Activin and follistatin (FS) messenger RNA and protein are expressed and localized to human prostate tissue from men with high grade cancer and to human prostate tumor cell lines LNCaP, DU145, and PC3. Although activin A induces apoptosis and inhibits cell proliferation in LNCaP cells, PC3 cells are insensitive to the effect of exogenous addition of activin A. The results of this study show that activin A and FS are produced and can be measured by specific enzyme-linked immunosorbent assays in

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... C3 cells and media but are not detectable in LNCaP cells. Over 10 days in culture, the production of activin A by PC3 cells declines and is inversely correlated (r ϭ Ϫ0.779) to FS288 production, which steadily increases and is signif- Materials and Methods Prostate tumor cell lines Human prostate tumor cell lines PC3 and LNCaP were obtained from American Type Culture Collection (Rockville, MD). Cell lines were routinely cultured in DMEM (Life Technologies, Inc., Grand Island, NY) with 10% heat inactivated FCS (CSL Limited, Parkville, Victoria, Australia) and antibiotics (100 UI/ml penicillin and 10 g/ml streptomycin; CSL Limited) in 75 cm 2 culture flasks (Falcon; Becton Dickinson and Co., Labware, Franklin Lakes, NJ) at 37 C in a humidified atmosphere of 5%