Complex formation between human prostate-specific antigen and protease inhibitors in mouse plasma.
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 alpha(2)-macroglobulin and members of the alpha(1)-antitrypsin (AAT) family.


CONCLUSIONS
In mouse plasma, PSA forms complexes similar to those in man, but the major immunoreactive complex contains AAT rather than alpha(1)-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.
Hekim
Can
C
Department of Clinical Chemistry, Biomedicum Helsinki, University of Helsinki, Helsinki University Central Hospital, Helsinki, Finland.
Riipi
Tero
T
Zhu
Lei
L
Laakkonen
Pirjo
P
Stenman
Ulf-Håkan
UH
Koistinen
Hannu
H
D000595:Amino Acid Sequence; D000818:Animals; D045744:Cell Line, Tumor; D005260:Female; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D009368:Neoplasm Transplantation; D017430:Prostate-Specific Antigen / Q000378:metabolism*; D011480:Protease Inhibitors / Q000378:metabolism*; D014183:Transplantation, Heterologous; D000514:alpha 1-Antichymotrypsin / Q000378:metabolism; D000515:alpha 1-Antitrypsin / Q000378:metabolism; D000511:alpha-Macroglobulins / Q000378:metabolism
D011480:Protease Inhibitors; D000514:alpha 1-Antichymotrypsin; D000515:alpha 1-Antitrypsin; D000511:alpha-Macroglobulins; D017430:Prostate-Specific Antigen