Degradation of collagen fibrils by live cells: role of expression and activation of procollagenase.

Abstract

We have examined the conditions for dissolution by live cells of an extracellular matrix composed of reconstituted type I collagen fibrils, using three different cell types which express varying constitutive or inducible levels of procollagenase and collagenase inhibitor. The two major conclusions from these studies were that (i) expression of collagenase is a necessary but not sufficient requirement for dissolution of the collagen fibrils and that (ii) activation of procollagenase is a rate-limiting step. Cells which secreted high levels of procollagenase dissolved collagen fibrils only to the extent that they were able to activate the enzyme. Cells which also expressed inhibitor failed to activate procollagenase in the culture medium and did not dissolve the collagen fibrils unless procollagenase-activation was assisted by exogenous proteinase activity. Cells that did not express inhibitor ultimately did activate procollagenase but the process was slow and incomplete. Introduction of exogenous proteinase activity either in the form of plasminogen, plasmin, or trypsin stimulated collagen breakdown by several fold. Analysis of the culture medium sampled from such cultures showed that the stimulating effect of exogenous proteinases could be ascribed to three separate, but synergistic events: elevated expression of procollagenase, conversion of procollagenase to active form and inactivation of collagenase inhibitor. Two lines of evidence suggested that the dissolution of collagen fibrils in these cultures was mediated by a collagenase-dependent pathway: (i) the rate of dissolution closely mirrored the level of expression of collagenase and (ii) the process was blocked by inhibitory collagenase-specific antibodies.