17 alpha-Hydroxylase gene expression in the bovine ovary: Mechanisms regulating expression differ from those in adrenal cells

17 alpha-Hydroxylase cytochrome P450 (P450(17 alpha)) is the enzyme which synthesizes C-19 steroids in a two-step reaction in which 17 alpha-OH pregnenolone is an intermediate. In the bovine and human adult female, 17 alpha-hydroxylase is expressed in adrenocortical cells where 17 alpha-OH pregnenolone and 17 alpha-OH progesterone are precursors of cortisol, and in theca cells of the ovary where these intermediates are precursors of C-19 steroids. In both adrenal cortex and theca, 17 alpha-hydroxylase gene expression is stimulated by cyclic AMP (cAMP). The aim of this study was to determine the mechanism regulating 17 alpha-hydroxylase gene expression in the bovine ovary. Our results indicate that the bovine 17 alpha-hydroxylase gene is regulated in a tissue-specific fashion. Primer extension and S1 nuclease protection assays reveal that the start site of transcription in the theca is identical to that in the adrenal. Transfection studies employing beta-globin reporter gene constructs fused to successive deletions of the 5' regulatory region of the bovine 17 alpha-hydroxylase gene indicate that sequences between -80 and -37 basepairs (bp) (CRS2) confer cAMP-regulated transcription in bovine theca cells in culture. These results are in contrast to similar studies conducted in bovine adrenocortical cells, which indicate that the major cAMP response element (referred to as CRS1) is located at -243 to -225 bp. The Ad4 element (AGGTCA, -42 to -37 bp) within CRS2, which has been shown to be involved in cAMP responsiveness in other steroidogenic P450 genes, cannot by itself confer cAMP-regulated reporter gene expression in bovine cells. These results indicate that in the cow, 17 alpha-hydroxylase gene expression is regulated in a tissue-specific fashion, and that this regulation may be conferred, at least in part, by the use of tissue-specific cis-acting elements in the bovine 17 alpha-hydroxylase gene. Copyright (C) 1996 Elsevier Science Ltd.