Key words: Matrix metalloproteinase; MT1-MMP; Extracellular matrix; Cancer; Invasion; Metastasis; Cell migration; Pericellular proteolysis

Abstract

Matrix metalloproteinases (MMPs) are believed to play a pivotal role in malignant behavior of cancer cells such as rapid tumor growth, invasion, and metastasis by degrading extracellular matrix (ECM). Different types of synthetic inhibitors against MMPs (MMPIs) were developed as candidates for anti-cancer therapeutics and so far clinical trials had led to no significant success. However, this does not diminish the importance of MMPS in the malignancy of cells. Details about MMPs, specifically when and how they take part in the development of cancer are necessary for more advanced application of MMPIs. In this paper, we summarize recent knowledge about membrane-type 1 matrix metalloproteinase (MT1-MMP) which is expressed on cancer cell surface as an invasion-promoting proteinase. By localizing at the leading edge of invasive cancer cells, MT1-MMP degrades components of the tissue barriers. One of the major targets is type I collagen, the most abundant ECM component. Although MT1-MMP itself cannot degrade type IV collagen in the basement membrane, it binds to and activates proMMP-2, one of the type IV collagenases. However, degradation of the ECM is not the sole function of MT1-MMP. MT1-MMP also regulates cell-ECM interaction by processing cell adhesion molecules such as CD44 and integrin Ąv chain, and eventually promotes cell migration as well. In addition to the transcriptional regulation, invasion-promoting activity of the MT1-MMP is also strictly monitored at the post-translational level. Precise knowledge about the regulation will give us insight to develop new methods for treating invasive cancer patients.

Introduction

Matrix metalloproteinases (MMPs) are a family of zinc-binding endopeptidases that collectively degrade most of the components of the extracellular matrix (ECM) [1, 2]. Extensive study in the last decade has revealed that MMPs are frequently overexpressed in most form of human tumor [3-5]. Based on their ECM-degrading activity, these MMPs are believed to contribute to the proliferation, invasion and metastasis of tumor cells by eliminating the surrounding ECM barrier. In addition, MMPs are required for tumor-induced angiogenesis. Thus, inhibition of the MMPs in tumor is expected to stabilize malignancy. Based on this assumption, different types of MMP inhibitors have been developed and indeed proved effective in animal models. However, recent clinical studies have failed to show a clear benefit from MMP inhibitors compared to conventional therapies [3, 6, 7]. Why aren¡¦t MMP inhibitors effective against human tumors? It is unlikely that MMPs do nothing. One possibility is their contribution differs depending on the stage of tumor development. Basically, MMP activity would be required for rapidly proliferating and invading tumors rather than the already established large tumors on which most of the clinical studies were carried out. Even in the animal models, MMP inhibitors are only effective in preventing an angiogenic switch and following tumor growth, having failed to reduce the size of late-stage tumors [8]. Thus, the protocols of clinical studies are now the subject of reevaluation taking into consideration the MMP inhibitor-sensitive stages and types of tumors.¡@
More than 20 MMPs have been identified for mammals all with relatively conserved domains; a propeptide, a catalytic domain, and a hemopexin-like domain from the N-terminus, though there are some exceptions (Fig. 1) [3]. Still each MMP also has additional sequences that presumably contribute to their unique function. A C-terminal hydrophobic stretch in MT1-MMP is one example that anchors the enzyme to the plasma membrane and restricts its activity to the cell surface. These enzymes are referred to as membrane-type MMPs (MT-MMPs) [9, 10]. Among the six MT-MMPs identified to date, MT1, MT2, MT3, and MT5 have a type I transmembrane domain, while MT4 and MT6-MMP are tethered to the plasma membrane by a GPI anchor [11, 12]. Since cells require remodeling of the pericellular ECM for proliferation, migration and morphogenesis, all of the MT-MMPs are presumably important for such cell functions [10, 13]. Among them, MT1-MMP has been additionally characterized as an enzyme required for tumor invasion.

MT1-MMP: Basic information

MT1-MMP was the first membrane-type MMP identified and was characterized as a specific activator of proMMP-2 (pro-gelatinase A) at the cell surface [9]. As with all MMPs, the propeptide has to be removed for MT1-MMP to function proteolytically on the cell surface. MT1-MMP has a basic amino acid motif (RXKR) at the C-terminal end of the propeptide [9, 14], and cleavage occurs at this position by furin or related enzymes to generate the active form [15-17]. However, alternative activation pathways may also exist [18-21]. Activated MT1-MMP digests extracellular matrix macromolecules such as fibronectin, vitronectin, laminin-1 and -5, fibrin and dermatan sulfate proteoglycans (Fig. 2) [15, 22-24]. The enzyme also degrades gelatin, casein and elastin [15, 25, 26] and shows activity against collagens type I, II and III [24]. The enzymatic activity of MT1-MMP is specifically inhibited by TIMP-2, TIMP-3 and TIMP-4 but not by TIMP-1 [26, 27]. Other than TIMPs, the unique membrane anchor type proteinase inhibitor RECK [28, 29] and testican 3 including its variant N-Tes [30] can also suppress the activity of MT1-MMP. On the other hand, the activation of MMP-2 by MT1-MMP is enhanced by association with claudin [31]. In addition to ECM molecules, MT1-MMP cleaves cell adhesion molecules such as CD44 which is a major hyaluronan receptor [32], pro-alpha v integrin [33], and a tissue transglutaminase that binds fibronectin [34].
The MMP-2 that degrades type IV collagen in the basement membrane is also activated by MT1-MMP [9]. For the activation, proMMP-2 binds MT1-MMP using TIMP-2 as an adaptor by forming a trimolecular complex on the cell surface [35]. In this complex, the N-terminal domain of TIMP-2 binds the catalytic domain of MT1-MMP for inhibition and its C-terminal domain binds the hemopexin-like domain of proMMP-2. Another MT1-MMP nearby the complex cleaves the propeptide bond of proMMP-2 and generates an intermediate form which is then converted into a fully activated enzyme by an autoproteolytic mechanism [26, 36]. These ¡§receptor¡¨ and ¡§activator¡¨ MT1-MMP molecules have to be in close proximity the on cell surface and this is accomplished by the formation of a homophilic complex through the hemopexin-like domain [37, 38]. Thus, the hemopexin-like domain of MT1-MMP plays a crucial role in its function to activate proMMP-2 [37]. In addition to the hemopexin-like domain, the cytoplasmic portion of MT1-MMP may modulate the oligomer formation as well [38, 39]. ProMMP-13 also can be activated by MT1-MMP in a cell-mediated manner [40]. A deficiency of MT1-MMP in mice also emphasized the importance of the degradation of ECM by MT1-MMP during development [41, 42]. The animal showed inadequate collagen turnover, resulting in dwarfism, osteopenia, arthritis, and connective tissue disease [41]. The angiogenic response was also delayed in the mice and the activation of proMMP-2 in fibroblasts was disturbed [42]. Although the activation of MMP-2 is defective in MT1-MMP-deficient mice, the phenotype cannot be attributed to this because MMP-2-deficient mice develop normally [43].

Expression of MT1-MMP in tumor

In the developing mouse embryo, MT1-MMP is mainly expressed in cells of mesenchymal origin including fibroblasts, muscular cells, and osteoblasts, and the expression decreases with maturation after birth¡@ [44, 45]. Expression can be re-induced, however, when the cells require remodeling ECM again. For example, the expression of MT1-MMP is induced in fibroblasts when tissue is damaged and continues throughout the healing process together with the expression of MMP-2 [46]. Since MT1-MMP has collagenase activity and MMP-2 degrades gelatin, these two enzymes cooperate as a system for type I collagen turnover [24]. MT1-MMP is also expressed in endothelial cells forming new vessels during angiogenesis [22, 47-49].
MT1-MMP was initially reported to be expressed in lung carcinoma cells in addition to the adjacent fibroblasts and acts as a specific activator of proMMP-2 [9]. Such patterns of MT1-MMP expression and MMP-2 activation were also observed in many types of tumors, such as lung [9, 50-52], gastric [53, 54, 55,] colon [56], liver [57], breast [51, 58, 59], bladder [60], head and neck [61], tyroid [62], ovarian [63, 64] and cervical carcinomas [65], and brain tumors [66-68]. Transcripts were also detected in both tumor cells and surrounding stroma cells [51, 56, 63, 69]. Expression levels of MT1-MMP and the rate of MMP-2 activation in tumors correlate with the poor prognosis for patients. Thus, tumor cells of epithelial origin express MT1-MMP, though normal epithelial cells, even those in a wound, do not. Presumably, the genetic events that render a normal epithelium cancerous cause the abnormal expression of MT1-MMP in cells. Such an induction of MT1-MMP expression could be mediated by the Wnt signaling pathway which is frequently aberrant in carcinoma cells (Fig. 3). This is based on the observation that depletion of b-catenin in colorectal carcinoma SW480 cells by expressing the wild-type APC gene down-regulates expression of MT1-MMP [70]. The promoter region of the gene contains an element for b-catenin/Tcf4 complex binding. Additional signals may also modulate the expression of MT1-MMP in tumor cells [71]. MMP-2 is frequently co-expressed with MT1-MMP in mesenchymal cells [44, 45]. However, carcinoma cells in tissue [72, 73] and cancer cell lines [74] rarely express MMP-2, even though they can use the MMP-2 that is derived from the surrounding fibroblasts by binding and activating it using MT1-MMP on the cell surface. This MT1-MMP/MMP-2 system would be important for tumor cells to invade the basement membrane by degrading type IV collagen and then the stroma by degrading type I collagen.
However, relatively strong signals for MT1-MMP have been reported in the stroma cells adjacent to tumor cell nests, especially in breast carcinomas, while signal strength was negligible in tumor cells [69, 75, 76]. Thus, there is debate over whether MT1-MMP is expressed in carcinoma cells. However, it should be noted that many breast carcinoma cell lines surely express MT1-MMP and their expression levels correlate well with their invasiveness in vitro and tumorigenic activity in mice [77].¡@ The expression of MT1-MMP in carcinoma cells may look negligible when it is very intense in the surrounding stroma cells. Quantitative measurements of the expression levels of MT1-MMP in carcinoma cell nests using laser-microdissected tissue samples should settle this argument.

Dynamic regulation of MT1-MMP during cell migration and invasion
Significance of membrane anchoring

Appearing as an active enzyme on the cell surface, MT1-MMP acts as part of the invasion machinery when it is expressed in migratory cells. MDCK cells derived from canine kidney epithelium develop a branched tubular structure when stimulated by hepatocyte growth factor (HGF) in 3-dimensional type I collagen gel. Surrounded by collagen, MDCK cells express MT1-MMP which was essential to the invasive and morphogenic responses of the cells to HGF [78]. Expression of excessive amounts of MT1-MMP in MDCK cells strongly promoted the invasion by the cells of the type I collagen gel, but severely disturbed the morphogenic response to HGF [79]. In contrast, secreted MMPs including the collagen-degrading MMP-1 and a form of MT1-MMP engineered to lack the membrane-anchoring sequences did not promote invasion or affect tubular formation [79]. Thus, membrane-anchoring is crucial to the involvement of MT1-MMP in invasion of the collagen matrix, and the formation of a tubular morphology.

Localization at the migration front
MT1-MMP localizes at the front of migrating cells and this localization aids in the degradation of the extracellular matrix barrier to facilitate invasion. A relatively stable association of MT1-MMP with the actin cytoskeleton can be seen when the cells are treated with cytochalasin D which disrupts polymerized actin and produces actin aggregates [80]. Although MT1-MMP has a cytoplasmic tail, the domain responsible for the actin association was mapped to the hemopexin-like domain. Thus, the association of MT1-MMP with actin must be mediated by some other cell surface molecule that has a cytoplasmic domain and anchors to actin. CD44, a major hyarunonan receptor that associates with actin within cells, also localizes at the migration front and was identified as a linker that mediates the association of MT1-MMP with actin [80]. MT1-MMP and CD44 form a complex by binding CD44 at the hemopexine-like domain. Thus, CD44 plays a pivotal role in the regulation of the polarized distribution of MT1-MMP during cell migration and invasion [80].

Homo-oligomer formation and MMP-2 activation
The activation of proMMP-2 requires at least two MT1-MMP molecules and is accomplished by forming a homophilic oligomer through the hemopexin-like domain. Such a formation can be visualized in situ using a chimeric protein in which the transmembrane/cytoplasmic portion of MT1-MMP is substituted with that of nerve growth factor receptor (NGF-R) [37]. NGF ligand binding is known to induce dimerization and auto-phosphorylation of NGF-R at the cytoplasmic tyrosine residues. Expression of a constitutively active Rac1 in COS-1 cells induces lamellipodia to form and the MT1-MMP chimera was found to localize with intense auto-phosphorylation signals indicating that homo-oligomer form there. At the same time, Rac1 enhanced the activation of MMP-2 [37, 81]. Thus, the ruffled edge that forms the migration front is likely the site of homo-olimoger formation and MMP-2 activation.

Regulation of cell migration by MT1-MMP
In some cell lines, such as COS-7 and CHO-K1, expression of MT1-MMP alone stimulates cell migration [32, 82] and activates extracellular signal-regulated kinase (ERK) [82]. One of the target molecules of MT1-MMP for cell migration is CD44H that binds MT1-MMP [80] and is shed by the enzyme [32]. CD44 is reported to be shed by metalloproteinases and is implicated in the migration of cells [83, 84]. MT1-MMP is one of the enzymes shedding CD44H and concurrently promotes cell migration [32]. Interestingly, a mutant CD44H that cannot be cleaved by MT1-MMP prevented migration induced by CD44H in combination with MT1-MMP. Based on such a dominant-negative effect of the processing mutant, cleavage of CD44H seems to be required for detachment from its ligand at the migration front. However, it is also possible that cleavage generates signals to promote migration. An interesting possibility is that the cleaved intracellular fragment acts as a transcription factor like Notch [85] and promotes cell migration through transcriptional activation of the target genes. Integrins are also a well-known adhesion system for cell migration, and their binding to and detachment from the ECM is regulated intracellularly, not by processing [86]. Cells may use two types of cell adhesion systems for migration in general. CD44 and other sugar receptors appear to mediate a flexible and provisional adhesion at lamellipodia and filopodia. Subsequently, a more stable adhesion mediated by integrins is achieved to generate an actin-based force to pull the cell body forward. An example of such co-operation between the two types of adhesion systems can be seen in the recruitment of leukocytes to inflammatory sites. Leukocytes attach to and start rolling on endothelial cells in the inflammatory tissue via selectins. This loose interaction is a prerequisite for the establishment of a strong attachment with integrins. Like CD44, E-selectin is cleaved by metalloproteinase, and TIMP-3 inhibits both the shedding of E-selectin and the rolling of leukocytes on endothelial cells [87].
The integrin avb3, which binds vitronectin, is expressed in endothelial cells during angiogenesis and malignant tumors, and is reported to play crucial roles in angiogenesis, invasion, and metastasis. The av chain, which is translated as a single polypeptide and converted into a two-chain form by proprotein convertases, is alternatively processed by MT1-MMP into a functional form [88]. The expression of avb3 and MT1-MMP in human breast carcinoma MCF-7 cells did not alter the adhesion to vitronectin but stimulated migration on the matrix accompanying phosphorylation of FAK [89]. Additionally, the cell surface transglutaminase (tTG) that associates with the integrin b1 or b3 chain is also cleaved at multiple sites by MT1-MMP. tTG binds fibronectin as a co-receptor with integrin. Cleavage of tTG by MT1-MMP suppressed cell adhesion to and migration on fibronectin. On the other hand, MT1-MMP promoted migration of the same cells on type I collagen [34]. Thus, the migration-promoting activity of MT1-MMP may differ depending on the combinations of adhesion molecules that co-operate with MT-MMP and ECM components.
Laminin-5, a major component of the basement membrane, can support the migration of epithelial cells and tumor cells. MMP-2 was first found to cleave the g2 chain of laminin-5 and promote migration of breast epithelial cells [90]. Later, cells which were constitutively motile on laminin 5 were found to express MT1-MMP rather than MMP-2. Antisense oligonucleotides against the MT1-MMP gene inhibited processing of the g 2 chain and cell migration [23]. Thus, cleavage of the g 2 chain converts it from a static to active form presumably exposing a new functional domain that was cryptic before processing. Since many malignant tumor cells secrete the laminin g 2 chain and CD44 (Fig. 3), the processing of these molecules may support the autonomous locomotion of tumor cells. The importance of g 2 chain processing was also seen during vasculogenic mimicry by malignant melanoma cells [91]. These malignant melanoma cells form branching tubular structures mimicking the capillaries formed by endothelial cells both in vivo and in vitro. Antisense oligonucleotide against the g 2 gene or neutralizing antibody against MT1-MMP inhibited such vasculogenic mimicry [91]. MT1-MMP is also required for tubular formation by endothelial cells in fibrin or type I collagen gel [22, 49]. Treatment of endothelial cells with neutralizing antibody against MT1-MMP reduced migration and capillary tube formation in matrigel [48].

Turnover of MT1-MMP
After appearing as an active enzyme on the surface, MT1-MMP can be inactivated either by TIMPs or proteolytic degradation. In HT1080 cells that express MT1-MMP at high levels, a 43-45 kDa degraded form can be detected in addition to the 60 kDa mature enzyme [92, 93]. This is a result of proteolytic cleavage of the Ala255-Ile bond located at the end of the catalytic domain of MT1-MMP by the action of either MT1-MMP or MMP-2. How are these molecules be cleared from the surface?¡@MT1-MMP has a short cytoplasmic tail of 20 amino acids that mediates internalization of the enzyme [94, 95]. The cytoplasmic tail has a binding site for the m2 subunit of adaptor protein 2 (AP2) that mediates incorporation of the target protein into clathrin-coated pits [94]. Although the internalization is not selective for inactivated MT1-MMP molecules, it is presumably an important part of the mechanism of turnover of MT1-MMP at the migration edge. This is based on the observation that the mutations or deletions of the cytoplasmic sequence that abolished internalization also abrogated the migration- and invasion-promoting activity of the enzyme [94]. In addition to internalization, the cytoplasmic tail has been reported to play a role in the formation of oligomers [38, 39], and the localization of the enzyme to proteolytically active protrusions (invadopodia) [96].

Conclusions
MT1-MMP is a potent ECM-degrading enzyme that acts as part of the invasion machinery when expressed in motile cells such as invasive tumor cells. To promote invasion, MT1-MMP has to be delivered to the migration front of cells as a complex with CD44, and shed CD44 to regulate CD44-dependent adhesion. Additionally it must from homo-oligomers to activate proMMP-2. On the other hand, down-regulation of MT1-MMP by internalization also looks important to keep the space for newly synthesized MT1-MMP molecules to localize at the front. Thus, MT1-MMP appears to be regulated in a coordinated manner with cell migration and invasion. Uncontrolled MT1-MMP expressed on the cell surface cannot promote invasion even though the enzyme retains the intact biochemical activity as observed with the cytoplasmic deletion mutants [94]. The dynamic regulation of MT1-MMP has now been unveiled.

References
1. Nagase, H., and Woessner, J. F., Jr., Matrix metalloproteinases, J Biol Chem 274 (1999) 21491-21494.
2. Brinckerhoff, C. E., and Matrisian, L., Matrix metalloproteinases: a tail of a frog that became a prince, Nature Reviews, Molecular Cell Biology 3 (2002) 207-214.
3. Egeblad, M., and Werb, Z., New functions for the matrix metalloproteinases in cancer progression, Nature Reviews Cancer 2 (2001) 163-176.
4. Edwards, D. R., and Murphy, G., Cancer. Proteases--invasion and more, Nature 394 (1998) 527-528.
5. Stetler-Stevenson, W. G., and Yu, A. E., Proteases in invasion: matrix metalloproteinases, Semin Cancer Biol 11 (2001) 143-152.
6. Zucker, S., Cao, J., and Chen, W. T., Critical appraisal of the use of matrix metalloproteinase inhibitors in cancer treatment, Oncogene 19 (2000) 6642-6650.
7. Coussens, L. M., Fingleton, B., and Matrisian, L. M., Matrix metalloproteinase inhibitors and cancer: trials and tribulations, Science 295 (2002) 2387-2392.
8. Bergers, G., Javaherian, K., Lo, K. M., Folkman, J., and Hanahan, D., Effects of angiogenesis inhibitors on multistage carcinogenesis in mice, Science 284 (1999) 808-812.
9. Sato, H., Takino, T., Okada, Y., Cao, J., Shinagawa, A., Yamamoto, E., and Seiki, M., A matrix metalloproteinase expressed on the surface of invasive tumour cells, Nature 370 (1994) 61-65.
10. Seiki, M., The cell surface: stage for matrix metalloproteinase regulation of migration, Current Opinion in Cell Biology (2002) in press.
11. Itoh, Y., Kajita, M., Kinoh, H., Mori, H., Okada, A., and Seiki, M., Membrane type 4 matrix metalloproteinase (MT4-MMP, MMP-17) is a glycosylphosphatidylinositol-anchored proteinase, J Biol Chem 274 (1999) 34260-34266.
12. Kojima, S., Itoh, Y., Matsumoto, S., Masuho, Y., and Seiki, M., Membrane-type 6 matrix metalloproteinase (MT6-MMP, MMP-25) is the second glycosyl-phosphatidyl inositol (GPI)-anchored MMP, FEBS Lett 480 (2000) 142-146.
13. Ellis, V., and Murphy, G., Cellular strategies for proteolytic targeting during migration and invasion, FEBS Lett 506 (2001) 1-5.
14. Takino, T., Sato, H., Yamamoto, E., and Seiki, M., Cloning of a human gene potentially encoding a novel matrix metalloproteinase having a C-terminal transmembrane domain, Gene 155 (1995) 293-298.
15. Pei, D., and Weiss, S. J., Transmembrane-deletion mutants of the membrane-type matrix metalloproteinase-1 process progelatinase A and express intrinsic matrix-degrading activity, J Biol Chem 271 (1996) 9135-9140.
16. Sato, H., Kinoshita, T., Takino, T., Nakayama, K., and Seiki, M., Activation of a recombinant membrane type 1-matrix metalloproteinase (MT1-MMP) by furin and its interaction with tissue inhibitor of metalloproteinases (TIMP)-2, FEBS Lett 393 (1996) 101-104.
17. Yana, I., and Weiss, S. J., Regulation of membrane type-1 matrix metalloproteinase activation by proprotein convertases, Mol Biol Cell 11 (2000) 2387-2401.
18. Cao, J., Rehemtulla, A., Bahou, W., and Zucker, S., Membrane type matrix metalloproteinase 1 activates pro-gelatinase A without furin cleavage of the N-terminal domain, J Biol Chem 271 (1996) 30174-30180.
19. Okumura, Y., Sato, H., Seiki, M., and Kido, H., Proteolytic activation of the precursor of membrane type 1 matrix metalloproteinase by human plasmin. A possible cell surface activator, FEBS Lett 402 (1997) 181-184.
20. Rozanov, D. V., Ghebrehiwet, B., Postnova, T. I., Eichinger, A., Deryugina, E. I., and Strongin, A. Y., The hemopexin-like C-terminal domain of membrane type-1 matrix metalloproteinase (MT1-MMP) regulates proteolysis of a multifunctional protein gC1qR, J Biol Chem 31 (2001) 31.
21. Sato, T., Kondo, T., Fujisawa, T., Seiki, M., and Ito, A., Furin-independent pathway of membrane type 1-matrix metalloproteinase activation in rabbit dermal fibroblasts, J Biol Chem 274 (1999) 37280-37284.
22. Hiraoka, N., Allen, E., Apel, I. J., Gyetko, M. R., and Weiss, S. J., Matrix metalloproteinases regulate neovascularization by acting as pericellular fibrinolysins, Cell 95 (1998) 365-377.
23. Koshikawa, N., Giannelli, G., Cirulli, V., Miyazaki, K., and Quaranta, V., Role of cell surface metalloprotease MT1-MMP in epithelial cell migration over laminin-5, J Cell Biol 148 (2000) 615-624.
24. Ohuchi, E., Imai, K., Fujii, Y., Sato, H., Seiki, M., and Okada, Y., Membrane type 1 matrix metalloproteinase digests interstitial collagens and other extracellular matrix macromolecules, J Biol Chem 272 (1997) 2446-2451.
25. Imai, K., Ohuchi, E., Aoki, T., Nomura, H., Fujii, Y., Sato, H., Seiki, M., and Okada, Y., Membrane-type matrix metalloproteinase 1 is a gelatinolytic enzyme and is secreted in a complex with tissue inhibitor of metalloproteinases 2, Cancer Res 56 (1996) 2707-2710.
26. Will, H., Atkinson, S. J., Butler, G. S., Smith, B., and Murphy, G., The soluble catalytic domain of membrane type 1 matrix metalloproteinase cleaves the propeptide of progelatinase A and initiates autoproteolytic activation. Regulation by TIMP-2 and TIMP-3, J Biol Chem 271 (1996) 17119-17123.
27. Toth, M., Bernardo, M. M., Gervasi, D. C., Soloway, P. D., Wang, Z., Bigg, H. F., Overall, C. M., DeClerck, Y. A., Tschesche, H., Cher, M. L., Brown, S., Mobashery, S., and Fridman, R., Tissue inhibitor of metalloproteinase (TIMP)-2 acts synergistically with synthetic matrix metalloproteinase (MMP) inhibitors but not with TIMP-4 to enhance the (Membrane type 1)-MMP-dependent activation of pro- MMP-2, J Biol Chem 275 (2000) 41415-41423.
28. Takahashi, C., Sheng, Z., Horan, T. P., Kitayama, H., Maki, M., Hitomi, K., Kitaura, Y., Takai, S., Sasahara, R. M., Horimoto, A., Ikawa, Y., Ratzkin, B. J., Arakawa, T., and Noda, M., Regulation of matrix metalloproteinase-9 and inhibition of tumor invasion by the membrane-anchored glycoprotein RECK, Proc Natl Acad Sci U S A 95 (1998) 13221-13226.
29. Oh, J., Takahashi, R., Kondo, S., Mizoguchi, A., Adachi, E., Sasahara, R. M., Nishimura, S., Imamura, Y., Kitayama, H., Alexander, D. B., Ide, C., Horan, T. P., Arakawa, T., Yoshida, H., Nishikawa, S., Itoh, Y., Seiki, M., Itohara, S., Takahashi, C., and Noda, M., The membrane-anchored MMP inhibitor RECK is a key regulator of extracellular matrix integrity and angiogenesis, Cell 107 (2001) 789-800.
30. Nakada, M., Yamada, A., Takino, T., Miyamori, H., Takahashi, T., Yamashita, J., and Sato, H., Suppression of membrane-type 1 matrix metalloproteinase (MMP)-mediated MMP-2 activation and tumor invasion by testican 3 and its splicing variant gene product, N-Tes, Cancer Res 61 (2001) 8896-8902.
31. Miyamori, H., Takino, T., Kobayashi, Y., Tokai, H., Itoh, Y., Seiki, M., and Sato, H., Claudin promotes activation of pro-matrix metalloproteinase-2 mediated by membrane-type matrix metalloproteinases, J Biol Chem 276 (2001) 28204-28211.
32. Kajita, M., Itoh, Y., Chiba, T., Mori, H., Okada, A., Kinoh, H., and Seiki, M., Membrane-type 1 matrix metalloproteinase cleaves CD44 and promotes cell migration, J Cell Biol 153 (2001) 893-904.
33. Deryugina, E. I., Bourdon, M. A., Jungwirth, K., Smith, J. W., and Strongin, A. Y., Functional activation of integrin alpha V beta 3 in tumor cells expressing membrane-type 1 matrix metalloproteinase, Int J Cancer 86 (2000) 15-23.
34. Belkin, A. M., Akimov, S. S., Zaritskaya, L. S., Ratnikov, B. I., Deryugina, E. I., and Strongin, A. Y., Matrix-dependent proteolysis of surface transglutaminase by membrane- type metalloproteinase regulates cancer cell adhesion and locomotion, J Biol Chem 276 (2001) 18415-18422.
35. Seiki, M., Membrane-type matrix metalloproteinases, Apmis 107 (1999) 137-143.
36. Atkinson, S. J., Crabbe, T., Cowell, S., Ward, R. V., Butler, M. J., Sato, H., Seiki, M., Reynolds, J. J., and Murphy, G., Intermolecular autolytic cleavage can contribute to the activation of progelatinase A by cell membranes, J Biol Chem 270 (1995) 30479-30485.
37. Itoh, Y., Takamura, A., Ito, N., Maru, Y., Sato, H., Suenaga, N., Aoki, T., and Seiki, M., Homophilic complex formation of MT1-MMP facilitates proMMP-2 activation on the cell surface and promotes tumor cell invasion, Embo J 20 (2001) 4782-4793.
38. Lehti, K., Lohi, J., Juntunen, M. M., Pei, D., and Keski-Oja, J., Oligomerization through hemopexin and cytoplasmic domains regulates the activity and turnover of membrane-type 1 matrix metalloproteinase, J Biol Chem 277 (2002) 8440-8448.
39. Rozanov, D. V., Deryugina, E. I., Ratnikov, B. I., Monosov, E. Z., Marchenko, G. N., Quigley, J. P., and Strongin, A. Y., Mutation analysis of membrane type-1 matrix metalloproteinase (MT1- MMP). The role of the cytoplasmic tail Cys(574), the active site Glu(240), and furin cleavage motifs in oligomerization, processing, and self-proteolysis of MT1-MMP expressed in breast carcinoma cells, J Biol Chem 276 (2001) 25705-25714.
40. Knauper, V., Will, H., Lopez-Otin, C., Smith, B., Atkinson, S. J., Stanton, H., Hembry, R. M., and Murphy, G., Cellular mechanisms for human procollagenase-3 (MMP-13) activation. Evidence that MT1-MMP (MMP-14) and gelatinase a (MMP-2) are able to generate active enzyme, J Biol Chem 271 (1996) 17124-17131.
41. Holmbeck, K., Bianco, P., Caterina, J., Yamada, S., Kromer, M., Kuznetsov, S. A., Mankani, M., Robey, P. G., Poole, A. R., Pidoux, I., Ward, J. M., and Birkedal-Hansen, H., MT1-MMP-deficient mice develop dwarfism, osteopenia, arthritis, and connective tissue disease due to inadequate collagen turnover, Cell 99 (1999) 81-92.
42. Zhou, Z., Apte, S. S., Soininen, R., Cao, R., Baaklini, G. Y., Rauser, R. W., Wang, J., Cao, Y., and Tryggvason, K., Impaired endochondral ossification and angiogenesis in mice deficient in membrane-type matrix metalloproteinase I, Proc Natl Acad Sci U S A 97 (2000) 4052-4057.
43. Itoh, T., Ikeda, T., Gomi, H., Nakao, S., Suzuki, T., and Itohara, S., Unaltered secretion of beta-amyloid precursor protein in gelatinase A (matrix metalloproteinase 2)-deficient mice, J Biol Chem 272 (1997) 22389-22392.
44. Kinoh, H., Sato, H., Tsunezuka, Y., Takino, T., Kawashima, A., Okada, Y., and Seiki, M., MT-MMP, the cell surface activator of proMMP-2 (pro-gelatinase A), is expressed with its substrate in mouse tissue during embryogenesis, J Cell Sci 109 (1996) 953-959.
45. Apte, S. S., Fukai, N., Beier, D. R., and Olsen, B. R., The matrix metalloproteinase-14 (MMP-14) gene is structurally distinct from other MMP genes and is co-expressed with the TIMP-2 gene during mouse embryogenesis, J Biol Chem 272 (1997) 25511-25517.
46. Okada, A., Tomasetto, C., Lutz, Y., Bellocq, J. P., Rio, M. C., and Basset, P., Expression of matrix metalloproteinases during rat skin wound healing: evidence that membrane type-1 matrix metalloproteinase is a stromal activator of pro-gelatinase A, J Cell Biol 137 (1997) 67-77.
47. Chan, V. T., Zhang, D. N., Nagaravapu, U., Hultquist, K., Romero, L. I., and Herron, G. S., Membrane-type matrix metalloproteinases in human dermal microvascular endothelial cells: expression and morphogenetic correlation, J Invest Dermatol 111 (1998) 1153-1159.
48. Galvez, B. G., Matias-Roman, S., Albar, J. P., Sanchez-Madrid, F., and Arroyo, A. G., Membrane type 1-matrix metalloproteinase is activated during migration of human endothelial cells and modulates endothelial motility and matrix remodeling, J Biol Chem 276 (2001) 37491-37500.
49. Haas, T. L., Davis, S. J., and Madri, J. A., Three-dimensional type I collagen lattices induce coordinate expression of matrix metalloproteinases MT1-MMP and MMP-2 in microvascular endothelial cells, J Biol Chem 273 (1998) 3604-3610.
50. Tokuraku, M., Sato, H., Murakami, S., Okada, Y., Watanabe, Y., and Seiki, M., Activation of the precursor of gelatinase A/72 kDa type IV collagenase/MMP-2 in lung carcinomas correlates with the expression of membrane-type matrix metalloproteinase (MT-MMP) and with lymph node metastasis, Int J Cancer 64 (1995) 355-359.
51. Polette, M., Nawrocki, B., Gilles, C., Sato, H., Seiki, M., Tournier, J. M., and Birembaut, P., MT-MMP expression and localisation in human lung and breast cancers, Virchows Arch 428 (1996) 29-35.
52. Nawrocki, B., Polette, M., Marchand, V., Monteau, M., Gillery, P., Tournier, J. M., and Birembaut, P., Expression of matrix metalloproteinases and their inhibitors in human bronchopulmonary carcinomas: quantificative and morphological analyses, Int J Cancer 72 (1997) 556-564.
53. Nomura, H., Sato, H., Seiki, M., Mai, M., and Okada, Y., Expression of membrane-type matrix metalloproteinase in human gastric carcinomas, Cancer Res 55 (1995) 3263-3266.
54. Mori, M., Mimori, K., Shiraishi, T., Fujie, T., Baba, K., Kusumoto, H., Haraguchi, M., Ueo, H., and Akiyoshi, T., Analysis of MT1-MMP and MMP2 expression in human gastric cancers, Int J Cancer 74 (1997) 316-321.
55. Bando, E., Yonemura, Y., Endou, Y., Sasaki, T., Taniguchi, K., Fujita, H., Fushida, S., Fujimura, T., Nishimura, G., Miwa, K., and Seiki, M., Immunohistochemical study of MT-MMP tissue status in gastric carcinoma and correlation with survival analyzed by univariate and multivariate analysis, Oncol Rep 5 (1998) 1483-1488.
56. Ohtani, H., Motohashi, H., Sato, H., Seiki, M., and Nagura, H., Dual over-expression pattern of membrane-type metalloproteinase-1 in cancer and stromal cells in human gastrointestinal carcinoma revealed by in situ hybridization and immunoelectron microscopy, Int J Cancer 68 (1996) 565-570.
57. Imamura, T., Ohshio, G., Mise, M., Harada, T., Suwa, H., Okada, N., Wang, Z., Yoshitomi, S., Tanaka, T., Sato, H., Arii, S., Seiki, M., and Imamura, M., Expression of membrane-type matrix metalloproteinase-1 in human pancreatic adenocarcinomas, J Cancer Res Clin Oncol 124 (1998) 65-72.
58. Ishigaki, S., Toi, M., Ueno, T., Matsumoto, H., Muta, M., Koike, M., and Seiki, M., Significance of membrane type 1 matrix metalloproteinase expression in breast cancer, Jpn J Cancer Res 90 (1999) 516-522.
59. Ueno, H., Nakamura, H., Inoue, M., Imai, K., Noguchi, M., Sato, H., Seiki, M., and Okada, Y., Expression and tissue localization of membrane-types 1, 2, and 3 matrix metalloproteinases in human invasive breast carcinomas, Cancer Res 57 (1997) 2055-2060.
60. Kanayama, H., Yokota, K., Kurokawa, Y., Murakami, Y., Nishitani, M., and Kagawa, S., Prognostic values of matrix metalloproteinase-2 and tissue inhibitor of metalloproteinase-2 expression in bladder cancer, Cancer 82 (1998) 1359-1366.
61. Yoshizaki, T., Sato, H., Maruyama, Y., Murono, S., Furukawa, M., Park, C. S., and Seiki, M., Increased expression of membrane type 1-matrix metalloproteinase in head and neck carcinoma, Cancer 79 (1997) 139-144.
62. Nakamura, H., Ueno, H., Yamashita, K., Shimada, T., Yamamoto, E., Noguchi, M., Fujimoto, N., Sato, H., Seiki, M., and Okada, Y., Enhanced production and activation of progelatinase A mediated by membrane-type 1 matrix metalloproteinase in human papillary thyroid carcinomas, Cancer Res 59 (1999) 467-473.
63. Afzal, S., Lalani, E. N., Poulsom, R., Stubbs, A., Rowlinson, G., Sato, H., Seiki, M., and Stamp, G. W., MT1-MMP and MMP-2 mRNA expression in human ovarian tumors: possible implications for the role of desmoplastic fibroblasts, Hum Pathol 29 (1998) 155-165.
64. Fishman, D. A., Bafetti, L. M., and Stack, M. S., Membrane-type matrix metalloproteinase expression and matrix metalloproteinase-2 activation in primary human ovarian epithelial carcinoma cells, Invasion Metastasis 16 (1996) 150-159.
65. Gilles, C., Polette, M., Piette, J., Munaut, C., Thompson, E. W., Birembaut, P., and Foidart, J. M., High level of MT-MMP expression is associated with invasiveness of cervical cancer cells, Int. J. Cancer 65 (1996) 209-213.
66. Yamamoto, M., Mohanam, S., Sawaya, R., Fuller, G. N., Seiki, M., Sato, H., Gokaslan, Z. L., Liotta, L. A., Nicolson, G. L., and Rao, J. S., Differential expression of membrane-type matrix metalloproteinase and its correlation with gelatinase A activation in human malignant brain tumors in vivo and in vitro, Cancer Res 56 (1996) 384-392.
67. Nakada, M., Nakamura, H., Ikeda, E., Fujimoto, N., Yamashita, J., Sato, H., Seiki, M., and Okada, Y., Expression and tissue localization of membrane-type 1, 2, and 3 matrix metalloproteinases in human astrocytic tumors, Am J Pathol 154 (1999) 417-428.
68. Forsyth, P. A., Wong, H., Laing, T. D., Rewcastle, N. B., Morris, D. G., Muzik, H., Leco, K. J., Johnston, R. N., Brasher, P. M., Sutherland, G., and Edwards, D. R., Gelatinase-A (MMP-2), gelatinase-B (MMP-9) and membrane type matrix metalloproteinase-1 (MT1-MMP) are involved in different aspects of the pathophysiology of malignant gliomas, Br J Cancer 79 (1999) 1828-1835.
69. Heppner, K. J., Matrisian, L. M., Jensen, R. A., and Rodgers, W. H., Expression of most matrix metalloproteinase family members in breast cancer represents a tumor-induced host response, Am J Pathol 149 (1996) 273-282.
70. Takahashi, M., Tsunoda, T., Seiki, M., Nakamura, Y., and Furukawa, Y., Identification of membrane-type matrix metalloproteinase-1 as a target of the b-catenin/Tcf4 complex in human colorectal cancers, Oncogene 22 (2002) in press.
71. Cha, H. J., Okada, A., Kim, K. W., Sato, H., and Seiki, M., Identification of cis-acting promoter elements that support expression of membrane-type 1 matrix metalloproteinase (MT1-MMP) in v-src transformed Madin-Darby canine kidney cells, Clin Exp Metastasis 18 (2000) 675-681.
72. Stetler-Stevenson, W. G., Aznavoorian, S., and Liotta, L. A., Tumor cell interactions with the extracellular matrix during invasion and metastasis, Annu Rev Cell Biol 9 (1993) 541-573.
73. Tryggvason, K., Hoyhtya, M., and Pyke, C., Type IV collagenases in invasive tumors, Breast Cancer Res Treat 24 (1993) 209-218.
74. Sato, H., Kida, Y., Mai, M., Endo, Y., Sasaki, T., Tanaka, J., and Seiki, M., Expression of genes encoding type IV collagen-degrading metalloproteinases and tissue inhibitors of metalloproteinases in various human tumor cells, Oncogene 7 (1992) 77-83.
75. Okada, A., Bellocq, J. P., Rouyer, N., Chenard, M. P., Rio, M. C., Chambon, P., and Basset, P., Membrane-type matrix metalloproteinase (MT-MMP) gene is expressed in stromal cells of human colon, breast, and head and neck carcinomas, Proceedings of the National Academy of Sciences of the United States of America 92 (1995) 2730-2734.
76. Chenard, M. P., Lutz, Y., Mechine-Neuville, A., Stoll, I., Bellocq, J. P., Rio, M. C., and Basset, P., Presence of high levels of MT1-MMP protein in fibroblastic cells of human invasive carcinomas, Int J Cancer 82 (1999) 208-212.
77. Pulyaeva, H., Bueno, J., Polette, M., Birembaut, P., Sato, H., Seiki, M., and Thompson, E. W., MT1-MMP correlates with MMP-2 activation potential seen after epithelial to mesenchymal transition in human breast carcinoma cells, Clin Exp Metastasis 15 (1997) 111-120.
78. Kadono, Y., Shibahara, K., Namiki, M., Watanabe, Y., Seiki, M., and Sato, H., Membrane type 1-matrix metalloproteinase is involved in the formation of hepatocyte growth factor/scatter factor-induced branching tubules in madin-darby canine kidney epithelial cells, Biochem Biophys Res Commun 251 (1998) 681-687.
79. Hotary, K., Allen, E., Punturieri, A., Yana, I., and Weiss, S. J., Regulation of cell invasion and morphogenesis in a three-dimensional type I collagen matrix by membrane-type matrix metalloproteinases 1, 2, and 3, J Cell Biol 149 (2000) 1309-1323.
80. Mori, H., Tomari, T., Koshikawa, N., Kajita, M., Itoh, Y., Sato, H., Tojo, H., Yana, I., and Seiki, M., CD44 directs membrane-type 1 matrix metalloproteinaseto lamellipodia by associating with its hemopexin-like domain, EMBO J in press (2002)
81. Zhuge, Y., and Xu, J., Rac1 mediates type I collagen-dependent MMP-2 activation. role in cell invasion across collagen barrier, J Biol Chem 276 (2001) 16248-16256.
82. Gingras, D., Bousquet-Gagnon, N., Langlois, S., Lachambre, M. P., Annabi, B., and Beliveau, R., Activation of the extracellular signal-regulated protein kinase (ERK) cascade by membrane-type-1 matrix metalloproteinase (MT1-MMP), FEBS Lett 507 (2001) 231-236.
83. Okamoto, I., Kawano, Y., Tsuiki, H., Sasaki, J., Nakao, M., Matsumoto, M., Suga, M., Ando, M., Nakajima, M., and Saya, H., CD44 cleavage induced by a membrane-associated metalloprotease plays a critical role in tumor cell migration, Oncogene 18 (1999) 1435-1446.
84. Okamoto, I., Kawano, Y., Matsumoto, M., Suga, M., Kaibuchi, K., Ando, M., and Saya, H., Regulated CD44 cleavage under the control of protein kinase C, calcium influx, and the Rho family of small G proteins, J Biol Chem 274 (1999) 25525-25534.
85. Okamoto, I., Kawano, Y., Murakami, D., Sasayama, T., Araki, N., Miki, T., Wong, A. J., and Saya, H., Proteolytic release of CD44 intracellular domain and its role in the CD44 signaling pathway, J Cell Biol 155 (2001) 755-762.
86. Webb, D. J., Parsons, T., and Horwitz, A. F., Adhesion assembly, disassembly and turnover in migrating cells-over and over and over again, Nature Cell Biology 4 (2002) 97-100.
87. Borland, G., Murphy, G., and Ager, A., Tissue inhibitor of metalloproteinases-3 inhibits shedding of L- selectin from leukocytes, J Biol Chem 274 (1999) 2810-2815.
88. Ratnikov, B. I., Rozanov, D. V., Postnova, T. I., Baciu, P. G., Zhang, H., DiScipio, R. G., Chestukhina, G. G., Smith, J. W., Deryugina, E. I., and Strongin, A. Y., An Alternative Processing of Integrin alpha v Subunit in Tumor Cells by Membrane Type-1 Matrix Metalloproteinase, J Biol Chem 277 (2002) 7377-7385.
89. Deryugina, E. I., Ratnikov, B. I., Postnova, T. I., Rozanov, D. V., and Strongin, A. Y., Processing of Integrin alpha v Subunit by Membrane Type 1 Matrix Metalloproteinase Stimulates Migration of Breast Carcinoma Cells on Vitronectin and Enhances Tyrosine Phosphorylation of Focal Adhesion Kinase, J Biol Chem 277 (2002) 9749-9756.
90. Giannelli, G., Falk-Marzillier, J., Schiraldi, O., Stetler-Stevenson, W. G., and Quaranta, V., Induction of cell migration by matrix metalloprotease-2 cleavage of laminin-5, Science 277 (1997) 225-228.
91. Seftor, R. E., Seftor, E. A., Koshikawa, N., Meltzer, P. S., Gardner, L. M., Bilban, M., Stetler-Stevenson, W. G., Quaranta, V., and Hendrix, M. J., Cooperative interactions of laminin 5 gamma2 chain, matrix metalloproteinase-2, and membrane type-1-matrix/metalloproteinase are required for mimicry of embryonic vasculogenesis by aggressive melanoma, Cancer Res 61 (2001) 6322-6327.
92. Stanton, H., Gavrilovic, J., Atkinson, S. J., d'Ortho, M. P., Yamada, K. M., Zardi, L., and Murphy, G., The activation of ProMMP-2 (gelatinase A) by HT1080 fibrosarcoma cells is promoted by culture on a fibronectin substrate and is concomitant with an increase in processing of MT1-MMP (MMP-14) to a 45 kDa form, J Cell Sci 111 (1998) 2789-2798.
93. Lehti, K., Lohi, J., Valtanen, H., and Keski-Oja, J., Proteolytic processing of membrane-type-1 matrix metalloproteinase is associated with gelatinase A activation at the cell surface, Biochem J 334 (1998) 345-353.
94. Uekita, T., Itoh, Y., Yana, I., Ohno, H., and Seiki, M., Cytoplasmic tail-dependent internalization of membrane-type 1 matrix metalloproteinase is important for its invasion-promoting activity, J Cell Biol 155 (2001) 1345-1356.
95. Jiang, A., Lehti, K., Wang, X., Weiss, S. J., Keski-Oja, J., and Pei, D., Regulation of membrane-type matrix metalloproteinase 1 activity by dynamin-mediated endocytosis, Proc Natl Acad Sci U S A 98 (2001) 13693-13698.
96. Nakahara, H., Howard, L., Thompson, E. W., Sato, H., Seiki, M., Yeh, Y., and Chen, W. T., Transmembrane/cytoplasmic domain-mediated membrane type 1-matrix metalloprotease docking to invadopodia is required for cell invasion, Proc Natl Acad Sci U S A 94 (1997) 7959-7964.
97. McCawley, L. J., and Matrisian, L. M., Matrix metalloproteinases: they're not just for matrix anymore!, Curr Opin Cell Biol 13 (2001) 534-540.
98. Cowell, S., Knauper, V., Stewart, M. L., D'Ortho, M. P., Stanton, H., Hembry, R. M., Lopez-Otin, C., Reynolds, J. J., and Murphy, G., Induction of matrix metalloproteinase activation cascades based on membrane-type 1 matrix metalloproteinase: associated activation of gelatinase A, gelatinase B and collagenase 3, Biochem J 331 (1998) 453-458.
99. Lohi, J., Lehti, K., Valtanen, H., Parks, W. C., and Keski-Oja, J., Structural analysis and promoter characterization of the human membrane- type matrix metalloproteinase-1 (MT1-MMP) gene, Gene 242 (2000) 75-86.
100. Haas, T. L., Stitelman, D., Davis, S. J., Apte, S. S., and Madri, J. A., Egr-1 mediates extracellular matrix-driven transcription of membrane type 1 matrix metalloproteinase in endothelium, J Biol Chem 274 (1999) 22679-22685.

Figure 1. Domain structure of MMPs.

The typical domain structure of proMMPs is composed of a propeptide, a catalytic (CAT) domain, and a hemopexine-like (PEX) domain from the N-terminus. The propeptide is needed to keep latency of proenzyme and has to be removed proteolytically to generate active mature enzyme. Some propeptide sequences contain RXKR motif that act as the cleavage site by proprotein convertases (PCs), and therefore, these proMMPs are activated during secretion (intracellular activation). Other proMMPs are activated by serine or metalloproteinases after secreted into tissue. The CAT domain holds a zinc ion (Zn) to carry out proteolytic reaction. The PEX domain has an ability to interact with proteins that modulate biochemical property of the enzyme. MMP-2 and MMP-9 have collagen-binding type II repeats of fibronectin (Fn II). MT-MMPs anchor plasma membrane either through transmembrane sequence or GPI anchor. Thus, MMPs can be calcified into two major classes according to the membrane-anchoring sequences at the C-terminus (MT-MMPs and secreted MMPs). MMP-23 is a unique intermediate type, having a type II transmembrane domain and a cystein array and immunoglobulin-like domain instead of a hemopexin-like domain. Each MMP has different substrate specificity with some overlap with others, and most of the ECM components in tissue can be degraded by a concerted action of multiple MMPs. Substrates of enzymes are summarized in recent review articles [3, 97].

Figure 2. Substrates of MT1-MMP

MT1-MMP digests ECM components directly as listed in the left of the figure and in the text. In addition, cell adhesion molecules on cell surface are also the substrates for MT1-MMP as listed in the middle. In the right, MT1-MMP mediates activation of proMMPs including proMMP-2 (pro-gelatinase A/72kDa type IV collagenase) and proMMP-13 (pro-collagenase 3). ProMMP-9 (pro-gelatinase B/92kDa type IV collagenase) can also be activated indirectly by the action of MMP-2 and MMP-13�@[98]. By activating other MMPs, MT1-MMP can degrade wider range of ECM components than by itself.

Figure 3. Transcriptional regulation of MT1-MMP gene.

In the 5�f flanking region of the MT1-MMP gene, four distinct regulatory sites have been identified. There are binding sites for Egr-1 and Sp-1 close to the multiple transcription start sites. Sp-1 binding site is critical for the basal promoter activity�@[71, 99]. Egr-1 mediates MT1-MMP transcription that is induced in endothelial cells cultivated in collagen gel [100]. In the upstream of these sites, there is a v-src-responsive element that mediates enhanced gene expression in the MDCK cells transformed by v-Src [71]. The Tcf-4 binding site is responsible for the expression of the gene in SW480 colon carcinoma cells that have mutation in the APC gene [70]. APC mediates the Wnt signal and negatively regulates b-catenin levels in the cytoplasm by degrading it. Mutations of APC gene abrogate this regulation, increase the level of b-catenin in cytoplasm, and promote its translocation into nucleus. By forming a complex with Tcf-4, b-catenin activates transcription of the target genes including MT1-MMP. Interestingly, the target gene products of this aberrant signal include CD44 and laminin g2 [70] that cooperate with MT1-MMP for invasion.

Figure 4. Localization of MT1-MMP at cell migration front and homo-oligomer formation.

During cell migration, CD44 localizes at the migration front and this localization is mediated by the cytoplasmic domain that associates with actin cytoskeleton. By forming a complex with CD44, MT1-MMP also localizes at the migration front [80]. The hemopexin-like domain of MT1-MMP is the site for the complex formation with CD44 and determines its localization on cell surface. Localization of MT1-MMP to the migration edge also induces homo-oligomer formation that augments proMMP-2 activation [37] as described in the text.

Back . . .