STEROIDOGENIC FACTOR-1 AND ESTRADIOL-RECEPTOR ACT IN SYNERGISM TO REGULATE THE EXPRESSION OF THE SALMON GONADOTROPIN-II-BETA SUBUNIT GENE

The orphan nuclear receptor steroidogenic factor-1 (SF-1) regulates th e expression of several genes involved in the reproductive function an d development of the adrenal, the gonads, and the pituitary gonadotrop es. It also confers the gonadotrope-specific expression of the glycopr otein hormone ru subunit gene by the binding to a gonadotrope-specific element (GSE). In this study, we have shown that SF-1 transactivates the salmon gonadotropin II beta subunit (sGTHII beta) gene expression. SF-1 alone offered a slight but significant enhancement on sGTHII bet a promoter activity (7.2 +/- 0.6 fold). However, it stimulated sGTHII beta gene expression dramatically (127 +/- 37 fold) when combined with the estrogen receptor (ER). This synergistic interaction was specific for sGTHII beta promoter as well as for both SF-1 and ER and was estr adiol-dose dependent 5'-Deletion studies of the sGTHII beta promoter i dentified two putative SF-1 binding sites (GSE) and one previously ide ntified proximal estrogen-responsive element (pERE) at -274 bp involve d in this activation. The two GSE sequences located at -354 bp (sGSE(3 )) and -162 bp (sGSE(2)) upstream of the transcription site, although imperfect as compared with the consensus GSE, bound specifically to th e in vitro-translated mouse SF-1 protein. 5'-Deletion studies, competi tion experiments, and site-directed mutagenesis showed that binding to pERE and GSE(2) were necessary for the SF-1/ER synergistic effect The se studies suggest that the synergistic interaction of SF-1 and ER, po ssibly through cooperative binding or protein-protein interaction, is essential in conferring a cell type-specific expression of the GTHII b eta subunit gene.