The Ras–ERK pathway is required for the induction of neuronal nitric oxide synthase in differentiating PC12 cells

We have studied the role of MAP kinase pathways in neuronal nitric oxide synthase (nNOS) induction during the differentiation of PC12 cells. In nerve growth factor (NGF)‐treated PC12 cells, we find nNOS induced at RNA and protein levels, resulting in increased NOS activity. We note that neither nNOS mRNA, nNOS protein nor NOS activity is induced by NGF treatment in cells that have been infected with a dominant negative Ras adenovirus. We have also used drugs that block MAP kinase pathways and assessed their ability to inhibit nNOS induction. Even though U0126 and PD98059 are both MEK inhibitors, we find that U0126, but not PD98059, blocks induction of nNOS protein and NOS activity in NGF‐treated PC12 cells. Also, the p38 kinase inhibitor, SB203580, does not block nNOS induction in our clone of PC12 cells. Since the JNK pathway is not activated in NGF‐treated PC12 cells, we conclude that the Ras–ERK pathway and not the p38 or JNK pathway is required for nNOS induction in NGF‐treated PC12 cells. We find that U0126 is much more effective than PD98059 in blocking the Ras–ERK pathway, thereby explaining the discrepancy in nNOS inhibition. We conclude that the Ras–ERK pathway is required for nNOS induction.