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 microM) 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 microM. 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.