Involvement of phosphatidylinositol 3-kinase and mitogen-activated protein kinase pathways in all-mediated enhanced expression of Gi proteins in vascular smooth muscle cells

We have previously demonstrated that angiotensin II increased Gi alpha-2 and Gi alpha-3 expression at both protein and mRNA levels in vascular smooth muscle cell (VSMC). The present study was undertaken to investigate the mechanisms responsible for AII-induced enhanced expression of Gi proteins. The levels of Gi protein were determinated by immunoblotting techniques using specific antibodies against Gi alpha-2 and Gi alpha-3. AII treatment of VSMC increased the levels of Gi alpha-2 and Gi alpha-3 proteins and actinomycin D, an inhibitor of RNA synthesis attenuated the AII-evoked enhanced expression of Gi alpha-2 and Gi alpha-3 proteins. In addition, wortmannin, an inhibitor of phosphatidylinositol 3-kinase (PI-3-R), rapamycin, an inhibitor of p70(S6K) and PD 098059, an inhibitor of mitogen-activated protein kinase (MAPK) kinase were able to inhibit AII-induced enhanced expression of Gi alpha-2 and Gi alpha-3 to various degrees. The attenuation of AII-evoked enhanced levels of Gi alpha-2 and Gi alpha-3 by PD 098059 was concentration dependent. At 50 mu M, PD 098059 was able to completely attenuate the enhanced levels of Gi alpha-2 and Gi alpha-3 caused by AII treatment. These data suggest that the enhanced expression of Gi-proteins by AII treatment may be attributed to increased RNA synthesis of Gi-proteins, and MAPK kinase, PI-3-Kinase and p70(S6K) may be involved in AII-mediated increased expression of Gi-proteins in VSMC. (C) 1998 Academic Press.