Tyrosine Phosphorylation of a 185 kDa Phosphoprotein (pp185) Inversely Correlates with the Cellular Activity of Human Prostatic Acid Phosphatase

Abstract

Human prostatic acid phosphatase (PAcP), a prostate epithelium-specific differentiation antigen, was determined to exhibit the endogenous protein tyrosine phosphatase activity. We investigated the phosphoprotein(s) that might be dephosphorylated by PAcP in human prostate carcinoma cells. Several lines of evidence were presented to show that the tyrosine phosphorylation level of a 185 kDa phosphoprotein (pp185) is negatively correlated with the cellular activity of PAcP. (i) In DU145, PC-3 and high passaged LNCaP prostate carcinoma cells that have no or low PAcP expression, the phosphotyrosine (p-tyr) level of pp185 was higher than that in low passaged LNCaP cells that express an endogenous PAcP. (ii) In LNCaP cells grown in the presence of L(+)-tartrate, an inhibitor of PAcP, the tyrosine phosphorylation of pp185 was increased. (iii) Mediated by Lipofectin, a cationic liposome, the incorporation of purified PAcP protein into DU145 cells resulted in the decreased phosphorylation of pp185. Thus, the results taken collectively demonstrated that the p-tyr level of pp185 is inversely correlated with the cellular activity of PAcP and indicated that the pp185 may be a putative substrate of PAcP in prostate carcinoma cells.