SNAP-25 is phosphorylated by glucose and GLP-1 in RIN 1046-38 cells

We investigated the possibility that tyrosine phosphorylation might play a role in insulin secretion in the insulinoma cell line, RIN 1046-38 cells. At least 4 proteins of 18, 25, 35, and 46 kDa size were found to be tyrosine phosphorylated in the presence of glucose and an insulin secretagogue, glucagon-like peptide-1 (GLP-1). The addition of glucose and GLP-1 to cells that were exposed to the tyrosine kinase inhibitor genistein resulted in a decrease in the extent of phosphorylation of the 18, 25, and 35 kDa proteins and a concomitant reduction in insulin secretion, whereas treatment with vanadate, a tyrosine phosphatase inhibitor, led to enhanced responses. Immunoprecipitation of cellular proteins with an anti-phosphotyrosine antibody followed by immunoblotting with a specific monoclonal antibody to SNAP-25 (synaptosome-associated protein of 25 kDa) revealed that the 25 kDa protein is SNAP-25. These results suggest that tyrosine phosphorylation of SNAP-25 may be involved in the regulation of insulin secretion in RIN 1046-38 cells.