Prostatic epithelium inhibiting factor (PEIF): organ specificity and production by prostatic fibroblasts

The effects of prostate fibroblast conditioned medium on two prostate epithelial cell lines (PC-3, LNCaP) and on two non-prostatic cell lines (MCF-7, K562) was investigated. As prostate fibroblast conditioned medium exerts its main effect on DNA synthesis, 3H thymidine incorporation was monitored to measure factor activity. Conditioned media of all prostatic fibroblast lines investigated were inhibitory for PC-3, LNCaP and MCF-7. Conditioned medium of prostatic fibroblasts was clearly stimulatory for K562. Prostate specificity of production of PEIF was demonstrated by the fact that conditioned medium from skin fibroblasts proved to be stimulatory for PC-3. Inhibitory activity from conditioned medium as well as from a BPH homogenate was precipitated by 33-67% ammonium sulfate. These partly purified fractions were respectively five and ten times as active as "crude" conditioned medium. The physical nature of PEIF (protein or macroglycolipid) as well as the possible function (as a signal messenger between stroma and epithelium) is discussed.