Effect of vanadate on protein phosphorylation and on acid phosphatase activity in the canine prostate

To evaluate the possible role of intracellular phosphatases in the local regulation of prostatic functions, the effect of sodium orthovanadate (VO 4), an inhibitor of phosphotyrosyl protein phosphatases, was studied on both protein phosphorylation and acid phosphatase activity. Secretory and non-secretory epithelial cells were isolated from normal and metaplastic prostates and incubated with [ 32P]phosphate in the presence and in the absence of VO 4; the phosphoproteins were separated by electrophoresis and the gels were either directly submitted to autoradiography or after an alkali treatment to reveal those proteins enriched in phosphotyrosine. Prior to alkali treatment, several phosphoproteins were evidenced and in less than half of the cell preparations a slight increase in labeling intensity under vanadate ( 85%) in all cell types. Tartrate was a more potent inhibitor of both PAP and p-Tyr phosphatase activities measured with cells from normal glands ( > 80%) as compared to those of cells from metaplastic prostates (35–60%). Thus, vanadate inhibits PAP and p-Tyr phosphatases in prostatic cells and enhances the level of specific phosphoproteins, namely among alkali-resistant phosphoproteins. It is propose