Differential expression of neutral endopeptidase-24.11 (neprilysin) and endothelin-converting enzyme in human prostate cancer cell lines

Neutral endopeptidase-24.11 (neprilysin; NEP/CD10) is a cell surface metallopeptidase expressed by prostatic epithelial cells that degrades various bioactive peptides including endothelin. Endothelin-converting enzyme (ECE), the key enzyme of endothelin biosynthesis, catalyses the final processing step in the pathway. Neuropeptide substrates of NEP, including endothelin, have been implicated in the growth of androgen-independent prostate cancer. We have surveyed the expression of NEP and ECE in a range of prostate cancer cell lines. Western analysis reveals that ECE-1 is expressed abundantly in all the malignant cell lines tested, except for LNCaP. In contrast, LNCaP cells express high levels of NEP, while NEP was not detected in PC-3, DU145 and other metastatic cell lines that were tested. Of the normal immortalized prostate epithelial cell lines, PNT1a shows equivalent amounts of NEP and ECE. PNT2-C2 shows poor NEP expression but an abundance of ECE. P4E6, by comparison, has low levels of both ECE and NEP. These differences in expression may render these cell lines useful in experimental models for future study. Benign prostatic hyperplasia primary epithelial cells express much higher levels of NEP than malignant primary epithelial cells, but neither show ECE expression. On the other hand, surrounding stromal cell populations have detectable ECE levels. An absence of ECE in malignant and benign prostatic hyperplasia cells of primary epithelial origin suggests an important role for stromal interaction and paracrine production of ECE within the host. The upregulation of ECE expression in metastatic cells in culture may be indicative of its role in metastatic progression. A differential profile of ECE and NEP could contribute to an abundance of mitogenic peptides aiding the progression of androgen-independent prostate cancer.