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Membrane type 1 metalloprotease (MT1‐MMP) is a transmembrane metalloprotease that plays a major role in the extracellular matrix remodeling, directly by degrading several of its components and indirectly by activating pro‐MMP 2. We investigated the effects of MT1‐MMP overexpression on in vitro and in vivo properties of human breast adenocarcinoma MCF7 cells, which do not express MT1‐MMP or MMP‐2. MT1‐MMP and MMP‐2 cDNAs were either transfected alone or cotransfected. All clones overexpressing MT1‐MMP 1) were able to activate endogenous or exogenous pro‐MMP‐2, 2) displayed an enhanced in vitro invasiveness through matrigel‐coated filters independent of MMP‐2 transfection, 3) induced the rapid development of highly vascularized tumors when injected subcutanously in nude mice, and 4) promoted blood vessels sprouting in the rat aortic ring assay. These effects were observed in all …