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 H2B 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.