Inhibition of c-Myc expression sensitizes hepatocytes to tumor necrosis factor-induced apoptosis and necrosis.
The typical proliferative response of hepatocytes to tumor necrosis factor (TNF) can be converted to a cytotoxic one by transcriptional arrest. Although NF-kappaB activation is critical for hepatocyte resistance to TNF toxicity, the contribution of other TNF-inducible transcription factors remains unknown. To determine the function of c-Myc in hepatocyte sensitivity to TNF, stable transfectants of the rat hepatocyte cell line RALA255-10G containing sense and antisense c-myc expression vectors were isolated with increased (S-Myc cells) and decreased (AN-Myc cells) c-Myc transcriptional activity. While S-Myc cells proliferated in response to TNF treatment, AN-Myc cells underwent 32% cell death within 6 h. Fluorescent microscopic studies indicated that TNF induced apoptosis and necrosis in AN-Myc cells. Cell death was associated with DNA hypoploidy and poly(ADP-ribose) polymerase cleavage but occurred in the absence of detectable caspase-3, -7, or -8 activation. TNF-induced, AN-Myc cell death was dependent on Fas-associated protein with death domain and partially blocked by caspase inhibitors. AN-Myc cells had decreased levels of NF-kappaB transcriptional activity, but S-Myc cells maintained resistance to TNF despite NF-kappaB inactivation, suggesting that c-Myc and NF-kappaB independently mediate TNF resistance. Thus, in the absence of sufficient c-Myc expression, hepatocytes are sensitized to TNF-induced apoptosis and necrosis. These findings demonstrate that hepatocyte resistance to TNF is regulated by multiple transcriptional activators.
Liu
H
H
Department of Medicine and Marion Bessin Liver Research Center, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
Lo
C R
CR
Jones
B E
BE
Pradhan
Z
Z
Srinivasan
A
A
Valentino
K L
KL
Stockert
R J
RJ
Czaja
M J
MJ
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D004789:Enzyme Activation; D022781:Hepatocytes / Q000166:cytology / Q000187:drug effects* / Q000473:pathology; D016328:NF-kappa B / Q000378:metabolism; D009336:Necrosis; D016376:Oligonucleotides, Antisense / Q000235:genetics; D016271:Proto-Oncogene Proteins c-myc / Q000037:antagonists & inhibitors* / Q000235:genetics; D051381:Rats
D016328:NF-kappa B; D016376:Oligonucleotides, Antisense; D016271:Proto-Oncogene Proteins c-myc; D020169:Caspases