NGF and EGF rapidly activate p21 ras in PC12 cells by distinct, convergent pathways involving tyrosine phosphorylation

Abstract

Activation of p21 ras , demonstrated directly as an increase in p21 ras -associated GTP, was induced rapidly but transiently by both nerve growth factor (NGF) and epidermal growth factor (EGF) in PC12 cells. The factors activate p21 ras equal extents and with virtually identical time courses. Growth factor-induced p21 ras activation and tyrosine phosphorylation have similar time courses and sensitivities to genistein inhibition, indicating that p21 ras activation is a result of tyrosine kinase activity. Furthermore, PC12 mutants lacking the Trk NGF receptor tyrosine kinase also lack NGF-inducible p21 ras activation. The protein kinase inhibitor K252a and the methyltransferase inhibitor MTA abolish NGF-induced, but not EGF-induced, p21 ras -activation-effects correlated with inhibition only of NGF-induced tyrosine phosphorylation. In spite of differences in sensitivity to genistein, MTA, and K252a, EGF- and NGF-stimulated p21 ras activation are not additive, implying that they do share at least one step in common.