Munc-18 associates with syntaxin and serves as a negative regulator of exocytosis in the pancreatic beta -cell |
| |
Authors: | Zhang W Efanov A Yang S N Fried G Kolare S Brown H Zaitsev S Berggren P O Meister B |
| |
Institution: | Department of Neuroscience, The Rolf Luft's Center for Diabetes Research, Karolinska Institutet, SE-171 77 Stockholm, Sweden. |
| |
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 beta-cells was investigated. Subcellular fractionation of insulin-secreting HIT-T15 cells revealed a 67-kDa 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 Ca(2+) channel activity. The findings taken together show that the Munc-18 protein is present in insulin-secreting beta-cells and implicate Munc-18 as a negative regulator of the insulin secretory machinery via a mechanism that does not involve syntaxin-associated Ca(2+) channels. |
| |
Keywords: | |
本文献已被 PubMed 等数据库收录! |
|