Glucose-induced insulin secretin is defective in type II diabetics mellitus. The biochemical mechanisms by which this nutrient secretagogue induces insulin secretion are incompletely known and their elucidation is fundamental to the future development of treatments or a cure for this disease. It is clear that an increased intracellular Ca2+ concentration is critical to glucose-induced insulin secretion and is implicated in glucose-regulated insulin gene expression. The hypothesis of the current proposal is that the activation of Ca2+/calmodulin-dependent protein kinases mediates glucose-induce insulin gene expression. The involvement of two enzymes in Beta-cell function will be studied. (i) the multifunctional Ca2+/calmodulin-dependent protein kinase II (CaM kinase II); and (ii) myosin light chain kinase (MLCK). CaM kinase II and MLCK may play complementary or alternative roles in insulin secretion and CaM kinase II may play an additional role in the regulation of gene expression.
The specific aims are: (1) to evaluate whether glucose and other secretagogues activate CaM kinase II in a manner that correlates quantitatively and temporally with insulin secretion; (2) to determine the effect of pharmacological inhibition or over expression of CaM kinase II activity on insulin secretion from intact and permeabilized islets and BetaTC3 cells; (3) to determine the effect of similar modulations of CaM kinase II activity on preproinsulin mRNA accumulation and synthesis; (4) to assess CaM kinase II-mediated phosphorylation of microtubule- association protein-2 (MAP-2) and cAMP-response element binding protein (CREB) or CCAAT-enhancer binding protein (C/EBPBeta), in insulin secretion and gene expression respectively; 5) to examine the activation of MLCK by glucose and to determine the effect of selective MLCK inhibitors on insulin secretion. This study is fundamental to the understanding of the mechanisms by which glucose and Ca2+ regulated B cell function.
