Steroidogenic factor 1 and estradiol receptor act in synergism to regulate the expression of the salmon gonadotropin II beta subunit gene

Abstract

The orphan nuclear receptor steroidogenic factor-1 (SF-1) regulates the expression of several genes involved in the reproductive function and development of the adrenal, the gonads, and the pituitary gonadotropes. It also confers the gonadotrope-specific expression of the glycoprotein hormone α subunit gene by the binding to a gonadotrope-specific element (GSE). In this study, we have shown that SF-1 transactivates the salmon gonadotropin IIβ subunit (sGTHIIβ) gene expression. SF-1 alone offered a slight but significant enhancement on sGTHIIβ promoter activity (7.2 ± 0.6 fold). However, it stimulated sGTHIIβ gene expression dramatically (127 ± 37 fold) when combined with the estrogen receptor (ER). This synergistic interaction was specific for sGTHIIβ promoter as well as for both SF-1 and ER and was estradiol-dose dependent. 5'-Deletion studies of the sGTHIIβ promoter identified two putative SF-1 binding sites (GSE) and one previously identified proximal estrogen-responsive element (pERE) at -274 bp involved 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 the in vitro- translated mouse SF-1 protein. 5'-Deletion studies, competition experiments, and site-directed mutagenesis showed that binding to pERE and GSE 2 were necessary for the SF-1/ER synergistic effect. These studies suggest that the synergistic interaction of SF-1 and ER, possibly through cooperative binding or protein-protein interaction, is essential in conferring a cell type- specific expression of the GTHIIβ subunit gene.