Differential Glycosylation of Cellular Prostate Specific Antigen and the Regulatory Mechanism of Its Secretion

Although serum prostate specific antigen (PSA), derived from cellular PSA through secretion, is widely used as a marker for prostate cancer (CAP), the exact regulatory mechanism of its secretion is not fully understood. To explore the regulation of serum PSA concentration, we examined whether the glycosylation state of cellular PSA might be associated with its secretion, thus determining its serum concentration. Blood and prostate tissue specimens were obtained from patients undergoing radical prostatectomy. Following preparation of cell extracts by tissue homogenization, the concentrations of serum and cellular PSA were determined using the Tandem-E PSA kit. The extent of cellular PSA glycosylation was then assessed by Western blot and affinoblott analyses. Neither serum nor cellular PSA concentrations correlated with the Gleason scores. Similarly, no direct relation between serum and cellular PSA levels was observed. However, the Western blots showed that the cellular PSA proteins were converted to the deglycosylated forms with glycosidase treatment, indicating differential glycosylation of cellular PSA. Affinoblotting further revealed that the various amounts of PSA glycosylation were associated wtih the serum PSA levels, with an inverse correlation between serum PSA and cellular PSA glycosylation: the greater the PSA glycosylation, the lower the serum PSA, and vice versa. The present study demonstrates that cellular PSAs in CAP specimens are differentially glycosylated and that such difference correlates well with the serum PSA concentration. Therefore, the concentrations of serum PSA appear to depend in part on a selective secretion of cellular PSA, which could be regulated primarily by its glycosylation state.