The Oncologist 2001;6:415-427 www.TheOncologist.com Correspondence: Ronald Hoekstra, M.D., Department of Medical Oncology, University Hospital Rotterdam, P.O. Box 2040, 3000 CA Rotterdam, The Netherlands. Fax: 31-10-463-4627; e-mail: hoekstra@oncd.azr.nl Received May 25, 2001; accepted for publication August 7, 2001. ©AlphaMed Press 1083-7159/2001
INTRODUCTIONThe importance of proteinases in tumor invasion was first recognized in 1925 when Fischer found that a lytic substance from sarcoma cells could degrade the fibrin stroma. Later it was found that the serine proteinase plasminogen activator (PA) played an important role in activating plasminogen to plasmin. Apart from PAs, proteinases such as serine, cysteine, and metalloproteinases have been associated with cancer [1]. It is important to realize that high levels of extracellular proteolytic activity are not restricted to the malignant phenotype, but are also seen in a number of physiological processes such as embryo implantation, wound healing, and angiogenesis. A common feature in these processes is the breaching of histological barriers with the degradation of the extracellular matrix (ECM) composed of basement membrane and extracellular stroma.Matrix metalloproteinases (MMPs) are enzymes able to degrade most components of the ECM such as collagens, laminins, fibronectins, elastins, and the protein core of proteoglycans. At this moment more than 20 different MMPs have been identified and classified. They show a consistent sequence homology and in general share a pre-domain, which is a signal peptide for secretion, a pro-domain, important for maintaining latency, a catalytic domain with a highly