Interleukin-1β stimulation of c-Jun NH2-terminal kinase activity in insulin-secreting cells -: Evidence for cytoplasmic restriction

Cytokines have been shown to have dramatic effects on pancreatic islets and insulin-secreting beta -cell lines. It is well established that cytokines such as interleukin-1 beta (IL-1 beta), tumor necrosis factor-alpha (TNF-alpha), and gamma -interferon (IFN-gamma) inhibit beta -cell function and are cytotoxic to human and rodent pancreatic islets in vitro. Despite the pleiotropic effects of cytokines on beta -cells, the specific signal transduction pathways and molecular events involved in beta -cell dysfunction remain largely unresolved. In this report, we have examined IL-1 beta stimulation of c-Jun NH2-terminal kinase (JNK) activity in insulin-secreting clonal cell lines. We demonstrate that IL-1 beta transiently activates 46- and 54-kDa isoforms of JNK in cultured RINm5F beta -cells. Furthermore, IL-1 beta stimulation of JNK activity is specific, because TNF-alpha and IFN-gamma were without effect. Stable overexpression of JNK1 in RINm5F cells increased levels of activated JNK without affecting kinase activity. JNK-interacting protein (JIP) associates with endogenous as well as overexpressed JNK, suggesting that JIP may serve to regulate JNK activity. Finally, we demonstrate that activated JNK is fully retained in cytoplasmic and membrane compartments without any nuclear translocation. Together, these data indicate that IL-1 beta -stimulated JNK activity may be distinctly targeted to cytoplasmic and/or membrane compartments in clonal insulin-producing cells, and that JIP may serve to localize JNK activity to specific substrates.