title: Hepatocytes sensitized to tumor necrosis factor-alpha cytotoxicity undergo apoptosis through caspase-dependent and caspase-independent pathways.
abstract: Hepatocytes can be sensitized to tumor necrosis factor (TNF)-alpha toxicity by repression of NF-kappaB activation or inhibition of RNA synthesis. To determine whether both forms of sensitization lead to TNF-alpha cytotoxicity by similar mechanisms, TNF-alpha-induced cell death in RALA255-10G hepatocytes was examined following infection with an adenovirus, Ad5IkappaB, that blocks NF-kappaB activation or following cotreatment with actinomycin D (ActD). TNF-alpha treatment of Ad5IkappaB-infected cells resulted in 44% cell death within 6 h. ActD/TNF-alpha 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 Ad5IkappaB/TNF-alpha-induced cell death but did not inhibit ActD/TNF-alpha-induced apoptosis. A Fas-associated protein with death domain (FADD) dominant negative decreased Ad5IkappaB/TNF-alpha- and ActD/TNF-alpha-induced cell death by 81 and 47%, respectively. However, downstream events differed, since Ad5IkappaB/TNF-alpha but not ActD/TNF-alpha treatment caused mitochondrial cytochrome c release. These results suggest that NF-kappaB inactivation and inhibition of RNA synthesis sensitize RALA255-10G hepatocytes to TNF-alpha toxicity through distinct cell death pathways that diverge below the level of FADD. ActD-induced hepatocyte sensitization to TNF-alpha cytotoxicity occurs through a FADD-dependent, caspase-independent pathway of apoptosis.
authors.affiliation: Department of Medicine, Marion Bessin Liver Research Center, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
authors.forename: B E
authors.initials: BE
authors.lastname: Jones
authors.forename: C R
authors.initials: CR
authors.lastname: Lo
authors.forename: H
authors.initials: H
authors.lastname: Liu
authors.forename: A
authors.initials: A
authors.lastname: Srinivasan
authors.forename: K
authors.initials: K
authors.lastname: Streetz
authors.forename: K L
authors.initials: KL
authors.lastname: Valentino
authors.forename: M J
authors.initials: MJ
authors.lastname: Czaja
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D017209:Apoptosis; D002352:Carrier Proteins / Q000378:metabolism; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D002460:Cell Line; D003574:Cytochrome c Group / Q000378:metabolism; D003609:Dactinomycin / Q000494:pharmacology; D004789:Enzyme Activation; D053200:Fas-Associated Death Domain Protein; D020672:I-kappa B Proteins; D008099:Liver / Q000166:cytology / Q000502:physiology*; D016328:NF-kappa B / Q000378:metabolism; D011003:Ploidies; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D051381:Rats; D015398:Signal Transduction; D014409:Tumor Necrosis Factor-alpha / Q000633:toxicity*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D061945:Caspase Inhibitors; D003574:Cytochrome c Group; C505535:Fadd protein, rat; D053200:Fas-Associated Death Domain Protein; D020672:I-kappa B Proteins; D016328:NF-kappa B; D014409:Tumor Necrosis Factor-alpha; D003609:Dactinomycin; D011065:Poly(ADP-ribose) Polymerases; D020169:Caspases