Distinct expression and activity profiles of largemouth bass (Micropterus salmoides) estrogen receptors in response to estradiol and nonylphenol

Abstract

AbstractThe estrogen receptor (ER) signaling cascade is a vulnerable target of exposure to environmental xenoestrogens, like nonylphenol (NP), which are causally associated with impaired health status. However, the impact of xenoestrogens on the individual receptor isotypes (α, βa, and βb) is not well understood. The goal of these studies was to determine the impact of NP on largemouth bass (Micropterus salmoides) ER isotype expression and activity. Here, we show that hepatic expression levels of three receptors are not equivalent in male largemouth bass exposed to NP by injection. Transcript levels of the ERα subtype were predominantly induced in concert with vitellogenin similarly to fish exposed to 17β-estradiol (E2) as measured by quantitative real-time PCR. NP also induced circulating plasma levels of estrogen, which may contribute to overall activation of the ERs. To measure the activation of each receptor isotype by E2 and NP, we employed reporter assays using an estrogen response element (ERE)–luciferase construct. Results from these studies show that ERα had the greatest activity following exposure to E2 and NP. This activity was inhibited by the antagonists ICI 182 780 and ZM 189 154. Furthermore, both βb and βa subtypes depressed ERα activation, suggesting that the cellular composition of receptor isotypes may contribute to the overall actions of estrogen and estrogenic contaminants via the receptors. Results from these studies collectively reveal the differential response of fish ER isotypes in response to xenoestrogens.