alpha(1) Adrenergic receptors activate phosphatidylinositol 3-kinase in human vascular smooth muscle cells - Role in mitogenesis

Activation of alpha(1) adrenergic receptors stimulates mitogenesis in human vascular smooth muscle cells (HVSMCs), To examine signaling pathways by which activation of alpha(1) receptors may induce mitogenesis in HVSMCs, we have found that alpha(1) receptor stimulated-DNA synthesis and activation of mitogen-activated protein (MAP) kinase are blocked by wortmannin, an inhibitor of phosphatidylinositol 3-kinase (PI 3-kinase), To determine directly if activation of alpha(1) receptors stimulated PI 3-kinase, in vitro assays of kinase activity were performed in immunocomplexes precipitated by an antibody against the p85 alpha subunit of PI 3-kinase, Noradrenaline stimulated a time- and concentration-dependent activation of PI 3-kinase in the presence of a beta adrenergic receptor antagonist, Noradrenaline-stimulated PI 3-kinase activation was blocked by antagonists of alpha(1) receptors and by pertussis toxin, suggesting that alpha(1) receptors activate PI 3-kinase via a pertussis toxin-sensitive G protein. Direct activation of protein kinase C by a phorbol ester did not stimulate PI 3-kinase; also, a Ca2+ L-channel blocker did not inhibit noradrenaline-stimulated PI 3-kinase activity, Increased PI S-kinase activity was detected in both anti-Pas and anti-phosphotyrosine immunoprecipitates from noradrenaline-stimulated HVSMCs, Moreover, noradrenaline stimulated formation of active Ras-GTP complexes, Because blockade of PI S-kinase by wortmannin inhibited formation of this complex, this result suggests that Pas might be a target of PI 3-kinase, Noradrenaline stimulated tyrosine phosphorylation of the p85 subunit of PI 3-kinase, and a phosphorylated tyrosine protein could be co-immuno precipitated with anti-p85 of PI 3-kinase, These results demonstrate that stimulation of alpha(1) receptors activates PI 3-kinase in HVSMCs and that alpha(1) receptor-activated PI 3-kinase is associated with an increase in active Ras-GTP and activation of tyrosine protein phosphorylation, These pathways may contribute to alpha(1) receptor-stimulated mitogenic responses including activation of MAP kinase and DNA synthesis in HVSMCs.