{"gene":"PPP1R14B","run_date":"2026-06-10T06:43:35","timeline":{"discoveries":[{"year":2002,"finding":"ILK phosphorylates PHI-1 (PPP1R14B) at Thr57, the critical inhibitory site; Thr57Ala mutation eliminates phosphorylation by ILK; thiophosphorylated PHI-1 inhibits myosin light-chain phosphatase (MLCP) activity and induces Ca2+ sensitization of smooth-muscle contraction, whereas the Thr57Ala mutant does not.","method":"In-gel kinase assay, solution phosphorylation assay, phosphopeptide mapping, phospho-amino acid analysis, phospho-specific immunoblotting, site-directed mutagenesis, MLCP activity assay, demembranated smooth-muscle contraction assay","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with mutagenesis (Thr57Ala) and direct functional readout (MLCP inhibition, muscle contraction), multiple orthogonal methods in one rigorous study","pmids":["12144526"],"is_preprint":false},{"year":2004,"finding":"PHI-1 (PPP1R14B) localizes juxtamembrane in distinct foci along the plasma membrane of smooth muscle cells (distinct from diffuse CPI-17 distribution), as determined by confocal and electron microscopy; first detected in embryonic heart at E10 and later in smooth muscle and endothelial cells of adult tissues.","method":"Immunohistochemistry, confocal microscopy, electron microscopy, tissue fractionation","journal":"Histochemistry and cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization by two orthogonal microscopy methods (confocal + electron microscopy), single lab","pmids":["15083373"],"is_preprint":false},{"year":2004,"finding":"Knockdown of PHI-1 (PPP1R14B) by siRNA reduced HeLa cell migration rate by ~45%, caused an elongated phenotype, and specifically impaired retraction of the trailing edge during migration without affecting protrusive activity; PHI-1 was concentrated at the trailing edge of migrating endothelial cells.","method":"siRNA knockdown, wound-healing migration assay, time-lapse microscopy, cell spreading/replating assay, immunostaining","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean KD with specific cellular phenotype and localization data, single lab, multiple assays","pmids":["15522888"],"is_preprint":false},{"year":2005,"finding":"In intact vascular smooth muscle cells, agonist stimulation (angiotensin II, thrombin, U-46619) induces PHI-1 (PPP1R14B) phosphorylation; this phosphorylation is selectively mediated by PKC (blocked by GF-109203X or PKC downregulation, induced by PMA), distinct from ROCK-dependent CPI-17 phosphorylation.","method":"2D-PAGE, immunoblot with phospho-specific PHI-1 antibody, pharmacological inhibitors (Y-27632, H-1152, GF-109203X), constitutively active RhoA expression, PMA stimulation in primary rat aortic VSMCs","journal":"American journal of physiology. Cell physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple pharmacological and genetic perturbations in primary cells with phospho-specific detection, single lab","pmids":["16267107"],"is_preprint":false},{"year":2005,"finding":"In chicken smooth muscle, G-protein stimulation via Rho-kinase leads to PHI-1 (PPP1R14B) phosphorylation (inhibitable by both Y-27632 and GF-109203X), correlating with increased myosin light chain phosphorylation; PHI-1 appears to act as a functional CPI-17 analog in this tissue where CPI-17 is absent.","method":"Western blot, pharmacological inhibitors (Y-27632, GF109203X), GTPγS stimulation, myosin light chain phosphorylation assay","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological dissection in intact smooth muscle tissue with multiple inhibitors, single lab","pmids":["16081075"],"is_preprint":false},{"year":2006,"finding":"Phosphorylated PHI-1 (P-PHI-1), but not unphosphorylated PHI-1, increases MLC20 phosphorylation and force in avian smooth muscle at constant [Ca2+]; phosphorylation of PHI-1 increases its direct interaction with the PP1 catalytic subunit (PP1c), and microcystin reduces this binding, indicating PHI-1 inhibits myosin light chain phosphatase by interacting with the active site of PP1c.","method":"Skinned smooth muscle fiber contractility assay, MLC20 phosphorylation assay, binding assay (PHI-1 vs PP1c), microcystin competition","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 1-2 / Moderate — direct binding assay between phospho-PHI-1 and PP1c with functional contractility readout, single lab, multiple orthogonal methods","pmids":["17022978"],"is_preprint":false},{"year":2020,"finding":"The PHIN (phosphatase holoenzyme inhibitory) domain, not the N- or C-termini, encodes the specificity difference between Cpi-17 (potent myosin phosphatase inhibitor) and Phi-1 (PPP1R14B; weak myosin phosphatase inhibitory activity); Phi-1 paralogs in zebrafish display weak myosin phosphatase inhibitory activity in vitro and do not alter myosin phosphorylation in cells, and cannot rescue Cpi-17 knockdown.","method":"In vitro phosphatase inhibition assay, cellular myosin phosphorylation assay, deletion and chimeric protein analysis, zebrafish knockdown rescue experiments","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 1-2 / Moderate — domain dissection with in vitro and cellular assays plus rescue genetics, single lab with multiple orthogonal approaches","pmids":["32784920"],"is_preprint":false},{"year":2023,"finding":"PPP1R14B is degraded via the ubiquitin-proteasome pathway; RPS27A recruits deubiquitinase USP9X to deubiquitinate and stabilize PPP1R14B. PPP1R14B in turn maintains phosphorylation and protein stability of STMN1 in a manner dependent on PP1 catalytic subunits α and γ, thereby decreasing α-tubulin acetylation and microtubule stability to promote paclitaxel resistance; rescue by wild-type but not phosphorylation-deficient STMN1 confirmed the mechanism.","method":"Co-IP, ubiquitination assay, siRNA knockdown, gain/loss-of-function, western blot, xenograft tumor model, microtubule stability assay, phosphorylation-deficient STMN1 rescue experiment","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP, ubiquitination assay, and phospho-mutant rescue in vitro and in vivo, single lab, multiple orthogonal methods","pmids":["36484700"],"is_preprint":false},{"year":2023,"finding":"PHI-1 (PPP1R14B) knockdown in HEK293 cells causes a 15-fold increase in ERK1/2 phosphorylation attributable to elevated Raf-1 protein levels (not Ras or B-Raf); PHI-1 knockdown stabilizes Raf-1 protein without affecting Raf-1 mRNA; ectopic PHI-1 overexpression suppresses Raf-1 protein in an inhibitory-potency-dependent manner; PP1 inhibition with tautomycin mimics PHI-1 function to reduce Raf-1, establishing a PHI-1–PP1 axis that governs Raf-1 proteostasis.","method":"siRNA knockdown, ectopic overexpression, western blot (ERK1/2, Raf-1, B-Raf, Ras), RT-PCR for Raf-1 mRNA, tautomycin PP1 inhibition assay, EGF stimulation/MEK pathway assay","journal":"Biomolecules","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — bidirectional perturbation (KD and OE) with pharmacological PP1 inhibitor corroboration, single lab, multiple orthogonal methods","pmids":["38136612"],"is_preprint":false},{"year":2024,"finding":"PPP1R14B maintains the protein stability and phosphorylation of RPS6KA1 (RSK1) and positively regulates activation of the AKT/NF-κB pathway in hepatocellular carcinoma cells; rescue by wild-type but not phosphorylation-deficient RPS6KA1 confirmed the mechanism.","method":"siRNA knockdown, ectopic overexpression, western blot, Co-IP, phospho-mutant rescue experiment, xenograft model","journal":"Biochimica et biophysica acta. Molecular cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, phospho-mutant rescue, bidirectional perturbation, single lab","pmids":["39216602"],"is_preprint":false},{"year":2025,"finding":"PPP1R14B regulates androgen receptor (AR) expression through the JAK2/STAT3 pathway and forms a positive feedback loop with STAT3; PPP1R14B knockdown reduces AR levels and sensitizes prostate cancer cells to enzalutamide, while overexpression has the opposite effect.","method":"siRNA knockdown, ectopic overexpression, western blot (JAK2, STAT3, AR), cell proliferation/migration/invasion assays, pharmacological STAT3 inhibition","journal":"Cellular signalling","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, mechanism inferred from pathway inhibitor and KD/OE without direct binding or epistasis experiments","pmids":["41067365"],"is_preprint":false},{"year":2026,"finding":"Astragaloside IV directly binds PPP1R14B (KD = 4.88 μM by SPR and CETSA), inducing its ubiquitin-proteasomal degradation; PPP1R14B depletion inhibits Wnt/β-catenin signaling via the AKT/GSK-3β axis and induces mitochondrial ROS, relieving CX3CL1 repression and promoting CD8+ T cell recruitment.","method":"Molecular docking, surface plasmon resonance (SPR), cellular thermal shift assay (CETSA), ubiquitination assay, ROS analysis, T cell co-culture, syngeneic mouse model with anti-PD-1","journal":"Phytomedicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct binding validated by SPR and CETSA (two orthogonal biophysical methods), plus mechanistic downstream readouts, single lab","pmids":["41950731"],"is_preprint":false}],"current_model":"PPP1R14B (PHI-1) is a phosphorylation-dependent inhibitor of protein phosphatase-1 (PP1): when phosphorylated at Thr57 by PKC, ILK, or Rho kinase, it binds and inhibits the PP1 catalytic subunit at its active site, thereby increasing myosin light-chain phosphorylation and promoting Ca2+-sensitized smooth muscle contraction; in addition, PHI-1 localizes to the juxtamembrane/trailing edge of migrating cells where it regulates retraction, stabilizes substrates including STMN1 and Raf-1 via the PP1 axis, and modulates oncogenic signaling (AKT/NF-κB, JAK2/STAT3/AR) in cancer contexts, with its own stability controlled by RPS27A/USP9X-mediated deubiquitination."},"narrative":{"mechanistic_narrative":"PPP1R14B (PHI-1) is a phosphorylation-dependent inhibitor of protein phosphatase-1 (PP1) that couples upstream kinase signaling to PP1-controlled substrate phosphorylation and proteostasis [PMID:12144526, PMID:17022978]. Phosphorylation at Thr57 — by ILK in vitro and by PKC in intact vascular smooth muscle — converts PHI-1 into an active inhibitor that binds the PP1 catalytic subunit at its active site, inhibiting myosin light-chain phosphatase and producing Ca2+-sensitized smooth-muscle contraction [PMID:12144526, PMID:16267107, PMID:17022978]. Its inhibitory potency is encoded by the PHIN domain and is intrinsically weaker than that of its paralog CPI-17, accounting for its distinct functional behavior [PMID:32784920]. In migrating cells PHI-1 concentrates at juxtamembrane foci and the trailing edge, where it is specifically required for retraction during migration [PMID:15083373, PMID:15522888]. Through the PP1 axis, PHI-1 governs the stability and phosphorylation state of downstream substrates: it stabilizes Raf-1 protein to restrain ERK signaling [PMID:38136612], and in cancer contexts maintains phospho-STMN1 to limit microtubule stability and drive paclitaxel resistance [PMID:36484700], sustains RPS6KA1 to activate AKT/NF-κB signaling in hepatocellular carcinoma [PMID:39216602], and supports Wnt/β-catenin signaling via the AKT/GSK-3β axis [PMID:41950731]. PHI-1's own abundance is controlled by ubiquitin-proteasomal turnover, antagonized by RPS27A-recruited USP9X-mediated deubiquitination [PMID:36484700].","teleology":[{"year":2002,"claim":"Established that PHI-1 is an inhibitory phosphoprotein and identified Thr57 as the kinase-controlled switch that activates its inhibition of myosin light-chain phosphatase to sensitize contraction.","evidence":"In vitro ILK phosphorylation with Thr57Ala mutagenesis, MLCP activity assay, and demembranated smooth-muscle contraction assay","pmids":["12144526"],"confidence":"High","gaps":["Did not establish which kinase phosphorylates Thr57 in intact cells","No structural detail of the PHI-1–PP1c interface"]},{"year":2004,"claim":"Defined the subcellular distribution of PHI-1, showing it occupies discrete juxtamembrane foci distinct from the diffuse CPI-17 pattern.","evidence":"Immunohistochemistry, confocal and electron microscopy, tissue fractionation in smooth muscle and embryonic tissues","pmids":["15083373"],"confidence":"Medium","gaps":["Molecular basis of juxtamembrane targeting unknown","Functional consequence of focal localization not tested here"]},{"year":2004,"claim":"Linked PHI-1 to a non-muscle process by showing it is required for trailing-edge retraction during cell migration, connecting its localization to a specific motility step.","evidence":"siRNA knockdown, wound-healing and time-lapse migration assays, immunostaining in HeLa and endothelial cells","pmids":["15522888"],"confidence":"Medium","gaps":["PP1 substrate mediating retraction not identified","Phosphorylation dependence of the migration role not tested"]},{"year":2005,"claim":"Identified the physiological kinase input, showing agonist-induced PHI-1 phosphorylation in vascular smooth muscle is PKC-dependent and pathway-distinct from ROCK-driven CPI-17 phosphorylation.","evidence":"Phospho-specific immunoblot with PKC/ROCK inhibitors and PMA in primary rat aortic VSMCs; pharmacological dissection in chicken smooth muscle","pmids":["16267107","16081075"],"confidence":"Medium","gaps":["Relative contribution of PKC vs Rho-kinase varies by tissue and is unresolved","In vivo signaling context not addressed"]},{"year":2006,"claim":"Demonstrated the mechanism of inhibition is phosphorylation-enhanced direct binding to the PP1 active site, providing a biochemical model for force generation at constant Ca2+.","evidence":"Skinned fiber contractility, PHI-1–PP1c binding assay, and microcystin active-site competition","pmids":["17022978"],"confidence":"Medium","gaps":["No atomic-resolution structure of the complex","Single-lab biochemistry"]},{"year":2020,"claim":"Mapped the determinant of inhibitory specificity to the PHIN domain, explaining why PHI-1 is a weak myosin phosphatase inhibitor relative to CPI-17.","evidence":"In vitro phosphatase inhibition, cellular myosin phosphorylation, chimeric/deletion constructs, and zebrafish knockdown-rescue","pmids":["32784920"],"confidence":"Medium","gaps":["Does not explain what physiological substrates PHI-1 preferentially regulates given its weak MLCP activity","Residues conferring specificity within PHIN not pinpointed"]},{"year":2023,"claim":"Extended PHI-1's PP1-axis role beyond contraction to substrate proteostasis, showing it controls Raf-1 protein levels and, in cancer, phospho-STMN1 stability to govern microtubule dynamics and drug resistance, with its own abundance set by USP9X deubiquitination.","evidence":"siRNA/overexpression with tautomycin PP1 inhibition for Raf-1; reciprocal Co-IP, ubiquitination assay, phospho-mutant STMN1 rescue, and xenograft for STMN1","pmids":["38136612","36484700"],"confidence":"Medium","gaps":["Direct PP1-dependent dephosphorylation events on these substrates not reconstituted","Mechanism by which PHI-1 selects substrates unclear"]},{"year":2024,"claim":"Implicated PHI-1 in hepatocellular carcinoma signaling by showing it maintains RPS6KA1 stability and phosphorylation to activate the AKT/NF-κB pathway.","evidence":"siRNA/overexpression, Co-IP, phospho-mutant RPS6KA1 rescue, and xenograft model","pmids":["39216602"],"confidence":"Medium","gaps":["Whether RPS6KA1 regulation requires PP1 catalytic activity not directly tested","Single tumor context"]},{"year":2025,"claim":"Connected PHI-1 to androgen receptor regulation via a JAK2/STAT3 positive feedback loop affecting enzalutamide sensitivity in prostate cancer.","evidence":"siRNA/overexpression, western blot of JAK2/STAT3/AR, and pharmacological STAT3 inhibition","pmids":["41067365"],"confidence":"Low","gaps":["Mechanism inferred from inhibitor and KD/OE without direct binding or epistasis","No demonstration of a direct PHI-1–STAT3 interaction"]},{"year":2026,"claim":"Validated PPP1R14B as a druggable target whose depletion suppresses Wnt/β-catenin signaling and remodels the tumor immune microenvironment, identifying a direct small-molecule binder.","evidence":"SPR and CETSA binding validation of Astragaloside IV, ubiquitination assay, ROS analysis, T-cell co-culture, and syngeneic anti-PD-1 model","pmids":["41950731"],"confidence":"Medium","gaps":["Binding site on PPP1R14B not mapped","Whether immune effects require the PP1 inhibitory function not established"]},{"year":null,"claim":"How a single weak PP1 inhibitor selectively directs PP1 toward distinct substrates (myosin light chain, Raf-1, STMN1, RPS6KA1) across tissues and what governs its juxtamembrane targeting remain unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of PHI-1 substrate/PP1 targeting","Mechanism of cell-type-specific substrate selection unknown","In vivo physiological function of PHI-1 not defined by genetic loss-of-function"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,5,6]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[5,8,7]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[1,2]}],"pathway":[{"term_id":"R-HSA-397014","term_label":"Muscle contraction","supporting_discovery_ids":[0,5]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[8,9,11]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[7,9]}],"complexes":[],"partners":["PPP1CA","PPP1CC","STMN1","RAF1","RPS6KA1","USP9X","RPS27A"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q96C90","full_name":"Protein phosphatase 1 regulatory subunit 14B","aliases":["Phospholipase C-beta-3 neighbouring gene protein"],"length_aa":147,"mass_kda":15.9,"function":"Inhibitor of PPP1CA. Has over 50-fold higher inhibitory activity when phosphorylated (By similarity)","subcellular_location":"Cytoplasm","url":"https://www.uniprot.org/uniprotkb/Q96C90/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/PPP1R14B","classification":"Common Essential","n_dependent_lines":846,"n_total_lines":1208,"dependency_fraction":0.7003311258278145},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/PPP1R14B","total_profiled":1310},"omim":[{"mim_id":"613256","title":"PROTEIN PHOSPHATASE 1, REGULATORY SUBUNIT 14D; PPP1R14D","url":"https://www.omim.org/entry/613256"},{"mim_id":"601140","title":"PROTEIN PHOSPHATASE 1, REGULATORY SUBUNIT 14B; PPP1R14B","url":"https://www.omim.org/entry/601140"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/PPP1R14B"},"hgnc":{"alias_symbol":["SOM172","PNG","PHI-1"],"prev_symbol":["PLCB3N"]},"alphafold":{"accession":"Q96C90","domains":[{"cath_id":"-","chopping":"61-136","consensus_level":"high","plddt":81.007,"start":61,"end":136}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96C90","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q96C90-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q96C90-F1-predicted_aligned_error_v6.png","plddt_mean":71.19},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PPP1R14B","jax_strain_url":"https://www.jax.org/strain/search?query=PPP1R14B"},"sequence":{"accession":"Q96C90","fasta_url":"https://rest.uniprot.org/uniprotkb/Q96C90.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q96C90/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96C90"}},"corpus_meta":[{"pmid":"12144526","id":"PMC_12144526","title":"Phosphorylation of the myosin phosphatase inhibitors, CPI-17 and PHI-1, by integrin-linked kinase.","date":"2002","source":"The Biochemical journal","url":"https://pubmed.ncbi.nlm.nih.gov/12144526","citation_count":117,"is_preprint":false},{"pmid":"36484700","id":"PMC_36484700","title":"Protein Phosphatase 1 Subunit PPP1R14B Stabilizes STMN1 to Promote Progression and Paclitaxel Resistance in Triple-Negative Breast Cancer.","date":"2023","source":"Cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/36484700","citation_count":66,"is_preprint":false},{"pmid":"17199048","id":"PMC_17199048","title":"The Drosophila PNG kinase complex regulates the translation of cyclin B.","date":"2007","source":"Developmental cell","url":"https://pubmed.ncbi.nlm.nih.gov/17199048","citation_count":58,"is_preprint":false},{"pmid":"9130664","id":"PMC_9130664","title":"Png-1, a nervous system-specific zinc finger gene, identifies regions containing postmitotic neurons during mammalian embryonic development.","date":"1997","source":"The Journal of comparative neurology","url":"https://pubmed.ncbi.nlm.nih.gov/9130664","citation_count":42,"is_preprint":false},{"pmid":"20130186","id":"PMC_20130186","title":"The N-glycanase png-1 acts to limit axon branching during organ formation in Caenorhabditis elegans.","date":"2010","source":"The Journal of neuroscience : the official journal of the Society for Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/20130186","citation_count":38,"is_preprint":false},{"pmid":"11853689","id":"PMC_11853689","title":"Methionine synthase activity and sulphur amino acid levels in the rat liver tumour cells HTC and Phi-1.","date":"2002","source":"Biochemical pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/11853689","citation_count":30,"is_preprint":false},{"pmid":"985747","id":"PMC_985747","title":"Studies on the role and mode of operation of the very-lysine-rich histones in eukaryote chromatin. 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\"method\": \"In-gel kinase assay, solution phosphorylation assay, phosphopeptide mapping, phospho-amino acid analysis, phospho-specific immunoblotting, site-directed mutagenesis, MLCP activity assay, demembranated smooth-muscle contraction assay\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with mutagenesis (Thr57Ala) and direct functional readout (MLCP inhibition, muscle contraction), multiple orthogonal methods in one rigorous study\",\n      \"pmids\": [\"12144526\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"PHI-1 (PPP1R14B) localizes juxtamembrane in distinct foci along the plasma membrane of smooth muscle cells (distinct from diffuse CPI-17 distribution), as determined by confocal and electron microscopy; first detected in embryonic heart at E10 and later in smooth muscle and endothelial cells of adult tissues.\",\n      \"method\": \"Immunohistochemistry, confocal microscopy, electron microscopy, tissue fractionation\",\n      \"journal\": \"Histochemistry and cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization by two orthogonal microscopy methods (confocal + electron microscopy), single lab\",\n      \"pmids\": [\"15083373\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Knockdown of PHI-1 (PPP1R14B) by siRNA reduced HeLa cell migration rate by ~45%, caused an elongated phenotype, and specifically impaired retraction of the trailing edge during migration without affecting protrusive activity; PHI-1 was concentrated at the trailing edge of migrating endothelial cells.\",\n      \"method\": \"siRNA knockdown, wound-healing migration assay, time-lapse microscopy, cell spreading/replating assay, immunostaining\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KD with specific cellular phenotype and localization data, single lab, multiple assays\",\n      \"pmids\": [\"15522888\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"In intact vascular smooth muscle cells, agonist stimulation (angiotensin II, thrombin, U-46619) induces PHI-1 (PPP1R14B) phosphorylation; this phosphorylation is selectively mediated by PKC (blocked by GF-109203X or PKC downregulation, induced by PMA), distinct from ROCK-dependent CPI-17 phosphorylation.\",\n      \"method\": \"2D-PAGE, immunoblot with phospho-specific PHI-1 antibody, pharmacological inhibitors (Y-27632, H-1152, GF-109203X), constitutively active RhoA expression, PMA stimulation in primary rat aortic VSMCs\",\n      \"journal\": \"American journal of physiology. Cell physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple pharmacological and genetic perturbations in primary cells with phospho-specific detection, single lab\",\n      \"pmids\": [\"16267107\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"In chicken smooth muscle, G-protein stimulation via Rho-kinase leads to PHI-1 (PPP1R14B) phosphorylation (inhibitable by both Y-27632 and GF-109203X), correlating with increased myosin light chain phosphorylation; PHI-1 appears to act as a functional CPI-17 analog in this tissue where CPI-17 is absent.\",\n      \"method\": \"Western blot, pharmacological inhibitors (Y-27632, GF109203X), GTPγS stimulation, myosin light chain phosphorylation assay\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological dissection in intact smooth muscle tissue with multiple inhibitors, single lab\",\n      \"pmids\": [\"16081075\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Phosphorylated PHI-1 (P-PHI-1), but not unphosphorylated PHI-1, increases MLC20 phosphorylation and force in avian smooth muscle at constant [Ca2+]; phosphorylation of PHI-1 increases its direct interaction with the PP1 catalytic subunit (PP1c), and microcystin reduces this binding, indicating PHI-1 inhibits myosin light chain phosphatase by interacting with the active site of PP1c.\",\n      \"method\": \"Skinned smooth muscle fiber contractility assay, MLC20 phosphorylation assay, binding assay (PHI-1 vs PP1c), microcystin competition\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — direct binding assay between phospho-PHI-1 and PP1c with functional contractility readout, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"17022978\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"The PHIN (phosphatase holoenzyme inhibitory) domain, not the N- or C-termini, encodes the specificity difference between Cpi-17 (potent myosin phosphatase inhibitor) and Phi-1 (PPP1R14B; weak myosin phosphatase inhibitory activity); Phi-1 paralogs in zebrafish display weak myosin phosphatase inhibitory activity in vitro and do not alter myosin phosphorylation in cells, and cannot rescue Cpi-17 knockdown.\",\n      \"method\": \"In vitro phosphatase inhibition assay, cellular myosin phosphorylation assay, deletion and chimeric protein analysis, zebrafish knockdown rescue experiments\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — domain dissection with in vitro and cellular assays plus rescue genetics, single lab with multiple orthogonal approaches\",\n      \"pmids\": [\"32784920\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PPP1R14B is degraded via the ubiquitin-proteasome pathway; RPS27A recruits deubiquitinase USP9X to deubiquitinate and stabilize PPP1R14B. PPP1R14B in turn maintains phosphorylation and protein stability of STMN1 in a manner dependent on PP1 catalytic subunits α and γ, thereby decreasing α-tubulin acetylation and microtubule stability to promote paclitaxel resistance; rescue by wild-type but not phosphorylation-deficient STMN1 confirmed the mechanism.\",\n      \"method\": \"Co-IP, ubiquitination assay, siRNA knockdown, gain/loss-of-function, western blot, xenograft tumor model, microtubule stability assay, phosphorylation-deficient STMN1 rescue experiment\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP, ubiquitination assay, and phospho-mutant rescue in vitro and in vivo, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"36484700\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PHI-1 (PPP1R14B) knockdown in HEK293 cells causes a 15-fold increase in ERK1/2 phosphorylation attributable to elevated Raf-1 protein levels (not Ras or B-Raf); PHI-1 knockdown stabilizes Raf-1 protein without affecting Raf-1 mRNA; ectopic PHI-1 overexpression suppresses Raf-1 protein in an inhibitory-potency-dependent manner; PP1 inhibition with tautomycin mimics PHI-1 function to reduce Raf-1, establishing a PHI-1–PP1 axis that governs Raf-1 proteostasis.\",\n      \"method\": \"siRNA knockdown, ectopic overexpression, western blot (ERK1/2, Raf-1, B-Raf, Ras), RT-PCR for Raf-1 mRNA, tautomycin PP1 inhibition assay, EGF stimulation/MEK pathway assay\",\n      \"journal\": \"Biomolecules\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — bidirectional perturbation (KD and OE) with pharmacological PP1 inhibitor corroboration, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"38136612\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"PPP1R14B maintains the protein stability and phosphorylation of RPS6KA1 (RSK1) and positively regulates activation of the AKT/NF-κB pathway in hepatocellular carcinoma cells; rescue by wild-type but not phosphorylation-deficient RPS6KA1 confirmed the mechanism.\",\n      \"method\": \"siRNA knockdown, ectopic overexpression, western blot, Co-IP, phospho-mutant rescue experiment, xenograft model\",\n      \"journal\": \"Biochimica et biophysica acta. Molecular cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, phospho-mutant rescue, bidirectional perturbation, single lab\",\n      \"pmids\": [\"39216602\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"PPP1R14B regulates androgen receptor (AR) expression through the JAK2/STAT3 pathway and forms a positive feedback loop with STAT3; PPP1R14B knockdown reduces AR levels and sensitizes prostate cancer cells to enzalutamide, while overexpression has the opposite effect.\",\n      \"method\": \"siRNA knockdown, ectopic overexpression, western blot (JAK2, STAT3, AR), cell proliferation/migration/invasion assays, pharmacological STAT3 inhibition\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, mechanism inferred from pathway inhibitor and KD/OE without direct binding or epistasis experiments\",\n      \"pmids\": [\"41067365\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Astragaloside IV directly binds PPP1R14B (KD = 4.88 μM by SPR and CETSA), inducing its ubiquitin-proteasomal degradation; PPP1R14B depletion inhibits Wnt/β-catenin signaling via the AKT/GSK-3β axis and induces mitochondrial ROS, relieving CX3CL1 repression and promoting CD8+ T cell recruitment.\",\n      \"method\": \"Molecular docking, surface plasmon resonance (SPR), cellular thermal shift assay (CETSA), ubiquitination assay, ROS analysis, T cell co-culture, syngeneic mouse model with anti-PD-1\",\n      \"journal\": \"Phytomedicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding validated by SPR and CETSA (two orthogonal biophysical methods), plus mechanistic downstream readouts, single lab\",\n      \"pmids\": [\"41950731\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PPP1R14B (PHI-1) is a phosphorylation-dependent inhibitor of protein phosphatase-1 (PP1): when phosphorylated at Thr57 by PKC, ILK, or Rho kinase, it binds and inhibits the PP1 catalytic subunit at its active site, thereby increasing myosin light-chain phosphorylation and promoting Ca2+-sensitized smooth muscle contraction; in addition, PHI-1 localizes to the juxtamembrane/trailing edge of migrating cells where it regulates retraction, stabilizes substrates including STMN1 and Raf-1 via the PP1 axis, and modulates oncogenic signaling (AKT/NF-κB, JAK2/STAT3/AR) in cancer contexts, with its own stability controlled by RPS27A/USP9X-mediated deubiquitination.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PPP1R14B (PHI-1) is a phosphorylation-dependent inhibitor of protein phosphatase-1 (PP1) that couples upstream kinase signaling to PP1-controlled substrate phosphorylation and proteostasis [#0, #5]. Phosphorylation at Thr57 — by ILK in vitro and by PKC in intact vascular smooth muscle — converts PHI-1 into an active inhibitor that binds the PP1 catalytic subunit at its active site, inhibiting myosin light-chain phosphatase and producing Ca2+-sensitized smooth-muscle contraction [#0, #3, #5]. Its inhibitory potency is encoded by the PHIN domain and is intrinsically weaker than that of its paralog CPI-17, accounting for its distinct functional behavior [#6]. In migrating cells PHI-1 concentrates at juxtamembrane foci and the trailing edge, where it is specifically required for retraction during migration [#1, #2]. Through the PP1 axis, PHI-1 governs the stability and phosphorylation state of downstream substrates: it stabilizes Raf-1 protein to restrain ERK signaling [#8], and in cancer contexts maintains phospho-STMN1 to limit microtubule stability and drive paclitaxel resistance [#7], sustains RPS6KA1 to activate AKT/NF-\\u03baB signaling in hepatocellular carcinoma [#9], and supports Wnt/\\u03b2-catenin signaling via the AKT/GSK-3\\u03b2 axis [#11]. PHI-1's own abundance is controlled by ubiquitin-proteasomal turnover, antagonized by RPS27A-recruited USP9X-mediated deubiquitination [#7].\",\n  \"teleology\": [\n    {\n      \"year\": 2002,\n      \"claim\": \"Established that PHI-1 is an inhibitory phosphoprotein and identified Thr57 as the kinase-controlled switch that activates its inhibition of myosin light-chain phosphatase to sensitize contraction.\",\n      \"evidence\": \"In vitro ILK phosphorylation with Thr57Ala mutagenesis, MLCP activity assay, and demembranated smooth-muscle contraction assay\",\n      \"pmids\": [\"12144526\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish which kinase phosphorylates Thr57 in intact cells\", \"No structural detail of the PHI-1–PP1c interface\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Defined the subcellular distribution of PHI-1, showing it occupies discrete juxtamembrane foci distinct from the diffuse CPI-17 pattern.\",\n      \"evidence\": \"Immunohistochemistry, confocal and electron microscopy, tissue fractionation in smooth muscle and embryonic tissues\",\n      \"pmids\": [\"15083373\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis of juxtamembrane targeting unknown\", \"Functional consequence of focal localization not tested here\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Linked PHI-1 to a non-muscle process by showing it is required for trailing-edge retraction during cell migration, connecting its localization to a specific motility step.\",\n      \"evidence\": \"siRNA knockdown, wound-healing and time-lapse migration assays, immunostaining in HeLa and endothelial cells\",\n      \"pmids\": [\"15522888\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"PP1 substrate mediating retraction not identified\", \"Phosphorylation dependence of the migration role not tested\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Identified the physiological kinase input, showing agonist-induced PHI-1 phosphorylation in vascular smooth muscle is PKC-dependent and pathway-distinct from ROCK-driven CPI-17 phosphorylation.\",\n      \"evidence\": \"Phospho-specific immunoblot with PKC/ROCK inhibitors and PMA in primary rat aortic VSMCs; pharmacological dissection in chicken smooth muscle\",\n      \"pmids\": [\"16267107\", \"16081075\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relative contribution of PKC vs Rho-kinase varies by tissue and is unresolved\", \"In vivo signaling context not addressed\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Demonstrated the mechanism of inhibition is phosphorylation-enhanced direct binding to the PP1 active site, providing a biochemical model for force generation at constant Ca2+.\",\n      \"evidence\": \"Skinned fiber contractility, PHI-1–PP1c binding assay, and microcystin active-site competition\",\n      \"pmids\": [\"17022978\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No atomic-resolution structure of the complex\", \"Single-lab biochemistry\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Mapped the determinant of inhibitory specificity to the PHIN domain, explaining why PHI-1 is a weak myosin phosphatase inhibitor relative to CPI-17.\",\n      \"evidence\": \"In vitro phosphatase inhibition, cellular myosin phosphorylation, chimeric/deletion constructs, and zebrafish knockdown-rescue\",\n      \"pmids\": [\"32784920\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Does not explain what physiological substrates PHI-1 preferentially regulates given its weak MLCP activity\", \"Residues conferring specificity within PHIN not pinpointed\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Extended PHI-1's PP1-axis role beyond contraction to substrate proteostasis, showing it controls Raf-1 protein levels and, in cancer, phospho-STMN1 stability to govern microtubule dynamics and drug resistance, with its own abundance set by USP9X deubiquitination.\",\n      \"evidence\": \"siRNA/overexpression with tautomycin PP1 inhibition for Raf-1; reciprocal Co-IP, ubiquitination assay, phospho-mutant STMN1 rescue, and xenograft for STMN1\",\n      \"pmids\": [\"38136612\", \"36484700\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct PP1-dependent dephosphorylation events on these substrates not reconstituted\", \"Mechanism by which PHI-1 selects substrates unclear\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Implicated PHI-1 in hepatocellular carcinoma signaling by showing it maintains RPS6KA1 stability and phosphorylation to activate the AKT/NF-κB pathway.\",\n      \"evidence\": \"siRNA/overexpression, Co-IP, phospho-mutant RPS6KA1 rescue, and xenograft model\",\n      \"pmids\": [\"39216602\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether RPS6KA1 regulation requires PP1 catalytic activity not directly tested\", \"Single tumor context\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Connected PHI-1 to androgen receptor regulation via a JAK2/STAT3 positive feedback loop affecting enzalutamide sensitivity in prostate cancer.\",\n      \"evidence\": \"siRNA/overexpression, western blot of JAK2/STAT3/AR, and pharmacological STAT3 inhibition\",\n      \"pmids\": [\"41067365\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Mechanism inferred from inhibitor and KD/OE without direct binding or epistasis\", \"No demonstration of a direct PHI-1–STAT3 interaction\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Validated PPP1R14B as a druggable target whose depletion suppresses Wnt/β-catenin signaling and remodels the tumor immune microenvironment, identifying a direct small-molecule binder.\",\n      \"evidence\": \"SPR and CETSA binding validation of Astragaloside IV, ubiquitination assay, ROS analysis, T-cell co-culture, and syngeneic anti-PD-1 model\",\n      \"pmids\": [\"41950731\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Binding site on PPP1R14B not mapped\", \"Whether immune effects require the PP1 inhibitory function not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How a single weak PP1 inhibitor selectively directs PP1 toward distinct substrates (myosin light chain, Raf-1, STMN1, RPS6KA1) across tissues and what governs its juxtamembrane targeting remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of PHI-1 substrate/PP1 targeting\", \"Mechanism of cell-type-specific substrate selection unknown\", \"In vivo physiological function of PHI-1 not defined by genetic loss-of-function\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 5, 6]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [5, 8, 7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1, 2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-397014\", \"supporting_discovery_ids\": [0, 5]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [8, 9, 11]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [7, 9]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"PPP1CA\", \"PPP1CC\", \"STMN1\", \"RAF1\", \"RPS6KA1\", \"USP9X\", \"RPS27A\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}