Munc-18 associates with syntaxin and serves as a negative regulator of exocytosis in the pancreatic β-cell

Wei Zhang, Alexander Efanov, Shao Nian Yang, Gabriel Fried, Susanne Kölare, Hilary Brown, Sergei Zaitsev, Per Olof Berggren, Björn Meister

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75 Scopus citations


The Munc-18 protein (mammalian homologue of the unc-18 gene; also called nSec1 or rbSec1) has been identified as an essential component of the synaptic vesicle fusion protein complex. The cellular and subcellular localization and functional role of Munc-18 protein in pancreatic β-cells was investigated. Subcellular fractionation of insulin-secreting HIT-T15 cells revealed a 67kDa protein in both cytosol and membrane fractions. Immunohistochemistry showed punctate Munc-18 immunoreactivity in the cytoplasm of rat pancreatic islet cells. Direct double-labeling immunofluorescence histochemistry combined with confocal laser microscopy revealed the presence of Munc-18 immunoreactivity in insulin-, glucagon-, pancreatic polypeptide-, and somatostatin-containing cells. Syntaxin 1 immunoreactivity was detected in extracts of HIT-T15 cells, which were immunoprecipitated using Munc-18 antiserum, suggesting an intimate association of Munc-18 with syntaxin 1. Administration of Munc-18 peptide or Munc-18 antiserum to streptolysin O-permeabilized HIT-T15 cells resulted in significantly increased insulin release, but did not have any significant effect on voltage-gated Ca2+ channel activity. The findings taken together show that the Munc-18 protein is present in insulin-secreting β-cells and implicate Munc-18 as a negative regulator of the insulin secretory machinery via a mechanism that does not involve syntaxin-associated Ca2+ channels.

Original languageEnglish (US)
Pages (from-to)41521-41527
Number of pages7
JournalJournal of Biological Chemistry
Issue number52
StatePublished - Dec 29 2000

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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