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 path ways by which activation of alpha(1) receptors may induce mitogenesis in HVSMCs, we have found that alpha(1) receptor stimulated-DNA synthes is and activation of mitogen-activated protein (MAP) kinase are blocke d by wortmannin, an inhibitor of phosphatidylinositol 3-kinase (PI 3-k inase), To determine directly if activation of alpha(1) receptors stim ulated PI 3-kinase, in vitro assays of kinase activity were performed in immunocomplexes precipitated by an antibody against the p85 alpha s ubunit of PI 3-kinase, Noradrenaline stimulated a time- and concentrat ion-dependent activation of PI 3-kinase in the presence of a beta adre nergic receptor antagonist, Noradrenaline-stimulated PI 3-kinase activ ation was blocked by antagonists of alpha(1) receptors and by pertussi s toxin, suggesting that alpha(1) receptors activate PI 3-kinase via a pertussis toxin-sensitive G protein. Direct activation of protein kin ase 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-stimul ated HVSMCs, Moreover, noradrenaline stimulated formation of active Ra s-GTP complexes, Because blockade of PI S-kinase by wortmannin inhibit ed formation of this complex, this result suggests that Pas might be a target of PI 3-kinase, Noradrenaline stimulated tyrosine phosphorylat ion of the p85 subunit of PI 3-kinase, and a phosphorylated tyrosine p rotein could be co-immuno precipitated with anti-p85 of PI 3-kinase, T hese results demonstrate that stimulation of alpha(1) receptors activa tes PI 3-kinase in HVSMCs and that alpha(1) receptor-activated PI 3-ki nase is associated with an increase in active Ras-GTP and activation o f tyrosine protein phosphorylation, These pathways may contribute to a lpha(1) receptor-stimulated mitogenic responses including activation o f MAP kinase and DNA synthesis in HVSMCs.