Membrane Type 1 Matrix Metalloproteinase Regulates Collagen-Dependent Mitogen-Activated Protein/Extracellular Signal-Related Kinase Activation and Cell Migration

The second dimer interface of MT1-MMP, the transmembrane domain, is essential for ProMMP-2 activation on the cell surface

Activation of proMMP-2 and cell surface collagenolysis are important activities of membrane-type 1 matrix metalloproteinase (MT1-MMP) to promote cell migration in tissue, and these activities are regulated by homodimerization of MT1-MMP on the cell surface. In this study, we have identified the transmembrane domain as a second dimer interface of MT1-MMP in addition to the previously identified hemopexin domain. Our analyses indicate that these two modes of dimerization have different roles; transmembrane-dependent dimerization is critical for proMMP-2 activation, whereas hemopexin-dependent dimerization is important for degradation of collagen on the cell surface. Our finding provides new insight into the potential molecular arrangement of MT1-MMP contributing to its function on the cell surface.

Granulocyte-macrophage colony stimulating factor induces endothelial capillary formation through induction of membrane-type 1 matrix metalloproteinase expression in vitro

In our study, we examined the mechanism by which granulocyte-macrophage colony stimulating factor (GM-CSF) regulates angiogenesis using in vitro models. GM-CSF significantly increased precapillary sprout-like formation from endothelial cell spheroids seeded in type-I collagen gels and tubule formation on coculture of endothelial cells with fibroblasts. In both cases, sprout and tubule formation was highly dependent on metalloproteinase activity. Tissue Inhibitor of metalloproteinase (TIMP) profiling in the spheroid and coculture models showed inhibition by TIMP-2 but not by TIMP-1, indicative of activity of membrane-type matrix metalloproteinases (MT-MMPs). GM-CSF induced sprout formation in spheroids was found to be potently inhibited by siRNA specific for MT1-MMP. Subsequent analysis showed that GM-CSF transiently increased MT1-MMP mRNA in endothelial cells in a MEK-dependent mechanism, which led to increased surface levels of MT1-MMP. This was accompanied by an increase in MT1-MMP-dependent degradation of DQ-collagen by lysates of GM-CSF stimulated endothelial cells. GM-CSF did not increase MT1-MMP levels in fibroblasts. The effect of GM-CSF on endothelial cell sprout formation could be mimicked by adenoviral transduction of intact spheroids with virus expressing MT1-MMP, but not by transduction of endothelial cells before spheroid formation, suggesting that upregulation of MT1-MMP must only occur in cells directly involved in tubule formation.

Inhibition of membrane-type 1 matrix metalloproteinase at cell-matrix adhesions

Membrane-type 1 matrix metalloproteinase (MT1-MMP) has been implicated in tumor invasion and metastasis. We previously reported that extracellular matrix degradation by MT1-MMP regulates cell migration via modulating sustained integrin-mediated signals. In this study, MT1-MMP-expressing cells were plated onto fibronectin-coated plates and monitored for cell-matrix adhesion formation and fibronectin degradation. The fibronectin was degraded and removed in line with the cell migration track. The migrating cells showed a polarized morphology and were in contact with the edge of fibronectin through the leading edge, in which cell-matrix adhesions are concentrated. Expression of MT1-MMP targeted to cell-matrix adhesions by fusing with the focal adhesion targeting (FAT) domain of focal adhesion kinase (FAK) promoted the initial fibronectin lysis at the cell periphery immediately after adhesion. These results suggest that fibronectin is degraded by MT1-MMP located at cell-matrix adhesions, which are concentrated at the leading edge of the migrating cells. To inhibit MT1-MMP at cell-matrix adhesion, the dominant negative form of MT1-MMP (MT1-Pex) was targeted to the cell-matrix adhesion by fusing with the FAT domain (MT1-Pex-FAT). MT1-Pex-FAT accumulated at cell-matrix adhesions and inhibited fibronectin degradation as well as FAK phosphorylation more effectively than parental MT1-Pex. MT1-Pex-FAT was also shown to suppress the invasion of tumor cells into three-dimensional collagen gel more strongly than MT1-Pex. These results suggest that MT1-MMP-mediated extracellular matrix lysis at cell-matrix adhesions induces the establishment of cell polarity, which facilitates cell-matrix adhesion turnover and subsequent cell migration. This model highlights the role of MT1-MMP at the leading edge of migrating cells.

Membrane type-1 matrix metalloproteinase is induced following cyclic compression of in vitro grown bovine chondrocytes

OBJECTIVE

To determine if membrane type-1 matrix metalloproteinase (MT1-MMP) will respond to cyclic compression of chondrocytes grown in vitro and the regulatory mechanisms underlying this response.

METHODS

Cyclic compression (30min, 1kPa, 1Hz) was applied to bovine chondrocytes (6-9-month-old animals) grown on top of a biodegradable substrate within 3 days of initiating culture. Luciferase assays using bovine articular chondrocytes were undertaken to demonstrate the mechanosensitivity of MT1-MMP. Semi-quantitative reverse-transcription polymerase chain reaction (RT-PCR) and western blot analysis were used to establish the time course of gene and protein upregulation in response to cyclic compression. The regulation of MT1-MMP was assessed by electrophoretic mobility shift assays, RT-PCR and western blot analysis. As well, an MT1-MMP decoy oligonucleotide and an extracellular signal-regulated kinase 1/2 (ERK1/2) pharmacological inhibitor were utilized to further characterize MT1-MMP regulation.

RESULTS

After cyclic compression, MT1-MMP showed a rapid and transient increase in gene expression. Elevated protein levels were detected within 2h of stimulation which returned to baseline by 6h. During cyclic compression, phosphorylation of the mitogen activated protein kinase ERK1/2 increased significantly. This was followed by increased gene and protein expression of the transcription factor; early growth factor-1 (Egr-1) and Egr-1 binding to the MT1-MMP promoter. Blocking Egr-1 DNA binding with a decoy MT1-MMP oligonucleotide, downregulated MT1-MMP gene expression. The ERK1/2 inhibitor U0126 also reduced Egr-1 DNA binding activity to MT1-MMP promoter sequences and subsequent transcription of MT1-MMP.

CONCLUSIONS

These data suggest that cyclic compression of chondrocytes in vitro upregulates MT1-MMP via ERK1/2 dependent activation of Egr-1 binding. Delineation of the regulatory pathways activated by mechanical stimulation will further our understating of the mechanisms influencing tissue remodeling.

Membrane-type 1-Matrix Metalloproteinase Regulates Intracellular Adhesion Molecule-1 (ICAM-1)-mediated Monocyte Transmigration

We examined the mechanism regulating intercellular cell adhesion molecule-1 (ICAM-1)-dependent monocyte transendothelial migration. Monocyte migration through endothelial cells expressing ICAM-1 alone was comparable to that of tumor necrosis factor-alpha-treated cells. Transmigration was reduced in ICAM-1 lacking the cytoplasmic tail and in tyrosine to alanine substitutions at Tyr-485 and Tyr-474. Tissue inhibitors of matrix metalloproteinases (TIMPs) -2 and -3 blocked transmigration, whereas TIMP-1 was ineffective. This profile suggested a role for membrane-type matrix metalloproteinases (MT-MMPs) in transmigration. Inhibitory antibodies and small interference RNA directed against MT1-MMP blocked transmigration, whereas overexpression of MT1-MMP in endothelial cells or monocytes promoted transmigration. MT1-MMP mediated the ectodomain cleavage of ICAM-1 that was blocked by TIMP-2 and -3. Overexpression of MT1-MMP rescued function in ICAM-1Y485A, and to a lesser extent in the cytoplasmic tail-deleted ICAM-1. In a binding assay, wild-type ICAM-1 bound to purified MT1-MMP while ICAM-1 mutants bound poorly. MT1-MMP co-localized with ICAM-1 at distinct structures in endothelial cells. MT1-MMP localization with cells expressing ICAM-1 mutations was reduced and diffused. These results indicate that the cytoplasmic tail of ICAM-1 regulates leukocyte transmigration through MT1-MMP interaction.

MT1-MMP is the critical determinant of matrix degradation and invasion by ovarian cancer cells

Membrane-type 1 matrix metalloproteinase (MT1-MMP), a transmembrane metalloprotease that plays an important role in the invasion of many solid tumour types, promotes pericellular matrix degradation and may also stimulate tumour cell motility. As both these processes are key contributors to intraperitoneal ovarian tumour metastasis, we examined six ovarian cancer cell lines to determine whether MT1 is a critical mediator of invasive behaviour for this tumour type. Our results indicated that only those cell lines that expressed MT1 were capable of penetrating a type I collagen barrier, with the capacity for both matrix degradation and invasion reflecting endogenous MT1 expression level. Ectopic MT1 expression endowed an invasive phenotype upon cell lines lacking MT1 that were previously non-invasive, indicating the crucial role of this protease. Conversely, invasion was abolished by tissue inhibitor of metalloproteinase-2 (TIMP-2), a potent inhibitor of MT1, yet was minimally affected when other (secreted) MMPs were inhibited using TIMP-1 and the gelatinase inhibitor SB-3CT. Whereas collagen I degradation was strikingly accelerated by ectopic MT1 expression, cell motility remained unchanged. We conclude that MT1 is necessary for collagen I invasion by ovarian cancer cells, and that its requisite activity is the promotion of matrix degradation, with no impact on cell motility.

Membrane-type 1 matrix metalloproteinase is regulated by sp1 through the differential activation of AKT, JNK, and ERK pathways in human prostate tumor cells

We and other investigators have previously shown that membrane-type 1 matrix metalloproteinase (MT1-MMP) is overexpressed in invasive prostate cancer cells. However, the mechanism for this expression is not known. Here, we show that MT1-MMP is minimally expressed in nonmalignant primary prostate cells, moderately expressed in DU-145 cells, and highly expressed in invasive PC-3 and PC-3N cells. Using human MT1-MMP promoter reporter plasmids and mobility shift assays, we show that Sp1 regulates MT1-MMP expression in DU-145, PC-3, and PC-3N cells and in PC3-N cells using chromatin immunoprecipitation analysis and silencing RNA. Investigation of signaling pathway showed that DU-145 cells express constitutively phosphorylated extracellular stress-regulated kinase (ERK), whereas PC-3 and PC-3N cells express constitutively phosphorylated AKT/PKB and c-Jun NH2 terminal kinase (JNK). We show that MT1-MMP and Sp1 levels are decreased in PC-3 and PC-3N cells when phosphatidylinositol-3 kinase and JNK are inhibited, and that MT1-MMP levels are decreased in DU-145 cells when MEK is inhibited. Transient transfection of PC-3 and PC-3N cells with a dominant-negative JNK or p85, and of DU-145 cells with a dominant negative ERK, reduces MT1-MMP promoter activity. These results indicate differential signaling control of Sp1-mediated transcriptional regulation of MT1-MMP in prostate cancer cell lines.

Pro-MMP-2 activation by the PPARgamma agonist, ciglitazone, induces cell invasion through the generation of ROS and the activation of ERK

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a nuclear receptor modulating a variety of biological functions including cancer cell proliferation and differentiation. However, the role of PPARgamma and its ligands in tumor invasion is unclear. To evaluate a possible role for PPARgamma ligands in tumor invasion, we examined whether PPARgamma agonists including pioglitazone, troglitazone, rosiglitazone, and ciglitazone could affect the activity of matrix metalloproteinases (MMPs) in the HT1080 cell line, a well-studied and well-characterized cell line for MMP research. The gelatin zymography assay showed that ciglitazone activated pro-MMP-2 significantly. In addition, ciglitazone increased the expression of MMP-2, which was accompanied by an increase of membrane type 1-MMP (MT1-MMP) expression. The PPARgamma antagonist, GW9662 attenuated the ciglitazone-induced PPARgamma activation but it did not affect the pro-MMP2 activation by ciglitazone, suggesting that the action of ciglitazone on the pro-MMP-2 activation bypassed the PPARgamma pathway. Antioxidants and various inhibitors of signal transduction were used to investigate the mechanism of ciglitazone-induced pro-MMP-2 activation. We found that the sustained production of reactive oxygen species (ROS) was required for pro-MMP-2 activation by ciglitazone. We also found that PB98059, an inhibitor of MEK-ERK, significantly blocked ciglitazone-induced pro-MMP-2 activation and that extracellular signal-regulated kinase (ERK) was hyperphosphorylated by ciglitazone. Moreover, cell invasion was significantly increased by ciglitazone in the HT1080 cell lines, whereas cell motility was not affected. This study suggests that ciglitazone-induced pro-MMP-2 activation increases PPARgamma-independent tumor cell invasion through ROS production and ERK activation in some types of cancer cells.

MT1-MMP: a key regulator of cell migration in tissue

Controlled cell migration is a fundamental and critical event in many physiological processes. However once control is lost, cell migration facilitates disease progression such as seen in cancer metastasis, atherosclerosis, and rheumatoid arthritis. One of the critical proteinases involved in cell migration is membrane-type 1 matrix metalloproteinase (MT1-MMP/MMP-14). MT1-MMP degrades extracellular matrix to make a path for cells to migrate, sheds cell surface molecules to give migratory signals, and activates ERK (extracellular signal-regulated protein kinase) enhancing cell migration. For MT1-MMP to promote cell migration, it needs to act in co-ordination with other cell migration machinery. Understanding such regulatory links may provide insights into the development of novel disease therapies.

Hemopexin domains as multifunctional liganding modules in matrix metalloproteinases and other proteins

The heme-binding hemopexin consists of two, four-bladed propeller domains connected by a linker region. Hemopexin domains are found in different species on the phylogenetic tree and in the human species represented in hemopexin, matrix metalloproteinases (MMPs), vitronectin, and products of the proteoglycan 4 gene. Hemopexin and hemopexin domains of human proteins fulfill functions in activation of MMPs, inhibition of MMPs, dimerization, binding of substrates or ligands, cleavage of substrates, and endocytosis by low-density lipoprotein receptor-related protein-1 (LRP-1; CD91) and LRP-2 (megalin, GP330). Insights into the structures and functions of hemopexin (domains) form the basis for positive or negative interference with the formation of molecular complexes and hence, might be exploited therapeutically in inflammation, cancer, and wound healing.

Downregulation of the RECK-tumor and metastasis suppressor gene in glioma invasiveness

Invasive behavior is the pathological hallmark of malignant gliomas, being responsible for the failure of surgery, radiation, and chemotherapy. Matrix metalloproteinases (MMPs) are essential for proper ECM remodeling and invasion. The tumor and metastasis suppressor RECK protein regulates at least three members of the MMPs family: MMP-2, MMP-9, and MT1-MMP. In order to mimic the in vivo invasion process, A172 and T98G, respectively, non-invasive and invasive human glioblastoma cell lines, were cultured onto uncoated (control) or type I collagen gel-coated surface, and maintained for up to 7 days to allow establishment of the invasive process. We show that the collagen substrate causes decreased growth rates and morphological alterations correlated with the invasive phenotype. Electronic transmission microscopy of T98G cells revealed membrane invaginations resembling podosomes, which are typically found in cells in the process of crossing tissue boundaries, since they constitute sites of ECM degradation. Real time PCR revealed higher RECK mRNA expression in A172 cells, when compared to T98G cells and, also, in samples obtained from cultures where the invasive process was fully established. Interestingly, the collagen substrate increases RECK expression in A172 cells and the same tendency is displayed by T98G cells. MMPs-2 and -9 displayed higher levels of expression and activity in T98G cells, and their activities are also upregulated by collagen. Therefore, we suggest that: (1) RECK downregulation is critical for the invasiveness process displayed by T98G cells; (2) type 1 collagen could be employed to modulate RECK expression in glioblastoma cell lines. Since a positive correlation between RECK expression and patients survival has been noted in several types of tumors, our results may contribute to elucidate the complex mechanisms of malignant gliomas invasiveness.

Enhanced neutrophil motility by granulocyte colony-stimulating factor: the role of extracellular signal-regulated kinase and phosphatidylinositol 3-kinase

The effect of granulocyte colony-stimulating factor (G-CSF) on human neutrophil motility was studied using videomicroscopy. Stimulation of neutrophils with G-CSF resulted in enhanced motility with morphological change and increased adherence. Enhanced neutrophil motility was detected within 3-5 min after G-CSF stimulation, reached a maximum at 10 min, and was sustained for approximately 35 min. The maximum migration rate was 84.4 +/- 2.9 microm/5 min. A study using the Boyden chamber method revealed that G-CSF-stimulated neutrophils exhibited random migration but not chemotaxis. Enhanced neutrophil motility and morphological change were inhibited by MEK [mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) kinase] inhibitors (PD98059 and U0126), and a phosphatidylinositol 3-kinase (PI3K) inhibitor (wortmannin), but not by a p38 MAPK inhibitor (SB203580). These findings are consistent with the fact that G-CSF selectively activates MEK/ERK and PI3K, but not p38, in neutrophils. MEK/ERK activation was associated with G-CSF-induced redistribution of F-actin and phosphorylated myosin light chain. Enhanced neutrophil motility was observed even in the presence of neutralizing anti-CD18 antibody, which prevented cell adherence. These findings indicate that G-CSF induces human neutrophil migration via activation of MEK/ERK and PI3K.

Membrane-type 1 matrix metalloproteinase modulates focal adhesion stability and cell migration

Membrane-type 1 matrix metalloproteinase (MT1-MMP) plays an important role in extracellular matrix-induced cell migration and the activation of extracellular signal-regulated kinase (ERK). We showed here that transfection of the MT1-MMP gene into HeLa cells promoted fibronectin-induced cell migration, which was accompanied by fibronectin degradation and reduction of stable focal adhesions, which function as anchors for actin-stress fibers. MT1-MMP expression attenuated integrin clustering that was induced by adhesion of cells to fibronectin. The attenuation of integrin clustering was abrogated by MT1-MMP inhibition with a synthetic MMP inhibitor, BB94. When cultured on fibronectin, HT1080 cells, which endogenously express MT1-MMP, showed so-called motile morphology with well-organized focal adhesion formation, well-oriented actin-stress fiber formation, and the lysis of fibronectin through trails of cell migration. Inhibition of endogenous MT1-MMP by BB94 treatment or expression of the MT1-MMP carboxyl-terminal domain, which negatively regulates MT1-MMP activity, resulted in the suppression of fibronectin lysis and cell migration. BB94 treatment promoted stable focal adhesion formation concomitant with enhanced phosphorylation of tyrosine 397 of focal adhesion kinase (FAK) and reduced ERK activation. These results suggest that lysis of the extracellular matrix by MT1-MMP promotes focal adhesion turnover and subsequent ERK activation, which in turn stimulates cell migration.

Matrix metalloproteinase-2 (MMP-2) regulates astrocyte motility in connection with the actin cytoskeleton and integrins

Matrix Metalloproteinases (MMPs) play a role in migration of many cell types outside the central nervous system (CNS). Among neural cells, astrocytes are one of the main sources of MMPs in physiological and postlesional conditions. However, no data are available on the possible role of MMPs in astrocyte motility. Using an in vitro model of 2D migration and broad spectrum and selective MMP inhibitors, the authors demonstrated that MMP-2, but not MMP-9, is a key enzyme for astrocyte migration. In support of these data, the authors found constitutive expression of MMP-2 in astrocytes, while MMP-9 was nearly undetectable by gel zymography and immunocytochemical methods. The inhibition of migration by MMP inhibitors correlated with changes in cell morphology and in the organization of the actin cytoskeleton. In parallel, the characteristic focalized distribution of MMP-2 at the migration front observed in control cells became more diffuse and internalized by treatments that inhibited migration. The disruption of actin by cytochalasin D caused the partial recruitment of MMP-2 and gelatinolytic activity into actin aggregates, indicating a connection between the proteinase and the actin cytoskeleton. Finally, the authors found a co-localization of beta1-integrin with MMP-2 at the leading edge of migrating astrocytes. Altogether, these data provide the first evidence for the implication of MMP-2 in astrocyte motility, probably through the interaction of the proteinase with beta1-integrin that could act as a linker between pericellular proteolysis and the actin cytoskeleton.

Type I collagen abrogates the clathrin-mediated internalization of membrane type 1 matrix metalloproteinase (MT1-MMP) via the MT1-MMP hemopexin domain

Type I collagen (Col I)-stimulated matrix metalloproteinase-2 (MMP-2) activation via membrane type 1 MMP (MT1-MMP) involves both a transcriptional increase in MT1-MMP expression and a nontranscriptional response mediated by preexisting MT1-MMP. In order to identify which MT1-MMP domains were required for the nontranscriptional response, MCF-7 cells that lack endogenous MT1-MMP were transfected with either wild type or domain mutant MT1-MMP constructs. We observed that mutant constructs lacking the MT1-MMP cytoplasmic tail were able to activate MMP-2 in response to Col I but not a construct lacking the MT1-MMP hemopexin domain. Col I did not alter total MT1-MMP protein levels; nor did it appear to directly induce MT1-MMP oligomerization. Col I did, however, redistribute preexisting MT1-MMP to the cell periphery compared with unstimulated cells that displayed a more diffuse staining pattern. In addition, Col I blocked the internalization of MT1-MMP in a dynamin-dependent manner via clathrin-coated pit-mediated endocytosis. This mechanism of impaired internalization is different from that reported for concanavalin A, since it is not mediated by the cytoplasmic tail of MT1-MMP but rather by the hemopexin domain. In summary, upon Col I binding to its cell surface receptor, MT1-MMP internalization via clathrin-coated pit-mediated endocytosis is impaired through interactions with the hemopexin domain, thereby regulating its function and ability to activate MMP-2.

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.

Activation of mitogen-activated protein kinase is required for migration and invasion of placental site trophoblastic tumor

Placental site trophoblastic tumor (PSTT) is a gestational neoplasm derived from the extravillous (intermediate) trophoblast of the implantation site. PSTT is characterized by a highly invasive phenotype, but the molecular mechanisms are poorly understood. In this report, we demonstrate that PSTTs expressed the activated (phosphorylated) form of mitogen-activated protein kinase (MAPK) in 84% of cases, whereas the normal extravillous trophoblastic cells did not. To characterize the role of MAPK activation in PSTT, we established the first PSTT cell culture, IST-2, from a surgically resected PSTT. IST-2 cells expressed HLA-G and Mel-CAM but not E-cadherin, an immunophenotype characteristic of PSTT. IST-2 cells were highly motile and invasive in culture as compared to choriocarcinoma JEG-3 cells and normal extravillous trophoblastic cells. Based on wound assay, time-lapse videomicroscopy for cell tracking, and invasion chamber assays, we found that the motility and invasion of IST-2 cells were significantly reduced (P<0.01) after treatment with the MEK inhibitors CI-1040 and PD 59089, which prevent activation of MAPK. In contrast, neither compound had any effect on normal extravillous trophoblastic cells or JEG-3 cells. In conclusion, our findings demonstrate a functional role of MAPK activation in the motility and invasion of PSTT.

Mechanism of metastasis by membrane type 1-matrix metalloproteinase in hepatocellular carcinoma

AIM: To investigate the precise role of membrane type 1-matrix metalloproteinase (MT1-MMP) in hepatocellular carcinoma (HCC) metastasis.

METHODS: Human HCC cells Hep3B with overexpression of MT1-MMP were established by stable transfection, and compared with control cells carrying the empty vector. Cells were examined in vivo for their differences in the metastatic ability of athymic nude mice, and analyzed in vitro for their differences in invasion ability by invasion chamber coated with Matrigel, adhesion towards collagen I and migration through culture chamber. Cell proliferation and apoptosis in adherent and suspension status were evaluated by MTT and flow cytometry analysis.

RESULTS: We found that overexpression of MT1-MMP could increase intrahepatic metastasis in nude mice with orthotopic implantation of HCC cells (incidence of 100% [MT1-MMP transfectants] vs 40% [vector control transfectants], P<0.05). MT1-MMP could also enhance cell invasion through Matrigel (107.7 vs 39.3 cells/field, P<0.001), adhesion towards matrix (0.30 vs 0.12 absorbance unit at 540 nm, P<0.001), cell migration (89.3 vs 39.0 cells/field, P<0.001), and cell proliferation (24.3 vs 40.5 h/doubling, P<0.001). We also observed that MT1-MMP supported cell survival (71.4% vs 23.9%, P<0.001) with reduced apoptosis (43.7% vs 51.0%, P<0.05) in an attachment-free environment.

CONCLUSION: MT1-MMP overexpression could enhance metastasis. In addition to its active role in matrix degradation during tumor invasion, MT1-MMP enhances tumor cell survival upon challenge of detachment, which is important during metastasis when cells enter the circulation.

Membrane type 1 matrix metalloprotease cleaves laminin-10 and promotes prostate cancer cell migration

Disruption of the extracellular matrix by proteases is crucial for tumor invasion. Laminin-10 (Ln-10) has previously been identified as a substrate for cell migration and cell adhesion, and is present in the basal lamina (BL) of both normal prostate and prostate cancer. Here, we investigate a role for membrane type 1 matrix metalloprotease (MT1-MMP) in modifying this Ln-10-rich BL. MT1-MMP is a transmembrane member of the MMP family that has been demonstrated to be upregulated as prostate cancer progresses from normal to prostate intraepithelial neoplasia to invasive cancer, suggesting a role for MT1-MMP in the invasion of prostate cancer. We show that MT1-MMP cleaves the alpha5 chain of purified human Ln-10 from its 350-kDa form into 310-, 190-, 160-, and 45-kDa fragments. This cleavage causes a decrease in DU-145 prostate cancer cell adhesion to purified Ln-10, and an increase in transmigration of DU-145 cells through cleaved Ln-10. We also show that prostate cancer cells expressing membrane-bound MT1-MMP cleave the alpha5 chain of Ln-10. Ln alpha5-chain cleavage is also observed in human prostate cancer tissues. These findings suggest that prostate cancer cells expressing high levels of MT1-MMP have increased invasive potential through their ability to degrade and invade Ln-10 barriers.

Loss of intercellular adhesion activates a transition from low- to high-grade human squamous cell carcinoma

The relationship between loss of intercellular adhesion and the biologic properties of human squamous cell carcinoma is not well understood. We investigated how abrogation of E-cadherin-mediated adhesion influenced the behavior and phenotype of squamous cell carcinoma in 3D human tissues. Cell-cell adhesion was disrupted in early-stage epithelial tumor cells (HaCaT-II-4) through expression of a dominant-negative form of E-cadherin (H-2Kd-Ecad). Three-dimensional human tissue constructs harboring either H-2Kd-Ecad-expressing or control II-4 cells (pBabe, H-2Kd-EcadDeltaC25) were cultured at an air-liquid interface for 8 days and transplanted to nude mice; tumor phenotype was analyzed 2 days and 2 and 4 weeks later. H-2Kd-Ecad-expressing tumors demonstrated a switch to a high-grade aggressive tumor phenotype characterized by poorly differentiated tumor cells that infiltrated throughout the stroma. This high-grade carcinoma revealed elevated cell proliferation in a random pattern, loss of keratin 1 and diffuse deposition of laminin 5 gamma2 chain. When II-4 cell variants were seeded into type I collagen gels as an in vitro assay for cell migration, we found that only E-cadherin-deficient cells detached, migrated as single cells and expressed N-cadherin. Function-blocking studies demonstrated that this migration was matrix metalloproteinase-dependent, as GM-6001 and TIMP-2, but not TIMP-1, could block migration. Gene expression profiles revealed that E-cadherin-deficient II-4 cells demonstrated increased expression of proteases and cell-cell and cell-matrix proteins. These findings showed that loss of E-cadherin-mediated adhesion plays a causal role in the transition from low- to high-grade squamous cell carcinomas and that the absence of E-cadherin is an important prognostic marker in the progression of this disease.

Signalling pathways regulating the invasive differentiation of human trophoblasts: a review

The invasive differentiation pathway of trophoblasts is an indispensable physiological process of early human placental development. Formation of anchoring villi, proliferation of cell columns and invasion of extravillous cytotrophoblasts into maternal decidual stroma and vessels induce vascular changes ensuring an adequate blood supply to the growing fetus. Extravillous trophoblast differentiation is regulated by numerous growth factors as well as by extracellular matrix proteins and adhesion molecules expressed at the fetal-maternal interface. These regulatory molecules control cell invasion by modulating activities of matrix-degrading protease systems and ECM adhesion. The differentiation process involves numerous signalling cascades/proteins such as the GTPases RhoA, the protein kinases ROCK, ERK1, ERK2, FAK, PI3K, Akt/protein kinase B and mTOR as well as TGF-beta-dependent SMAD factors. While an increasing number of signalling pathways regulating trophoblast differentiation are being unravelled, downstream effectors such as executing transcription factors remain largely elusive. Here, we summarise our current knowledge on signal transduction cascades regulating invasive trophoblast differentiation. We will focus on cell model systems which are used to study the particular differentiation process and discuss signalling pathways which regulate trophoblast proliferation and motility.

Membrane type-matrix metalloproteinases and tumor progression

Matrix metalloproteinases (MMPs) are a family of zinc endopeptidases that process growth factors, growth factor binding proteins, cell surface proteins, degrade extracellular matrix (ECM) components and thereby play a central role in tissue remodeling and tumor progression. Membrane-type matrix metalloproteinases (MT-MMPs) are a recently discovered subgroup of intrinsic plasma membrane proteins. Their functions have been extended from pericellular proteolysis and control of cell migration to cell signaling, control of cell proliferation and regulation of multiple stages of tumor progression including growth and angiogenesis. This review sheds light on the new functions of MT-MMPs and their inhibitors in tumor development and angiogenesis, and presents recent investigations that document their influence on various cell functions.

Gene expression in Barrett’s esophagus and reflux esophagitis induced by gastroduodenoesophageal reflux in rats

AIM: To investigate the difference of gene expression profiles between Barrett’s esophagus and reflux eso-phagitis induced by gastroduodenoesophageal reflux in rats.

METHODS: Eight-week-old Sprague-Dawley rats were treated esophagoduodenostomy to produce gastroduode-noesophageal reflux, and another group received sham operation as control. Esophageal epithelial tissues were dissected and frozen in liquid nitrogen immediately for pathology 40 wk after surgery. The expression profiles of 4096 genes in reflux esophagitis and Barrett’s esophagus tissues were compared with normal esophageal epithelium by cDNA microarray.

RESULTS: Four hundred and forty-eight genes in Barrett’s esophagus were more than three times different from those in normal esophageal epithelium, including 312 up-regulated and 136 down-regulated genes. Two hundred and thirty-two genes in RE were more than three times different from those in normal esophageal epithelium, 90 up-regulated and 142 down-regulated genes. Compared to reflux esophagitis, there were 214 up-regulated and 142 down-regulated genes in Barrett’s esophagus.

CONCLUSION: Esophageal epithelium exposed excessively to harmful ingredients of duodenal and gastric reflux can develop esophagitis and Barrett’s esophagus gradually. The gene expression level is different between reflux esophagitis and Barrett’s esophagus and the differentially expressed genes might be related to the occurrence and development of Barrett’s esophagus and the promotion or progression in adenocarcinoma.

MT1-MMP: A potent modifier of pericellular microenvironment

Cells are regulated by many different means, and there is more and more evidence emerging that changes in the microenvironment greatly affect cell function. MT1-MMP is a type I transmembrane proteinase which participates in pericellular proteolysis of extracellular matrix (ECM) macromolecules. The enzyme is cellular collagenase essential for skeletal development, cancer invasion, growth, and angiogenesis. MT1-MMP promotes cell invasion and motility by pericellular ECM degradation, shedding of CD44 and syndecan1, and by activating ERK. Thus MT1-MMP is one of the factors that influence the cellular microenvironment and thereby affect cell-signaling pathways and eventually alters cellular behavior. As a proteinase, MT1-MMP is regulated by inhibitors, but it also requires formation of a homo-oligomer complex, localization to migration front of the cells, and internalization to become a "functionally active" cell function modifier. Developing new means to inhibit "functional activity" of MT1-MMP may be a new direction to establish treatments for the diseases that MT1-MMP mediates such as cancer and rheumatoid arthritis.

Mutational and structural analyses of the hinge region of membrane type 1-matrix metalloproteinase and enzyme processing

Membrane type 1 (MT1)-matrix metalloproteinase (MMP) is a major mediator of collagen degradation in the pericellular space in both physiological and pathological conditions. Previous evidence has shown that on the cell surface, active MT1-MMP undergoes autocatalytic processing to a major membrane-tethered 44-kDa product lacking the catalytic domain and displaying Gly285 at its N terminus, which is at the beginning of the hinge domain. However, the importance of this site and the hinge region in MT1-MMP processing is unknown. In the current study, we generated mutations and deletions in the hinge of MT1-MMP and followed their effect on processing. These studies established Gly284-Gly285 as the main cleavage site involved in the formation of the 44-kDa species. However, alterations at this site did not prevent processing. Instead, they forced downstream cleavages within the stretch of residues flanked by Gln296 and Ser304 in the hinge region, as determined by the processing profile of various hinge deletion mutants. Also, replacement of the hinge of MT1-MMP with the longer MT3-MMP hinge did not prevent processing of MT1-MMP. Molecular dynamic studies using a computational model of MT1-MMP revealed that the hinge region is a highly motile element that undergoes significant motion in the highly exposed loop formed by Pro295-Arg302 consistent with being a prime target for proteolysis, in agreement with the mutational data. These studies suggest that the hinge of MT1-MMP evolved to facilitate processing, a promiscuous but compulsory event in the destiny of MT1-MMP, which may play a key role in the control of pericellular proteolysis.

Oxidative stress stimulates proliferation and invasiveness of hepatic stellate cells via a MMP2-mediated mechanism

Experimental evidence indicates that reactive oxygen species (ROS) are involved in the development of hepatic fibrosis; they induce hepatic stellate cells (HSC) proliferation and collagen synthesis. To address the role of matrix metalloproteinase (MMP)-2 in promoting HSC proliferation during hepatic injury, we investigated whether oxidative stress modulates the growth and invasiveness of HSC by influencing MMP-2 activation. Cell invasiveness and proliferation, which were studied using Boyden chambers and by counting cells under a microscope, were evaluated after treatment with a superoxide-producing system, xanthine plus xanthine oxidase (X/XO), in the presence or absence of antioxidants and MMP inhibitors. Expression and activation of MMP-2 were evaluated via gel zymography, immunoassay, and ribonuclease protection assay. The addition of X/XO induced proliferation and invasiveness of human HSC in a dose-dependent manner. The addition of antioxidants as well as MMP-2-specific inhibitors impaired these phenomena. X/XO treatment increased MMP-2 expression and secretion appreciably and significantly induced members of its activation complex, specifically membrane-type 1 MMP and tissue inhibitor metalloproteinase 2. To study the intracellular signaling pathways involved in X/XO-induced MMP-2 expression, we evaluated the effects of different kinase inhibitors. The inhibition of extracellular signal-regulated kinase 1/2 (ERK1/2) and phosphatidyl inositol 3-kinase (PI3K) abrogated X/XO-elicited MMP-2 upregulation and completely prevented X/XO-induced growth and invasiveness of HSC. In conclusion, our findings suggest that MMP-2 is required for the mitogenic and proinvasive effects of ROS on HSC and demonstrate that ERK1/2 and PI3K are the main signals involved in ROS-mediated MMP-2 expression.

Roles of membrane-type matrix metalloproteinase-1 in tumor invasion and metastasis

Degradation of extracellular matrix (ECM) is one of the first steps in tumor invasion and metastasis. Matrix metalloproteinases (MMP) have been strongly implicated in this step. Membrane-type MMP-1 (MT1-MMP) was first identified as an activator of proMMP-2 expressed on the surface of tumor cells and later, not only ECM macromolecules but also various biologically important molecules, were shown to serve as substrates for MT1-MMP. Accumulated lines of evidence have demonstrated that MT1-MMP expression level is closely associated with invasiveness and malignancy of tumors, suggesting that MT1-MMP is one of the most critical factors for tumor invasion and metastasis. Despite enthusiasm for MMP inhibitors, phase III trials have not yet demonstrated significance in overall survival and side-effects remain an issue. An understanding of the functions of MT1-MMP could supply clues for developing novel therapeutic strategies targeting MT1-MMP.

An MT1-MMP-PDGF receptor-beta axis regulates mural cell investment of the microvasculature

Platelet-derived growth factor (PDGF)/PDGFRbeta-dependent investment of the vascular endothelium by mural cells (i.e., pericytes and vascular smooth muscle cells; VSMCs) is critical for normal vessel wall structure and function. In the developing vasculature, mural cell recruitment is associated with the functionally undefined expression of the type I transmembrane proteinase, membrane-type 1 matrix metalloproteinase (MT1-MMP). In this paper, using VSMCs and tissues isolated from gene-targeted mice, we identify MT1-MMP as a PDGF-B-selective regulator of PDGFRbeta-dependent signal transduction and mural cell function. In VSMCs, catalytically active MT1-MMP associates with PDGFRbeta in membrane complexes that support the efficient induction of mitogenic signaling by PDGF-B in a matrix metalloproteinase inhibitor-sensitive fashion. In contrast, MT1-MMP-deficient VSMCs display PDGF-B-selective defects in chemotaxis and proliferation as well as ERK1/2 and Akt activation that can be rescued in tandem fashion following retroviral transduction with the wild-type protease. Consistent with these in vitro findings, MT1-MMP-deficient brain tissues display a marked reduction in mural cell density as well as abnormal vessel wall morphology similar to that reported in mice expressing PDGF-B or PDGFRbeta hypomorphic alleles. Together, these data identify MT1-MMP as a novel proteolytic modifier of PDGF-B/PDGFRbeta signal transduction that cooperatively regulates vessel wall architecture in vivo.

Membrane-type-1 matrix metalloproteinase confers tumorigenicity on nonmalignant epithelial cells

Overexpression of membrane-type-1 matrix metalloproteinase (MT1-MMP) in tumor cells has previously been shown to enhance tumor growth and metastasis. To establish if MT1-MMP is also able to confer tumorigenicity on nonmalignant epithelial cells, we transfected human MT1-MMP cDNA into Madin-Darby canine kidney (MDCK) cells expressing a tetracycline-repressible transactivator. Induction of MT1-MMP in the absence of doxycycline (Dox) was associated with activation of exogenous MMP-2 as well as with formation of large cysts and increased invasiveness in collagen matrices. Transfected cells were inoculated subcutaneously into two groups of nude mice, one of which received Dox to inhibit expression of MT1-MMP. Formation of tumor xenografts was observed in 11 of 17 mice maintained without Dox, but only in two of nine mice that received Dox (P<0.05). The xenografts were composed of tubular structures interspersed within a highly cellular stroma. The epithelial cells delimiting the lumen were polarized, as indicated by the basolateral distribution of Na,K-ATPase. Despite their differentiated appearance, the tumors lacked a well-defined boundary, and epithelial tubules invaded adjacent muscular layers. These results demonstrate that conditional expression of MT1-MMP in nonmalignant MDCK epithelial cells is by itself sufficient to drive formation of invasive tumors.

The Hemopexin Domain of Membrane-type Matrix Metalloproteinase-1 (MT1-MMP) Is Not Required for Its Activation of proMMP2 on Cell Surface but Is Essential for MT1-MMP-mediated Invasion in Three-dimensional Type I Collagen

Membrane-type matrix metalloproteinase-1 (MT1-MMP) plays a key role in tumor invasion and metastasis by degrading the extracellular matrix and activating proMMP2. Here we show that the conserved hemopexin domain is required for MT1-MMP-mediated invasion and growth in three-dimensional type I collagen matrix but not proMMP2 activation. Deletion of the hemopexin domains in MT1-, MT2-, MT3-, MT5-, and MT6-MMP does not impair their abilities to activate proMMP2. In fact, hemopexin-less MT5- and MT6-MMP activate proMMP2 better than their wild type counterparts. On the other hand, hemopexin-less MT1-MMP fails to promote cell invasion into type I collagen but retains the capacity to enhance the growth of Madin-Darby canine kidney cells as cysts in three-dimensional collagen matrix. Moreover, the hemopexin domain is also required for MT1-MMP-mediated invasion/scattering of MCF-7 cells in three-dimensional collagen matrix. Because growth and invasion in a three-dimensional model may correlate with tumor invasiveness in vivo, our data suggest that the hemopexin domains of MT-MMPs should be targeted for the development of anti-cancer therapies by employing screening assays developed for three-dimensional models rather than their enzymatic activity toward proMMP2.

Regulation of malignant progression by the hypoxia-sensitive transcription factors HIF-1alpha and MTF-1

Solid tumors are known to develop microenvironmental hypoxia or anoxia due to malfunction and malformation of blood vessels and the energy demands of the highly proliferative tumor cells. Oxygen deprivation can cause aberrant modifications of signaling pathways and their downstream transcription factors that are believed to contribute to malignancy. Here, we review the latest studies related to the involvement of hypoxia-inducible transcription factor-1alpha (HIF-1alpha), the first known mammalian intracellular hypoxia sensor, in tumor development. We propose that a second far less studied protein, metal transcription factor-1 (MTF-1), acts as a more general oxygen sensor, responding to both hypoxia and oxidative stress, and is also intimately involved in malignant progression. Existing evidence suggests that activation of these two ubiquitous proteins, by hypoxia and genetic modifications, modulate the expression patterns of a number of important proteins involved in tumorigenesis.

Differential regulation of membrane type 1-matrix metalloproteinase activity by ERK 1/2- and p38 MAPK-modulated tissue inhibitor of metalloproteinases 2 expression controls transforming growth factor-beta1-induced pericellular collagenolysis

Acquisition of matrix metalloproteinase-2 (MMP-2) activity is temporally associated with increased migration and invasiveness of cancer cells. ProMMP-2 activation requires multimolecular complex assembly involving proMMP-2, membrane type 1-MMP (MT1-MMP, MMP-14), and tissue inhibitor of metalloproteinases-2 (TIMP-2). Because transforming growth factor-beta1 (TGF-beta1) promotes tumor invasion in advanced squamous cell carcinomas, the role of TGF-beta1 in the regulation of MMP activity in a cellular model of invasive oral squamous cell carcinoma was examined. Treatment of oral squamous cell carcinoma cells with TGF-beta1 promoted MMP-dependent cell scattering and collagen invasion, increased expression of MMP-2 and MT1-MMP, and enhanced MMP-2 activation. TGF-beta1 induced concomitant activation of ERK1/2 and p38 MAPK, and kinase inhibition studies revealed a negative regulatory role for ERK1/2 in modulating acquisition of MMP-2 activity. Thus, a reciprocal effect on proMMP-2 activation was observed whereupon blocking ERK1/2 phosphorylation promoted proMMP-2 activation and MT1-MMP activity, whereas inhibiting p38 MAPK activity decreased proteolytic potential. The cellular mechanism for the control of MT1-MMP catalytic activity involved concurrent reciprocal modulation of TIMP-2 expression by ERK1/2 and p38 MAPKs, such that inhibition of ERK1/2 phosphorylation decreased TIMP-2 production, and down-regulation of p38 MAPK activity enhanced TIMP-2 synthesis. Further, p38 MAPK inhibition promoted ERK1/2 phosphorylation, providing additional evidence for cross-talk between MAPK pathways. These observations demonstrate the complex reciprocal effects of ERK1/2 and p38 MAPK in the regulation of MMP activity, which could complicate the use of MAPK-specific inhibitors as therapeutic agents to down-regulate the biologic effects of TGF-beta1 on pericellular collagen degradation and tumor invasion.

Cellular cholesterol regulates MT1 MMP dependent activation of MMP 2 via MEK-1 in HT1080 fibrosarcoma cells

Unstimulated human fibrosarcoma cells (HT1080) constitutively secrete matrix metalloproteinase 2 (MMP 2) as a proenzyme requiring proteolytic cleavage by membrane type-1 MMP (MT1 MMP) for activation. Physiological and pharmacological stimuli induce clustering of MT1 MMP/tissue inhibitor of MMP 2 "receptors", promoting binding and activation of MMP 2. We now report that cholesterol depleted HT1080 cells accumulated MT1 MMP on the cell surface and activated MMP 2. A specific inhibitor of mitogen activated protein kinase kinase 1/2 inhibited both MMP 2 activation and extracellular signal-related kinase phosphorylation induced by cholesterol depletion. Our data indicate that the cholesterol content of unstimulated cells is critical for secretion of MMP 2 as an inactive zymogen and control of pericellular proteolysis.