R. Ivell et al., Acute regulation of the bovine gene for the steroidogenic acute regulatoryprotein in ovarian theca and adrenocortical cells, J MOL ENDOC, 24(1), 2000, pp. 109-118
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.