Increased susceptibility of the c-Myc overexpressing cell line, SNU-16, to TNF-alpha

Tumor necrosis factor-alpha (TNF-α) is a macrophage-derived multifunctional cytokine that acts as a cytostatic or cytotoxic agent in many tumor cells. However, the molecular mechanisms by which tumor cells become sensitive to the cytotoxic action of TNF-α are not clear. In this study we demonstrated that the cytotoxicity of TNF-α markedly increased in c-Myc overexpressing tumor cells. The stomach cancer cell line, SNU-16, in which c-Myc expression is high due to gene amplification, showed programmed cell death detected by DNA fragmentation and morphological changes. An antisense c-myc S-oligonucleotide specifically inhibited the TNF-α-induced apoptosis of SNU-16 cells, provided that the oligonucleotide was added 4 h prior to TNF-α treatment. Western immunoblot analysis of p53 and Bax showed that in this cell line, TNF-α increased the level of these proteins in a time-dependent manner and that this effect lasted for 12 h. Taken together these data indicate that the deregulation of c-Myc plays an important role in sensitizing tumor cells to TNF-α. Furthermore, TNF-α-induced apoptosis in the SNU-16 cell line showed increased expression of p53 and Bax protein levels following TNF-α treatment. Therefore, we suggest that TNF-α-induced apoptosis, which is cytotoxic to tumor cells, is coupled with a p53 and Bax apoptotic pathway.