Mosaic structure of the secreted ECM metalloproteases and interaction of the type IV collagenases with inhibitors.

Abstract

SV-40 transformed human lung fibroblasts and HT 1080 fibrosarcoma cells secrete a 92-kDa type IV collagenase (in addition to 72-kDa type IV collagenase identical to that found in macrophages, phorbol ester differentiated U937 cells, and keratinocytes. The expression of this protease is induced by the tumor promoter TPA, and interleukin-1 and was not detected in the parental human lung fibroblast. The 92-kDa preproenzyme has a predicted Mr of 78,426, including a 19 amino acid long hydrophobic signal peptide. The apparent discrepancy between the predicted molecular weight and the molecular weight of the secreted protein is due to a post-translational modification of the enzyme through glycosylation. The 92-kDa type IV collagenase consists of five distinct domains, including a unique 54 amino acid long collagen--like domain, and is a member of the secreted ECM metalloprotease gene family. Both the 72 and 92-kDa type IV collagenase contain a fibronectin-like collagen binding domain. The mosaic structure of the secreted ECM metalloproteases is a result of a recruitment of the functional units from ECM structural macromolecules into an enzyme protein in the process of evolution. The 92-kDa and 72-kDa type IV collagenase proenzymes form a noncovalent complex with inhibitors, which is activatable by APMA, yielding an enzymes with similar if not identical substrate specificity profile. Our results demonstrate that while the 92-kDa type IV collagenase forms a stoichiometric complex with TIMP, the 72-kDa type IV collagenase, purified from the same starting material, contains a novel 24-kDa inhibitor-TIMP-2.