Involvement of regulatory and catalytic subunits of phosphoinositide 3-kinase in NF-kappa B activation

Hypoxia, reoxygenation, and the tyrosine phosphatase inhibitor pervanadate activate the transcription factor NF-kappa B, involving phosphorylation of its inhibitor I kappa B-alpha on tyrosine 42. This modification does not le ad to degradation of I kappa B by the proteasome/ubiquitin pathway, as is s een on stimulation of cells with proinflammatory cytokines. It is currently unknown how tyrosine-phosphorylated I kappa B is removed from NF-kappa B. Here we show that p85 alpha, the regulatory subunit of PI3-kinase, specific ally associates through its Src homology 2 domains with tyrosine-phosphoryl ated I kappa B-alpha in vitro and in vivo after stimulation of T cells with pervanadate. This association could provide a mechanism by which newly tyr osine-phosphorylated I kappa B is sequestered from NF-kappa B. Another mech anism by which PI3-kinase contributed to NF-kappa B activation in response to pervanadate appeared to involve its catalytic p110 subunit. This was evi dent from the inhibition of pervanadate-induced NF-kappa B activation and r eporter gene induction by treatment of cells with nanomolar amounts of the PI3-kinase inhibitor wortmannin. The compound had virtually no effect on tu mor necrosis factor- and interleukin-1-induced NF-kappa B activities. Wortm annin did not inhibit tyrosine phosphorylation of I kappa B-alpha or alter the stability of the PI3-kinase complex but inhibited Akt kinase activation in response to pervanadate. Our data suggest that both the regulatory and the catalytic subunit of PI3-kinase play a role in NF-kappa B activation by the tyrosine phosphorylation-dependent pathway.