PROTEOLYSIS OF INSULIN-LIKE GROWTH-FACTOR BINDING PROTEIN-3 DURING RAT PREGNANCY - A ROLE FOR MATRIX METALLOPROTEINASES

Insulin-like growth factor binding protein-3 (IGFBP-3) is degraded by a cation-dependent protease(s) present in the serum of late gestation rats. Proteolysis of IGFBP-3 results in an increase in IGF-I clearance and possibly in IGF bioavailability. Based on our previous findings t hat matrix metalloproteinases (MMPs) degrade IGFBP-3 in fibroblast con ditioned media, we hypothesized that MMPs might be involved in the deg radation of IGFBP-3 by rat pregnancy serum. In the present study, we d emonstrate that tissue inhibitor of metalloproteinases (TIMP-1), a spe cific inhibitor of all MMPs, inhibited significantly the degradation o f I-125-rhIGFBP-3 by both rat pregnancy serum and rat placental extrac ts. Purified human MMPs (principally MMP-1 and MMP-3) degraded IGFBP-3 in solution; MMP-3 produced a pattern of IGFBP-3 degradation products identical in size to the fragments produced by pregnancy serum. Furth ermore, the combined addition of antihuman MMP-1 IgG and anti-human MM P-3 IgG to rat pregnancy serum blocked almost completely the degradati on of I-125-rhIGFBP-3, suggesting that these two MMPs are the principa l MMPs involved in IGFBP-3 degradation in rat pregnancy serum. Togethe r, these data suggest that MMPs function as IGFBP-3-degrading protease s in the serum of late gestational pregnant rats.