DIFFERENTIAL-EFFECTS OF TRANSFORMING GROWTH-FACTOR TYPE-BETA ON THE GROWTH AND FUNCTION OF ADRENOCORTICAL-CELLS INVITRO

Transforming growth factor type .beta. (TGF-.beta.) suppresses basal as well as corticoptropin (ACTH)-stimulated steroid formation by bovine adrenocortical cells in culture. The effect is dose dependent and is not accompanied by any change in adrenocortical cell growth. The minimum effective dose of TGF-.beta. is 4 .times. 10-13M (10 pg/ml), and maximal inhibition is observed at a concentration of 4 .times. 10-11 M (1 ng/ml). At 16- to 20-hr incubation with TGF-.beta. is required to decrease steroidogenesis, and 12-18 hr are required before cells treated with TGF-.beta. recover complete responsiveness to corticotropin. Increases in cAMP mediated by corticotropin, forskolin, and isobutylmethylxanthine are not modified by the addition of TGF-.beta.; thus adenylate cyclase activity is unaffected by TGF-.beta.. Although TGF-.beta. inhibits the formation of all of the .DELTA.4-steroids measured (including cortisol, corticosterone, aldosterone, and androstenedione), its effect can be completely reversed by the addition of 25-hydroxycholesterol, pregnenolone, or progesterone to the cells. In contrast, the addition of low density lipoprotein has no effect suggesting that TGF-.beta. targets the conversion of cholesterol precursors to cholesterol. The results demonstrate a highly potent effect of TGF-.beta. on the differentiated function of the adrenocortical cell. The inhibition of steroidogenesis can be dissociated from any effect on cell proliferation and it occurs distal to the formation of cAMP but proximal to the formation of cholesterol. The results suggest that in the adrenal, TGF-.beta. or TGF-.beta.-like proteins may be playing an important role in modifying the differentiated state of the adrenocortical cell.