Human prostatic acid phosphatase in prostate carcinogenesis

Human prostatic acid phosphatase (PAcP) is classically known as a prostate epithelium-specific differentiation antigen and was used as a surrogate marker for detecting prostate cancer (PCa) and monitoring its progression until the availability of prostate-specific antigen. Mature human PAcP protein is a 100 kDa glycoprotein containing two subunits of approximately 50 kDa each. Classically, two forms of human PAcP proteins have been identified: the cellular form (cPAcP) and the secretory form (sPAcP). Recent studies reveal the existence of a transmembrane form (TM-PAcP). While the function of sPAcP and TM-PAcP in human remains under further investigation, cPAcP functions as a neutral protein tyrosine phosphatase in PCa cells and dephosphorylates human epidermal growth factor receptor-2 (HER-2/ErbB-2/Neu) resulting in decreased cell growth as well as tumor suppression. Clinically, cPAcP levels decrease in PCa tissues and correlate with PCa progression, despite elevated levels of sPAcP in circulation. Data from xenograft animal models validate the tumor suppressor activity of cPAcP in prostate carcinomas. Further, activation of ErbB-2 upon knockdown of cPAcP expression results in a castration-resistant phenotype. Expression of PAcP is regulated by different factors in human PCa cells. PAcP is also a useful immunogen in PCa immunotherapy. Further investigation of the regulatory mechanism of cPAcP expression will likely provide valuable insights into novel PCa therapy.