Activin-A, Inhibin and Transforming Growth Factor-β Modulate Growth of Two Gonadal Cell Lines*

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Abstract
The proliferative and differentiating effects of the gonadal hormones inhibin and activin-A were examined on cell lines derived from the ovary and testis. Activin-A was found to inhibit the growth of CHO-K1 (Chinese hamster ovary) cells in culture, with an IC50 of 3 ng/ml. The maximal response (50% inhibition) required 3 days of incubation in the presence of 40 ng/ml activin-A, and the inhibitory effect was accompanied by morphological changes. Inhibin (10 ng/ml) partially blocked the inhibition of growth by activin. Transforming growth factor-.beta. (TGF.beta.), which is structurally related to activin and inhibin, was a very potent inhibitor of the proliferation of CHO-K1 cells, with an IC50 of 0.2 ng/ml and a maximal effect (70% inhibition) at 2 ng/ml. The combination of high concentrations of both TGF.beta. and activin-A did not result in a greater inhibitory effect than that observed with TGF.beta. alone, suggesting an overlapping step in the mechanism of action for both factors. In contrast to the results with CHO-K1 cells, differential effects of activin-A and TGF.beta. were observed in R2C (rat Leydig cells testicular tumor) cells. Activin-A had only a slight effect on proliferation over a 4-day incubation, but inhibited progesterone accumulation in a concentration-dependent fashion within 12 h TGF.beta., on the other hand, was a potent inhibitor of both growth and steroidogenesis in R2C cells. These studies suggest that activin-A and inhibin may regulate proliferation as well as functions of gonadal cells.