Protein Kinase C δ Activation and Translocation to the Nucleus Are Required for Fatty Acid-Induced Apoptosis of Insulin-Secreting Cells

Abstract

Insulin resistance as well as pancreatic β-cell failure can be induced by elevated free fatty acid (FFA) levels. We studied the mechanisms of FFA-induced apoptosis in rat and human β-cells. Chronic treatment with high physiological levels of saturated fatty acids (palmitate and stearate), but not with monounsaturated (palmitoleate and oleate) or polyunsaturated fatty acids (linoleate), triggers apoptosis in ∼20% of cultured RIN1046-38 cells. Apoptosis restricted to saturated FFAs was also observed in primary cultured human β-cells, suggesting that this mechanism is potentially relevant in vivo in humans. To further analyze FFA-induced signaling pathways leading to apoptosis, we used RIN1046-38 cells. Apoptosis was accompanied by a rapid (within 15 min) nuclear translocation of protein kinase C (PKC)-δ and subsequent lamin B1 disassembly. This translocation was impaired by the phospholipase C inhibitor U-73122, which also substantially reduced apoptosis. Furthermore, lamin B1 disassembly and apoptosis were decreased by cell transfection with a dominant-negative mutant form of PKC-δ. These data suggest that nuclear translocation and kinase activity of PKC-δ are both necessary for saturated fatty acid-induced apoptosis.