Genomic cloning and sequence analyses of the bovine alpha-, beta A- and beta B-inhibin/activin genes. Identification of transcription factor AP-2-binding sites in the 5'-flanking regions by DNase I footprinting

Abstract

Inhibins and activins are dimeric peptide hormones that regulate the circulating levels of follicle-stimulating hormone (FSH). In turn, FSH stimulates inhibin gene expression in the ovarian follicle; studies to date suggest that this effect is mediated by cAMP and that a cAMP-responsive element, identified in the 5'-flanking region of the alpha-inhibin gene, at least partially effects this response. To explore further the transcriptional regulation of the inhibin/activin genes, we have isolated and sequenced the 5'-flanking regions of the bovine alpha-, beta A- and beta B-inhibin/activin subunit genes and have analysed these regions by primer-extension analysis and DNase I footprinting with the transcription factor AP-2. Analyses indicated that all three gene promoter regions have a number of AP-2-binding sites that are resistant to competition by poly(dI-dC), suggesting that cAMP may control the inhibin/activin ratio by operating through alternative signal-transduction pathways or that inhibin/activin gene expression may be controlled by signals operating through the protein kinase C pathway. A comparison of the DNA sequences protected by AP-2 against DNase I digestion revealed a consensus AP-2-binding site of 5'-GSCCCDSS-3', where S represents a base pairing involving three (C or G) hydrogen bonds and D represents any base other than C. The nucleotide sequences of the bovine beta-subunit structural genes also are reported.