Calcium has a permissive role in interleukin-1β-induced c-Jun N-terminal kinase activation in insulin-secreting cells

The c- jun N- terminal kinase (JNK) signaling pathway mediates IL-1 beta-induced apoptosis in insulin-secreting cells, a mechanism relevant to the destruction of pancreatic beta-cells in type 1 and 2 diabetes. However, the mechanisms that contribute to IL-1 beta activation of JNK in beta-cells are largely unknown. In this study, we investigated whether Ca2+ plays a role for IL-1 beta-induced JNK activation. In insulin-secreting rat INS-1 cells cultured in the presence of 11 mM glucose, combined pharmacological blockade of L- and T-type Ca2+ channels suppressed IL-1 beta-induced in vitro phosphorylation of the JNK substrate c- jun and reduced IL-1 beta-stimulated activation of JNK1/2 as assessed by immunoblotting. Inhibition of IL-1 beta-induced in vitro kinase activity toward c- jun after collective L- and T-type Ca2+ channel blockade was confirmed in primary rat and ob/ob mouse islets and in mouse beta TC3 cells. Ca2+ influx, specifically via L-type but not T-type channels, contributed to IL-1 beta activation of JNK. Activation of p38 and ERK in response to IL-1 beta was also dependent on L-type Ca2+ influx. Membrane depolarization by KCl, exposure to high glucose, treatment with Ca2+ ionophore A23187, or exposure to thapsigargin, an inhibitor of sarco( endo) plasmic reticulum Ca2+ ATPase, all caused an amplification of IL-1 beta-induced JNK activation in INS-1 cells. Finally, a chelator of intracellular free Ca2+ [ bis-( o- aminophenoxy)- N, N, N', N'-tetraaceticacid-acetoxymethyl], an inhibitor of calmodulin (W7), and inhibitors of Ca2+/calmodulin-dependent kinase (KN62 and KN93) partially reduced IL-1 beta-stimulated c-jun phosphorylation in INS-1 or beta TC3 cells. Our data suggest that Ca2+ plays a permissive role in IL-1 beta activation of the JNK signaling pathway in insulin-secreting cells.