Regulation of hepatic estrogen receptor isoform mRNA expression in rainbow trout (Oncorhynchus mykiss)

The complete nuclear estrogen receptor family in rainbow trout consists of two subtypes (ER alpha and ER beta) each of which consists of two isoforms (alpha 1/alpha 2 and beta 1/beta 2). Transcription rate and mRNA stability of ER alpha 1 is affected by 17 beta-estradiol (E2) but no information on estrogen regulation exists for the other isoforms. The objective of this study was to compare the mRNA expression patterns of the four ER isoforms in the liver of male trout and in immortalized trout hepatocyte lines (RTH-149 and SOB-15) treated with E2 or 17 alpha-ethynylestradiol (EE2) using quantitative RT-PCR. To determine the in vivo dose-response, isogenic male trout were injected intra-peritoneally with 0, 1.5, 15 or 150 mu g E2 or an equimolar amount of EE2 and the liver sampled 24 h later. Treatment with either E2 or EE2 significantly (p<0.05) increased the level of ER alpha 1 mRNA at all doses tested compared to vehicle, while the response of mRNAs for the other three isoforms did not change. The in vitro dose-response was tested by treating both cell lines with 0, 0.1, 1.0 or 10.0 mu M E2 for 48 h. In RTH-149 cells, ER alpha 1, ER alpha 2 and ER beta 2 mRNAs were significantly higher in cells incubated with 10 mu M E2 as compared to cells treated with only vehicle (p<0.05). In SOB-15 cells, ER alpha 2 and ER beta 1 mRNAs were significantly higher in cells incubated with 1.0 mu M E2 as compared to cells incubated with only vehicle (p<0.05). These results support the conclusion that the mRNAs for the four ER isoforms respond differentially to estrogen regulation. (c) 2008 Elsevier Inc. All rights reserved.