Biochemical characteristics and biological profile of prostate specific antigen (PSA)

Since its identification in seminai fluid in 1971, a tot more knowledge has been obtained about the biology and expression of prostate specific antigen (PSA). PSA is a glycoprotein consisting of 93% aminoacids and 7% carbohydrates with a molecular weight of about 30000 dalton. Functionally and structurally PSA is a kallikrein-like serine protease and its physiological role is the degradation of the major proteins of the seminal coagulum (semenogelin I and II, fibronectin) leading to semen liquefaction. The PSA gene is located on the 13q region of chromosome 19 and has a high degree of homology (more than 80%) with the gene of human glandular kallikrein (hGK1). PSA production and expression are preferentially but not exclusively associated with the normal, benign hyperplastic and cancerous tissues of the prostate. In fact, it has been demonstrated that PSA is also present in the accessory male sex glands of Cowper, Littre and Morgagni and other extra-prostatic neoplasms, such as salivary gland tumours and breast cancer. Many factors may influence PSA synthesis and production and among them the most important are androgen and growth factor stimulation. Advances have recently been made on the molecular isoforms of PSA. In the seminai fluid PSA seems partially bound to a serpine (protein C inhibitor), whilst in the serum PSA is predominantly associated to α-antichymotrypsin (ACT) and in low quantity to α2-macroglobulin (α2M). All these findings will have implications on clinical applications of PSA as a tumour marker for prostate cancer.