Affinage

STX4

Syntaxin-4 · UniProt Q12846

Round 2 corrected
Length
297 aa
Mass
34.2 kDa
Annotated
2026-04-28
41 papers in source corpus 14 papers cited in narrative 14 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

STX4 is a plasma membrane-localized t-SNARE that partners with SNAP-23 to mediate the docking and fusion of diverse vesicle populations with the cell surface in both neuronal and non-neuronal tissues. In adipocytes and skeletal muscle, STX4 forms a ternary SNARE complex with SNAP-23 and VAMP2 that is essential for insulin-stimulated GLUT4 translocation, regulated by the inhibitory binding of Munc-18c and the insulin-responsive factor Synip (PMID:9045631, PMID:18439908); it also pairs with VAMP7/TI-VAMP for Ca²⁺-regulated lysosomal exocytosis (PMID:14993220), with VAMP3 for recycling endosome delivery during macrophage migration (PMID:21586284), and with the ER-SNARE Sec22b for ER-protein recruitment to phagosomes in dendritic cell cross-presentation (PMID:22153078). Beyond the plasma membrane, STX4 localizes at or near the mitochondrial outer membrane in skeletal muscle where it directly interacts with Drp1 to suppress mitochondrial fragmentation via AMPK-mediated Drp1 S637 phosphorylation, and is required for mitochondrial biogenesis, electron transport chain integrity, and PINK1/PARKIN-dependent mitophagy (PMID:35058456, PMID:41214862). In hippocampal neurons, STX4 defines a postsynaptic exocytic microdomain in dendritic spines that is essential for activity-dependent AMPA receptor insertion and long-term potentiation (PMID:20434989).

Mechanistic history

Synthesis pass · year-by-year structured walk · 11 steps
  1. 1993 High

    Identification of STX4 as a new syntaxin-family vesicular transport receptor established that multiple syntaxins exist with distinct subcellular targeting, raising the question of which membrane fusion events STX4 mediates.

    Evidence Molecular cloning and heterologous expression in COS cells with subcellular fractionation

    PMID:7690687

    Open questions at the time
    • Endogenous binding partners unknown
    • Tissue-specific function not addressed
    • Target membrane identity unresolved
  2. 1996 High

    Discovery that SNAP-23 binds STX4 in non-neuronal cells identified the cognate Q-SNARE partner and implied that STX4/SNAP-23 constitutes a ubiquitous plasma membrane docking platform analogous to neuronal syntaxin-1/SNAP-25.

    Evidence Yeast two-hybrid and in vitro recombinant protein binding

    PMID:8663154

    Open questions at the time
    • v-SNARE partners not yet identified
    • No functional fusion assay performed
  3. 1997 High

    Demonstration that Munc-18c specifically binds and regulates STX4, and that blocking STX4 prevents insulin-stimulated GLUT4 translocation in adipocytes, established the first defined physiological fusion event requiring STX4.

    Evidence Recombinant binding assays, subcellular fractionation, and anti-STX4 antibody microinjection in 3T3-L1 adipocytes

    PMID:9045631

    Open questions at the time
    • Structural basis of Munc-18c/STX4 interaction unknown
    • Mechanism of insulin-triggered release of Munc-18c not established
  4. 2004 High

    Showing that STX4 forms SDS-resistant SNARE complexes with SNAP-23 and TI-VAMP7 upon Ca²⁺ elevation revealed STX4 mediates a second, calcium-regulated exocytic pathway—lysosomal exocytosis—broadening its role beyond GLUT4 trafficking.

    Evidence Co-immunoprecipitation, SDS-resistant complex detection, dominant-negative SNARE overexpression, and lysosomal exocytosis assays

    PMID:14993220

    Open questions at the time
    • Precise Ca²⁺ sensor coupling mechanism not fully resolved
    • Relative contribution versus other plasma membrane syntaxins not quantified
  5. 2008 Medium

    Mapping the Synip–STX4 interaction and demonstrating that insulin triggers Synip dissociation to permit VAMP2 binding provided a molecular switch model for regulated SNARE complex assembly at the plasma membrane.

    Evidence Co-expression/co-purification of recombinant proteins, deletion mutagenesis

    PMID:18439908

    Open questions at the time
    • Insulin-dependent phosphorylation events on Synip not fully mapped
    • In vivo validation of Synip switch model limited
    • Single study with in vitro reconstitution only
  6. 2010 High

    Identifying STX4 as the t-SNARE defining a postsynaptic exocytic microdomain in dendritic spines, required for AMPA receptor insertion and LTP, extended STX4 function from metabolic tissues to neuronal synaptic plasticity.

    Evidence Live-cell TIRF microscopy, dominant-negative and siRNA knockdown, LTP electrophysiology in hippocampal slices

    PMID:20434989

    Open questions at the time
    • Identity of the v-SNARE partner in spines not resolved
    • How STX4 microdomain is spatially organized relative to PSD scaffolds remains unclear
  7. 2011 High

    Two studies simultaneously expanded STX4's repertoire: VAMP3/STX4/SNAP23-mediated recycling endosome fusion during macrophage migration, and Sec22b/STX4 pairing for ER-to-phagosome protein delivery in dendritic cell cross-presentation, demonstrating STX4 engages distinct v-SNAREs in different immune cell contexts.

    Evidence siRNA knockdown and localization in macrophages (migration assays); Co-IP, knockdown, and cross-presentation assays in primary DCs

    PMID:21586284 PMID:22153078

    Open questions at the time
    • Essentiality of Sec22b/STX4 for cross-presentation later questioned by KO studies
    • Whether VAMP3/STX4 pathway operates outside macrophages not tested
  8. 2022 High

    Transgenic STX4 enrichment in skeletal muscle revealed a non-canonical role at or near mitochondria: STX4 directly binds Drp1, promotes its inhibitory S637 phosphorylation via AMPK, and prevents diet-induced mitochondrial fragmentation and insulin resistance, establishing STX4 as a regulator of mitochondrial dynamics.

    Evidence Skeletal muscle-specific transgenic mice, electron microscopy localization, Co-IP of STX4–Drp1, phospho-Drp1 immunoblot, metabolic phenotyping

    PMID:35058456

    Open questions at the time
    • How STX4 is targeted to mitochondria versus plasma membrane is unknown
    • Whether SNARE function per se is involved at mitochondria is untested
  9. 2022 Medium

    Loss of stx4 in zebrafish caused bradycardia, reduced sarcolemmal vesicle docking, and impaired L-type Ca²⁺ channel modulation, linking STX4 to cardiac conduction and identifying the human R240W variant as a hypomorphic allele associated with dilated cardiomyopathy.

    Evidence CRISPR/Cas9 zebrafish knockout, optical mapping, live Vamp2+ vesicle imaging, pharmacological Ca²⁺ modulation

    PMID:35599850

    Open questions at the time
    • Human genetic association based on limited case data
    • Mechanism linking vesicle docking to L-type Ca²⁺ channel surface density not established
    • Single study in zebrafish model
  10. 2023 Medium

    CRISPR knockout of STX4 in murine APC lines showed minimal impact on cross-presentation of certain antigens, challenging the model that the Sec22b/STX4 axis is universally required and suggesting SNARE redundancy in the cytosolic cross-presentation pathway.

    Evidence CRISPR/Cas9 KO in APC lines, cross-presentation assay with PLGA microspheres and long peptides

    PMID:37638825

    Open questions at the time
    • Limited to specific antigen delivery formats—vacuolar pathway not tested
    • Does not identify which alternative SNARE compensates
    • Immortalized APC lines may differ from primary DCs
  11. 2025 High

    Inducible skeletal muscle-specific STX4 knockout demonstrated that STX4 is indispensable for mitochondrial homeostasis: its loss impairs oxygen consumption, electron transport chain complex abundance, mitochondrial biogenesis gene expression, and PINK1/PARKIN-dependent mitophagy, confirming and extending the 2022 gain-of-function findings.

    Evidence Inducible muscle KO mice and siRNA in L6 myotubes; OCR, EM, ¹³C-glucose tracing, mt-Keima mitophagy imaging, immunoblotting

    PMID:41214862

    Open questions at the time
    • Direct mechanistic link between STX4 and mitophagy initiation (e.g., PINK1 stabilization) not delineated
    • Whether mitochondrial role extends to non-muscle tissues is unknown

Open questions

Synthesis pass · forward-looking unresolved questions
  • Key unresolved questions include how STX4 is dually targeted to the plasma membrane versus mitochondria, whether its mitochondrial role involves canonical SNARE complex formation, the structural basis of STX4's selectivity for multiple v-SNARE partners, and the extent to which SNARE redundancy limits STX4's essentiality in cross-presentation and other immune functions.
  • Dual-targeting mechanism unknown
  • No structural model of full-length STX4 in any SNARE complex
  • Mitochondrial SNARE function not reconstituted in vitro

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0005198 structural molecule activity 5
Localization
GO:0005886 plasma membrane 7 GO:0005739 mitochondrion 2 GO:0031410 cytoplasmic vesicle 2
Pathway
R-HSA-5653656 Vesicle-mediated transport 8 R-HSA-168256 Immune System 2 R-HSA-1852241 Organelle biogenesis and maintenance 2 R-HSA-382551 Transport of small molecules 2 R-HSA-112316 Neuronal System 1 R-HSA-9612973 Autophagy 1
Partners
DNM1LSEC22BSNAP23STXBP3SYNIPVAMP2VAMP3VAMP7
Complex memberships
STX4/SNAP-23/VAMP2 SNARE complexSTX4/SNAP-23/VAMP3 SNARE complexSTX4/SNAP-23/VAMP7 SNARE complexSTX4/Sec22b SNARE complex

Evidence

Reading pass · 14 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1993 STX4 (syntaxin-4) was identified as a member of the syntaxin family of vesicular transport receptors; it contains a carboxy-terminal hydrophobic membrane anchor, is expressed broadly across tissues, and when expressed in COS cells is targeted to specific subcellular compartments distinct from other syntaxin family members, implicating it as a receptor for intracellular transport vesicles at a defined target membrane. Molecular cloning, COS-cell heterologous expression, subcellular fractionation, microinjection Cell High 7690687
1996 STX4 interacts with SNAP-23 (a ubiquitously expressed SNAP-25 homolog) in non-neuronal tissues; the SNAP-23/syntaxin complex serves as a binding site for the general membrane fusion machinery, implicating STX4/SNAP-23 in vesicle docking and fusion in non-neuronal cells. Yeast two-hybrid, in vitro binding assay with recombinant proteins The Journal of Biological Chemistry High 8663154
1997 Munc-18c specifically binds syntaxin-4 (but not syntaxin-1A, -2, or -3 for Munc-18c) at the plasma membrane of 3T3-L1 adipocytes and inhibits syntaxin-4 interaction with VAMP-2; insulin stimulates movement of syntaxin-4 and Munc-18c from an intracellular fraction; microinjection of syntaxin-4 antibody blocks insulin-dependent GLUT4 recruitment to the cell surface, establishing the Munc-18c/syntaxin-4/VAMP-2 complex as required for insulin-stimulated GLUT4 vesicle docking/fusion. In vitro recombinant protein binding assay, subcellular fractionation, antibody microinjection into 3T3-L1 adipocytes, immunofluorescence The Journal of Biological Chemistry High 9045631
2004 STX4 facilitates Ca2+-regulated lysosomal exocytosis by forming a SNARE complex with SNAP-23 and the lysosomal v-SNARE TI-VAMP/VAMP7 at the plasma membrane; Ca2+-dependent interaction of synaptotagmin VII C2A domain with SNAP-23 is facilitated by syntaxin-4; SDS-resistant ternary SNARE complexes containing SNAP-23, syntaxin-4, and TI-VAMP7 form after cytosolic Ca2+ elevation; SNARE domain of syntaxin-4 inhibits lysosomal exocytosis when overexpressed. Co-immunoprecipitation from cell lysates, SDS-PAGE of SDS-resistant SNARE complexes, dominant-negative SNARE domain overexpression, lysosomal exocytosis assay The Journal of Biological Chemistry High 14993220
2008 The C-terminal domain of Synip directly interacts with STX4; in the basal state this interaction prevents VAMP2 from binding STX4; insulin induces dissociation of Synip from STX4, allowing VAMP2 to interact with STX4 to form the SNARE complex and promote GLUT4 vesicle fusion; the N-terminal 1-28 residues of STX4 are dispensable for Synip interaction. Co-expression in E. coli using dual-vector system (pGEX6p-1/pET28a), co-purification, in vitro binding assay, deletion mutagenesis Biochemical and Biophysical Research Communications Medium 18439908
2010 STX4 defines a postsynaptic exocytic microdomain adjacent to the PSD in dendritic spines; during elevated synaptic activity, large AMPA receptor-containing recycling compartments fuse preferentially at STX4-enriched plasma membrane microdomains; disruption of STX4 (dominant-negative or knockdown) impairs spine exocytosis and long-term potentiation (LTP) at hippocampal synapses, establishing STX4 as the t-SNARE mediating postsynaptic membrane fusion for synaptic plasticity. Live-cell TIRF microscopy, dominant-negative STX4 expression, siRNA knockdown, LTP electrophysiology in hippocampal slices, immunofluorescence localization Cell High 20434989
2011 The SNARE complex VAMP3/STX4/SNAP23 mediates polarized exocytosis of recycling endosome membrane during macrophage spreading and migration on fibronectin; STX4/SNAP23 accumulate at sites of membrane expansion where VAMP3-positive vesicles fuse; knockdown of VAMP3 disrupts podosome ring superstructures and polarized podosome localisation, reducing persistent macrophage migration. siRNA knockdown, immunofluorescence, live-cell imaging, cell spreading/migration assays on fibronectin Experimental Cell Research Medium 21586284
2011 STX4 is present in phagosomes of dendritic cells and serves as the plasma membrane SNARE partner for the ER-ERGIC SNARE Sec22b; Sec22b-STX4 pairing mediates recruitment of ER-resident proteins to phagosomes and is required for antigen cross-presentation; depletion of Sec22b impairs ER protein recruitment to phagosomes and reduces antigen export to the cytosol. Co-immunoprecipitation, subcellular fractionation, siRNA knockdown in DCs, cross-presentation functional assay, immunofluorescence Cell High 22153078
2022 Skeletal muscle-specific transgenic enrichment of STX4 (skmSTX4tg) reverses high-fat diet-induced insulin resistance in mice without altering body weight; electron microscopy localizes STX4 at or proximal to the mitochondrial membrane in muscle; STX4 enrichment prevents HFD-induced mitochondrial fragmentation through a direct STX4-Drp1 interaction and elevated AMPK-mediated phosphorylation of Drp1 at S637 (favoring fusion), demonstrating that STX4 acts not only at the plasma membrane but also regulates mitochondrial dynamics. Transgenic mouse model (skmSTX4tg), glucose/insulin tolerance tests, electron microscopy, Co-immunoprecipitation (STX4-Drp1), phospho-Drp1 S637 immunoblot, mitochondrial morphology quantification Nature Communications High 35058456
2022 STX4 is required for normal vertebrate cardiac conduction and vesicular transport; loss of stx4 in zebrafish (CRISPR/Cas9 knockout) causes linearized hearts, bradycardia, and reduced docking of Vamp2+ vesicles to the cardiomyocyte sarcolemma; optical mapping and pharmacological Ca2+ modulation reveal that stx4 mutants have reduced L-type Ca2+ channel modulation; human STX4 R240W is a hypomorphic variant associated with dilated cardiomyopathy. CRISPR/Cas9 zebrafish knockout, optical mapping of embryonic hearts, live imaging of Vamp2+ vesicles, pharmacological Ca2+ channel modulation, transgenic overexpression of STX4R241W HGG Advances Medium 35599850
2023 CRISPR/Cas9 knockout of STX4 in murine APC lines had very limited effects on cross-presentation of PLGA microsphere-encapsulated antigen or synthetic long peptides, suggesting SNARE redundancy in the cytosolic pathway of cross-presentation and questioning the essential role of the Sec22b/STX4 axis in this specific context. CRISPR/Cas9 gene knockout in murine APC lines, cross-presentation functional assay, flow cytometry Journal of Immunology Medium 37638825
2025 STX4 is indispensable for mitochondrial homeostasis in skeletal muscle: inducible skeletal muscle-specific STX4 knockout (skmSTX4-iKO) causes insulin resistance, reduced energy expenditure, impaired mitochondrial oxygen consumption, mitochondrial fragmentation (oxidative fibers) or swelling (glycolytic fibers), and decreased electron transport chain complex abundance; STX4 depletion also reduces mitochondrial biogenesis genes (PGC1-α, NRF1, Tfam) and impairs PINK1/PARKIN-dependent mitophagy, as demonstrated by live mt-Keima biosensor imaging. Inducible skeletal muscle-specific knockout mice, siRNA knockdown in L6 myotubes, mitochondrial oxygen consumption rate, electron microscopy, [U-13C]glucose isotope tracing, mt-Keima live-cell mitophagy imaging, immunoblotting for ETC complexes and mitophagy markers Journal of Cachexia, Sarcopenia and Muscle High 41214862
2025 STX4 (together with SNAP23) participates as a Q-SNARE in secretory autophagy-mediated exocytosis of the Alzheimer-associated ubiquitin variant UBB+1; disruption of STX4 impairs fusion of UBB+1-containing autophagosome-like vesicles with the plasma membrane, reducing UBB+1 secretion. SNARE knockdown/knockout, UBB+1 secretion assay, vesicle-plasma membrane fusion assessment bioRxivpreprint Low bio_10.1101_2024.12.31.630908
2025 STX4 silencing in ovarian cancer cell lines (SK-OV-3, CAOV-3) via shRNA reduces proliferation, migration, and invasion and decreases E-cadherin, MMP2, and CCND1 levels, implicating STX4 in regulating EMT and cell cycle progression in cancer cells; in vivo tumor xenograft models confirmed reduced tumorigenicity. shRNA knockdown, CCK-8 proliferation assay, Transwell migration/invasion assay, scratch assay, immunoblotting for EMT/MMP/cyclin markers, xenograft mouse model Journal of Ovarian Research Low 40483481

Source papers

Stage 0 corpus · 41 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2005 Towards a proteome-scale map of the human protein-protein interaction network. Nature 2090 16189514
2002 Generation and initial analysis of more than 15,000 full-length human and mouse cDNA sequences. Proceedings of the National Academy of Sciences of the United States of America 1479 12477932
2015 The BioPlex Network: A Systematic Exploration of the Human Interactome. Cell 1118 26186194
2017 Architecture of the human interactome defines protein communities and disease networks. Nature 1085 28514442
2014 A proteome-scale map of the human interactome network. Cell 977 25416956
2002 Regulated transport of the glucose transporter GLUT4. Nature reviews. Molecular cell biology 899 11994746
2020 A reference map of the human binary protein interactome. Nature 849 32296183
2003 Complete sequencing and characterization of 21,243 full-length human cDNAs. Nature genetics 754 14702039
2021 Dual proteome-scale networks reveal cell-specific remodeling of the human interactome. Cell 705 33961781
2012 A census of human soluble protein complexes. Cell 689 22939629
2011 Phylogenetic-based propagation of functional annotations within the Gene Ontology consortium. Briefings in bioinformatics 656 21873635
1993 The syntaxin family of vesicular transport receptors. Cell 610 7690687
1995 Ca(2+)-dependent and -independent activities of neural and non-neural synaptotagmins. Nature 552 7791877
2021 Multilevel proteomics reveals host perturbations by SARS-CoV-2 and SARS-CoV. Nature 532 33845483
2015 ATG14 promotes membrane tethering and fusion of autophagosomes to endolysosomes. Nature 467 25686604
2015 Widespread macromolecular interaction perturbations in human genetic disorders. Cell 454 25910212
2004 The status, quality, and expansion of the NIH full-length cDNA project: the Mammalian Gene Collection (MGC). Genome research 438 15489334
2022 OpenCell: Endogenous tagging for the cartography of human cellular organization. Science (New York, N.Y.) 432 35271311
2000 Three ways to make a vesicle. Nature reviews. Molecular cell biology 410 11252894
2000 Secretory protein trafficking and organelle dynamics in living cells. Annual review of cell and developmental biology 380 11031247
2021 A proximity-dependent biotinylation map of a human cell. Nature 339 34079125
2008 A genome-wide scan for common genetic variants with a large influence on warfarin maintenance dose. Blood 328 18535201
1996 Identification of a novel syntaxin- and synaptobrevin/VAMP-binding protein, SNAP-23, expressed in non-neuronal tissues. The Journal of biological chemistry 294 8663154
2004 Identification of SNAREs involved in synaptotagmin VII-regulated lysosomal exocytosis. The Journal of biological chemistry 273 14993220
2011 Sec22b regulates phagosomal maturation and antigen crosspresentation by dendritic cells. Cell 247 22153078
2010 Syntaxin-4 defines a domain for activity-dependent exocytosis in dendritic spines. Cell 226 20434989
2010 MHC class II-associated proteins in B-cell exosomes and potential functional implications for exosome biogenesis. Immunology and cell biology 221 20458337
2009 Proteomic analysis of integrin-associated complexes identifies RCC2 as a dual regulator of Rac1 and Arf6. Science signaling 207 19738201
2011 Next-generation sequencing to generate interactome datasets. Nature methods 200 21516116
1997 Characterization of Munc-18c and syntaxin-4 in 3T3-L1 adipocytes. Putative role in insulin-dependent movement of GLUT-4. The Journal of biological chemistry 191 9045631
2011 VAMP3 regulates podosome organisation in macrophages and together with Stx4/SNAP23 mediates adhesion, cell spreading and persistent migration. Experimental cell research 31 21586284
2022 Enrichment of the exocytosis protein STX4 in skeletal muscle remediates peripheral insulin resistance and alters mitochondrial dynamics via Drp1. Nature communications 23 35058456
2019 STX4 expression is associated with classification, clinical stage and lymphatic metastasis in ovarian cancer. Translational cancer research 7 35116778
2022 Stx4 is required to regulate cardiomyocyte Ca2+ handling during vertebrate cardiac development. HGG advances 5 35599850
2008 An efficient co-expression and purification system for the complex of Stx4 and C-terminal domain of Synip. Biochemical and biophysical research communications 5 18439908
2023 Sec22b and Stx4 Depletion Has No Major Effect on Cross-Presentation of PLGA Microsphere-Encapsulated Antigen and a Synthetic Long Peptide In Vitro. Journal of immunology (Baltimore, Md. : 1950) 4 37638825
2025 Silencing of STX4 inhibits the proliferation, migration and invasion of ovarian cancer cells via EMT/MMP2/ CCND1 signaling pathway. Journal of ovarian research 2 40483481
2025 A multi-omics and mediation-based genetic screening approach identifies STX4 as a key link between epigenetic regulation, immune cells, and childhood asthma. Clinical epigenetics 2 40514687
2025 STX4 Is Indispensable for Mitochondrial Homeostasis in Skeletal Muscle. Journal of cachexia, sarcopenia and muscle 2 41214862
2025 Clinicopathologic significance of FUT8, STX4, and calpain2 expression in ovarian cancer. American journal of translational research 0 39959200
2025 STX4 is indispensable for mitochondrial homeostasis in skeletal muscle. bioRxiv : the preprint server for biology 0 40949942