Enhanced expression of unique gangliosides with GM2-determinant in human uterine cervical carcinoma-derived cell lines

Pathophysiological roles and applications of glycosphingolipids in the diagnosis and treatment of cancer diseases

Glycosphingolipids (GSLs) are major amphiphilic glycolipids present on the surface of living cell membranes. They have important biological functions, including maintaining plasma membrane stability, regulating signal transduction, and mediating cell recognition and adhesion. Specific GSLs and related enzymes are abnormally expressed in many cancer diseases and affect the malignant characteristics of tumors. The regulatory roles of GSLs in signaling pathways suggest that they are involved in tumor pathogenesis. GSLs have therefore been widely studied as diagnostic markers of cancer diseases and important targets of immunotherapy. This review describes the tumor-related biological functions of GSLs and systematically introduces recent progress in using diverse GSLs and related enzymes to diagnose and treat tumor diseases. Development of drugs and biomarkers for personalized cancer therapy based on GSL structure is also discussed. These advances, combined with recent progress in the preparation of GSLs derivatives through synthetic biology technologies, suggest a strong future for the use of customized GSL libraries in treating human diseases.

Reduced expression of gangliosides with GM2-determinant in cervical carcinoma-derived cells after subcutaneous transplantation into nude mice

Human cervical carcinoma-derived cell lines have been frequently found to contain gangliosides with GM2-determinant, i.e., GM2, GalNAc-GM1b and GalNAc-GD1a, but GM2 was only detected in 5 of 15 tissues, and GalNAc-GM1b and GalNAc-GD1a were not found in any tissues from patients with several histological types of cervical carcinomas. To further characterize the ganglioside expression in cervical carcinomas, cells were grown by subcutaneous transplantation into nude mice, and gangliosides were quantitated by TLC-immunostaining with the anti-GM2 (YHD-06) antibody and a newly developed anti-GM3 (5H6) antibody, which reacts with GM3 and GM1b, but not with GD1a. Gangliosides with GM2-determinant in cells disappeared in transplanted cells, and the amount of GM3, a precursor for GM2, in transplanted cells was greater than in cultured cells. Also, transplanted cells containing GalNAc-GM1b newly expressed GM1b, suggesting that the activity of GalNAc transferase for synthesis of GalNAc-GM1b is retarded on subcutaneous transplantation. The ganglioside composition, with GM3 as the major one, in the transplanted cells was similar to that in cervical carcinoma tissues, and thus, the expression of gangliosides with GM2-determinant seemed to be accelerated under cell-cultivation conditions.

Novel Thieno [2,3-b]pyridine Anticancer Compound Lowers Cancer Stem Cell Fraction Inducing Shift of Lipid to Glucose Metabolism

Due to the role of cancer stem cells (CSCs) in tumor resistance and glycosphingolipid (GSL) involvement in tumor pathogenesis, we investigated the effect of a newly synthesized compound (3-amino-N-(3-chloro-2-methylphenyl)-5-oxo-5,6,7,8-tetrahydrothieno[2,3-b]quinoline-2-carboxamide 1 on the percentage of CSCs and the expression of six GSLs on CSCs and non-CSCs on breast cancer cell lines (MDA-MB-231 and MCF-7). We also investigated the effect of 1 on the metabolic profile of these cell lines. The MTT assay was used for cytotoxicity determination. Apoptosis and expression of GSLs were assessed by flow cytometry. A GC–MS-coupled system was used for the separation and identification of metabolites. Compound 1 was cytotoxic for both cell lines, and the majority of cells died by treatment-induced apoptosis. The percentage of CSCs was significantly lower in the MDA-MB-231 cell line. Treatment with 1 caused a decrease of CSC IV⁶Neu₅Ac-nLc₄Cer+ MDA-MB-231 cells. In the MCF-7 cell line, the percentage of GalNAc-GM1b+ CSCs was increased, while the expression of Gg₃Cer was decreased in both CSC and non-CSC. Twenty-one metabolites were identified by metabolic profiling. The major impact of the treatment was in glycolysis/gluconeogenesis, pyruvate and inositol metabolism. Compound 1 exhibited higher potency in MBA-MB-231 cells, and it deserves further examination.

Gangliosides and CD82 inhibit the motility of colon cancer by downregulating the phosphorylation of EGFR at different tyrosine sites and signaling pathways

Previous studies have shown that (GM3), a ganglioside, suppresses hepatoma cell motility and migration by inhibiting phosphorylation of EGFR and the activity of the PI3K/AKT signaling pathway. Therefore, the aim of the present study was to investigate whether the combined treatment of CD82 with gangliosides can exert a synergistic inhibitory effect on cell motility and migration. Epidermal growth factor receptor (EGFR) signaling was studied for its role in the mechanism through which CD82 and gangliosides synergistically inhibit the motility and migration of SW620 human colon adenocarcinoma cells. GM3 and/or GM2 treatment, and/or overexpression of CD82 was performed in SW620 cells. High-performance thin layer chromatography, reverse transcription-quantitative PCR, western blotting and flow cytometry assays were used to confirm the content changes of GM2, GM3 and CD82. In addition, the phosphorylation of EGFR, MAPK and Akt were evaluated by western blot analysis. SW620 cell motility was investigated using wound healing analysis and chemotaxis migration assay. The combination of GM3 and GM2 with CD82 was found to markedly suppress EGF-stimulated SW620 cell motility compared with the individual factors or combination of GM2 or GM3 with CD82 by inhibiting the phosphorylation of EGFR. The results suggested that CD82 in combination with either GM2 or GM3 can exert a synergistic inhibitory effect on cell motility and migration; however, the synergistic mechanisms elicited by GM2 or GM3 with CD82 differ.

Characterization of a novel glycolipid with a difucosylated H-antigen in human blood group O erythrocytes with monoclonal antibody HMMC-1 and its detection in human uterine cervical carcinoma tissues

Humanized monoclonal antibody HMMC-1 established by immunizing transchromosomal mice with a human uterine endometrial cancer cell line has been found to react with the H-antigen carried on core l O-glycans through cotransfection of glycosyltransferases for O-glycans and inhibition of antibody-binding with synthetic oligosaccharides. However, direct binding analysis of an antibody against glycosphingolipids from human erythrocytes with different ABO blood groups revealed that it was able to bind selectively with polar glycolipids in blood group O, but not blood group A, B and AB erythrocytes. Unexpectedly, typical monofucosylated H-glycolipids, IV²Fucα-nLc₄Cer and VI²Fucα-nLc₆Cer, which are the precursors for A and B-glycolipids, and were present not only in blood group O, but also A, B and AB-erythrocytes, were not the antigens for the HMMC-1 antibody. The antigen comprised less than 0.001% of the total glycolipids in blood group O-erythrocytes, and was purified by conventional silica gel column chromatography. Structural determination by permethylation, GC-MS, and ESI-TOFMS demonstrated that the structure was a novel glycolipid with a difucosylated H-antigen, Fucα1-2Galβ1-4GlcNAcβ1-3Gal(2-1αFuc)β1-4GlcNAcβ1-3Galβ1-4GlcNAcβ1-3Galβ1-4Glcβ1-1'Cer, VI²,VIII²(Fucα)₂-nLc₈Cer, whose terminal difucosylated structure was the epitope of the HMMC-1 antibody. The HMMC-1 glycolipid was detected in five out of 29 tissues from patients suffering from uterine cervical carcinomas, irrespective of their ABO-blood groups.

Gangliosides and Tumors

Tumor-associated gangliosides play important roles in regulation of signal transduction induced by growth-factor receptors including EGFR, FGFR, HGF and PDGFR in a specific microdomain called glycosynapse in the cancer cell membranes, and in interaction with glycan recognition molecules involved in cell adhesion and immune regulation including selectins and siglecs. As the genes involved in the synthesis and degradation of tumor-associated gangliosides were identified, biological functions became clearer from the experimental results employing forced overexpression and/or knockdown/knockout of the genes. Studies on the regulatory mechanisms for their expression also achieved great advancements. Epigenetic silencing of glycan-related genes is a dominant mechanism in glycan alteration at early stages of carcinogenesis. Development of hypoxia resistance involving activation of a transcription factor HIF, and acquisition of cancer stem cell-like characteristics through epithelial-mesenchymal transition are important mechanisms for glycan modulations in the later stages of cancer progression. In the initial stages of studies, the gangliosides which specifically appear in cancers attracted attention under the name of tumor-associated gangliosides. However, it became apparent that not only the cancer-associated gangliosides but also the normal gangliosides present in nonmalignant cells and tissues perform important biological functions, and some of them tend to disappear in cancer cells resulting in the loss of the physiological functions, and this sometimes facilitates progression of cancers.

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.

Glycolipids and Lectins in Endocytic Uptake Processes

A host of endocytic processes has been described at the plasma membrane of eukaryotic cells. Their categorization has most commonly referenced cytosolic machinery, of which the clathrin coat has occupied a preponderant position. In what concerns intra-membrane constituents, the focus of interest has been on phosphatidylinositol lipids and their capacity to orchestrate endocytic events on the cytosolic leaflet of the membrane. The contribution of extracellular determinants to the construction of endocytic pits has received much less attention, depite the fact that (glyco)sphingolipids are exoplasmic leaflet fabric of membrane domains, termed rafts, whose contributions to predominantly clathrin-independent internalization processes is well recognized. Furthermore, sugar modifications on extracellular domains of proteins, and sugar-binding proteins, termed lectins, have also been linked to the uptake of endocytic cargoes at the plasma membrane. In this review, we first summarize these contributions by extracellular determinants to the endocytic process. We thus propose a molecular hypothesis - termed the GL-Lect hypothesis - on how GlycoLipids and Lectins drive the formation of compositional nanoenvrionments from which the endocytic uptake of glycosylated cargo proteins is operated via clathrin-independent carriers. Finally, we position this hypothesis within the global context of endocytic pathway proposals that have emerged in recent years.