Rapid activation of matrix metalloproteinase-2 by glioma cells occurs through a posttranslational MT1-MMP-dependent mechanism

Matrix metalloproteinase-2 (MMP-2) has been suggested to play a crucial rol e in tumor invasion and angiogenesis. In order to understand the mechanisms underlying proMMP-2 activation, we compared the biochemical and cellular e vents triggered by two potent MMP-2 activators, the lectin concanavalin A ( ConA) and the cytoskeleton disrupting agent cytochalasin D (CytoD). Incubat ion of U87 human glioma cells for 24 h in the presence of ConA or CytoD ind uced a marked activation of proMMP-2 and this activation was correlated in both cases with an increase in the mRNA levels of MT1-MMP. At the protein l evel, proMMP-2 activation induced by CytoD or ConA strongly correlated with the appearance of a 43-kDa MT1-MMP proteolytic breakdown product in cell l ysates. Interestingly, CytoD also induced a very rapid (2 h) activation of proMMP-2 that was independent of protein synthesis. Under these conditions, CytoD also promoted the rapid proteolytic breakdown of the 63 kDa pro form of MT1-MMP, resulting in the appearance of the 43 kDa MT1-MMP processed fo rm. Overexpression of a recombinant full-length MT1-MMP protein in glioma c ells resulted in the activation of proMMP-2 that was correlated with the ge neration of the 43 kDa fragment of the protein. By contrast, overexpression of the protein in COS-7 cells promoted proMMP-2 activation without inducin g the production of the 43 kDa fragment. These results thus suggest that ac tivation of proMMP-2 occurs through both translational and post-translation al mechanisms, both involving proteolytic processing of membrane-associated MT1-MMP. This processing of MT1-MMP is, however, not essential to proMMP-2 activation but may represent a regulatory mechanism to control the activit y of MT1-MMP. (C) 2000 Elsevier Science B.V. All rights reserved.