Inhibition of c-Myc Expression Sensitizes Hepatocytes to Tumor Necrosis Factor-induced Apoptosis and Necrosis

Hailing Liu, Chau R. Lo, Brett E. Jones, Zehra Pradhan, Anu Srinivasan, Karen L. Valentino, Richard J. Stockert, Mark J. Czaja
2000 Journal of Biological Chemistry  
The typical proliferative response of hepatocytes to tumor necrosis factor (TNF) can be converted to a cytotoxic one by transcriptional arrest. Although NF-B 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
more » ... sion vectors were isolated with in- creased (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. TNFinduced, 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-B transcriptional activity, but S-Myc cells maintained resistance to TNF despite NF-B inactivation, suggesting that c-Myc and NF-B independently mediate TNF resist- ance. 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.
doi:10.1074/jbc.m001565200 pmid:11016920 fatcat:6sfssmbgrzfindzre27pievvuu