Abstract
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 language | English (US) |
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Pages (from-to) | 41521-41527 |
Number of pages | 7 |
Journal | Journal of Biological Chemistry |
Volume | 275 |
Issue number | 52 |
DOIs | |
State | Published - Dec 29 2000 |
ASJC Scopus subject areas
- Biochemistry
- Molecular Biology
- Cell Biology