CORRELATION BETWEEN SUSTAINED C-JUN N-TERMINAL PROTEIN-KINASE ACTIVATION AND APOPTOSIS INDUCED BY TUMOR-NECROSIS-FACTOR-ALPHA IN RAT MESANGIAL CELLS

Rat mesangial cells are normally resistant to tumor necrosis factor-al pha (TNF-alpha)-induced apoptosis, In this report we show that the cel ls can be made susceptible to the apoptotic effect of TNF-alpha when p retreated with actinomycin D, cycloheximide, or vanadate. c-Jun N-term inal protein kinase (JNK) has been thought to mediate apoptotic proces ses elicited by some stimuli, but its involvement in TNF-alpha-induced apoptosis has been controversial, JNK activation was investigated und er conditions where the mesangial cells were either resistant or susce ptible to TNF-alpha-induced apoptosis, TNF-alpha alone stimulated a si ngle transient JNK activity peak, However, when the cells were pretrea ted with actinomycin D or cycloheximide, TNF-alpha stimulated a second sustained JNK activity peak. When the cells were pretreated with the phosphatase inhibitor vanadate, TNF-alpha-induced JNK activation was g reatly prolonged, In all three cases, a sustained JNK activation was a ssociated with the initiation of apoptosis. Our data suggest that a su stained activation of JNK induced by these reagents may be associated with blocking the expression of a phosphatase that inactivates JNK, Fu rther studies reveal that the expression of mitogen-activated protein kinase phosphatase-1 (MKP-1) was induced by TNF-alpha, indicating that MKP-1 may be involved in protecting the cells from apoptosis by preve nting a prolonged activation of JNK under normal conditions. Additiona l studies showed that extracellular signal-regulated protein kinase ac tivation stimulated by TNF-alpha was unlikely to contribute to the res istance of mesangial cells to TNF-alpha cytotoxicity.