Estrogen Receptors α and β: Prevalence of Estrogen Receptor β mRNA in Human Vascular Smooth Muscle and Transcriptional Effects

Abstract

Background —Estrogens have vascular effects through the activation of estrogen receptors (ERs). In addition to ERα, the first ER to be cloned, a second subtype called ERβ has recently been discovered. Methods and Results —Using a reverse-transcriptase polymerase chain reaction assay that employs the same primer pair to simultaneously amplify ERα and ERβ transcripts, we found that ERβ is the ER form that is predominantly expressed in human vascular smooth muscle, particularly in women. The transcriptional effects of the 2 ERs in transfected HeLa cells differed. In response to 17β-estradiol, ERα is a stronger transactivator than ERβ at low receptor concentrations. However, at higher receptor concentrations, ERα activity self-squelches, and ERβ is a stronger transactivator. Tamoxifen has partial agonist effects with ERα but not with ERβ. Conclusions —The protective effects of estrogens in the cardiovascular system of women may be due to the genomic effects of ERβ in vascular tissue.