Acute regulation of the bovine gene for the steroidogenic acute regulatoryprotein in ovarian theca and adrenocortical cells

Upregulation of the steroidogenic acute regulatory protein (StAR) is implic ated in the rapid synthesis and secretion of steroidogenic cells to produce steroids in response to stimulation by trophic hormones of the gonadal and stress axes. In the present study, we have assessed the kinetics of both S tAR gene transcription and protein biosynthesis in primary cell cultures of bovine adrenocortical and ovarian theca cells, under conditions of acute s timulation by corticotrophin (ACTH) and luteinizing hormone (LH), respectiv ely. In both cell systems, detectable upregulation of StAR gene transcripti on occurred within 1-2 h, reaching maxima at 4 h (theca cells) or 6 h (adre nocortical cells), mRNA levels returned rapidly to baseline, by 12 h or 24 h, respectively. Specific StAR protein levels were assessed by western blot ting using a novel antibody raised against a bovine StAR peptide, and showe d a similar fast upregulation, albeit delayed by 1-2 h compared with the mR NA. The response of the cultured theca cells was more acute than that of th e adrenocortical cells, possibly reflecting the propensity of the LH recept or to desensitize rapidly, unlike the ACTH receptor. The primary bovine the ca cell cultures were also used for fully homologous transfection studies u sing various deletion promoter-reporter constructs of the bovine StAR gene. Kinetic analysis of the results indicated that the acute transcriptional r esponse resides within the proximal (- 315 bp) promoter region, which inclu des two putative responsive elements for the steroidogenic factor-1. More d istal promoter regions may be involved in modulating the specificity of exp ression by combining enhancer and inhibitory functions.