Aurélie Cazet

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.

Therapeutic targets in triple negative breast cancer

Outcomes have improved significantly for many women diagnosed with breast cancer. For the heterogeneous group of tumours lacking expression of the oestrogen, progesterone and HER2 receptors, ‘triple negative’ breast cancers (TNBC), the prognosis overall has remained quite poor. When TNBC recurs, there is often little response to chemotherapy, and there are a few treatment options in this setting. Thus, there is an urgent clinical need to identify new therapeutic targets in order to improve the outlook for these patients. This review highlights the most promising therapeutic targets identified through new sequencing technologies, as well as through studies of apoptosis. We also present mounting evidence that the developmental signalling pathways Wnt/β-catenin, NOTCH and Hedgehog play an important role in the pathogenesis and progression of TNBC with new therapeutic approaches inhibiting these pathways in advanced preclinical studies or early clinical trials.

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.

IL-6 and IL-8 increase the expression of glycosyltransferases and sulfotransferases involved in the biosynthesis of sialylated and/or sulfated Lewisx epitopes in the human bronchial mucosa

Bronchial mucins from patients suffering from CF (cystic fibrosis) exhibit glycosylation alterations, especially increased amounts of the sialyl-Lewis(x) (NeuAcalpha2-3Galbeta1-4[Fucalpha1-3]GlcNAc-R) and 6-sulfo-sialyl-Lewis(x) (NeuAcalpha2-3Galbeta1-4[Fucalpha1-3][SO(3)H-6]GlcNAc-R) terminal structures. These epitopes are preferential receptors for Pseudomonas aeruginosa, the bacteria responsible for the chronicity of airway infection and involved in the morbidity and early death of CF patients. However, these glycosylation changes cannot be directly linked to defects in CFTR (CF transmembrane conductance regulator) gene expression since cells that secrete airway mucins express no or very low amounts of the protein. Several studies have shown that inflammation may affect glycosylation and sulfation of various glycoproteins, including mucins. In the present study, we show that incubation of macroscopically healthy fragments of human bronchial mucosa with IL-6 (interleukin-6) or IL-8 results in a significant increase in the expression of alpha1,3/4-fucosyltransferases [FUT11 (fucosyltransferase 11 gene) and FUT3], alpha2-6- and alpha2,3-sialyltransferases [ST3GAL6 (alpha2,3-sialyltransferase 6 gene) and ST6GAL2 (alpha2,6-sialyltransferase 2 gene)] and GlcNAc-6-O-sulfotransferases [CHST4 (carbohydrate sulfotransferase 4 gene) and CHST6] mRNA. In parallel, the amounts of sialyl-Lewis(x) and 6-sulfo-sialyl-Lewis(x) epitopes at the periphery of high-molecular-mass proteins, including MUC4, were also increased. In conclusion, our results indicate that IL-6 and -8 may contribute to the increased levels of sialyl-Lewis(x) and 6-sulfo-sialyl-Lewis(x) epitopes on human airway mucins from patients with CF.

The Hedgehog signalling pathway in breast development, carcinogenesis and cancer therapy

Despite the progress achieved in breast cancer screening and therapeutic innovations, the basal-like subtype of breast cancer (BLBC) still represents a particular clinical challenge. In order to make an impact on survival in this type of aggressive breast cancer, new targeted therapeutic agents are urgently needed. Aberrant activation of the Hedgehog (Hh) signalling pathway has been unambiguously tied to cancer development and progression in a variety of solid malignancies, and the recent approval of vismodegib, an orally bioavailable small-molecule inhibitor of Smoothened, validates Hh signalling as a valuable therapeutic target. A number of recent publications have highlighted a role for Hh signalling in breast cancer models and clinical specimens. Interestingly, Hh ligand overexpression is associated with the BLBC phenotype and a poor outcome in terms of metastasis and breast cancer-related death. In this review, we provide a comprehensive overview of the canonical Hh signalling pathway in mammals, highlight its roles in mammary gland development and breast carcinogenesis and discuss its potential therapeutic value in BLBC.

G D3 Synthase Expression Enhances Proliferation and Tumor Growth of MDA-MB-231 Breast Cancer Cells through c-Met Activation

The disialoganglioside GD3 is overexpressed in ∼50% of invasive ductal breast carcinoma, and the GD3 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 GD3 synthase induces the accumulation of b- and c-series gangliosides (GD3, GD2, and GT3) 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 GD3 synthase–expressing cells. Analysis of phosphorylation of tyrosine kinase receptors shows a specific c-Met constitutive activation in GD3 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 GD3 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 GD3 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. Mol Cancer Res; 8(11); 1526–35. ©2010 AACR.

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

Abstract The disialoganglioside GD3 is an oncofetal marker of a variety of human tumors including melanoma and neuroblastoma, playing a key role in tumor progression. GD3 and 9-O-acetyl-GD3 are overexpressed in approximately 50% of invasive ductal breast carcinoma, but no relationship has been established between disialoganglioside expression and breast cancer progression. In order to determine the effect of GD3 expression on breast cancer development, we analyzed the biosynthesis of gangliosides in several breast epithelial cell lines including MDA-MB-231, MCF-7, BT-20, T47-D, and MCF10A, by immunocytochemistry, flow cytometry, and real-time PCR. Our results show that, in comparison to tumors, cultured breast cancer cells express a limited pattern of gangliosides. Disialogangliosides were not detected in any cell line and GM3 was only observed at the cell surface of MDA-MB-231 cells. To evaluate the influence of GD3 in breast cancer cell behavior, we established and characterized MDA-MB-231 cells overexpressing GD3 synthase. We show that GD3 synthase expressing cells accumulate GD3, GD2, and GT3 at the cell surface. Moreover, GD3 synthase overexpression bypasses the need of serum for cell growth and increases cell migration. This suggests that GD3 synthase overexpression may contribute to increasing the malignant properties of breast cancer cells.

The ganglioside GD2 induces the constitutive activation of c-Met in MDA-MB-231 breast cancer cells expressing the GD3 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.

Glycosyltransferase and sulfotransferase gene expression profiles in human monocytes, dendritic cells and macrophages.

Using a focused glycan-gene microarray, we compared the glycosyltransferase (GT) and sulfotransferase gene expression profiles of human monocytes, dendritic cells (DCs) and macrophages (Mϕs), isolated or differentiated from the same donors. Microarray analysis indicated that monocytes express transcripts for a full set of enzymes involved in the biosynthesis of multi-multiantennary branched N-glycans, potentially elongated by poly-N-acetyl-lactosamine chains, and of mucin-type Core 1 and Core 2 sialylated O-glycans. Monocytes also express genes involved in the biosynthesis and modification of glycosaminoglycans, but display a limited expression of GTs implicated in glycolipid synthesis. Among genes expressed in monocytes (90 out of 175), one third is significantly modulated in DCs and Mϕ respectively, most of them being increased in both cell types relative to monocytes. These changes might potentially enforce the capacity of differentiated cells to synthesize branched N-glycans and mucin-type O-glycans and to remodel cell surface proteoglycans. Stimulation of DCs and Mϕs with lipopolysaccharide caused a general decrease in gene expression, mainly affecting genes found to be positively modulated during the differentiation steps. Interestingly, although a similar set of enzymes are modulated in the same direction in mature DCs and Mϕs, cell specific genes are also differentially regulated during maturation, a phenomenon that may sustain functional specificities. Validation of this analysis was provided by quantitative real-time PCR and flow cytometry of cell surface glycan antigens. Collectively, this study implies an important modification of the pattern of glycosylation in DCs and Mϕs undergoing differentiation and maturation with potential biological consequences.

ID4 controls mammary stem cells and marks breast cancers with a stem cell-like phenotype

Basal-like breast cancer (BLBC) is a heterogeneous disease with poor prognosis; however, its cellular origins and aetiology are poorly understood. In this study, we show that inhibitor of differentiation 4 (ID4) is a key regulator of mammary stem cell self-renewal and marks a subset of BLBC with a putative mammary basal cell of origin. Using an ID4GFP knock-in reporter mouse and single-cell transcriptomics, we show that ID4 marks a stem cell-enriched subset of the mammary basal cell population. ID4 maintains the mammary stem cell pool by suppressing key factors required for luminal differentiation. Furthermore, ID4 is specifically expressed by a subset of human BLBC that possess a very poor prognosis and a transcriptional signature similar to a mammary stem cell. These studies identify ID4 as a mammary stem cell regulator, deconvolute the heterogeneity of BLBC and link a subset of mammary stem cells to the aetiology of BLBC.