Expression and function of matrix metalloproteinase (MMP)-28

Matrix metalloproteinase-28 (MMP-28, epilysin) is highly expressed in the skin by keratinocytes, the developing and regenerating nervous system and a number of other normal human tissues. In epithelial cells, over-expression of MMP-28 mediates irreversible epithelial to mesenchymal transition concomitant with loss of E-cadherin from the cell surface and an increase in active transforming growth factor beta. We recently reported the expression of MMP-28 in both cartilage and synovium where expression is increased in patients with osteoarthritis. In human chondrosarcoma cells MMP-28 was activated by proprotein convertases and the active form of the enzyme preferentially associated with the extracellular matrix in a C-terminal independent manner. over-expression of MMP-28 in chondrosarcoma cells led to altered cell morphology with increased organisation of actin. Adhesion to type II collagen and fibronectin was increased, and migration across the former was decreased. MMP-28 was localised to the cell surface, at least transiently, in a C-terminal dependent manner. Heparin prevented both extracellular matrix association and cell surface binding of MMP-28 suggesting that both are via heparan sulphate proteoglycans. Over-expression of activatable MMP-28, but not catalytically inactive EA mutant increased the expression and activity of MMP-2, and all forms of MMP-28 tested increased expression of MMP19 and TIMP3 mRNA. These data demonstrate that expression of MMP28 alters cell phenotype towards a more adhesive, less migratory behaviour. Further, MMP-28 activity may reside predominantly in the extracellular matrix, and we are currently searching for substrates in this compartment.