Glutathione-S-Transferase as a selective inhibitor of oncogenic ras-p21-induced mitogenic signaling through blockade of activation of jun by jun-N-terminal kinase.

We have identified the intracellular detoxification enzyme, glutathione-S-transferase (GST), as a potent inhibitor of the activation of jun by its kinase, jun-N-terminal kinase (JNK), in vitro. All three major isozymes (alpha, mu, and pi) bind to JNK-jun complexes and inhibit activation of jun by JNK. We now find that GST inhibits JNK-induced oocyte maturation in vivo and strongly inhibits oocyte maturation induced by oncogenic ras-p21 protein, but not by insulin-activated normal cellular p21 protein. These results correlate with the finding that oncogenic, but not insulin-activated normal, p21 induces high levels of activated JNK. GST also strongly blocks induction of oocyte maturation by protein kinase C (PKC) which is a critical downstream target of oncogenic but not normal ras-p21. Thus, we have established a new function for GST as a potent physiological inhibitor of the ras-JNK-jun pathway.