Biochemical Characterization and Immunolocalization of Prostate-specific Antigen in Human Term Placenta

Abstract

Prostate-specific antigen (PSA) has been biochemically and molecularly characterized as a 33-kDa androgen-dependent glycoprotein related to the kallikrein family of serine proteases, with chymotrypsin- and kallikrein-like enzymatic activity (1)(2)(3)(4). PSA has long been thought to be produced exclusively by the prostate cells and has been used as a tumor marker for diagnosis and monitoring of prostate cancer (5)(6). Recently, it was found in several nonprostatic tissues and body fluids (7), although no physiologic role of PSA is known in these tissues (8). Immunoreactivity and gene expression studies have characterized human PSA as a steroid hormone-regulated serine protease (9)(10)(11)(12). Considering the studies carried out in amniotic fluids and in healthy endometrium (13)(14)(15), we undertook the present study on PSA characterization and immunolocalization in the term placentas collected from five women (ages, 25–37 years) undergoing routine deliveries (40 ± 2 weeks). After the membranes were stripped, each placenta was weighed and placed on ice in a sterile solution of 9 g/L NaCl and 5 mmol/L glucose, transported to the laboratory, and processed within 30 min. Samples of entire placentas were minced and homogenized as described (16). After sonication, the lysates were centrifuged at 9000 g at 4 °C for 30 min, and the supernatants were stored at −80 °C until analysis. n-Butanol-extracted fractions were prepared from cytosolic extracts, according to a previously described method (17). Blood was also drawn from healthy pregnant women (n = 15; ages, 23–38 years); after the blood clotted, the sample was centrifuged at 500 g for 10 min and the serum stored at −30 °C until assay. Free and total PSA concentrations were determined in serum and cytosolic extracts of placentas, using an automated enzyme immunoassay with a detection …