Regulation by adrenocorticotropin (ACTH), angiotensin II, transforming growth factor-β, and insulin-like growth factor I of bovine adrenal cell steroidogenic capacity and expression of ACTH receptor, steroidogenic acute regulatory protein, cytochrome P450c17, and 3β-hydroxysteroid dehydrogenase

The purpose of this study was to evaluate the time-course effect of a 36-h treatment with ACTH(10(-s) M), transforming growth factor-pi (TGF beta 1; 10(-10) M), angiotensin II (AngII; 10(-7) M), and insulin-like growth factor I (IGF-I; 10(-8) M) on the steroidogenic capacity of bovine adrenocortical cells (BAC) and on messenger RNA (mRNA) levels of ACTH receptor, cytochrome P450c17, 3 beta-hydroxysteroid dehydrogenase (3 beta HSD), steroidogenic acute regulatory protein (StAR), and StAR protein. ACTH and IGF-I enhanced, in a time-dependent manner, the acute 2-h ACTH-induced cortisol production, whereas TGF beta 1 and AngII markedly reduced it. ACTH, IGF-I, and AngII increased ACTH receptor mRNA, but the opposite was observed after TGF beta 1 treatment. ACTH and IGF-I increased P450c17 and 3 beta HSD mRNAs, whereas AngII and TGF beta 1 had the opposite effects. However, the effects of the four peptides on ACTH-induced cortisol production appeared before any significant alterations of the mRNA levels occurred. The most marked and rapid effect of the four peptides was on StAR mRNA. The stimulatory effect of ACTH was seen within 1.5 h, peaked at 4-6 h, and declined thereafter, but at the end of the 36-h pretreatment, the levels of StAR mRNA and protein were higher than those in control cells. IGF-I also enhanced StAR mRNA levels within 1.5 h, and these level remained fairly constant. The effects of AngII on StAR mRNA expression were biphasic, with a peak within 1.5-3 h, followed by a rapid decline to almost undetectable levels of both mRNA and protein. TGF beta 1 had no significant effect during the first 3 h, but thereafter StAR mRNA declined, and at the end of the experiment the StAR mRNA and protein were almost undetectable. Similar results were observed when cells were treated with ACTH plus TGF beta 1. A 2-h acute ACTH stimulation at the end of the 36-h pretreatment caused a higher increase in StAR mRNA and protein in ACTH- or IGF-I-pretreated cells than in control cells, which, in turn, had higher levels than cells pretreated with TGF beta 1, ACTH plus TGF beta 1, or AngII. These results and the fact that the stimulatory (IGF-I) or inhibitory (AngII and TGF beta 1) effects on ACTH-induced cortisol production were more pronounced than those on the ability of cells to transform pregnenolone into cortisol strongly suggest that regulation of StAR expression is one of the main factors, but not the only one, involved in the positive (IGF-I) or negative (TGF beta 1 and AngII) regulation of BAC for ACTH steroidogenic responsiveness. A high correlation between steady state mRNA level and acute ACTH-induced cortisol production favors this conclusion.