title: Prostate-specific antigen and other prostate-derived proteases cleave IGFBP-3, but prostate cancer is not associated with proteolytically cleaved circulating IGFBP-3.
abstract: 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.
authors.affiliation: Department of Obstetrics and Gynecology, Biomedicum Helsinki, Helsinki University Central Hospital, Helsinki, Finland.
authors.forename: Hannu
authors.initials: H
authors.lastname: Koistinen
authors.forename: Annukka
authors.initials: A
authors.lastname: Paju
authors.forename: Riitta
authors.initials: R
authors.lastname: Koistinen
authors.forename: Patrik
authors.initials: P
authors.lastname: Finne
authors.forename: Janita
authors.initials: J
authors.lastname: Lövgren
authors.forename: Ping
authors.initials: P
authors.lastname: Wu
authors.forename: Markku
authors.initials: M
authors.lastname: Seppälä
authors.forename: Ulf-Håkan
authors.initials: UH
authors.lastname: Stenman
mesh_terms: 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
chemical_list: D018972:Insulin-Like Growth Factor Binding Protein 3; D010450:Endopeptidases; D020840:Tissue Kallikreins; D014357:Trypsin; D017430:Prostate-Specific Antigen