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Hepatocytes Sensitized to Tumor Necrosis Factor-α Cytotoxicity Undergo Apoptosis through Caspase-dependent and Caspase-independent Pathways

2000; Elsevier BV; Volume: 275; Issue: 1 Linguagem: Inglês

10.1074/jbc.275.1.705

1083-351X

Brett Jones, Chau R. Lo, Hailing Liu, Anu Srinivasan, Konrad L. Streetz, Karen L. Valentino, Mark J. Czaja,

Cell death mechanisms and regulation

Hepatocytes can be sensitized to tumor necrosis factor (TNF)-α toxicity by repression of NF-κB activation or inhibition of RNA synthesis. To determine whether both forms of sensitization lead to TNF-α cytotoxicity by similar mechanisms, TNF-α-induced cell death in RALA255-10G hepatocytes was examined following infection with an adenovirus, Ad5IκB, that blocks NF-κB activation or following cotreatment with actinomycin D (ActD). TNF-α treatment of Ad5IκB-infected cells resulted in 44% cell death within 6 h. ActD/TNF-α induced no death within 6 h but did lead to 37% cell death by 24 h. In both instances, cell death occurred by apoptosis and was associated with caspase activation, although caspase activation in ActD-sensitized cells was delayed. CrmA and chemical caspase inhibitors blocked Ad5IκB/TNF-α-induced cell death but did not inhibit ActD/TNF-α-induced apoptosis. A Fas-associated protein with death domain (FADD) dominant negative decreased Ad5IκB/TNF-α- and ActD/TNF-α-induced cell death by 81 and 47%, respectively. However, downstream events differed, since Ad5IκB/TNF-α but not ActD/TNF-α treatment caused mitochondrial cytochrome c release. These results suggest that NF-κB inactivation and inhibition of RNA synthesis sensitize RALA255-10G hepatocytes to TNF-α toxicity through distinct cell death pathways that diverge below the level of FADD. ActD-induced hepatocyte sensitization to TNF-α cytotoxicity occurs through a FADD-dependent, caspase-independent pathway of apoptosis.