Matrix metalloproteinase-2 (MMP-2) has been suggested to play a crucial role in
tumor invasion and angiogenesis. In order to understand the mechanisms underlying
proMMP-2 activation, we compared the biochemical and cellular events triggered by two potent MMP-2 activators, the
lectin concanavalin A (ConA) and the cytoskeleton disrupting agent
cytochalasin D (CytoD). Incubation of U87 human
glioma cells for 24 h in the presence of ConA or CytoD induced 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 level,
proMMP-2 activation induced by CytoD or ConA strongly correlated with the appearance of a 43-kDa
MT1-MMP proteolytic breakdown product in cell lysates. 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 form. Overexpression of a recombinant full-length
MT1-MMP protein in
glioma cells resulted in the activation of
proMMP-2 that was correlated with the generation of the 43 kDa fragment of the
protein. By contrast, overexpression of the
protein in COS-7 cells promoted
proMMP-2 activation without inducing the production of the 43 kDa fragment. These results thus suggest that activation of
proMMP-2 occurs through both translational and post-translational 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 activity of
MT1-MMP.