Transcriptional and post-transcriptional regulation of rainbow trout estrogen receptor and vitellogenin gene expression

Abstract

Estrogen receptor (ER) and vitellogenin (Vg) gene expression are strongly up-regulated by estrogens in rainbow trout liver. In this paper, we have used primary cultured hepatocytes to examine the mechanisms implicated in estrogen regulation of ER and Vg gene expression. Treatment of hepatocytes with 1 μM estradiol (E2) led to a rapid increase in ER mRNA level (15 fold) followed by Vg mRNA induction. Transcription rate and mRNA half-life determination carried out in the presence or absence of E2, demonstrated that E2 increases both the ER and Vg gene transcriptional activity and mRNA stability (ca. 3 fold). The effect of E2 was inhibited by an excess of antiestrogens, showing that E2-stimulation of ER and Vg mRNA level is mediated by the estrogen receptor. Our data show that ER and Vg genes have different hormonal sensitivity. In fact, the Vg gene required a higher concentration of E2 to be stimulated compared to the ER gene. Examination of the mechanisms involved in post-transcriptional regulation of ER mRNA showed that the setting up and maintenance of this regulation process implies the estrogen receptor and the general translational activity within the cells, suggesting that E2-stabilization of ER mRNA depends on the synthesis of an estrogen-dependent protein. However, the cis and trans elements involved in this E2-stabilization process remain to be identified.