OGT Controls the Expression and the Glycosylation of E-cadherin, and Affects Glycosphingolipid Structures in Human Colon Cell Lines

Colorectal cancer (CRC) affects both women and men living in societies with a high sedentary lifestyle. Amongst the phenotypic changes exhibited by tumor cells, a wide range of glycosylation has been reported for colon cancer-derived cell lines and CRC tissues. These aberrant modifications affect different aspects of glycosylation, including an increase in core fucosylation and GlcNAc branching on N-glycans, alteration of O-glycans, upregulated sialylation, and O-GlcNAcylation. Although O-GlcNAcylation and complex glycosylations differ in many aspects, sparse evidences report on the interference of O-GlcNAcylation with complex glycosylation. Nevertheless, this relationship is still a matter of debate. Combining different approaches on three human colon cell lines (HT29, HCT116 and CCD841CoN), it is herein reported that silencing O-GlcNAc transferase (OGT, the sole enzyme driving O-GlcNAcylation), only slightly affects overall N- and O-glycosylation patterns. Interestingly, silencing of OGT in HT29 cells upregulates E-cadherin (a major actor of epithelial-to-mesenchymal transition) and changes its glycosylation. On the other hand, OGT silencing perturbs biosynthesis of glycosphingolipids resulting in a decrease in gangliosides and an increase in globosides. Together, these results provide novel insights regarding the selective regulation of complex glycosylations by O-GlcNAcylation in colon cancer cells.

Separation-based glycoprofiling approaches using fluorescent labels

Glycoprotein analysis is essential within the biopharmaceutical industry, as the structure of the different glycans present can affect the safety and efficacy of products. However analysis of cleaved glycans presents a major analytical challenge, due to their inherent complexity, lack of chromophore and the existence of various isoforms (both position and linkage). In addition, almost all glycoproteins consist of a heterogeneous collection of differently glycosylated variants, so the released glycan pool contains a range of structures. Both normal phase chromatography and capillary gel electrophoresis offer excellent selectivity for the analysis of fluorescently labelled glycans. The normal phase (NP) chromatographic approach is sensitive, reliable and well established, with databases available for searching structures assigned relative to retention times. Capillary gel electrophoresis with laser induced fluorescence (CGE-LIF) offers faster analysis times, though currently no databases are available to search mobilities against structures, therefore data has to be cross-correlated with either normal phase chromatography or mass spectrometry approaches when developing and validating methods. The principles of both methods are described and a review is presented that includes evaluation against a set of criteria established through consultation with the biopharmaceutical industry.