Binding and localization of M(r) 72,000 matrix metalloproteinase at cell surface invadopodia

Degradation (turnover) of collagenous matrix occurs on the surface of specialized membrane extensions termed "invadopodia," which are sites of cell invasion into the extracellular matrix. Here we show the localization of the M(r) 72,000 type IV collagenase of the matrix metalloproteinase family at invadopodia. When added exogenously, latent M(r) 72,000 collagenase binds to invadopodia of chicken embryo fibroblasts transformed by Rous sarcoma virus, whereupon the bound collagenase loses its propeptide. The collagenase binds to a component contained within the detergent extract of transformed cells, and increased levels of the active M(r) 62,000 form of the collagenase are seen here. Such an association is not detected in the detergent extract derived from normal cells. Using a recently developed cell fractionation procedure to collect cell surfaces enriched in invadopodia, we show that the M(r) 72,000 collagenase associates with the invadopodial fraction and active forms of the enzyme become immobilized on the collagenous surface. Thus, invadopodia direct intense localized degradation of the extracellular matrix by concentrating active membrane-associated collagenases at sites of cellular invasion.