The autocrine effect of activin A on human ovarian clear cell adenocarcinoma cells

The functions of activin, a member of TGF-β superfamily, in ovarian clear cell adenocarcinoma remain unsolved, although we recently found that inhibin βA-subunit, activin A, activin receptor type IA, type IB, type IIA, type IIB, Smad2, Smad3 and Smad4 were localized in tumor cells of the ovarian clear cell adenocarcinoma tissue by immunohistochemistry. In the present study, in order to investigate the role of activin concerning cell growth in ovarian clear cell adenocarcinoma cells, we determined the production of activin A and inhibin A, and the expression of activin receptors and Smads using the human ovarian clear cell adenocarcinoma cell line JHOC-5. Moreover, we examined the effects of activin A on the activation of activin signaling pathway and on the proliferation in JHOC-5 cells. We detected a measurable amount of activin A in the culture medium of JHOC-5 cells, although inhibin A was not detected. The expression of activin receptor type IA, IB, IIA, IIB, Smad2, Smad3 and Smad4 was observed in JHOC-5 cells. Activin A induced a significant increase in proliferation of JHOC-5 cells compared with the untreated control. On the other hand, activin A did not affect the growth of JHOC-5 cells and no statistically significant difference was observed in the presence of follistatin which is a specific binding protein of activin. Phosphorylated Smad2, an activated form of Smad2, was detected both in treated JHOC-5 cells and in untreated cells by activin A. Activin A significantly increased the expression of phosphorylated Smad2 in JHOC-5 cells. Therefore, it is possible that activin has autocrine roles in tumor growth of ovarian clear cell adenocarcinoma cells.