Coordinate action of membrane-type matrix metalloproteinase-1 (MT1-MMP) and MMP-2 enhances pericellular proteolysis and invasion

Abstract

Membrane-type matrix metalloproteinase-1 (MT1-MMP) mediates cleavage of not only MMP-2/gelatinase A for activation, but also a variety of substrates including type I collagen (reviewed in Cancer Sci 2005; 96: 212-7). MMP-2 activation involves tissue inhibitor of MMP (TIMP)-2 as a bridging molecule between MT1-MMP and pro-MMP-2. Thus, net activity of MT1-MMP and MMP-2 is regulated in a complex manner depending on TIMP-2 concentration. During invasive growth of tumor cells in type I collagen matrix, MT1-MMP initiates denaturation of collagen into gelatin, which is subsequently digested further by MMP-2 adjacent to MT1-MMP. Coordinate action of MT1-MMP and MMP-2 may facilitate pericellular proteolysis, and enhance not only tumor invasion/migration but also cell growth. Tetraspanins as binding proteins of MT1-MMP regulate MT1-MMP subcellular localization and compartmentalization, leading to efficient MMP-2 activation and proteolysis coupled with cellular function.

Figure 1

Fate of membrane‐type matrix metalloproteinase‐1 (MT1‐MMP) on the cell surface. MT1‐MMP on cell surface rapidly turns over by auto‐degradation or clathrin‐dependent internalization. The internalized MT1‐MMP is recycled or degraded in lysozome. MT1‐MMP inactivated by tissue inhibitor of MMP (TIMP)‐2 avoids auto‐degradation, and accumulates on the cell surface. Accumulated MT1‐MMP/TIMP‐2 complex serves as a receptor for pro‐MMP‐2. It should be noted that concentration of active MT1‐MMP on cell surface is quite low due to rapid auto‐degradation, and only TIMP‐2‐inactivated MT1‐MMP accumulates.

Figure 2

Tissue inhibitor of MMP (TIMP)‐2 concentra‐tion dictates substrate choice of membrane‐type matrix metalloproteinase‐1 (MT1‐MMP). Left, MT1‐MMP forms a complex with TIMP‐2, and the complex serves as a receptor for pro‐MMP‐2. Pro‐MMP‐2, which binds to MT1‐MMP/TIMP‐2 complex is then processed by the neighboring TIMP‐2‐free MT1‐MMP. The processed MMP‐2 is inactivated by TIMP‐2 depending on its concentration. Right, under TIMP‐2‐free condition, MT1‐MMP directly cleaves its own substrates, such as extracellular matrix components, cell‐surface molecules and so on.

Figure 3

Schematic illustration of tissue inhibitor of MMP (TIMP)‐2‐regulated membrane‐type matrix metalloproteinase‐1 (MT1‐MMP) and MMP‐2 activities. The level of active MT1‐MMP and the ratio between MT1‐MMP of TIMP‐2 complex and TIMP‐2‐free (active) in the cells expressing MT1‐MMP and different levels of TIMP‐2 are schematically illustrated. The level of MMP‐2 processed by these cells is also shown, which includes TIMP‐2‐free and TIMP‐2‐bound forms. In the absence of TIMP‐2, MT1‐MMP activity is the highest, and decreases proportionally to the TIMP‐2 level. MMP‐2 activated under a low TIMP‐2 level is free from TIMP‐2, and shows the highest activity. MMP‐2 is processed most effectively at medium level of TIMP‐2, in which most of MT1‐MMP serves as a receptor for pro‐MMP‐2 by binding with MT1‐MMP and processed MMP‐2 is inactivated by TIMP‐2. MMP‐2 processing is blocked when MT1‐MMP is all bound by a high level of TIMP‐2. MSP‐TIMP‐2 does not affect MT1‐MMP activity, and generates a maximum level of processed MMP‐2 which is free from TIMP‐2.

Figure 4

Artificial receptor for pro‐matrix metalloproteinaise‐2 (MMP‐2) (MSP‐TIMP‐2). (a) MSP‐TIMP‐2 consists of the transmembrane domain of type II transmembrane protein mosaic serine ptotease (MSP) and tissue inhibitor of MMP (TIMP)‐2. Pro‐MMP‐2 binds to the C‐terminus of MSP‐TIMP‐2. (b) Left, MSP‐TIMP‐2‐expressing HT1080 cells generate more active MMP‐2 than mock cells. Right, MSP‐TIMP‐2‐expressing cells were cultured in collagen gel, which caused intensive degradation of collagen gel. Dotted line, border of collagen gel. Mag‐nification, ×100.