INSULIN ACTIVATES CASPASE-3 BY A PHOSPHATIDYLINOSITOL 3'-KINASE-DEPENDENT PATHWAY

Activation of the caspase proteases by c-Jun N-terminal kinase 1 (JNK1 ) has been proposed as a mechanism of apoptotic cell death. Here we re port that insulin activates caspase-3 by a pathway requiring phosphati dylinositol 3'-kinase (PI3-kinase). JNK1 assays demonstrated that insu lin treatment of myeloma cells induced 3-fold activation of JNK1. Inhi bition of PI3-kinase with wortmannin and LY294002 blocked insulin-depe ndent activation of JNK1. Caspase assays demonstrated that insulin inc reased caspase-3 activity 3-fold and that inhibition of PI3-kinase bla cked this effect. Cell death was doubled by insulin and was due to a 3 -fold increase in apoptosis of cells in the G1/G0 phase of the cell cy cle. Inhibition of PI3-kinase completely blocked this effect. Finally, inhibition of caspase-3 with oxycarbonyl-Asp-2,6-dichlorobenzoyloxyme thylketone blocked cell death due to insulin. Taken together, these fi ndings indicate that insulin activates caspase-3 by a PI3-kinase-depen dent pathway resulting in increased apoptosis and cell death. (C) 1998 Elsevier Science Inc.