Selection of the Dominant Follicle and Insulin-Like Growth Factor (IGF)-Binding Proteins: Evidence that Pregnancy-Associated Plasma Protein A Contributes to Proteolysis of IGF-Binding Protein 5 in Bovine Follicular Fluid

• DOI: 10.1210/en.2002-220657
• Publication Date: 2003-01-21T21:24:46Z
• Authors: G. M. Rivera; J. E. Fortune
• Keywords: Follicular fluid; Proteolysis; Immunoprecipitation

Development of a dominant follicle is associated with decreased intrafollicular low molecular weight IGF-binding proteins (namely IGFBP-2, -4, and -5) increased proteolysis IGFBP-4 by pregnancy-associated plasma protein A (PAPP-A). In addition to proteolytic activity, bovine follicular fluid contains strong activity for IGFBP-5, but not IGFBP-2. Here we show that the IGFBP-5 protease present in neutral/basic pH-favoring, Zn2+ metalloprotease very similar previously described protease. We hypothesized immunoneutralization immunoprecipitation anti-PAPP-A antibodies would result abrogation IGFBP-4, fluid. As expected, were able neutralize precipitate human pregnancy serum, which was used as positive control PAPP-A. Surprisingly, from preovulatory follicles abrogated both proteolysis. Quantitative results derived phosphorimaging revealed complete inhibition -5 incubated 2 or 5 h presence antibodies. After 18 incubation, still inhibited degradation, although an efficiency lower than degradation. Both activities have identical electrophoretic mobility, single band (∼400 kDa) detected Western immunoblotting Proteolysis readily detectable negligible subordinate same cohort. These suggest active IGFBP-4/-5 system, PAPP-A major involved, important determinant fate.