Cell surfaces are coated with a variety of intricately arranged glycoconjugates such as glycoproteins, glycolipids and proteoglycans. Therefore, elucidating the expression profiles of glycans derived from various classes of glycoconjugates is important to understand cellular glycosylation homeostasis and systems biology glycomics. We have established a series of methodologies for the analysis of N-and O-glycans derived from glycoproteins, glycosphingolipid glycans, glycosaminoglycans, and free oligosaccharides using mass spectrometry and liquid chromatography. Procedures to analyze each class of glycan were then combined to visualize the entire complement of sugars in the cellular glycome, so-called total cellular glycomics. When this technique was applied to various human cells including embryonic stem cells, induced pluripotent stem cells and various cells derived from normal and carcinoma cells, total cellular glycomes were found to be highly cell type-specific, demonstrating their utility as unique cellular descriptors. Total cellular glycomics can streamline the discovery of cellular biomarkers as demonstrated by the identification of known pluripotency biomarkers as well as novel candidate biomarkers.
The O-glycan branching enzyme, core2 β-1,6-N-acetylglucosaminyltransferase (C2GnT) forms O-glycans containing a branch of β-1,6-linkage of N-acetylglucosamine and N-acetylgalctosamine (core2 O-glycans) on cell-surface glycoproteins. It was reported that expression of C2GnT, a key enzyme for core2 O-glycans expression, was closely correlated with high-metastatic phenotypes of numbers of cancers. Recently, it has been revealed that C2GnT-expressing cancer cells synthesize core2 O-glycans which have immunosuppressive functions against natural killer (NK) cell immunity by using their cell-surface core2 O-glycans, resulting in acquiring high-metastatic phenotypes. C2GnT-expressing cancer cells have two different types of immunosuppressive functions against NK cell immunity, molecular shield and tumor-ligand masking. Here, we highlight recent advances in our understanding of the detailed molecular mechanisms of those immunosuppressive functions of core2 O-glycans.