Complex formation between human prostate-specific antigen and protease inhibitors in mouse plasma

• Published in: The Prostate 2010-04, Vol.70 (5), p.482-490
• Main Authors: Hekim, Can, Riipi, Tero, Zhu, Lei, Laakkonen, Pirjo, Stenman, Ulf-Håkan, Koistinen, Hannu
• Format: Article
• Language: English
• Subjects: alpha 1-Antichymotrypsin - metabolism; alpha 1-Antitrypsin - metabolism; alpha-Macroglobulins - metabolism; Amino Acid Sequence; Animals; antitrypsin; Biological and medical sciences; Cell Line, Tumor; Female; Gynecology. Andrology. Obstetrics; Humans; Medical sciences; Mice; Molecular Sequence Data; Neoplasm Transplantation; Nephrology. Urinary tract diseases; Prostate-Specific Antigen - metabolism; Protease Inhibitors - metabolism; serpin; Transplantation, Heterologous; xenograft tumor
• ISSN: 0270-4137; 1097-0045
• DOI: 10.1002/pros.21082

BACKGROUND When secreted from the prostate, most of prostate‐specific antigen (PSA) is free and enzymatically active. Upon reaching circulation, active PSA is inactivated by complex formation with protease inhibitors. To justify the use of mouse models for evaluation of the function of PSA and for studies on therapeutic modalities based on modulation of PSA activity, it is important to know whether PSA complexation is similar in mouse and man. METHODS To characterize the circulating forms of PSA in mouse, we used subcutaneous LNCaP and 22RV1 human prostate cancer cell xenograft tumor models. We also added PSA directly to mouse serum. Free and total PSA were measured by immunoassay, and PSA complexes were extracted by immunopurification followed by SDS–PAGE, in‐gel trypsin digestion and identification of signature peptides by mass spectrometry. RESULTS In mice bearing xenograft tumors, 68% of the immunoreactive PSA occurred in complex, and when added to mouse serum, over 70% of PSA forms complexes that comprises α2‐macroglobulin and members of the α1‐antitrypsin (AAT) family. CONCLUSION In mouse plasma, PSA forms complexes similar to those in man, but the major immunoreactive complex contains AAT rather than α1‐antichymotrypsin, which is the main complex forming serpin in man. The complex formation of PSA produced by xenograft tumor models in mice is similar to that of human prostate tumors with respect to the complexation of PSA. Prostate 70: 482–490, 2010. © 2009 Wiley‐Liss, Inc.