Aminopeptidase N regulated by zinc in human prostate participates in tumor cell invasion

Aminopeptidase N (AP‐N) degrades collagen type IV and is proposed to play a role in tumor invasion. However, the precise functions of AP‐N in tumor cells and the relationship of AP‐N to prostate cancer remains unclear. In our study, we examined a possible role for zinc in the regulation of AP‐N enzymatic activity in relation to tumor cell invasion in human prostate. AP‐N purified from human prostate was irreversibly inhibited by low concentrations of zinc (Ki = 11.2 μM) and bestatin. AP‐N, which has zinc in the active center, was also inhibited by the chelating agents, EDTA, o‐phenanthroline and EGTA. EDTA was shown to remove zinc from the enzyme. When the effects of zinc and bestatin on invasion of PC‐3 cells were investigated in vitro using a Transwell cell‐culture chamber, zinc and bestatin effectively suppressed cell invasion into Matrigel at the concentration range of 50–100 μM. These results strongly suggest that the suppression of PC‐3 cell invasion by zinc is based on the inhibition of AP‐N activity by zinc. We also evaluated the expression of AP‐N to investigate the relationship with the progression of prostate disease in human cancerous prostate. AP‐N was found to be located at the cytoplasmic membranes of prostate gland epithelial cells and to be expressed more in prostate cancer, while the expression of prostate‐specific antigen (PSA), which is a useful marker for prostate cancer, was shown in normal and cancer tissues, suggesting that AP‐N is potentially a good histological marker of prostate cancer. Thus, highly expressed AP‐N in human cancerous prostate probably plays an important role in the invasion and metastasis of prostate cancer cells. © 2001 Wiley‐Liss, Inc.