Critical role for matrix metalloproteinase-9 in platelet-activating factor-induced experimental tumor metastasis

Diverse Functions of Plasma PAF-AH in Tumorigenesis

This chapter is focused on the role of the plasma form of platelet-activating factor-acetylhydrolase (PAF-AH), heretofore referred to as PAF-AH, in tumorigenic responses. Biochemical and other properties of this enzyme were discussed in detail in chapter "Plasma PAF-AH (PLA2G7): Biochemical Properties, Association with LDLs and HDLs, and Regulation of Expression" by Stafforini and in other chapters. Although phospholipases tend not to be drivers of tumorigenesis themselves, these enzymes and the lipid mediators whose levels they regulate interact with a variety of oncogenes and tumor suppressors [1]. Like other phospholipases, the functions of PAF-AH in cancer likely are related to its ability to regulate the levels of lipid mediators that participate in cellular processes related to initial tumorigenic events (e.g., proliferation, growth, inflammation) and/or spreading of the disease (e.g., matrix metalloproteinase secretion, actin cytoskeleton reorganization, migration, and angiogenesis) [1]. The importance of substrates and products of PAF-AH on key cellular functions has been evaluated in cell-based analyses which revealed that these metabolites can have pro- and antitumorigenic functions. Studies in genetically engineered mice lacking PAF-AH expression and genetic manipulation of PAF-AH levels in cancer cells demonstrated diverse functions of the protein in models of melanoma, prostate cancer, colon cancer, and others. The following sections highlight lessons learned from studies in cell lines and in mouse models regarding the diversity of functions of PAF-AH in cancer, and the potential of PAFAH transcripts, protein, and/or activity levels to become cancer biomarkers and therapeutic targets.

Systemic Platelet-activating Factor Receptor Activation Augments Experimental Lung Tumor Growth and Metastasis

Pro-oxidative stressors including cigarette smoke (CS) generate novel lipids with platelet-activated factor-receptor (PAF-R) agonistic activity mediate systemic immunosuppression, one of the most recognized events in promoting carcinogenesis. Our previous studies have established that these oxidized-PAF-R-agonists augment murine B16F10 melanoma tumor growth in a PAF-R-dependent manner because of its effects on host immunity. As CS generates PAF-R agonists, the current studies sought to determine the impact of PAF-R agonists on lung cancer growth and metastasis. Using the murine Lewis Lung Carcinoma (LLC1) model, we demonstrate that treatment of C57BL/6 mice with a PAF-R agonist augments tumor growth and lung metastasis in a PAF-R-dependent manner as these findings were not seen in PAF-R-deficient mice. Importantly, this effect was because of host rather than tumor cells PAF-R dependent as LLC1 cells do not express functional PAF-R. These findings indicate that experimental lung cancer progression can be modulated by the PAF system.

Neuroprotection by platelet-activating factor acetylhydrolase in a mouse model of transient cerebral ischemia

Neuronal damage after transient cerebral ischemia is exacerbated by signaling pathways involving activated platelet-activating factor (PAF) and ameliorated by PAF-acetylhydrolase (PAF-AH); but whether cerebral neurons can be rescued by human recombinant PAF-AH (rPAF-AH) remains unknown. Adult male mice underwent a 60 min middle cerebral artery occlusion (MCAO) and reperfusion for 24h. Then, the mice received intravenous tail injections with different drugs. Neurological behavioral function was evaluated by Bederson's test, and cerebral infarction volume was assessed with tetrazolium chloride (TTC) staining. mRNA and protein expression levels of matrix metalloproteinase-2 (MMP-2, collagenase-1), MMP-9 (gelatinase-B), and vascular endothelial growth factor (VEGF) were determined by quantitative real-time PCR (RT-PCR) and western blot analysis, respectively. Compared with the vehicle group, rPAF-AH significantly improved sensorimotor function (42%, P=0.0001). The volume of non-infarcted brain tissue was increased by the rPAF-AH treatment (16.3±4.6% vs. 46.0±10.3%, respectively). rPAF-AH significantly reduced mRNA and protein levels of MMP-2 and MMP-9, but increased the mRNA (P<0.001) and protein levels (P<0.01) of VEGF. These results demonstrate that rPAF-AH provides neuroprotection against ischemic injury. Neuroprotection might be induced not only by decrease in MMP-2 and MMP-9 expression, but also by increased VEGF expression.

PTEN/MAPK pathways play a key role in platelet-activating factor-induced experimental pulmonary tumor metastasis

In this study, we investigated the role of PTEN (phosphatase and tensin homolog deleted on chromosome 10) in a platelet-activating factor (PAF)-induced experimental pulmonary tumor metastasis model. An adenovirus carrying PTEN cDNA (Ad-PTEN) reversed PAF-induced increase in phosphorylation of AKT as well as pulmonary metastasis of B16F10. PAF-induced pulmonary metastasis was inhibited by MAPK inhibitors, but not by PI3K inhibitor. Ad-PTEN abrogated PAF-induced phosphorylation of MAPKs. These data indicate PTEN/MAPK pathways play a key role in PAF-induced tumor metastasis.

Megakaryocytes, malignancy and bone marrow vascular niches

Dynamic interactions between hematopoietic cells and their specialized bone marrow microenvironments, namely the vascular and osteoblastic 'niches', regulate hematopoiesis. The vascular niche is conducive for thrombopoiesis and megakaryocytes may, in turn, regulate the vascular niche, especially in supporting vascular and hematopoietic regeneration following irradiation or chemotherapy. A role for platelets in tumor growth and metastasis is well established and, more recently, the vascular niche has also been implicated as an area for preferential homing and engraftment of malignant cells. This article aims to provide an overview of the dynamic interactions between cellular and molecular components of the bone marrow vascular niche and the potential role of megakaryocytes in bone marrow malignancy.

Pomegranate fruit extract inhibits UVB-induced inflammation and proliferation by modulating NF-κB and MAPK signaling pathways in mouse skin

There is considerable interest in the identification of natural agents capable of affording protection to skin from the adverse effects of solar ultraviolet B (UVB) radiation. Pomegranate (Punica granatum L.) fruit possesses as strong antioxidant, anti-inflammatory and antiproliferative properties. Recently, we have shown that oral feeding of pomegranate fruit extract (PFE) to mice afforded substantial protection from the adverse effects of single UVB radiation via modulation in early biomarkers of photocarcinogenesis. This study was designed to investigate the photochemopreventive effects of PFE (0.2%, wt/vol) after multiple UVB irradiations (180 mJ cm(-2), on alternative day, for a total of seven treatments) to the skin of SKH-1 hairless mice. Oral feeding of PFE to SKH-1 mice inhibited UVB-induced epidermal hyperplasia, infiltration of leukocytes, protein oxidation and lipid peroxidation. Immunoblot analysis demonstrated that oral feeding of PFE to mice inhibited UVB-induced (1) nuclear translocation and phosphorylation of nuclear factor kappa B/p65, (2) phosphorylation and degradation of IκBα, (3) activation of IKKα/ΙΚΚβ and (4) phosphorylation of mitogen-activated protein kinase proteins and c-Jun. PFE consumption also inhibited UVB-induced protein expression of (1) COX-2 and iNOS, (2) PCNA and cyclin D1 and (3) matrix metalloproteinases-2,-3 and -9 in mouse skin. Taken together, these data show that PFE consumption afforded protection to mouse skin against the adverse effects of UVB radiation by modulating UVB-induced signaling pathways.

Pivotal role of reduced let-7g expression in breast cancer invasion and metastasis

Screening of the entire let-7 family of microRNAs (miRNA) by in situ hybridization identified let-7g as the only member, the diminished expression of which was significantly associated with lymph node metastasis and poor survival in breast cancer patients. Abrogation of let-7g expression in otherwise nonmetastatic mammary carcinoma cells elicited rapid metastasis from the orthotopic location, through preferential targets, Grb2-associated binding protein 2 (GAB2) and fibronectin 1 (FN1), and consequent activation of p44/42 mitogen-activated protein kinase (MAPK) and specific matrix metalloproteinases. Treatment with estrogen or epidermal growth factor specifically reduced the expression of mature let-7g through activation of p44/42 MAPK and subsequently stimulated expression of GAB2 and FN1, which, in turn, promoted tumor invasion. We thus identify let-7g as a unique member of the let-7 miRNA family that can serve as a prognostic biomarker in breast cancer and also propose a paradigm used by specific signaling molecules via let-7g to cooperatively promote breast cancer invasion and metastasis. Thus, let-7 family members neither possess equivalent clinicopathologic correlation nor function in breast cancer.

Enhancement of HLA class II-restricted CD4+ T cell recognition of human melanoma cells following treatment with bryostatin-1

The majority of melanoma cells express detectable levels of HLA class II proteins, and an increased threshold of cell surface class II is crucial for the stimulation of CD4+ T cells. Bryostatin-1, a protein kinase C (PKC) activator, has been considered as a potent chemotherapeutic agent in a variety of in vitro tumor models. Little is known about the role of bryostatin-1 in HLA class II Ag presentation and immune activation in malignant tumors, especially in melanoma. In this study, we show that bryostatin-1 treatment enhances CD4+ T cell recognition of melanoma cells in the context of HLA class II molecules. We also show that bryostatin-1 treatment of melanoma cells increases class II protein levels by upregulating the class II transactivator (CIITA) gene. Flow cytometry and confocal microscopic analyses revealed that bryostatin-1 treatment upregulated the expression of costimulatory molecules (CD80 and CD86) in melanoma cells, which could prolong the interaction of immune cells and tumors. Bryostatin-1 also induced cellular differentiation in melanoma cells, and reduced tumorigenic factors such as pro-cathepsins and matrix-metalloproteinase-9. These data suggest that bryostatin-1 could be used as a chemo-immunotherapeutic agent for reducing tumorigenic potential of melanoma cells while enhancing CD4+ T cell recognition to prevent tumor recurrence.

Angiogenesis and melanoma

Angiogenesis occurs in pathological conditions, such as tumors, where a specific critical point in tumor progression is the transition from the avascular to the vascular phase. Tumor angiogenesis depends mainly on the release by neoplastic cells of growth factors specific for endothelial cells, which are able to stimulate the growth of the host's blood vessels. This article summarizes the literature concerning the relationship between angiogenesis and human melanoma progression. The recent applications of antiangiogenic agents which interfere with melanoma progression are also described.

Non-apoptotic Fas signaling regulates invasiveness of glioma cells and modulates MMP-2 activity via NFkappaB-TIMP-2 pathway

Fas (CD95/APO-1) is a cell surface "death receptor" that mediates apoptosis upon engagement by its ligand, FasL. Paradoxically, Fas/FasL can also promote cell invasion among non-apoptotic cells; here, we show that Fas/FasL signaling can promote tumor invasion when apoptosis is compromised. We have developed a recombinant FasL Interfering Protein (FIP) to interfere with Fas signaling in C6 glioma cells expressing both Fas receptor and its ligand. FIP administration did not affect cell viability but impaired cell motility and invasiveness of glioma cells. Blockade of Fas signaling reduced MMP-2 activity in glioma cells, that was associated with down-regulation of MAPK signaling, and AP-1 and NFkappaB-driven transcription. FIP treatment did not affect mmp-2 and mt1-mmp expression but significantly attenuated timp-2 expression and TIMP-2 amount in the culture medium. Studies with pharmacological inhibitors of JNK/c-Jun (SP600125) and NFkappaB (BAY11-7082) signaling pathways demonstrated that timp-2 expression is regulated by NFkappaB transcription factor. Our findings show that non-apoptotic Fas signaling activated in the autocrine manner or through microenvironment derived factors can regulate invasiveness of glioma cells via modulation of MMP-2 activation, likely by controlling TIMP-2 expression.

Inflammation and melanoma metastasis

Metastatic melanoma is extremely refractory to existing chemotherapeutic drugs and bioimmune adjuvant therapies, and the life span of patients with metastatic melanoma is often measured in months. Understanding the mechanisms responsible for the development of tumor metastasis is critical for finding successful curative measures. An expending amount of data reveal the importance of inflammatory microenvironment and stroma in cancer initiation and progression, which brings new directions and approaches to cancer treatment. This review will summarize current data on the role of the tumor microenvironment in shaping the metastatic phenotype of melanoma.

TIMP-1-GPI in combination with hyperthermic treatment of melanoma increases sensitivity to FAS-mediated apoptosis

Resistance to apoptosis is a prominent feature of malignant melanoma. Hyperthermic therapy can be an effective adjuvant treatment for some tumors including melanoma. We developed a fusion protein based on the tissue inhibitor of matrix metalloproteinase-1 linked to a glycosylphosphatidylinositol anchor (TIMP-1-GPI). The TIMP-1-GPI-fusion protein shows unique properties. Exogenous administration of TIMP-1-GPI can result in transient morphological changes to treated cells including modulation of proliferation and decreased resistance to apoptosis. The effect of TIMP-1-GPI on the biology of melanoma in the context of a defined hyperthermic dose was evaluated in vitro. Clonogenic assays were used to measure cell survival. Gelatinase zymography determined secretion of MMP-2 and MMP-9. Monoclonal antibody against FAS/CD95 was applied to induce apoptosis. The expression of pro- and anti-apoptotic proteins and the secretion of immunoregulatory cytokines were then evaluated using Western blot and ELISA. TIMP-1-GPI combined with a sub-lethal hyperthermic treatment (41.8 degrees C for 2 h) suppressed tumor cell growth capacity as measured by clonogenic assay. The co-treatment also significantly suppressed tumor cell proliferation, enhanced FAS receptor surface expression increased tumor cell susceptibility to FAS-mediated killing. The increased sensitivity to FAS-induced apoptosis was linked to alterations in the apoptotic mediators Bcl-2, Bax, Bcl-XL and Apaf-1. The agent works in concert with sub-lethal hyperthermic treatment to render melanoma cells sensitive to FAS killing. The targeted delivery of TIMP-1-GPI to tumor environments in the context of regional hyperthermic therapy could be optimized through the use of thermosensitive liposomes.

Emerging roles of PAR-1 and PAFR in melanoma metastasis

Melanoma growth, angiogenesis and metastatic progression are strongly promoted by the inflammatory tumor microenvironment due to high levels of cytokine and chemokine secretion by the recruited inflammatory and stromal cells. In addition, platelets and molecular components of procoagulant pathways have been recently emerging as critical players of tumor growth and metastasis. In particular, thrombin, through the activity of its receptor protease-activated receptor-1 (PAR-1), regulates tumor cell adhesion to platelets and endothelial cells, stimulates tumor angiogenesis, and promotes tumor growth and metastasis. Notably, in many tumor types including melanoma, PAR-1 expression directly correlates with their metastatic phenotype and is directly responsible for the expression of interleukin-8, matrix metalloproteinase-2 (MMP-2), vascular endothelial growth factor, platelet-derived growth factor, and integrins. Another proinflammatory receptor–ligand pair, platelet-activating factor (PAF) and its receptor (PAFR), have been shown to act as important modulators of tumor cell adhesion to endothelial cells, angiogenesis, tumor growth and metastasis. PAF is a bioactive lipid produced by a variety of cells from membrane glycerophospholipids in the same reaction that releases arachidonic acid, and can be secreted by platelets, inflammatory cells, keratinocytes and endothelial cells. We have demonstrated that in metastatic melanoma cells, PAF stimulates the phosphorylation of cyclic adenosine monophosphate response element-binding protein (CREB) and activating transcription factor 1 (ATF-1), which results in overexpression of MMP-2 and membrane type 1-MMP (membrane type 1-MMP). Since only metastatic melanoma cells overexpress CREB/ATF-1, we propose that metastatic melanoma cells are better equipped than their non-metastatic counterparts to respond to PAF within the tumor microenvironment. The evidence supporting the hypothesis that the two G-protein coupled receptors, PAR-1 and PAFR, contribute to the acquisition of the metastatic phenotype of melanoma is presented and discussed.

Inflammation and melanoma growth and metastasis: the role of platelet-activating factor (PAF) and its receptor

An inflammatory tumor microenvironment fosters tumor growth, angiogenesis and metastatic progression. Platelet-activating factor (PAF) is an inflammatory biolipid produced from membrane glycerophospholipids. Through the activity of its G-protein coupled receptor, PAF triggers a variety of pathological reactions including tumor neo-angiogenesis. Several groups have demonstrated that inhibiting PAF-PAF receptor pathway at the level of a ligand or receptor results in an effective inhibition of experimental tumor growth and metastasis. In particular, our group has recently demonstrated that PAF receptor antagonists can effectively inhibit the metastatic potential of human melanoma cells in nude mice. Furthermore, we showed that PAF stimulated the phosphorylation of CREB and ATF-1 in metastatic melanoma cells, which resulted in overexpression of MMP-2 and MT1-MMP. Our data indicate that PAF acts as a promoter of melanoma metastasis in vivo. Since only metastatic melanoma cells overexpress CREB/ATF-1, we propose that these cells are better equipped to respond to PAF within the tumor microenvironment when compared to their non-metastatic counterparts.

Induction of matrix metalloproteinase-2 and matrix metalloproteinase-9 expression in gastric cancer cells by tumor necrosis factor-α

AIM: To investigate the inductive effect of tumor necrosis factor-α (TNF-α) on the expression of matrix metalloproteinase-2 (MMP-2) and matrix metalloproteinase-9 (MMP-9) in gastric cancer cells.

METHODS: Gastric cancer cells were stimulated by exogenous TNF-α and the cells without stimulation served as controls. The contents of MMP-2 and MMP-9 in the supernatant fluid of gastric cancer cells were measured by enzyme-linked immunosorbnent assay (ELISA). The expression of MMP-2 and MMP-9 mRNA were detected by reverse transcription-polymerase chain reaction (RT-PCR). Western blot was used to detect the expression of MMP-2 and MMP-9 protein in gastric cancer cells.

RESULTS: Following stimulation with 1, 10 and 100 mg/L TNF-α, the contents of MMP-2 (8.24 ± 1.36, 23.65 ± 3.45, 14.83 ± 2.54 ng/L) and MMP-9 (12.47 ± 2.66, 34.12 ± 6.78, 23.31 ± 4.45 ng/L) in the supernatant fluid of gastric cancer cells were increased significantly as compared with those in the control group (MMP-2: 1.56 ± 0.23 ng/L; 5.25 ± 0.89 ng/L; all P < 0.01). After 16 h of stimulation with TNF-α, the contents of MMP-2 and MMP-9 in the supernatant fluid reached the peak values, which were 23.65 ± 3.45 and 34.12 ± 6.78 ng/L, respectively. MMP-2 and MMP-9 expression were up-regulated both at mRNA and protein level.

CONCLUSION: TNF-α can up-regulate the expression of MMP-2 and MMP-9 in gastric cancer cells.