Activation of phosphatidylinositol 3 kinase by muscarinic receptors in astrocytoma cells

Stimulation of Gq-coupled acetylcholine muscarinic receptors leads to proliferation of astroglial cells, but the signal transduction pathway(s) that mediate this mitogenic response have not been fully elucidated. In this study, we report on the ability of carbachol to stimulate the phosphorylation of Akt/PKB, an important target of phosphatidylinositol 3 kinase (P13 kinase) in 132INI human astrocytoma cells. Carbachol induced a dose-dependent phosphorylation of Ser⁴⁷³ on Akt, peaking after 15 min. This effect was mediated by activation of the M₃ subtype of muscarinic receptors and was inhibited by two P13 kinase inhibitors. Inhibitors of protein kinase C, mitogen-activated protein kinase and p70S6 kinase, had no effect on carbachol-induced Akt phosphorylation. Carbachol-induced DNA synthesis was strongly inhibited by two P13 kinase inhibitors, wortmannin and LY294002, suggesting that P13 kinase activation plays an important role in carbachol-induced proliferation of 132INI astrocytoma cells.