SPECIFIC ACTIVATION OF A C-JUN NH2-TERMINAL KINASE ISOFORM AND INDUCTION OF NEURITE OUTGROWTH IN PC-12 CELLS BY STAUROSPORINE

Staurosporine, a protein kinase inhibitor, is known to mimic the effec t of nerve growth factor (NGF) in promoting neurite outgrowth, To eluc idate the mechanism by which staurosporine induces neurite outgrowth i n PC-12 cells, we performed an in-gel kinase assay using myelin basic protein as a substrate, and found that staurosporine induced the activ ation of a kinase with an apparent molecular mass of 57 kDa, The dose of staurosporine required to activate this kinase was consistent with that required to induce neurite outgrowth, Interestingly, the staurosp orine-activated kinase was immunoprecipitated by anti-c-Jun NH2-termin al kinase (JNK) isoforms antibody, but not by anti-JNK1-specific antib ody or anti-ERK1 antibody, raising the possibility that this kinase is a novel JNK isoform, The substrate specificity of the kinase was dist inct from those of osmotic shock-activated JNKs and NGF-activated ERK1 , The kinase phosphorylates transcription factors including c-Jun, Elk -l, and ATF2, as well as myelin basic protein, suggesting that it play s a role in gene induction. Furthermore, staurosporine induced immedia te-early genes including Nur77 and fos, but not jun. The activation of the staurosporine-activated kinase, as well as the induction of neuri te outgrowth, did not require Res function, while Pas was required for the activation of ERKs and neurite outgrowth induced by NGF. Taken to gether, these results indicate staurosporine specifically activates a JNK isoform, which may contribute to biological activities including n eurite outgrowth.