Differential Regulation of Estrogen Receptor Subtypes α and β in Human Aortic Smooth Muscle Cells by Oligonucleotides and Estradiol

Abstract

We investigated the mechanisms regulating estrogen receptor (ER) expression in human aortic smooth muscle cells (HASMCs) and the mechanisms by which estradiol inhibits HASMC growth. The autologous down-regulation pathway involves binding of liganded ER to the ER gene, thus suppressing transcription. Blockade of this pathway with sense and AS-OLIGOs to ERs up-regulated the expression of ERα but not ERβ. Activation of the autologous down-regulation pathway with ER agonists down-regulated the expression of ERα but not ERβ. The proteasomal degradation pathway entails ubiquination of liganded ER, followed by proteasome-mediated degradation. Blockade of the proteasomal degradation pathway increased the expression of ERβ. Up-regulation of ERα by AS-OLIGOs did not increase the antimitogenic effects of estradiol on HASMCs; the estradiol metabolites 2-hydroxyestradiol and 2-methoxyestradiol were more potent inhibitors of HASMC growth, compared with estradiol; and blockade of metabolism of estradiol to hydroxyestradiols and methoxyestradiols abrogated the inhibitory effects of estradiol on HASMC growth. We conclude that, in HASMCs: 1) the expression of ERα is regulated by the autologous down-regulation pathway; 2) the expression of ERβ is governed by the proteasomal degradation pathway; and 3) the antigrowth effects of estradiol are not mediated by ERα, but rather by metabolism of estradiol to methoxyestradiols.