17-ALPHA-HYDROXYLASE GENE-EXPRESSION IN THE BOVINE OVARY - MECHANISMSREGULATING EXPRESSION DIFFER FROM THOSE IN ADRENAL-CELLS

17 alpha-Hydroxylase cytochrome P450 (P450(17 alpha)) is the enzyme wh ich synthesizes C-19 steroids in a two-step reaction in which 17 alpha -OH pregnenolone is an intermediate. In the bovine and human adult fem ale, 17 alpha-hydroxylase is expressed in adrenocortical cells where 1 7 alpha-OH pregnenolone and 17 alpha-OH progesterone are precursors of cortisol, and in theca cells of the ovary where these intermediates a re precursors of C-19 steroids. In both adrenal cortex and theca, 17 a lpha-hydroxylase gene expression is stimulated by cyclic AMP (cAMP). T he aim of this study was to determine the mechanism regulating 17 alph a-hydroxylase gene expression in the bovine ovary. Our results indicat e that the bovine 17 alpha-hydroxylase gene is regulated in a tissue-s pecific fashion. Primer extension and S1 nuclease protection assays re veal that the start site of transcription in the theca is identical to that in the adrenal. Transfection studies employing beta-globin repor ter gene constructs fused to successive deletions of the 5' regulatory region of the bovine 17 alpha-hydroxylase gene indicate that sequence s between -80 and -37 basepairs (bp) (CRS2) confer cAMP-regulated tran scription in bovine theca cells in culture. These results are in contr ast to similar studies conducted in bovine adrenocortical cells, which indicate that the major cAMP response element (referred to as CRS1) i s 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 responsivenes s in other steroidogenic P450 genes, cannot by itself confer cAMP-regu lated 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 i n the bovine 17 alpha-hydroxylase gene. Copyright (C) 1996 Elsevier Sc ience Ltd.