Syntaxin, but not soluble NSF attachment protein (SNAP), biosynthesis by rat pancreatic islets is regulated by glucose in parallel with proinsulin biosynthesis

Abstract

Recent studies have revealed that soluble N-ethylmaleimide sensitive factor attachment receptor (SNARE)-related proteins, originally identified in neural tissues, are also expressed in pancreatic beta cells. In this study, we investigated the effect of glucose on syntaxin 1 and alpha/beta SNAP biosynthesis in pancreatic beta cells and we demonstrated that syntaxin 1, but not alpha/beta SNAP biosynthesis by rat isolated pancreatic islets was stimulated specifically by glucose nearly in parallel with proinsulin biosynthesis. Stimulation of syntaxin 1 and proinsulin biosynthesis by glucose was dose-dependent (Km = approximately 8 mmol/l) and reached the maximum (about 8-12 fold) at concentrations over 11 mmol/l. In contrast, 22 mmol/l glucose increased alpha/beta SNAP biosynthesis about 2-fold only, similar to the increase in total protein synthesis. Stimulation of syntaxin 1 biosynthesis by glucose was also time-dependent, taking around 3 h to reach the maximum, and was not affected by actinomycin-D, suggesting regulation at the translational level. On the other hand, glucose had a similar stimulating effect on both syntaxin 1 and alpha/beta SNAP biosynthesis by mouse insulinoma betaTC3 cells as it did on proinsulin biosynthesis. The evidence showing coordinated stimulation of syntaxin 1 and proinsulin biosynthesis by glucose in rat islets suggested the critical functional role of syntaxin 1 in the insulin exocytotic mechanism.