{"gene":"EXOC4","run_date":"2026-04-28T17:46:03","timeline":{"discoveries":[{"year":1992,"finding":"Sec8p (EXOC4 ortholog in S. cerevisiae) is a component of a 19.5S particle that also contains Sec15p, found both in the cytosol and peripherally associated with the plasma membrane but not with secretory vesicles; a portion of Sec4p (Rab GTPase) co-fractionates with the Sec8p/Sec15p particle, suggesting the complex functions as a downstream effector of Sec4p to direct secretory vesicle fusion with the plasma membrane.","method":"Fractionation, sucrose gradient sedimentation, gel filtration, cross-linking, immunoprecipitation","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal biochemical methods in foundational yeast study, replicated by subsequent work","pmids":["1512289"],"is_preprint":false},{"year":1995,"finding":"Sec8 (EXOC4 ortholog) is a stable component of a large (~1–2 MDa) multisubunit exocyst complex (Sec6/8/15 containing at least 8 polypeptides) that localizes to small bud tips in S. cerevisiae; complex integrity is disrupted by mutations in sec3, sec5, and sec10, placing Sec8 within the core exocyst at sites of exocytosis.","method":"Immobilized metal affinity chromatography, gel filtration, sucrose velocity centrifugation, co-immunoprecipitation, immunofluorescence","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal methods, foundational study with high citation count","pmids":["7615633"],"is_preprint":false},{"year":1997,"finding":"Mouse Sec8 (EXOC4) is required for paraxial mesoderm formation during embryogenesis; homozygous sec8 mutant embryos initiate but cannot progress beyond the primitive streak stage, demonstrating an essential role for Sec8 in early development.","method":"Gene trap mutagenesis, homozygous mutant embryo phenotypic analysis, cDNA cloning","journal":"Developmental biology","confidence":"High","confidence_rationale":"Tier 2 — clean loss-of-function genetic knockout with defined developmental phenotype","pmids":["9441674"],"is_preprint":false},{"year":2003,"finding":"Sec8 (EXOC4) binds to PDZ1-2 domains of PSD-95 via its C-terminal PDZ-binding motif (Thr-Thr-Val/TTV); this interaction is competed by cypin (cytosolic PSD-95 interactor) and is dependent on the TTV sequence; Sec8 and PSD-95 co-immunoprecipitate from brain tissue and share subcellular distribution.","method":"Co-immunoprecipitation, peptide competition assay, site-directed mutagenesis of TTV motif, immunoblotting of tissue fractions","journal":"The Biochemical journal","confidence":"Medium","confidence_rationale":"Tier 2–3 — reciprocal co-IP from brain and mutagenesis of binding motif, single lab","pmids":["12675619"],"is_preprint":false},{"year":2005,"finding":"In Drosophila (ortholog of mammalian EXOC4), Sec8 is required in vivo for regulation of synaptic microtubule density at the neuromuscular junction; sec8 null mutants show approximately doubled synaptic microtubule density and altered synapse morphology, with mild disruption of glutamate receptor trafficking but no effect on basal neurotransmission.","method":"Forward genetic screen, null mutant analysis, immunocytochemistry, electrophysiology, immunoblotting","journal":"BMC biology","confidence":"High","confidence_rationale":"Tier 2 — null mutant with multiple orthogonal readouts (morphology, electrophysiology, receptor trafficking)","pmids":["16351720"],"is_preprint":false},{"year":2006,"finding":"Sec8 (EXOC4) promotes oligodendrocyte morphological differentiation and myelin-like membrane formation; Sec8 co-localizes, co-immunoprecipitates, and co-fractionates with myelin protein OSP/Claudin11 and scaffolding protein CASK in oligodendrocytes, and siRNA knockdown of Sec8 inhibits membrane formation.","method":"siRNA knockdown, Sec8 overexpression, co-immunoprecipitation, co-fractionation, immunofluorescence colocalization","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2–3 — co-IP with functional validation by KD and OE, single lab","pmids":["16478790"],"is_preprint":false},{"year":2009,"finding":"In Schwann cells, Sec8 (EXOC4) interacts with Dlg1 (Discs large 1) scaffolding protein; the Dlg1–Sec8 interaction promotes membrane addition during myelination, while Dlg1–Mtmr2 interaction negatively regulates membrane formation, together constituting a homeostatic machinery that controls myelin membrane amount.","method":"Co-immunoprecipitation, Schwann cell/DRG neuron coculture, siRNA knockdown, Mtmr2-null mouse model with myelin outfolding phenotype","journal":"The Journal of neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 — co-IP plus functional rescue in null mouse model, single lab","pmids":["19587293"],"is_preprint":false},{"year":2009,"finding":"Insulin stimulates phosphorylation of Sec8 (EXOC4) at Ser-32 in 3T3-L1 adipocytes via a PI3K-dependent pathway consistent with Akt as the kinase; however, overexpression of non-phosphorylatable (S32A) or phosphomimetic (S32E) Sec8 mutants had no effect on GLUT4 or transferrin receptor trafficking to the plasma membrane.","method":"Phosphoproteomics (MS), wortmannin inhibitor assay, site-directed mutagenesis (S32A/S32E), surface GLUT4 assay","journal":"Bioscience reports","confidence":"Medium","confidence_rationale":"Tier 1–2 — MS identification plus mutagenesis, but functional effect was negative, single lab","pmids":["19006485"],"is_preprint":false},{"year":2012,"finding":"Sec8 (EXOC4) knockdown reduces the secretion of matrix metalloproteinases MMP-2, proMMP-2, and proMMP-9 and reduces cellular invasiveness in oral squamous-cell carcinoma cells, consistent with a role for Sec8 in vesicle-mediated MMP secretion.","method":"siRNA knockdown, gelatin zymography, invasion assay, proliferation assay","journal":"Journal of cancer research and clinical oncology","confidence":"Low","confidence_rationale":"Tier 3 — single method (KD + functional assay), no direct pathway placement","pmids":["23207790"],"is_preprint":false},{"year":2014,"finding":"Sec8 (EXOC4) knockdown promotes G1/S cell-cycle arrest by increasing p21(Cip1) expression; mechanistically, Sec8 regulates FOXO family transcription factors through ubiquitin-proteasome degradation by controlling Mdm2 protein expression (but not Skp2), thereby controlling p21 levels and Rb phosphorylation.","method":"siRNA knockdown, cell-cycle analysis, immunoblotting, proteasome inhibition","journal":"The FEBS journal","confidence":"Low","confidence_rationale":"Tier 3 — KD with phenotypic readout and partial mechanistic follow-up, single lab","pmids":["24299491"],"is_preprint":false},{"year":2014,"finding":"Sec8 (EXOC4) binds to JIP4 (JNK-interacting protein 4) scaffold protein; Sec8 knockdown enhances JIP4 binding to MKK4, decreasing phosphorylation of MKK4, JNK, and p38 under apoptotic conditions, indicating Sec8 regulates the JIP4-MKK4-JNK/p38 MAPK signaling cascade.","method":"siRNA knockdown, co-immunoprecipitation, immunoblotting of phosphorylated MAPK pathway components","journal":"The FEBS journal","confidence":"Low","confidence_rationale":"Tier 3 — single co-IP plus KD functional readout, single lab","pmids":["25244576"],"is_preprint":false},{"year":2015,"finding":"Sec8 (EXOC4) knockdown suppresses cell migration by reducing phosphorylation of cytokeratin8 at Ser73; this is mediated through the ERK and p38 MAPK signaling pathways via downregulation of p21-activated kinases by Pirh2 and Siah1.","method":"siRNA knockdown, migration assay, immunoblotting of phosphorylated cytokeratin8 and MAPK pathway components","journal":"Cellular signalling","confidence":"Low","confidence_rationale":"Tier 3 — KD with partial pathway placement, single lab","pmids":["25725287"],"is_preprint":false},{"year":2016,"finding":"Sec8 (EXOC4) regulates N-cadherin expression by controlling Smad3 and Smad4 expression at the basal transcriptional level through CBP (CREB-binding protein), thereby modulating TGF-β-induced epithelial-mesenchymal transition (EMT), cell migration, and adhesion.","method":"siRNA knockdown, immunoblotting, RT-PCR for transcriptional regulation, cell migration and adhesion assays","journal":"Cellular signalling","confidence":"Low","confidence_rationale":"Tier 3 — KD with partial mechanistic follow-up on transcriptional regulators, single lab","pmids":["27769780"],"is_preprint":false},{"year":2016,"finding":"CREG1 directly interacts with Sec8 (EXOC4), and this interaction is required for cardiomyocyte differentiation and cell-cell cohesion; CREG1, Sec8, and N-cadherin co-localize at intercalated discs and are enriched at cell-cell junctions; CREG1 overexpression enhances adherens and gap junction assembly, while CREG1 knockout inhibits the Sec8–N-cadherin interaction and induces their degradation.","method":"Co-immunoprecipitation, site-directed mutagenesis, CREG1 knockout ES cells rescue assay, immunofluorescence colocalization, gain/loss-of-function","journal":"Stem cells (Dayton, Ohio)","confidence":"Medium","confidence_rationale":"Tier 2 — co-IP with mutagenesis and functional rescue experiments, single lab","pmids":["27334848"],"is_preprint":false},{"year":2021,"finding":"LRRK2 interacts with Sec8 (EXOC4) and regulates the assembly of exocyst complex subunits through its kinase activity; overexpression of Sec8 significantly rescues the pathological effects of the LRRK2 G2019S Parkinson's disease mutation, suggesting LRRK2 modulates vesicle trafficking via the exocyst.","method":"Co-immunoprecipitation, LRRK2 kinase inhibitor/domain truncation analysis, Sec8 overexpression rescue of LRRK2 G2019S mutant phenotype","journal":"Cells","confidence":"Low","confidence_rationale":"Tier 3 — single co-IP plus rescue experiment, single lab","pmids":["33498474"],"is_preprint":false},{"year":2022,"finding":"EXOC4 promotes diffuse-type gastric cancer metastasis by regulating phosphorylation of focal adhesion kinase (FAK) at Y397; mechanistically, EXOC4 stimulates secretion of integrin α5/β1 and EGF, enhancing the interaction of FAK with integrin or EGFR and thereby activating FAK signaling.","method":"LC/MS-MS proteomics, cell migration/invasion assays, FAK phosphorylation immunoblotting, FAK inhibitor (VS-4718) treatment, patient-derived xenograft models","journal":"Molecular cancer research : MCR","confidence":"Medium","confidence_rationale":"Tier 2 — proteomics-guided identification with functional validation using inhibitor and in vivo PDX model, single lab","pmids":["35471457"],"is_preprint":false},{"year":2023,"finding":"Crystal structure (2.5 Å resolution) of the C-terminal half of Sec8 (EXOC4) reveals an unusually long C-terminal helix with a 14-residue spacer bridging the ITTV PDZ-binding motif to the compact Sec8 core; Sec8 preferentially binds PDZ2 over PDZ1 and PDZ3 of SAP102, and deletion of the spacer completely abolishes SAP102 binding.","method":"X-ray crystallography, binding assays, deletion mutagenesis, structural modeling","journal":"Frontiers in cell and developmental biology","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with mutagenesis validation of binding interface","pmids":["37849738"],"is_preprint":false},{"year":2025,"finding":"EXOC4/SEC8 stabilizes STING1 by suppressing K27-linked ubiquitination of STING1 at K338, K347, and K370 catalyzed by E3 ligase FBXL19, thereby preventing SQSTM1-mediated autophagic degradation of STING1 and promoting type I interferon signaling in response to DNA viruses; conditional Exoc4/Sec8 knockout mice show increased susceptibility to HSV-1 infection.","method":"Co-immunoprecipitation, ubiquitination assays (K27-linkage specific), site-directed mutagenesis of STING1 ubiquitination sites, conditional knockout mouse, viral infection assays, microscale thermophoresis","journal":"Autophagy","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal biochemical methods plus in vivo conditional KO, single lab","pmids":["40413753"],"is_preprint":false},{"year":2026,"finding":"EXOC4 undergoes p300-mediated acetylation at lysine 433, which triggers its nuclear translocation; in the nucleus, EXOC4 facilitates interaction between PRMT5 and KU70, inducing PRMT5-catalyzed methylation of KU70 at arginine 318, which increases KU complex DNA-binding affinity and accelerates double-strand break repair by non-homologous end joining (NHEJ), thereby promoting chemoradiotherapy resistance.","method":"Acetylation mutagenesis (K433), nuclear fractionation, co-immunoprecipitation, PRMT5 methylation assay, DNA-binding affinity assay, peptide inhibitor targeting K433, preclinical models","journal":"Cell death and differentiation","confidence":"Medium","confidence_rationale":"Tier 1–2 — mutagenesis of PTM site, biochemical reconstitution of PRMT5-KU70 interaction, in vivo models, single lab","pmids":["41826730"],"is_preprint":false},{"year":2026,"finding":"Sec8 (EXOC4) stabilizes RIG-I by competing with E3 ligase STUB1 for binding to RIG-I's CARD domain and by suppressing STUB1 mRNA expression through reducing p53 levels, thereby preventing K48-linked ubiquitination of RIG-I at Lys190 and its proteasomal degradation, and enhancing type I interferon signaling against RNA viruses; Sec8-deficient mice show increased susceptibility to RNA virus infection.","method":"Co-immunoprecipitation (binding competition), ubiquitination assays (K48-linkage), site-directed mutagenesis (Lys190), Sec8-deficient mouse, viral infection assays, immunoblotting","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal biochemical methods plus in vivo KO model, single lab","pmids":["41580425"],"is_preprint":false}],"current_model":"EXOC4 (Sec8) is a core subunit of the evolutionarily conserved octameric exocyst complex that tethers secretory vesicles to the plasma membrane at sites of polarized exocytosis, acting downstream of Rab GTPases; beyond vesicle tethering, EXOC4 interacts with synaptic scaffolds (PSD-95, SAP102) via its C-terminal ITTV/TTV PDZ-binding motif, participates in myelination by interacting with Dlg1, regulates cell migration via FAK signaling and cytokeratin8 phosphorylation, undergoes insulin-stimulated Akt-dependent phosphorylation at Ser-32, promotes antiviral immunity by stabilizing both STING1 (against DNA viruses) and RIG-I (against RNA viruses) through blocking their ubiquitin-mediated degradation, and in the nucleus undergoes p300-mediated acetylation at K433 to facilitate PRMT5-dependent KU70 methylation and NHEJ-mediated DNA repair."},"narrative":{"teleology":[{"year":1992,"claim":"Establishing that Sec8p is a component of a multisubunit particle at the plasma membrane acting downstream of the Rab GTPase Sec4p resolved how secretory vesicles are directed to fusion sites, framing Sec8 as an effector in polarized exocytosis.","evidence":"Fractionation, sucrose gradient sedimentation, gel filtration, cross-linking, and immunoprecipitation in S. cerevisiae","pmids":["1512289"],"confidence":"High","gaps":["Mammalian ortholog function not yet demonstrated","Complete subunit composition of the particle unknown","Direct vesicle tethering activity not reconstituted"]},{"year":1995,"claim":"Defining the exocyst as an ~8-subunit complex localized to sites of active exocytosis, with Sec8 as a core subunit whose incorporation depends on other exocyst members, established the architectural framework of the tethering machinery.","evidence":"Metal affinity chromatography, gel filtration, sucrose sedimentation, co-IP, and immunofluorescence in S. cerevisiae","pmids":["7615633"],"confidence":"High","gaps":["Structure of Sec8 within the complex unknown","Stoichiometry and assembly order not defined"]},{"year":1997,"claim":"Demonstrating that homozygous Sec8 knockout mouse embryos arrest at the primitive streak stage established that EXOC4 is essential for early mammalian development, likely reflecting a fundamental requirement for polarized membrane trafficking.","evidence":"Gene trap mutagenesis and phenotypic analysis of homozygous mutant mouse embryos","pmids":["9441674"],"confidence":"High","gaps":["Specific cellular process disrupted (membrane delivery vs. signaling) not distinguished","Tissue-specific requirements not explored"]},{"year":2003,"claim":"Identifying that EXOC4 binds PSD-95 via its C-terminal TTV PDZ-binding motif connected exocyst-mediated vesicle delivery to synaptic scaffolding, suggesting a mechanism for targeted receptor/membrane protein insertion at postsynaptic sites.","evidence":"Co-immunoprecipitation from brain tissue, peptide competition, and TTV motif mutagenesis","pmids":["12675619"],"confidence":"Medium","gaps":["Functional consequence for receptor trafficking at synapses not directly shown","Specificity among PDZ-domain partners not resolved"]},{"year":2005,"claim":"Showing that Drosophila sec8 null mutants exhibit doubled synaptic microtubule density with mild receptor trafficking defects revealed a role for EXOC4 in cytoskeletal regulation at synapses, beyond canonical vesicle tethering.","evidence":"Null mutant analysis with immunocytochemistry, electrophysiology, and immunoblotting at Drosophila NMJ","pmids":["16351720"],"confidence":"High","gaps":["Mechanism linking exocyst to microtubule regulation unknown","Whether this is a direct or indirect effect not established"]},{"year":2006,"claim":"Demonstrating that EXOC4 interacts with OSP/Claudin11 and CASK in oligodendrocytes and that its knockdown inhibits myelin-like membrane formation extended the exocyst's role to glial cell myelination, later reinforced by the Dlg1-Sec8 interaction in Schwann cells.","evidence":"siRNA knockdown, co-IP, co-fractionation in oligodendrocytes; Dlg1 co-IP and Schwann cell/DRG coculture with Mtmr2-null rescue","pmids":["16478790","19587293"],"confidence":"Medium","gaps":["Whether EXOC4's role in myelination is exocyst-dependent or independent not distinguished","In vivo myelination phenotype from EXOC4 conditional knockout not shown"]},{"year":2009,"claim":"Identifying insulin-stimulated PI3K-dependent phosphorylation of EXOC4 at Ser-32 defined a post-translational modification site, although S32A/S32E mutants showed no effect on GLUT4 trafficking, leaving the functional significance unresolved.","evidence":"Phosphoproteomics (MS), wortmannin inhibition, S32A/S32E mutagenesis, surface GLUT4 assay in 3T3-L1 adipocytes","pmids":["19006485"],"confidence":"Medium","gaps":["Functional role of Ser-32 phosphorylation remains unknown","Other trafficking cargoes not tested","Whether Akt is the direct kinase not confirmed by in vitro kinase assay"]},{"year":2014,"claim":"Knockdown studies linking EXOC4 to MAPK signaling (via JIP4-MKK4-JNK/p38), cell cycle regulation (via FOXO-p21-Mdm2), and cell migration (via cytokeratin8-FAK) suggested signaling roles beyond vesicle tethering, though these findings rest on single-lab knockdown approaches.","evidence":"siRNA knockdown with co-IP and phosphorylation immunoblotting in cancer cell lines","pmids":["24299491","25244576","25725287"],"confidence":"Low","gaps":["None confirmed by independent labs","Direct vs. indirect effects of exocyst disruption not separated","Reliance on siRNA without rescue experiments limits confidence"]},{"year":2016,"claim":"Identifying CREG1 as a direct EXOC4 interactor required for N-cadherin stabilization at intercalated discs linked the exocyst to adherens junction assembly during cardiomyocyte differentiation.","evidence":"Co-IP, site-directed mutagenesis, CREG1 KO ES cell rescue, immunofluorescence colocalization","pmids":["27334848"],"confidence":"Medium","gaps":["In vivo cardiac phenotype of EXOC4 loss not shown","Whether EXOC4 delivers N-cadherin-containing vesicles or stabilizes junctional complexes not resolved"]},{"year":2022,"claim":"Showing that EXOC4 promotes FAK Y397 phosphorylation by stimulating secretion of integrin α5/β1 and EGF in gastric cancer provided a mechanistic link between exocyst-mediated secretion and outside-in FAK signaling that drives metastasis.","evidence":"LC-MS/MS proteomics, FAK inhibitor treatment, migration/invasion assays, patient-derived xenograft models","pmids":["35471457"],"confidence":"Medium","gaps":["Generalizability beyond diffuse-type gastric cancer not tested","Whether FAK activation is entirely secondary to secretion not fully excluded"]},{"year":2023,"claim":"The 2.5 Å crystal structure of the C-terminal half of EXOC4 revealed an unusually long C-terminal helix with a 14-residue spacer essential for SAP102 PDZ2 binding, providing the first structural basis for how the exocyst engages synaptic PDZ scaffolds.","evidence":"X-ray crystallography, deletion mutagenesis, binding assays","pmids":["37849738"],"confidence":"High","gaps":["Full-length EXOC4 structure not available","Structure of the EXOC4-PDZ complex not solved","How the spacer positions the ITTV motif for PDZ recognition not modeled at atomic resolution"]},{"year":2025,"claim":"Demonstrating that EXOC4 stabilizes STING1 by blocking FBXL19-mediated K27-linked ubiquitination and subsequent autophagic degradation, with conditional knockout mice showing increased HSV-1 susceptibility, established EXOC4 as a positive regulator of antiviral innate immunity against DNA viruses.","evidence":"Co-IP, K27-linkage-specific ubiquitination assays, STING1 mutagenesis, conditional KO mouse, viral infection, microscale thermophoresis","pmids":["40413753"],"confidence":"Medium","gaps":["Whether this function is exocyst-complex-dependent or an independent moonlighting role not distinguished","Relevance to human antiviral immunity not validated"]},{"year":2026,"claim":"Discovering that p300-mediated acetylation at K433 triggers EXOC4 nuclear translocation where it facilitates PRMT5-dependent KU70 methylation to enhance NHEJ established a non-canonical nuclear function for this exocyst subunit in DNA repair.","evidence":"K433 mutagenesis, nuclear fractionation, co-IP, PRMT5 methylation assay, DNA-binding affinity assay, peptide inhibitor, preclinical models","pmids":["41826730"],"confidence":"Medium","gaps":["How nuclear EXOC4 is distinguished from cytoplasmic exocyst pool not defined","Whether acetylation disrupts exocyst complex integrity not tested","Independent replication needed"]},{"year":2026,"claim":"Showing that EXOC4 stabilizes RIG-I by competing with STUB1 for CARD domain binding and suppressing STUB1 transcription via p53, with KO mice more susceptible to RNA virus infection, extended EXOC4's immune role to RNA virus sensing and provided a parallel to its STING1-stabilizing function.","evidence":"Co-IP binding competition, K48-linkage ubiquitination assays, K190 mutagenesis, Sec8-deficient mouse, viral infection assays","pmids":["41580425"],"confidence":"Medium","gaps":["Dual mechanism (competitive binding + transcriptional suppression of STUB1) not independently confirmed","Whether STING1 and RIG-I stabilization are coordinated not explored"]},{"year":null,"claim":"It remains unresolved whether EXOC4's emerging non-canonical functions — innate immune sensor stabilization, nuclear DNA repair, and signaling regulation — operate independently of the exocyst complex or require its assembly, and how post-translational modifications (acetylation, phosphorylation) partition EXOC4 between these distinct functional pools.","evidence":"","pmids":[],"confidence":"Low","gaps":["No study has tested whether immune and nuclear functions require intact exocyst complex","Full-length EXOC4 structure in the context of the holocomplex not available","Relative physiological importance of vesicle tethering vs. moonlighting functions unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,1,3,16,17,19]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,1]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,1,13,15]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0,7]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[18]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[0,15]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[0,1,5,6,15]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[17,19]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[18]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[10,15]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[2,13]},{"term_id":"R-HSA-1500931","term_label":"Cell-Cell communication","supporting_discovery_ids":[3,13]}],"complexes":["exocyst complex"],"partners":["PSD-95","SAP102","DLG1","STING1","RIG-I","KU70","PRMT5","CREG1"],"other_free_text":[]},"mechanistic_narrative":"EXOC4 (Sec8) is a core subunit of the octameric exocyst complex that tethers secretory vesicles to the plasma membrane at sites of polarized exocytosis, functioning downstream of Rab GTPases in processes spanning embryonic development, synaptic organization, and myelination [PMID:1512289, PMID:7615633, PMID:9441674, PMID:16478790]. Its C-terminal ITTV PDZ-binding motif, separated from the helical core by a structurally critical 14-residue spacer, mediates interactions with synaptic scaffolds such as SAP102 and PSD-95 to direct membrane protein delivery at neuronal junctions [PMID:12675619, PMID:37849738]. Beyond vesicle tethering, EXOC4 stabilizes innate immune sensors STING1 and RIG-I by blocking their E3-ligase-mediated ubiquitination and degradation, thereby promoting type I interferon responses to both DNA and RNA viruses [PMID:40413753, PMID:41580425]. In the nucleus, p300-mediated acetylation of EXOC4 at K433 drives its nuclear translocation, where it facilitates PRMT5-dependent methylation of KU70 to enhance non-homologous end joining DNA repair [PMID:41826730]."},"prefetch_data":{"uniprot":{"accession":"Q96A65","full_name":"Exocyst complex component 4","aliases":["Exocyst complex component Sec8"],"length_aa":974,"mass_kda":110.5,"function":"Component of the exocyst complex involved in the docking of exocytic vesicles with fusion sites on the plasma membrane","subcellular_location":"Midbody, Midbody ring; Cell projection; Cytoplasm, cytoskeleton, microtubule organizing center, centrosome","url":"https://www.uniprot.org/uniprotkb/Q96A65/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/EXOC4","classification":"Common Essential","n_dependent_lines":465,"n_total_lines":1208,"dependency_fraction":0.3849337748344371},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"ARL1","stoichiometry":0.2},{"gene":"CAPZB","stoichiometry":0.2},{"gene":"SLC7A6","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/EXOC4","total_profiled":1310},"omim":[{"mim_id":"621438","title":"GLUTAMATE RECEPTOR-INTERACTING PROTEIN 2; GRIP2","url":"https://www.omim.org/entry/621438"},{"mim_id":"617368","title":"SH3 DOMAIN-BINDING PROTEIN 1; SH3BP1","url":"https://www.omim.org/entry/617368"},{"mim_id":"616927","title":"EXOCYST COMPLEX COMPONENT 3-LIKE 2; EXOC3L2","url":"https://www.omim.org/entry/616927"},{"mim_id":"614117","title":"EXOCYST COMPLEX COMPONENT 3-LIKE 1; EXOC3L1","url":"https://www.omim.org/entry/614117"},{"mim_id":"608185","title":"EXOCYST COMPLEX COMPONENT 4; EXOC4","url":"https://www.omim.org/entry/608185"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/EXOC4"},"hgnc":{"alias_symbol":["KIAA1699","MGC27170","SEC8","Sec8p"],"prev_symbol":["SEC8L1"]},"alphafold":{"accession":"Q96A65","domains":[{"cath_id":"-","chopping":"40-122","consensus_level":"medium","plddt":83.5055,"start":40,"end":122},{"cath_id":"-","chopping":"570-662_671-734_750-904","consensus_level":"medium","plddt":90.0507,"start":570,"end":904}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96A65","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q96A65-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q96A65-F1-predicted_aligned_error_v6.png","plddt_mean":78.75},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=EXOC4","jax_strain_url":"https://www.jax.org/strain/search?query=EXOC4"},"sequence":{"accession":"Q96A65","fasta_url":"https://rest.uniprot.org/uniprotkb/Q96A65.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q96A65/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96A65"}},"corpus_meta":[{"pmid":"7615633","id":"PMC_7615633","title":"Sec6, Sec8, and Sec15 are components of a multisubunit complex which localizes to small bud tips in Saccharomyces cerevisiae.","date":"1995","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/7615633","citation_count":257,"is_preprint":false},{"pmid":"16040664","id":"PMC_16040664","title":"SEC8, a subunit of the putative Arabidopsis exocyst complex, facilitates pollen germination and competitive pollen tube growth.","date":"2005","source":"Plant physiology","url":"https://pubmed.ncbi.nlm.nih.gov/16040664","citation_count":140,"is_preprint":false},{"pmid":"20618910","id":"PMC_20618910","title":"Arabidopsis exocyst subunits SEC8 and EXO70A1 and exocyst interactor ROH1 are involved in the localized deposition of seed coat pectin.","date":"2010","source":"The New phytologist","url":"https://pubmed.ncbi.nlm.nih.gov/20618910","citation_count":98,"is_preprint":false},{"pmid":"1512289","id":"PMC_1512289","title":"Sec8p and Sec15p are components of a plasma membrane-associated 19.5S particle that may function downstream of Sec4p to control exocytosis.","date":"1992","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/1512289","citation_count":96,"is_preprint":false},{"pmid":"19587293","id":"PMC_19587293","title":"Dlg1, Sec8, and Mtmr2 regulate membrane homeostasis in Schwann cell myelination.","date":"2009","source":"The Journal of neuroscience : the official journal of the Society for Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/19587293","citation_count":89,"is_preprint":false},{"pmid":"9441674","id":"PMC_9441674","title":"The secretory protein Sec8 is required for paraxial mesoderm formation in the mouse.","date":"1997","source":"Developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/9441674","citation_count":67,"is_preprint":false},{"pmid":"12675619","id":"PMC_12675619","title":"Exocyst complex subunit sec8 binds to postsynaptic density protein-95 (PSD-95): a novel interaction regulated by cypin (cytosolic PSD-95 interactor).","date":"2003","source":"The Biochemical journal","url":"https://pubmed.ncbi.nlm.nih.gov/12675619","citation_count":34,"is_preprint":false},{"pmid":"16351720","id":"PMC_16351720","title":"Increased synaptic microtubules and altered synapse development in Drosophila sec8 mutants.","date":"2005","source":"BMC biology","url":"https://pubmed.ncbi.nlm.nih.gov/16351720","citation_count":31,"is_preprint":false},{"pmid":"27769780","id":"PMC_27769780","title":"Sec8 modulates TGF-β induced EMT by controlling N-cadherin via regulation of Smad3/4.","date":"2016","source":"Cellular signalling","url":"https://pubmed.ncbi.nlm.nih.gov/27769780","citation_count":29,"is_preprint":false},{"pmid":"16478790","id":"PMC_16478790","title":"A role for Sec8 in oligodendrocyte morphological differentiation.","date":"2006","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/16478790","citation_count":28,"is_preprint":false},{"pmid":"27334848","id":"PMC_27334848","title":"CREG1 Interacts with Sec8 to Promote Cardiomyogenic Differentiation and Cell-Cell Adhesion.","date":"2016","source":"Stem cells (Dayton, Ohio)","url":"https://pubmed.ncbi.nlm.nih.gov/27334848","citation_count":25,"is_preprint":false},{"pmid":"24299491","id":"PMC_24299491","title":"Knockdown of Sec8 promotes cell-cycle arrest at G1/S phase by inducing p21 via control of FOXO proteins.","date":"2014","source":"The FEBS journal","url":"https://pubmed.ncbi.nlm.nih.gov/24299491","citation_count":24,"is_preprint":false},{"pmid":"23207790","id":"PMC_23207790","title":"Exocyst complex component Sec8: a presumed component in the progression of human oral squamous-cell carcinoma by secretion of matrix metalloproteinases.","date":"2012","source":"Journal of cancer research and clinical oncology","url":"https://pubmed.ncbi.nlm.nih.gov/23207790","citation_count":23,"is_preprint":false},{"pmid":"25725287","id":"PMC_25725287","title":"Sec8 regulates cytokeratin8 phosphorylation and cell migration by controlling the ERK and p38 MAPK signalling pathways.","date":"2015","source":"Cellular signalling","url":"https://pubmed.ncbi.nlm.nih.gov/25725287","citation_count":20,"is_preprint":false},{"pmid":"25244576","id":"PMC_25244576","title":"Knockdown of Sec8 enhances the binding affinity of c-Jun N-terminal kinase (JNK)-interacting protein 4 for mitogen-activated protein kinase kinase 4 (MKK4) and suppresses the phosphorylation of MKK4, p38, and JNK, thereby inhibiting apoptosis.","date":"2014","source":"The FEBS journal","url":"https://pubmed.ncbi.nlm.nih.gov/25244576","citation_count":20,"is_preprint":false},{"pmid":"18498660","id":"PMC_18498660","title":"Polymorphisms near EXOC4 and LRGUK on chromosome 7q32 are associated with Type 2 Diabetes and fasting glucose; the NHLBI Family Heart Study.","date":"2008","source":"BMC medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/18498660","citation_count":16,"is_preprint":false},{"pmid":"15880602","id":"PMC_15880602","title":"Association between single-nucleotide polymorphisms in the SEC8L1 gene, which encodes a subunit of the exocyst complex, and rheumatoid arthritis in a Japanese population.","date":"2005","source":"Arthritis and rheumatism","url":"https://pubmed.ncbi.nlm.nih.gov/15880602","citation_count":15,"is_preprint":false},{"pmid":"19006485","id":"PMC_19006485","title":"Insulin stimulates the phosphorylation of the exocyst protein Sec8 in adipocytes.","date":"2009","source":"Bioscience reports","url":"https://pubmed.ncbi.nlm.nih.gov/19006485","citation_count":15,"is_preprint":false},{"pmid":"36180927","id":"PMC_36180927","title":"Altered methylation pattern in EXOC4 is associated with stroke outcome: an epigenome-wide association study.","date":"2022","source":"Clinical epigenetics","url":"https://pubmed.ncbi.nlm.nih.gov/36180927","citation_count":13,"is_preprint":false},{"pmid":"35471457","id":"PMC_35471457","title":"EXOC4 Promotes Diffuse-Type Gastric Cancer Metastasis via Activating FAK Signal.","date":"2022","source":"Molecular cancer research : MCR","url":"https://pubmed.ncbi.nlm.nih.gov/35471457","citation_count":12,"is_preprint":false},{"pmid":"33671441","id":"PMC_33671441","title":"The Association of an SNP in the EXOC4 Gene and Reproductive Traits Suggests Its Use as a Breeding Marker in Pigs.","date":"2021","source":"Animals : an open access journal from MDPI","url":"https://pubmed.ncbi.nlm.nih.gov/33671441","citation_count":9,"is_preprint":false},{"pmid":"20180855","id":"PMC_20180855","title":"Different steps of sexual development are differentially regulated by the Sec8p and Exo70p exocyst subunits.","date":"2010","source":"FEMS microbiology letters","url":"https://pubmed.ncbi.nlm.nih.gov/20180855","citation_count":7,"is_preprint":false},{"pmid":"40413753","id":"PMC_40413753","title":"Unveiling EXOC4/SEC8: a key player in enhancing antiviral immunity by inhibiting the FBXL19-STING1-SQSTM1 signaling axis.","date":"2025","source":"Autophagy","url":"https://pubmed.ncbi.nlm.nih.gov/40413753","citation_count":3,"is_preprint":false},{"pmid":"37849738","id":"PMC_37849738","title":"Sec8 specifically interacts with the PDZ2 domain of synapse associated protein 102 (SAP102).","date":"2023","source":"Frontiers in cell and developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/37849738","citation_count":1,"is_preprint":false},{"pmid":"33498474","id":"PMC_33498474","title":"LRRK2 Modulates the Exocyst Complex Assembly by Interacting with Sec8.","date":"2021","source":"Cells","url":"https://pubmed.ncbi.nlm.nih.gov/33498474","citation_count":1,"is_preprint":false},{"pmid":"37152017","id":"PMC_37152017","title":"Case Report: Co-existence of a novel EXOC4-TRHDE gene fusion with PML-RARA in acute promyelocytic leukemia.","date":"2023","source":"Frontiers in oncology","url":"https://pubmed.ncbi.nlm.nih.gov/37152017","citation_count":1,"is_preprint":false},{"pmid":"41826730","id":"PMC_41826730","title":"Acetylation-dependent nuclear translocation of EXOC4 regulates KU70 methylation to facilitate non-homologous end joining.","date":"2026","source":"Cell death and differentiation","url":"https://pubmed.ncbi.nlm.nih.gov/41826730","citation_count":0,"is_preprint":false},{"pmid":"41580425","id":"PMC_41580425","title":"Sec8: a novel positive regulator of RIG-I in anti-RNA viral defense.","date":"2026","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/41580425","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":14717,"output_tokens":4986,"usd":0.059471},"stage2":{"model":"claude-opus-4-6","input_tokens":8510,"output_tokens":3708,"usd":0.202875},"total_usd":0.262346,"stage1_batch_id":"msgbatch_0118RScg3WGaGkaZRtWZbtce","stage2_batch_id":"msgbatch_01Cpfzvtbj42aqp5oYZ5Te2s","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1992,\n      \"finding\": \"Sec8p (EXOC4 ortholog in S. cerevisiae) is a component of a 19.5S particle that also contains Sec15p, found both in the cytosol and peripherally associated with the plasma membrane but not with secretory vesicles; a portion of Sec4p (Rab GTPase) co-fractionates with the Sec8p/Sec15p particle, suggesting the complex functions as a downstream effector of Sec4p to direct secretory vesicle fusion with the plasma membrane.\",\n      \"method\": \"Fractionation, sucrose gradient sedimentation, gel filtration, cross-linking, immunoprecipitation\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal biochemical methods in foundational yeast study, replicated by subsequent work\",\n      \"pmids\": [\"1512289\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Sec8 (EXOC4 ortholog) is a stable component of a large (~1–2 MDa) multisubunit exocyst complex (Sec6/8/15 containing at least 8 polypeptides) that localizes to small bud tips in S. cerevisiae; complex integrity is disrupted by mutations in sec3, sec5, and sec10, placing Sec8 within the core exocyst at sites of exocytosis.\",\n      \"method\": \"Immobilized metal affinity chromatography, gel filtration, sucrose velocity centrifugation, co-immunoprecipitation, immunofluorescence\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal methods, foundational study with high citation count\",\n      \"pmids\": [\"7615633\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Mouse Sec8 (EXOC4) is required for paraxial mesoderm formation during embryogenesis; homozygous sec8 mutant embryos initiate but cannot progress beyond the primitive streak stage, demonstrating an essential role for Sec8 in early development.\",\n      \"method\": \"Gene trap mutagenesis, homozygous mutant embryo phenotypic analysis, cDNA cloning\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean loss-of-function genetic knockout with defined developmental phenotype\",\n      \"pmids\": [\"9441674\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Sec8 (EXOC4) binds to PDZ1-2 domains of PSD-95 via its C-terminal PDZ-binding motif (Thr-Thr-Val/TTV); this interaction is competed by cypin (cytosolic PSD-95 interactor) and is dependent on the TTV sequence; Sec8 and PSD-95 co-immunoprecipitate from brain tissue and share subcellular distribution.\",\n      \"method\": \"Co-immunoprecipitation, peptide competition assay, site-directed mutagenesis of TTV motif, immunoblotting of tissue fractions\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — reciprocal co-IP from brain and mutagenesis of binding motif, single lab\",\n      \"pmids\": [\"12675619\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"In Drosophila (ortholog of mammalian EXOC4), Sec8 is required in vivo for regulation of synaptic microtubule density at the neuromuscular junction; sec8 null mutants show approximately doubled synaptic microtubule density and altered synapse morphology, with mild disruption of glutamate receptor trafficking but no effect on basal neurotransmission.\",\n      \"method\": \"Forward genetic screen, null mutant analysis, immunocytochemistry, electrophysiology, immunoblotting\",\n      \"journal\": \"BMC biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — null mutant with multiple orthogonal readouts (morphology, electrophysiology, receptor trafficking)\",\n      \"pmids\": [\"16351720\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Sec8 (EXOC4) promotes oligodendrocyte morphological differentiation and myelin-like membrane formation; Sec8 co-localizes, co-immunoprecipitates, and co-fractionates with myelin protein OSP/Claudin11 and scaffolding protein CASK in oligodendrocytes, and siRNA knockdown of Sec8 inhibits membrane formation.\",\n      \"method\": \"siRNA knockdown, Sec8 overexpression, co-immunoprecipitation, co-fractionation, immunofluorescence colocalization\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — co-IP with functional validation by KD and OE, single lab\",\n      \"pmids\": [\"16478790\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"In Schwann cells, Sec8 (EXOC4) interacts with Dlg1 (Discs large 1) scaffolding protein; the Dlg1–Sec8 interaction promotes membrane addition during myelination, while Dlg1–Mtmr2 interaction negatively regulates membrane formation, together constituting a homeostatic machinery that controls myelin membrane amount.\",\n      \"method\": \"Co-immunoprecipitation, Schwann cell/DRG neuron coculture, siRNA knockdown, Mtmr2-null mouse model with myelin outfolding phenotype\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — co-IP plus functional rescue in null mouse model, single lab\",\n      \"pmids\": [\"19587293\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Insulin stimulates phosphorylation of Sec8 (EXOC4) at Ser-32 in 3T3-L1 adipocytes via a PI3K-dependent pathway consistent with Akt as the kinase; however, overexpression of non-phosphorylatable (S32A) or phosphomimetic (S32E) Sec8 mutants had no effect on GLUT4 or transferrin receptor trafficking to the plasma membrane.\",\n      \"method\": \"Phosphoproteomics (MS), wortmannin inhibitor assay, site-directed mutagenesis (S32A/S32E), surface GLUT4 assay\",\n      \"journal\": \"Bioscience reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 — MS identification plus mutagenesis, but functional effect was negative, single lab\",\n      \"pmids\": [\"19006485\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Sec8 (EXOC4) knockdown reduces the secretion of matrix metalloproteinases MMP-2, proMMP-2, and proMMP-9 and reduces cellular invasiveness in oral squamous-cell carcinoma cells, consistent with a role for Sec8 in vesicle-mediated MMP secretion.\",\n      \"method\": \"siRNA knockdown, gelatin zymography, invasion assay, proliferation assay\",\n      \"journal\": \"Journal of cancer research and clinical oncology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single method (KD + functional assay), no direct pathway placement\",\n      \"pmids\": [\"23207790\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Sec8 (EXOC4) knockdown promotes G1/S cell-cycle arrest by increasing p21(Cip1) expression; mechanistically, Sec8 regulates FOXO family transcription factors through ubiquitin-proteasome degradation by controlling Mdm2 protein expression (but not Skp2), thereby controlling p21 levels and Rb phosphorylation.\",\n      \"method\": \"siRNA knockdown, cell-cycle analysis, immunoblotting, proteasome inhibition\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — KD with phenotypic readout and partial mechanistic follow-up, single lab\",\n      \"pmids\": [\"24299491\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Sec8 (EXOC4) binds to JIP4 (JNK-interacting protein 4) scaffold protein; Sec8 knockdown enhances JIP4 binding to MKK4, decreasing phosphorylation of MKK4, JNK, and p38 under apoptotic conditions, indicating Sec8 regulates the JIP4-MKK4-JNK/p38 MAPK signaling cascade.\",\n      \"method\": \"siRNA knockdown, co-immunoprecipitation, immunoblotting of phosphorylated MAPK pathway components\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single co-IP plus KD functional readout, single lab\",\n      \"pmids\": [\"25244576\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Sec8 (EXOC4) knockdown suppresses cell migration by reducing phosphorylation of cytokeratin8 at Ser73; this is mediated through the ERK and p38 MAPK signaling pathways via downregulation of p21-activated kinases by Pirh2 and Siah1.\",\n      \"method\": \"siRNA knockdown, migration assay, immunoblotting of phosphorylated cytokeratin8 and MAPK pathway components\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — KD with partial pathway placement, single lab\",\n      \"pmids\": [\"25725287\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Sec8 (EXOC4) regulates N-cadherin expression by controlling Smad3 and Smad4 expression at the basal transcriptional level through CBP (CREB-binding protein), thereby modulating TGF-β-induced epithelial-mesenchymal transition (EMT), cell migration, and adhesion.\",\n      \"method\": \"siRNA knockdown, immunoblotting, RT-PCR for transcriptional regulation, cell migration and adhesion assays\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — KD with partial mechanistic follow-up on transcriptional regulators, single lab\",\n      \"pmids\": [\"27769780\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"CREG1 directly interacts with Sec8 (EXOC4), and this interaction is required for cardiomyocyte differentiation and cell-cell cohesion; CREG1, Sec8, and N-cadherin co-localize at intercalated discs and are enriched at cell-cell junctions; CREG1 overexpression enhances adherens and gap junction assembly, while CREG1 knockout inhibits the Sec8–N-cadherin interaction and induces their degradation.\",\n      \"method\": \"Co-immunoprecipitation, site-directed mutagenesis, CREG1 knockout ES cells rescue assay, immunofluorescence colocalization, gain/loss-of-function\",\n      \"journal\": \"Stem cells (Dayton, Ohio)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — co-IP with mutagenesis and functional rescue experiments, single lab\",\n      \"pmids\": [\"27334848\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"LRRK2 interacts with Sec8 (EXOC4) and regulates the assembly of exocyst complex subunits through its kinase activity; overexpression of Sec8 significantly rescues the pathological effects of the LRRK2 G2019S Parkinson's disease mutation, suggesting LRRK2 modulates vesicle trafficking via the exocyst.\",\n      \"method\": \"Co-immunoprecipitation, LRRK2 kinase inhibitor/domain truncation analysis, Sec8 overexpression rescue of LRRK2 G2019S mutant phenotype\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single co-IP plus rescue experiment, single lab\",\n      \"pmids\": [\"33498474\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"EXOC4 promotes diffuse-type gastric cancer metastasis by regulating phosphorylation of focal adhesion kinase (FAK) at Y397; mechanistically, EXOC4 stimulates secretion of integrin α5/β1 and EGF, enhancing the interaction of FAK with integrin or EGFR and thereby activating FAK signaling.\",\n      \"method\": \"LC/MS-MS proteomics, cell migration/invasion assays, FAK phosphorylation immunoblotting, FAK inhibitor (VS-4718) treatment, patient-derived xenograft models\",\n      \"journal\": \"Molecular cancer research : MCR\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — proteomics-guided identification with functional validation using inhibitor and in vivo PDX model, single lab\",\n      \"pmids\": [\"35471457\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Crystal structure (2.5 Å resolution) of the C-terminal half of Sec8 (EXOC4) reveals an unusually long C-terminal helix with a 14-residue spacer bridging the ITTV PDZ-binding motif to the compact Sec8 core; Sec8 preferentially binds PDZ2 over PDZ1 and PDZ3 of SAP102, and deletion of the spacer completely abolishes SAP102 binding.\",\n      \"method\": \"X-ray crystallography, binding assays, deletion mutagenesis, structural modeling\",\n      \"journal\": \"Frontiers in cell and developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with mutagenesis validation of binding interface\",\n      \"pmids\": [\"37849738\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"EXOC4/SEC8 stabilizes STING1 by suppressing K27-linked ubiquitination of STING1 at K338, K347, and K370 catalyzed by E3 ligase FBXL19, thereby preventing SQSTM1-mediated autophagic degradation of STING1 and promoting type I interferon signaling in response to DNA viruses; conditional Exoc4/Sec8 knockout mice show increased susceptibility to HSV-1 infection.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assays (K27-linkage specific), site-directed mutagenesis of STING1 ubiquitination sites, conditional knockout mouse, viral infection assays, microscale thermophoresis\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal biochemical methods plus in vivo conditional KO, single lab\",\n      \"pmids\": [\"40413753\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"EXOC4 undergoes p300-mediated acetylation at lysine 433, which triggers its nuclear translocation; in the nucleus, EXOC4 facilitates interaction between PRMT5 and KU70, inducing PRMT5-catalyzed methylation of KU70 at arginine 318, which increases KU complex DNA-binding affinity and accelerates double-strand break repair by non-homologous end joining (NHEJ), thereby promoting chemoradiotherapy resistance.\",\n      \"method\": \"Acetylation mutagenesis (K433), nuclear fractionation, co-immunoprecipitation, PRMT5 methylation assay, DNA-binding affinity assay, peptide inhibitor targeting K433, preclinical models\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 — mutagenesis of PTM site, biochemical reconstitution of PRMT5-KU70 interaction, in vivo models, single lab\",\n      \"pmids\": [\"41826730\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Sec8 (EXOC4) stabilizes RIG-I by competing with E3 ligase STUB1 for binding to RIG-I's CARD domain and by suppressing STUB1 mRNA expression through reducing p53 levels, thereby preventing K48-linked ubiquitination of RIG-I at Lys190 and its proteasomal degradation, and enhancing type I interferon signaling against RNA viruses; Sec8-deficient mice show increased susceptibility to RNA virus infection.\",\n      \"method\": \"Co-immunoprecipitation (binding competition), ubiquitination assays (K48-linkage), site-directed mutagenesis (Lys190), Sec8-deficient mouse, viral infection assays, immunoblotting\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal biochemical methods plus in vivo KO model, single lab\",\n      \"pmids\": [\"41580425\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"EXOC4 (Sec8) is a core subunit of the evolutionarily conserved octameric exocyst complex that tethers secretory vesicles to the plasma membrane at sites of polarized exocytosis, acting downstream of Rab GTPases; beyond vesicle tethering, EXOC4 interacts with synaptic scaffolds (PSD-95, SAP102) via its C-terminal ITTV/TTV PDZ-binding motif, participates in myelination by interacting with Dlg1, regulates cell migration via FAK signaling and cytokeratin8 phosphorylation, undergoes insulin-stimulated Akt-dependent phosphorylation at Ser-32, promotes antiviral immunity by stabilizing both STING1 (against DNA viruses) and RIG-I (against RNA viruses) through blocking their ubiquitin-mediated degradation, and in the nucleus undergoes p300-mediated acetylation at K433 to facilitate PRMT5-dependent KU70 methylation and NHEJ-mediated DNA repair.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"EXOC4 (Sec8) is a core subunit of the octameric exocyst complex that tethers secretory vesicles to the plasma membrane at sites of polarized exocytosis, functioning downstream of Rab GTPases in processes spanning embryonic development, synaptic organization, and myelination [PMID:1512289, PMID:7615633, PMID:9441674, PMID:16478790]. Its C-terminal ITTV PDZ-binding motif, separated from the helical core by a structurally critical 14-residue spacer, mediates interactions with synaptic scaffolds such as SAP102 and PSD-95 to direct membrane protein delivery at neuronal junctions [PMID:12675619, PMID:37849738]. Beyond vesicle tethering, EXOC4 stabilizes innate immune sensors STING1 and RIG-I by blocking their E3-ligase-mediated ubiquitination and degradation, thereby promoting type I interferon responses to both DNA and RNA viruses [PMID:40413753, PMID:41580425]. In the nucleus, p300-mediated acetylation of EXOC4 at K433 drives its nuclear translocation, where it facilitates PRMT5-dependent methylation of KU70 to enhance non-homologous end joining DNA repair [PMID:41826730].\",\n  \"teleology\": [\n    {\n      \"year\": 1992,\n      \"claim\": \"Establishing that Sec8p is a component of a multisubunit particle at the plasma membrane acting downstream of the Rab GTPase Sec4p resolved how secretory vesicles are directed to fusion sites, framing Sec8 as an effector in polarized exocytosis.\",\n      \"evidence\": \"Fractionation, sucrose gradient sedimentation, gel filtration, cross-linking, and immunoprecipitation in S. cerevisiae\",\n      \"pmids\": [\"1512289\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mammalian ortholog function not yet demonstrated\", \"Complete subunit composition of the particle unknown\", \"Direct vesicle tethering activity not reconstituted\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Defining the exocyst as an ~8-subunit complex localized to sites of active exocytosis, with Sec8 as a core subunit whose incorporation depends on other exocyst members, established the architectural framework of the tethering machinery.\",\n      \"evidence\": \"Metal affinity chromatography, gel filtration, sucrose sedimentation, co-IP, and immunofluorescence in S. cerevisiae\",\n      \"pmids\": [\"7615633\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of Sec8 within the complex unknown\", \"Stoichiometry and assembly order not defined\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Demonstrating that homozygous Sec8 knockout mouse embryos arrest at the primitive streak stage established that EXOC4 is essential for early mammalian development, likely reflecting a fundamental requirement for polarized membrane trafficking.\",\n      \"evidence\": \"Gene trap mutagenesis and phenotypic analysis of homozygous mutant mouse embryos\",\n      \"pmids\": [\"9441674\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific cellular process disrupted (membrane delivery vs. signaling) not distinguished\", \"Tissue-specific requirements not explored\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Identifying that EXOC4 binds PSD-95 via its C-terminal TTV PDZ-binding motif connected exocyst-mediated vesicle delivery to synaptic scaffolding, suggesting a mechanism for targeted receptor/membrane protein insertion at postsynaptic sites.\",\n      \"evidence\": \"Co-immunoprecipitation from brain tissue, peptide competition, and TTV motif mutagenesis\",\n      \"pmids\": [\"12675619\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence for receptor trafficking at synapses not directly shown\", \"Specificity among PDZ-domain partners not resolved\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Showing that Drosophila sec8 null mutants exhibit doubled synaptic microtubule density with mild receptor trafficking defects revealed a role for EXOC4 in cytoskeletal regulation at synapses, beyond canonical vesicle tethering.\",\n      \"evidence\": \"Null mutant analysis with immunocytochemistry, electrophysiology, and immunoblotting at Drosophila NMJ\",\n      \"pmids\": [\"16351720\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism linking exocyst to microtubule regulation unknown\", \"Whether this is a direct or indirect effect not established\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Demonstrating that EXOC4 interacts with OSP/Claudin11 and CASK in oligodendrocytes and that its knockdown inhibits myelin-like membrane formation extended the exocyst's role to glial cell myelination, later reinforced by the Dlg1-Sec8 interaction in Schwann cells.\",\n      \"evidence\": \"siRNA knockdown, co-IP, co-fractionation in oligodendrocytes; Dlg1 co-IP and Schwann cell/DRG coculture with Mtmr2-null rescue\",\n      \"pmids\": [\"16478790\", \"19587293\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether EXOC4's role in myelination is exocyst-dependent or independent not distinguished\", \"In vivo myelination phenotype from EXOC4 conditional knockout not shown\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Identifying insulin-stimulated PI3K-dependent phosphorylation of EXOC4 at Ser-32 defined a post-translational modification site, although S32A/S32E mutants showed no effect on GLUT4 trafficking, leaving the functional significance unresolved.\",\n      \"evidence\": \"Phosphoproteomics (MS), wortmannin inhibition, S32A/S32E mutagenesis, surface GLUT4 assay in 3T3-L1 adipocytes\",\n      \"pmids\": [\"19006485\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional role of Ser-32 phosphorylation remains unknown\", \"Other trafficking cargoes not tested\", \"Whether Akt is the direct kinase not confirmed by in vitro kinase assay\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Knockdown studies linking EXOC4 to MAPK signaling (via JIP4-MKK4-JNK/p38), cell cycle regulation (via FOXO-p21-Mdm2), and cell migration (via cytokeratin8-FAK) suggested signaling roles beyond vesicle tethering, though these findings rest on single-lab knockdown approaches.\",\n      \"evidence\": \"siRNA knockdown with co-IP and phosphorylation immunoblotting in cancer cell lines\",\n      \"pmids\": [\"24299491\", \"25244576\", \"25725287\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"None confirmed by independent labs\", \"Direct vs. indirect effects of exocyst disruption not separated\", \"Reliance on siRNA without rescue experiments limits confidence\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Identifying CREG1 as a direct EXOC4 interactor required for N-cadherin stabilization at intercalated discs linked the exocyst to adherens junction assembly during cardiomyocyte differentiation.\",\n      \"evidence\": \"Co-IP, site-directed mutagenesis, CREG1 KO ES cell rescue, immunofluorescence colocalization\",\n      \"pmids\": [\"27334848\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo cardiac phenotype of EXOC4 loss not shown\", \"Whether EXOC4 delivers N-cadherin-containing vesicles or stabilizes junctional complexes not resolved\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Showing that EXOC4 promotes FAK Y397 phosphorylation by stimulating secretion of integrin α5/β1 and EGF in gastric cancer provided a mechanistic link between exocyst-mediated secretion and outside-in FAK signaling that drives metastasis.\",\n      \"evidence\": \"LC-MS/MS proteomics, FAK inhibitor treatment, migration/invasion assays, patient-derived xenograft models\",\n      \"pmids\": [\"35471457\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Generalizability beyond diffuse-type gastric cancer not tested\", \"Whether FAK activation is entirely secondary to secretion not fully excluded\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"The 2.5 Å crystal structure of the C-terminal half of EXOC4 revealed an unusually long C-terminal helix with a 14-residue spacer essential for SAP102 PDZ2 binding, providing the first structural basis for how the exocyst engages synaptic PDZ scaffolds.\",\n      \"evidence\": \"X-ray crystallography, deletion mutagenesis, binding assays\",\n      \"pmids\": [\"37849738\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length EXOC4 structure not available\", \"Structure of the EXOC4-PDZ complex not solved\", \"How the spacer positions the ITTV motif for PDZ recognition not modeled at atomic resolution\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Demonstrating that EXOC4 stabilizes STING1 by blocking FBXL19-mediated K27-linked ubiquitination and subsequent autophagic degradation, with conditional knockout mice showing increased HSV-1 susceptibility, established EXOC4 as a positive regulator of antiviral innate immunity against DNA viruses.\",\n      \"evidence\": \"Co-IP, K27-linkage-specific ubiquitination assays, STING1 mutagenesis, conditional KO mouse, viral infection, microscale thermophoresis\",\n      \"pmids\": [\"40413753\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether this function is exocyst-complex-dependent or an independent moonlighting role not distinguished\", \"Relevance to human antiviral immunity not validated\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Discovering that p300-mediated acetylation at K433 triggers EXOC4 nuclear translocation where it facilitates PRMT5-dependent KU70 methylation to enhance NHEJ established a non-canonical nuclear function for this exocyst subunit in DNA repair.\",\n      \"evidence\": \"K433 mutagenesis, nuclear fractionation, co-IP, PRMT5 methylation assay, DNA-binding affinity assay, peptide inhibitor, preclinical models\",\n      \"pmids\": [\"41826730\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How nuclear EXOC4 is distinguished from cytoplasmic exocyst pool not defined\", \"Whether acetylation disrupts exocyst complex integrity not tested\", \"Independent replication needed\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Showing that EXOC4 stabilizes RIG-I by competing with STUB1 for CARD domain binding and suppressing STUB1 transcription via p53, with KO mice more susceptible to RNA virus infection, extended EXOC4's immune role to RNA virus sensing and provided a parallel to its STING1-stabilizing function.\",\n      \"evidence\": \"Co-IP binding competition, K48-linkage ubiquitination assays, K190 mutagenesis, Sec8-deficient mouse, viral infection assays\",\n      \"pmids\": [\"41580425\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Dual mechanism (competitive binding + transcriptional suppression of STUB1) not independently confirmed\", \"Whether STING1 and RIG-I stabilization are coordinated not explored\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved whether EXOC4's emerging non-canonical functions — innate immune sensor stabilization, nuclear DNA repair, and signaling regulation — operate independently of the exocyst complex or require its assembly, and how post-translational modifications (acetylation, phosphorylation) partition EXOC4 between these distinct functional pools.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No study has tested whether immune and nuclear functions require intact exocyst complex\", \"Full-length EXOC4 structure in the context of the holocomplex not available\", \"Relative physiological importance of vesicle tethering vs. moonlighting functions unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 1, 3, 16, 17, 19]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 1, 13, 15]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 7]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [18]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [0, 15]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [0, 1, 5, 6, 15]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [17, 19]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [18]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [10, 15]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [2, 13]},\n      {\"term_id\": \"R-HSA-1500931\", \"supporting_discovery_ids\": [3, 13]}\n    ],\n    \"complexes\": [\n      \"exocyst complex\"\n    ],\n    \"partners\": [\n      \"PSD-95\",\n      \"SAP102\",\n      \"Dlg1\",\n      \"STING1\",\n      \"RIG-I\",\n      \"KU70\",\n      \"PRMT5\",\n      \"CREG1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}