Involvement of regulatory and catalytic subunits of phosphoinositide 3-kinase in NF-κB 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 lead to degradation of I kappa B by the proteasome/ubiquitin pathway, as is seen 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, specifically associates through its Src homology 2 domains with tyrosine-phosphorylated 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 tyrosine-phosphorylated I kappa B is sequestered from NF-kappa B. Another mechanism by which PI3-kinase contributed to NF-kappa B activation in response to pervanadate appeared to involve its catalytic p110 subunit. This was evident from the inhibition of pervanadate-induced NF-kappa B activation and reporter gene induction by treatment of cells with nanomolar amounts of the PI3-kinase inhibitor wortmannin. The compound had virtually no effect on tumor necrosis factor- and interleukin-1-induced NF-kappa B activities. Wortmannin 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.