GD3 synthase overexpression enhances proliferation and migration of MDA-MB-231 breast cancer cells

Glycosylation in breast cancer progression and mammary development: Molecular connections and malignant transformations

INTRODUCTION

The cellular behavior in normal mammary gland development and the progression of breast cancer is like the relationship between an object and its mirror image: they may appear similar, but their essence is completely different. Breast cancer can be considered as temporal and spatial aberrations of normal development in mammary gland. Glycans have been shown to regulate key pathophysiological steps during mammary development and breast cancer progression, and the glycoproteins that play a key role in both processes can affect the normal differentiation and development of mammary cells, and even cause malignant transformation or accelerate tumorigenesis due to differences in their type and level of glycosylation.

KEY FINDINGS

In this review, we summarize the roles of glycan alterations in essential cellular behaviors during breast cancer progression and mammary development, and also highlight the importance of key glycan-binding proteins such as epidermal growth factor receptor, transforming growth factor β receptors and other proteins, which are pivotal in the modulation of cellular signaling in mammary gland. Our review takes an overall view of the molecular interplay, signal transduction and cellular behaviors in mammary gland development and breast cancer progression from a glycobiological perspective.

SIGNIFICANCE

This review will give a better understanding of the similarities and differences in glycosylation between mammary gland development and breast cancer progression, laying the foundation for elucidating the key molecular mechanisms of glycobiology underlying the malignant transformation of mammary cells.

The biological role and immunotherapy of gangliosides and GD3 synthase in cancers

Gangliosides are a large subfamily of glycosphingolipids that broadly exist in the nervous system and interact with signaling molecules in the lipid rafts. GD3 and GD2 are two types of disialogangliosides (GDs) that include two sialic acid residues. The expression of GD3 and GD2 in various cancers is mostly upregulated and is involved in tumor proliferation, invasion, metastasis, and immune responses. GD3 synthase (GD3S, ST8SiaI), a subclass of sialyltransferases, regulates the biosynthesis of GD3 and GD2. GD3S is also upregulated in most tumors and plays an important role in the development and progression of tumors. Many clinical trials targeting GD2 are ongoing and various immunotherapy studies targeting gangliosides and GD3S are gradually attracting much interest and attention. This review summarizes the function, molecular mechanisms, and ongoing clinical applications of GD3, GD2, and GD3S in abundant types of tumors, which aims to provide novel targets for future cancer therapy.

Glycosphingolipids are mediators of cancer plasticity through independent signaling pathways

The molecular repertoire promoting cancer cell plasticity is not fully elucidated. Here, we propose that glycosphingolipids (GSLs), specifically the globo and ganglio series, correlate and promote the transition between epithelial and mesenchymal cells. The epithelial character of ovarian cancer remains stable throughout disease progression, and spatial glycosphingolipidomics reveals elevated globosides in the tumor compartment compared with the ganglioside-rich stroma. CRISPR-Cas9 knockin mediated truncation of endogenous E-cadherin induces epithelial-to-mesenchymal transition (EMT) and decreases globosides. The transcriptomics analysis identifies the ganglioside-synthesizing enzyme ST8SIA1 to be consistently elevated in mesenchymal-like samples, predicting poor outcome. Subsequent deletion of ST8SIA1 induces epithelial cell features through mTOR^S2448 phosphorylation, whereas loss of globosides in ΔA4GALT cells, resulting in EMT, is accompanied by increased ERK^Y202/T204 and AKT^S124. The GSL composition dynamics corroborate cancer cell plasticity, and further evidence suggests that mesenchymal cells are maintained through ganglioside-dependent, calcium-mediated mechanisms.

Attenuation of Bone Formation through a Decrease in Osteoblasts in Mutant Mice Lacking the GM2/GD2 Synthase Gene

The ganglioside GD1a has been reported to promote the differentiation of mesenchymal stem cells to osteoblasts in cell culture systems. However, the involvement of gangliosides, including GD1a, in bone formation in vivo remains unknown; therefore, we herein investigated their roles in GM2/GD2 synthase-knockout (GM2/GD2S KO) mice without GD1a. The femoral cancellous bone mass was analyzed using three-dimensional micro-computed tomography. A histomorphometric analysis of bone using hematoxylin and eosin (HE) and tartrate-resistant acid phosphatase was performed to examine bone formation and resorption, respectively. Calcein double labeling was also conducted to evaluate bone formation. Although no significant differences were observed in bone mass or resorption between GM2/GD2S KO mice and wild-type (WT) mice, analyses of the parameters of bone formation using HE staining and calcein double labeling revealed less bone formation in GM2/GD2S KO mice than in WT mice. These results suggest that gangliosides play roles in bone formation.

Role of GD3 Synthase ST8Sia I in Cancers

Simple Summary

The carbohydrate moiety of cell surface glycolipids is modified in cancers of neuro–ectoderm origin, leading to the expression of more complex structures with two or more sialic acid residues. These alterations result from the upregulation of the ST8SIA1 gene that encodes GD3 synthase, the enzyme controlling the biosynthesis of complex gangliosides, and are usually associated with a more aggressive phenotype and a poor outcome for patients, making GD3 synthase an interesting target for cancer therapy. This review reports our general knowledge of GD3 synthase gene expression and regulation, its role in both epithelial–mesenchymal transition (EMT) and cancer progression, and the different approaches targeting GD3S expression in cancers.

Abstract

GD3 synthase controls the biosynthesis of complex gangliosides, bearing two or more sialic acid residues. Disialylated gangliosides GD3 and GD2 are tumor-associated carbohydrate antigens (TACA) in neuro–ectoderm-derived cancers, and are directly involved in cell malignant properties, i.e., migration, invasion, stemness, and epithelial–mesenchymal transition. Since GD3 and GD2 levels are directly linked to GD3 synthase expression and activity, targeting GD3 synthase appears to be a promising strategy through which to interfere with ganglioside-associated malignant properties. We review here the current knowledge on GD3 synthase expression and regulation in cancers, and the consequences of complex ganglioside expression on cancer cell signaling and properties, highlighting the relationships between GD3 synthase expression and epithelial–mesenchymal transition and stemness. Different strategies were used to modulate GD3 synthase expression in cancer cells in vitro and in animal models, such as inhibitors or siRNA/lncRNA, which efficiently reduced cancer cell malignant properties and the proportion of GD2 positive cancer stem cells, which are associated with high metastatic properties, resistance to therapy, and cancer relapse. These data show the relevance of targeting GD3 synthase in association with conventional therapies, to decrease the number of cancer stem cells in tumors.

The Distinct Roles of Sialyltransferases in Cancer Biology and Onco-Immunology

Aberrant glycosylation is a key feature of malignant transformation. Hypersialylation, the enhanced expression of sialic acid-terminated glycoconjugates on the cell surface, has been linked to immune evasion and metastatic spread, eventually by interaction with sialoglycan-binding lectins, including Siglecs and selectins. The biosynthesis of tumor-associated sialoglycans involves sialyltransferases, which are differentially expressed in cancer cells. In this review article, we provide an overview of the twenty human sialyltransferases and their roles in cancer biology and immunity. A better understanding of the individual contribution of select sialyltransferases to the tumor sialome may lead to more personalized strategies for the treatment of cancer.

[Reticular and Golgi glycosylation: Advances and associated diseases]

Glycosylation is one of the essential modifications of proteins and lipids. It is carried out mainly in the endoplasmic reticulum and Golgi apparatus, and requires a specific molecular machinery associating several hundreds of glycosyltransferases, glycosidases, transporters and regulating proteins. Modifications of glycosylation are found in numerous diseases, notably in cancers. All types of glycosylation can be affected and this leads to dysfunctions of cellular metabolism. In this review, we present the current knowledge on the regulation of glycosylation mechanisms and illustrate how the alteration of these regulatory mechanisms can lead to abnormal protein and lipid glycosylation, and take part in the development of cancers.

Cancer-Associated Glycosphingolipids as Tumor Markers and Targets for Cancer Immunotherapy

Aberrant expression of glycosphingolipids is a hallmark of cancer cells and is associated with their malignant properties. Disialylated gangliosides GD2 and GD3 are considered as markers of neuroectoderm origin in tumors, whereas fucosyl-GM1 is expressed in very few normal tissues but overexpressed in a variety of cancers, especially in small cell lung carcinoma. These gangliosides are absent in most normal adult tissues, making them targets of interest in immuno-oncology. Passive and active immunotherapy strategies have been developed, and have shown promising results in clinical trials. In this review, we summarized the current knowledge on GD2, GD3, and fucosyl-GM1 expression in health and cancer, their biosynthesis pathways in the Golgi apparatus, and their biological roles. We described how their overexpression can affect intracellular signaling pathways, increasing the malignant phenotypes of cancer cells, including their metastatic potential and invasiveness. Finally, the different strategies used to target these tumor-associated gangliosides for immunotherapy were discussed, including the use and development of monoclonal antibodies, vaccines, immune system modulators, and immune effector-cell therapy, with a special focus on adoptive cellular therapy with T cells engineered to express chimeric antigen receptors.

ST8SIA1 inhibition sensitizes triple negative breast cancer to chemotherapy via suppressing Wnt/β-catenin and FAK/Akt/mTOR

BACKGROUND

Chemoresistance is the major cause of therapeutic failure in triple negative breast cancer (TNBC). In this work, we investigated the molecular mechanism for the development of TNBC chemoresistance.

METHODS

mRNA and protein levels of ST8SIA1 were analyzed in chemosensitive and chemoresistant TNBC cells and tissues. Proliferation and survival assays were performed to determine the role of ST8SIA1 in TNBC chemoresistance.

RESULTS

We found that ST8SIA1 mRNA and protein levels were increased in multiple TNBC cell lines after prolonged exposure to chemotherapeutic drugs. Consistently, retrospective study demonstrated that the majority of TNBC patients who developed chemoresistance displayed upregulation of ST8SIA1. We further found that chemoresistant TNBC cells were more sensitive than chemosensitive cells to ST8SIA1 inhibition in decreasing growth and viability. Consistently, ST8SIA1 inhibition augmented the efficacy of chemotherapy in TNBC cells. Mechanism studies demonstrated that ST8SIA1 inhibition led to suppression of FAK/Akt/mTOR and Wnt/β-catenin signalling pathways.

CONCLUSIONS

These findings provide an explanation for the heterogeneity of chemotherapy responses across TNBC individuals and reveal the supportive roles of ST8SIA1in TNBC chemoresistance.

Profiling of O-acetylated Gangliosides Expressed in Neuroectoderm Derived Cells

The expression and biological functions of oncofetal markers GD2 and GD3 were extensively studied in neuroectoderm-derived cancers in order to characterize their potential as therapeutic targets. Using immunological approaches, we previously identified GD3, GD2, and OAcGD2 expression in breast cancer (BC) cell lines. However, antibodies specific for O-acetylated gangliosides are not exempt of limitations, as they only provide information on the expression of a limited set of O-acetylated ganglioside species. Consequently, the aim of the present study was to use structural approaches in order to apprehend ganglioside diversity in melanoma, neuroblastoma, and breast cancer cells, focusing on O-acetylated species that are usually lost under alkaline conditions and require specific analytical procedures. We used purification and extraction methods that preserve the O-acetyl modification for the analysis of native gangliosides by MALDI-TOF. We identified the expression of GM1, GM2, GM3, GD2, GD3, GT2, and GT3 in SK-Mel28 (melanoma), LAN-1 (neuroblastoma), Hs 578T, SUM 159PT, MDA-MB-231, MCF-7 (BC), and BC cell lines over-expressing GD3 synthase. Among O-acetylated gangliosides, we characterized the expression of OAcGM1, OAcGD3, OAcGD2, OAcGT2, and OAcGT3. Furthermore, the experimental procedure allowed us to clearly identify the position of the sialic acid residue that carries the O-acetyl group on b- and c-series gangliosides by MS/MS fragmentation. These results show that ganglioside O-acetylation occurs on both inner and terminal sialic acid residue in a cell type-dependent manner, suggesting different O-acetylation pathways for gangliosides. They also highlight the limitation of immuno-detection for the complete identification of O-acetylated ganglioside profiles in cancer cells.

Gangliosides: The Double-Edge Sword of Neuro-Ectodermal Derived Tumors

Gangliosides, the glycosphingolipids carrying one or several sialic acid residues, are mostly localized at the plasma membrane in lipid raft domains and implicated in many cellular signaling pathways mostly by interacting with tyrosine kinase receptors. Gangliosides are divided into four series according to the number of sialic acid residues, which can be also modified by O-acetylation. Both ganglioside expression and sialic acid modifications can be modified in pathological conditions such as cancer, which can induce either pro-cancerous or anti-cancerous effects. In this review, we summarize the specific functions of gangliosides in neuro-ectodermal derived tumors, and their roles in reprogramming the lipidomic profile of cell membrane occurring with the induction of epithelial-mesenchymal transition.

Exploration of the Sialic Acid World

Sialic acids are cytoprotectors, mainly localized on the surface of cell membranes with multiple and outstanding cell biological functions. The history of their structural analysis, occurrence, and functions is fascinating and described in this review. Reports from different researchers on apparently similar substances from a variety of biological materials led to the identification of a 9-carbon monosaccharide, which in 1957 was designated "sialic acid." The most frequently occurring member of the sialic acid family is N-acetylneuraminic acid, followed by N-glycolylneuraminic acid and O-acetylated derivatives, and up to now over about 80 neuraminic acid derivatives have been described. They appeared first in the animal kingdom, ranging from echinoderms up to higher animals, in many microorganisms, and are also expressed in insects, but are absent in higher plants. Sialic acids are masks and ligands and play as such dual roles in biology. Their involvement in immunology and tumor biology, as well as in hereditary diseases, cannot be underestimated. N-Glycolylneuraminic acid is very special, as this sugar cannot be expressed by humans, but is a xenoantigen with pathogenetic potential. Sialidases (neuraminidases), which liberate sialic acids from cellular compounds, had been known from very early on from studies with influenza viruses. Sialyltransferases, which are responsible for the sialylation of glycans and elongation of polysialic acids, are studied because of their significance in development and, for instance, in cancer. As more information about the functions in health and disease is acquired, the use of sialic acids in the treatment of diseases is also envisaged.

GD3 ganglioside-enriched extracellular vesicles stimulate melanocyte migration

Melanomas often accumulate gangliosides, sialic acid-containing glycosphingolipids found in the outer leaflet of plasma membranes, as disialoganglioside G_D3 and its derivatives. Here, we have transfected the G_D3 synthase gene (ST8Sia I) in a normal melanocyte cell line in order to evaluate changes in the biological behavior of non-transformed cells. G_D3-synthase expressing cells converted G_M3 into G_D3 and accumulated both G_D3 and its acetylated form, 9-O-acetyl-G_D3. Melanocytes were rendered more migratory on laminin-1 surfaces. Cell migration studies using the different transfectants, either treated or not with the glucosylceramide synthase inhibitor d-1-threo-1-phenyl-2-palmitoylamino-3-pyrrolidino-1-propanol (PPPP), allowed us to show that while G_M3 is a negative regulator of melanocyte migration, G_D3 increases it. We showed that gangliosides were shed to the matrix by migrating cells and that G_D3 synthase transfected cells shed extracellular vesicles (EVs) enriched in G_D3. EVs enriched in G_D3 stimulated cell migration of G_D3 negative cells, as observed in time lapse microscopy studies. Otherwise, EVs shed by G_M3^+veG_D3^-ve cells impaired migration and diminished cell velocity in cells overexpressing G_D3. The balance of antimigratory G_M3 and promigratory G_D3 gangliosides in melanocytes could be altered not only by the overexpression of enzymes such as ST8Sia I, but also by the horizontal transfer of ganglioside enriched extracellular vesicles. This study highlights that extracellular vesicles transfer biological information also through their membrane components, which include a variety of glycosphingolipids remodeled in disease states such as cancer.

Downregulation of aquaporin 3 inhibits cellular proliferation, migration and invasion in the MDA-MB-231 breast cancer cell line

Aquaporins are membrane proteins that regulate cellular water flow. Recently, aquaporins have been proposed as mediators of cancer cell biology. A subset of aquaporins, referred to as aquaglyceroporins are known to facilitate the transport of glycerol. The present study describes the effect of gene knockdown of the aquaglyceroporin AQP3 on MDA-MB-231 breast cancer cell proliferation, migration, invasion, adherence and response to the chemotherapeutic agent 5-fluorouracil. shRNA mediated AQP3 gene knockdown induced a 28% reduction in cellular proliferation (P<0.01), a 39% decrease in migration (P<0.0001), a 24% reduction in invasion (P<0.05) and a 25% increase in cell death at 100 µM 5-FU (P<0.01). Analysis of cell permeability to water and glycerol revealed that MDA-MB-231 cells with knocked down AQP3 demonstrated a modest decrease in water permeability (17%; P<0.05) but a more marked decrease in glycerol permeability (77%; P<0.001). These results suggest that AQP3 has a role in multiple aspects of breast cancer cell pathophysiology and therefore represents a novel target for therapeutic intervention.

TNF differentially regulates ganglioside biosynthesis and expression in breast cancer cell lines

Gangliosides are glycosphingolipids concentrated in glycolipid-enriched membrane microdomains. Mainly restricted to the nervous system in healthy adult, complex gangliosides such as GD3 and GD2 have been shown to be involved in aggressiveness and metastasis of neuro-ectoderm derived tumors such as melanoma and neuroblastoma. GD3 synthase (GD3S), the key enzyme that controls the biosynthesis of complex gangliosides, was shown to be over-expressed in Estrogen Receptor (ER)-negative breast cancer tumors, and associated with a decreased overall survival of patients. We previously demonstrated that GD3S expression in ER-negative breast cancer cells induced a proliferative phenotype and an increased tumor growth. In addition, our results clearly indicate that Tumor Necrosis Factor (TNF) induced GD3S over-expression in breast cancer cells via NFκB pathway. In this study, we analyzed the effect of TNF on ganglioside biosynthesis and expression in breast cancer cells from different molecular subtypes. We showed that TNF up-regulated the expression of GD3S in MCF-7 and Hs578T cells, whereas no change was observed for MDA-MB-231. We also showed that TNF induced an increased expression of complex gangliosides at the cell surface of a small proportion of MCF-7 cells. These results demonstrate that TNF differentially regulates gangliosides expression in breast cancer cell lines and establish a possible link between inflammation at the tumor site environment, expression of complex gangliosides and tumor development.

Glycosylation as a Main Regulator of Growth and Death Factor Receptors Signaling

Glycosylation is a very frequent and functionally important post-translational protein modification that undergoes profound changes in cancer. Growth and death factor receptors and plasma membrane glycoproteins, which upon activation by extracellular ligands trigger a signal transduction cascade, are targets of several molecular anti-cancer drugs. In this review, we provide a thorough picture of the mechanisms bywhich glycosylation affects the activity of growth and death factor receptors in normal and pathological conditions. Glycosylation affects receptor activity through three non-mutually exclusive basic mechanisms: (1) by directly regulating intracellular transport, ligand binding, oligomerization and signaling of receptors; (2) through the binding of receptor carbohydrate structures to galectins, forming a lattice thatregulates receptor turnover on the plasma membrane; and (3) by receptor interaction with gangliosides inside membrane microdomains. Some carbohydrate chains, for example core fucose and β1,6-branching, exert a stimulatory effect on all receptors, while other structures exert opposite effects on different receptors or in different cellular contexts. In light of the crucial role played by glycosylation in the regulation of receptor activity, the development of next-generation drugs targeting glyco-epitopes of growth factor receptors should be considered a therapeutically interesting goal.

Inhibition of hepatocellular carcinoma growth by blockade of glycosphingolipid synthesis

Hepatocellular carcinoma (HCC) is one of the most frequent cancers. In vitro studies suggest that growth and response to therapy of human carcinomas may depend on glycosphingolipid (GSL) expression. Glucosylceramide synthase (GCS), encoded by the gene Ugcg, is the basic enzyme required for the synthesis of GSLs. Gene array analysis implied that Ugcg is significantly overexpressed in human HCC as compared to non-tumorous liver tissue. Therefore we have investigated whether tumor - genesis and - growth is altered in the absence of GSLs. An endogenous liver cancer model has been initiated by application of diethylnitrosamine in mice lacking Ugcg specifically in hepatocytes. We have now shown that hepatocellular tumor initiation and growth in mice is significantly inhibited by hepatic GSL deficiency in vivo. Neither the expression of cell cycle proteins, such as cyclins and pathways such as the MAP-kinase/Erk pathway nor the mTOR/Akt pathway as well as the number of liver infiltrating macrophages and T cells were essentially changed in tumors lacking GSLs. Significantly elevated bi-nucleation of atypical hepatocytes, a feature for impaired cytokinesis, was detected in tumors of mice lacking liver-specific GSLs. A reduction of proliferation and restricted growth of tumor microspheres due to delayed, GSL-dependent cytokinesis, analogous to the histopathologic phenotype in vivo could be demonstrated in vitro. GSL synthesis inhibition may thus constitute a potential therapeutic target for hepatocellular carcinoma.

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.

Oldenlandia diffusa suppresses metastatic potential through inhibiting matrix metalloproteinase-9 and intercellular adhesion molecule-1 expression via p38 and ERK1/2 MAPK pathways and induces apoptosis in human breast cancer MCF-7 cells

ETHNOPHARMACOLOGY RELEVANCE

Oldenlandia diffusa (OD) has long been known as an apoptotic inducer in breast tumors in ethnomedicine.

AIM OF THE STUDY

To scientifically confirm the anti-breast cancer effects of water, methanol (MeOH) and butanol (BuOH) extracts of O. diffusa on cell apoptosis, matrix metalloproteinases (MMPs), intercellular adhesion molecule (ICAM)-1 and intracellular signaling in MCF-7 breast cancer cells.

MATERIALS AND METHODS

MeOH extracts (MOD) and BuOH extracts (BOD) were prepared and examined for their ability to inhibit phorbol myristate acetate (PMA)-induced matrix metalloproteinase (MMP)-9 and intercellular adhesion molecule (ICAM)-1 expressions in MCF-7 human breast cancer cells. Additionally, transwell migration, invasion and transcriptional activity were assessed. Results of immunofluorescence confocal microscopy for translocation of NF-κB and p-ERK and p-p38 were also checked. Finally, apoptotic signals including processed caspase-8, caspase-7, poly ADP-ribose polymerase, Bax and Bcl-2 were examined.

RESULTS

MOD and BOD specifically inhibited PMA-induced MMP-9 expression as well as invasive and migration potential via ICAM-1. The inhibitory activity was also based on the suppressed transcriptional activity in MCF-7 breast cancer cells. Results of immunofluorescence confocal microscopy showed that translocation of NF-κB decreased upon BOD and MOD treatments, with a decreased level of p-ERK and p-p38 phosphorylation. In addition, treatment of MCF-7 cells with MOD and BOD activated apoptosis-linked proteins including enzymatically active forms of processed caspase-8, caspase-7 and poly ADP-ribose polymerase, together with increased expression of mitochondrial apoptotic protein, Bax and decreased expression of Bcl-2.

CONCLUSION

The results indicate that OD as an anti-metastatic agent suppresses the metastatic response by targeting p-ERK, p-38 and NF-κB, thus reducing the invasion capacity of MCF-7 breast cancer cells through inhibition of MMP-9 and ICAM-1 expression and plays an important role in the regulation of breast cancer cell apoptosis.

Role of Cytokine-Induced Glycosylation Changes in Regulating Cell Interactions and Cell Signaling in Inflammatory Diseases and Cancer

Glycosylation is one of the most important modifications of proteins and lipids, and cell surface glycoconjugates are thought to play important roles in a variety of biological functions including cell-cell and cell-substrate interactions, bacterial adhesion, cell immunogenicity and cell signaling. Alterations of glycosylation are observed in number of diseases such as cancer and chronic inflammation. In that context, pro-inflammatory cytokines have been shown to modulate cell surface glycosylation by regulating the expression of glycosyltransferases involved in the biosynthesis of carbohydrate chains. These changes in cell surface glycosylation are also known to regulate cell signaling and could contribute to disease pathogenesis. This review summarizes our current knowledge of the glycosylation changes induced by pro-inflammatory cytokines, with a particular focus on cancer and cystic fibrosis, and their consequences on cell interactions and signaling.

Glycosphingolipid-Protein Interaction in Signal Transduction

Glycosphingolipids (GSLs) are a class of ceramide-based glycolipids essential for embryo development in mammals. The synthesis of specific GSLs depends on the expression of distinctive sets of GSL synthesizing enzymes that is tightly regulated during development. Several reports have described how cell surface receptors can be kept in a resting state or activate alternative signalling events as a consequence of their interaction with GSLs. Specific GSLs, indeed, interface with specific protein domains that are found in signalling molecules and which act as GSL sensors to modify signalling responses. The regulation exerted by GSLs on signal transduction is orthogonal to the ligand–receptor axis, as it usually does not directly interfere with the ligand binding to receptors. Due to their properties of adjustable production and orthogonal action on receptors, GSLs add a new dimension to the control of the signalling in development. GSLs can, indeed, dynamically influence progenitor cell response to morphogenetic stimuli, resulting in alternative differentiation fates. Here, we review the available literature on GSL–protein interactions and their effects on cell signalling and development.

The complex nature of oestrogen signalling in breast cancer: enemy or ally?

The pleiotropic nature of oestradiol, the main oestrogen found in women, has been well described in the literature. Oestradiol is positioned to play a unique role since it can respond to environmental, genetic and non-genetic cues to affect genetic expression and cellular signalling. In breast cancer, oestradiol signalling has a dual effect, promoting or inhibiting cancer growth. The potential impact of oestradiol on tumorigenesis depends on the molecular and cellular characteristics of the breast cancer cell. In this review, we provide a broad survey discussing the cellular and molecular consequences of oestrogen signalling in breast cancer. First, we review the structure of the classical oestrogen receptors and resultant transcriptional (genomic) and non-transcriptional (non-genomic) signalling. We then discuss the nature of oestradiol signalling in breast cancer including the specific receptors that initiate these signalling cascades as well as potential outcomes, such as cancer growth, proliferation and angiogenesis. Finally, we examine cellular and molecular mechanisms underlying the dimorphic effect of oestrogen signalling in breast cancer.

Exogenous and Endogeneous Disialosyl Ganglioside GD1b Induces Apoptosis of MCF-7 Human Breast Cancer Cells

Gangliosides have been known to play a role in the regulation of apoptosis in cancer cells. This study has employed disialyl-ganglioside GD1b to apoptosis in human breast cancer MCF-7 cells using exogenous treatment of the cells with GD1b and endogenous expression of GD1b in MCF-7 cells. First, apoptosis in MCF-7 cells was observed after treatment of GD1b. Treatment of MCF-7 cells with GD1b reduced cell growth rates in a dose and time dependent manner during GD1b treatment, as determined by XTT assay. Among the various gangliosides, GD1b specifically induced apoptosis of the MCF-7 cells. Flow cytometry and immunofluorescence assays showed that GD1b specifically induces apoptosis in the MCF-7 cells with Annexin V binding for apoptotic actions in early stage and propidium iodide (PI) staining the nucleus of the MCF-7 cells. Treatment of MCF-7 cells with GD1b activated apoptotic molecules such as processed forms of caspase-8, -7 and PARP (Poly(ADP-ribose) polymerase), without any change in the expression of mitochondria-mediated apoptosis molecules such as Bax and Bcl-2. Second, to investigate the effect of endogenously produced GD1b on the regulation of cell function, UDP-gal: β1,3-galactosyltransferase-2 (GD1b synthase, Gal-T2) gene has been transfected into the MCF-7 cells. Using the GD1b synthase-transfectants, apoptosis-related signal proteins linked to phenotype changes were examined. Similar to the exogenous GD1b treatment, the cell growth of the GD1b synthase gene-transfectants was significantly suppressed compared with the vector-transfectant cell lines and transfection activated the apoptotic molecules such as processed forms of caspase-8, -7 and PARP, but not the levels of expression of Bax and Bcl-2. GD1b-induced apoptosis was blocked by caspase inhibitor, Z-VAD. Therefore, taken together, it was concluded that GD1b could play an important role in the regulation of breast cancer apoptosis.

Selection of a Relevant In Vitro Blood-Brain Barrier Model to Investigate Pro-Metastatic Features of Human Breast Cancer Cell Lines

Around 7–17% of metastatic breast cancer patients will develop brain metastases, associated with a poor prognosis. To reach the brain parenchyma, cancer cells need to cross the highly restrictive endothelium of the Blood-Brain Barrier (BBB). As treatments for brain metastases are mostly inefficient, preventing cancer cells to reach the brain could provide a relevant and important strategy. For that purpose an in vitro approach is required to identify cellular and molecular interaction mechanisms between breast cancer cells and BBB endothelium, notably at the early steps of the interaction. However, while numerous studies are performed with in vitro models, the heterogeneity and the quality of BBB models used is a limitation to the extrapolation of the obtained results to in vivo context, showing that the choice of a model that fulfills the biological BBB characteristics is essential. Therefore, we compared pre-established and currently used in vitro models from different origins (bovine, mice, human) in order to define the most appropriate tool to study interactions between breast cancer cells and the BBB. On each model, the BBB properties and the adhesion capacities of breast cancer cell lines were evaluated. As endothelial cells represent the physical restriction site of the BBB, all the models consisted of endothelial cells from animal or human origins. Among these models, only the in vitro BBB model derived from human stem cells both displayed BBB properties and allowed measurement of meaningful different interaction capacities of the cancer cell lines. Importantly, the measured adhesion and transmigration were found to be in accordance with the cancer cell lines molecular subtypes. In addition, at a molecular level, the inhibition of ganglioside biosynthesis highlights the potential role of glycosylation in breast cancer cells adhesion capacities.

Glycosphingolipids and cell death: one aim, many ways

Glycosphingolipids (GSLs) are a family of bioactive lipids that in addition to their role in the regulation of structural properties of membrane bilayers have emerged as crucial players in many biological processes and signal transduction pathways. Rather than being uniformly distributed within membrane bilayers, GSLs are localized in selective domains called lipid rafts where many signaling platforms operate. One of the most important functions of GSLs, particularly ceramide, is their ability to regulate cell death pathways and hence cell fate. This complex role is accomplished by the ability of GSLs to act in distinct subcellular strategic centers, such as mitochondria, endoplasmic reticulum (ER) or lysosomes to mediate apoptosis, ER stress, autophagy, lysosomal membrane permeabilization and necroptosis. Hence better understanding the role of GSLs in cell death may be of relevance for a number of pathological processes and diseases, including neurodegeneration, metabolic liver diseases and cancer.

Synthesis and cell-selective antitumor properties of amino acid conjugated tumor-associated carbohydrate antigen-coated gold nanoparticles

The Thomsen Friedenreich antigen (TFag) disaccharide is a tumor-associated carbohydrate antigen (TACA) found primarily on carcinoma cells and rarely expressed in normal tissue. The TFag has been shown to interact with Galectin-3 (Gal-3), one in a family of β-galactoside binding proteins. Galectins have a variety of cellular functions, and Gal-3 has been shown to be the sole galectin with anti-apoptotic activity. We have previously prepared gold nanoparticles (AuNP) coated with the TFag in various presentations as potential anti-adhesive therapeutic tools or antitumor vaccine platforms. Here we describe the synthesis of TFag-glycoamino acid conjugates attached to gold nanoparticles through a combined alkane/PEG linker, where the TFag was attached to either a serine or threonine amino acid. Particles were fully characterized by a host of biophysical techniques, and along with a control particle carrying hydroxyl-terminated linker units, were evaluated in both Gal-3 positive and negative cell lines. We show that the particles bearing the saccharides selectively inhibited tumor cell growth of the Gal-3 positive cells significantly more than the Gal-3 negative cells. In addition, the threonine-attached TF particles were more potent than the serine-attached constructs. These results support the use of AuNP as antitumor therapeutic platforms, targeted against cell lines that express specific lectins that interact with TFag.

How Do Gangliosides Regulate RTKs Signaling?

Gangliosides, the glycosphingolipids carrying one or several sialic acid residues, are located on the outer leaflet of the plasma membrane in glycolipid-enriched microdomains, where they interact with molecules of signal transduction pathways including receptors tyrosine kinases (RTKs). The role of gangliosides in the regulation of signal transduction has been reported in many cases and in a large number of cell types. In this review, we summarize the current knowledge on the biosynthesis of gangliosides and the mechanism by which they regulate RTKs signaling.

Expression of ST3GAL4 leads to SLe(x) expression and induces c-Met activation and an invasive phenotype in gastric carcinoma cells

Sialyl-Lewis X (SLe(x)) is a sialylated glycan antigen expressed on the cell surface during malignant cell transformation and is associated with cancer progression and poor prognosis. The increased expression of sialylated glycans is associated with alterations in the expression of sialyltransferases (STs). In this study we determined the capacity of ST3GAL3 and ST3GAL4 sialyltransferases to synthesize the SLe(x) antigen in MKN45 gastric carcinoma cells and evaluated the effect of SLe(x) overexpression in cancer cell behavior both in vitro and in vivo using the chicken chorioallantoic membrane (CAM) model. The activation of tyrosine kinase receptors and their downstream molecular targets was also addressed. Our results showed that the expression of ST3GAL4 in MKN45 gastric cancer cells leads to the synthesis of SLe(x) antigens and to an increased invasive phenotype both in vitro and in the in vivo CAM model. Analysis of phosphorylation of tyrosine kinase receptors showed a specific increase in c-Met activation. The characterization of downstream molecular targets of c-Met activation, involved in the invasive phenotype, revealed increased phosphorylation of FAK and Src proteins and activation of Cdc42, Rac1 and RhoA GTPases. Inhibition of c-Met and Src activation abolished the observed increased cell invasive phenotype. In conclusion, the expression of ST3GAL4 leads to SLe(x) antigen expression in gastric cancer cells which in turn induces an increased invasive phenotype through the activation of c-Met, in association with Src, FAK and Cdc42, Rac1 and RhoA GTPases activation.

Estradiol represses the G(D3) synthase gene ST8SIA1 expression in human breast cancer cells by preventing NFκB binding to ST8SIA1 promoter

Recent data have underlined a possible role of G(D3) synthase (GD3S) and complex gangliosides in Estrogen Receptor (ER) negative breast cancer progression. Here, we describe the main transcript of the GD3S coding gene ST8SIA1 expressed in breast tumors. We characterized the corresponding core promoter in Hs578T breast cancer cells and showed that estradiol decreases ST8SIA1 mRNA expression in ER-positive MCF-7 cells and ERα-transfected ER-negative Hs578T cells. The activity of the core promoter sequence of ST8SIA1 is also repressed by estradiol. The core promoter of ST8SIA1 contains two putative Estrogen Response Elements (ERE) that were not found to be involved in the promoter activity pathway. However, NFκB was shown to be involved in ST8SIA1 transcriptional activation and we demonstrated that estradiol prevents NFκB to bind to ST8SIA1 core promoter in ERα expressing breast cancer cells by inhibiting p65 and p50 nucleus localization. The activation of NFκB pathway in ER-negative tumors, due to the absence of estradiol signaling, might explain the overexpression of G(D3) synthase in this tumor subtype.

Cell-specific in vivo functions of glycosphingolipids: lessons from genetic deletions of enzymes involved in glycosphingolipid synthesis

Glycosphingolipids (GSLs) are believed to be involved in many cellular events including trafficking, signaling and cellular interactions. Over the past decade considerable progress was made elucidating the function of GSLs by generating and exploring animal models with GSL-deficiency. Initial studies focused on exploring the role of complex sialic acid containing GSLs (gangliosides) in neuronal tissue. Although complex gangliosides were absent, surprisingly, the phenotype observed was rather mild. In subsequent studies, several mouse models with combinations of gene-deletions encoding GSL-synthesizing enzymes were developed. The results indicated that reduction of GSL-complexity correlated with severity of phenotypes. However, in these mice, accumulation of precursor GSLs or neobiosynthesized GSL-series seemed to partly compensate the loss of GSLs. Thus, UDP-glucose:ceramide glucosyltransferase (Ugcg), catalyzing the basic step of the glucosylceramide-based GSL-biosynthesis, was genetically disrupted. A total systemic deletion of Ugcg caused early embryonic lethality. Therefore, Ugcg was eliminated in a cell-specific manner using the cre/loxP-system. New insights into the cellular function of GSLs were gained. It was demonstrated that neurons require GSLs for differentiation and maintenance. In keratinocytes, preservation of the skin barrier depends on GSL synthesis and in enterocytes of the small intestine GSLs are involved in endocytosis and vesicular transport.

Tumor-associated glycans and their role in gynecological cancers: accelerating translational research by novel high-throughput approaches

Glycans are important partners in many biological processes, including carcinogenesis. The rapidly developing field of functional glycomics becomes one of the frontiers of biology and biomedicine. Aberrant glycosylation of proteins and lipids occurs commonly during malignant transformation and leads to the expression of specific tumor-associated glycans. The appearance of aberrant glycans on carcinoma cells is typically associated with grade, invasion, metastasis and overall poor prognosis. Cancer-associated carbohydrates are mostly located on the surface of cancer cells and are therefore potential diagnostic biomarkers. Currently, there is increasing interest in cancer-associated aberrant glycosylation, with growing numbers of characteristic cancer targets being detected every day. Breast and ovarian cancer are the most common and lethal malignancies in women, respectively, and potential glycan biomarkers hold promise for early detection and targeted therapies. However, the acceleration of research and comprehensive multi-target investigation of cancer-specific glycans could only be successfully achieved with the help of a combination of novel high-throughput glycomic approaches.

Accumulation of unusual gangliosides G(Q3) and G(P3) in breast cancer cells expressing the G(D3) synthase

Glycosphingolipids from the ganglio-series are usually classified in four series according to the presence of 0 to 3 sialic acid residues linked to lactosylceramide. The transfer of sialic acid is catalyzed in the Golgi apparatus by specific sialyltransferases that show high specificity toward glycolipid substrates. ST8Sia I (EC 2.4.99.8, SAT-II, SIAT 8a) is the key enzyme controlling the biosynthesis of b- and c-series gangliosides. ST8Sia I is expressed at early developmental stages whereas in adult human tissues, ST8Sia I transcripts are essentially detected in brain. ST8Sia I together with b- and c-series gangliosides are also over-expressed in neuroectoderm-derived malignant tumors such as melanoma, glioblastoma, neuroblastoma and in estrogen receptor (ER) negative breast cancer, where they play a role in cell proliferation, migration, adhesion and angiogenesis. We have stably expressed ST8Sia I in MCF-7 breast cancer cells and analyzed the glycosphingolipid composition of wild type (WT) and GD3S+ clones. As shown by mass spectrometry, MCF-7 expressed a complex pattern of neutral and sialylated glycosphingolipids from globo- and ganglio-series. WT MCF-7 cells exhibited classical monosialylated gangliosides including G(M3), G(M2), and G(M1a). In parallel, the expression of ST8Sia I in MCF-7 GD3S+ clones resulted in a dramatic change in ganglioside composition, with the expression of b- and c-series gangliosides as well as unusual tetra- and pentasialylated lactosylceramide derivatives G(Q3) (II(3)Neu5Ac(4)-Gg(2)Cer) and G(P3) (II(3)Neu5Ac(5)-Gg(2)Cer). This indicates that ST8Sia I is able to act as an oligosialyltransferase in a cellular context.

The ganglioside G(D2) induces the constitutive activation of c-Met in MDA-MB-231 breast cancer cells expressing the G(D3) synthase

We have recently established and characterized cellular clones deriving from MDA-MB-231 breast cancer cells that express the human G(D3) synthase (GD3S), the enzyme that controls the biosynthesis of b- and c-series gangliosides. The GD3S positive clones show a proliferative phenotype in the absence of serum or growth factors and an increased tumor growth in severe immunodeficient mice. This phenotype results from the constitutive activation of the receptor tyrosine kinase c-Met in spite of the absence of ligand and subsequent activation of mitogen-activated protein kinase/extracellular signal-regulated kinase and phosphoinositide 3-kinase/Akt pathways. Here, we show by mass spectrometry analysis of total glycosphingolipids that G(D3) and G(D2) are the main gangliosides expressed by the GD3S positive clones. Moreover, G(D2) colocalized with c-Met at the plasma membrane and small interfering RNA silencing of the G(M2)/G(D2) synthase efficiently reduced the expression of G(D2) as well as c-Met phosphorylation and reversed the proliferative phenotype. Competition assays using anti-G(D2) monoclonal antibodies also inhibit proliferation and c-Met phosphorylation of GD3S positive clones in serum-free conditions. Altogether, these results demonstrate the involvement of the disialoganglioside G(D2) in MDA-MB-231 cell proliferation via the constitutive activation of c-Met. The accumulation of G(D2) in c-Met expressing cells could therefore reinforce the tumorigenicity and aggressiveness of breast cancer tumors.

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.

GD₃ synthase expression enhances proliferation and tumor growth of MDA-MB-231 breast cancer cells through c-Met activation

The disialoganglioside G(D3) is overexpressed in ∼50% of invasive ductal breast carcinoma, and the G(D3) synthase gene (ST8SIA1) displays higher expression among estrogen receptor-negative breast cancer tumors, associated with a decreased overall survival of breast cancer patients. However, no relationship between ganglioside expression and breast cancer development and aggressiveness has been reported. We have previously shown that overexpression of G(D3) synthase induces the accumulation of b- and c-series gangliosides (G(D3), G(D2), and G(T3)) at the cell surface of MDA-MB-231 breast cancer cells together with the acquisition of a proliferative phenotype in the absence of serum. Here, we show that phosphoinositide 3-kinase/Akt and mitogen-activated protein kinase/extracellular signal-regulated kinase pathways are constitutively activated in G(D3) synthase-expressing cells. Analysis of phosphorylation of tyrosine kinase receptors shows a specific c-Met constitutive activation in G(D3) synthase-expressing cells, in the absence of its ligand, hepatocyte growth factor/scatter factor. In addition, inhibition of c-Met or downstream signaling pathways reverses the proliferative phenotype. We also show that G(D3) synthase expression enhances tumor growth in severe combined immunodeficient mice. Finally, a higher expression of ST8SIA1 and MET in the basal subtype of human breast tumors are observed. Altogether, our results show that G(D3) synthase expression is sufficient to enhance the tumorigenicity of MDA-MB-231 breast cancer cells through a ganglioside-dependent activation of the c-Met receptor.

Tumour-associated carbohydrate antigens in breast cancer

Glycosylation changes that occur in cancer often lead to the expression of tumour-associated carbohydrate antigens. In breast cancer, these antigens are usually associated with a poor prognosis and a reduced overall survival. Cellular models have shown the implication of these antigens in cell adhesion, migration, proliferation and tumour growth. The present review summarizes our current knowledge of glycosylation changes (structures, biosynthesis and occurrence) in breast cancer cell lines and primary tumours, and the consequences on disease progression and aggressiveness. The therapeutic strategies attempted to target tumour-associated carbohydrate antigens in breast cancer are also discussed.

Ganglioside synthase knockout in oncogene-transformed fibroblasts depletes gangliosides and impairs tumor growth

Biologically active membrane gangliosides, expressed and released by many human tumors, are hypothesized to significantly impact tumor progression. Lack of a model of complete and specific tumor ganglioside depletion in vivo, however, has hampered elucidation of their role. Here we report the creation of a novel, stable, genetically induced tumor cell system resulting in specific and complete blockade of ganglioside synthesis. Wild type (WT) and GM3 synthase/GM2 synthase double knockout (DKO) murine embryonic fibroblasts were transformed using amphotropic retrovirus-transduced oncogenes (pBABE-c-Myc^T58A+H-Ras^G12V). The transformed cells, WT_t and DKO_t respectively, evidenced comparable integrated copy numbers and oncogene expression. Ganglioside synthesis was completely blocked in the DKO_t cells, importantly without triggering an alternate pathway of ganglioside synthesis. Ganglioside depletion (to <0.5 nmol/10⁷ cells from 9-11 nmol/10⁷ WT_t or untransfected normal fibroblasts) did not adversely affect cell proliferation kinetics but did reduce cell migration on fibronectin-coated wells, consistent with our previous observations in ganglioside-depleted normal human fibroblasts. Strikingly, despite similar oncogene expression and growth kinetics, DKO_t cells evidenced significantly impaired tumor growth in syngeneic immunocompetent mice, underscoring the pivotal role of tumor cell gangliosides and providing an ideal system for probing their mechanisms of action in vivo.

Consequences of the expression of sialylated antigens in breast cancer

Changes in cell surface glycosylation are common modifications that occur during oncogenesis, leading to the over-expression of tumour-associated carbohydrate antigens (TACA). Most of these antigens are sialylated and the increase of sialylation is a well-known feature of transformed cells. In breast cancer, expression of TACA such as sialyl-Lewis(x) or sialyl-Tn is usually associated with a poor prognosis and a decreased overall survival of patients. However, the specific role of these sialylated antigens in breast tumour development and aggressiveness is not clearly understood. These glycosylation changes result from the modification of the expression of genes encoding specific glycosyltransferases involved in glycan biosynthesis and the level of expression of sialyltransferase genes has been proposed to be a prognostic marker for the follow-up of breast cancer patients. Several human cellular models have been developed in order to explain the mechanisms by which carbohydrate antigens can reinforce breast cancer progression and aggressiveness. TACA expression is associated with changes in cell adhesion, migration, proliferation and tumour growth. In addition, recent data on glycolipid biosynthesis indicate an important role of G(D3) synthase expression in breast cancer progression. The aim of this review is to summarize our current knowledge of sialylation changes that occur in breast cancer and to describe the cellular models developed to analyze the consequences of these changes on disease progression and aggressiveness.