Gelatin zymography and substrate cleavage assays of matrix metalloproteinase-2 in breast carcinoma cells overexpressing membrane type-1 matrix metalloproteinase.

Gelatin zymography is the common method for examining matrix metalloproteinase-2 (MMP-2) in cells and media samples. Activation of the latent MMP-2 zymogen involves its binding to the cell surface MT1-MMP*TIMP-2 (membrane type-1 matrix metalloproteinase/tissue inhibitor of matrix metalloproteinase-2) complex with subsequent cleavage of proMMP-2 by TIMP-2-free adjacent MT1-MMP. This is followed by autolytic maturation of the activation intermediate and the release of the mature MMP-2 species from cell surfaces into the extracellular milieu. To observe the MMP-2 activation pathway in more detail, proMMP-2-deficient MCF7 breast carcinoma cells expressing MT1-MMP were incubated with excess proMMP-2 to saturate the available MT1-MMP*TIMP-2 surface receptors. After removal of the unbound material, the kinetics of proMMP-2 activation and MMP-2 release from cells into media was monitored by gelatin zymography and substrate cleavage. Our observations demonstrate that gelatin zymography is insufficient for providing meaningful information about the status of MMP-2. The proteolytically competent mature MMP-2 moiety alone, but not in its complex with TIMP-2, was released from the cells. In tissue culture conditions, the enzyme's proteolytic activity was suppressed in the next 30 to 60 minutes by tissue inhibitors of MMPs, especially by TIMP-1. The picture emerges that there is a likely temporal regulation of MMP-2 activity by TIMPs in tumor cells. These relatively rapid changes of the MMP-2 status cannot be detected by gelatin zymography. Additional studies are needed to examine the significance of this phenomenon in vivo.