Activation of Akt by nerve growth factor via phosphatidylinositol-3 kinase in PC12 pheochromocytoma cells

Akt, a serine/threonine kinase has been recently shown to be activated by mitogenic growth factors via phosphatidylinositol-3 kinase (PI-3 kinase). PI-3 kinase can also be activated by a G-protein linked receptor as well as a receptor tyrosine kinase (RTK). In this study, activation of Akt by a nerve growth factor (NGF) in pheochromocytoma 12 (PC12) cells was analyzed using histone E2B as a kinase substrate. Akt was activated by NGF in a time- and a dose-dependent manner in PC12 cells. This activation was blocked by wortmannin, a PI-3 kinase inhibitor, indicating that PI-3 kinase mediated the NGF-induced activation of Akt. However, treatment of human neutrophils and human myeloid-derived U 937 cells with formylated methionylleucylphenylalanine (fMLP) showed no effect on Akt activity, although activation of PI-3 kinase by fMLP-stimulated G-protein induced an increase in the tyrosine phosphorylation of p56(lyn) protein. These results indicate that, like by mitogenic growth factors, activation of Akt by NGF in PC12 cells is mediated by RTK-associated PI-3 kinase, and suggest a possible role of Akt in the physiological functions of NGF as well.