NF-kappaB inactivation converts a hepatocyte cell line TNF-alpha response from proliferation to apoptosis.
Toxins convert the hepatocellular response to tumor necrosis factor-alpha (TNF-alpha) stimulation from proliferation to cell death, suggesting that hepatotoxins somehow sensitize hepatocytes to TNF-alpha toxicity. Because nuclear factor-kappaB (NF-kappaB) activation confers resistance to TNF-alpha cytotoxicity in nonhepatic cells, the possibility that toxin-induced sensitization to TNF-alpha killing results from inhibition of NF-kappaB-dependent gene expression was examined in the RALA rat hepatocyte cell line sensitized to TNF-alpha cytotoxicity by actinomycin D (ActD). ActD did not affect TNF-alpha-induced hepatocyte NF-kappaB activation but decreased NF-kappaB-dependent gene expression. Expression of an IkappaB superrepressor rendered RALA hepatocytes sensitive to TNF-alpha-induced apoptosis in the absence of ActD. Apoptosis was blocked by caspase inhibitors, and TNF-alpha treatment led to activation of caspase-2, caspase-3, and caspase-8 only when NF-kappaB activation was blocked. Although apoptosis was blocked by the NF-kappaB-dependent factor nitric oxide (NO), inhibition of endogenous NO production did not sensitize cells to TNF-alpha-induced cytotoxicity. Thus NF-kappaB activation is the critical intracellular signal that determines whether TNF-alpha stimulates hepatocyte proliferation or apoptosis. Although exogenous NO blocks RALA hepatocyte TNF-alpha cytotoxicity, endogenous production of NO is not the mechanism by which NF-kappaB activation inhibits this death pathway.
Xu
Y
Y
Department of Medicine, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
Bialik
S
S
Jones
B E
BE
Iimuro
Y
Y
Kitsis
R N
RN
Srinivasan
A
A
Brenner
D A
DA
Czaja
M J
MJ
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D061945:Caspase Inhibitors; D002455:Cell Division / Q000187:drug effects / Q000502:physiology*; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004247:DNA / Q000096:biosynthesis; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects* / Q000502:physiology; D020672:I-kappa B Proteins; D016328:NF-kappa B / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009569:Nitric Oxide / Q000502:physiology; D020030:Nitric Oxide Donors / Q000494:pharmacology; D010396:Penicillamine / Q000031:analogs & derivatives / Q000494:pharmacology; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D026423:S-Nitroso-N-Acetylpenicillamine; D013936:Thymidine / Q000378:metabolism; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
D061945:Caspase Inhibitors; D015853:Cysteine Proteinase Inhibitors; D004268:DNA-Binding Proteins; D020672:I-kappa B Proteins; D016328:NF-kappa B; D020030:Nitric Oxide Donors; D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha; D009569:Nitric Oxide; D026423:S-Nitroso-N-Acetylpenicillamine; D004247:DNA; D010396:Penicillamine; D013936:Thymidine