TNF-α exerts cytotoxic effects on multidrug resistant breast cancer MCF-7/MX cells via a non-apoptotic death pathway

Tumor necrosis factor-alpha (TNF-alpha) is a cytokine involved in the various physiopathological processes such as autoimmune disorders and inflammation related diseases. Some multidrug resistant (MDR) cancer cell lines including MCF-7/MX are more vulnerable to cytotoxic effects of TNF-alpha than their parental lines. In this study, breast cancer cell line MCF-7 and its MDR derivative MCF-7/MX were exposed to TNF-alpha afterward various downstream signaling mediators of TNF-alpha were analyzed. Although, treatment of MCF-7 cells with TNF-alpha activated NF-kB and caused RIP1 ubiquitination, TNF-alpha exposure led to JNK and RIP1 phosphorylation in MCF-7/ MX cells. In both cell lines TNF-alpha did not activate the caspase cascade. Moreover, AnexinV/PI analysis showed that cytotoxic effects of TNF-alpha on MCF-7/MX is mediated via apoptosis independent mechanisms and inhibition of RIP1 kinase activity using necrostatin-1 revealed that kinase activity of RIP1 plays role in the production of ROS, activation of JNK and cellular death following exposure of MCF-7/MX cells to TNF-alpha. Overall, it seems that RIP1 ubiquitination and NF-kB activation are prosurvival signaling mediators protecting MCF-7 cells against cytotoxic effects of TNF-alpha while TNF-alpha drives MCF-7/MX cells to non-apoptotic cellular death via kinase activity of RIP1, activation of JNK and ROS production.