Differential implication of StAR and P450c17 in TGFbeta1-induced decrease of adrenocortical steroidogenesis

In primary cultures of bovine adrenocortical fasciculata cells, we have previously identified two targets of TGFbeta action: StAR and P450c17. Since it is well known that adrenocortical cells tend to dedifferentiate as soon as they are placed in culture, we investigated the regulation of StAR and P450c17 expression by TGFbeta1 at different times of primary culture. On day 1, TGFbeta1 decreased the expression of basal levels of both genes. However, in the presence of ACTH, it down-regulated StAR mRNA levels but did not modify P450c17 mRNA levels. On day 4, P450c17 and StAR mRNAs were down-regulated by TGFbeta1, both in the absence and in the presence of ACTH. These observations indicate that StAR is likely to represent the major in vivo target of TGFbeta1 action in the adrenal cortex.