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 effect of nerve growth factor (NGF) in promoting neurite outgrowth, To elucidate the mechanism by which staurosporine induces neurite outgrowth in PC-12 cells, we performed an in-gel kinase assay using myelin basic protein as a substrate, and found that staurosporine induced the activation 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 staurosporine-activated kinase was immunoprecipitated by anti-c-Jun NH2-terminal kinase (JNK) isoforms antibody, but not by anti-JNK1-specific antibody or anti-ERK1 antibody, raising the possibility that this kinase is a novel JNK isoform, The substrate specificity of the kinase was distinct 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 plays a role in gene induction. Furthermore, staurosporine induced immediate-early genes including Nur77 and fos, but not jun. The activation of the staurosporine-activated kinase, as well as the induction of neurite outgrowth, did not require Res function, while Pas was required for the activation of ERKs and neurite outgrowth induced by NGF. Taken together, these results indicate staurosporine specifically activates a JNK isoform, which may contribute to biological activities including neurite outgrowth.