EXPRESSION OF P75(NTR) IN A HUMAN PROSTATE EPITHELIAL TUMOR-CELL LINEREDUCES NERVE GROWTH FACTOR-INDUCED CELL-GROWTH BY ACTIVATION OF PROGRAMMED CELL-DEATH

Epithelial expression of the 75-kDa low-affinity neurotrophin receptor (p75(NTR)) is inversely associated with the malignant progression of the human prostate. To elucidate the function of p75(NTR) in the prost ate, the human prostate epithelial tumor cell line TSU-pr1, which does not express p75(NTR), was Stably and transiently transfected with the cDNA for the receptor. The stably transfected cells were assessed for levels of p75(NTR) expression and categorized into low, intermediate, and high receptor-expressing clones by immunocytochemical and immunob lot analyses. Incorporation of [H-3]thymidine was used to assess nerve growth factor (NGF)-induced changes in cell proliferation. TSU-pr1 ep ithelial cells transfected with a neomycin-resistance vector alone dem onstrated a dose-dependent increase in the rate of NGF-stimulated [H-3 ]thymidine uptake. Expression of p75(NTR) decreased the dose-dependent NGF-mediated proliferation of the TSU-pr1 prostate epithelial cells. The greater the degree of expression of p75(NTR) in the transfected cl ones, the less the stimulatory effect of exogenous NGF on cell prolife ration. Furthermore, the ratio of p75(NTR) to tropomyosin receptor kin ase for each clone was inversely correlated with the ability of NGF to stimulate growth of the TSU-pr1 transfectants. To determine whether p 75(NTR)-mediated growth inhibition of prostate epithelia occurs by ind uction of programmed cell death, transiently transfected clones were a nalyzed by an in situ DNA nick-translation assay. NGF deprivation and anti-NGF treatment of transiently transfected TSU-pr1 cells significan tly increased the proportion of epithelial cells undergoing programmed cell death by approximately fourfold above control levels. Conversely , addition of NGF was able to rescue p75(NTR)-expressing clones from u ndergoing programmed cell death at levels not significantly different from those of mock-transfected clones. These results demonstrate that p75(NTR) is a negative regulator of human prostate epithelial cell gro wth by induction of programmed cell death. Hence, loss of p75(NTR) exp ression in human prostate epithelia eliminates a growth-inhibitory pat hway thereby contributing to the malignant progression of the prostate . (C) 1998 Wiley-Liss, Inc.