STEROIDOGENIC FACTOR-I AND EARLY GROWTH-RESPONSE PROTEIN-1 ACT THROUGH 2 COMPOSITE DNA-BINDING SITES TO REGULATE LUTEINIZING-HORMONE BETA-SUBUNIT GENE-EXPRESSION

Recent in vivo and in vitro studies have implicated the orphan nuclear receptor, steroidogenic factor-1 (SF-1), and the early growth respons e protein 1 (Egr-1) in the transcriptional regulation of the luteinizi ng hormone beta-subunit (LH beta) gene. We have previously demonstrate d the ability of SF-1 to bind to and transactivate the rat LH beta gen e promoter acting at a consensus gonadotrope-specific element (GSE) lo cated 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 putativ e Egr-1 binding sites (positions -112 and -50), which appear to be pai red with the identified GSE sites. By transient transfection assay in pituitary-derived GH, cells, it was seen that Egr-1 increases promoter activity of region -207/+5 of the rat LH beta gene promoter through a ction at both Egr-1 sites. Furthermore, LHP gene promoter activity is markedly augmented in the presence of both factors together relative t o 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 SF-1- Egr-1 response-elements in the proximal LH beta gene promoter and sugg est that SF-1 and Egr-1 act synergistically to increase expression of the LH beta gene in the gonadotrope.