NF-κB activation results in rapid inactivation of JNK in TNFα-treated Ewing sarcoma cells:: a mechanism for the anti-apoptotic effect of NF-κB

We recently reported that inhibition of NF-kappaB activation as a consequence of the overexpression of a degradation-resistant form of I kappa -B alpha [I kappaB alpha (A32/36)] sensitized Ewing sarcoma cells to TNF alpha -induced killing. The c-Jun N-terminal kinases (JNK) have been shown to participate in death signaling triggered by certain stimuli and are activated by TNF. To obtain insight into the mechanism of the anti-apoptotic effect of NF-kappaB, we compared the profiles of JNK activation by TNF alpha in control cells and in cells in which NF-kappaB activation was impaired. We show here that JNK activation was transient in control cells but remained elevated in I kappa -B alpha (A32/36)-expressing cells. NF-kappaB repressed specifically the JNK pathway, since the kinetics of activation of the other TNF alpha -activated-MAP kinase p38 were identical in both cells, Prolongation of JNK activation in I kappaB alpha (A32/36)-expressing cells was not inhibited by the broad spectrum caspase inhibitor Z-VAD-FMK and thus was not the consequence of caspase activation, Pretreatment of control cells with the phosphatase inhibitor vanadate greatly prolonged JNK activation by TNF alpha and resulted in induction of apoptosis by this cytokine. Moreover, overexpression of a dominant-negative mutant of JNK1 decreased TNF alpha -induced apoptosis in cells expressing the super repressor of NF-kappaB, indicating that the sustained activation of JNK1 participated in death signaling triggered by TNF alpha, Our results provide evidence that the repression of JNK activation by NF-kappaB participates in the anti-apoptotic effect of this transcription factor in TNF alpha -treated Ewing sarcoma cells.