Estrogen receptors alpha and beta - Prevalence of estrogen receptor beta mRNA in human vascular smooth muscle and transcriptional effects

Background-Estrogens have vascular effects through the activation of estrog en receptors (ERs). In addition to ER alpha, the first ER to be cloned, a s econd subtype called ER beta has recently been discovered. Methods and Results-Using a reverse-transcriptase polymerase chain reaction assay that employs the same primer pair to simultaneously amplify ER alpha and ER beta transcripts, we found that ER beta is the ER form that is pred ominantly expressed in human vascular smooth muscle, particularly in women. The transcriptional effects of the 2 ERs in transfected HeLa cells differe d. In response to 17 beta-estradiol, ER alpha is a stronger transactivator than ER beta at low receptor concentrations. However, at higher receptor co ncentrations, ER alpha activity self-squelches, and ER beta is a stronger t ransactivator. Tamoxifen has partial agonist effects with ER alpha but not with ER beta. Conclusions-The protective effects of estrogens in the cardiovascular syste m of women may be due to the genomic effects of ER beta in vascular tissue.