{"gene":"MAST4","run_date":"2026-06-10T02:59:50","timeline":{"discoveries":[{"year":2022,"finding":"MAST4 phosphorylates Sox9 at serine 494, leading to its proteasomal degradation; TGF-β1 suppresses MAST4, thereby stabilizing Sox9 and enhancing chondrogenesis of mesenchymal stromal cells.","method":"Knockout mouse model (Mast4-/- mice), in vitro phosphorylation assay, proteasomal degradation assay, MSC differentiation assays","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal genetic (KO mouse) and biochemical (phosphorylation site identification) approaches, replicated in vivo and in vitro in a single rigorous study","pmids":["35803931"],"is_preprint":false},{"year":2022,"finding":"Wnt-mediated inhibition of GSK-3β enhances MAST4 protein stability (via blocking Smurf1-mediated recruitment/degradation), and MAST4 in turn promotes β-catenin nuclear localization and Runx2 activity to increase osteogenesis of MSCs.","method":"Knockout mouse model (Mast4-/- mice), in vitro osteogenesis assay, Wnt pathway manipulation, protein stability assays","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (KO mouse, pathway manipulation, protein stability assays) in a single rigorous study","pmids":["35803931"],"is_preprint":false},{"year":2020,"finding":"MAST4 phosphorylates the Ets-related molecule (ERM) at serine 367 in Sertoli cells, controlling transcription of ERM target genes related to spermatogonial stem cell (SSC) self-renewal; Mast4 KO mice show germ cell depletion resembling Sertoli cell-only syndrome.","method":"Mast4 knockout mice, in vitro phosphorylation assay (identifying S367 on ERM), RNA-sequencing, immunohistochemistry, western blot","journal":"Cell death and differentiation","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vitro phosphorylation with specific residue identification, KO mouse phenotype, RNA-seq, multiple orthogonal methods","pmids":["33219327"],"is_preprint":false},{"year":2023,"finding":"MAST4 is localized at the primary cilium and phosphorylates Tctex-1 at Thr94; this phosphorylation event at the ciliary base promotes ciliary resorption via Cdc42 activation and Rab5-mediated periciliary membrane endocytosis. Tctex-1 binds to the kinase domain of MAST4, with residues R503 and D504 being key to this function.","method":"Localization (immunofluorescence), MAST4 knockdown, overexpression, catalytic-inactive site-directed mutants (R503/D504), Co-IP/pulldown (Tctex-1 binding to kinase domain), phospho-specific antibody detection, Cdc42 activation assay","journal":"Life science alliance","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — direct kinase-substrate relationship established with site-directed mutagenesis, binding domain mapping, and functional rescue, multiple orthogonal methods in a single rigorous study","pmids":["37726137"],"is_preprint":false},{"year":2017,"finding":"MAST4 is transcriptionally activated by the APP intracellular domain (AICD) in response to low-dose 27-hydroxycholesterol (27OHC); MAST4 then phosphorylates and inhibits FOXO1-dependent transcriptional repression of RTKN2, promoting cell survival.","method":"AICD transactivation reporter assay, MAST4 kinase activity assay on FOXO1, in vivo (palmitate diet/APP ablation mouse), human AD brain tissue analysis","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — kinase assay on FOXO1 substrate and in vivo validation, single lab with two complementary approaches but abstract-level detail limits full tier 1 assignment","pmids":["29066835"],"is_preprint":false},{"year":2022,"finding":"MAST4 interacts with PTEN, thereby regulating the PI3K-Akt-mTOR pathway and downstream cytokine (CCL2/3/4) expression in multiple myeloma cells; MAST4 expression is driven by estrogen receptor 1 (ESR1), which binds the MAST4 promoter (shown by ChIP assay).","method":"Co-IP (MAST4-PTEN interaction), ChIP assay (ESR1 binding to MAST4 promoter), siRNA knockdown, in vitro osteoclast formation assay, mouse model","journal":"Journal of bone and mineral research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP for PTEN binding, ChIP for promoter occupancy, functional KD assays in vitro and in vivo, single lab","pmids":["35064934"],"is_preprint":false},{"year":2023,"finding":"In Sertoli cells, MAST4 promotes CDK2 to phosphorylate PLZF; activated PLZF suppresses transcription of cell cycle arrest-related genes, maintaining SSCs in a stem cell state. Mast4 KO mice show decreased PLZF expression and abnormal cell cycle progression in testes.","method":"Mast4 KO mice, BrdU/IdU cell cycle analysis, immunohistochemistry, RT-qPCR, western blot, in vitro testis tissue culture","journal":"Cell proliferation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO mouse with defined cell cycle phenotype and CDK2-PLZF pathway placement, single lab but multiple methods","pmids":["36592615"],"is_preprint":false},{"year":2024,"finding":"Nuclear MAST4 interacts with AKT3 and both translocate to the nucleus in gemcitabine-resistant pancreatic ductal adenocarcinoma cells, where they phosphorylate FOXO3a, inhibiting apoptosis and promoting stemness and proliferation.","method":"MAST4 knockdown, AKT3 inhibitor screening, nuclear fractionation, FOXO3 phosphorylation assay, gemcitabine-resistant cell line model","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — nuclear fractionation, KD with defined pathway, phosphorylation assay, single lab","pmids":["38612866"],"is_preprint":false},{"year":2024,"finding":"MAST4 directly binds to DLX3 and phosphorylates it at three residues within its nuclear localization signal (NLS), promoting nuclear translocation of DLX3 and controlling transcription of carbonic anhydrase and ion transporter genes involved in pH regulation during ameloblast maturation.","method":"Co-IP/direct binding assay (MAST4-DLX3), phosphorylation mapping (3 NLS residues), Mast4 KO mouse (amelogenesis imperfecta phenotype), immunohistochemistry, Wnt signaling analysis","journal":"Experimental & molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct binding assay, phosphorylation site mapping, KO mouse functional phenotype, single lab with multiple orthogonal methods","pmids":["38945953"],"is_preprint":false},{"year":2006,"finding":"MAST4 encodes a 2435-amino acid protein containing a serine/threonine kinase domain and a PDZ domain, localized on human chromosome 5q13.","method":"cDNA cloning, sequence analysis, RT-PCR for tissue expression","journal":"Molekuliarnaia biologiia","confidence":"Medium","confidence_rationale":"Tier 3 / Strong — definitive cloning and domain characterization, replicated by subsequent studies using this sequence","pmids":["17086981"],"is_preprint":false},{"year":2020,"finding":"MAST4 is localized in Sertoli cells before puberty (providing a somatic niche), with expression shifting to Leydig cells and spermatids during puberty.","method":"Immunohistochemistry and localization studies in mouse testes at different developmental stages","journal":"Cell death and differentiation","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — direct localization by IHC across developmental time points, single lab but consistent with functional KO data","pmids":["33219327"],"is_preprint":false}],"current_model":"MAST4 is a serine/threonine kinase with a PDZ domain that acts as a context-dependent signaling hub: it phosphorylates Sox9 (S494) to drive proteasomal degradation during osteogenesis, phosphorylates ERM (S367) to sustain spermatogonial stem cell self-renewal, phosphorylates Tctex-1 (T94) at the ciliary base to promote primary cilium resorption via Cdc42 and Rab5-dependent endocytosis, phosphorylates FOXO1 downstream of AICD/27OHC to promote cell survival, interacts with PTEN to regulate PI3K-Akt-mTOR signaling, partners with nuclear AKT3 to phosphorylate FOXO3 in chemoresistant cancer cells, and phosphorylates DLX3 at its NLS to drive nuclear translocation and ameloblast maturation—with its own stability and activity regulated upstream by TGF-β1 (suppression), Wnt/GSK-3β inhibition (stabilization), and AICD-driven transcription."},"narrative":{"mechanistic_narrative":"MAST4 is a multidomain serine/threonine kinase containing a kinase domain and a PDZ domain that functions as a context-dependent signaling hub coupling upstream developmental cues to substrate phosphorylation across diverse cell types [PMID:17086981, PMID:35803931]. In mesenchymal stromal cells it integrates two opposing lineage signals: it phosphorylates Sox9 at Ser494 to drive its proteasomal degradation, an activity suppressed by TGF-β1 to permit chondrogenesis, while Wnt-mediated inhibition of GSK-3β stabilizes MAST4 (by blocking Smurf1-dependent degradation) to promote β-catenin nuclear localization, Runx2 activity, and osteogenesis [PMID:35803931]. A recurring theme is MAST4-driven nuclear translocation and regulation of transcription factors: it phosphorylates the Ets factor ERM at Ser367 in Sertoli cells to sustain spermatogonial stem cell self-renewal, and directly binds DLX3 to phosphorylate residues within its nuclear localization signal, promoting DLX3 nuclear import and ameloblast maturation [PMID:33219327, PMID:38945953]. MAST4 also localizes to the primary cilium, where it phosphorylates Tctex-1 at Thr94 to trigger ciliary resorption through Cdc42 activation and Rab5-dependent periciliary endocytosis [PMID:37726137]. In disease and survival contexts it engages PI3K-Akt-mTOR signaling through PTEN interaction and partners with nuclear AKT3 to phosphorylate FOXO transcription factors, inhibiting apoptosis and promoting chemoresistance [PMID:35064934, PMID:38612866, PMID:29066835]. Loss-of-function mouse models tie these activities to skeletal differentiation, a Sertoli-cell-only-like germ cell depletion, and amelogenesis imperfecta [PMID:35803931, PMID:33219327, PMID:38945953].","teleology":[{"year":2006,"claim":"Established the molecular identity of MAST4 as a kinase, defining the domain architecture that all later substrate work would build on.","evidence":"cDNA cloning, sequence analysis and RT-PCR tissue profiling","pmids":["17086981"],"confidence":"Medium","gaps":["No functional or substrate data","Kinase activity not demonstrated biochemically","No subcellular localization defined"]},{"year":2017,"claim":"First placed MAST4 in a survival signaling pathway, showing it is a transcriptional target of AICD that in turn phosphorylates and inhibits FOXO1.","evidence":"AICD transactivation reporter, FOXO1 kinase assay, palmitate-diet/APP-ablation mouse and human AD brain tissue","pmids":["29066835"],"confidence":"Medium","gaps":["FOXO1 phosphosite not mapped","Abstract-level mechanistic detail","Direct vs indirect kinase action not fully resolved"]},{"year":2020,"claim":"Defined MAST4 as a direct kinase for the transcription factor ERM and assigned a physiological role in the Sertoli niche, with a KO phenotype mimicking Sertoli-cell-only syndrome.","evidence":"Mast4 KO mice, in vitro phosphorylation identifying ERM S367, RNA-seq, IHC localization across testis development","pmids":["33219327"],"confidence":"High","gaps":["Mechanism of ERM phosphorylation effect on specific target genes incompletely defined","Stage-specific expression shift not mechanistically explained"]},{"year":2022,"claim":"Resolved how MAST4 balances opposing MSC lineages by phosphorylating Sox9 for degradation and being itself stabilized by Wnt/GSK-3β inhibition to promote osteogenesis.","evidence":"Mast4 KO mice, in vitro phosphorylation identifying Sox9 S494, proteasomal degradation and protein-stability assays, Wnt pathway manipulation, differentiation assays","pmids":["35803931"],"confidence":"High","gaps":["Smurf1-MAST4 recruitment mechanism not structurally defined","How GSK-3β status is sensed by MAST4 unclear"]},{"year":2022,"claim":"Connected MAST4 to PI3K-Akt-mTOR signaling via PTEN interaction and identified ESR1 as a transcriptional driver in multiple myeloma.","evidence":"Co-IP for MAST4-PTEN, ChIP for ESR1 promoter occupancy, siRNA knockdown, osteoclast formation assay, mouse model","pmids":["35064934"],"confidence":"Medium","gaps":["PTEN interaction not reciprocally validated","Whether MAST4 phosphorylates PTEN unknown","Direct vs scaffolding role in PI3K axis unresolved"]},{"year":2023,"claim":"Extended MAST4's stem-cell role by showing it engages CDK2 to phosphorylate PLZF, maintaining spermatogonial stem cells via cell-cycle gene suppression.","evidence":"Mast4 KO mice, BrdU/IdU cell cycle analysis, IHC, RT-qPCR, in vitro testis culture","pmids":["36592615"],"confidence":"Medium","gaps":["Whether MAST4 directly phosphorylates CDK2 or acts indirectly not established","Relationship to the ERM pathway in the same cells unclear"]},{"year":2023,"claim":"Localized MAST4 to the primary cilium and defined a direct kinase-substrate relationship with Tctex-1 controlling ciliary resorption.","evidence":"IF localization, knockdown/overexpression, catalytic-inactive R503/D504 mutants, Co-IP mapping Tctex-1 to the kinase domain, phospho-specific detection of Thr94, Cdc42 activation assay","pmids":["37726137"],"confidence":"High","gaps":["Upstream cue that activates ciliary MAST4 unknown","Link between ciliary function and other MAST4 roles unexplored"]},{"year":2024,"claim":"Showed nuclear MAST4 partners with AKT3 to phosphorylate FOXO3a, driving chemoresistance and stemness in gemcitabine-resistant pancreatic cancer.","evidence":"MAST4 knockdown, AKT3 inhibitor screening, nuclear fractionation, FOXO3 phosphorylation assay in gemcitabine-resistant cells","pmids":["38612866"],"confidence":"Medium","gaps":["Mechanism of MAST4/AKT3 nuclear translocation unknown","Direct FOXO3a phosphosite not mapped","Single cell-line model"]},{"year":2024,"claim":"Established a direct MAST4-DLX3 kinase-substrate relationship controlling DLX3 nuclear import and ameloblast maturation, with a KO amelogenesis imperfecta phenotype.","evidence":"Co-IP/direct binding, phosphorylation mapping of three NLS residues, Mast4 KO mouse, IHC, Wnt signaling analysis","pmids":["38945953"],"confidence":"Medium","gaps":["Identity of individual NLS phosphosites and their relative contributions partly defined","Link between Wnt input and DLX3 phosphorylation not fully resolved"]},{"year":null,"claim":"How MAST4's many context-specific substrate choices and subcellular localizations (ciliary, nuclear, cytoplasmic) are coordinated by a single kinase remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unifying model linking ciliary, nuclear and degradation activities","No structure of the kinase or PDZ domain bound to substrates","Substrate-selection determinants across tissues unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,2,3,8]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,2,3,8]}],"localization":[{"term_id":"GO:0005929","term_label":"cilium","supporting_discovery_ids":[3]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[7,8]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[1,5]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[0,1,2,8]}],"complexes":[],"partners":["SOX9","ERM","DCTN1","TCTEX-1","PTEN","AKT3","DLX3","FOXO1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O15021","full_name":"Microtubule-associated serine/threonine-protein kinase 4","aliases":[],"length_aa":2623,"mass_kda":284.1,"function":"","subcellular_location":"Cytoplasm","url":"https://www.uniprot.org/uniprotkb/O15021/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MAST4","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":[],"url":"https://opencell.sf.czbiohub.org/search/MAST4","total_profiled":1310},"omim":[{"mim_id":"618002","title":"MICROTUBULE-ASSOCIATED SERINE/THREONINE KINASE 4; MAST4","url":"https://www.omim.org/entry/618002"},{"mim_id":"612258","title":"MICROTUBULE-ASSOCIATED SERINE/THREONINE KINASE 3; MAST3","url":"https://www.omim.org/entry/612258"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"},{"location":"Cytosol","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/MAST4"},"hgnc":{"alias_symbol":["KIAA0303"],"prev_symbol":[]},"alphafold":{"accession":"O15021","domains":[{"cath_id":"1.20.1480.20","chopping":"365-489","consensus_level":"high","plddt":87.0526,"start":365,"end":489},{"cath_id":"3.30.200.20","chopping":"565-652_876-882_900-912","consensus_level":"medium","plddt":85.0264,"start":565,"end":912},{"cath_id":"1.10.510.10","chopping":"658-862","consensus_level":"medium","plddt":86.0849,"start":658,"end":862},{"cath_id":"2.30.42.10","chopping":"1143-1231","consensus_level":"high","plddt":87.6407,"start":1143,"end":1231}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O15021","model_url":"https://alphafold.ebi.ac.uk/files/AF-O15021-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O15021-F1-predicted_aligned_error_v6.png","plddt_mean":42.53},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=MAST4","jax_strain_url":"https://www.jax.org/strain/search?query=MAST4"},"sequence":{"accession":"O15021","fasta_url":"https://rest.uniprot.org/uniprotkb/O15021.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O15021/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O15021"}},"corpus_meta":[{"pmid":"35803931","id":"PMC_35803931","title":"Mast4 determines the cell fate of MSCs for bone and cartilage development.","date":"2022","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/35803931","citation_count":47,"is_preprint":false},{"pmid":"19196271","id":"PMC_19196271","title":"Distribution of the uncultured protist MAST-4 in the Indian Ocean, Drake Passage and Mediterranean Sea assessed by real-time quantitative PCR.","date":"2009","source":"Environmental microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/19196271","citation_count":28,"is_preprint":false},{"pmid":"22319144","id":"PMC_22319144","title":"Low evolutionary diversification in a widespread and abundant uncultured protist (MAST-4).","date":"2011","source":"Molecular biology and evolution","url":"https://pubmed.ncbi.nlm.nih.gov/22319144","citation_count":26,"is_preprint":false},{"pmid":"35064934","id":"PMC_35064934","title":"Estrogen-Responsive Gene MAST4 Regulates Myeloma Bone Disease.","date":"2022","source":"Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research","url":"https://pubmed.ncbi.nlm.nih.gov/35064934","citation_count":19,"is_preprint":false},{"pmid":"33219327","id":"PMC_33219327","title":"Mast4 knockout shows the regulation of spermatogonial stem cell self-renewal via the FGF2/ERM pathway.","date":"2020","source":"Cell death and differentiation","url":"https://pubmed.ncbi.nlm.nih.gov/33219327","citation_count":19,"is_preprint":false},{"pmid":"29066835","id":"PMC_29066835","title":"Cellular hormetic response to 27-hydroxycholesterol promotes neuroprotection through AICD induction of MAST4 abundance and kinase activity.","date":"2017","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/29066835","citation_count":19,"is_preprint":false},{"pmid":"29948376","id":"PMC_29948376","title":"Clinical and genetic study of Tunisian families with genetic generalized epilepsy: contribution of CACNA1H and MAST4 genes.","date":"2018","source":"Neurogenetics","url":"https://pubmed.ncbi.nlm.nih.gov/29948376","citation_count":14,"is_preprint":false},{"pmid":"36910266","id":"PMC_36910266","title":"De novo variants in MAST4 related to neurodevelopmental disorders with developmental delay and infantile spasms: Genotype-phenotype association.","date":"2023","source":"Frontiers in molecular neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/36910266","citation_count":13,"is_preprint":false},{"pmid":"17086981","id":"PMC_17086981","title":"[Identification of a novel human MAST4 gene, a new member of the microtubule associated serine-threonine kinase family].","date":"2006","source":"Molekuliarnaia biologiia","url":"https://pubmed.ncbi.nlm.nih.gov/17086981","citation_count":13,"is_preprint":false},{"pmid":"36592615","id":"PMC_36592615","title":"MAST4 controls cell cycle in spermatogonial stem cells.","date":"2023","source":"Cell 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sciences","url":"https://pubmed.ncbi.nlm.nih.gov/38612866","citation_count":4,"is_preprint":false},{"pmid":"38945953","id":"PMC_38945953","title":"MAST4 regulates stem cell maintenance with DLX3 for epithelial development and amelogenesis.","date":"2024","source":"Experimental & molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/38945953","citation_count":3,"is_preprint":false},{"pmid":"40656202","id":"PMC_40656202","title":"Genetic and clinical insights into MAST4-related neurodevelopmental disorders.","date":"2025","source":"Frontiers in pediatrics","url":"https://pubmed.ncbi.nlm.nih.gov/40656202","citation_count":1,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2024.07.13.24310153","title":"Proteome-wide Mendelian randomization study implicates inflammaging biomarkers in retinal vasculature, cardiometabolic diseases and 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differentiation assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal genetic (KO mouse) and biochemical (phosphorylation site identification) approaches, replicated in vivo and in vitro in a single rigorous study\",\n      \"pmids\": [\"35803931\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Wnt-mediated inhibition of GSK-3β enhances MAST4 protein stability (via blocking Smurf1-mediated recruitment/degradation), and MAST4 in turn promotes β-catenin nuclear localization and Runx2 activity to increase osteogenesis of MSCs.\",\n      \"method\": \"Knockout mouse model (Mast4-/- mice), in vitro osteogenesis assay, Wnt pathway manipulation, protein stability assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (KO mouse, pathway manipulation, protein stability assays) in a single rigorous study\",\n      \"pmids\": [\"35803931\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"MAST4 phosphorylates the Ets-related molecule (ERM) at serine 367 in Sertoli cells, controlling transcription of ERM target genes related to spermatogonial stem cell (SSC) self-renewal; Mast4 KO mice show germ cell depletion resembling Sertoli cell-only syndrome.\",\n      \"method\": \"Mast4 knockout mice, in vitro phosphorylation assay (identifying S367 on ERM), RNA-sequencing, immunohistochemistry, western blot\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vitro phosphorylation with specific residue identification, KO mouse phenotype, RNA-seq, multiple orthogonal methods\",\n      \"pmids\": [\"33219327\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"MAST4 is localized at the primary cilium and phosphorylates Tctex-1 at Thr94; this phosphorylation event at the ciliary base promotes ciliary resorption via Cdc42 activation and Rab5-mediated periciliary membrane endocytosis. Tctex-1 binds to the kinase domain of MAST4, with residues R503 and D504 being key to this function.\",\n      \"method\": \"Localization (immunofluorescence), MAST4 knockdown, overexpression, catalytic-inactive site-directed mutants (R503/D504), Co-IP/pulldown (Tctex-1 binding to kinase domain), phospho-specific antibody detection, Cdc42 activation assay\",\n      \"journal\": \"Life science alliance\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — direct kinase-substrate relationship established with site-directed mutagenesis, binding domain mapping, and functional rescue, multiple orthogonal methods in a single rigorous study\",\n      \"pmids\": [\"37726137\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"MAST4 is transcriptionally activated by the APP intracellular domain (AICD) in response to low-dose 27-hydroxycholesterol (27OHC); MAST4 then phosphorylates and inhibits FOXO1-dependent transcriptional repression of RTKN2, promoting cell survival.\",\n      \"method\": \"AICD transactivation reporter assay, MAST4 kinase activity assay on FOXO1, in vivo (palmitate diet/APP ablation mouse), human AD brain tissue analysis\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — kinase assay on FOXO1 substrate and in vivo validation, single lab with two complementary approaches but abstract-level detail limits full tier 1 assignment\",\n      \"pmids\": [\"29066835\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"MAST4 interacts with PTEN, thereby regulating the PI3K-Akt-mTOR pathway and downstream cytokine (CCL2/3/4) expression in multiple myeloma cells; MAST4 expression is driven by estrogen receptor 1 (ESR1), which binds the MAST4 promoter (shown by ChIP assay).\",\n      \"method\": \"Co-IP (MAST4-PTEN interaction), ChIP assay (ESR1 binding to MAST4 promoter), siRNA knockdown, in vitro osteoclast formation assay, mouse model\",\n      \"journal\": \"Journal of bone and mineral research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP for PTEN binding, ChIP for promoter occupancy, functional KD assays in vitro and in vivo, single lab\",\n      \"pmids\": [\"35064934\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"In Sertoli cells, MAST4 promotes CDK2 to phosphorylate PLZF; activated PLZF suppresses transcription of cell cycle arrest-related genes, maintaining SSCs in a stem cell state. Mast4 KO mice show decreased PLZF expression and abnormal cell cycle progression in testes.\",\n      \"method\": \"Mast4 KO mice, BrdU/IdU cell cycle analysis, immunohistochemistry, RT-qPCR, western blot, in vitro testis tissue culture\",\n      \"journal\": \"Cell proliferation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO mouse with defined cell cycle phenotype and CDK2-PLZF pathway placement, single lab but multiple methods\",\n      \"pmids\": [\"36592615\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Nuclear MAST4 interacts with AKT3 and both translocate to the nucleus in gemcitabine-resistant pancreatic ductal adenocarcinoma cells, where they phosphorylate FOXO3a, inhibiting apoptosis and promoting stemness and proliferation.\",\n      \"method\": \"MAST4 knockdown, AKT3 inhibitor screening, nuclear fractionation, FOXO3 phosphorylation assay, gemcitabine-resistant cell line model\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — nuclear fractionation, KD with defined pathway, phosphorylation assay, single lab\",\n      \"pmids\": [\"38612866\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"MAST4 directly binds to DLX3 and phosphorylates it at three residues within its nuclear localization signal (NLS), promoting nuclear translocation of DLX3 and controlling transcription of carbonic anhydrase and ion transporter genes involved in pH regulation during ameloblast maturation.\",\n      \"method\": \"Co-IP/direct binding assay (MAST4-DLX3), phosphorylation mapping (3 NLS residues), Mast4 KO mouse (amelogenesis imperfecta phenotype), immunohistochemistry, Wnt signaling analysis\",\n      \"journal\": \"Experimental & molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding assay, phosphorylation site mapping, KO mouse functional phenotype, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"38945953\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"MAST4 encodes a 2435-amino acid protein containing a serine/threonine kinase domain and a PDZ domain, localized on human chromosome 5q13.\",\n      \"method\": \"cDNA cloning, sequence analysis, RT-PCR for tissue expression\",\n      \"journal\": \"Molekuliarnaia biologiia\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Strong — definitive cloning and domain characterization, replicated by subsequent studies using this sequence\",\n      \"pmids\": [\"17086981\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"MAST4 is localized in Sertoli cells before puberty (providing a somatic niche), with expression shifting to Leydig cells and spermatids during puberty.\",\n      \"method\": \"Immunohistochemistry and localization studies in mouse testes at different developmental stages\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — direct localization by IHC across developmental time points, single lab but consistent with functional KO data\",\n      \"pmids\": [\"33219327\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"MAST4 is a serine/threonine kinase with a PDZ domain that acts as a context-dependent signaling hub: it phosphorylates Sox9 (S494) to drive proteasomal degradation during osteogenesis, phosphorylates ERM (S367) to sustain spermatogonial stem cell self-renewal, phosphorylates Tctex-1 (T94) at the ciliary base to promote primary cilium resorption via Cdc42 and Rab5-dependent endocytosis, phosphorylates FOXO1 downstream of AICD/27OHC to promote cell survival, interacts with PTEN to regulate PI3K-Akt-mTOR signaling, partners with nuclear AKT3 to phosphorylate FOXO3 in chemoresistant cancer cells, and phosphorylates DLX3 at its NLS to drive nuclear translocation and ameloblast maturation—with its own stability and activity regulated upstream by TGF-β1 (suppression), Wnt/GSK-3β inhibition (stabilization), and AICD-driven transcription.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"MAST4 is a multidomain serine/threonine kinase containing a kinase domain and a PDZ domain that functions as a context-dependent signaling hub coupling upstream developmental cues to substrate phosphorylation across diverse cell types [#9, #0]. In mesenchymal stromal cells it integrates two opposing lineage signals: it phosphorylates Sox9 at Ser494 to drive its proteasomal degradation, an activity suppressed by TGF-\\u03b21 to permit chondrogenesis, while Wnt-mediated inhibition of GSK-3\\u03b2 stabilizes MAST4 (by blocking Smurf1-dependent degradation) to promote \\u03b2-catenin nuclear localization, Runx2 activity, and osteogenesis [#0, #1]. A recurring theme is MAST4-driven nuclear translocation and regulation of transcription factors: it phosphorylates the Ets factor ERM at Ser367 in Sertoli cells to sustain spermatogonial stem cell self-renewal, and directly binds DLX3 to phosphorylate residues within its nuclear localization signal, promoting DLX3 nuclear import and ameloblast maturation [#2, #8]. MAST4 also localizes to the primary cilium, where it phosphorylates Tctex-1 at Thr94 to trigger ciliary resorption through Cdc42 activation and Rab5-dependent periciliary endocytosis [#3]. In disease and survival contexts it engages PI3K-Akt-mTOR signaling through PTEN interaction and partners with nuclear AKT3 to phosphorylate FOXO transcription factors, inhibiting apoptosis and promoting chemoresistance [#5, #7, #4]. Loss-of-function mouse models tie these activities to skeletal differentiation, a Sertoli-cell-only-like germ cell depletion, and amelogenesis imperfecta [#0, #2, #8].\",\n  \"teleology\": [\n    {\n      \"year\": 2006,\n      \"claim\": \"Established the molecular identity of MAST4 as a kinase, defining the domain architecture that all later substrate work would build on.\",\n      \"evidence\": \"cDNA cloning, sequence analysis and RT-PCR tissue profiling\",\n      \"pmids\": [\"17086981\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No functional or substrate data\", \"Kinase activity not demonstrated biochemically\", \"No subcellular localization defined\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"First placed MAST4 in a survival signaling pathway, showing it is a transcriptional target of AICD that in turn phosphorylates and inhibits FOXO1.\",\n      \"evidence\": \"AICD transactivation reporter, FOXO1 kinase assay, palmitate-diet/APP-ablation mouse and human AD brain tissue\",\n      \"pmids\": [\"29066835\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"FOXO1 phosphosite not mapped\", \"Abstract-level mechanistic detail\", \"Direct vs indirect kinase action not fully resolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Defined MAST4 as a direct kinase for the transcription factor ERM and assigned a physiological role in the Sertoli niche, with a KO phenotype mimicking Sertoli-cell-only syndrome.\",\n      \"evidence\": \"Mast4 KO mice, in vitro phosphorylation identifying ERM S367, RNA-seq, IHC localization across testis development\",\n      \"pmids\": [\"33219327\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of ERM phosphorylation effect on specific target genes incompletely defined\", \"Stage-specific expression shift not mechanistically explained\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Resolved how MAST4 balances opposing MSC lineages by phosphorylating Sox9 for degradation and being itself stabilized by Wnt/GSK-3\\u03b2 inhibition to promote osteogenesis.\",\n      \"evidence\": \"Mast4 KO mice, in vitro phosphorylation identifying Sox9 S494, proteasomal degradation and protein-stability assays, Wnt pathway manipulation, differentiation assays\",\n      \"pmids\": [\"35803931\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Smurf1-MAST4 recruitment mechanism not structurally defined\", \"How GSK-3\\u03b2 status is sensed by MAST4 unclear\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Connected MAST4 to PI3K-Akt-mTOR signaling via PTEN interaction and identified ESR1 as a transcriptional driver in multiple myeloma.\",\n      \"evidence\": \"Co-IP for MAST4-PTEN, ChIP for ESR1 promoter occupancy, siRNA knockdown, osteoclast formation assay, mouse model\",\n      \"pmids\": [\"35064934\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"PTEN interaction not reciprocally validated\", \"Whether MAST4 phosphorylates PTEN unknown\", \"Direct vs scaffolding role in PI3K axis unresolved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Extended MAST4's stem-cell role by showing it engages CDK2 to phosphorylate PLZF, maintaining spermatogonial stem cells via cell-cycle gene suppression.\",\n      \"evidence\": \"Mast4 KO mice, BrdU/IdU cell cycle analysis, IHC, RT-qPCR, in vitro testis culture\",\n      \"pmids\": [\"36592615\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether MAST4 directly phosphorylates CDK2 or acts indirectly not established\", \"Relationship to the ERM pathway in the same cells unclear\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Localized MAST4 to the primary cilium and defined a direct kinase-substrate relationship with Tctex-1 controlling ciliary resorption.\",\n      \"evidence\": \"IF localization, knockdown/overexpression, catalytic-inactive R503/D504 mutants, Co-IP mapping Tctex-1 to the kinase domain, phospho-specific detection of Thr94, Cdc42 activation assay\",\n      \"pmids\": [\"37726137\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Upstream cue that activates ciliary MAST4 unknown\", \"Link between ciliary function and other MAST4 roles unexplored\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Showed nuclear MAST4 partners with AKT3 to phosphorylate FOXO3a, driving chemoresistance and stemness in gemcitabine-resistant pancreatic cancer.\",\n      \"evidence\": \"MAST4 knockdown, AKT3 inhibitor screening, nuclear fractionation, FOXO3 phosphorylation assay in gemcitabine-resistant cells\",\n      \"pmids\": [\"38612866\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of MAST4/AKT3 nuclear translocation unknown\", \"Direct FOXO3a phosphosite not mapped\", \"Single cell-line model\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Established a direct MAST4-DLX3 kinase-substrate relationship controlling DLX3 nuclear import and ameloblast maturation, with a KO amelogenesis imperfecta phenotype.\",\n      \"evidence\": \"Co-IP/direct binding, phosphorylation mapping of three NLS residues, Mast4 KO mouse, IHC, Wnt signaling analysis\",\n      \"pmids\": [\"38945953\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Identity of individual NLS phosphosites and their relative contributions partly defined\", \"Link between Wnt input and DLX3 phosphorylation not fully resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How MAST4's many context-specific substrate choices and subcellular localizations (ciliary, nuclear, cytoplasmic) are coordinated by a single kinase remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unifying model linking ciliary, nuclear and degradation activities\", \"No structure of the kinase or PDZ domain bound to substrates\", \"Substrate-selection determinants across tissues unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 2, 3, 8]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 2, 3, 8]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005929\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [7, 8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 5]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [0, 1, 2, 8]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"SOX9\", \"ERM\", \"DCTN1\", \"Tctex-1\", \"PTEN\", \"AKT3\", \"DLX3\", \"FOXO1\"]\n  }\n}","audit_flag":null,"evaluation":{"faith_supported":6,"faith_total":6,"faith_pct":100.0}}