INTACT RAS FUNCTION IS REQUIRED FOR SUSTAINED ACTIVATION AND NUCLEAR TRANSLOCATION OF EXTRACELLULAR SIGNAL-REGULATED KINASES IN NERVE GROWTH FACTOR-STIMULATED PC12 CELLS

PC12 pheochromocytoma cell lines expressing the dominant negative Ha-R as Asn-17 protein at different levels were used in this study to analy ze the relationship between nerve growth factor (NGF)-induced activati on of members of the mitogen-activated protein kinase (MAPK) family, a nd neuritogenesis, In wild-type PC12 cells. NGF rapidly stimulated the extracellular signal-regulated kinases (ERKs), Kinase activation was sustained and was followed by the translocation of ERK 1 and ERK 2 int o the nucleus ultimately leading to neurite outgrowth. In cells expres sing relatively high levels of the inhibitory Res protein, NGF stimula tion of ERK 1 and ERK 2 as well as nuclear translocation of these prot ein kinases were greatly inhibited, In contrast, in PC12 subclones exp ressing low amounts of Ha-Ras Asn-17 the peak of ERK activation was on ly slightly reduced, but became transient in nature and was not follow ed by nuclear translocation of ERKs 1 and 2. Since all PC12 subclones expressing detectable levels of the dominant inhibitory Ras protein ar e resistant to NGF induction of neurite formation, our observations su pport the notion that sustained activation and translocation of ERKs i nto the nucleus are essential for NGF-induced neuronal differentiation of PC12 cells.