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 (ΔMT3) and characterized the enzyme biochemically. ΔMT3 digested type III collagen into characteristic 3/4‐ and 1/4‐fragments by cleaving the Gly781‐Ile782 and Gly784‐Ile785 bonds of α1(III) chains. Although ΔMT3 did not have such an activity against type I collagen, it attacked the Gly4‐Ile5 bond of the triple helical portion of α2(I) chains, leading to removal of the crosslink containing N‐terminal telopeptides. By quantitative analyses of the activities of ΔMT3 and a similar deletion mutant of MT1‐MMP (ΔMT1), ΔMT3 was approximately fivefold more efficient at cleaving type III collagen. ΔMT3 also digested cartilage proteoglycan, gelatin, fibronectin, vitronectin, laminin‐1, α1‐proteinase inhibitor and α2‐macroglobulin into almost identical fragments to those given by ΔMT1, although carboxymethylated transferrin digestion by ΔMT3 generated some extra fragments. The activity of ΔMT3 was 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 ΔMT3 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.