Expression, Localization and Activity of Neutral Endopeptidase in Cultured Cells of Benign Prostatic Hyperplasia and Prostate Cancer

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Abstract
Purpose: Neutral endopeptidase is a cell surface enzyme that cleaves and inactivates neuropeptides. Neutral endopeptidase is expressed by prostatic epithelial cells and is thought to have a key role in the growth of androgen independent prostate cancer. In contrast to the encouraging data dealing with neutral endopeptidase and prostate cancer progression, only few studies are available of the significance of neutral endopeptidase in prostatic stromal cells and benign prostatic hyperplasia (BPH). We report the expression and activity of neutral endopeptidase in human prostatic stromal cells. Materials and Methods: We recently established and characterized human prostatic stromal cells from BPH tissue. Reverse transcriptase-polymerase chain reaction, Western blot experiments and immunohistochemistry were performed to investigate the expression levels of neutral endopeptidase and show the cellular localization of the enzyme in these cells. Enzymatic neutral endopeptidase activity was evaluated using a colorimetric assay in nonstimulated cells, and after androgen and estrogen application. Results: Stromal BPH cells showed strong expression of the neutral endopeptidase messenger RNA and protein, equaling the neutral endopeptidase expression level in prostate cancer cells. The neutral endopeptidase protein located in the plasma membrane of the cells showed a mean enzymatic activity plus or minus standard deviation of 75% ± 2.5% compared with LNCaP prostate cancer cells. Interestingly enzymatic activity of the membrane bound neutral endopeptidase in stromal cells was not regulated by androgen and estrogen. Conclusions: These data suggest that neutral endopeptidase is expressed by prostatic stromal cells. In addition to its role in the progression of prostate cancer, it may also be involved in regulatory processes in the stroma, namely the degradation of neuropeptides released from prostatic neuroendocrine cells.