Stimulation of luteinizing hormone beta gene promoter activity by the orphan nuclear receptor, steroidogenic factor-1

The orphan nuclear receptor, steroidogenic factor-1 (SF-1), is expressed in the pituitary and in the gonadotrope precursor cell line, alpha T3-1, where it is believed to enhance expression of the common gonadotropin alpha-subunit gene through transactivation of the gonadotrope-specific element (GSE), Sequence analysis of the rat luteinizing hormone beta-subunit (LH beta) gene promoter revealed the presence of a consensus GSE at -127 to -119 (TGACCTTGT). We have demonstrated the ability of SF-l to bind specifically to this putative GSE sequence by electrophoretic mobility shift assay, utilizing both alpha T3-1 nuclear extracts and in vitro translated SF-l. In addition, mutation of the putative LH beta-GSE (TGAAATTGT) eliminated specific DNA binding, To examine the ability of SF-l to enhance LHP promoter activity, CV-1 cells, which lack endogenous SF-l, were cotransfected with an SF-l-containing expression vector and an LH beta-luciferase reporter construct, When cotransfected with -209/+5 of the LH beta promoter, SF-1 increased luciferase activity by 56-fold, SF-1 responsiveness was markedly diminished with loss of the putative GSE region in deletion constructs and in the presence of a two base pair mutation, analogous to the mutation which eliminated DNA binding, Finally, the LH beta-GSE was able to confer SF-1 responsiveness on a heterologous minimal growth hormone promoter, GH50 (57-fold), We conclude that SF-l both binds to and transactivates the rat LHP promoter, These data suggest that SF-1 may participate in the expression of the LH beta gene by the gonadotrope.