MEMBRANE TYPE-1 MATRIX METALLOPROTEINASE DIGESTS INTERSTITIAL COLLAGENS AND OTHER EXTRACELLULAR-MATRIX MACROMOLECULES

Membrane type 1 matrix metalloproteinase (MT1-MMP) is expressed on can cer cell membranes and activates the zymogen of MMP-2 (gelatinase A). We have recently isolated MT1-MMP complexed with tissue inhibitor of m etalloproteinases 2 (TIMP-2) and demonstrated that MT1-MMP exhibits ge latinolytic activity by gelatin zymography (Imai, H., Ohuchi, E., Aoki , T., Nomura, H., Fujii, Y., Sate, H., Seiki, M., and Okada, Y. (1996) Cancer Res. 56, 2707-2710). In the present study, we have further pur ified to homogeneity a deletion mutant of MT1-MMP lacking the transmem brane domain (Delta MT1) and native MT1-MMP secreted from a human brea st carcinoma cell line (MDA-MB-231 cells) and examined their substrate specificities. Both proteinases are active, without any treatment for activation, and digest type I (guinea pig), II (bovine), and III (hum an) collagens into characteristic 3/4 and 1/4 fragments. The cleavage sites of type I collagen are the Gly(775)/Ile(776) bond for alpha 1(I) chains and the Gly(775)-Leu(776) and Gly(781)-Ile(782) bonds for alph a 2(I) chains. Delta MT1 hydrolyzes type I collagen 6.5- or 4-fold mor e preferentially than type II or III collagen, whereas MMP-1 (tissue c ollagenase) digests type III collagen more efficiently than the other two collagens. Quantitative analyses of the activity of Delta MT1 and MMP-1 indicate that Delta MT1 is 5-7.1-fold less efficient at cleaving type I collagen. On the other hand, gelatinolytic activity of Delta M T1 is 8-fold higher than that of MMP-1. Delta MT1 also digests cartila ge proteoglycan, fibronectin, vitronectin and laminin-1 as well as alp ha(1)-proteinase inhibitor and alpha(2)-macroglobulin. The activity of Delta MT1 on type I collagen is synergistically increased with co-inc ubation with MMP-2. These results indicate that MT1-MMP is an extracel lular matrix-degrading enzyme sharing the substrate specificity with i nterstitial collagenases, and suggest that MT1-MMP plays a dual role i n pathophysiological digestion of extracellular matrix through direct cleavage of the substrates and activation of proMMP-2.