Steroidogenic factor-1 and early growth response protein 1 act through two composite DNA binding sites to regulate luteinizing hormone β-subunit gene expression

Abstract

Recent in vivo and in vitro studies have implicated the orphan nuclear receptor, steroidogenic factor-1 (SF-1), and the early growth response protein 1 (Egr-1) in the transcriptional regulation of the luteinizing hormone β-subunit (LHβ) gene. We have previously demonstrated the ability of SF-1 to bind to and transactivate the rat LHβ gene promoter acting at a consensus gonadotropespecific element (GSE) located at position -127. We have now identified a second functional GSE site at position -59. In addition, based on electrophoretic mobility shift assay, in vitro translated Egr-1 is shown to bind to two putative Egr-1 binding sites (positions -112 and -50), which appear to be paired with the identified GSE sites. By transient transfection assay in pituitary-derived GH3 cells, it was seen that Egr-1 increases promoter activity of region -207/+ 5 of the rat LHβ gene promoter through action at both Egr-1 sites. Furthermore, LHβ gene promoter activity is markedly augmented in the presence of both factors together relative to activity in the presence of SF-1 or Egr-1 alone (150-fold versus 14-fold and 12-fold, respectively). These data define two composite SF1-Egr-1 response- elements in the proxima) LHβ gene promoter and suggest that SF-1 and Egr-1 act synergistically to increase expression of the LHβ gene in the gonadotrope.