Akt protects mouse hepatocytes from TNF-a- and Fas-mediated apoptosis through NK-kB activation

Hatano, Etsuro, and David A. Brenner Akt protects mouse hepatocytes from TNF-aand Fas-mediated apoptosis through NK-kB activation. Am J Physiol Gastrointest Liver Physiol 282: G1357–G1368, 2002.—To determine the role of phosphatidylinositol 3-kinase (PI3K)/Akt and nuclear factor-kB (NF-kB) in protecting hepatocytes from tumor necrosis factor-a (TNF-a)and Fas-mediated apoptosis, we pretreated primary cultures of mouse hepatocytes with pharmacological and adenovirus-mediated inhibitors of the PI3K/Akt and NF-kB pathways followed by treatment with TNF-a or Jo2, an anti-Fas antibody. Jo2 and, to a lesser extent, TNF-a phosphorylate Akt. The PI3K inhibitor LY294002 blocks TNF-aand Fas-mediated Akt phosphorylation. LY-294002 pretreatment reduces NF-kB binding activity and transcriptional activity and NF-kB-responsive gene expression by TNF-a or Jo2. LY-294002 promotes apoptosis after TNF-a or Jo2. The expression of dominant-negative Akt blocks NF-kB activation and sensitizes hepatocytes to TNF-aand Fas-mediated apoptosis. The expression of constitutively active Akt rescues LY-294002-pretreated cells from TNF-aand Fas-mediated apoptosis. Active Akt induces NF-kB transcriptional activity but not NF-kB binding activity or IkB degradation. Furthermore, LY-294002 pretreatment blocks TNF-aand Jo2-induced Bcl-xL levels in hepatocytes, with no effect on the phosphorylation levels of Bad. Bcl-xL overexpression protects hepatocytes from Fasbut not TNF-a-induced apoptosis after sensitization by actinomycin D or the IkB superrepressor. Together, the PI3K/Akt pathway has a protective role in Fas-mediated apoptosis, which requires NF-kB activation, partially through the subsequent induction of Bcl-xL.