TRANSCRIPTIONAL AND POSTTRANSCRIPTIONAL REGULATION OF RAINBOW-TROUT ESTROGEN-RECEPTOR AND VITELLOGENIN GENE-EXPRESSION

Estrogen receptor (ER) and vitellogenin (Vg) gene expression are stron gly up-regulated by estrogens in rainbow trout liver. In this paper, w e have used primary cultured hepatocytes to examine the mechanisms imp licated in estrogen regulation of ER and Vg gene expression. Treatment of hepatocytes with I mu M estradiol (E2) led to a rapid increase in ER mRNA level (15 fold) followed by Vg mRNA induction. Transcription r ate and mRNA half-life determination carried out in the presence or ab sence of E2, demonstrated that E2 increases both the ER and Vg gene tr anscriptional activity and mRNA stability (ca. 3 fold). The effect of E2 was inhibited by an excess of antiestrogens, showing that E2-stimul ation of ER and Vg mRNA level is mediated by the estrogen receptor, Ou r data show that ER and Vg genes have different hormonal sensitivity. In fact, the Vg gene required a higher concentration of E2 to be stimu lated 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 rec eptor and the general translational activity within the cells, suggest ing that E2-stabilization of ER mRNA depends on the synthesis of an es trogen-dependent protein. However, the cis and trans elements involved in this E2-stabilization process remain to be identified. Copyright ( C) 1996 Elsevier Science Ireland Ltd.