Insulin Regulation Of Nuclear Factor-kappa B Activity

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Summary of work: The aim of this study was to examine the signaling pathways by which insulin promotes activation of NF{kappa}B through the regulation of I{kappa}Balpha. We show here that although insulin increased {kappa}B dependent reporter gene expression and augment nuclear translocation of the p65/RelA subunit of NF{kappa}B and its DNA binding, it was able to induce a time-dependent accumulation of phosphorylated and ubiquitinated I{kappa}Balpha without its proteolytic degradation. In contrast, cell stimulation with the cytokine TNFalpha allowed activation of NF{kappa}B through phosphorylation, ubiquitination and subsequent degradation of I{kappa}Balpha. Immunofluorescence studies revealed the presence of a large pool of phosphorylated I{kappa}Balpha in the nucleus of unstimulated and insulin-treated cells. I{kappa}B kinase alpha and beta, central players in the phosphorylation of I{kappa}Balpha, were rapidly induced following exposure to TNFalpha, but not insulin. Furthermore, insulin-stimulated I{kappa}Balpha phosphorylation did not depend on activation of the Ras/ERK cascade. Expression of a dominant negative mutant of Akt1 or of class I phosphatidylinositol 3-kinase (PI 3-kinase) inhibited the insulin stimulation of PI 3-kinase/Akt1 signaling without affecting phosphorylation of I{kappa}Balpha. Interestingly, the PI 3-kinase inhibitors wortmannin and LY294002 blocked insulin-stimulated class I PI 3-kinase-dependent events at much lower doses than that required to inhibit phosphorylation of I{kappa}Balpha. These data demonstrate that insulin regulates I{kappa}Balpha function through a distinct low-affinity wortmannin-sensitive pathway.