Ikuo Yana

CD44 directs membrane‐type 1 matrix metalloproteinase to lamellipodia by associating with its hemopexin‐like domain

Membrane‐type 1 matrix metalloproteinase (MT1‐ MMP) localizes at the front of migrating cells and degrades the extracellular matrix barrier during cancer invasion. However, it is poorly understood how the polarized distribution of MT1‐MMP at the migration front is regulated. Here, we demonstrate that MT1‐MMP forms a complex with CD44H via the hemopexin‐like (PEX) domain. A mutant MT1‐MMP lacking the PEX domain failed to bind CD44H and did not localize at the lamellipodia. The cytoplasmic tail of CD44H, which comprises interfaces that associate with the actin cytoskeleton, was important for its localization at lamellipodia. Overexpression of a CD44H mutant lacking the cytoplasmic tail also prevented MT1‐MMP from localizing at the lamellipodia. Modulation of F‐actin with cytochalasin D revealed that both CD44H and MT1‐MMP co‐localize closely with the actin cytoskeleton, dependent on the cytoplasmic tail of CD44H. Thus, CD44H appears to act as a linker that connects MT1‐MMP to the actin cytoskeleton and to play a role in directing MT1‐MMP to the migration front. The PEX domain of MT1‐MMP was indispensable in promoting cell migration and CD44H shedding.

Cytoplasmic tail-dependent internalization of membrane-type 1 matrix metalloproteinase is important for its invasion-promoting activity.

Membrane-type 1 matrix metalloproteinase (MT1-MMP) is an integral membrane proteinase that degrades the pericellular extracellular matrix (ECM) and is expressed in many migratory cells, including invasive cancer cells. MT1-MMP has been shown to localize at the migration edge and to promote cell migration; however, it is not clear how the enzyme is regulated during the migration process. Here, we report that MT1-MMP is internalized from the surface and that this event depends on the sequence of its cytoplasmic tail. Di-leucine (Leu571–572 and Leu578–579) and tyrosine573 residues are important for the internalization, and the μ2 subunit of adaptor protein 2, a component of clathrin-coated pits for membrane protein internalization, was found to bind to the LLY573 sequence. MT1-MMP was internalized predominantly at the adherent edge and was found to colocalize with clathrin-coated vesicles. The mutations that disturb internalization caused accumulation of the enzyme at the adherent edge, though the net proteolytic activity was not affected much. Interestingly, whereas expression of MT1-MMP enhances cell migration and invasion, the internalization-defective mutants failed to promote either activity. These data indicate that dynamic turnover of MT1-MMP at the migration edge by internalization is important for proper enzyme function during cell migration and invasion.

Negative Regulation of Osteoclastogenesis by Ectodomain Shedding of Receptor Activator of NF-κB Ligand

Receptor activator of NF-κB ligand (RANKL) is a transmembrane glycoprotein that has an essential role in the development of osteoclasts. The extracellular portion of RANKL is cleaved proteolytically to produce soluble RANKL, but definite RANKL sheddase(s) and the physiologic function of RANKL shedding have not yet been determined. In the present study, we found that matrix metalloproteinase (MMP) 14 and a disintegrin and metalloproteinase (ADAM) 10 have strong RANKL shedding activity. In Western blot analysis, soluble RANKL was detected as two different molecular weight products, and RNA interference of MMP14 and ADAM10 resulted in a reduction of both the lower and higher molecular weight products. Suppression of MMP14 in primary osteoblasts increased membrane-bound RANKL and promoted osteoclastogenesis in cocultures with macrophages. Soluble RANKL produced by osteoblasts from MMP14-deficient mice was markedly reduced, and their osteoclastogenic activity was promoted, consistent with the findings of increased osteoclastogenesis in vivo. RANKL shedding is an important process that down-regulates local osteoclastogenesis.

Crosstalk between neovessels and mural cells directs the site-specific expression of MT1-MMP to endothelial tip cells

The membrane-anchored matrix metalloproteinase MT1-MMP (also known as Mmp14) plays a key role in the angiogenic process, but the mechanisms underlying its spatiotemporal regulation in the in vivo setting have not been defined. Using whole-mount immunohistochemical analysis and the lacZ gene inserted into the Mmp14 gene, we demonstrate that MT1-MMP vascular expression in vivo is confined largely to the sprouting tip of neocapillary structures where endothelial cell proliferation and collagen degradation are coordinately localized. During angiogenesis in vitro, wherein endothelial cells are stimulated to undergo neovessel formation in the presence or absence of accessory mural cells, site-specific MT1-MMP expression is shown to be controlled by crosstalk between endothelial cells and vascular smooth muscle cells (VSMC). When vessel maturation induced by VSMCs is inhibited by introducing a soluble form of the receptor tyrosine kinase Tek, MT1-MMP distribution is no longer restricted to the endothelial tip cells, but instead distributes throughout the neovessel network in vitro as well as ex vivo. Taken together, these data demonstrate that vascular maturation coordinated by endothelial cell/mural cell interactions redirects MT1-MMP expression to the neovessel tip where the protease regulates matrix remodeling at the leading edge of the developing vasculature.

Roles of pericellular proteolysis by membrane type-1 matrix metalloproteinase in cancer invasion and angiogenesis.

Behavior of cancer cells is profoundly affected by their microenvironment, which is often controlled by pericellular proteolysis or the processing of protein components, including extracellular matrices, growth factors, cytokines, receptors, cell adhesion molecules, and so on. Matrix metalloproteinases (MMPs) are a family of zinc‐dependent proteases responsible for the proteolytic events in the extracellular milieu. Among the multiple MMPs expressed in a wide range of tumors, membrane type‐1 MMP (MT1‐MMP), which is expressed especially in tumor cells with significant invasive properties, is thought to be particularly important for pericellular proteolysis. Recent studies have elucidated in part how MT1‐MMP is regulated biologically for the promotion of invasion by tumors or for angiogenesis by endothelial cells. Understanding of the proteolysis by, and the regulation of MT1‐MMP, which probably promotes cell invasion, could provide a therapeutic hint as to how to block or delay the progression of cancer.

Role of pericellular proteolysis by membrane-type 1 matrix metalloproteinase in cancer invasion and angiogenesis.

Membrane-type 1 matrix metalloproteinase (MT1-MMP) is an integral membrane proteinase that is frequently expressed in malignant cancer cells and has potent invasion-promoting activity. When expressed on the cell surface, MT1-MMP degrades the extracellular matrix (ECM) barrier adjacent to the cells to maintain the migration route to traverse the tissue. But MT1-MMP is not just an enzyme that degrades ECM. MT1-MMP also introduces limited cleavage into proteins at the cell-ECM interspaces and converts their functions. The target molecules are ECM components, cell adhesion molecules, and latent forms of MMPs. Through these processing events MT1-MMP modulates the migratory and invasive behavior of the cells.

MT-MMPs play pivotal roles in cancer dissemination.

Matrix metalloproteinases (MMPs), a family of zinc-binding endopeptidases, play important roles in cancer proliferation and dissemination, and may be further associated with other diseases. In particular, membrane-type MMPs (MT-MMPs) are crucial for cancer cell invasion. In this report, we summarize the current views on the role of MT-MMPs in cancer dissemination. The regulated and restricted degradation of the extracellular matrix (ECM) surrounding the tumor surface is a trigger event for cell protrusion and invasion. This is thought to be primarily organized by MT-MMPs, since a shift in balance between cell adhesion molecules, ECM and proteolysis at the focal cell surface may result in conditions especially suitable for cancer cells to progress and invade the ECM. To resolve the physiological mechanisms of cancer invasion and migration, molecular milieu surrounding the MT-MMPs expressed on tumor cell surfaces should be further examined for each cell type, which may consequently provide a novel clinical tool to regulate cancer behavior.

Stroma-Derived Matrix Metalloproteinase (MMP)-2 Promotes Membrane Type 1-MMP–Dependent Tumor Growth in Mice

Matrix metalloproteinase-2 (MMP-2) is a stroma-derived MMP belonging to the type IV collagenase family. It is believed to mediate tumor cell behavior by degrading deposits of type IV collagen, a major component of the basement membrane. The membrane type 1-MMP (MT1-MMP) is a highly potent activator of MMP-2 and is expressed in many tumor and stromal cells. However, the roles played by stromal MMP-2 in tumor progression in vivo remain poorly understood. We established a colon epithelial cell line from an Mt1-mmp(-/-) mouse strain and transfected these cells with an inducible expression system for MT1-MMP (MT1rev cells). Following s.c. implantation into Mmp-2(+/+) mice and induction of MT1-MMP expression, MT1rev cells grew rapidly, whereas they grew very slowly in Mmp-2(-/-) mice, even in the presence of MT1-MMP. This MT1-MMP-dependent tumor growth of MT1rev cells was enhanced in Mmp-2(-/-) mice as long as MMP-2 was supplied via transfection or coimplantation of MMP-2-positive fibroblasts. MT1rev cells cultured in vitro in a three-dimensional collagen gel matrix also required the MT1-MMP/MMP-2 axis for rapid proliferation. MT1rev cells deposit type IV collagen primarily at the cell-collagen interface, and these deposits seem scarce at sites of invasion and proliferation. These data suggest that cooperation between stroma-derived MMP-2 and tumor-derived MT1-MMP may play a role in tumor invasion and proliferation via remodeling of the tumor-associated basement membrane. To our knowledge, this is the first study demonstrating that MT1-MMP-dependent tumor growth in vivo requires stromal-derived MMP-2. It also suggests that MMP-2 represents a potential target for tumor therapeutics.

Absence of mechanical allodynia and Aβ‐fiber sprouting after sciatic nerve injury in mice lacking membrane‐type 5 matrix metalloproteinase

Matrix metalloproteinases (MMPs) are a family of endopeptidases that degrade extracellular matrix components. Membrane‐type 5 MMP (MT5‐MMP/MMP‐24) was identified as neuron‐specific, and is believed to contribute to neuronal circuit formation and plasticity. To elucidate its function in vivo, we have generated mice lacking MT5‐MMP by gene targeting. MT5‐MMP‐deficient mice were born without obvious morphological abnormalities. No apparent histological defects were observed in the nervous system either. However, MT5‐MMP‐deficient mice did not develop neuropathic pain with mechanical allodynia after sciatic nerve injury, though responses to acute noxious stimuli were normal. Neuropathic pain induced by peripheral nerve lesions is known to accompany structural reorganization of the nervous system. Intraneural injection of cholera toxin B subunit, a transganglionic tracer, into the injured sciatic nerve of wild‐type mice revealed that the myelinated Aβ‐fiber primary afferents sprouted from laminae III–VI of the dorsal horn of the spinal cord and invaded lamina II. However, no such sprouting and invasion of Aβ‐fibers were observed in MT5‐MMP‐deficient mice. These findings suggest that MT5‐MMP is essential for the development of mechanical allodynia and plays an important role in neuronal plasticity in this mouse model.

Competitive disruption of the tumor-promoting function of membrane type 1 matrix metalloproteinase/matrix metalloproteinase-14 in vivo

Membrane type 1 matrix metalloproteinase (MT1-MMP) is a potent modulator of the pericellular environment and promotes tumor cell invasion and proliferation in many types of tumor. The activation of proMMP-2 and processing of collagen I by MT1-MMP have been thought to be important for its tumor-promoting function. These activities can be inhibited by mutant forms of MT1-MMP lacking the catalytic domain. However, the effect of such dominant-negative mutants has never been evaluated in vivo. Various mutants lacking the catalytic domain (dCAT) were prepared and confirmed to inhibit MT1-MMP activity in human fibrosarcoma HT1080 cells, and tumor cells expressing these mutants were implanted s.c. into nude mice to monitor tumor formation. Only the membrane-anchored form of a dCAT construct through the transmembrane domain [dCAT(1)] showed potent antitumor activity not only in HT1080 cells but also in gastric carcinoma MKN28 and MKN45 cells expressing MT1-MMP. A soluble form of dCAT lacking the transmembrane domain did not show such activity. The expression of dCAT(1) in MKN28 or MKN45 further prevented the metastatic spread of tumor cells into the peritoneal cavity; however, dCAT(1) showed no effect against TMK-1, another gastric carcinoma cell line expressing no MT1-MMP. It is of note that the tumorigenicity of TMK-1 cells enhanced by MT1-MMP overexpression was, in turn, canceled by the additional expression of dCAT(1). Thus, MT1-MMP expressed in tumor cells seems to play a pivotal role in tumor growth in mice. The results also suggest new possibilities to abrogate the tumor-promoting function of MT1-MMP other than the conventional protease inhibitor–based approach.