Metastatic Potential of Mouse Lewis Lung Cancer Cells Is Regulated via Ganglioside GM1 by Modulating the Matrix Metalloprotease-9 Localization in Lipid Rafts

Vesicular Ganglioside GM1 From Breast Tumor Cells Stimulated Epithelial-to-Mesenchymal Transition of Recipient MCF-10A Cells

Small extracellular vesicles (sEVs) are a type of membrane structure secreted by cells, which are involved in physiological and pathological processes by participating in intercellular communication. Glycosphingolipids (GSLs) are enriched in sEV and can be delivered to recipient cells. In this study, we found that overexpression of B3GALT4, the glycosyltransferase responsible for ganglioside GM1 synthesis, can induce the epithelial-mesenchymal transition (EMT) process in MCF-10A cells. Moreover, GM1 was verified to be presented on sEV from breast cancer cells. Overexpression of B3GALT4 resulted in elevated vesicular GM1 levels and increased sEV secretion in breast cancer cells. Proteomic analysis revealed that eleven sEV secretion-related proteins were differentially expressed, which might contribute to the altered sEV secretion. Of the identified proteins, 15 oncogenic differentially expressed proteins were documented to be presented in sEV. With the treatment of GM1-enriched sEV from breast cancer cells, the EMT process was induced in recipient non-tumorigenic epithelial MCF-10A cells. Our findings demonstrated that GM1-enriched sEVs derived from breast cancer cells induced the EMT process of recipient cells, which might provide essential information on the biological function of vesicular GM1.

Sphingolipid metabolism in the development and progression of cancer: one cancer's help is another's hindrance

Cancer development is a multistep process in which cells must overcome a series of obstacles before they can become fully developed tumors. First, cells must develop the ability to proliferate unchecked. Once this is accomplished, they must be able to invade the neighboring tissue, as well as provide themselves with oxygen and nutrients. Finally, they must acquire the ability to detach from the newly formed mass in order to spread to other tissues, all the while evading an immune system that is primed for their destruction. Furthermore, increased levels of inflammation have been shown to be linked to the development of cancer, with sites of chronic inflammation being a common component of tumorigenic microenvironments. In this Review, we give an overview of the impact of sphingolipid metabolism in cancers, from initiation to metastatic dissemination, as well as discussing immune responses and resistance to treatments. We explore how sphingolipids can either help or hinder the progression of cells from a healthy phenotype to a cancerous one.

Rafting Down the Metastatic Cascade: The Role of Lipid Rafts in Cancer Metastasis, Cell Death, and Clinical Outcomes

Lipid rafts are tightly packed, cholesterol- and sphingolipid-enriched microdomains within the plasma membrane that play important roles in many pathophysiologic processes. Rafts have been strongly implicated as master regulators of signal transduction in cancer, where raft compartmentalization can promote transmembrane receptor oligomerization, shield proteins from enzymatic degradation, and act as scaffolds to enhance intracellular signaling cascades. Cancer cells have been found to exploit these mechanisms to initiate oncogenic signaling and promote tumor progression. This review highlights the roles of lipid rafts within the metastatic cascade, specifically within tumor angiogenesis, cell adhesion, migration, epithelial-to-mesenchymal transition, and transendothelial migration. In addition, the interplay between lipid rafts and different modes of cancer cell death, including necrosis, apoptosis, and anoikis, will be described. The clinical role of lipid raft-specific proteins, caveolin and flotillin, in assessing patient prognosis and evaluating metastatic potential of various cancers will be presented. Collectively, elucidation of the complex roles of lipid rafts and raft components within the metastatic cascade may be instrumental for therapeutic discovery to curb prometastatic processes.

Heterogeneity of circulating tumor cell dissemination and lung metastases in a subcutaneous Lewis lung carcinoma model

Subcutaneous (s.c.) tumor models are widely used in pre-clinical cancer metastasis research. Despite this, the dynamics and natural progression of circulating tumor cells (CTCs) and CTC clusters (CTCCs) in peripheral blood are poorly understood in these models. In this work, we used a new technique called 'diffuse in vivo flow cytometry' (DiFC) to study CTC and CTCC dissemination in an s.c. Lewis lung carcinoma (LLC) model in mice. Tumors were grown in the rear flank and we performed DiFC up to 31 days after inoculation. At the study endpoint, lungs were excised and bioluminescence imaging (BLI) was performed to determine the extent of lung metastases. We also used fluorescence macro-cryotome imaging to visualize infiltration and growth of the primary tumor. DiFC revealed significant heterogeneity in CTC and CTCC numbers amongst all mice studied, despite using clonally identical LLC cells and tumor placement. Maximum DiFC count rates corresponded to 0.1 to 14 CTCs per mL of peripheral blood. In general, CTC numbers did not necessarily increase monotonically over time and were poorly correlated with tumor volume. However, there was a good correlation between CTC and CTCC numbers in peripheral blood and lung metastases. We attribute the differences in CTC numbers primarily due to growth patterns of the primary tumor. This study is one of the few reports of CTC shedding dynamics in sub-cutaneous metastasis models and underscores the value of in vivo methods for continuous, non-invasive CTC monitoring.

Influence of glycosphingolipids on cancer cell energy metabolism

A growing number of studies describe a connection between glycosphingolipids (GSLs) and glutamine metabolism, glucose metabolism and mitochondrial dysfunction in cancer cells. Since deregulated cell energy metabolism is one of cancer cells hallmarks, investigating this connection is an important step in the development of anti-cancer therapies. GSL species are often aberrantly regulated in human cancers. They cluster in signaling platforms in the plasma membrane and organelle membranes in so called glycosphingolipid enriched microdomains (GEMs), thereby regulating cell signaling pathways. The most important glutamine transporter for epithelial cells, alanine-serine-cysteine transporter 2 (ASCT2) locates in GEMs and is regulated by GEM composition. The accumulation of glucosylceramide and lactosylceramide in mitochondria associated ER membranes (MAMs) leads to increased oxidative phosphorylation. This increases mitochondrial reactive oxygen species (ROS) levels and influences mitochondrial dynamics. Here, we review current knowledge about deregulated GSL species in cancer, GSL influence on glutamine and glucose metabolism. In addition, the role of GSLs in MAMs, oxidative phosphorylation (OXPHOS) and mitochondrial dynamics with a special focus on mechanistic target of rapamycin (mTOR) signaling is discussed. mTOR seems to play a pivotal role in the connection between GSLs and glutamine metabolism as well as in mitochondrial signaling.

Comprehensive Profiling of Surface Gangliosides Extracted from Various Cell Lines by LC-MS/MS

Gangliosides act as a surface marker at the outer cellular membrane and play key roles in cancer cell invasion and metastasis. Despite the biological importance of gangliosides, they have been still poorly characterized due to the lack of effective analytical tools. Herein, we performed molecular profiling and structural elucidation of intact gangliosides in various cell lines including CFPAC1, A549, NCI-H358, MCF7, and Caski. We identified and quantified a total of 76 gangliosides on cell membrane using C18 LC-MS/MS. Gangliosides found in each cell line exhibited high complexity and diversity both qualitatively and quantitatively. The most abundant species was GM3(d34:1) in CFPAC1, NCI-H358, and MCF7, while GM2(d34:1) and GM1(d34:1) were major components in A549 and Caski, respectively. Notably, glycan moieties showed more diversity between cancer cell lines than ceramide moieties. In addition, noncancerous pancreatic cell line (hTERT/HPNE) could be distinguished by gangliosides containing different levels of sialic acid compared with cancerous pancreatic cell line (CFPAC1). These results clearly demonstrated the feasibility of our analytical platform to comprehensive profile of cell surface gangliosides for identifying cell types and subgrouping cancer cell types.

Inotilone from Inonotus linteus suppresses lung cancer metastasis in vitro and in vivo through ROS-mediated PI3K/AKT/MAPK signaling pathways

Metastasis is one of the main causes of mortality in cancer patients. Inotilone, a major component of Inonotus linteus, is a traditional Chinese medical herb. In this study, MTT results showed that inotilone had no obvious cytotoxicity. Animal model results revealed that inotilone suppressed cancer metastatic efficacy. Serum results showed that inotilone reduced the activity of matrix metalloproteinase (MMP)-2 and -9 and tumor necrosis factor alpha (TNF-α) activity as well as NO content. Additionally, inotilone affected MMP-9 and tissue inhibitor of metalloproteinase (TIMP)-2 protein expression and improved the activity of the antioxidant enzymes in the lung tissues of LLC-bearing mice. In addition, cell experimental results showed that inotilone reduced the activity of MMP-2/-9 and inhibited the ability for cellular migration and invasion. Inotilone decreased interleukin (IL)-8 expression in A549 cells. Western blot results revealed that inotilone affected the protein expression of MMPs, nitric oxide synthase (iNOS), cyclooxygenase (COX)-2, anti-oxidant enzymes, mitogen activated protein kinase (MAPK), focal adhesion kinase (FAK), phosphoinositide-3 kinase (PI3K)-AKT, and nuclear factor (NF)κB. Therefore, we propose that inotilone is a potential therapeutic candidate against metastatic lung cancer cells.

Loss of Enzyme Activity in Mutated B4GALNT1 Gene Products in Patients with Hereditary Spastic Paraplegia Results in Relatively Mild Neurological Disorders: Similarity with Phenotypes of B4galnt1 Knockout Mice

B4GALNT1 is an enzyme essential for the synthesis of complex gangliosides, whose absence leads to progressive neurodegeneration with aging in mice. Recently, eleven cases of hereditary spastic paraplegia with mutation in the coding region of B4GALNT1 were reported. However, changes in the enzymatic activity of their products have never been studied. We have constructed expression vectors for individual mutant cDNAs, and examined their activities by cell-free in vitro enzyme assays, and flow cytometry of cells transfected with their expression vectors. Among them, almost all mutant genes showed the complete loss of B4GALNT1 activity in both the in vitro enzyme assays and flow cytometry. Two mutants exceptionally showed weak activity. One of them, M4, had a mutation at amino acid 228 with a premature termination codon. Interestingly, the intensity of fluorescence of GM2 measured by flow cytometry was equivalent between the WT and M4 mutant, although the positive cell population was relatively small in M4. Western immunoblotting of cell lysates from transfectants with cDNA plasmids revealed 67-kDa bands except those containing premature termination codons or frame-shift mutation. Taken together with the clinical findings of patients, loss of enzyme activity may be responsible for the clinical features of hereditary spastic paraplegia, whereas the intensity of neurological disorders was relatively milder than expected. These clinical features of patients including those with male hypogonadism are very similar to the abnormal phenotypes detected in B4galnt1-deficient mice.

Differential roles of gangliosides in malignant properties of melanomas

Ganglioside GD3 is widely expressed in human malignant melanomas, and has been reported to be involved in the increased cell proliferation and invasion. In this study, we established GM3-, GM2-, GM1-, GD3-, or GD2-expressing melanoma cell lines by transfecting cDNAs of glyscosyltransferases, and effects of individual gangliosides on the cell phenotypes and signals were examined. The phenotypes of established ganglioside-expressing cells were quite different, i.e. cell growth increased as following order; GD2+, GD3+ > GM1+, GM2+, GM3+ cells. Cell invasion activity increased as GD3+ ≧ GM2+ > GM1+, GM3+, GD2+ cells. Intensity of cell adhesion to collagen I (CL-I) and spreading increased as GD2+ >> GD3+, GM1+ > GM2+, GM3+ cells. In particular, cell adhesion of GD2+ cells was markedly strong. As for cell migration velocity, GD2+ cells were slower than all other cells. The immunocytostaining revealed close localization of gangliosides and F-actin in lamellipodia. Immunoblotting of phosphorylated p130Cas and paxillin by serum treatment reveled that these phosphorylations were more increased in GD3+ cells than in GD2+ or GM3+ cells, while phosphorylation of Akt underwent similarly increased phosphorylation between GD3+ and GD2+ cells compared with GM3+ cells. While GD2 and GD3 enhanced cell growth, GD3 might also contribute in cell invasion. On the other hand, GD2 might contribute in the solid fixation of melanoma cells at metastasized sites. These results suggested that individual gangliosides exert distinct roles in the different aspects of melanomas by differentially regulating cytoskeletons and signaling molecules.

Complex polymorphisms in endocytosis genes suggest alpha-cyclodextrin as a treatment for breast cancer

Most breast cancer deaths are caused by metastasis and treatment options beyond radiation and cytotoxic drugs, which have severe side effects, and hormonal treatments, which are or become ineffective for many patients, are urgently needed. This study reanalyzed existing data from three genome-wide association studies (GWAS) using a novel computational biostatistics approach (muGWAS), which had been validated in studies of 600-2000 subjects in epilepsy and autism. MuGWAS jointly analyzes several neighboring single nucleotide polymorphisms while incorporating knowledge about genetics of heritable diseases into the statistical method and about GWAS into the rules for determining adaptive genome-wide significance. Results from three independent GWAS of 1000-2000 subjects each, which were made available under the National Institute of Health's "Up For A Challenge" (U4C) project, not only confirmed cell-cycle control and receptor/AKT signaling, but, for the first time in breast cancer GWAS, also consistently identified many genes involved in endo-/exocytosis (EEC), most of which had already been observed in functional and expression studies of breast cancer. In particular, the findings include genes that translocate (ATP8A1, ATP8B1, ANO4, ABCA1) and metabolize (AGPAT3, AGPAT4, DGKQ, LPPR1) phospholipids entering the phosphatidylinositol cycle, which controls EEC. These novel findings suggest scavenging phospholipids as a novel intervention to control local spread of cancer, packaging of exosomes (which prepare distant microenvironment for organ-specific metastases), and endocytosis of β1 integrins (which are required for spread of metastatic phenotype and mesenchymal migration of tumor cells). Beta-cyclodextrins (βCD) have already been shown to be effective in in vitro and animal studies of breast cancer, but exhibits cholesterol-related ototoxicity. The smaller alpha-cyclodextrins (αCD) also scavenges phospholipids, but cannot fit cholesterol. An in-vitro study presented here confirms hydroxypropyl (HP)-αCD to be twice as effective as HPβCD against migration of human cells of both receptor negative and estrogen-receptor positive breast cancer. If the previous successful animal studies with βCDs are replicated with the safer and more effective αCDs, clinical trials of adjuvant treatment with αCDs are warranted. Ultimately, all breast cancer are expected to benefit from treatment with HPαCD, but women with triple-negative breast cancer (TNBC) will benefit most, because they have fewer treatment options and their cancer advances more aggressively.

A Simple Bioluminescence Imaging Method for Studying Cancer Cell Growth and Metastasis after Subcutaneous Injection of Lewis Lung Carcinoma Cells in Syngeneic C57BL/6 Mice

In vivo imaging of cancer cell growth and invasion is instrumental in studying cancer cell behavior and in developing effective anticancer agents. In this ROS Protocols article, we report the experimental protocol and steps involving the implantation of luciferase-expressing Lewis lung carcinoma (LLC) cells in normal syngeneic C57BL/6 mice. Using the Berthold NightOwl LB981 in vivo imaging system, we observe the time-dependent growth and invasion of the lung cancer cells following subcutaneous injection of luciferase-expressing LLC cells. The three-dimensional image and counts of photon emission of the tumor mass are obtained to estimate the relative size of the tumor. Ex vivo imaging of the isolated lungs supplemented with D-luciferin and adenosine triphosphate (ATP) is obtained to determine lung metastasis of the LLC cells. The LLC cell load in entire mouse lungs is further determined by quantitative bioluminometry with a concurrently run standard curve of the number of LLC cells versus bioluminescence intensity. This in vivo imaging system in live mice, in combination with ex vivo imaging of isolated lungs as well as quantitative bioluminometry of target tissues, may provide important information on the in vivo cancer cell dynamics in immunocompetent syngeneic C57BL/6 mice and offer a valuable tool for studying experimental anticancer agents, including redox-modulating compounds, which are promising anticancer modalities.

Integrative Analysis of Subcellular Quantitative Proteomics Studies Reveals Functional Cytoskeleton Membrane-Lipid Raft Interactions in Cancer

Lipid rafts are dynamic membrane microdomains that orchestrate molecular interactions and are implicated in cancer development. To understand the functions of lipid rafts in cancer, we performed an integrated analysis of quantitative lipid raft proteomics data sets modeling progression in breast cancer, melanoma, and renal cell carcinoma. This analysis revealed that cancer development is associated with increased membrane raft-cytoskeleton interactions, with ∼40% of elevated lipid raft proteins being cytoskeletal components. Previous studies suggest a potential functional role for the raft-cytoskeleton in the action of the putative tumor suppressors PTRF/Cavin-1 and Merlin. To extend the observation, we examined lipid raft proteome modulation by an unrelated tumor suppressor opioid binding protein cell-adhesion molecule (OPCML) in ovarian cancer SKOV3 cells. In agreement with the other model systems, quantitative proteomics revealed that 39% of OPCML-depleted lipid raft proteins are cytoskeletal components, with microfilaments and intermediate filaments specifically down-regulated. Furthermore, protein-protein interaction network and simulation analysis showed significantly higher interactions among cancer raft proteins compared with general human raft proteins. Collectively, these results suggest increased cytoskeleton-mediated stabilization of lipid raft domains with greater molecular interactions as a common, functional, and reversible feature of cancer cells.

Increased expression levels of ppGalNAc-T13 in lung cancers: Significance in the prognostic diagnosis

ppGalNAc-T13 is upregulated along with reduced expression of GM1 in high metastatic sublines of the murine Lewis lung cancer cell line, but little is known about the implication of ppGalNAc-T13 expression in human cancers. Since lung cancer cell lines showed high expression levels of ppGalNAc-T13, we analyzed ppGalNAc-T13 expression in surgical lung cancer specimens to examine whether ppGalNAc-T13 can be used as a prognostic marker or a therapeutic target. We analyzed mRNA expression levels of GALNT13 and its variant exon usages in surgical specimens by real-time RT-PCR, and the results were evaluated by correlating with clinical data. Ninety-one surgical specimens were analyzed. Consequently, recurrence-free survival was significantly shorter (P=0.045) in high expression group of GALNT13 mRNA. In the analysis of tumor specific exon usage in GALNT13 RNA sequence, one variant exon was significantly associated with worse prognosis. By contrast, in another variant exon, positive variant expression group showed better prognosis than negative group. We also tried to detect GALNT13 mRNA in 63 serum samples from patients with lung cancers to examine whether GALNT13 mRNA can be measured in body fluids, detecting significant levels in 4 samples. Finally, expression of GM1, ppGalNAc-T13 and trimeric Tn antigen was examined by immunohistochemistry in order to evaluate them as a prognostic factor. It was demonstrated that ppGalNAc-T13 and trimeric Tn antigen had a relationship with worse prognosis in 35 investigated lung cancer patients. In conclusion, our results suggest that ppGalNAc-T13 might be a useful prognostic factor of lung cancers.

Short O-GalNAc glycans: regulation and role in tumor development and clinical perspectives

BACKGROUND

While the underlying causes of cancer are genetic modifications, changes in cellular states mediate cancer development. Tumor cells display markedly changed glycosylation states, of which the O-GalNAc glycans called the Tn and TF antigens are particularly common. How these antigens get over-expressed is not clear. The expression levels of glycosylation enzymes fail to explain it.

SCOPE OF REVIEW

We describe the regulation of O-GalNAc glycosylation initiation and extension with emphasis on the initiating enzymes ppGalNAcTs (GALNTs), and introduce the GALA pathway--a change in GALNTs compartmentation within the secretory pathway that regulates Tn levels. We discuss the roles of O-GalNAc glycans and GALNTs in tumorigenic processes and finally consider diagnostic and therapeutic perspectives.

MAJOR CONCLUSIONS

Contrary to a common hypothesis, short O-glycans in tumors are not the result of an incomplete glycosylation process but rather reveal the activation of regulatory pathways. Surprisingly, high Tn levels reveal a major shift in the O-glycoproteome rather than a shortening of O-glycans. These changes are driven by membrane trafficking events.

GENERAL SIGNIFICANCE

Many attempts to use O-glycans for biomarker, antibody and therapeutic vaccine development have been made, but suffer limitations including poor sensitivity and/or specificity that may in part derive from lack of a mechanistic understanding. Deciphering how short O-GalNAc glycans are regulated would open new perspectives to exploit this biology for therapeutic usage. This article is part of a Special Issue entitled "Glycans in personalised medicine" Guest Editor: Professor Gordan Lauc.

Cyclodextrins, blood-brain barrier, and treatment of neurological diseases

Biological barriers are the main defense systems of the homeostasis of the organism and protected organs. The blood-brain barrier (BBB), formed by the endothelial cells of brain capillaries, not only provides nutrients and protection to the central nervous system but also restricts the entry of drugs, emphasizing its importance in the treatment of neurological diseases. Cyclodextrins are increasingly used in human pharmacotherapy. Due to their favorable profile to form hydrophilic inclusion complexes with poorly soluble active pharmaceutical ingredients, they are present as excipients in many marketed drugs. Application of cyclodextrins is widespread in formulations for oral, parenteral, nasal, pulmonary, and skin delivery of drugs. Experimental and clinical data suggest that cyclodextrins can be used not only as excipients for centrally acting marketed drugs like antiepileptics, but also as active pharmaceutical ingredients to treat neurological diseases. Hydroxypropyl-β-cyclodextrin received orphan drug designation for the treatment of Niemann-Pick type C disease. In addition to this rare lysosomal storage disease with neurological symptoms, experimental research revealed the potential therapeutic use of cyclodextrins and cyclodextrin nanoparticles in neurodegenerative diseases, stroke, neuroinfections and brain tumors. In this context, the biological effects of cyclodextrins, their interaction with plasma membranes and extraction of different lipids are highly relevant at the level of the BBB.

Squalene synthase induces tumor necrosis factor receptor 1 enrichment in lipid rafts to promote lung cancer metastasis

RATIONALE

Metabolic alterations contribute to cancer development and progression. However, the molecular mechanisms relating metabolism to cancer metastasis remain largely unknown.

OBJECTIVES

To identify a key metabolic enzyme that is aberrantly overexpressed in invasive lung cancer cells and to investigate its functional role and prognostic value in lung cancer.

METHODS

The differential expression of metabolic enzymes in noninvasive CL1-0 cells and invasive CL1-5 cells was analyzed by a gene expression microarray. The expression of target genes in clinical specimens from patients with lung cancer was examined by immunohistochemistry. Pharmacologic and gene knockdown/overexpression approaches were used to investigate the function of the target gene during invasion and metastasis in vitro and in vivo. The association between the target gene expression and clinicopathologic parameters was further analyzed. Bioinformatic analyses were used to discover the signaling pathways involved in target gene-regulated invasion and migration.

MEASUREMENTS AND MAIN RESULTS

Squalene synthase (SQS) was up-regulated in CL1-5 cells and in the tumor regions of the lung cancer specimens. Loss of function or knockdown of SQS significantly inhibited invasion/migration and metastasis in cell and animal models and vice versa. High expression of SQS was significantly associated with poor prognosis among patients with lung cancer. Mechanistically, SQS contributed to a lipid-raft-localized enrichment of tumor necrosis factor receptor 1 in a cholesterol-dependent manner, which resulted in the enhancement of nuclear factor-κB activation leading to matrix metallopeptidase 1 up-regulation.

CONCLUSIONS

Up-regulation of SQS promotes metastasis of lung cancer by enhancing tumor necrosis factor-α receptor 1 and nuclear factor-κB activation and matrix metallopeptidase 1 expression. Targeting SQS may have considerable potential as a novel therapeutic strategy to treat metastatic lung cancer.

RaftProt: mammalian lipid raft proteome database

RaftProt (http://lipid-raft-database.di.uq.edu.au/) is a database of mammalian lipid raft-associated proteins as reported in high-throughput mass spectrometry studies. Lipid rafts are specialized membrane microdomains enriched in cholesterol and sphingolipids thought to act as dynamic signalling and sorting platforms. Given their fundamental roles in cellular regulation, there is a plethora of information on the size, composition and regulation of these membrane microdomains, including a large number of proteomics studies. To facilitate the mining and analysis of published lipid raft proteomics studies, we have developed a searchable database RaftProt. In addition to browsing the studies, performing basic queries by protein and gene names, searching experiments by cell, tissue and organisms; we have implemented several advanced features to facilitate data mining. To address the issue of potential bias due to biochemical preparation procedures used, we have captured the lipid raft preparation methods and implemented advanced search option for methodology and sample treatment conditions, such as cholesterol depletion. Furthermore, we have identified a list of high confidence proteins, and enabled searching only from this list of likely bona fide lipid raft proteins. Given the apparent biological importance of lipid raft and their associated proteins, this database would constitute a key resource for the scientific community.

Trimeric Tn antigen on syndecan 1 produced by ppGalNAc-T13 enhances cancer metastasis via a complex formation with integrin α5β1 and matrix metalloproteinase 9

We demonstrated previously that ppGalNAc-T13 (T13), identified as an up-regulated gene with increased metastasis in a DNA microarray, generated trimeric Tn (tTn) antigen (GalNAcα1-Ser/Thr)3 on Syndecan 1 in highly metastatic sublines of Lewis lung cancer. However, it is not known how tTn antigen regulates cancer metastasis. Here, we analyzed the roles of tTn antigen in cancer properties. tTn antigen on Syndecan 1 increased cell adhesion to fibronectin in an integrin-dependent manner. Furthermore, cell adhesion to fibronectin induced phosphorylation of focal adhesion kinase and paxillin in T13-transfectant cells. In the search of Syndecan 1-interacting molecules, it was demonstrated that tTn antigen-carrying Syndecan 1 interacted with integrin α5β1 and matrix metalloproteinase 9 and that these molecules shifted to a glycolipid-enriched microdomain/rafts along with increased metastatic potential in T13-transfectant cells. We also identified a tTn substitution site on Syndecan 1, demonstrating that tTn on Syndecan 1 is essential for the interaction with integrin α5β1 as well as for the reaction with mAb MLS128. These data suggest that high expression of the ppGalNAc-T13 gene generates tTn antigen on Syndecan 1 under reduced expression of GM1, leading to enhanced invasion and metastasis via the formation of a molecular complex consisting of integrin α5β1, Syndecan 1, and MMP-9 in the glycolipid-enriched microdomain/rafts.

Development of a metastatic fluorescent Lewis Lung carcinoma mouse model: identification of mRNAs and microRNAs involved in tumor invasion

Cancer metastasis is the foremost cause of death in cancer patients. A series of observable pathological changes takes place during progression and metastasis of cancer, but the underlying genetic changes remain unclear. Therefore, new approaches are required, including insights from cancer mouse models. To examine the mechanisms involved in tumor metastasis, we first generated a stably transfected Lewis Lung carcinoma cell line expressing a far-red fluorescent protein, called Katushka. After in vivo growth in syngeneic mice, two fluorescent Lewis Lung cancer subpopulations were isolated from primary tumors and lung metastases. The metastasis-derived cells exhibited a significant improvement in in vitro invasive activity compared to the primary tumor-derived cells, using a quantitative invasion chamber assay. Moreover, expression levels of 84 tumor metastasis-related mRNAs, 88 cancer-related microRNAs as well as Dicer and Drosha were determined using RT-qPCR. Compared to the primary Lewis Lung carcinoma subculture, the metastasis-derived cells exhibited statistically significantly increased mRNA levels for several matrix metalloproteinases as well as hepatocyte growth factor (HGF) and spleen tyrosine kinase (SYK). A modest decrease in Drosha and Dicer mRNA levels was accompanied by significant downregulation of ten microRNAs, including miR-9 and miR-203, in the lung metastatic Lewis Lung carcinoma cell culture. Thus, a tool for cancer metastasis studies has been established and the model is well suited for the identification of novel microRNAs and mRNAs involved in malignant progression. Our results suggest that increases in metalloproteinase expression and impairment of microRNA processing are involved in the acquirement of metastatic ability.

Glycans as targets for therapeutic antitumor antibodies

Glycans represent a vast class of molecules that modify either proteins or lipids. They exert and regulate important and complex functions in both normal and cancer cell metabolism. As such, the most immunogenic glycans have been targeted in passive and active immunotherapy in human cancer for the past 25 years but it is only recently that techniques have become available to uncover novel glycan targets. The main focus of this review article is to highlight why and how monoclonal antibodies (mAbs) recognizing glycans, and in particular the glycans expressed on glycolipids, are being used in various strategies to target and kill cancer cells. The article reports on the historical use of mAbs and on very recent progress made in antitumor therapy using the anti-GD2 mAb and the antiganglioside mAbs, anti-N-glycolylneuraminic acid mAb and anti-Lewis mAb. Anti-GD2 is showing great promise in Phase III clinical trials in adjuvant treatment of neuroblastoma. Racotumomab, an anti-idiotypic mAb mimicking N-glycolylneuraminic acid-containing gangliosides, is currently being tested in a randomized, controlled Phase II/III clinical trial. This article also presents various strategies used by different groups to develop mAbs against these naturally poorly immunogenic glycans.

Enhancement of malignant properties of human osteosarcoma cells with disialyl gangliosides GD2/GD3

The expression and implications of gangliosides in human osteosarcomas have not been systematically analyzed. In this study, we showed that gangliosides GD3 and GD2 are highly expressed in the majority of human osteosarcoma cell lines derived from oral cavity regions. Introduction of GD3 synthase cDNA into a GD3/GD2-negative (GD3/GD2-) human osteosarcoma subline resulted in the establishment of GD3/GD2+ transfectant cells. They showed increased cell migration and invasion activities in wound healing and Boyden chamber invasion assays, respectively, compared to the control cells. When treated with serum, GD3/GD2+ cells showed stronger tyrosine phosphorylation of p130Cas, focal adhesion kinase, and paxillin than GD3/GD2- cells. In particular, paxillin underwent much stronger phosphorylation, suggesting its role in cell motility. Furthermore, we tried to dissect the roles of GD3 and GD2 in the malignant properties of the transfectant cells by establishing single ganglioside-expressing cells, that is, either GD3 or GD2. Although GD3/GD2+ cells showed the most malignant properties, GD2+ cells showed almost equivalent levels to GD3/GD2+ cells in invasion and migration activities, and in the intensities of tyrosine phosphorylation of paxillin. Among Src family kinases, Lyn was expressed predominantly, and was involved in the invasion and motility of GD3- and/or GD2-expressing transfectants. Furthermore, it was elucidated by gene silencing that Lyn was located in a different pathway from that of FAK to eventually lead paxillin activation. These results suggested that GD2/GD3 are responsible for the enhancement of the malignant features of osteosarcomas, and might be candidate targets in molecular-targeted therapy.

Disialyl gangliosides enhance tumor phenotypes with differential modalities

Sialic acid-containing glycosphingolipids, gangliosides are highly expressed in human cancer cells and regulate cell signals transduced via membrane microdomains. Generally, disialyl gangliosides enhance tumor phenotypes, while monosialyl gangliosides suppress them. In particular, gangliosides GD3 and GD2 are highly expressed in melanomas and small cell lung cancer cells, and their expression cause increased cell growth and invasion. In osteosarcomas, expression of GD3 and GD2 also enhanced cell invasion and motility, and caused increased phosphorylation of focal adhesion kinase and paxillin. In addition to focal adhesion kinase, Lyn kinase was also activated by GD3/GD2 expression, leading to the phosphorylation of paxillin. In contrast with melanoma cells, osteosarcomas showed reduced cell adhesion with increased phosphorylation of paxillin. Thus, increased expression of GD3/GD2 caused enhanced activation of signaling molecules, leading to distinct phenotypes between melanomas and osteosarcomas, i.e. increased and decreased adhesion activity. Thus, whole features of glycolipid-enriched microdomain/rafts formed in the individual cancer types seem to determine the main signaling pathway and biological outcome.

Fine tuning of cell signals by glycosylation

Carbohydrates on the glycoproteins and glycosphingolipids expressed on the cell surface membrane play crucial roles in the determination of cell fates by being involved in the fine tuning of cell signalling as reaction molecules in the front line to various extrinsic stimulants. In glycoproteins, modification of proteins is performed by substitution of sugar chains to one or multiple sites of individual proteins, leading to quantitative and qualitative changes of receptor functions in the cell membrane. As for glycosphingolipids, majority of them consist of two moieties, i.e. carbohydrates and ceramides, and are localized in the microdomains such as lipid rafts or detergent-resistant microdomains. They generate and/or modulate cell signals to determine the cell fates by interacting with various carbohydrate-recognizing proteins. Modes of glycosylation and mechanisms by which glycosylation is involved in the regulation of cell signals are now hot subjects in glycobiology.

pp-GalNAc-T13 induces high metastatic potential of murine Lewis lung cancer by generating trimeric Tn antigen

In order to analyze the mechanisms for cancer metastasis, high metastatic sublines (H7-A, H7-Lu, H7-O, C4-sc, and C4-ly) were obtained by repeated injection of mouse Lewis lung cancer sublines H7 and C4 into C57BL/6 mice. These sublines exhibited increased proliferation and invasion activity in vitro. Ganglioside profiles exhibited lower expression of GM1 in high metastatic sublines than the parent lines. Then, we established GM1-Si-1 and GM1-Si-2 by stable silencing of GM1 synthase in H7 cells. These GM1-knockdown clones exhibited increased proliferation and invasion. Then, we explored genes that markedly altered in the expression levels by DNA microarray in the combination of C4 vs. C4-ly or H7 vs. H7 (GM1-Si). Consequently, pp-GalNAc-T13 gene was identified as up-regulated genes in the high metastatic sublines. Stable transfection of pp-GalNAc-T13 cDNA into C4 (T13-TF) resulted in increased invasion and motility. Then, immunoblotting and flow cytometry using various antibodies and lectins were performed. Only anti-trimeric Tn antibody (mAb MLS128), showed increased expression levels of trimeric Tn antigen in T13-TF clones. Moreover, immunoprecipitation/immunoblotting was performed by mAb MLS128, leading to the identification of an 80 kDa band carrying trimeric Tn antigen, i.e. Syndecan-1. Stable silencing of endogenous pp-GalNAc-T13 in C4-sc (T13-KD) revealed that primary tumors generated by subcutaneous injection of T13-KD clones showed lower coalescence to fascia and peritoneum, and significantly reduced lung metastasis than control clones. These data suggested that high expression of pp-GalNAc-T13 gene generated trimeric Tn antigen on Syndecan-1, leading to the enhanced metastasis.

Assessment of the molecular expression and structure of gangliosides in brain metastasis of lung adenocarcinoma by an advanced approach based on fully automated chip-nanoelectrospray mass spectrometry

Gangliosides (GGs), sialic acid-containing glycosphingolipids, are known to be involved in the invasive/metastatic behavior of brain tumor cells. Development of modern methods for determination of the variations in GG expression and structure during neoplastic cell transformation is a priority in the field of biomedical analysis. In this context, we report here on the first optimization and application of chip-based nanoelectrospray (NanoMate robot) mass spectrometry (MS) for the investigation of gangliosides in a secondary brain tumor. In our work a native GG mixture extracted and purified from brain metastasis of lung adenocarcinoma was screened by NanoMate robot coupled to a quadrupole time-of-flight MS. A native GG mixture from an age-matched healthy brain tissue, sampled and analyzed under identical conditions, served as a control. Comparative MS analysis demonstrated an evident dissimilarity in GG expression in the two tissue types. Brain metastasis is characterized by many species having a reduced N-acetylneuraminic acid (Neu5Ac) content, however, modified by fucosylation or O-acetylation such as Fuc-GM4, Fuc-GM3, di-O-Ac-GM1, O-Ac-GM3. In contrast, healthy brain tissue is dominated by longer structures exhibiting from mono- to hexasialylated sugar chains. Also, significant differences in ceramide composition were discovered. By tandem MS using collision-induced dissociation at low energies, brain metastasis-associated GD3 (d18:1/18:0) species as well as an uncommon Fuc-GM1 (d18:1/18:0) detected in the normal brain tissue could be structurally characterized. The novel protocol was able to provide a reliable compositional and structural characterization with high analysis pace and at a sensitivity situated in the fmol range.

Induction of GM1a/GD1b synthase triggers complex ganglioside expression and alters neuroblastoma cell behavior; a new tumor cell model of ganglioside function

Neuroblastoma is the most common extracranial solid tumor in children and tumor ganglioside composition has been linked to its biological and clinical behavior. We recently found that high expression of complex gangliosides that are products of the enzyme GM1a/GD1b synthase predicts a more favorable outcome in human neuroblastoma, and others have shown that complex gangliosides such as GD1a inhibit metastasis of murine tumors. To determine how a switch from structurally simple to structurally complex ganglioside expression affects neuroblastoma cell behavior, we engineered IMR32 human neuroblastoma cells, which contain almost exclusively (89%) the simple gangliosides (SG) GM2, GD2, GM3, and GD3, to overexpress the complex gangliosides (CG) GM1, GD1a, GD1b and GT1b, by stable retroviral-mediated transduction of the cDNA encoding GM1a/GD1b synthase. This strikingly altered cellular ganglioside composition without affecting total ganglioside content: There was a 23-fold increase in the ratio of complex to simple gangliosides in GM1a/GD1b synthase-transduced cells (IMR32-CG) vs. wild type (IMR32) or vector-transfected (IMR32-V) cells with essentially no expression of the clinical neuroblastoma marker, GD2, confirming effectiveness of this molecular switch from simple to complex ganglioside synthesis. Probing for consequences of the switch, we found that among functional properties of IMR32-CG cells, cell migration was inhibited and Rho/Rac1 activities were altered, while proliferation kinetics and cell differentiation were unaffected. These findings further implicate cellular ganglioside composition in determining cell migration characteristics of tumor cells. This IMR32 model system should be useful in delineating the impact of ganglioside composition on tumor cell function.

Functional activation of Src family kinase yes protein is essential for the enhanced malignant properties of human melanoma cells expressing ganglioside GD3

The possible roles of Src family kinases in the enhanced malignant properties of melanomas related to GD3 expression were analyzed. Among Src family kinases only Yes, not Fyn or Src, was functionally involved in the increased cell proliferation and invasion of GD3-expressing transfectant cells (GD3+). Yes was located upstream of p130Cas and paxillin and at an equivalent level to focal adhesion kinase. Yes underwent autophosphorylation even before serum treatment and showed stronger kinase activity in GD3+ cells than in GD3- cells following serum treatment. Coimmunoprecipitation experiments revealed that Yes bound to focal adhesion kinase or p130Cas more strongly in GD3+ cells than in GD3- cells. As a possible mechanism for the enhancing effects of GD3 on cellular phenotypes, it was shown that majority of Yes was localized in glycolipid-enriched microdomain/rafts in GD3+ cells even before serum treatment, whereas it was scarcely detected in glycolipid-enriched microdomain/rafts in GD3- cells. An in vitro kinase assay of Yes revealed that coexistence of GD3 with Yes in membranous environments enhances the kinase activity of GD3- cell-derived Yes toward enolase, p125, and Yes itself. Knockdown of GD3 synthase resulted in the alleviation of tumor phenotypes and reduced activation levels of Yes. Taken together, these results suggest a role of GD3 in the regulation of Src family kinases.

Gangliosides are essential in the protection of inflammation and neurodegeneration via maintenance of lipid rafts: elucidation by a series of ganglioside-deficient mutant mice

Gangliosides are considered to be involved in the maintenance and repair of nervous tissues. Recently, novel roles of gangliosides in the regulation of complement system were reported by us. In this study, we compared complement activation, inflammatory reaction and disruption of glycolipid-enriched microdomain (GEM)/rafts among various mutant mice of ganglioside synthases, i.e. GM2/GD2 synthase knockout (KO), GD3 synthase KO, double KO (DKO) of these two enzymes and wild type. Up-regulation of complement-related genes, deposits of C1q, proliferation of astrocytes and infiltration of microglia also showed similar gradual severity depending on the defects in ganglioside compositions. In the expression of inflammatory cytokines such as IL-1β and tumor necrosis factor α, only DKO showed definite up-regulation. Immunoblotting of fractions from sucrose density gradient ultracentrifugation revealed that lipid raft markers such as caveolin-1 and flotillin-1 tended to disperse from the raft fractions with intensities of DKO > GM2/GD2 synthase KO > GD3 synthase KO > wild type. Decay-accelerating factor and neural cell adhesion molecule tended to disappear from the raft fraction. Phospholipids and cholesterol also tended to decrease in GEM/rafts in GM2/GD2 synthase KO and DKO, although total amounts were almost equivalent. These results indicate that destruction of GEM/rafts is caused by ganglioside deficiency with gradual intensity depending on the degree of defects of their compositions.

Localization of uPAR and MMP-9 in lipid rafts is critical for migration, invasion and angiogenesis in human breast cancer cells

Background

uPAR and MMP-9, which play critical roles in tumor cell invasion, migration and angiogenesis, have been shown to be associated with lipid rafts.

Methods

To investigate whether cholesterol could regulate uPAR and MMP-9 in breast carcinoma, we used MβCD (methyl beta cyclodextrin, which extracts cholesterol from lipid rafts) to disrupt lipid rafts and studied its effect on breast cancer cell migration, invasion, angiogenesis and signaling.

Results

Morphological evidence showed the association of uPAR with lipid rafts in breast carcinoma cells. MβCD treatment significantly reduced the colocalization of uPAR and MMP-9 with lipid raft markers and also significantly reduced uPAR and MMP-9 at both the protein and mRNA levels. Spheroid migration and invasion assays showed inhibition of breast carcinoma cell migration and invasion after MβCD treatment. In vitro angiogenesis studies showed a significant decrease in the angiogenic potential of cells pretreated with MβCD. MβCD treatment significantly reduced the levels of MMP-9 and uPAR in raft fractions of MDA-MB-231 and ZR 751 cells. Phosphorylated forms of Src, FAK, Cav, Akt and ERK were significantly inhibited upon MβCD treatment. Increased levels of soluble uPAR were observed upon MβCD treatment. Cholesterol supplementation restored uPAR expression to basal levels in breast carcinoma cell lines. Increased colocalization of uPAR with the lysosomal marker LAMP1 was observed in MβCD-treated cells when compared with untreated cells.

Conclusion

Taken together, our results suggest that cholesterol levels in lipid rafts are critical for the migration, invasion, and angiogenesis of breast carcinoma cells and could be a critical regulatory factor in these cancer cell processes mediated by uPAR and MMP-9.

GM1 / GD1b / GA1 synthase expression results in the reduced cancer phenotypes with modulation of composition and raft-localization of gangliosides in a melanoma cell line

Gangliosides are expressed in neuroectoderm-derived tumors, and seemed to play roles in the regulation of cancer properties. To examine the behavior and roles of individual gangliosides, GM1/GD1b/GA1 synthase cDNA was introduced into the melanoma cell line SK-MEL-37, and changes in tumor phenotypes were analyzed. The transfectant cells showed neo-expression of GD1b, GT1b, and GM1, and reduced expression of GM3, GM2, GD2, and GD3. Function analyses revealed that the transfectant cells had definite reduction in cell growth and invasion. Tyrosine-phosphorylation levels of proteins such as p130Cas and paxillin were also reduced in the transfectants. These results suggested that the expression of GM1/GD1b/GA1 synthase resulted in the suppression of tumor properties. In the analyses of the floating patterns of gangliosides using fractions from sucrose density gradient ultracentrifugation of TritonX-100 extracts, the majority of gangliosides were found in glycolipid-enriched microdomain (GEM)/raft fractions, while GD3, GD1b, and GT1b in the transfectant cells tended to disperse to non-GEM/raft fractions. Furthermore, GD3, GD1b, and GT1b in non-GEM/raft dominantly had unsaturated fatty acids, while those in GEM/rafts contained more saturated forms than in non-GEM/rafts. This might be a mechanism for the decreased tumor properties in the transfectants of GM1/GD1b/GA1 synthase cDNA.

Guanylyl cyclase C prevents colon cancer metastasis by regulating tumor epithelial cell matrix metalloproteinase-9

Matrix metalloproteinase-9 (MMP-9) produced by colorectal cancer cells is a critical determinant of metastatic disease progression and an attractive target for antimetastatic strategies to reduce colon cancer mortality. Cellular signaling by cyclic GMP (cGMP) regulates MMP-9 dynamics in various cell systems, and the bacterial enterotoxin receptor guanylyl cyclase C (GCC), the principle source of cGMP in colonocytes, which is overexpressed in colorectal cancers, inhibits tumor initiation and progression in the intestine. Here, we show that ligand-dependent GCC signaling through cGMP induces functional remodeling of cancer cell MMP-9 reflected by a compartmental redistribution of this gelatinase, in which intracellular retention resulted in reciprocal extracellular depletion. Functional remodeling of MMP-9 by GCC signaling reduced the ability of colon cancer cells to degrade matrix components, organize the actin cytoskeleton to form locomotory organelles and spread, and hematogenously seed distant organs. Of significance, GCC effects on cancer cell MMP-9 prevented establishment of metastatic colonies by colorectal cancer cells in the mouse peritoneum in vivo. Because endogenous hormones for GCC are uniformly deficient in intestinal tumors, reactivation of dormant GCC signaling with exogenous administration of GCC agonists may represent a specific intervention to target MMP-9 functions in colon cancer cells. The notion that GCC-mediated regulation of cancer cell MMP-9 disrupts metastasis, in turn, underscores the unexplored utility of GCC hormone replacement therapy in the chemoprevention of colorectal cancer progression.

Reduced motor and sensory functions and emotional response in GM3-only mice: emergence from early stage of life and exacerbation with aging

Sialic acid-containing glycosphingolipids (gangliosides) have been believed to play a role in the regulation and protection of nervous tissues. To clarify their function in the nervous system in vivo, double knockout (DKO) mice of GM2/GD2 synthase and GD3 synthase genes were generated and abnormal behaviors were analyzed. Mutant mice exhibited reduced weight and a round shape of the whole brain that progressively emerged with aging, and displayed motor dysfunction in the footprint, traction, open-field, and 24h locomotion activity tests. Sensory functions were also reduced in the von Frey and hot plate tests and greatly reduced in the acoustic startle response test. For emotional behavior, fear response was clearly decreased. Numerous neuronal dysfunctions were found even in younger mutant mice examined at 10-23 weeks after birth, which were exacerbated with aging. These results suggest that a lack of gangliosides other than GM3 induces severe neuronal degeneration in the early stage of life, and that the expression of complex gangliosides is essential to maintain the integrity of the nervous system throughout life.

Sodium hydrogen exchanger and phospholipase D are required for alpha1-adrenergic receptor stimulation of metalloproteinase-9 and cellular invasion in CCL39 fibroblasts

Matrix metalloproteinase 9 (MMP-9) plays a critical role in digesting the extracellular matrix and has a vital function in tumor metastasis and invasion; this protease activity is significantly increased in non-small cell lung cancers. The sodium hydrogen exchanger isoform 1 (NHE1) functions as a focal point for signal coordination and cytoskeletal reorganization. NHE1 is thought to play a central role in establishing signaling components at the leading edge of a migrating cell. Therefore, we studied the relationship between NHE1 and MMP-9 activity in Chinese hamster lung fibroblasts (CCL39) stimulated with phenylephrine (PE). We show that PE increases MMP-9 gelatinolytic activity in CCL39 cells. The inhibition of phospholipase D (PLD) signaling abrogated PE-induced MMP-9 activity. The role of PLD as an essential signaling intermediate was confirmed when the addition of permeable phosphatidic acid increased MMP-9 activity in the same cells. PE-induced invasion was increased 1.9-fold over controls and the PE response was lost when 1-butanol was used to block PLD signaling. Cells pre-treated with the NHE1 inhibitor, 5-(N-ethyl-N-isopropyl) amiloride (EIPA) prior to PE addition resulted in a notable decrease in MMP-9 activation and cell invasion as compared to untreated PE-stimulated cells. CCL39 NHE1 null cells demonstrated no increase in MMP-9 protease activity or cell invasion in response to PE treatment. Reconstitution of NHE1 expression recovered the PE-induced activation of protease activity and cell invasion. MMP-9 processing was altered in cells expressing a proton transport defective NHE1 but retained the ability to respond to PE. Conversely, cells expressing an ezrin, radixin, moesin (ERM)-binding deficient NHE1 had a lower MMP-9 activity and the protease did not respond to PE addition. Parallel studies on NCI-H358 non-small cell lung cancer (NSCL) cells showed that PE stimulated both MMP-9 activity and cell invasion in an NHE1 dependent manner. This work describes for the first time a PE-induced relationship between NHE1 and MMP-9 and a new potential mechanism by which NHE1 could promote tumor formation and metastasis.

Clustering of monosialyl-Gb5 initiates downstream signalling events leading to invasion of MCF-7 breast cancer cells

Invasion is a complex process controlled by secretion and activation of proteases, alteration of integrin levels and GSL (glycosphingolipid) patterns. Differential organization of GSLs with specific membrane proteins and signal transducers in GEMs (GSL-enriched microdomains), initiates signalling events to modify cellular phenotype. Although the GSL monosialyl-Gb5 has been linked with invasion, its functional role in invasion is poorly described and understood. To investigate this problem, we induced the invasion of human breast cancer cells and subsequently explored the underlying mechanism. In the present study, the invasion of human MCF-7 breast cancer cells is highly dependent on clustering of monosialyl-Gb5, and the subsequent activation of monosialyl-Gb5-associated focal adhesion kinase and cSrc in GEM leading to the downstream activation of extracellular-signal-regulated kinase (ERK). As a result, we observed increased expression levels and activity of matrix metalloproteinases-2 and -9, which correlated with decreased expression of integrins alpha1 and beta1. Together these results suggest that the organization of crucial molecules in GEMs of MCF-7 cells is critical for their invasive properties.

Ganglioside GD1a negatively regulates matrix metalloproteinase-9 expression in mouse FBJ cell lines at the transcriptional level

Mouse FBJ virus-induced osteosarcoma FBJ-S1 cells rich in GD1a are not readily metastatic, whereas FBJ-LL cells with low levels of GD1a are highly metastatic. GD1a was previously shown to suppress metastasis of mouse FBJ cells and to upregulate caveolin-1 and stromal interaction molecule 1 expression. The present study demonstrates that matrix metalloproteinase-9 (MMP-9) expression renders FBJ-LL cells invasive. MMP-9 is inversely regulated by GD1a, based upon four observations: MMP-9 mRNA content was 5 times higher in FBJ-LL cells than FBJ-S1 cells; a GD1a-re-expressing FBJ-LL cell variant produced through beta1,4GalNAcT-1 cDNA transfection expressed lower levels of MMP-9; exogenous addition of GD1a to FBJ-LL cells decreased MMP-9 production in a dose- and time-dependent manner; and treatment of GD1a-rich cells with D-PDMP or siRNA targeting St3gal2 decreased GD1a expression, but augmented MMP-9 expression. This is the first report demonstrating that GD1a negatively regulates expression of MMP-9 at the transcriptional level.