Altered bcl-2 and bax expression and intracellular Ca2+ signaling in apoptosis of pancreatic cells and the impairment of glucose-induced insulin secretion.

Apoptosis is the process of cellular self-destruction, and genes such as bcl-2 and bax are known to inhibit and promote apoptosis, respectively. In this study, we show that apoptosis can be induced in pancreatic beta-cell lines, and we investigate the apoptotic pathways through the bcl-2 and bax genes and intracellular Ca2+. Serum deprivation induces apoptosis in the MIN6 and RINm5F pancreatic beta-cell lines, and alters the bcl-2 messenger RNA (mRNA) and protein. KCl, BayK, A23187, and ionomycin elicit an elevation of cytosolic/nuclear Ca2+, which, however, is insufficient to evoke apoptosis or to alter bcl-2 or bax mRNA expression in MIN6 cells. The extracellular Ca2+ chelators, EGTA and 1,2-Bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, tetrapotassium salt, hydrate, evoke apoptosis and also alter the ratio of bcl-2 to bax mRNA and protein concomitantly with the depletion of cytosolic/nuclear Ca2+. This indicates that there are at least two apoptotic pathways in pancreatic beta-cells: through serum deprivation and through a decrease in cytosolic/nuclear Ca2+. MIN6 cells exhibit reduced insulin secretion induced by glucose regardless of the molecular pathway of apoptosis. Apoptosis in pancreatic beta-cells, therefore, may be closely related to the impairment of insulin secretion in certain pathological conditions such as diabetes mellitus.