STX11

STX11 encodes a SNARE protein that mediates lytic granule exocytosis in NK cells and cytotoxic T lymphocytes, and loss-of-function mutations cause familial hemophagocytic lymphohistiocytosis type 4 (FHL-4) (PMID:16278825, PMID:20486178). Syntaxin-11 binds Munc18-2 (STXBP2) through its N-terminal Habc domain and requires its C-terminus for degranulation function, as shown by rescue experiments in Stx11-knockout mice and mutagenesis of critical residues (L58P, R4A) that abolish the interaction and impair NK cell degranulation (PMID:23160464, PMID:24459464). Beyond immune cell degranulation, STX11 physically interacts with ATGL via its C-terminus to sequester ATGL at the endoplasmic reticulum, thereby inhibiting lipid droplet degradation and lipophagy in hepatocytes, and interacts with SNAP25 to promote autophagy and suppress the PI3K/AKT/mTOR pathway in fibroblasts (PMID:35372814, PMID:39523374). STX11 also promotes de novo lipogenesis in colorectal cancer through palmitoylation-dependent suppression of AMPK-mediated ACC phosphorylation (PMID:41621610).

1. 2006 Medium

   Identifying STX11 as a t-SNARE whose loss-of-function mutations cause defective granule exocytosis in NK cells and CTLs established the gene's causal role in familial hemophagocytic lymphohistiocytosis type 4 (FHL-4).

   Evidence Mutational analysis in FHL patient cohorts combined with classification of STX11 as a t-SNARE

   PMID:16278825

   Open questions at the time

   • Precise membrane fusion step mediated by STX11 not defined
   • Domain requirements for degranulation function unknown
   • Binding partners in the SNARE complex not identified
2. 2010 Medium

   Demonstrating that a nonsense mutation (E25X) abolishes STX11 protein expression and NK cell degranulation while certain missense mutations preserve both linked protein abundance to functional output.

   Evidence Western blot for protein expression and in vitro NK cell degranulation/cytotoxicity assays on patient-derived cells

   PMID:20486178

   Open questions at the time

   • Mechanism by which residual protein maintains function not characterized
   • Contribution of specific STX11 domains to degranulation not tested
3. 2012 High

   Using a knockout mouse model with rescue experiments resolved that the C-terminus of syntaxin-11 is essential for degranulation, since wild-type but not C-terminally truncated human STX11 rescued the lymphocyte defect.

   Evidence Stx11-knockout mice with LCMV-induced HLH; rescue by WT vs. truncated human STX11 constructs

   PMID:23160464

   Open questions at the time

   • Identity of the C-terminal binding partner(s) not yet determined
   • Structural basis for C-terminal requirement unknown
4. 2014 High

   Mapping the STX11–Munc18-2 (STXBP2) interaction to the N-terminal Habc domain and showing that point mutations L58P and R4A abolish binding and impair degranulation defined the molecular interface required for effector function.

   Evidence Co-immunoprecipitation with domain and point mutants; NK cell degranulation assays

   PMID:24459464

   Open questions at the time

   • Atomic-resolution structure of the STX11–Munc18-2 complex not solved
   • Other SNARE partners forming the fusogenic complex with STX11 not identified
   • How Munc18-2 binding enables membrane fusion mechanistically remains open
5. 2022 Medium

   Discovery of a non-immune role: STX11 physically sequesters ATGL at the ER via a C-terminal interaction with ATGL's patatin domain, preventing ATGL translocation to lipid droplets and inhibiting lipophagy in hepatocytes.

   Evidence Co-IP with domain mapping; subcellular localization imaging; STX11 overexpression/knockdown in hepatocytes with lipid droplet and lipophagy quantification

   PMID:35372814

   Open questions at the time

   • Physiological triggers controlling STX11-ATGL interaction not identified
   • Whether SNARE activity is required for ATGL sequestration is unclear
   • In vivo hepatic phenotype of STX11 loss not fully characterized
6. 2024 Medium

   STX11 forms a complex with SNAP25 to promote fibroblast autophagy and block PI3K/AKT/mTOR signaling, revealing a SNARE-dependent anti-fibrotic mechanism validated in a bleomycin pulmonary fibrosis model.

   Evidence Co-IP of STX11–SNAP25; autophagy flux assays; PI3K/AKT/mTOR pathway analysis; bleomycin mouse model with STX11 overexpression

   PMID:39523374

   Open questions at the time

   • Whether STX11–SNAP25 interaction mediates autophagosome fusion or upstream signaling is unresolved
   • Specificity of STX11 vs. other syntaxins in this pathway not tested
7. 2026 Medium

   STX11 promotes de novo lipogenesis in colorectal cancer by suppressing AMPK-mediated ACC phosphorylation in a palmitoylation-dependent manner, and its ablation impedes tumorigenesis in vivo.

   Evidence AOM/DSS colorectal cancer mouse model with STX11 genetic ablation; AMPK/ACC signaling and palmitoylation assays

   PMID:41621610

   Open questions at the time

   • How palmitoylation alters STX11's ability to modulate AMPK is mechanistically undefined
   • Whether this lipogenic function is generalizable beyond colorectal cancer is unknown
   • Independent replication in a second CRC model not reported

• A complete structural model of STX11 in complex with Munc18-2 and other SNARE partners is lacking, and the mechanistic relationship between its immune degranulation function and its non-immune roles in lipid metabolism and autophagy remains unresolved.
• No high-resolution structure of STX11 or its complexes
• Whether STX11's SNARE fusogenic activity is required for its metabolic and autophagic roles is untested
• The full set of v-SNARE partners for STX11-mediated lytic granule fusion is undefined