Prostate-specific antigen and other prostate-derived proteases cleave IGFBP-3, but prostate cancer is not associated with proteolytically cleaved circulating IGFBP-3.
BACKGROUND
Proteolysis of insulin-like growth factor-binding proteins (IGFBPs) may increase IGF-mediated growth stimulation and development of cancer in the organs producing large amounts of proteases, such as the prostate.


METHODS
We studied proteolysis of IGFBP-3 by three prostate-derived proteases, namely prostate specific antigen (PSA), human kallikrein 2 (hK2), and trypsin, and also by native seminal plasma. Cleavage of 125I-IGFBP-3 was studied by SDS-PAGE and autoradiography. We also used two different sandwich-type IGFBP-3 immunoassays, called "intact" and "total" IGFBP-3 assays. These assays differ in their capacity to recognize proteolytically degraded IGFBP-3.


RESULTS
HK2, PSA, and trypsin all cleaved IGFBP-3 at the concentrations normally present in seminal plasma. The IGFBP-3 cleavage by seminal plasma was inhibited by ZnCl2, which strongly inhibits hK2 and PSA, but not by a specific trypsin inhibitor. The IGFBP-3 fragments resulting from proteolytic cleavage by PSA, hK2, or trypsin were undetectable in the "intact IGFBP-3 assay," whereas the "total IGFBP-3 assay" also detected the proteolytic fragments. No increased fragmentation of IGFBP-3 was found in serum of 659 men with elevated PSA concentrations, of whom 178 had a proven prostate cancer. Furthermore, the IGFBP-3 levels were not associated with the PSA concentrations.


CONCLUSIONS
These results show that, while seminal plasma and prostate-derived proteases can cleave IGFBP-3, in patients with prostate cancer the circulating IGFBP-3 is not significantly proteolyzed by either PSA, hK2, or trypsin.
Koistinen
Hannu
H
Department of Obstetrics and Gynecology, Biomedicum Helsinki, Helsinki University Central Hospital, Helsinki, Finland.
Paju
Annukka
A
Koistinen
Riitta
R
Finne
Patrik
P
Lövgren
Janita
J
Wu
Ping
P
Seppälä
Markku
M
Stenman
Ulf-Håkan
UH
D002455:Cell Division; D004591:Electrophoresis, Polyacrylamide Gel; D010450:Endopeptidases / Q000378:metabolism*; D015200:Fluoroimmunoassay; D006801:Humans; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000378:metabolism*; D008297:Male; D017430:Prostate-Specific Antigen / Q000494:pharmacology*; D011471:Prostatic Neoplasms / Q000503:physiopathology*; D020840:Tissue Kallikreins / Q000494:pharmacology; D014357:Trypsin / Q000494:pharmacology
D018972:Insulin-Like Growth Factor Binding Protein 3; D010450:Endopeptidases; D020840:Tissue Kallikreins; D014357:Trypsin; D017430:Prostate-Specific Antigen