Alteration of ganglioside composition by stable transfection with antisense vectors against GD3-synthase gene expression

Current state-of-the-art on ganglioside-mediated immune modulation in the tumor microenvironment

Gangliosides are sialylated glycolipids, mainly present at the cell surface membrane, involved in a variety of cellular signaling events. During malignant transformation, the composition of these glycosphingolipids is altered, leading to structural and functional changes, which are often negatively correlated to patient survival. Cancer cells have the ability to shed gangliosides into the tumor microenvironment, where they have a strong impact on anti-tumor immunity and promote tumor progression. Since most ganglioside species show prominent immunosuppressive activities, they might be considered checkpoint molecules released to counteract ongoing immunosurveillance. In this review, we highlight the current state-of-the-art on the ganglioside-mediated immunomodulation, specified for the different immune cells and individual gangliosides. In addition, we address the dual role that certain gangliosides play in the tumor microenvironment. Even though some ganglioside species have been more extensively studied than others, they are proven to contribute to the defense mechanisms of the tumor and should be regarded as promising therapeutic targets for inclusion in future immunotherapy regimens.

Brain Cancer-Activated Microglia: A Potential Role for Sphingolipids

Almost no neurological disease exists without microglial activation. Microglia has exert a pivotal role in the maintenance of the central nervous system and its response to external and internal insults. Microglia have traditionally been classified as, in the healthy central nervous system, "resting", with branched morphology system and, as a response to disease, "activated", with amoeboid morphology; as a response to diseases but this distinction is now outmoded. The most devastating disease that hits the brain is cancer, in particular glioblastoma. Glioblastoma multiforme is the most aggressive glioma with high invasiveness and little chance of being surgically removed. During tumor onset, many brain alterations are present and microglia have a major role because the tumor itself changes microglia from the pro-inflammatory state to the anti-inflammatory and protects the tumor from an immune intervention. What are the determinants of these changes in the behavior of the microglia? In this review, we survey and discuss the role of sphingolipids in microglia activation in the progression of brain tumors, with a particular focus on glioblastoma.

Induction of GD3/α1-adrenergic receptor/transglutaminase 2-mediated erythroid differentiation in chronic myelogenous leukemic K562 cells

The disialic acid-containing glycosphingolipid GD3 recruited membrane transglutaminase 2 (TG2) as a signaling molecule for erythroid differentiation in human chronic myelogenous leukemia (CML) K562 cells. The α1-adrenergic receptor (α1-AR)/TG2-mediated signaling pathway regulated GD3 functions, including gene expression and production, to differentiate CML K562 cells into erythroid lineage cells. Epinephrine, an AR agonist, increased membrane recruitment as well as GTP-photoaffinity of TG2, inducing GD3 synthase gene expression. Epinephrine activated PI3K/Akt signaling and GTPase downstream of TG2 activated Akt. The coupling of TG2 and GD3 production was specifically suppressed by prazosin (α1-AR antagonist), but not by propranolol (β-AR antagonist) or rauwolscine (α2-AR antagonist), indicating α1-AR specificity. Small interfering RNA (siRNA) experiment results indicated that the α1-AR/TG2-mediated signaling pathway activated PKCs α and δ to induce GD3 synthase gene expression. Transcription factors CREB, AP-1, and NF-κB regulated GD3 synthase gene expression during α1-AR-induced differentiation in CML K562 cells. In addition, GD3 synthase gene expression was upregulated in TG2-transfected cells via α1-AR with expression of erythroid lineage markers and benzidine-positive staining. α1-AR/TG2 signaling pathway-directed GD3 production is a crucial step in erythroid differentiation of K562 cells and GD3 interacts with α1-AR/TG2, inducing GD3/α1-AR/TG2-mediated erythroid differentiation. These results suggest that GD3, which acts as a membrane mediator of erythroid differentiation in CML cells, provides a therapeutic avenue for leukemia treatment.

Gangliosides: Structures, Biosynthesis, Analysis, and Roles in Cancer

Gangliosides are acidic glycosphingolipids containing one or more sialic acid residues. They are essential compounds at the outer leaflet of the plasma membrane, where they interact with phospholipids, cholesterol, and transmembrane proteins, forming lipid rafts. They are involved in cell adhesion, proliferation, and recognition processes, as well as in the modulation of signal transduction pathways. These functions are mainly governed by the glycan moiety, and changes in the structures of gangliosides occur under pathological conditions, particularly in neuro-ectoderm-derived cancers. With the progress in mass spectrometry analysis of gangliosides, their role in cancer progression can be now investigated in more detail. In this review we summarize the current knowledge on the biosynthesis of gangliosides and their role in cancers, together with the recent development of cancer immunotherapy targeting gangliosides.

Disialyl GD2 ganglioside suppresses ICAM-1-mediated invasiveness in human breast cancer MDA-MB231 cells

The disialoganglioside GD3 has been considered to be involved in tumor progression or suppression in various tumor cells. However, the significance of the biological functions of GD3 in breast cancer cells is still controversial. This prompted us to study the possible relationship(s) between GD3 expression and the metastatic potential of a breast cancer MDA-MB231 cells as an estrogen receptor negative (ER-) type. The human GD3 synthase cDNA was transfected into MDA-MB231 cells, and G-418 bulk selection was used to select cells stably overexpressing the GD3 synthase. In vitro invasion potentials of the GD3 synthase over-expressing cells (pc3-GD3s) were significantly suppressed when compared with control cells. Expression of intercellular adhesion molecule-1 (ICAM-1; CD54) was down-regulated in the pc3-GD3s cells and the decrease in ICAM-I expression is directly related to the decrease in invasiveness of the pc3-GD3s cells. Another type of ER negative SK-BR3 cells exhibited the similar level of ICAM-1 expression as MDA-MB231 cells, while the ER positive MCF-7 cells (ER+) showed the increased expression level of ICAM-1. Then, we investigated signaling pathways known to control ICAM-1 expression. No difference was observed in the phosphorylation of ERK and p38 between the pc3-GD3s and control cells (pc3), but the activation of AKT was inhibited in pc3-GD3s, and not in the control (pc3). In addition, the composition of total gangliosides was changed between control (pc3) and pc3-GD3s cells, as confirmed by HPTLC. The pc3-GD3s cells had an accumulation of the GD2 instead of the GD3. RT-PCR results showed that not only GD3 synthase, but also GM2/GD2 synthase (β4-GalNc T) expression was increased in pc3-GD3s cells. Overexpression of GD3 synthase suppresses the invasive potential of human breast cancer MDA-MB-231 cells through down-regulation of ICAM-1 and the crucial pathway to allow the apoptotic effect has been attributed to accumulation of the GD2 ganglioside. ER has been linked to the ICAM-1 expression with GD3 to GD2 conversion in human breast cancer cells. This is the first finding of the endogenous sialyltransferase functions in tumor cells.

A monoclonal antibody to O-acetyl-GD2 ganglioside and not to GD2 shows potent anti-tumor activity without peripheral nervous system cross-reactivity

Background

Monoclonal antibodies (mAb) against GD2 ganglioside have been shown to be effective for the treatment of neuroblastoma. Beneficial actions are, however, associated with generalized pain due to the binding of anti- GD2 mAbs to peripheral nerve fibers followed by complement activation. Neuroblastoma cells that express GD2 also express its O-acetyl derivative, O-acetyl- GD2 ganglioside (OAcGD2). Hence, we investigated the distribution of OAcGD2 in human tissues using mAb 8B6 to study the cross-reactivity of mAb 8B6 with human tissues.

Methodology/Principal Findings

The distribution of OAcGD2 was performed in normal and malignant tissues using an immunoperoxydase technique. Anti-tumor properties of mAb 8B6 were studied in vitro and in vivo in a transplanted tumor model in mice. We found that OAcGD2 is not expressed by peripheral nerve fibers. Furthermore, we demonstrated that mAb 8B6 was very effective in the in vitro and in vivo suppression of the growth of tumor cells. Importantly, mAb 8B6 anti-tumor efficacy was comparable to that of mAb 14G2a specific to GD2.

Conclusion/Significance

Development of therapeutic antibodies specific to OAcGD2 may offer treatment options with reduced adverse side effects, thereby allowing dose escalation of antibodies.

Inhibitors of Glioma Growth that Reveal the Tumour to the Immune System

Treated glioblastoma patients survive from 6 to 14 months. In the first part of this review, we describe glioma origins, cancer stem cells and the genomic alterations that generate dysregulated cell division, with enhanced proliferation and diverse response to radiation and chemotherapy. We review the pathways that mediate tumour cell proliferation, neo-angiogenesis, tumor cell invasion, as well as necrotic and apoptotic cell death. Then, we examine the ability of gliomas to evade and suppress the host immune system, exhibited at the levels of antigen recognition and immune activation, limiting the effective signaling between glioma and host immune cells.The second part of the review presents current therapies and their drawbacks. This is followed by a summary of the work of our laboratory during the past 20 years, on oligosaccharide and glycosphingolipid inhibitors of astroblast and astrocytoma division. Neurostatins, the O-acetylated forms of gangliosides GD1b and GT1b naturally present in mammalian brain, are cytostatic for normal astroblasts, but cytotoxic for rat C6 glioma cells and human astrocytoma grades III and IV, with ID50 values ranging from 200 to 450 nM. The inhibitors do not affect neurons or fibroblasts up to concentrations of 4 μM or higher.At least four different neurostatin-activated, cell-mediated antitumoral processes, lead to tumor destruction: (i) inhibition of tumor neovascularization; (ii) activation of microglia; (iii) activation of natural killer (NK) cells; (iv) activation of cytotoxic lymphocytes (CTL). The enhanced antigenicity of neurostatin-treated glioma cells, could be related to their increased expression of connexin 43. Because neurostatins and their analogues show specific activity and no toxicity for normal cells, a clinical trial would be the logical next step.

A glycobiology review: carbohydrates, lectins and implications in cancer therapeutics

This review is intended for general readers who would like a basic foundation in carbohydrate structure and function, lectin biology, and the implications of glycobiology in human health and disease, particularly in cancer therapeutics. These topics are among the hundreds included in the field of glycobiology and are treated here because they form the cornerstone of glycobiology or the focus of many advances in this rapidly expanding field.

Disialoganglioside GD3 synthase expression recruits membrane transglutaminase 2 during erythroid differentiation of the human chronic myelogenous leukemia K562 cells

By employing proteomics analysis tool, we examined the effects of GD3 synthase expression on the differentiation properties of chronic myelogenous leukemia (CML)-derived leukemia cells K562. Forced expression of GD3 synthase induced erythroid differentiation as determined by an increase in glycophorin A expression and synthesis of hemoglobins. The proteomic analysis revealed that 15 proteins were increased by GD3 synthase. In contrast, we observed three protein gel spots decreased in contents in the cell membranes of GD3 synthase-transfected K562 cells. Among the increased proteins, membrane transglutaminase 2 (TG2) was specifically increased in the cell membrane of GD3 synthase-transfected K562 cells. Then, we generated the GD3 synthase-transfected cells in the K562 cells. Interestingly, the TG2 level was increased in GD3 synthase-transfected cells compared with vector- and plasma membrane-associated ganglioside sialidase (Neu3)-transfected cells. In addition, its ability to be photoaffinity-labeled with [alpha-(32)P]GTP was also increased in the GD3 synthase- and TG2-transfected cells. Moreover, small interfering RNA (siRNA) analysis for the GD3 synthase showed the decrease or abolishment of the membrane TG2. Finally, GD3 synthase-transfected cells accelerated the erythroid differentiation. Therefore, we propose that the recruitment of TG2 into membranes by GD3 might play an important role in the erythroid differentiation in K562 cells.

Cloning and transcriptional regulation of genes responsible for synthesis of gangliosides

Ganglioside synthases are glycosyltransferases involved in the biosynthesis of glycoconjugates. A number of ganglioside synthase genes have been cloned and characterized. They are classified into different families of glycosyltransferases based on similarities of their amino acid sequences. Tissue-specific expression of these genes has been analyzed by hybridization using cDNA fragments. Enzymatic characterization with the expressed recombinant enzymes showed these enzymes differ in their donor and acceptor substrate specificities and other biochemical parameters. In vitro enzymatic analysis also showed that one linkage can be synthesized by multiple enzymes and one enzyme may be responsible for synthesis of multiple gangliosides. Following the cloning of the ganglioside synthase genes, the promoters of the key synthase genes in the ganglioside biosynthetic pathway have been cloned and analyzed. All of the promoters are TATA-less, lacking a CCAAT box but containing GC-rich boxes, characteristic of the house-keeping genes, although transcription of ganglioside synthase genes is subject to complex developmental and tissue-specific regulation. A set of cis-acting elements and transcription factors, including Sp1, AP2, and CREB, function in the proximal promoters. Negative-regulatory regions have also been defined in most of the promoters. We present here an overview of these genes and their transcriptional regulation.

Disialoganglioside GD3 increases in the secretion of apoB-containing lipoproteins

The function of gangliosides, sialic acid-containing glycolipids, on the secretion and assembly of apoB-containing lipoproteins is poorly understood. Here, we report that the GD3 synthase is involved in apoB secretion in retinoic acid (RA)-treated Chang liver cells via transcriptional induction of microsomal triglyceride transfer protein (MTP). The overexpression of GD3 synthase in Chang liver cells increases the expression of the MTP gene, but GM3 synthase-transfected cells did not. The levels of GM3 and GD3 gangliosides in each of the transfected cells were increased in the cell extract as well as the medium. In addition, GD3 synthase-transfected cells showed an increased secretion of triglyceride-enriched apoB. In contrast, the triglyceride content in GM3 synthase-transfected cells was relatively lower. Treatment with small interfering RNAs (siRNAs) and GD3 antibody decreased apoB secretion. These results indicate that plasma membrane associated GD3 play important roles in apoB secretion, and that an enhancement in GD3 levels might be a risk factor for the development of atherosclerosis by increasing the secretion of triglyceride-enriched apoB containing lipoproteins.

Down-regulation of WNK1 protein kinase in neural progenitor cells suppresses cell proliferation and migration

WNK1, a Ser/Thr protein kinase, is widely expressed in many tissues. Its biological functions are largely unknown. Disruption of the WNK1 gene in mice leads to embryonic lethality at day 13, implicating a critical role of WNK1 in embryonic development. To investigate this potential function, we used antisense strategy to knock down the expression of WNK1 in a mouse neural progenitor cell line, C17.2. Down-regulation of WNK1 in C17.2 cells greatly reduced cell growth. Addition of epidermal growth factor (EGF), a mitogen for C17.2 cells, had no effect on growth. The WNK1-knockdown cells showed a flat and rounded morphology, characteristic of the immature and non-differentiated phenotype of the progenitor cells; this was further demonstrated by immunostaining for the progenitor and neuronal markers. Migration of the WNK1-knockdown C17.2 cells was reduced as tested in culture dishes or Matrigel-covered chambers. Moreover, activation of extracellular signal-regulated kinase (ERK1)/2 and ERK5 by EGF in the WNK1-knockdown cells was suppressed. These results demonstrate a novel function of WNK1 in proliferation, migration, and differentiation of neural progenitor cells, likely by mechanisms involving activation of the mitogen-activated protein (MAP) kinase ERK1/2 and/or ERK5 pathways.

Sphingolipids in tumor metastases and angiogenesis

This review article summarizes data on the involvement of sphingolipids (sphingosine-1-phosphate, sphingosine-1-phosphocholine, neutral glycosphingolipids, and gangliosides) in tumor metastases and angiogenesis.

Sphingolipids as modulators of cancer cell death: potential therapeutic targets

Through modifications in the fine membrane structure, cell-cell or cell-matrix interactions, and/or modulation of intracellular signaling pathways, sphingolipids can affect the tumorigenic potential of numerous cell types. Whereas ceramide and its metabolites have been described as regulators of cell growth and apoptosis, these lipids as well as other sphingolipid molecules can modulate the ability of malignant cells to grow and resist anticancer treatments, and their susceptibility to non-apoptotic cell deaths. This review summarizes our current knowledge on the properties of sphingolipids in the regulation of cancer cell death and tumor development. It also provides an update on the potential perspectives of manipulating sphingolipid metabolism and using sphingolipid analogues in anticancer therapy.

Cancer stem cells in the mammalian central nervous system

Malignant tumours intrinsic to the central nervous system (CNS) are among the most difficult of neoplasms to treat effectively. The major biological features of these tumours that preclude successful therapy include their cellular heterogeneity, which renders them highly resistant to both chemotherapy and radiotherapy, and the propensity of the component tumour cells to invade, diffusely, the contiguous nervous tissues. The tumours are classified according to perceived cell of origin, gliomas being the most common generic group. In the 1970s transplacental administration of the potent neurocarcinogen, N-ethyl-N-nitrosourea (ENU), enabled investigation of the sequential development of brain and spinal neoplasms by electron microscopy and immunohistochemistry. The significance of the primitive cells of the subependymal plate in cellular origin and evolution of a variety of glial tumours was thereby established. Since then, the development of new cell culture methods, including the in vitro growth of neurospheres and multicellular tumour spheroids, and new antigenic markers of stem cells and glial/neuronal cell precursor cells, including nestin, Mushashi-1 and CD133, have led to a reappraisal of the histological classification and origins of CNS tumours. Moreover, neural stem cells may also provide new vectors in exciting novel therapeutic strategies for these tumours. In addition to the gliomas, stem cells may have been identified in paediatric tumours including cerebellar medulloblastoma, thought to be of external granule cell neuronal derivation. Interestingly, while the stem cell marker CD133 is expressed in these primitive neuroectodermal tumours (PNETs), the chondroitin sulphate proteoglycan neuronal/glial 2 (NG2), which appears to denote increased proliferative, but reduced migratory activity in adult gliomas, is rarely expressed. This is in contrast to the situation in the histologically similar supratentorial PNETs. A possible functional 'switch' between proliferation and migration in developing neural tumour cells may exist between NG2 and ganglioside GD3. The divergent pathways of differentiation of CNS tumours and the possibility of stem cell origin, for some, if not all, such neoplasms remain a matter for debate and continued research, but the presence of self-renewing neural stem cells in the CNS of both children and adults strongly suggests a role for these cells in tumour initiation and resistance to current therapeutic strategies.

Expression of the mouse WNK1 gene in correlation with ganglioside GD3 and functional analysis of the mouse WNK1 promoter

WNK1 is one of WNK (With No K=Lysine) protein kinases which comprise a newly described subfamily. Our studies showed that expression of the mouse WNK1 gene was dramatically suppressed in a tumor cell line when its phenotype was altered by suppression of the GD3-synthase gene expression. The mouse WNK1 gene was expressed at a high level at early stage of embryonic brain and its expression decreased as brain developed, similar to the expression pattern of the GD3-synthase gene. To study transcriptional regulation, we cloned a 5'-flanking 1239-bp fragment of the mouse WNK1 gene. This fragment contains a number of potential consensus binding sites for transcription factors, including Sp1, AP2, CCAAT, Est-1, Oct-1, CNBP, and NFkB, but lacks a TATA box. Primer extension identified multiple putative transcriptional initiation sites, including several sites downstream of the ATG codon. Activities of the promoter fragments were assessed in mouse breast Sa/R-MT cells by transient transfection and the results showed that the promoter elements between -700 and -977 is required for maintaining a high level of promoter activity of the TATA-less mouse WNK1 gene.

Increased expression of O-acetyl disialoganglioside synthase during rat liver fibrogenesis relates to stellate cell activation

The activation of the hepatic stellate cell (HSC) is a key step in liver fibrogenesis. Utilizing large scale sequencing of a 3'-directed cDNA library, we investigated expression profiles of quiescent and activated rat HSCs. During the activation process, O-acetyl disialoganglioside synthase (OAcGD3S) was identified as one of the significant upregulated factors. Upregulation of OAcGD3S in cultured HSCs was confirmed by both Northern and Western blot analyses. OAcGD3S expression in models of experimental liver fibrosis was investigated at the mRNA level using RT-PCR. The expression of OAcGD3S protein in activated rat HSCs and in experimental fibrotic livers was demonstrated by immunohistochemistry. In situ hybridization revealed OAcGD3S mRNA expression in areas of ductular proliferation. Furthermore, O-acetyl GD3 protein was detected in activated rat HSCs and human cirrhosis livers. This study shows that OAcGD3S is strongly expressed during liver fibrogenesis and HSCs seem to be the major cellular sources of OAcGD3S in the liver.

Role of tumor-associated gangliosides in cancer progression

Neuroectodermic tumors can mostly be characterized by the presence of tumor-associated glycosphingolipid antigens, such as gangliosides, defined by monoclonal antibodies. Recently, cumulative evidence indicates that gangliosides modify the biological effects of several trophic factors, in vitro and in vivo, as well as the mitogenic signaling cascade that these factors generate. The functional roles of gangliosides in tumor progression can be revisited: (i) ganglioside antigens on the cell surface, or shed from the cells, act as immunosuppressors, as typically observed for the suppression of cytotoxic T cells and dendritic cells, (ii) certain gangliosides, such as GD3 or GM2, promote tumor-associated angiogenesis, (iii) gangliosides strongly regulate cell adhesion/motility and thus initiate tumor metastasis, (iv) ganglioside antigens are directly connected with transducer molecules in microdomains to initiate adhesion coupled with signaling, and (v) ganglioside antigens and their catabolites are modulators of signal transduction through interaction with tyrosine kinases associated with growth factor receptors or other protein kinases. Given the potential importance of these sialylated gangliosides and their modulating biological behavior in vivo, further studies on the role of gangliosides are warranted.

GD3 ganglioside and apoptosis

Lipid and glycolipid mediators are important messengers of the adaptive responses to stress, including apoptosis. In mammalian cells, the intracellular accumulation of ganglioside GD3, an acidic glycosphingolipid, contributes to mitochondrial damage, a crucial event during the apoptopic program. GD3 is a minor ganglioside in most normal tissues. Its expression increases during development and in pathological conditions such as cancer and neurodegenerative disorders. Intriguingly, GD3 can mediate additional biological events such as cell proliferation and differentiation. These diverse and opposing effects indicate that tightly regulated mechanisms, including 9-O-acetylation, control GD3 function, by affecting intracellular levels, localization and structure of GD3, and eventually dictate biological outcomes and cell fate decisions.

GD3 in cellular ageing and apoptosis

Lipid and glycolipid mediators are important components of the adaptive responses to stress, including apoptosis. In mammalian cells, the intracellular accumulation of ganglioside GD3, an acidic glycosphingolipid, contributes to mitochondrial damage, a crucial event during the apoptotic program. GD3 is a minor ganglioside in most normal tissues. Its expression increases during development and in pathological conditions such as cancer and neurodegenerative disorders. Interestingly, GD3 expression also increases with the normal ageing process. Moreover, GD3 can also mediate biological events like proliferation and differentiation. Since organism integrity requires a tight balance between cell proliferation, apoptosis and senescence, controlling the intracellular level of GD3 appears of particular importance for cell fate determination.

Ceramide generated by acidic sphingomyelinase contributes to tumor necrosis factor-alpha-mediated apoptosis in human colon HT-29 cells through glycosphingolipids formation. Possible role of ganglioside GD3

In the present study we assessed the contribution of acidic sphingomyelinase (ASMase), a ceramide generating enzyme, in tumor necrosis factor (TNF)-mediated apoptosis in human colon HT-29 cells. TNF induced apoptosis in HT-29 cells in a time- and dose-dependent fashion. Downregulation of the active endogenous ASMase form prevented TNF-stimulated ASMase activity and apoptosis. Furthermore, inhibition of glucosylceramide synthase, which blunted TNF-stimulated GD3 levels, abolished TNF-mediated cell death. Immunocytochemical staining revealed the co-localization of GD3 with mitochondria induced by TNF. The knockdown of targeted GD3 synthase by antisense expression vector protected HT-29 cells against TNF-induced cell death. Thus, ASMase plays a key role in TNF-induced cell death in human colon epithelial cells possibly through GD3 generation.

Gangliosides with O-acetylated sialic acids in tumors of neuroectodermal origin

Gangliosides, carrying an O-acetylated sialic acid in their carbohydrate moiety, are often found in growing and developing tissues, especially of neuro-ectodermal origin. The most prominent one is 9-O-Ac-GD3, which is considered as an oncofetal marker in animal and human tumors like neuronal tumors, melanoma, basalioma or breast cancer, as well as in psoriatic lesions. Also other gangliosides like GD2 or GT3 were found to be O-acetylated in their terminal sialic acid. In this review we are summarising the occurrence of such gangliosides in normal and transformed tissues and delineate a more general theory that O-acetylated sialic acids in gangliosides are a universal marker for growing cells and tissues.

Variations in gene expression patterns correlated with phenotype of F-11 tumor cells whose expression of GD3-synthase is suppressed

Alteration in ganglioside composition in F-11 cells by suppression of GD3-synthase gene expression resulted in greatly reduced tumor growth and metastasis when the cells were injected into nude mice. To identify genes whose expression is correlated with the decreased level of ganglioside GD3, we analyzed gene expression profiles of the GD3-suppressed F-11 cells and the control F-11 cells using DNA microarrays. We identified a set of GD3-related genes, most of which are involved in tumor growth and development. The genes that define the proliferation-transformation signature are down-regulated, such as creatine kinase-B (CKB), upstream stimulation factor 1 (USF-1), type II cAMP-dependent protein kinase regulatory subunit (RII PKA), and tyrosine hydroxylase (TH). On the other hand, the genes that define the differentiation-reverse transformation signature are up-regulated, including p160 myb-binding protein (P160), brain factor-2, insulin-like growth factor-binding protein (IGFBP), and growth/differentiation factor 11. Transcriptional levels of the genes that showed the most distinct GD3-related expression change were validated by reverse transcription-polymerase chain reaction (RT-PCR). Defining GD3-related genes may lead to identification of clinically relevant therapeutics and to understanding of the mechanism(s) by which ganglioside GD3 affects tumor growth and metastasis.

Transfection of glucosylceramide synthase antisense inhibits mouse melanoma formation

MEB4 murine melanoma cells synthesize G(M3) as the major ganglioside. Inhibition of G(M3) synthesis by a specific glucosylceramide synthase inhibitor resulted in reduced tumorigenicity and metastatic potential of these cells. We used a molecular approach--antisense transfection targeting the glucosylceramide synthase gene--to regulate glycosphingolipid synthesis by MEB4 cells and examine the influence on tumor formation. Antisense transfection inhibited the synthesis of the direct product of glucosylceramide synthase, glucosylceramide, and consequently G(M3) ganglioside, by MEB4 cells, reducing the concentration of G(M3) in the transfectants by up to 58%. Although neither morphology nor proliferation kinetics of the cultured cells was affected, the inhibition of glycosphingolipid synthesis and reduction of total ganglioside content caused a striking reduction in melanoma formation in mice. Only 1/60 (2%) of mice injected ID with 10(4) antisense-transfected MA173 cells formed a tumor, compared to 31/60 (52%) of mice receiving MEB4 cells and 7/15 (47%) of mice receiving the MS2 sense-transfected cells (p < 0.001 and p = 0.005, respectively). These findings demonstrate that stable transfection of glucosylceramide synthase antisense reduces cellular glycosphingolipid levels and reduces tumorigenicity, providing further experimental support for an enhancing role of gangliosides in tumor formation.

Sialyltransferases in cancer

It has long been known that cancer cells often express more heavily sialylated glycans on their surface and that this feature sometimes correlates with invasion. It is now well established that specific sialylated structures, such as the Thomsen-Friedenreich-related antigens, the sialyl Lewis antigens, the sialyl alpha2-6 lactosaminyl structure, the polysialic acid or some gangliosides, can mediate cellular interactions and are altered in cancer cells. This review summarizes the current knowledge on the cancer-associated alterations in sialyltransferase expression which are often at the basis of the deranged expression of sialylated structures.

Detection of sialic acids and gangliosides with special reference to 9-O-acetylated species in basaliomas and normal human skin

Basal cell carcinomas and normal skin were examined in relation to the abnormal expression of gangliosides. The content of gangliosides with 9-O-acetylated sialic acids of 26 sample pairs was analyzed by a microtiter assay using influenza C virus as well as by fluorimetric high-performance liquid chromatography of the sialic acids released. The 9-O-acetylation levels were significantly (up to 56-fold) higher in basal cell carcinoma tissues than in the skin surrounding basal cell carcinomas. Slightly elevated amounts of O-acetylated gangliosides were also seen in the skin marginal to the basaliomas. The ganglioside composition of four sets of pooled samples of basal cell carcinoma and one pool of normal skin were studied by high-performance thin-layer chromatography and immune high-performance thin-layer chromatography using monoclonal antibodies against 9-O-acetyl GD3. The lipid-bound sialic acid content of normal skin was 0.029 microg dry weight, whereas in nodular basal cell carcinomas it was approximately twice as much. Several O-acetylated sialic acids were seen by high-performance liquid chromatography analysis, but N-acetyl-9-O-acetylneuraminic acid prevailed. Only in the tumor ganglioside fraction, a small amount of N-glycolylneuraminic acid was found. The 9-O-acetylated gangliosides with mainly 9-O-acetyl-GD3 can be considered as tumor-associated antigens or markers for basal cell carcinomas. This finding about tumor-associated carbohydrates may contribute to new strategies in current tumor diagnosis and therapy.

Reduced cell migration, tumor growth and experimental metastasis of rat F-11 cells whose expression of GD3-synthase is suppressed

We previously established a rat F-11 cell line whose expression of ganglioside GD3 was inhibited by stable transfection of the anti-sense vector against the GD3-synthase gene, showing that specific inhibition of GD3-synthase expression in tumor cells greatly reduced their growth rate in nude mice. Here, we report that down-regulation of GD3-synthase expression in anti-sense-transfected F-11 cells correlates with reduced cell migration and invasion in vitro and tumor growth and metastasis in vivo. When cultures were denuded of cells in a 1-mm-wide strip, the anti-sense-transfected F-11 cells migrated very slowly into the denuded area. Differences in migration between anti-sense-transfected cells and control parental cells were easily apparent. In vitro invasion assay of F-11 cells revealed a 3-fold decrease in invasion ability from the GD3-synthase-suppressed cells; colony formation in soft agar was not affected. Injection (i.v.) of control sense-transfected and untransfected F-11 cells resulted in multiple, large metastatic nodules in each of the 12 mice, whereas i.v. injection of anti-sense-transfected F-11 cells formed a single, small metastatic nodule in only 2 of the 8 nude mice. In addition, even if metastasis occurred, the anti-sense-induced metastatic nodules were much smaller than the metastatic nodules formed by control F-11 cells. These results demonstrate that suppression of GD3-synthase expression, which results primarily in a marked decrease in the concentration of ganglioside GD3, greatly reduces cell spreading, invasion and both the incidence and growth rate of experimental metastasis of F-11 cells.

Purification and structure of neurostatin, an inhibitor of astrocyte division of mammalian brain

Neurostatin was originally described as an inhibitor of astroblast and astrocytoma division present in rat brain extracts and immunologically related to the sugar moiety of epidermal growth factor receptor and to blood group antigens. It was purified recently from mammalian brain extracts and characterized as a glycosphingolipid, but its precise structure remained unknown. Neurostatin has now been purified to apparent homogeneity from ganglioside extracts of rat, bovine, and porcine brain. It is cytostatic for astroblasts, C6 glioma cells, and various human astrocytomas grades III and IV, with IC(50) values ranging from 250 to 450 nM, but does not affect the division of primary or transformed fibroblasts up to concentrations >4 microM. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry of purified pig neurostatin showed a molecular ion of 1, 905 Da and ions of 1,863 and 1,934 Da, compatible with a disialoganglioside. Mono- and bidimensional NMR spectra, together with biochemical studies, suggest that neurostatin may be the 9-O-monoacetyl ester of GD1b.