ANGIOTENSIN-II TYPE-1 RECEPTOR - RELATIONSHIP WITH CAVEOLAE AND CAVEOLIN AFTER INITIAL AGONIST STIMULATION

Caveolae are membrane domains that have been implicated in signal tran sduction, and caveolins are major structural components of these domai ns. We found that all reported caveolin isoforms (caveolin-1, -2, and -3) were expressed in vascular smooth muscle cells (VSMCs); however, o nly caveolin-1 mRNA was regulated by angiotensin II (Ang II). Ang II ( 100 nmol/L) increased caveolin-1 mRNA, with a peak at 2 hours (193+/-6 % of control, P<0.01, n=4). In contrast, Ang II significantly decrease d caveolin-1 protein, with a nadir at 4 hours (64+/-5% of control, P<0 .01, n=6). [S-35]Methionine labeling showed that Ang II increased cave olin biosynthesis (226+/-33% of control labeling at 4 hours), suggesti ng that the transient decrease in caveolin protein levels is due to in creased degradation. When cells were fractionated with sucrose, on ago nist stimulation, AT(1) receptors appeared in fraction 5 where caveoli n was fractionated. This migration was blocked by low temperature and treatment with phenylarsine oxide, interventions that interfere with a gonist-induced Ang II type 1 (AT(1)) receptor sequestration and tonic phase signaling. In addition, caveolin-1 coimmunoprecipitates with AT( 1) receptor only on agonist stimulation. These data support the concep t that the caveola is a specialized signaling domain in VSMCs that can be dynamically accessed by the AT(1) receptor. Because of the signali ng and coupling proteins that are localized in caveolae and because of evidence that these proteins may interact directly with caveolin, cav eola-AT(1) receptor interaction likely represents an important focus f or dynamic control of receptor signaling in VSMCs.