Characterization of a truncated recombinant form of human membrane type 3 matrix metalloproteinase

Membrane type 3 matrix metalloproteinase (MT3-MMP), an activator for the zymogen of MMP-2 (proMMP-2, or progelatinase A), is known to be expressed in human placenta, brain, lung and rat vascular smooth muscle cells, but information about its biochemical properties is limited. In the present study, we expressed and purified a truncated form of MT3-MMP lacking the transmembrane and intracytoplasmic domain (Delta MT3) and characterized the enzyme biochemically. Delta MT3 digested type III collagen into characteristic 3/4- and 1/4-fragments by cleaving the Gly781- Ile782 and Gly784-Ile 785 bonds of alpha 1(III) chains. Although Delta MT3 did not have such an activity against type I collagen, it attacked the Gly4-Ile5 bond of the triple helical portion of alpha 2(I) chains, leading to removal of the crosslink containing N-terminal telopeptides. By quantitative analyses of the activities of Delta MT3 and a similar deletion mutant of MT1-MMP (Delta MT1), Delta MT3 was approximately fivefold more efficient at cleaving type III collagen. Delta MT3 also digested cartilage proteoglycan, gelatin, fibronectin, vitronectin, laminin-1, alpha 1-proteinase inhibitor and alpha 2-macroglobulin into almost identical fragments to those given by Delta MT1, although carboxymethylated transferrin digestion by Delta MT3 generated some extra fragments. The activity of Delta MT3 alas inhibited by tissue inhibitor of metalloproteinases-2 (TIMP-2) and TIMP-3 in a 1 : 1 stoichiometry, but not by TIMP-1. ProMMP-2 was partially activated by Delta MT3 to give the intermediate form. These results indicate that, like MT1-MMP. MT3-MMP exhibits proteolytic activities against a wide range of extracellular matrix molecules. However, differences in the proMMP-2 activation and tissue distribution suggest that MT3-MMP and MT1-MMP play different roles in the pathophysiological digestion of extracellular matrix.