NONFUNCTIONAL ROLE OF SYNTAXIN-2 IN INSULIN EXOCYTOSIS BY PANCREATIC BETA-CELLS

This study was designed in order to examine the expression and functio nal role of syntaxin 2/epimorphin in pancreatic beta cells. Northern b lot analysis revealed that syntaxin 2 mRNA was able to be detected in mouse beta TC3 cells, but not in isolated mouse islets. In agreement w ith this result, immunoblot analysis detected an appreciable amount of syntaxin 2 protein in beta TC3 cells, but not in mouse islets. Immuno histochemistry of the mouse pancreas demonstrated that syntaxin 2 was little evident in islet cells of Langerhans, and somewhat predominant in exocrine tissues. In order to examine whether syntaxin 2 is anchore d to cell surfaces in beta TC3 cells, living cells were incubated with a monoclonal antibody against syntaxin 2 (MC-I). The antibody bound t o their surfaces, indicating that syntaxin 2 was localized on cell sur faces. The addition of MC-I to the culture medium of beta TC3 cells di d not affect insulin release under the presence or absence of 11 mM gl ucose, indicating that syntaxin 2 is not associated with insulin exocy tosis. Thus, the expression of syntaxin 2 in islets of Langerhans is v ery low and the function of this protein is probably unrelated to the insulin exocytosis pathway. (C) 1997 John Wiley & Sons, Ltd.