How do cells degrade their surrounding matrix? Constitutive and induced cellular secretion of several classes of proteinases have been implicated in extracellular degradation (1 ) and many of these proteinases have the ability to degrade extracellular matrix proteins in vitro. However, clear evidence of focal matrix degradation adjacent to cells in which enzyme synthesis occurs is sparse. In this chapter we describe a method we have developed that allows unambiguous detection of focal extracellular matrix (ECM) degradation below cells, although at the same time localizing cellular expression of enzyme: we illustrate the use of this method to demonstrate focal proteolysis by cells overexpressing the membrane-type matrix metalloproteinase-1 (MT1-MMP) on the cell surface.
