NF-κB stimulates inducible nitric oxide synthase to protect mouse hepatocytes from TNF-α- and Fas-mediated apoptosis

Background & Aims: Hepatocyte apoptosis is induced by tumor necrosis factor or (TNF-alpha) and Fas ligand. Although nuclear factor-kappaB (NF-KB) activation protects hepatocytes from TNF-alpha -mediated apoptosis, the NF-kappaB responsive genes that protect hepatocytes are unknown, Our aim was to study the role of NF-kappaB activation and inducible nitric oxide synthases (iNOSs) in TNF-alpha- and Fas-mediated apoptosis in hepatocytes. Methods: Primary cultures of hepatocytes from wild-type and iNOS knockout mice were treated with TNF-alpha, the Fas agonistic antibody Jo2, a nitric oxide (NO) donor (S-nitroso-N-acetylpenicillamine), an NO inhibitor (N-G-methyl-L-arginine acetate), and/or adenovirus-expressing NF-kappaB inhibitors, Results: The I kappaB superrepressor and a dominant-negative form of I kappaB kinase beta (IKKP) inhibited NF-kappaB binding activity by TNF-alpha or Jo2 and sensitized hepatocytes to TNF-alpha- and Jo2-mediated apoptosis, TNF-alpha and Jo2 induced iNOS messenger RNA and protein levels through the induction of NF-kappaB, S-nitroso-N-acetylpenicillamine inhibited Bid cleavage, the mitocfiondrial permeability transition, cytochrome c release, and caspase-8 and -3 activity, and reduced TNF-alpha- and Fas-mediated death in hepatocytes expressing I kappaB superrepressor, N-G-methyl-L-arginine acetate partially sensitized hepatocytes to TNF-alpha- and Fas-mediated cell killing, TNF-alpha alone or Jo2 alone induced moderate cell death in hepatocytes from iNOS(-/-) mice, Conclusions: NO protects hepatocytes from TNF-alpha- and Fas-mediated apoptosis, Endogenous iNOS, which is activated by NF-kappaB via IKK beta, provides partial protection from apoptosis.