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Prostatic acid phosphatase is not a prostate specific target.

Quintero I.B., Araujo C.L., Pulkka A.E., Wirkkala R.S., Herrala A.M., Eskelinen E.-L., Jokitalo E., Hellstroem P.A., Tuominen H.J., Hirvikoski P.P., Vihko P.T.

Prostatic acid phosphatase (PAP) is currently evaluated as a target for vaccine immunotherapy of prostate cancer. This is based on the previous knowledge about secretory PAP and its high prostatic expression. We describe a novel PAP spliced variant mRNA encoding a type I transmembrane (TM) protein with the extracellular NH(2)-terminal phosphatase activity and the COOH-terminal lysosomal targeting signal (YxxPhi). TM-PAP is widely expressed in nonprostatic tissues like brain, kidney, liver, lung, muscle, placenta, salivary gland, spleen, thyroid, and thymus. TM-PAP is also expressed in fibroblast, Schwann, and LNCaP cells, but not in PC-3 cells. In well-differentiated human prostate cancer tissue specimens, the expression of secretory PAP, but not TM-PAP, is significantly decreased. TM-PAP is localized in the plasma membrane-endosomal-lysosomal pathway and is colocalized with the lipid raft marker flotillin-1. No cytosolic PAP is detected. We conclude that the wide expression of TM-PAP in, for instance, neuronal and muscle tissues must be taken into account in the design of PAP-based immunotherapy approaches.

Cancer Res. 67:6549-6554(2007) [PubMed] [Europe PMC]