{"gene":"CDC42BPA","run_date":"2026-06-09T22:57:18","timeline":{"discoveries":[{"year":2007,"finding":"Notch1 negatively regulates MRCKα kinase expression/activity in keratinocytes; loss of Notch1 signaling leads to upregulation of MRCKα (together with ROCK1/2), promoting squamous cell carcinoma formation downstream of oncogenic Ras. MRCKα is thus positioned as a downstream effector of Notch1-mediated tumor suppression.","method":"Genetic suppression of Notch signaling in primary human keratinocytes combined with oncogenic Ras expression; pharmacological inhibitor of Notch signaling in mouse grafts; western blot/expression analysis of MRCKα","journal":"Genes & development","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis in primary human cells and in vivo mouse model, two orthogonal approaches (genetic + pharmacological), single lab","pmids":["17344417"],"is_preprint":false},{"year":2006,"finding":"MRCKα mRNA contains a functional iron responsive element (IRE) in its 3′UTR that mediates post-transcriptional regulation by cellular iron levels: MRCKα mRNA is stabilized under low-iron conditions and destabilized under iron-rich conditions, analogous to transferrin receptor 1 regulation.","method":"Bioinformatic identification of IRE followed by biochemical analysis of IRE functionality; mRNA stability assays under varying iron conditions","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — biochemical IRE functional assay with iron manipulation, single lab, two orthogonal methods (bioinformatics + biochemical validation)","pmids":["16412980"],"is_preprint":false},{"year":2010,"finding":"MRCKα protein expression is regulated by cellular iron levels; MRCKα colocalizes with transferrin-loaded transferrin receptors, and shRNA-mediated silencing of MRCKα significantly decreases transferrin-mediated iron uptake, implicating MRCKα in transferrin-TfR endocytosis/endosome trafficking via cytoskeletal regulation.","method":"shRNA knockdown of MRCKα; colocalization of MRCKα with Tf-loaded TfR by imaging; iron uptake assay","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function with defined cellular phenotype (iron uptake), colocalization, single lab, two orthogonal methods","pmids":["20188707"],"is_preprint":false},{"year":2014,"finding":"PDK1 binds and activates MRCKα to regulate directional epithelial cell migration and lamellipodia retraction downstream of EGF signaling. The effect of PDK1 does not require PDK1 kinase activity but depends on PDK1 binding to membrane PIP3. Upon EGF stimulation, PDK1 and MRCKα colocalize at the cell membrane in lamellipodia. PDK1 positively modulates MRCKα activity, linking EGF signaling to myosin contraction.","method":"Co-immunoprecipitation; kinase-dead PDK1 mutant experiments; subcellular colocalization by fluorescence microscopy; lamellipodia retraction assays; cell migration/invasion assays with knockdown and rescue","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, dominant-negative and kinase-dead mutant analysis, live imaging, defined cellular phenotypes, multiple orthogonal methods in single lab","pmids":["25092657"],"is_preprint":false},{"year":2017,"finding":"Caspase-mediated cleavage of MRCKα during apoptosis activates a signaling pathway that drives assembly of an apical actin ring (EAAR) within the apoptotic cell, leading to actomyosin contraction and compaction required for epithelial cell extrusion. Expression of the caspase cleavage product of MRCKα is sufficient to assemble the EAAR.","method":"Live-cell imaging; expression of caspase-cleavage product of MRCKα; F-actin flow measurement; myosin contraction inhibition; actin polymerization assays; epithelial extrusion assays","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (live imaging, dominant cleavage product expression, inhibitor studies), defined mechanistic pathway, single lab","pmids":["29162624"],"is_preprint":false},{"year":2017,"finding":"ICAP-1 monoubiquitylation by Smurf1 regulates a switch from ROCK2-mediated to MRCKα-mediated cell contractility. Non-ubiquitylatable ICAP-1 increases MRCKα-dependent myosin phosphorylation and cell contractility independently of substrate rigidity, positioning MRCKα downstream of the ICAP-1/β1-integrin axis in mechanosensing.","method":"Non-ubiquitylatable ICAP-1 mutant expression; myosin light chain phosphorylation assays; cell migration assays on substrates of varying stiffness; genetic manipulation of ROCK2 and MRCKα","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — epistasis via mutant expression, phosphorylation assays, defined cellular phenotype, single lab","pmids":["28049720"],"is_preprint":false},{"year":2021,"finding":"MRCKα interacts with the Na+,K+-ATPase β1 subunit (identified by IP-mass spectrometry) and its downstream activation of myosin light chain is required for the NKA β1 subunit-mediated upregulation of tight junction proteins and alveolar epithelial barrier function.","method":"Co-immunoprecipitation and mass spectrometry to identify interaction; doxycycline-inducible overexpression of MRCKα; MRCKα knockdown; tight junction protein expression assays; barrier function assays","journal":"JCI insight","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP/MS interaction identification, inducible overexpression, knockdown with defined barrier phenotype, single lab","pmids":["33507884"],"is_preprint":false},{"year":2021,"finding":"In vivo gene transfer of MRCKα to mouse lungs attenuates LPS-induced acute lung injury by restoring tight junction protein expression and reducing pulmonary edema/leakage, without altering alveolar fluid clearance rates. MRCKα acts in both alveolar epithelial and capillary endothelial cells to upregulate junctional complexes.","method":"Electroporation-mediated plasmid gene delivery in mice; LPS-induced ALI model; pulmonary edema measurement; tight junction protein western blot; lung leakage assay","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo loss/gain of function with defined phenotypic readouts, single lab, extends prior in vitro finding","pmids":["34675326"],"is_preprint":false},{"year":2022,"finding":"MRCKα physically binds ABCB4 (the hepatocyte canalicular phosphatidylcholine transporter) and its downstream effector myosin II regulatory light chain (MRLC) also binds ABCB4. Dominant-negative MRCKα mutant expression, MRCKα inhibition (chelerythrine), RNAi knockdown, or CRISPR-Cas9 knockout all increase ABCB4 steady-state protein expression at the cell surface, indicating MRCKα negatively regulates ABCB4 membrane expression via MRLC.","method":"Co-immunoprecipitation; dominant-negative mutant expression; pharmacological inhibition; siRNA knockdown; CRISPR-Cas9 knockout; ABCB4 surface expression assays in primary hepatocytes and HEK-293 cells","journal":"Cells","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal loss-of-function approaches (DN mutant, inhibitor, RNAi, CRISPR-KO) in two cell models, Co-IP interaction confirmed, convergent results","pmids":["35203270"],"is_preprint":false},{"year":2023,"finding":"MRCKα physically interacts with Gli transcription factors and directly phosphorylates Gli2 on multiple sites. Double knockout of MRCKα and MRCKβ affects Gli2 ciliary and nuclear localization and reduces Gli2 binding to the Gli1 promoter, positively regulating Hedgehog pathway transcriptional output.","method":"Co-immunoprecipitation; in vitro kinase assay (direct phosphorylation of Gli2); CRISPR-Cas9 double knockout of MRCKα/β; Gli2 localization by immunofluorescence; ChIP assay for Gli2 binding to Gli1 promoter","journal":"Cellular signalling","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro kinase assay establishing direct phosphorylation, Co-IP, CRISPR-KO with multiple functional readouts (localization, promoter binding, transcriptional output), single lab","pmids":["37019250"],"is_preprint":false},{"year":2021,"finding":"Double knockout of MRCKα and MRCKβ in MDA-MB-231 triple-negative breast cancer cells reduces invasion, but single MRCKα knockout mice show no developmental phenotype and no effect on mammary tumor onset, growth, or metastasis in the MMTV-PyMT model.","method":"Conditional MRCKα gene knockout mice; MMTV-PyMT breast cancer model; invasion/migration assays in cell lines with double MRCKα/β CRISPR-KO","journal":"Cells","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo knockout model with defined tumor phenotypes, cell-based invasion assay, single lab; finding is partly negative (no in vivo tumor effect for single KO)","pmids":["33921698"],"is_preprint":false},{"year":2026,"finding":"MRCKα interacts with GEF-H1 (ARHGEF2, a RhoA-selective guanine nucleotide exchange factor) and phosphorylates GEF-H1 on Ser174, suppressing GEF-H1 activity and thereby repressing RhoA activation. MRCK inhibition reduces GEF-H1 Ser174 phosphorylation, increases GEF-H1 activity and RhoA activation, disrupts cell-cell contacts, and impairs compaction of multicellular spheroids in HGSOC.","method":"Mass spectrometry identification of GEF-H1 as MRCKα interacting partner; Co-IP; phosphorylation site mapping (Ser174); pharmacological MRCK inhibition; GEF-H1 activity assays; RhoA activation assays; live-cell imaging; 3D spheroid assays; patient-derived organoids","journal":"bioRxiv","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — MS-identified interaction, direct phosphorylation site identified, multiple functional assays (RhoA activation, GEF-H1 activity, 3D organoids), multiple orthogonal methods, preprint","pmids":["41726953"],"is_preprint":true},{"year":2026,"finding":"MRCKα interacts with GEF-H1 in tubular cells (confirmed by immunoprecipitation and proximity ligation assay) and suppresses GEF-H1/RhoA/MRTF signaling. MRCKα silencing elevates GEF-H1 activity, RhoA activation, stress fibre formation, myosin light chain phosphorylation, cofilin phosphorylation, and MRTF nuclear translocation, leading to upregulation of fibrogenic genes including ACTA2. TGFβ1 increases GEF-H1/MRCKα binding.","method":"Co-immunoprecipitation; proximity ligation assay; siRNA knockdown of MRCKα; GEF-H1 activity assay; RhoA activity assay; myosin light chain and cofilin phosphorylation; MRTF nuclear translocation imaging; fibrogenic gene mRNA array; in vivo kidney fibrosis model with IHC","journal":"Cells","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP and PLA for interaction, multiple orthogonal readouts (RhoA activation, MLC phosphorylation, MRTF localization, gene expression), in vivo confirmation, independently convergent with preprint 41726953","pmids":["41827880"],"is_preprint":false},{"year":2025,"finding":"MRCKα is modified by D-2-hydroxyglutarate (D2HG) via O-2-hydroxyglutarylation, and this modification is associated with reduced phosphorylation of MRCKα substrates, suggesting an inhibitory effect of D2HG modification on MRCKα kinase activity.","method":"Chemical proteomics identification of O-2-hydroxyglutarylation; substrate phosphorylation assays comparing modified vs unmodified kinase","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 3 / Weak — chemical proteomics identification, substrate phosphorylation reduction observed but mechanism not fully dissected; preprint, single lab, MRCKα is one of two kinases briefly mentioned","pmids":["bio_10.1101_2025.01.24.634716"],"is_preprint":true},{"year":2022,"finding":"MRCKα mediates prolactin-induced lactogenesis in bovine mammary epithelial cells via the mTOR/SREBP1/cyclin D1 signaling pathway. MRCKα silencing prevents prolactin-stimulated β-casein production, triglyceride secretion, and mTOR phosphorylation; MRCKα overexpression reverses these effects.","method":"siRNA knockdown and overexpression of MRCKα in primary bovine mammary epithelial cells; prolactin stimulation; western blot for β-casein, SREBP1, cyclin D1, phospho-mTOR; triglyceride secretion assay","journal":"Animal nutrition","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — bidirectional loss-of-function and gain-of-function with defined molecular pathway readouts, single lab","pmids":["35891685"],"is_preprint":false},{"year":2025,"finding":"MRCKα acts downstream of PI3K and upstream of PKB (Akt) in methionine- and leucine-stimulated β-casein synthesis in bovine mammary epithelial cells, regulating mTOR phosphorylation. PI3K inhibition blocks Met/Leu-induced MRCKα expression; MRCKα silencing blocks PKB phosphorylation; PKB inhibitor blocks MRCKα-overexpression-induced mTOR activation.","method":"siRNA knockdown and overexpression of MRCKα; PI3K inhibitor (LY294002); PKB inhibitor (MK2206); western blot for phospho-mTOR, phospho-PKB, phospho-PI3K, β-casein; amino acid dose-response experiments in primary BMEC","journal":"Animal nutrition","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — epistasis established by pharmacological inhibitors combined with KD/OE, multiple pathway nodes measured, single lab","pmids":["40487111"],"is_preprint":false}],"current_model":"MRCKα (CDC42BPA) is a serine/threonine kinase that acts as a key downstream effector of CDC42-Rho GTPase signaling to regulate actomyosin cytoskeleton organization: it is activated by PDK1 downstream of EGF/PIP3 to drive directional cell migration and lamellipodia retraction; is cleaved and activated by caspases to assemble an apical actin ring for epithelial cell extrusion; phosphorylates and suppresses the RhoA-GEF GEF-H1 (Ser174), thereby restraining RhoA/MRTF-dependent fibrogenic and contractile programs; directly phosphorylates Gli2 transcription factors to promote Hedgehog pathway output; regulates myosin light chain phosphorylation downstream of NKA β1 subunit to maintain epithelial tight junction integrity; controls membrane trafficking of ABCB4 via its effector MRLC; participates in transferrin-iron uptake via cytoskeletal regulation of TfR endocytosis; and is itself regulated post-transcriptionally by cellular iron levels through a functional 3′UTR IRE, and by D2HG-mediated O-2-hydroxyglutarylation that inhibits its activity."},"narrative":{"mechanistic_narrative":"CDC42BPA (MRCKα) is a serine/threonine kinase that functions as a downstream effector linking Rho-family GTPase and growth-factor signaling to actomyosin cytoskeletal organization, driving directional cell migration, epithelial barrier integrity, and contractility [PMID:25092657, PMID:33507884]. Downstream of EGF, PDK1 binds and activates MRCKα — independently of PDK1 kinase activity but dependent on its PIP3 membrane recruitment — and the two colocalize in lamellipodia to couple growth-factor signaling to myosin contraction and directional migration [PMID:25092657]. MRCKα activates myosin light chain to enforce epithelial functions: it cooperates with the Na+,K+-ATPase β1 subunit to upregulate tight-junction proteins and maintain alveolar barrier function, and restoring MRCKα in vivo attenuates LPS-induced acute lung injury [PMID:33507884, PMID:34675326]. During apoptosis, caspase cleavage generates an active MRCKα fragment sufficient to assemble an apical actomyosin ring that compacts and extrudes dying epithelial cells [PMID:29162624]. MRCKα also constrains RhoA signaling by phosphorylating the RhoA-GEF GEF-H1 (ARHGEF2) on Ser174, suppressing GEF-H1 activity; loss of MRCKα elevates GEF-H1/RhoA/MRTF signaling, stress fibre formation, and fibrogenic gene programs including ACTA2 [PMID:41726953, PMID:41827880]. Beyond cytoskeletal effectors, MRCKα directly phosphorylates Gli2 to promote its ciliary/nuclear localization and Hedgehog transcriptional output, and negatively regulates surface expression of the canalicular transporter ABCB4 via myosin regulatory light chain [PMID:37019250, PMID:35203270]. MRCKα expression is itself controlled post-transcriptionally by iron through a functional 3′UTR iron-responsive element, and the kinase participates in transferrin-receptor-mediated iron uptake [PMID:16412980, PMID:20188707].","teleology":[{"year":2006,"claim":"Established that MRCKα is not constitutively expressed but is post-transcriptionally tuned by cellular iron via a functional IRE, embedding the kinase in iron homeostasis regulation.","evidence":"Bioinformatic IRE identification and biochemical mRNA stability assays under varying iron conditions","pmids":["16412980"],"confidence":"Medium","gaps":["Does not identify which IRE-binding proteins act on the MRCKα transcript","Does not connect IRE regulation to a kinase-dependent function"]},{"year":2007,"claim":"Placed MRCKα downstream of Notch1 tumor-suppression, showing its upregulation cooperates with oncogenic Ras in keratinocyte carcinogenesis.","evidence":"Genetic and pharmacological Notch suppression with oncogenic Ras in primary keratinocytes and mouse grafts","pmids":["17344417"],"confidence":"Medium","gaps":["Mechanism by which MRCKα promotes SCC not resolved at the substrate level","Co-upregulation with ROCK1/2 leaves relative contribution unclear"]},{"year":2010,"claim":"Linked iron-regulated MRCKα to a cellular function — transferrin receptor endocytosis/trafficking — implicating its cytoskeletal activity in iron uptake.","evidence":"shRNA knockdown, colocalization with Tf-loaded TfR, and iron uptake assay","pmids":["20188707"],"confidence":"Medium","gaps":["The cytoskeletal step in TfR endocytosis controlled by MRCKα is not defined","No kinase substrate identified in this pathway"]},{"year":2014,"claim":"Defined the upstream activation mechanism, showing PDK1 binds and activates MRCKα via PIP3-dependent membrane recruitment to couple EGF signaling to lamellipodial myosin contraction and directional migration.","evidence":"Reciprocal Co-IP, kinase-dead PDK1 mutants, lamellipodia retraction and migration assays with knockdown/rescue","pmids":["25092657"],"confidence":"High","gaps":["How PDK1 binding activates MRCKα kinase mechanistically is not detailed","Does not map the relevant phosphorylation events on MRCKα"]},{"year":2017,"claim":"Demonstrated MRCKα drives a discrete morphogenetic event — assembly of an apical actomyosin ring for apoptotic epithelial extrusion — activated by caspase cleavage.","evidence":"Live imaging, expression of the caspase-cleavage product, F-actin flow and myosin inhibition, extrusion assays","pmids":["29162624"],"confidence":"High","gaps":["Caspase cleavage site and the resulting activation mechanism not fully mapped","Substrates within the extrusion ring not enumerated"]},{"year":2017,"claim":"Positioned MRCKα as a rigidity-independent contractility module, with an ICAP-1/Smurf1 ubiquitylation switch toggling between ROCK2- and MRCKα-mediated contractility.","evidence":"Non-ubiquitylatable ICAP-1 mutants, MLC phosphorylation assays, migration on variable-stiffness substrates","pmids":["28049720"],"confidence":"Medium","gaps":["Direct biochemical link between ICAP-1 and MRCKα activation not established","How the switch selects MRCKα over ROCK2 mechanistically unclear"]},{"year":2021,"claim":"Connected MRCKα to epithelial barrier maintenance, showing it binds the Na+,K+-ATPase β1 subunit and uses MLC phosphorylation to upregulate tight junction proteins, with in vivo rescue of acute lung injury.","evidence":"Co-IP/MS, inducible overexpression and knockdown, barrier assays, and in vivo LPS-ALI gene transfer","pmids":["33507884","34675326"],"confidence":"Medium","gaps":["Direct MRCKα substrate driving tight-junction upregulation not identified","Whether NKA β1 directly modulates MRCKα kinase activity is unclear"]},{"year":2021,"claim":"Tested in vivo requirement in cancer, revealing functional redundancy: dual MRCKα/β loss reduces TNBC invasion, but single MRCKα knockout has no developmental or mammary tumor phenotype.","evidence":"Conditional MRCKα knockout mice, MMTV-PyMT model, and double-knockout invasion assays","pmids":["33921698"],"confidence":"Medium","gaps":["Does not dissect distinct versus redundant roles of MRCKα and MRCKβ","Negative in vivo single-KO result limits inference on isolated MRCKα function"]},{"year":2022,"claim":"Identified ABCB4 as a regulated target, showing MRCKα and MRLC bind ABCB4 and MRCKα negatively controls its surface expression, extending the kinase into membrane transporter trafficking.","evidence":"Co-IP plus convergent loss-of-function (DN mutant, inhibitor, RNAi, CRISPR-KO) and surface expression assays in hepatocytes and HEK-293","pmids":["35203270"],"confidence":"High","gaps":["The MRLC-dependent trafficking step controlling ABCB4 not mechanistically resolved","Whether MRCKα phosphorylates ABCB4 directly not addressed"]},{"year":2022,"claim":"Extended MRCKα into metabolic/secretory signaling, placing it in a PI3K→MRCKα→Akt→mTOR/SREBP1/cyclin D1 axis driving prolactin- and amino-acid-stimulated lactogenesis.","evidence":"Bidirectional knockdown/overexpression with pharmacological pathway inhibitors in bovine mammary epithelial cells","pmids":["35891685","40487111"],"confidence":"Medium","gaps":["Direct MRCKα substrate in the mTOR pathway not identified","Findings restricted to bovine mammary cells; human relevance not tested"]},{"year":2023,"claim":"Revealed a non-cytoskeletal substrate, establishing MRCKα as a direct Gli2 kinase that promotes Gli2 localization, promoter binding, and Hedgehog transcriptional output.","evidence":"In vitro kinase assay, Co-IP, MRCKα/β CRISPR double-knockout, Gli2 localization and ChIP","pmids":["37019250"],"confidence":"High","gaps":["Specific Gli2 phosphosites and their functional consequences not mapped","Relative roles of MRCKα versus MRCKβ in Hedgehog output unresolved"]},{"year":2026,"claim":"Defined a RhoA-restraining function, showing MRCKα phosphorylates GEF-H1 on Ser174 to suppress GEF-H1/RhoA/MRTF signaling, controlling spheroid compaction and fibrogenic gene programs.","evidence":"MS-identified interaction, Co-IP, PLA, Ser174 phosphosite mapping, RhoA/GEF-H1 activity assays, MRTF translocation, 3D organoids, and in vivo kidney fibrosis model","pmids":["41726953","41827880"],"confidence":"High","gaps":["One key supporting study is a preprint (41726953)","How TGFβ1 enhances GEF-H1/MRCKα binding mechanistically not resolved"]},{"year":2025,"claim":"Proposed a metabolite-based inhibitory regulation, with D2HG-mediated O-2-hydroxyglutarylation associated with reduced MRCKα substrate phosphorylation.","evidence":"Chemical proteomics and substrate phosphorylation comparison (preprint)","pmids":["bio_10.1101_2025.01.24.634716"],"confidence":"Low","gaps":["Preprint; modification site and direct effect on kinase activity not dissected","MRCKα is one of two kinases briefly examined, limiting specificity"]},{"year":null,"claim":"The unifying question of how distinct upstream inputs (PDK1/EGF, caspase cleavage, ICAP-1 switch, metabolite modification) selectively direct MRCKα toward its diverse substrates (MLC, GEF-H1, Gli2, ABCB4) remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model linking activation mode to substrate selection","Functional separation of MRCKα from redundant MRCKβ not established across contexts"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[3,9,11,12]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[9,11]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[3,8]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[2,4]},{"term_id":"GO:0005929","term_label":"cilium","supporting_discovery_ids":[9]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[3,11,12]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[4]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[9,12]}],"complexes":[],"partners":["PDK1","ARHGEF2","GLI2","ABCB4","ATP1B1","MRLC"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q5VT25","full_name":"Serine/threonine-protein kinase MRCK alpha","aliases":["CDC42-binding protein kinase alpha","DMPK-like alpha","Myotonic dystrophy kinase-related CDC42-binding kinase alpha","MRCK alpha","Myotonic dystrophy protein kinase-like alpha"],"length_aa":1732,"mass_kda":197.3,"function":"Serine/threonine-protein kinase which is an important downstream effector of CDC42 and plays a role in the regulation of cytoskeleton reorganization and cell migration (PubMed:15723050, PubMed:9092543, PubMed:9418861). Regulates actin cytoskeletal reorganization via phosphorylation of PPP1R12C and MYL9/MLC2 (PubMed:21457715). In concert with MYO18A and LURAP1, is involved in modulating lamellar actomyosin retrograde flow that is crucial to cell protrusion and migration (PubMed:18854160). Phosphorylates: PPP1R12A, LIMK1 and LIMK2 (PubMed:11340065, PubMed:11399775). May play a role in TFRC-mediated iron uptake (PubMed:20188707). In concert with FAM89B/LRAP25 mediates the targeting of LIMK1 to the lamellipodium resulting in its activation and subsequent phosphorylation of CFL1 which is important for lamellipodial F-actin regulation (By similarity). Triggers the formation of an extrusion apical actin ring required for epithelial extrusion of apoptotic cells (PubMed:29162624)","subcellular_location":"Cytoplasm; Cell projection, lamellipodium","url":"https://www.uniprot.org/uniprotkb/Q5VT25/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CDC42BPA","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"CDC42","stoichiometry":0.2},{"gene":"KRT18","stoichiometry":0.2},{"gene":"CDC42BPB","stoichiometry":0.2},{"gene":"GRK2","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/CDC42BPA","total_profiled":1310},"omim":[{"mim_id":"616129","title":"LEUCINE-RICH ADAPTOR PROTEIN 1; LURAP1","url":"https://www.omim.org/entry/616129"},{"mim_id":"616128","title":"FAMILY WITH SEQUENCE SIMILARITY 89, MEMBER B; FAM89B","url":"https://www.omim.org/entry/616128"},{"mim_id":"614062","title":"CDC42-BINDING PROTEIN KINASE, BETA; CDC42BPB","url":"https://www.omim.org/entry/614062"},{"mim_id":"613991","title":"CDC42-BINDING PROTEIN KINASE, GAMMA; CDC42BPG","url":"https://www.omim.org/entry/613991"},{"mim_id":"613245","title":"PROTEIN PHOSPHATASE 1, REGULATORY SUBUNIT 12C; PPP1R12C","url":"https://www.omim.org/entry/613245"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Plasma membrane","reliability":"Approved"},{"location":"Cytosol","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/CDC42BPA"},"hgnc":{"alias_symbol":["MRCKA","PK428","FLJ23347","KIAA0451","MRCKalpha"],"prev_symbol":[]},"alphafold":{"accession":"Q5VT25","domains":[{"cath_id":"1.10.510.10","chopping":"22-406","consensus_level":"medium","plddt":90.7149,"start":22,"end":406},{"cath_id":"3.30.60.20","chopping":"1011-1073","consensus_level":"medium","plddt":84.4684,"start":1011,"end":1073},{"cath_id":"2.30.29.30","chopping":"1076-1211","consensus_level":"medium","plddt":83.6787,"start":1076,"end":1211},{"cath_id":"2.130.10.10","chopping":"1216-1531","consensus_level":"medium","plddt":86.882,"start":1216,"end":1531}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q5VT25","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q5VT25-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q5VT25-F1-predicted_aligned_error_v6.png","plddt_mean":75.06},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CDC42BPA","jax_strain_url":"https://www.jax.org/strain/search?query=CDC42BPA"},"sequence":{"accession":"Q5VT25","fasta_url":"https://rest.uniprot.org/uniprotkb/Q5VT25.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q5VT25/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q5VT25"}},"corpus_meta":[{"pmid":"17344417","id":"PMC_17344417","title":"Notch1 is a p53 target gene involved in human keratinocyte tumor suppression through negative regulation of ROCK1/2 and MRCKalpha kinases.","date":"2007","source":"Genes & development","url":"https://pubmed.ncbi.nlm.nih.gov/17344417","citation_count":267,"is_preprint":false},{"pmid":"16412980","id":"PMC_16412980","title":"A novel iron responsive element in the 3'UTR of human MRCKalpha.","date":"2006","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/16412980","citation_count":54,"is_preprint":false},{"pmid":"25092657","id":"PMC_25092657","title":"PDK1-mediated activation of MRCKα regulates directional cell migration and lamellipodia retraction.","date":"2014","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/25092657","citation_count":32,"is_preprint":false},{"pmid":"32071169","id":"PMC_32071169","title":"Functional proteomics interrogation of the kinome identifies MRCKA as a therapeutic target in high-grade serous ovarian carcinoma.","date":"2020","source":"Science signaling","url":"https://pubmed.ncbi.nlm.nih.gov/32071169","citation_count":25,"is_preprint":false},{"pmid":"29162624","id":"PMC_29162624","title":"MRCKα is activated by caspase cleavage to assemble an apical actin ring for epithelial cell extrusion.","date":"2017","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/29162624","citation_count":25,"is_preprint":false},{"pmid":"29039592","id":"PMC_29039592","title":"Inhibition of cell migration and invasion by miR‑29a‑3p in a colorectal cancer cell line through suppression of CDC42BPA mRNA expression.","date":"2017","source":"Oncology reports","url":"https://pubmed.ncbi.nlm.nih.gov/29039592","citation_count":22,"is_preprint":false},{"pmid":"33507884","id":"PMC_33507884","title":"The Na+, K+-ATPase β1 subunit regulates epithelial tight junctions via MRCKα.","date":"2021","source":"JCI insight","url":"https://pubmed.ncbi.nlm.nih.gov/33507884","citation_count":15,"is_preprint":false},{"pmid":"23151005","id":"PMC_23151005","title":"Cycloartane-3,24,25-triol inhibits MRCKα kinase and demonstrates promising anti prostate cancer activity in vitro.","date":"2012","source":"Cancer cell international","url":"https://pubmed.ncbi.nlm.nih.gov/23151005","citation_count":15,"is_preprint":false},{"pmid":"20188707","id":"PMC_20188707","title":"Human MRCKalpha is regulated by cellular iron levels and interferes with transferrin iron uptake.","date":"2010","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/20188707","citation_count":13,"is_preprint":false},{"pmid":"34675326","id":"PMC_34675326","title":"Gene transfer of MRCKα rescues lipopolysaccharide-induced acute lung injury by restoring alveolar capillary barrier function.","date":"2021","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/34675326","citation_count":10,"is_preprint":false},{"pmid":"28049720","id":"PMC_28049720","title":"ICAP-1 monoubiquitylation coordinates matrix density and rigidity sensing for cell migration through ROCK2-MRCKα balance.","date":"2017","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/28049720","citation_count":10,"is_preprint":false},{"pmid":"37019250","id":"PMC_37019250","title":"MRCKα/β positively regulates Gli protein activity.","date":"2023","source":"Cellular signalling","url":"https://pubmed.ncbi.nlm.nih.gov/37019250","citation_count":5,"is_preprint":false},{"pmid":"33921698","id":"PMC_33921698","title":"MRCKα Is Dispensable for Breast Cancer Development in the MMTV-PyMT Model.","date":"2021","source":"Cells","url":"https://pubmed.ncbi.nlm.nih.gov/33921698","citation_count":4,"is_preprint":false},{"pmid":"35891685","id":"PMC_35891685","title":"MRCKα is a novel regulator of prolactin-induced lactogenesis in bovine mammary epithelial cells.","date":"2022","source":"Animal nutrition (Zhongguo xu mu shou yi xue hui)","url":"https://pubmed.ncbi.nlm.nih.gov/35891685","citation_count":3,"is_preprint":false},{"pmid":"35203270","id":"PMC_35203270","title":"MRCK-Alpha and Its Effector Myosin II Regulatory Light Chain Bind ABCB4 and Regulate Its Membrane Expression.","date":"2022","source":"Cells","url":"https://pubmed.ncbi.nlm.nih.gov/35203270","citation_count":3,"is_preprint":false},{"pmid":"40487111","id":"PMC_40487111","title":"Myotonic dystrophy-related CDC42-binding kinase alpha (MRCKα) mediates methionine- and leucine-stimulated β-casein synthesis in bovine mammary epithelial cells via targeting mTOR.","date":"2025","source":"Animal nutrition (Zhongguo xu mu shou yi xue hui)","url":"https://pubmed.ncbi.nlm.nih.gov/40487111","citation_count":1,"is_preprint":false},{"pmid":"41726953","id":"PMC_41726953","title":"MRCKα represses GEF-H1 mediated RhoA activation to promote ovarian cancer spheroid growth and invasion.","date":"2026","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/41726953","citation_count":0,"is_preprint":false},{"pmid":"41827880","id":"PMC_41827880","title":"MRCKα Is a Suppressor of GEF-H1/RhoA/MRTF Signaling in Tubular Cells.","date":"2026","source":"Cells","url":"https://pubmed.ncbi.nlm.nih.gov/41827880","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.01.24.634716","title":"Discovery of Chirally-dependent Protein O-2-Hydroxyglutarylation by D2HG and L2HG","date":"2025-01-27","source":"bioRxiv","url":"https://doi.org/10.1101/2025.01.24.634716","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":11112,"output_tokens":4759,"usd":0.05236,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":13125,"output_tokens":4452,"usd":0.088462,"stage2_stop_reason":"end_turn"},"total_usd":0.140822,"stage1_batch_id":"msgbatch_01ACAxJQabDsht39JXeWG22d","stage2_batch_id":"msgbatch_01QEU22A9U5sbPTgsMzTmvSf","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2007,\n      \"finding\": \"Notch1 negatively regulates MRCKα kinase expression/activity in keratinocytes; loss of Notch1 signaling leads to upregulation of MRCKα (together with ROCK1/2), promoting squamous cell carcinoma formation downstream of oncogenic Ras. MRCKα is thus positioned as a downstream effector of Notch1-mediated tumor suppression.\",\n      \"method\": \"Genetic suppression of Notch signaling in primary human keratinocytes combined with oncogenic Ras expression; pharmacological inhibitor of Notch signaling in mouse grafts; western blot/expression analysis of MRCKα\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis in primary human cells and in vivo mouse model, two orthogonal approaches (genetic + pharmacological), single lab\",\n      \"pmids\": [\"17344417\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"MRCKα mRNA contains a functional iron responsive element (IRE) in its 3′UTR that mediates post-transcriptional regulation by cellular iron levels: MRCKα mRNA is stabilized under low-iron conditions and destabilized under iron-rich conditions, analogous to transferrin receptor 1 regulation.\",\n      \"method\": \"Bioinformatic identification of IRE followed by biochemical analysis of IRE functionality; mRNA stability assays under varying iron conditions\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biochemical IRE functional assay with iron manipulation, single lab, two orthogonal methods (bioinformatics + biochemical validation)\",\n      \"pmids\": [\"16412980\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"MRCKα protein expression is regulated by cellular iron levels; MRCKα colocalizes with transferrin-loaded transferrin receptors, and shRNA-mediated silencing of MRCKα significantly decreases transferrin-mediated iron uptake, implicating MRCKα in transferrin-TfR endocytosis/endosome trafficking via cytoskeletal regulation.\",\n      \"method\": \"shRNA knockdown of MRCKα; colocalization of MRCKα with Tf-loaded TfR by imaging; iron uptake assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function with defined cellular phenotype (iron uptake), colocalization, single lab, two orthogonal methods\",\n      \"pmids\": [\"20188707\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"PDK1 binds and activates MRCKα to regulate directional epithelial cell migration and lamellipodia retraction downstream of EGF signaling. The effect of PDK1 does not require PDK1 kinase activity but depends on PDK1 binding to membrane PIP3. Upon EGF stimulation, PDK1 and MRCKα colocalize at the cell membrane in lamellipodia. PDK1 positively modulates MRCKα activity, linking EGF signaling to myosin contraction.\",\n      \"method\": \"Co-immunoprecipitation; kinase-dead PDK1 mutant experiments; subcellular colocalization by fluorescence microscopy; lamellipodia retraction assays; cell migration/invasion assays with knockdown and rescue\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, dominant-negative and kinase-dead mutant analysis, live imaging, defined cellular phenotypes, multiple orthogonal methods in single lab\",\n      \"pmids\": [\"25092657\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Caspase-mediated cleavage of MRCKα during apoptosis activates a signaling pathway that drives assembly of an apical actin ring (EAAR) within the apoptotic cell, leading to actomyosin contraction and compaction required for epithelial cell extrusion. Expression of the caspase cleavage product of MRCKα is sufficient to assemble the EAAR.\",\n      \"method\": \"Live-cell imaging; expression of caspase-cleavage product of MRCKα; F-actin flow measurement; myosin contraction inhibition; actin polymerization assays; epithelial extrusion assays\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (live imaging, dominant cleavage product expression, inhibitor studies), defined mechanistic pathway, single lab\",\n      \"pmids\": [\"29162624\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"ICAP-1 monoubiquitylation by Smurf1 regulates a switch from ROCK2-mediated to MRCKα-mediated cell contractility. Non-ubiquitylatable ICAP-1 increases MRCKα-dependent myosin phosphorylation and cell contractility independently of substrate rigidity, positioning MRCKα downstream of the ICAP-1/β1-integrin axis in mechanosensing.\",\n      \"method\": \"Non-ubiquitylatable ICAP-1 mutant expression; myosin light chain phosphorylation assays; cell migration assays on substrates of varying stiffness; genetic manipulation of ROCK2 and MRCKα\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis via mutant expression, phosphorylation assays, defined cellular phenotype, single lab\",\n      \"pmids\": [\"28049720\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"MRCKα interacts with the Na+,K+-ATPase β1 subunit (identified by IP-mass spectrometry) and its downstream activation of myosin light chain is required for the NKA β1 subunit-mediated upregulation of tight junction proteins and alveolar epithelial barrier function.\",\n      \"method\": \"Co-immunoprecipitation and mass spectrometry to identify interaction; doxycycline-inducible overexpression of MRCKα; MRCKα knockdown; tight junction protein expression assays; barrier function assays\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP/MS interaction identification, inducible overexpression, knockdown with defined barrier phenotype, single lab\",\n      \"pmids\": [\"33507884\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"In vivo gene transfer of MRCKα to mouse lungs attenuates LPS-induced acute lung injury by restoring tight junction protein expression and reducing pulmonary edema/leakage, without altering alveolar fluid clearance rates. MRCKα acts in both alveolar epithelial and capillary endothelial cells to upregulate junctional complexes.\",\n      \"method\": \"Electroporation-mediated plasmid gene delivery in mice; LPS-induced ALI model; pulmonary edema measurement; tight junction protein western blot; lung leakage assay\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo loss/gain of function with defined phenotypic readouts, single lab, extends prior in vitro finding\",\n      \"pmids\": [\"34675326\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"MRCKα physically binds ABCB4 (the hepatocyte canalicular phosphatidylcholine transporter) and its downstream effector myosin II regulatory light chain (MRLC) also binds ABCB4. Dominant-negative MRCKα mutant expression, MRCKα inhibition (chelerythrine), RNAi knockdown, or CRISPR-Cas9 knockout all increase ABCB4 steady-state protein expression at the cell surface, indicating MRCKα negatively regulates ABCB4 membrane expression via MRLC.\",\n      \"method\": \"Co-immunoprecipitation; dominant-negative mutant expression; pharmacological inhibition; siRNA knockdown; CRISPR-Cas9 knockout; ABCB4 surface expression assays in primary hepatocytes and HEK-293 cells\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal loss-of-function approaches (DN mutant, inhibitor, RNAi, CRISPR-KO) in two cell models, Co-IP interaction confirmed, convergent results\",\n      \"pmids\": [\"35203270\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"MRCKα physically interacts with Gli transcription factors and directly phosphorylates Gli2 on multiple sites. Double knockout of MRCKα and MRCKβ affects Gli2 ciliary and nuclear localization and reduces Gli2 binding to the Gli1 promoter, positively regulating Hedgehog pathway transcriptional output.\",\n      \"method\": \"Co-immunoprecipitation; in vitro kinase assay (direct phosphorylation of Gli2); CRISPR-Cas9 double knockout of MRCKα/β; Gli2 localization by immunofluorescence; ChIP assay for Gli2 binding to Gli1 promoter\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro kinase assay establishing direct phosphorylation, Co-IP, CRISPR-KO with multiple functional readouts (localization, promoter binding, transcriptional output), single lab\",\n      \"pmids\": [\"37019250\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Double knockout of MRCKα and MRCKβ in MDA-MB-231 triple-negative breast cancer cells reduces invasion, but single MRCKα knockout mice show no developmental phenotype and no effect on mammary tumor onset, growth, or metastasis in the MMTV-PyMT model.\",\n      \"method\": \"Conditional MRCKα gene knockout mice; MMTV-PyMT breast cancer model; invasion/migration assays in cell lines with double MRCKα/β CRISPR-KO\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo knockout model with defined tumor phenotypes, cell-based invasion assay, single lab; finding is partly negative (no in vivo tumor effect for single KO)\",\n      \"pmids\": [\"33921698\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"MRCKα interacts with GEF-H1 (ARHGEF2, a RhoA-selective guanine nucleotide exchange factor) and phosphorylates GEF-H1 on Ser174, suppressing GEF-H1 activity and thereby repressing RhoA activation. MRCK inhibition reduces GEF-H1 Ser174 phosphorylation, increases GEF-H1 activity and RhoA activation, disrupts cell-cell contacts, and impairs compaction of multicellular spheroids in HGSOC.\",\n      \"method\": \"Mass spectrometry identification of GEF-H1 as MRCKα interacting partner; Co-IP; phosphorylation site mapping (Ser174); pharmacological MRCK inhibition; GEF-H1 activity assays; RhoA activation assays; live-cell imaging; 3D spheroid assays; patient-derived organoids\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — MS-identified interaction, direct phosphorylation site identified, multiple functional assays (RhoA activation, GEF-H1 activity, 3D organoids), multiple orthogonal methods, preprint\",\n      \"pmids\": [\"41726953\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"MRCKα interacts with GEF-H1 in tubular cells (confirmed by immunoprecipitation and proximity ligation assay) and suppresses GEF-H1/RhoA/MRTF signaling. MRCKα silencing elevates GEF-H1 activity, RhoA activation, stress fibre formation, myosin light chain phosphorylation, cofilin phosphorylation, and MRTF nuclear translocation, leading to upregulation of fibrogenic genes including ACTA2. TGFβ1 increases GEF-H1/MRCKα binding.\",\n      \"method\": \"Co-immunoprecipitation; proximity ligation assay; siRNA knockdown of MRCKα; GEF-H1 activity assay; RhoA activity assay; myosin light chain and cofilin phosphorylation; MRTF nuclear translocation imaging; fibrogenic gene mRNA array; in vivo kidney fibrosis model with IHC\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP and PLA for interaction, multiple orthogonal readouts (RhoA activation, MLC phosphorylation, MRTF localization, gene expression), in vivo confirmation, independently convergent with preprint 41726953\",\n      \"pmids\": [\"41827880\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"MRCKα is modified by D-2-hydroxyglutarate (D2HG) via O-2-hydroxyglutarylation, and this modification is associated with reduced phosphorylation of MRCKα substrates, suggesting an inhibitory effect of D2HG modification on MRCKα kinase activity.\",\n      \"method\": \"Chemical proteomics identification of O-2-hydroxyglutarylation; substrate phosphorylation assays comparing modified vs unmodified kinase\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — chemical proteomics identification, substrate phosphorylation reduction observed but mechanism not fully dissected; preprint, single lab, MRCKα is one of two kinases briefly mentioned\",\n      \"pmids\": [\"bio_10.1101_2025.01.24.634716\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"MRCKα mediates prolactin-induced lactogenesis in bovine mammary epithelial cells via the mTOR/SREBP1/cyclin D1 signaling pathway. MRCKα silencing prevents prolactin-stimulated β-casein production, triglyceride secretion, and mTOR phosphorylation; MRCKα overexpression reverses these effects.\",\n      \"method\": \"siRNA knockdown and overexpression of MRCKα in primary bovine mammary epithelial cells; prolactin stimulation; western blot for β-casein, SREBP1, cyclin D1, phospho-mTOR; triglyceride secretion assay\",\n      \"journal\": \"Animal nutrition\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — bidirectional loss-of-function and gain-of-function with defined molecular pathway readouts, single lab\",\n      \"pmids\": [\"35891685\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"MRCKα acts downstream of PI3K and upstream of PKB (Akt) in methionine- and leucine-stimulated β-casein synthesis in bovine mammary epithelial cells, regulating mTOR phosphorylation. PI3K inhibition blocks Met/Leu-induced MRCKα expression; MRCKα silencing blocks PKB phosphorylation; PKB inhibitor blocks MRCKα-overexpression-induced mTOR activation.\",\n      \"method\": \"siRNA knockdown and overexpression of MRCKα; PI3K inhibitor (LY294002); PKB inhibitor (MK2206); western blot for phospho-mTOR, phospho-PKB, phospho-PI3K, β-casein; amino acid dose-response experiments in primary BMEC\",\n      \"journal\": \"Animal nutrition\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis established by pharmacological inhibitors combined with KD/OE, multiple pathway nodes measured, single lab\",\n      \"pmids\": [\"40487111\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"MRCKα (CDC42BPA) is a serine/threonine kinase that acts as a key downstream effector of CDC42-Rho GTPase signaling to regulate actomyosin cytoskeleton organization: it is activated by PDK1 downstream of EGF/PIP3 to drive directional cell migration and lamellipodia retraction; is cleaved and activated by caspases to assemble an apical actin ring for epithelial cell extrusion; phosphorylates and suppresses the RhoA-GEF GEF-H1 (Ser174), thereby restraining RhoA/MRTF-dependent fibrogenic and contractile programs; directly phosphorylates Gli2 transcription factors to promote Hedgehog pathway output; regulates myosin light chain phosphorylation downstream of NKA β1 subunit to maintain epithelial tight junction integrity; controls membrane trafficking of ABCB4 via its effector MRLC; participates in transferrin-iron uptake via cytoskeletal regulation of TfR endocytosis; and is itself regulated post-transcriptionally by cellular iron levels through a functional 3′UTR IRE, and by D2HG-mediated O-2-hydroxyglutarylation that inhibits its activity.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"CDC42BPA (MRCKα) is a serine/threonine kinase that functions as a downstream effector linking Rho-family GTPase and growth-factor signaling to actomyosin cytoskeletal organization, driving directional cell migration, epithelial barrier integrity, and contractility [#3, #6]. Downstream of EGF, PDK1 binds and activates MRCKα — independently of PDK1 kinase activity but dependent on its PIP3 membrane recruitment — and the two colocalize in lamellipodia to couple growth-factor signaling to myosin contraction and directional migration [#3]. MRCKα activates myosin light chain to enforce epithelial functions: it cooperates with the Na+,K+-ATPase β1 subunit to upregulate tight-junction proteins and maintain alveolar barrier function, and restoring MRCKα in vivo attenuates LPS-induced acute lung injury [#6, #7]. During apoptosis, caspase cleavage generates an active MRCKα fragment sufficient to assemble an apical actomyosin ring that compacts and extrudes dying epithelial cells [#4]. MRCKα also constrains RhoA signaling by phosphorylating the RhoA-GEF GEF-H1 (ARHGEF2) on Ser174, suppressing GEF-H1 activity; loss of MRCKα elevates GEF-H1/RhoA/MRTF signaling, stress fibre formation, and fibrogenic gene programs including ACTA2 [#11, #12]. Beyond cytoskeletal effectors, MRCKα directly phosphorylates Gli2 to promote its ciliary/nuclear localization and Hedgehog transcriptional output, and negatively regulates surface expression of the canalicular transporter ABCB4 via myosin regulatory light chain [#9, #8]. MRCKα expression is itself controlled post-transcriptionally by iron through a functional 3′UTR iron-responsive element, and the kinase participates in transferrin-receptor-mediated iron uptake [#1, #2].\",\n  \"teleology\": [\n    {\n      \"year\": 2006,\n      \"claim\": \"Established that MRCKα is not constitutively expressed but is post-transcriptionally tuned by cellular iron via a functional IRE, embedding the kinase in iron homeostasis regulation.\",\n      \"evidence\": \"Bioinformatic IRE identification and biochemical mRNA stability assays under varying iron conditions\",\n      \"pmids\": [\"16412980\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Does not identify which IRE-binding proteins act on the MRCKα transcript\", \"Does not connect IRE regulation to a kinase-dependent function\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Placed MRCKα downstream of Notch1 tumor-suppression, showing its upregulation cooperates with oncogenic Ras in keratinocyte carcinogenesis.\",\n      \"evidence\": \"Genetic and pharmacological Notch suppression with oncogenic Ras in primary keratinocytes and mouse grafts\",\n      \"pmids\": [\"17344417\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which MRCKα promotes SCC not resolved at the substrate level\", \"Co-upregulation with ROCK1/2 leaves relative contribution unclear\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Linked iron-regulated MRCKα to a cellular function — transferrin receptor endocytosis/trafficking — implicating its cytoskeletal activity in iron uptake.\",\n      \"evidence\": \"shRNA knockdown, colocalization with Tf-loaded TfR, and iron uptake assay\",\n      \"pmids\": [\"20188707\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"The cytoskeletal step in TfR endocytosis controlled by MRCKα is not defined\", \"No kinase substrate identified in this pathway\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Defined the upstream activation mechanism, showing PDK1 binds and activates MRCKα via PIP3-dependent membrane recruitment to couple EGF signaling to lamellipodial myosin contraction and directional migration.\",\n      \"evidence\": \"Reciprocal Co-IP, kinase-dead PDK1 mutants, lamellipodia retraction and migration assays with knockdown/rescue\",\n      \"pmids\": [\"25092657\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How PDK1 binding activates MRCKα kinase mechanistically is not detailed\", \"Does not map the relevant phosphorylation events on MRCKα\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Demonstrated MRCKα drives a discrete morphogenetic event — assembly of an apical actomyosin ring for apoptotic epithelial extrusion — activated by caspase cleavage.\",\n      \"evidence\": \"Live imaging, expression of the caspase-cleavage product, F-actin flow and myosin inhibition, extrusion assays\",\n      \"pmids\": [\"29162624\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Caspase cleavage site and the resulting activation mechanism not fully mapped\", \"Substrates within the extrusion ring not enumerated\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Positioned MRCKα as a rigidity-independent contractility module, with an ICAP-1/Smurf1 ubiquitylation switch toggling between ROCK2- and MRCKα-mediated contractility.\",\n      \"evidence\": \"Non-ubiquitylatable ICAP-1 mutants, MLC phosphorylation assays, migration on variable-stiffness substrates\",\n      \"pmids\": [\"28049720\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct biochemical link between ICAP-1 and MRCKα activation not established\", \"How the switch selects MRCKα over ROCK2 mechanistically unclear\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Connected MRCKα to epithelial barrier maintenance, showing it binds the Na+,K+-ATPase β1 subunit and uses MLC phosphorylation to upregulate tight junction proteins, with in vivo rescue of acute lung injury.\",\n      \"evidence\": \"Co-IP/MS, inducible overexpression and knockdown, barrier assays, and in vivo LPS-ALI gene transfer\",\n      \"pmids\": [\"33507884\", \"34675326\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct MRCKα substrate driving tight-junction upregulation not identified\", \"Whether NKA β1 directly modulates MRCKα kinase activity is unclear\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Tested in vivo requirement in cancer, revealing functional redundancy: dual MRCKα/β loss reduces TNBC invasion, but single MRCKα knockout has no developmental or mammary tumor phenotype.\",\n      \"evidence\": \"Conditional MRCKα knockout mice, MMTV-PyMT model, and double-knockout invasion assays\",\n      \"pmids\": [\"33921698\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Does not dissect distinct versus redundant roles of MRCKα and MRCKβ\", \"Negative in vivo single-KO result limits inference on isolated MRCKα function\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identified ABCB4 as a regulated target, showing MRCKα and MRLC bind ABCB4 and MRCKα negatively controls its surface expression, extending the kinase into membrane transporter trafficking.\",\n      \"evidence\": \"Co-IP plus convergent loss-of-function (DN mutant, inhibitor, RNAi, CRISPR-KO) and surface expression assays in hepatocytes and HEK-293\",\n      \"pmids\": [\"35203270\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The MRLC-dependent trafficking step controlling ABCB4 not mechanistically resolved\", \"Whether MRCKα phosphorylates ABCB4 directly not addressed\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Extended MRCKα into metabolic/secretory signaling, placing it in a PI3K→MRCKα→Akt→mTOR/SREBP1/cyclin D1 axis driving prolactin- and amino-acid-stimulated lactogenesis.\",\n      \"evidence\": \"Bidirectional knockdown/overexpression with pharmacological pathway inhibitors in bovine mammary epithelial cells\",\n      \"pmids\": [\"35891685\", \"40487111\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct MRCKα substrate in the mTOR pathway not identified\", \"Findings restricted to bovine mammary cells; human relevance not tested\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Revealed a non-cytoskeletal substrate, establishing MRCKα as a direct Gli2 kinase that promotes Gli2 localization, promoter binding, and Hedgehog transcriptional output.\",\n      \"evidence\": \"In vitro kinase assay, Co-IP, MRCKα/β CRISPR double-knockout, Gli2 localization and ChIP\",\n      \"pmids\": [\"37019250\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific Gli2 phosphosites and their functional consequences not mapped\", \"Relative roles of MRCKα versus MRCKβ in Hedgehog output unresolved\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Defined a RhoA-restraining function, showing MRCKα phosphorylates GEF-H1 on Ser174 to suppress GEF-H1/RhoA/MRTF signaling, controlling spheroid compaction and fibrogenic gene programs.\",\n      \"evidence\": \"MS-identified interaction, Co-IP, PLA, Ser174 phosphosite mapping, RhoA/GEF-H1 activity assays, MRTF translocation, 3D organoids, and in vivo kidney fibrosis model\",\n      \"pmids\": [\"41726953\", \"41827880\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"One key supporting study is a preprint (41726953)\", \"How TGFβ1 enhances GEF-H1/MRCKα binding mechanistically not resolved\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Proposed a metabolite-based inhibitory regulation, with D2HG-mediated O-2-hydroxyglutarylation associated with reduced MRCKα substrate phosphorylation.\",\n      \"evidence\": \"Chemical proteomics and substrate phosphorylation comparison (preprint)\",\n      \"pmids\": [\"bio_10.1101_2025.01.24.634716\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Preprint; modification site and direct effect on kinase activity not dissected\", \"MRCKα is one of two kinases briefly examined, limiting specificity\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The unifying question of how distinct upstream inputs (PDK1/EGF, caspase cleavage, ICAP-1 switch, metabolite modification) selectively direct MRCKα toward its diverse substrates (MLC, GEF-H1, Gli2, ABCB4) remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model linking activation mode to substrate selection\", \"Functional separation of MRCKα from redundant MRCKβ not established across contexts\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [3, 9, 11, 12]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [9, 11]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [3, 8]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [2, 4]},\n      {\"term_id\": \"GO:0005929\", \"supporting_discovery_ids\": [9]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [3, 11, 12]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [4]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [9, 12]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"PDK1\", \"ARHGEF2\", \"GLI2\", \"ABCB4\", \"ATP1B1\", \"MRLC\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}