TRANSCRIPTIONAL REPRESSION OF THE GLYCOPROTEIN HORMONE ALPHA-SUBUNIT GENE BY ANDROGEN MAY INVOLVE DIRECT BINDING OF ANDROGEN RECEPTOR TO THE PROXIMAL PROMOTER

Testicular androgens suppress the synthesis and secretion of the pitui tary gonadotropins, in particular, luteinizing hormone. This suppressi ve effect includes transcription of both the common alpha subunit gene and the unique beta subunit genes. Herein, we demonstrate that 1500 b ase pairs (bp) of proximal 5'-flanking region derived from the human a lpha subunit gene and a shorter 315-bp segment of the bovine alpha sub unit gene confer negative regulation by androgen to the gene encoding bacterial chloramphenicol acetyltransferase in transgenic mice. Cotran sfection assays with human androgen receptor indicated that the 1500-b p promoter region of the human alpha subunit gene also confers androge n regulation (transcriptional suppression) to reporter genes in both p ituitary and placental cell lines. This raises the possibility of a ro le for DNA binding in suppression of alpha subunit transcription by ac tivated androgen receptor. Consistent with this possibility, we have u sed a gel-mobility shift assay to detect several high affinity binding sites for androgen receptor located in the proximal promoter of the h uman alpha subunit gene. The strongest androgen receptor binding site is located at approximately -101 in the proximal 5'-flanking region. T his steroid receptor binding site overlaps another binding site that d efines one of several contiguous cis-acting regulatory elements requir ed for basal transcriptional activity. Thus, binding of activated andr ogen receptor to this region may block the binding of a requisite tran sacting factor and lead to an attenuation in transcription. We conclud e that this interaction, which occurs directly at the level of the pit uitary, represents one of several physiological avenues through which androgens regulate gonadotropin gene expression.