Epilysin (MMP-28) is deposited to the basolateral extracellular matrix of epithelial cells

Epilysin (MMP-28) is a conserved member of the matrix metalloproteinase (MMP) family. It is expressed in various normal tissues, and induced in wounds and in developing and regenerating nerves. Epilysin induces TGF-beta mediated epithelial to mesenchymal transition, but its other functions are largely unknown. We have characterized the localization of both catalytically active and mutated inactive, overexpressed epilysin in established epithelial cell lines. We found that epilysin was localized abundantly to the basolateral side of the cells and associated with the extracellular matrix (ECM) as verified by immunoblotting and confocal microscopy. Overexpression of epilysin in MDCK cells resulted in a drastic reduction of basolateral ECM, as observed by the disappearance of collagen type IV, laminin and fibronectin. Cultivation of epilysin expressing MDCK cells in defined serum free medium resulted in the restoration of these proteins to the ECM. The levels of fibronectin and collagen IV were, however, reduced in epilysin expressing cells under the serum free conditions, and degradation fragments of collagen IV were detected supporting the activation of proteolysis by epilysin. Epilysin was observed in its unprocessed 50 kDa active form in the ECM of MDCK cells under serum free conditions whereas in cells cultured in serum containing it was processed to the 48 kDa form. Current results indicate that epilysin associates with the basolateral ECM of cultured epithelial cells, where it plausibly plays a role in the regulation of matrix composition and turnover.