BET1

BET1 is a SNARE protein essential for vesicular transport from the endoplasmic reticulum to the Golgi complex. It forms a SNARE complex with GOSR2/GS28, SEC22b, and Syntaxin-5 to mediate fusion of ER-derived vesicles with the ERGIC and cis-Golgi, and it physically interacts with the cargo receptor ERGIC-53 at the ERGIC compartment; loss-of-function variants impair ER-to-Golgi transport and mislocalize ERGIC-53 (PMID:2192256, PMID:11323436, PMID:34779586). In invasive cancer cells, MT1-MMP redirects BET1 from its canonical ER-Golgi role to endosomal compartments, where BET1 assembles a non-canonical SNARE complex with syntaxin 4 to promote MT1-MMP trafficking to invadopodia (PMID:31519727).

1. 1990 High

   Establishing BET1 as a component of ER-to-Golgi transport resolved its pathway placement: genetic epistasis in yeast showed BET1 interacts functionally with BOS1 and SEC22, and double-mutant lethality confirmed a non-redundant role in vesicular traffic from the ER.

   Evidence Genetic complementation, multicopy suppression, and double-mutant lethality analysis in S. cerevisiae

   PMID:2192256

   Open questions at the time

   • Biochemical mechanism of BET1 action (e.g., SNARE complex composition) not yet defined
   • Mammalian homolog function not addressed
2. 2001 High

   Identifying the mammalian BET1-containing SNARE complex (with Ykt6, syntaxin 5, and GS28) and showing that disrupting it blocks a late stage of ER-to-Golgi transport established the biochemical basis for BET1's fusogenic role.

   Evidence Reciprocal co-immunoprecipitation and in vitro ER-Golgi transport assay with inhibitory antibodies in mammalian cells

   PMID:11323436

   Open questions at the time

   • Identity of the target membrane (ERGIC vs. cis-Golgi) not distinguished
   • No structural information on the assembled SNARE complex
3. 2019 Medium

   Discovering that MT1-MMP redirects BET1 to endosomal SNARE complexes containing syntaxin 4 revealed a non-canonical trafficking role for BET1 in invasive cells, linking SNARE reprogramming to invadopodia formation.

   Evidence Co-immunoprecipitation, fluorescence co-localization, and knockdown with trafficking phenotype readout in invasive cancer cell lines

   PMID:31519727

   Open questions at the time

   • Not independently replicated in a second study or laboratory
   • Structural basis for MT1-MMP-dependent BET1 recruitment unknown
   • Generality across cancer types not tested
4. 2021 High

   Demonstrating that BET1 loss-of-function variants impair ER-to-Golgi transport and mislocalize ERGIC-53, combined with endogenous co-immunoprecipitation of BET1 with ERGIC-53, pinpointed BET1's fusogenic activity to the ERGIC compartment and linked it to human disease.

   Evidence Endogenous co-immunoprecipitation, immunofluorescence co-localization, and functional analysis of patient-derived fibroblasts with BET1 loss-of-function variants

   PMID:34779586

   Open questions at the time

   • Structural model of BET1–ERGIC-53 interaction not experimentally validated
   • Relative contributions of BET1 vs. BET1L at the ERGIC remain unresolved

• How BET1 is selectively incorporated into canonical versus non-canonical SNARE complexes (e.g., syntaxin-5 vs. syntaxin-4 containing), and what regulatory signals control this partitioning, remain unresolved.
• No structural data for any BET1-containing SNARE complex
• Regulatory post-translational modifications on BET1 not characterized
• In vivo phenotype of complete BET1 loss in mammalian models not fully described