A role for nuclear factor κB in the antiapoptotic function of insulin

We previously reported that insulin activates nuclear factor kappa B (NF-kappa B) in Chinese hamster ovary (CHO)-R cells overexpressing wild-type insulin receptors (IRs) through a pathway requiring IR tyrosine kinase and Raf-1 kinase activities, We now investigated whether the activation of NF-kappa B by insulin could serve an antiapoptotic function. Insulin (10(-9)-10(-7) M) inhibited apoptosis induced by serum withdrawal in CHO-R cells in a concentration-dependent manner. Insulin antiapoptotic signaling: (i) was dependent on IR number and IR tyrosine kinase activity since it was reduced in parental CHO cells and was abolished in CHO-YB cells overexpressing IRs mutated at Tyr(1162/1163); (ii) was, like insulin activation of NF-KB, dependent on Raf-1 but not on mitogen activated protein kinase activity since both processes were decreased by the dominant-negative Raf-1 mutant Raf-C4 whereas they persisted in mitogen-activated protein kinase-depleted cells; and (iii) required NF-kappa B activation since it was decreased by proteasome inhibitors and the dominant-negative I kappa B-alpha (A32/36) mutant and was mimicked by overexpression of the NF-KB c-Rel subunit, We also show that insulin antiapoptotic signaling but not insulin activation of NF-kappa B involved phosphatidylinositol 3-kinase (PI 3-kinase), as supported by the inhibition of the former but not of the latter process by the PI S-kinase inhibitor LY294002. Inhibition of both NF-kappa B and PI 3-kinase totally abolished insulin antiapoptotic signaling, Thus insulin exerts a specific antiapoptotic function which is dependent on IR tyrosine kinase activity and is mediated by both a Raf-1-dependent pathway that leads to NF-kappa B activation and a PI 3-kinase-dependent pathway.