Insulin-like growth factor binding protein (IGFBP) substrate zymography. A new tool to identify and characterize IGFBP-degrading proteinases.

Insulin-like growth factor binding protein (IGFBP) degrading proteinase activities have been described in biological fluids and conditioned media from numerous cell lines. To identify and characterize IGFBP-degrading proteinases, our laboratory has developed IGFBP substrate zymography. Herein, we illustrate how IGFBP substrate zymography can be used both to identify candidate IGFBP-degrading proteinases and characterize their degradative capabilities. For this purpose, human matrix metalloproteinase-3 (MMP-3), a proteinase that degrades IGFBP-3 in human fibroblast cultures, was first electrophoresed through a polyacrylamide gel containing IGFBP-3 as substrate and then analyzed for its ability to degrade the substrate into immunoreactive fragments that were absorbed onto a polyvinylidene difluoride membrane. IGFBP-3 substrate zymography was capable of detecting as little as 20 ng of human MMP-3, demonstrating a sensitivity similar to casein substrate zymography. Using the zymogram as a template, MMP-3 was identified in a standard SDS-polyacrylamide gel run in parallel with the zymogram, and the corresponding area of the gel was excised. Electroelution of the gel slice yielded active MMP-3 when examined by casein substrate zymography. Furthermore, digestion of IGFBP-3 in solution by the electroeluted MMP-3 revealed the same fragmentation pattern of the binding protein as that produced by MMP-3, which had not been electroeluted. Together, these studies demonstrate that IGFBP substrate zymography can be a useful tool for both the identification and the characterization of IGFBP-degrading proteinases.