Tumor necrosis factor
regulation of canonical NF-kappaB signal transduction
A phosphatidylinositol 3-kinase/Akt pathway, activated by tumor necrosis factor or interleukin-1, inhibits apoptosis but does not activate NFkappaB in human endothelial cells.
Tumor necrosis factor (TNF) and interleukin-1 (IL-1) activate the transcription of both anti-apoptotic and pro-inflammatory gene products in human endothelial cells (EC) via NFkappaB. Here we report that both TNF and IL-1 activate the anti-apoptotic protein kinase Akt in growth factor and serum-deprived EC, assessed by Western blotting for phospho-Akt. Phosphorylation of Akt is blocked by LY294002 or wortmannin, inhibitors of phosphatidylinositol 3-kinase (PI 3-kinase). Consistent with these biochemical observations, TNF and IL-1 reduce apoptosis caused by growth factor and serum deprivation, and this action is also blocked by LY294002. Although Akt has been reported to activate NFkappaB, LY294002 does not prevent TNF- or IL-1-induced degradation of IkappaBalpha, beta, or epsilon, transcription of NFkappaB-dependent E-selectin or ICAM-1 promoter-reporter genes, or surface expression of E-selectin or ICAM-1 in human EC. LY294002 potentiates the activation of mitogen-activated protein kinases and stress-activated protein kinases by TNF and IL-1, suggesting Akt inhibits these responses. We conclude that TNF and IL-1 activate a PI 3-kinase/Akt anti-apoptotic pathway and that the anti-apoptotic effects of Akt are independent of NFkappaB. Moreover, the PI 3-kinase/Akt pathway does not play a major role in the pro-inflammatory responses of EC to TNF or IL-1.