Abstract 10458: Steroid Hormones Induce Caveolin-1 (cav-1) and Attenuate Vascular Endothelial Growth Factor (VEGF) Responses in Cultured Vascular Endothelial Cells (EC)
Steroid hormones play key roles in mediating stress responses in various organs including cardiovascular systems, often associated with attenuated blood vessel responses to extracellular stimuli. However, molecular mechanisms whereby these hormones perturb EC functions remain incompletely understood. We explored whether or not and how steroid hormones may modulate expression of cav-1, a key regulatory protein of cell-surface receptor pathways that thereby determines the degrees of EC responses to growth factors. Western blot and RT-PCR assays of cultured bovine aortic EC (BAEC) revealed that dexamethasone (Dex), a glucocorticoid, augments expression of cav-1 at both levels of protein and mRNA in a time- and dose-dependent manner (7.8 ± 1.2 fold at 1 uM for 48 h in western blots, p<0.05). This cav-1 induction by Dex is mediated by canonical nuclear steroid receptors, since it was sensitive to RU-486 (1 uM), a specific inhibitor of glucocorticoid receptors. Cav-1 serves as a scaffolding protein within plasmalemmal caveolae, specialized signal transducing microdomains that are critically enriched in various signaling proteins. We therefore explored functional consequences of Dex induction of cav-1 on signaling events activated by VEGF, which represents a pivotal modulator of EC functions. Phospho-western analyses revealed that pretreatment with Dex (1 uM for 48 h) leads to markedly attenuated phosphorylation responses for VEGF (10 ng/mL for 5 min) of VEGF receptor 2, protein kinases Akt as well as ERK1/2, and endothelial NO synthase, in a manner sensitive to RU−486. Dex also led to decreased degrees of NO production (28 ± 3 %, p<0.05, high sensitivity nitrite assay) as wells as a small-G protein Rac1 activation (59 ± 8 %, p<0.05, pull down assay) both evoked by VEGF. Aldosterone, a mineralocorticoid, but not sex steroids 17beta-estradiol, testosterone, or progesterone, elicits similar induction of cav-1 protein/mRNA albeit to a lesser extent than does Dex, inhibited by spironolactone, a specific antagonist for mineralocorticoid receptors. Collectively, these results indicate that steroid hormones attenuate EC responses to VEGF via cav-1 induction, identifying a novel point of crosstalk between nuclear and cell-surface receptor signaling pathways.
- © 2010 by American Heart Association, Inc.