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Effects of transforming growth factor beta on ovine adrenocortical cells
W E Rainey1, I Viard, J I Mason
1INSERM U.307, Hôpital Debrousse, Lyon, France.
Abstract:
Transforming growth factor beta (TGF beta) is a potent regulator of steroidogenic cell function. However, the mechanisms of the effects are not well understood. We studied the actions of TGF beta on primary cultures of ovine adrenocortical (OAC) cells. OAC cells had high affinity receptors for TGF beta (KD congruent to 7.6 +/- 1.5 X 16(-11) M). In addition, TGF beta inhibited the following markers of adrenocortical function: (1) ACTH, cholera toxin and forskolin acute stimulation of cAMP and steroid production; (2) the acute 8-bromo-cAMP stimulation of corticosteroid and pregnenolone production; and (3) the activity and amount of P-450 17 alpha-hydroxylase protein as well as activities of 11 beta- and 21-hydroxylases. The inhibitory effects of TGF beta on ACTH-induced cAMP and steroid production were time (half inhibition at 6 and 3 h respectively) and dose dependent (ID50 congruent to 10(-12) M). From these data we concluded that TGF beta acted rapidly on sites of OAC cell acute responses to stimulation by ACTH before and after the production of cAMP. Pregnenolone production in these cells was not inhibited by TGF beta when steroid production was stimulated on the addition of the readily permeable cholesterol derivative, 22 R-hydroxycholesterol. Thus, the rapid effect on OAC cells was manifest by TGF beta action on the utilization of cellular pools of cholesterol for the acute stimulation of steroid formation and not by direct action on the cholesterol side-chain cleavage enzyme. In addition, cells stimulated with ACTH in the absence or presence of lipoproteins (for up to 36 h) were susceptible to the inhibitory action of TGF beta. Taken together, these data amplify the pleiotropic actions of TGF beta on adrenocortical cell function and demonstrate that one acute action of TGF beta is on the utilization of endogenous supplies of cholesterol for steroid production.
Insights
Transforming growth factor beta (TGF-β) rapidly inhibits ovine adrenocortical cell steroidogenesis by affecting cholesterol utilization, not cholesterol side-chain cleavage. This reveals a key mechanism in TGF-β
Area of Science:
- Endocrinology
- Cell Biology
- Biochemistry
Background:
- Transforming growth factor beta (TGF-β) is a key regulator of steroidogenic cells.
- The precise mechanisms underlying TGF-β's effects on steroidogenesis remain unclear.
- Understanding these mechanisms is crucial for comprehending adrenal function.
Purpose of the Study:
- To investigate the specific actions of TGF-β on primary ovine adrenocortical (OAC) cells.
- To elucidate the molecular targets and pathways affected by TGF-β in steroidogenesis.
- To determine the role of TGF-β in regulating cholesterol utilization for steroid production.
Main Methods:
- Primary cultures of ovine adrenocortical (OAC) cells were utilized.
- Cells were treated with TGF-β and various stimulators (ACTH, cholera toxin, forskolin, 8-bromo-cAMP).
- Steroid production, cAMP levels, and specific enzyme activities (P-450 17α-hydroxylase, 11β-hydroxylase, 21-hydroxylase) were measured.
Main Results:
- TGF-β demonstrated high-affinity binding to OAC cells.
- TGF-β significantly inhibited ACTH-, cholera toxin-, and forskolin-stimulated cAMP and steroid production.
- TGF-β reduced P-450 17α-hydroxylase activity and protein, and inhibited 11β- and 21-hydroxylase activities.
- Inhibition occurred rapidly, before or after cAMP production, and was dose-dependent.
- TGF-β did not inhibit pregnenolone production when stimulated by 22R-hydroxycholesterol, indicating action on cholesterol utilization rather than the side-chain cleavage enzyme.
- Cells remained susceptible to TGF-β inhibition even with prolonged ACTH stimulation and lipoprotein presence.
Conclusions:
- TGF-β exerts rapid, pleiotropic inhibitory effects on ovine adrenocortical cell function.
- A primary acute action of TGF-β involves regulating the utilization of endogenous cholesterol for steroid production.
- TGF-β's mechanism of action precedes or occurs post-cAMP production and does not directly target the cholesterol side-chain cleavage enzyme.