative contribution of methylation to each holoenzyme not fully mapped\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Established the structural basis of PP4 substrate selectivity (FxxP/MxPP SLiM recognition by the R3 EVH1 domain) and added cohesin regulation, AMPK/metabolism, HDAC3-driven axon regeneration, and CDK5-gated 53BP1 recruitment to its functional repertoire.\",\n      \"evidence\": \"X-ray crystallography and proteomics of FxxP recognition; WAPL/cohesin, AMPK (MCU knockout mice/zebrafish), HDAC3 ChIP-seq in nerve injury, and CDK5 kinase/phosphomimetic 53BP1 assays\",\n      \"pmids\": [\"31585692\", \"33352067\", \"30917323\", \"31268609\", \"31534152\", \"31544936\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How a single SLiM pocket discriminates among hundreds of FxxP-bearing proteins unclear\", \"Drosophila EVH1 leucine-substitution finding is Medium confidence/single lab\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Confirmed the C-terminal leucine as the methylation site governing PP4R1/PP4R3\\u03b2 holoenzyme assembly and added sNASP-directed termination of TLR4/TRAF6 signaling and a spermiogenesis requirement.\",\n      \"evidence\": \"MS proteomics with C-terminal leucine deletion mutants and BN-PAGE; sNASP Co-IP with in vivo sepsis model; conditional knockout mouse spermiogenesis analysis\",\n      \"pmids\": [\"34845248\", \"34789577\", \"33543287\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct PP4 substrate underlying the infertility phenotype not identified\", \"sNASP recruitment mechanism rests on single lab\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identified PLK1-Ser137 as a PP4C substrate coordinating the embryonic DSB response and revealed CCDC6 as a sequestering inhibitor whose loss confers BRCAness.\",\n      \"evidence\": \"Conditional knockout in oocytes/embryos with in vitro PLK1 dephosphorylation and CHK2/CDK1 readouts; CCDC6 Co-IP, phosphomimetics, and PARP-inhibitor sensitivity assays\",\n      \"pmids\": [\"35546066\", \"35964058\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"CCDC6 sequestration mechanism from single lab\", \"Whether PLK1-S137 regulation generalizes beyond early embryos untested\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Added a post-translational inhibitory input by showing SIRT1 deacetylates the R3 WH1 domain to restrain PP4 activity on \\u03b3-H2AX and RPA2 after DNA damage.\",\n      \"evidence\": \"Co-IP, deacetylation assays, and \\u03b3-H2AX/RPA2 phosphorylation analysis in SIRT1-deficient cells\",\n      \"pmids\": [\"37309898\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; specific acetyl-lysines and their direct effect on substrate docking not fully defined\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Established FBXO42 ubiquitination as a regulator of PP4 holoenzyme assembly and extended PP4's roles to YAP1/Hippo signaling in cancer and macrophage/neutrophil control during sepsis.\",\n      \"evidence\": \"MS proteomics and ubiquitination assays (glioma); PPP4C\\u2013MST4 Co-IP and YAP1 assays with syngeneic tumors; myeloid-specific PP4 knockout sepsis models with TBK1 dephosphorylation\",\n      \"pmids\": [\"41484364\", \"41690452\", \"41723906\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"MST4/YAP1 and FBXO42 axes each from single labs\", \"Direct vs indirect PP4 effects on YAP1 not fully separated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How a single catalytic subunit achieves pathway-specific substrate selection across DDR, immune, metabolic, and developmental programs in vivo, and how the converging regulatory inputs (methylation, ubiquitination, deacetylation, metal-ion reduction, sequestration) are integrated, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified structural model linking SLiM recognition to substrate-specific outcomes\", \"CYB5R4 metal-ion activation and FBXO42/CCDC6 regulation captured largely in preprints\", \"Mendelian disease association in humans not established in this corpus\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 2, 5, 8, 14, 24]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [2, 5, 8, 14, 24, 17]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [11, 14, 22, 18]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005815\", \"supporting_discovery_ids\": [1, 39]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [1, 3]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0000228\", \"supporting_discovery_ids\": [2, 3, 8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [2, 5, 8, 9, 24]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [11, 14, 22, 28, 13]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [3, 24, 31, 16]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [17]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [4, 29]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [10]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [15, 21, 27]}\n    ],\n    \"complexes\": [\n      \"PP4 holoenzyme (PP4C-PP4R2-PP4R3\\u03b2)\",\n      \"PP4C-PP4R1 complex\",\n      \"PP4:SMEK1 complex\"\n    ],\n    \"partners\": [\n      \"PPP4R2\",\n      \"PPP4R3B\",\n      \"PPP4R1\",\n      \"SMEK1\",\n      \"KAP1\",\n      \"TBK1\",\n      \"CCDC6\",\n      \"FBXO42\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":7,"faith_pct":85.71428571428571}}