Syntaxin-3 Regulates Biphasic Glucose Stimulated Insulin Secretion in the Pancreatic Beta Cell

Our study aims to investigate the role of Syntaxin-3 in glucose stimulated insulin secretion (GSIS) and how it regulates the recruitment to plasma membrane and/or exocytotic fusion of insulin granules. We examined endogenous Syn-3 function by down-regulating its expression using siRNA/lenti-shRNA, which impaired GSIS. Although Syn-3 depleted cells showed no change in the number and fusion of docked granules, there was a reduction in newcomer granules and their subsequent exocytotic fusion. We then examined the effects of overexpressing Syn-3-WT, which enhanced biphasic GSIS. Since open conformation (OF) Syn-1A was reported to enhance exocytosis by promoting SNARE complex formation, we constructed OF Syn-3. Exogenous OF Syn-3 had no effect on secretion as it is unable to be trafficked to insulin granules. Taken together, we conclude that Syn-3 facilitates mobilization of newcomer insulin granules to the plasma membrane, to contribute to both first and second phase of GSIS in pancreatic beta cells.