I kappa B alpha is essential for maintaining basal c-Jun N-terminal kinase(JNK) activation and regulating JNK-mediated resistance to tumor necrosis factor cytotoxicity in L929 cells

Early activation of c-Jun N-terminal kinase (JNK) is believed to block apop tosis in response to death signals such as tumor necrosis factor (TNF). Bri ef exposure of murine L929 fibroblasts to anisomycin for 1 hr to activate J NK resulted in resistance to TNF killing. TNF rapidly induced cytoplasmic s hrinkage in control cells, but not in the anisomycin-pretreated L929 cells. However, the induced TNF resistance was suppressed in the L929 cells which were engineered to stably inhibit I kappa B alpha protein expression by an tisense mRNA (similar to 80% reduction in protein expression). No constitut ive NF-kappa B nuclear translocation and increased TNF resistance were foun d in these I kappa B alpha antisense cells. Notably, these cells had a sign ificantly reduced basal level of JNK activation (50-70%), compared to vecto r control cells. Furthermore, brief exposure of L929 cells to wortmannin, a n inhibitor of phosphatidylinositol 3-kinase (PI3-kinase), resulted in resi stance to TNF killing, probably due to preconsumption of caspases by wortma nnin. Nonetheless, wortmannin-induced TNF resistance was suppressed in the I kappa B alpha antisense cells. Thus, these observations indicate that I k appa B alpha is essential for maintaining the basal level of JNK activation and regulating the JNK-induced TNF resistance. (C) 1999 Academic Press.