{"gene":"SEPTIN4","run_date":"2026-04-28T20:42:07","timeline":{"discoveries":[{"year":2004,"finding":"ARTS (SEPT4_i2), a mitochondrial septin-like protein, is released from mitochondria upon pro-apoptotic stimuli and directly binds XIAP to antagonize its caspase-inhibitory function, leading to decreased XIAP protein levels and caspase activation. Recombinant ARTS and XIAP bind each other in vitro, and ARTS mutants that fail to bind XIAP fail to induce apoptosis.","method":"In vitro binding assay with recombinant proteins, Co-immunoprecipitation, cell-based apoptosis assays with mutant ARTS, Drosophila genetic epistasis (peanut mutations suppress Reaper/Hid/Grim killing)","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1–2 — in vitro reconstitution of direct binding + mutagenesis + genetic epistasis, replicated across multiple papers","pmids":["15029247"],"is_preprint":false},{"year":2010,"finding":"ARTS binds XIAP at the BIR1 domain (distinct from caspase-binding sites) and interacts with the E3 ubiquitin ligase Siah-1, acting as an adaptor to bridge Siah-1 to XIAP and target it for ubiquitination and proteasomal degradation. Cells lacking either Siah or ARTS have elevated steady-state XIAP levels.","method":"Co-immunoprecipitation, domain mapping, knockdown/knockout cell lines with XIAP level measurement","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP, domain mapping, loss-of-function in multiple cell lines, moderate evidence","pmids":["21185211"],"is_preprint":false},{"year":2017,"finding":"ARTS forms a ternary complex with XIAP and Bcl-2, enabling XIAP to act as an E3 ligase that ubiquitinates Bcl-2 at Lys17, leading to its proteasomal degradation. ARTS binding to Bcl-2 involves the BH3 domain of Bcl-2. XIAP- and Sept4/ARTS-deficient MEFs both show reduced Bcl-2 ubiquitylation.","method":"Co-immunoprecipitation, ubiquitylation assays, K17A Bcl-2 mutant stability analysis, knockout MEFs","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 1–2 — mechanistic mutagenesis (K17A), ternary complex demonstration, genetic confirmation in KO MEFs","pmids":["29020630"],"is_preprint":false},{"year":2010,"finding":"Deletion of mouse Sept4 gene leads to increased numbers of hematopoietic stem and progenitor cells, elevated XIAP protein levels, increased resistance to apoptosis, and accelerated tumor development; these phenotypes are partially suppressed by XIAP inactivation, placing ARTS upstream of XIAP in stem cell apoptosis.","method":"Sept4-null mouse model, genetic epistasis with XIAP knockout, flow cytometry of hematopoietic progenitors, tumor development assay in Eμ-Myc background","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 — clean KO mouse with defined cellular phenotype, genetic epistasis with XIAP","pmids":["20952537"],"is_preprint":false},{"year":2013,"finding":"Sept4/ARTS-deficient mice have elevated numbers of hair follicle stem cells (HFSCs) protected against apoptosis, display improved wound healing and hair follicle regeneration; these phenotypes depend on HFSCs (shown by lineage tracing) and are abrogated by XIAP inactivation, demonstrating ARTS regulates stem cell apoptosis via XIAP.","method":"Sept4/ARTS knockout mice, lineage tracing, XIAP genetic inactivation, wound healing assay","journal":"Science (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 2 — knockout mouse, lineage tracing, genetic epistasis with XIAP, published in high-impact journal","pmids":["23788729"],"is_preprint":false},{"year":2005,"finding":"In healthy cells, ARTS protein levels are kept low through constant ubiquitin-mediated proteasomal degradation; upon pro-apoptotic stimuli, ubiquitination is inhibited, ARTS levels rise, leading to decreased Bcl-2 and Bcl-xL levels, cytochrome c release, and apoptosis.","method":"Ubiquitination assays, proteasome inhibitor experiments, overexpression and knockdown in cell lines","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — biochemical ubiquitination assays with defined mechanistic outcome, single lab","pmids":["15837787"],"is_preprint":false},{"year":2012,"finding":"Parkin acts as an E3 ubiquitin ligase for ARTS (Sept4_i2), binding both ARTS and Sept4_i1 but selectively ubiquitinating and degrading only ARTS; Parkin overexpression protects neuronal cells from ARTS-induced apoptosis, and Parkin loss-of-function increases ARTS levels and promotes apoptosis.","method":"Co-immunoprecipitation, ubiquitination assays, Parkin overexpression/knockdown, neuronal cell apoptosis assays","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 — direct ubiquitination assay, specificity demonstrated by isoform selectivity, single lab","pmids":["22792159"],"is_preprint":false},{"year":2021,"finding":"ARTS is a transcriptional target of p53; p53 binds the ARTS promoter and activates its expression in response to genotoxic stress. In turn, ARTS binds p53 and sequesters it at mitochondria, enhancing p53 interaction with Bcl-XL to promote mitochondrial apoptosis.","method":"Chromatin immunoprecipitation (ChIP), luciferase reporter assay, Co-immunoprecipitation, p53 ablation/ectopic expression, apoptosis assays","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP confirmation of promoter binding, Co-IP of ARTS-p53 interaction, functional rescue experiments","pmids":["33627621"],"is_preprint":false},{"year":2011,"finding":"The SEPT4 gene encodes two major isoforms via distinct promoters, differential splicing, and intron retention: Sept4_i1 (H5/PNUTL2), a canonical septin involved in cytokinesis and filament formation, and Sept4_i2 (ARTS), which localizes to mitochondria and promotes apoptosis — distinguishing ARTS structurally and functionally from all other human septins.","method":"Molecular characterization of isoforms, structural and functional comparison, literature synthesis","journal":"Biological chemistry","confidence":"Medium","confidence_rationale":"Tier 3 — review synthesizing experimental data from multiple sources on isoform structure and localization","pmids":["21824006"],"is_preprint":false},{"year":2023,"finding":"SIRT2 deacetylates SEPTIN4 at lysine 174 (K174); hyperacetylation of K174 (mimicked by K174Q mutant) activates the cleaved-PARP1/cleaved-caspase3 apoptotic pathway and exacerbates Ang II-induced hypertensive renal injury in podocytes, while K174R (deacetylation mimic) is renoprotective. Immunoprecipitation and mass spectrometry identified SIRT2 as the deacetylase that interacts with the SEPTIN4 GTPase domain.","method":"Proteomics and acetyl-proteomics, Co-immunoprecipitation with mass spectrometry, transgenic K174Q and K174R mutant mice, SIRT2 knockout and transgenic mice, Western blotting","journal":"Circulation research","confidence":"High","confidence_rationale":"Tier 1–2 — site-specific mutagenesis, in vivo transgenic models, Co-IP/MS identification of writer, multiple orthogonal methods","pmids":["36786216"],"is_preprint":false},{"year":2018,"finding":"ARTS (Septin4 isoform) is highly expressed in intestinal stem cell niche cells; deletion of Sept4/ARTS protects Lgr5+ and Paneth cells from apoptosis, enhances Wnt/β-catenin signaling, and generates resistance to intestinal damage; ARTS interacts with XIAP in intestinal crypt cells and XIAP deletion abrogates these phenotypes.","method":"Sept4/ARTS knockout mice, organoid culture, Co-immunoprecipitation of ARTS-XIAP in intestinal crypts, β-catenin signaling assays, genetic epistasis with XIAP knockout","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — knockout mouse with defined cellular phenotype, genetic epistasis, Co-IP in relevant tissue","pmids":["30389919"],"is_preprint":false},{"year":2022,"finding":"Biallelic loss-of-function variants in SEPTIN4 in human patients cause thin midpiece spermatozoa and male infertility by disrupting the septin-based annulus structure, impairing localization of SEPTIN subunits at the annulus, disorganizing the mitochondrial sheath, and causing mislocalisation of SLC26A8 (a testis-specific anion transporter that colocalizes with SEPT4 at the sperm annulus).","method":"Whole-exome sequencing, immunofluorescence, immunoblotting, ultrastructural electron microscopy analysis of patient sperm","journal":"Human mutation","confidence":"Medium","confidence_rationale":"Tier 2 — human loss-of-function with defined ultrastructural phenotype and molecular consequence, but single study","pmids":["36135717"],"is_preprint":false},{"year":2020,"finding":"Septin4 acts as a novel interacting protein of both STAT3 and SIRT1, forming a complex that enhances SIRT1-STAT3 interaction, promotes SIRT1-mediated deacetylation of STAT3-K685, and STAT3-Y705 dephosphorylation, thereby inhibiting PDGF-BB-induced HAVSMC proliferation, migration, and phenotypic transformation.","method":"Co-immunoprecipitation, knockdown and overexpression in HAVSMCs, phospho- and acetylation-specific immunoblotting","journal":"International journal of biological sciences","confidence":"Medium","confidence_rationale":"Tier 2–3 — Co-IP demonstration of ternary complex, modification-specific readouts, single lab","pmids":["32025217"],"is_preprint":false},{"year":2020,"finding":"Septin4 overexpression in VSMCs reduces autophagy and decreases Ang-II-induced proliferation and migration; inhibiting autophagy with chloroquine further restrains proliferation/migration in Septin4-overexpressing cells, indicating Septin4 modulates VSMC behavior through autophagy regulation.","method":"Overexpression in VSMCs, autophagy inhibition with chloroquine, proliferation and migration assays","journal":"Biochemical and biophysical research communications","confidence":"Low","confidence_rationale":"Tier 3 — single lab, single method category, no direct molecular mechanism for autophagy modulation identified","pmids":["32085901"],"is_preprint":false},{"year":2014,"finding":"Septin4_i1 (H5/PNUTL2 isoform) induces apoptosis in hepatic stellate cells (LX-2) through the PPAR-γ/Akt/Bcl-2 pathway: overexpression upregulates PPAR-γ and cleaved-caspase-3, and reduces phospho-Akt and Bcl-2; effects are reversed by a PPAR-γ antagonist or Akt activator.","method":"Overexpression in LX-2 cells, PPAR-γ antagonist and agonist treatment, Western blotting of pathway components","journal":"The journal of histochemistry and cytochemistry","confidence":"Low","confidence_rationale":"Tier 3 — overexpression only, pharmacological pathway placement, single lab","pmids":["25527525"],"is_preprint":false},{"year":2014,"finding":"Parkin-mediated ubiquitination of mutant glucocerebrosidase (GCase) competes with ubiquitination of its substrates ARTS and PARIS; accumulation of mutant GCase leads to increased ARTS levels and apoptosis in dopaminergic cells, linking mutant GCase, Parkin substrate competition, and ARTS-dependent apoptosis.","method":"Co-immunoprecipitation, competition ubiquitination assays, caspase activation assays in dopaminergic cells","journal":"Orphanet journal of rare diseases","confidence":"Low","confidence_rationale":"Tier 3 — single lab, indirect competition mechanism, limited direct mechanistic follow-up on ARTS specifically","pmids":["24935484"],"is_preprint":false}],"current_model":"SEPTIN4 encodes two functionally distinct isoforms from the same gene: Sept4_i1 (H5/PNUTL2), a canonical septin involved in cytoskeletal and cytokinetic functions, and Sept4_i2 (ARTS), a mitochondrially-localized pro-apoptotic protein that, upon apoptotic stimulation, is released from mitochondria and binds XIAP at its BIR1 domain, recruits the E3 ligase Siah-1 to ubiquitinate and degrade XIAP, forms a ternary complex with Bcl-2 allowing XIAP-mediated ubiquitination and degradation of Bcl-2 at K17, sequesters p53 at mitochondria to enhance its interaction with Bcl-XL, and is itself regulated by ubiquitin-mediated degradation (written by Parkin) and by SIRT2-mediated deacetylation at K174; physiologically, ARTS controls stem cell pool size in hair follicles and intestinal crypts by promoting XIAP-dependent apoptosis, and loss-of-function mutations cause male infertility through annulus disruption in sperm."},"narrative":{"teleology":[{"year":2004,"claim":"Establishing the core pro-apoptotic mechanism of ARTS: the discovery that ARTS is released from mitochondria and directly binds XIAP to antagonize caspase inhibition resolved how a septin-family protein could function as an IAP antagonist, distinct from canonical Smac/DIABLO.","evidence":"In vitro binding of recombinant ARTS–XIAP, ARTS mutant analysis, Drosophila genetic epistasis","pmids":["15029247"],"confidence":"High","gaps":["Precise ARTS residues mediating XIAP binding not mapped","Mechanism of mitochondrial release not defined","In vivo physiological role in mammals not yet tested"]},{"year":2005,"claim":"Demonstrating that ARTS protein abundance is constitutively restrained by ubiquitin-mediated degradation explained how cells keep the apoptotic trigger latent until needed, with stabilization upon stress leading to Bcl-2/Bcl-xL downregulation and cytochrome c release.","evidence":"Ubiquitination assays and proteasome inhibitor experiments in cell lines","pmids":["15837787"],"confidence":"Medium","gaps":["Identity of the E3 ligase responsible not determined in this study","In vivo relevance of ARTS turnover not shown"]},{"year":2010,"claim":"Two advances defined how ARTS promotes XIAP destruction and revealed its physiological role in stem cells: ARTS was shown to bridge Siah-1 to XIAP for ubiquitin-dependent degradation via the BIR1 domain, and Sept4-knockout mice exhibited expanded hematopoietic stem/progenitor pools with elevated XIAP, a phenotype reversed by XIAP deletion.","evidence":"Co-IP domain mapping and knockdown/knockout XIAP level analysis; Sept4-null mice with XIAP genetic epistasis and Eμ-Myc tumor assay","pmids":["21185211","20952537"],"confidence":"High","gaps":["Whether ARTS-Siah-1-XIAP ternary complex forms in primary stem cells not shown","Structural basis of BIR1 recognition undefined"]},{"year":2011,"claim":"Molecular characterization clarified that SEPT4 produces two structurally and functionally divergent isoforms — Sept4_i1 (canonical septin) and Sept4_i2 (ARTS, mitochondrial pro-apoptotic) — through alternative promoters and splicing, contextualizing why the same locus controls both cytokinesis and apoptosis.","evidence":"Isoform characterization, structural comparison, literature synthesis","pmids":["21824006"],"confidence":"Medium","gaps":["Tissue-specific promoter usage not fully resolved","Relative expression levels of isoforms in different tissues poorly characterized"]},{"year":2012,"claim":"Identification of Parkin as the E3 ligase that selectively ubiquitinates and degrades ARTS (but not Sept4_i1) connected ARTS turnover to Parkinson's disease-relevant pathways and explained the isoform-specific degradation observed earlier.","evidence":"Co-IP, ubiquitination assays with Parkin overexpression/knockdown in neuronal cells","pmids":["22792159"],"confidence":"Medium","gaps":["Parkin-ARTS interaction not validated in primary neurons or brain tissue","Specific ubiquitination sites on ARTS not identified"]},{"year":2013,"claim":"Extension of the ARTS–XIAP axis to hair follicle stem cells demonstrated that ARTS controls tissue-resident stem cell apoptosis in vivo, with Sept4-knockout mice showing enhanced wound healing and hair regeneration reversed by XIAP deletion.","evidence":"Sept4-knockout mice with lineage tracing, wound healing assays, XIAP genetic epistasis","pmids":["23788729"],"confidence":"High","gaps":["Molecular signals triggering ARTS activation in the hair follicle niche unknown","Human relevance not tested"]},{"year":2017,"claim":"Discovery that ARTS assembles a ternary complex with XIAP and Bcl-2 to enable XIAP-mediated ubiquitination of Bcl-2 at K17 revealed a second anti-survival target beyond XIAP itself, showing ARTS amplifies apoptotic commitment by simultaneously degrading both an IAP and an anti-apoptotic Bcl-2 family member.","evidence":"Co-IP, ubiquitylation assays, K17A Bcl-2 mutant stability, XIAP and Sept4 knockout MEFs","pmids":["29020630"],"confidence":"High","gaps":["Whether other Bcl-2 family members are similarly targeted unknown","Temporal order of XIAP versus Bcl-2 degradation not resolved"]},{"year":2018,"claim":"Demonstration that ARTS operates in the intestinal stem cell niche — protecting Lgr5+ and Paneth cells from apoptosis when deleted, and enhancing Wnt/β-catenin signaling — broadened its physiological role to gut homeostasis and showed the ARTS–XIAP axis is a general stem cell apoptosis regulator.","evidence":"Sept4-knockout mice, intestinal organoids, Co-IP of ARTS–XIAP in crypts, genetic epistasis with XIAP knockout","pmids":["30389919"],"confidence":"High","gaps":["Whether ARTS loss predisposes to intestinal tumorigenesis long-term not fully addressed","Mechanism linking XIAP degradation to Wnt activation unclear"]},{"year":2020,"claim":"Identification of SEPTIN4 as a scaffold bridging SIRT1 and STAT3 to promote STAT3-K685 deacetylation and Y705 dephosphorylation revealed a non-apoptotic signaling function of SEPTIN4 in vascular smooth muscle cell phenotypic modulation.","evidence":"Co-IP of SEPTIN4–SIRT1–STAT3 complex, knockdown/overexpression in HAVSMCs with modification-specific immunoblotting","pmids":["32025217"],"confidence":"Medium","gaps":["Which isoform mediates STAT3 regulation not specified","Single-lab finding without independent replication","Direct physical bridging not reconstituted with purified components"]},{"year":2021,"claim":"Establishing a positive feedback loop between p53 and ARTS — p53 transcriptionally activates ARTS, and ARTS in turn sequesters p53 at mitochondria to enhance p53–Bcl-XL interaction — linked the ARTS pathway to the canonical DNA damage response.","evidence":"ChIP on ARTS promoter, luciferase reporter, Co-IP of ARTS–p53, apoptosis assays with p53 manipulation","pmids":["33627621"],"confidence":"Medium","gaps":["Physiological importance of p53–ARTS loop in stem cells or tumors not tested in vivo","Whether ARTS-mediated p53 mitochondrial sequestration is independent of XIAP pathway unclear"]},{"year":2022,"claim":"Human genetic evidence that biallelic SEPTIN4 loss-of-function causes male infertility through disrupted sperm annulus structure established a Mendelian disease link and confirmed the canonical septin isoform's structural role in spermatogenesis.","evidence":"Whole-exome sequencing of infertile patients, immunofluorescence and EM of sperm ultrastructure","pmids":["36135717"],"confidence":"Medium","gaps":["Single study without independent cohort replication","Whether ARTS isoform loss contributes to any aspect of the infertility phenotype unknown"]},{"year":2023,"claim":"Identifying SIRT2-mediated deacetylation of SEPTIN4 at K174 as a regulatory switch — where hyperacetylation activates the caspase-3/PARP1 apoptotic pathway and exacerbates renal injury — added a post-translational regulatory layer controlling SEPTIN4's pro-apoptotic output.","evidence":"Acetyl-proteomics, Co-IP/MS, K174Q and K174R transgenic mice, SIRT2-knockout mice, podocyte injury models","pmids":["36786216"],"confidence":"High","gaps":["Whether K174 acetylation affects ARTS–XIAP binding specifically not tested","Acetylation writers not identified","Relevance to stem cell apoptosis function not assessed"]},{"year":null,"claim":"Key unresolved questions include: the structural basis of ARTS–XIAP BIR1 recognition, the mechanism by which ARTS is released from mitochondria, whether the ARTS–XIAP stem cell apoptosis axis is relevant in human cancer suppression, and how the two isoforms are differentially regulated at the transcriptional level across tissues.","evidence":"","pmids":[],"confidence":"Low","gaps":["No crystal or cryo-EM structure of ARTS or ARTS–XIAP complex","Mitochondrial release mechanism undefined","Human disease relevance of ARTS-mediated stem cell apoptosis not established beyond infertility"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[1,2,12]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,1,3]}],"localization":[{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[0,7,8]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0,8]}],"pathway":[{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[0,1,2,3,4,5,7,9,10]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[1,2,5,6,9]}],"complexes":["ARTS-XIAP-Siah-1","ARTS-XIAP-Bcl-2"],"partners":["XIAP","SIAH1","BCL2","TP53","PRKN","SIRT2","STAT3","SIRT1"],"other_free_text":[]},"mechanistic_narrative":"SEPTIN4 encodes two functionally distinct isoforms: Sept4_i1, a canonical septin that participates in cytokinesis and filament formation, and Sept4_i2 (ARTS), a mitochondrially localized pro-apoptotic protein that controls stem cell pool size and tissue homeostasis by promoting XIAP-dependent apoptosis [PMID:21824006, PMID:20952537, PMID:23788729, PMID:30389919]. Upon apoptotic stimulation, ARTS is released from mitochondria and directly binds the BIR1 domain of XIAP, recruiting the E3 ligase Siah-1 to ubiquitinate and degrade XIAP; ARTS further assembles a ternary complex with XIAP and Bcl-2, enabling XIAP-mediated ubiquitination of Bcl-2 at Lys17 [PMID:15029247, PMID:21185211, PMID:29020630]. ARTS itself is regulated by Parkin-mediated ubiquitination that keeps its basal levels low, by SIRT2-mediated deacetylation at K174 that restrains its apoptotic activity, and by p53-driven transcription that amplifies ARTS expression under genotoxic stress [PMID:22792159, PMID:36786216, PMID:33627621]. Biallelic loss-of-function mutations in SEPTIN4 cause male infertility in humans by disrupting the septin-based annulus of spermatozoa [PMID:36135717]."},"prefetch_data":{"uniprot":{"accession":"O43236","full_name":"Septin-4","aliases":["Bradeion beta","Brain protein H5","CE5B3 beta","Cell division control-related protein 2","hCDCREL-2","Peanut-like protein 2"],"length_aa":996,"mass_kda":112.4,"function":"Filament-forming cytoskeletal GTPase (Probable). Pro-apoptotic protein involved in LGR5-positive intestinal stem cell and Paneth cell expansion in the intestines, via its interaction with XIAP (By similarity). May also play a role in the regulation of cell fate in the intestine (By similarity). Positive regulator of apoptosis involved in hematopoietic stem cell homeostasis; via its interaction with XIAP (By similarity). Negative regulator of repair and hair follicle regeneration in response to injury, due to inhibition of hair follicle stem cell proliferation, potentially via its interaction with XIAP (By similarity). Plays an important role in male fertility and sperm motility (PubMed:36135717). During spermiogenesis, essential for the establishment of the annulus (a fibrous ring structure connecting the midpiece and the principal piece of the sperm flagellum) which is a requisite for the structural and mechanical integrity of the sperm (PubMed:36135717). Involved in the migration of cortical neurons and the formation of neuron leading processes during embryonic development (By similarity). Required for dopaminergic metabolism in presynaptic autoreceptors; potentially via activity as a presynaptic scaffold protein (By similarity) Required for the induction of cell death mediated by TGF-beta and possibly by other apoptotic stimuli (PubMed:11146656, PubMed:15837787). Induces apoptosis through binding and inhibition of XIAP resulting in significant reduction in XIAP levels, leading to caspase activation and cell death (PubMed:15029247). Mediates the interaction between BCL2 and XIAP, thereby positively regulating the ubiquitination and degradation of BCL2 and promoting apoptosis (PubMed:29020630)","subcellular_location":"Mitochondrion; Nucleus","url":"https://www.uniprot.org/uniprotkb/O43236/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SEPTIN4","classification":"Not Classified","n_dependent_lines":2,"n_total_lines":1208,"dependency_fraction":0.0016556291390728477},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SEPTIN4","total_profiled":1310},"omim":[{"mim_id":"621194","title":"SPERMATOGENIC FAILURE 99; SPGF99","url":"https://www.omim.org/entry/621194"},{"mim_id":"614779","title":"HETEROTAXY, VISCERAL, 6, AUTOSOMAL; HTX6","url":"https://www.omim.org/entry/614779"},{"mim_id":"614759","title":"CILIA- AND FLAGELLA-ASSOCIATED PROTEIN 53; CFAP53","url":"https://www.omim.org/entry/614759"},{"mim_id":"608480","title":"SOLUTE CARRIER FAMILY 26 (SULFATE TRANSPORTER), MEMBER 8; SLC26A8","url":"https://www.omim.org/entry/608480"},{"mim_id":"603696","title":"SEPTIN 4; SEPTIN4","url":"https://www.omim.org/entry/603696"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Annulus","reliability":"Supported"}],"tissue_specificity":"Group enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"brain","ntpm":1097.2},{"tissue":"retina","ntpm":375.4}],"url":"https://www.proteinatlas.org/search/SEPTIN4"},"hgnc":{"alias_symbol":["H5","CE5B3","hucep-7","ARTS","hCDCREL-2","MART","FLJ40121","Septin-4"],"prev_symbol":["PNUTL2","C17orf47","SEPT4"]},"alphafold":{"accession":"O43236","domains":[{"cath_id":"3.40.50.300","chopping":"145-174_184-413","consensus_level":"high","plddt":89.1187,"start":145,"end":413}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O43236","model_url":"https://alphafold.ebi.ac.uk/files/AF-O43236-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O43236-F1-predicted_aligned_error_v6.png","plddt_mean":71.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SEPTIN4","jax_strain_url":"https://www.jax.org/strain/search?query=SEPTIN4"},"sequence":{"accession":"O43236","fasta_url":"https://rest.uniprot.org/uniprotkb/O43236.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O43236/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O43236"}},"corpus_meta":[{"pmid":"1899917","id":"PMC_1899917","title":"Alteration 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caspase-inhibitory function, leading to decreased XIAP protein levels and caspase activation. Recombinant ARTS and XIAP bind each other in vitro, and ARTS mutants that fail to bind XIAP fail to induce apoptosis.\",\n      \"method\": \"In vitro binding assay with recombinant proteins, Co-immunoprecipitation, cell-based apoptosis assays with mutant ARTS, Drosophila genetic epistasis (peanut mutations suppress Reaper/Hid/Grim killing)\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro reconstitution of direct binding + mutagenesis + genetic epistasis, replicated across multiple papers\",\n      \"pmids\": [\"15029247\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"ARTS binds XIAP at the BIR1 domain (distinct from caspase-binding sites) and interacts with the E3 ubiquitin ligase Siah-1, acting as an adaptor to bridge Siah-1 to XIAP and target it for ubiquitination and proteasomal degradation. Cells lacking either Siah or ARTS have elevated steady-state XIAP levels.\",\n      \"method\": \"Co-immunoprecipitation, domain mapping, knockdown/knockout cell lines with XIAP level measurement\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, domain mapping, loss-of-function in multiple cell lines, moderate evidence\",\n      \"pmids\": [\"21185211\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"ARTS forms a ternary complex with XIAP and Bcl-2, enabling XIAP to act as an E3 ligase that ubiquitinates Bcl-2 at Lys17, leading to its proteasomal degradation. ARTS binding to Bcl-2 involves the BH3 domain of Bcl-2. XIAP- and Sept4/ARTS-deficient MEFs both show reduced Bcl-2 ubiquitylation.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitylation assays, K17A Bcl-2 mutant stability analysis, knockout MEFs\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — mechanistic mutagenesis (K17A), ternary complex demonstration, genetic confirmation in KO MEFs\",\n      \"pmids\": [\"29020630\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Deletion of mouse Sept4 gene leads to increased numbers of hematopoietic stem and progenitor cells, elevated XIAP protein levels, increased resistance to apoptosis, and accelerated tumor development; these phenotypes are partially suppressed by XIAP inactivation, placing ARTS upstream of XIAP in stem cell apoptosis.\",\n      \"method\": \"Sept4-null mouse model, genetic epistasis with XIAP knockout, flow cytometry of hematopoietic progenitors, tumor development assay in Eμ-Myc background\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO mouse with defined cellular phenotype, genetic epistasis with XIAP\",\n      \"pmids\": [\"20952537\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Sept4/ARTS-deficient mice have elevated numbers of hair follicle stem cells (HFSCs) protected against apoptosis, display improved wound healing and hair follicle regeneration; these phenotypes depend on HFSCs (shown by lineage tracing) and are abrogated by XIAP inactivation, demonstrating ARTS regulates stem cell apoptosis via XIAP.\",\n      \"method\": \"Sept4/ARTS knockout mice, lineage tracing, XIAP genetic inactivation, wound healing assay\",\n      \"journal\": \"Science (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — knockout mouse, lineage tracing, genetic epistasis with XIAP, published in high-impact journal\",\n      \"pmids\": [\"23788729\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"In healthy cells, ARTS protein levels are kept low through constant ubiquitin-mediated proteasomal degradation; upon pro-apoptotic stimuli, ubiquitination is inhibited, ARTS levels rise, leading to decreased Bcl-2 and Bcl-xL levels, cytochrome c release, and apoptosis.\",\n      \"method\": \"Ubiquitination assays, proteasome inhibitor experiments, overexpression and knockdown in cell lines\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — biochemical ubiquitination assays with defined mechanistic outcome, single lab\",\n      \"pmids\": [\"15837787\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Parkin acts as an E3 ubiquitin ligase for ARTS (Sept4_i2), binding both ARTS and Sept4_i1 but selectively ubiquitinating and degrading only ARTS; Parkin overexpression protects neuronal cells from ARTS-induced apoptosis, and Parkin loss-of-function increases ARTS levels and promotes apoptosis.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assays, Parkin overexpression/knockdown, neuronal cell apoptosis assays\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct ubiquitination assay, specificity demonstrated by isoform selectivity, single lab\",\n      \"pmids\": [\"22792159\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"ARTS is a transcriptional target of p53; p53 binds the ARTS promoter and activates its expression in response to genotoxic stress. In turn, ARTS binds p53 and sequesters it at mitochondria, enhancing p53 interaction with Bcl-XL to promote mitochondrial apoptosis.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP), luciferase reporter assay, Co-immunoprecipitation, p53 ablation/ectopic expression, apoptosis assays\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP confirmation of promoter binding, Co-IP of ARTS-p53 interaction, functional rescue experiments\",\n      \"pmids\": [\"33627621\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The SEPT4 gene encodes two major isoforms via distinct promoters, differential splicing, and intron retention: Sept4_i1 (H5/PNUTL2), a canonical septin involved in cytokinesis and filament formation, and Sept4_i2 (ARTS), which localizes to mitochondria and promotes apoptosis — distinguishing ARTS structurally and functionally from all other human septins.\",\n      \"method\": \"Molecular characterization of isoforms, structural and functional comparison, literature synthesis\",\n      \"journal\": \"Biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — review synthesizing experimental data from multiple sources on isoform structure and localization\",\n      \"pmids\": [\"21824006\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SIRT2 deacetylates SEPTIN4 at lysine 174 (K174); hyperacetylation of K174 (mimicked by K174Q mutant) activates the cleaved-PARP1/cleaved-caspase3 apoptotic pathway and exacerbates Ang II-induced hypertensive renal injury in podocytes, while K174R (deacetylation mimic) is renoprotective. Immunoprecipitation and mass spectrometry identified SIRT2 as the deacetylase that interacts with the SEPTIN4 GTPase domain.\",\n      \"method\": \"Proteomics and acetyl-proteomics, Co-immunoprecipitation with mass spectrometry, transgenic K174Q and K174R mutant mice, SIRT2 knockout and transgenic mice, Western blotting\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — site-specific mutagenesis, in vivo transgenic models, Co-IP/MS identification of writer, multiple orthogonal methods\",\n      \"pmids\": [\"36786216\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"ARTS (Septin4 isoform) is highly expressed in intestinal stem cell niche cells; deletion of Sept4/ARTS protects Lgr5+ and Paneth cells from apoptosis, enhances Wnt/β-catenin signaling, and generates resistance to intestinal damage; ARTS interacts with XIAP in intestinal crypt cells and XIAP deletion abrogates these phenotypes.\",\n      \"method\": \"Sept4/ARTS knockout mice, organoid culture, Co-immunoprecipitation of ARTS-XIAP in intestinal crypts, β-catenin signaling assays, genetic epistasis with XIAP knockout\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — knockout mouse with defined cellular phenotype, genetic epistasis, Co-IP in relevant tissue\",\n      \"pmids\": [\"30389919\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Biallelic loss-of-function variants in SEPTIN4 in human patients cause thin midpiece spermatozoa and male infertility by disrupting the septin-based annulus structure, impairing localization of SEPTIN subunits at the annulus, disorganizing the mitochondrial sheath, and causing mislocalisation of SLC26A8 (a testis-specific anion transporter that colocalizes with SEPT4 at the sperm annulus).\",\n      \"method\": \"Whole-exome sequencing, immunofluorescence, immunoblotting, ultrastructural electron microscopy analysis of patient sperm\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — human loss-of-function with defined ultrastructural phenotype and molecular consequence, but single study\",\n      \"pmids\": [\"36135717\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Septin4 acts as a novel interacting protein of both STAT3 and SIRT1, forming a complex that enhances SIRT1-STAT3 interaction, promotes SIRT1-mediated deacetylation of STAT3-K685, and STAT3-Y705 dephosphorylation, thereby inhibiting PDGF-BB-induced HAVSMC proliferation, migration, and phenotypic transformation.\",\n      \"method\": \"Co-immunoprecipitation, knockdown and overexpression in HAVSMCs, phospho- and acetylation-specific immunoblotting\",\n      \"journal\": \"International journal of biological sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — Co-IP demonstration of ternary complex, modification-specific readouts, single lab\",\n      \"pmids\": [\"32025217\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Septin4 overexpression in VSMCs reduces autophagy and decreases Ang-II-induced proliferation and migration; inhibiting autophagy with chloroquine further restrains proliferation/migration in Septin4-overexpressing cells, indicating Septin4 modulates VSMC behavior through autophagy regulation.\",\n      \"method\": \"Overexpression in VSMCs, autophagy inhibition with chloroquine, proliferation and migration assays\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, single method category, no direct molecular mechanism for autophagy modulation identified\",\n      \"pmids\": [\"32085901\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Septin4_i1 (H5/PNUTL2 isoform) induces apoptosis in hepatic stellate cells (LX-2) through the PPAR-γ/Akt/Bcl-2 pathway: overexpression upregulates PPAR-γ and cleaved-caspase-3, and reduces phospho-Akt and Bcl-2; effects are reversed by a PPAR-γ antagonist or Akt activator.\",\n      \"method\": \"Overexpression in LX-2 cells, PPAR-γ antagonist and agonist treatment, Western blotting of pathway components\",\n      \"journal\": \"The journal of histochemistry and cytochemistry\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — overexpression only, pharmacological pathway placement, single lab\",\n      \"pmids\": [\"25527525\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Parkin-mediated ubiquitination of mutant glucocerebrosidase (GCase) competes with ubiquitination of its substrates ARTS and PARIS; accumulation of mutant GCase leads to increased ARTS levels and apoptosis in dopaminergic cells, linking mutant GCase, Parkin substrate competition, and ARTS-dependent apoptosis.\",\n      \"method\": \"Co-immunoprecipitation, competition ubiquitination assays, caspase activation assays in dopaminergic cells\",\n      \"journal\": \"Orphanet journal of rare diseases\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, indirect competition mechanism, limited direct mechanistic follow-up on ARTS specifically\",\n      \"pmids\": [\"24935484\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SEPTIN4 encodes two functionally distinct isoforms from the same gene: Sept4_i1 (H5/PNUTL2), a canonical septin involved in cytoskeletal and cytokinetic functions, and Sept4_i2 (ARTS), a mitochondrially-localized pro-apoptotic protein that, upon apoptotic stimulation, is released from mitochondria and binds XIAP at its BIR1 domain, recruits the E3 ligase Siah-1 to ubiquitinate and degrade XIAP, forms a ternary complex with Bcl-2 allowing XIAP-mediated ubiquitination and degradation of Bcl-2 at K17, sequesters p53 at mitochondria to enhance its interaction with Bcl-XL, and is itself regulated by ubiquitin-mediated degradation (written by Parkin) and by SIRT2-mediated deacetylation at K174; physiologically, ARTS controls stem cell pool size in hair follicles and intestinal crypts by promoting XIAP-dependent apoptosis, and loss-of-function mutations cause male infertility through annulus disruption in sperm.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"SEPTIN4 encodes two functionally distinct isoforms: Sept4_i1, a canonical septin that participates in cytokinesis and filament formation, and Sept4_i2 (ARTS), a mitochondrially localized pro-apoptotic protein that controls stem cell pool size and tissue homeostasis by promoting XIAP-dependent apoptosis [PMID:21824006, PMID:20952537, PMID:23788729, PMID:30389919]. Upon apoptotic stimulation, ARTS is released from mitochondria and directly binds the BIR1 domain of XIAP, recruiting the E3 ligase Siah-1 to ubiquitinate and degrade XIAP; ARTS further assembles a ternary complex with XIAP and Bcl-2, enabling XIAP-mediated ubiquitination of Bcl-2 at Lys17 [PMID:15029247, PMID:21185211, PMID:29020630]. ARTS itself is regulated by Parkin-mediated ubiquitination that keeps its basal levels low, by SIRT2-mediated deacetylation at K174 that restrains its apoptotic activity, and by p53-driven transcription that amplifies ARTS expression under genotoxic stress [PMID:22792159, PMID:36786216, PMID:33627621]. Biallelic loss-of-function mutations in SEPTIN4 cause male infertility in humans by disrupting the septin-based annulus of spermatozoa [PMID:36135717].\",\n  \"teleology\": [\n    {\n      \"year\": 2004,\n      \"claim\": \"Establishing the core pro-apoptotic mechanism of ARTS: the discovery that ARTS is released from mitochondria and directly binds XIAP to antagonize caspase inhibition resolved how a septin-family protein could function as an IAP antagonist, distinct from canonical Smac/DIABLO.\",\n      \"evidence\": \"In vitro binding of recombinant ARTS–XIAP, ARTS mutant analysis, Drosophila genetic epistasis\",\n      \"pmids\": [\"15029247\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Precise ARTS residues mediating XIAP binding not mapped\", \"Mechanism of mitochondrial release not defined\", \"In vivo physiological role in mammals not yet tested\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Demonstrating that ARTS protein abundance is constitutively restrained by ubiquitin-mediated degradation explained how cells keep the apoptotic trigger latent until needed, with stabilization upon stress leading to Bcl-2/Bcl-xL downregulation and cytochrome c release.\",\n      \"evidence\": \"Ubiquitination assays and proteasome inhibitor experiments in cell lines\",\n      \"pmids\": [\"15837787\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Identity of the E3 ligase responsible not determined in this study\", \"In vivo relevance of ARTS turnover not shown\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Two advances defined how ARTS promotes XIAP destruction and revealed its physiological role in stem cells: ARTS was shown to bridge Siah-1 to XIAP for ubiquitin-dependent degradation via the BIR1 domain, and Sept4-knockout mice exhibited expanded hematopoietic stem/progenitor pools with elevated XIAP, a phenotype reversed by XIAP deletion.\",\n      \"evidence\": \"Co-IP domain mapping and knockdown/knockout XIAP level analysis; Sept4-null mice with XIAP genetic epistasis and Eμ-Myc tumor assay\",\n      \"pmids\": [\"21185211\", \"20952537\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether ARTS-Siah-1-XIAP ternary complex forms in primary stem cells not shown\", \"Structural basis of BIR1 recognition undefined\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Molecular characterization clarified that SEPT4 produces two structurally and functionally divergent isoforms — Sept4_i1 (canonical septin) and Sept4_i2 (ARTS, mitochondrial pro-apoptotic) — through alternative promoters and splicing, contextualizing why the same locus controls both cytokinesis and apoptosis.\",\n      \"evidence\": \"Isoform characterization, structural comparison, literature synthesis\",\n      \"pmids\": [\"21824006\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Tissue-specific promoter usage not fully resolved\", \"Relative expression levels of isoforms in different tissues poorly characterized\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Identification of Parkin as the E3 ligase that selectively ubiquitinates and degrades ARTS (but not Sept4_i1) connected ARTS turnover to Parkinson's disease-relevant pathways and explained the isoform-specific degradation observed earlier.\",\n      \"evidence\": \"Co-IP, ubiquitination assays with Parkin overexpression/knockdown in neuronal cells\",\n      \"pmids\": [\"22792159\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Parkin-ARTS interaction not validated in primary neurons or brain tissue\", \"Specific ubiquitination sites on ARTS not identified\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Extension of the ARTS–XIAP axis to hair follicle stem cells demonstrated that ARTS controls tissue-resident stem cell apoptosis in vivo, with Sept4-knockout mice showing enhanced wound healing and hair regeneration reversed by XIAP deletion.\",\n      \"evidence\": \"Sept4-knockout mice with lineage tracing, wound healing assays, XIAP genetic epistasis\",\n      \"pmids\": [\"23788729\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular signals triggering ARTS activation in the hair follicle niche unknown\", \"Human relevance not tested\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Discovery that ARTS assembles a ternary complex with XIAP and Bcl-2 to enable XIAP-mediated ubiquitination of Bcl-2 at K17 revealed a second anti-survival target beyond XIAP itself, showing ARTS amplifies apoptotic commitment by simultaneously degrading both an IAP and an anti-apoptotic Bcl-2 family member.\",\n      \"evidence\": \"Co-IP, ubiquitylation assays, K17A Bcl-2 mutant stability, XIAP and Sept4 knockout MEFs\",\n      \"pmids\": [\"29020630\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether other Bcl-2 family members are similarly targeted unknown\", \"Temporal order of XIAP versus Bcl-2 degradation not resolved\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Demonstration that ARTS operates in the intestinal stem cell niche — protecting Lgr5+ and Paneth cells from apoptosis when deleted, and enhancing Wnt/β-catenin signaling — broadened its physiological role to gut homeostasis and showed the ARTS–XIAP axis is a general stem cell apoptosis regulator.\",\n      \"evidence\": \"Sept4-knockout mice, intestinal organoids, Co-IP of ARTS–XIAP in crypts, genetic epistasis with XIAP knockout\",\n      \"pmids\": [\"30389919\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether ARTS loss predisposes to intestinal tumorigenesis long-term not fully addressed\", \"Mechanism linking XIAP degradation to Wnt activation unclear\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Identification of SEPTIN4 as a scaffold bridging SIRT1 and STAT3 to promote STAT3-K685 deacetylation and Y705 dephosphorylation revealed a non-apoptotic signaling function of SEPTIN4 in vascular smooth muscle cell phenotypic modulation.\",\n      \"evidence\": \"Co-IP of SEPTIN4–SIRT1–STAT3 complex, knockdown/overexpression in HAVSMCs with modification-specific immunoblotting\",\n      \"pmids\": [\"32025217\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Which isoform mediates STAT3 regulation not specified\", \"Single-lab finding without independent replication\", \"Direct physical bridging not reconstituted with purified components\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Establishing a positive feedback loop between p53 and ARTS — p53 transcriptionally activates ARTS, and ARTS in turn sequesters p53 at mitochondria to enhance p53–Bcl-XL interaction — linked the ARTS pathway to the canonical DNA damage response.\",\n      \"evidence\": \"ChIP on ARTS promoter, luciferase reporter, Co-IP of ARTS–p53, apoptosis assays with p53 manipulation\",\n      \"pmids\": [\"33627621\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological importance of p53–ARTS loop in stem cells or tumors not tested in vivo\", \"Whether ARTS-mediated p53 mitochondrial sequestration is independent of XIAP pathway unclear\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Human genetic evidence that biallelic SEPTIN4 loss-of-function causes male infertility through disrupted sperm annulus structure established a Mendelian disease link and confirmed the canonical septin isoform's structural role in spermatogenesis.\",\n      \"evidence\": \"Whole-exome sequencing of infertile patients, immunofluorescence and EM of sperm ultrastructure\",\n      \"pmids\": [\"36135717\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single study without independent cohort replication\", \"Whether ARTS isoform loss contributes to any aspect of the infertility phenotype unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Identifying SIRT2-mediated deacetylation of SEPTIN4 at K174 as a regulatory switch — where hyperacetylation activates the caspase-3/PARP1 apoptotic pathway and exacerbates renal injury — added a post-translational regulatory layer controlling SEPTIN4's pro-apoptotic output.\",\n      \"evidence\": \"Acetyl-proteomics, Co-IP/MS, K174Q and K174R transgenic mice, SIRT2-knockout mice, podocyte injury models\",\n      \"pmids\": [\"36786216\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether K174 acetylation affects ARTS–XIAP binding specifically not tested\", \"Acetylation writers not identified\", \"Relevance to stem cell apoptosis function not assessed\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include: the structural basis of ARTS–XIAP BIR1 recognition, the mechanism by which ARTS is released from mitochondria, whether the ARTS–XIAP stem cell apoptosis axis is relevant in human cancer suppression, and how the two isoforms are differentially regulated at the transcriptional level across tissues.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No crystal or cryo-EM structure of ARTS or ARTS–XIAP complex\", \"Mitochondrial release mechanism undefined\", \"Human disease relevance of ARTS-mediated stem cell apoptosis not established beyond infertility\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [1, 2, 12]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 1, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [0, 7, 8]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [0, 1, 2, 3, 4, 5, 7, 9, 10]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [1, 2, 5, 6, 9]}\n    ],\n    \"complexes\": [\n      \"ARTS-XIAP-Siah-1\",\n      \"ARTS-XIAP-Bcl-2\"\n    ],\n    \"partners\": [\n      \"XIAP\",\n      \"SIAH1\",\n      \"BCL2\",\n      \"TP53\",\n      \"PRKN\",\n      \"SIRT2\",\n      \"STAT3\",\n      \"SIRT1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}