Pregnancy-associated plasma protein-A accounts for the insulin-like growth factor (IGF)-binding protein-4 (IGFBP-4) proteolytic activity in human pregnancy serum and enhances the mitogenic activity of IGF by degrading IGFBP-4 in vitro.
Pregnancy-associated plasma protein-A (PAPP-A) has been identified as the insulin-like growth factor (IGF)-dependent IGF-binding protein-4 (IGFBP-4) protease produced by human fibroblasts. Recently, we found that serum proteases induced during human pregnancy cleaved IGFBP-4 in both an IGF-II-dependent and an IGF-II-independent fashion. This study sought to determine whether PAPP-A is the predominant IGFBP-4 protease in human pregnancy serum (PS) and to assess the in vitro role of serum PAPP-A. Immunoprecipitation with PAPP-A antibody effectively depleted PAPP-A from the PS and completely abolished both IGF-II-dependent and IGF-II-independent IGFBP-4 proteolytic activity in PS. Direct addition of PAPP-A antibody to PS completely blocked IGFBP-4 proteolysis and partially blocked IGFBP-5 proteolysis, but had no effect on IGFBP-3 proteolysis. To evaluate the role of serum PAPP-A, we tested whether PAPP-A in PS modulated the inhibitory activity of IGFBP-4 on IGF-II-induced cell proliferation in human osteosarcoma MG63 cells. The wild-type IGFBP-4 (WTBP-4; 200 ng/mL) failed to inhibit proliferation of the cells treated with PS (0.1% or 0.3%) alone or in combination with IGF-II (40 ng/mL), whereas the inhibitory effect of WTBP-4 was observed in the cells treated with nonpregnancy serum alone or in combination with IGF-II (P < 0.05). In contrast to WTBP-4, a protease-resistant IGFBP-4 was able to inhibit proliferation of the cells treated with PS alone or in combination with IGF-II (P < 0.05). In the presence of PAPP-A neutralizing antibody, the inhibitory effect of WTBP-4 on proliferation of the cells treated with IGF-II and PS was restored. In summary, these data demonstrate 1) that PAPP-A represents the predominant IGFBP-4 protease in PS; 2) that PAPP-A may in part contribute to IGFBP-5, but not IGFBP-3, proteolytic activity in PS; and 3) that PAPP-A enhances the bioactivity of IGFs in vitro by degrading IGFBP-4.
Byun
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D
Musculoskeletal Disease Center, J. L. Pettis Memorial Veterans Affairs Medical Center and Loma Linda University, Loma Linda, California 92357, USA.
Mohan
S
S
Yoo
M
M
Sexton
C
C
Baylink
D J
DJ
Qin
X
X
D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D005260:Female; D006801:Humans; D018974:Insulin-Like Growth Factor Binding Protein 4 / Q000097:blood*; D007335:Insulin-Like Growth Factor II / Q000378:metabolism / Q000494:pharmacology; D008666:Metalloendopeptidases / Q000097:blood*; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects; D011247:Pregnancy / Q000097:blood*; D011266:Pregnancy-Associated Plasma Protein-A / Q000302:isolation & purification / Q000378:metabolism*; D012016:Reference Values
D018974:Insulin-Like Growth Factor Binding Protein 4; D007335:Insulin-Like Growth Factor II; D008666:Metalloendopeptidases; D011266:Pregnancy-Associated Plasma Protein-A