Phosphatidylinositol 3-kinase as a mediator of TNF-induced NF-B kappa activation

The activation of transcription factor NF-kappa B by TNF involves the stimu lation of a novel signaling cascade. In this paper we show that phosphatidy linositol 3-kinase (PI 3-kinase) may play a pivotal role in TNF-mediated ac tivation of NF-kappa B-dependent genes, Consistent with its involvement in TNF signaling, PI 3-kinase activities in HepG2 and U937 cells can be stimul ated by TNF in a rapid but transient manner through a mechanism that may in volve its association with the insulin receptor substrate-1. A dominant-neg ative mutant of the p85 regulatory subunit of PI 3-kinase, which is a poten t inhibitor of PI 3-kinase signaling, effectively blocked the TNF-induced e xpression of an NF-kappa B-dependent reporter gene. Although PI 3-kinase ma y be required for NF-kappa B activation, overexpression of its p110 catalyt ic subunit alone was unable to induce an NF-kappa B/chloramphenicol acetylt ransferase (CAT) reporter gene. However, when TNF was added to p110-overexp ressing cells, there was a synergistic activation of the NF-kappa B/CAT rep orter, suggesting that other TNF-inducible signals may cooperate with PI 3- kinase to activate NF-kappa B, Consistent with its role in NF-kappa B activ ation, inhibition of PI 3-kinase activity by wortmannin or LY294002 greatly potentiated TNF-induced apoptosis, This TNF/wortmannin-induced apoptosis w as markedly prevented in cells overexpressing Rel A, Taken together, our re sults indicate that a PI 3-kinase-regulated step in TNF-signaling is critic al for the expression of NF-kappa B-dependent genes.