INCREASED SUSCEPTIBILITY OF THE C-MYC OVEREXPRESSING CELL-LINE, SNU-16, TO TNF-ALPHA

Tumor necrosis factor-alpha (TNF-alpha) is a macrophage-derived multif unctional cytokine that acts as a cytostatic or cytotoxic agent in man y tumor cells. However, the molecular mechanisms by which tumor cells become sensitive to the cytotoxic action of TNF-alpha are not clear. I n this study we demonstrated that the cytotoxicity of TNF-alpha marked ly increased in c-Myc overexpressing tumor cells. The stomach cancer c ell line, SNU-16, in which c-Myc expression is high due to gene amplif ication, showed programmed cell death detected by DNA fragmentation an d morphological changes. An antisense c-myc S-oligonucleotide specific ally inhibited the TNF-alpha-induced apoptosis of SNU-16 cells, provid ed that the oligonucleotide was added 4 h prior to TNF-alpha treatment . Western immunoblot analysis of p53 and Bar showed that in this cell line, TNF-alpha increased the level of these proteins in a time-depend ent manner and that this effect lasted for 12 h. Taken together these data indicate that the deregulation of c-Myc plays an important role i n sensitizing tumor cells to TNF-alpha. Furthermore, TNF-alpha-induced apoptosis in the SNU-16 cell line showed increased expression of p53 and Bar protein levels following TNF-cu treatment. Therefore, we sugge st that TNF-alpha-induced apoptosis, which is cytotoxic to tumor cells , is coupled with a p53 and Bar apoptotic pathway. (C) 1998 Elsevier S cience Ireland Ltd.