MMP14 and cancer: Mint3 also requires the membrane-type matrix metalloproteinase MT1-MMP to activate HIF-1.11, 14 Mint3 is expressed in many cell types and increases moderately in tumour tissues.15, 16 On the other hand, MT1-MMP is not expressed in normal epithelial cells, but in cancer cells, macrophages, fibroblasts and endothelial tip cells.17, 18, 19 Thus, Mint3-mediated HIF-1 activation is limited to these cells.