Combined action of ERK and NF kappa B mediates the protective effect of phorbol ester on Fas-induced apoptosis in Jurkat cells.

The mechanisms whereby phorbol esters antagonize Fas-induced apoptosis in Jurkat T cells are poorly defined. In the present study, we report that protection from Fas-induced apoptosis by 12-O-tetradecanoylphorbol 13-acetate (TPA) is dependent on both ERK and NF kappa B activation. First, we showed that two specific mitogen-activated protein kinase/ERK kinase-inhibitors, PD98059 and U0126, both counteracted TPA-mediated suppression of Fas-induced apoptosis. Moreover, the dose-dependence of U0126-mediated inhibition of ERK phosphorylation correlated with that of reversion of the anti-apoptotic effect of TPA. Second, we observed an excellent correlation between repression of TPA-induced NF kappa B activation by an irreversible inhibitor of I kappa B alpha phosphorylation, BAY11-7082, and its ability to abrogate TPA-induced suppression of Fas-mediated apoptosis. Furthermore, we located the anti-apoptotic effect of both ERK and NF kappa B to lie upstream of the mitochondrial membrane potential depolarization event. Finally, although each inhibitor at optimal, non-toxic concentration by itself only partly reversed TPA-mediated repression of apoptosis, the combination of U0126 and BAY11-7082 completely abolished the anti-apoptotic effect of TPA. Together these findings suggest that TPA-induced activation of ERK and NF kappa B are parallel events that are both required for maximal inhibition of Fas-induced apoptosis in Jurkat T cells.