Recent studies using gene-targeted mice have revealed various physiological functions of sulfated glycans. Studies using gene-targeted mice deficient in two sulfotransferases, N-acetylglucosamine-6-O-sulfotransferase (GlcNAc6ST)-1 and GlcNAc6ST-2, showed that these sulfotransferases catalyze sulfation of mucin-like glycoproteins expressed on high endothelial venules (HEVs) in lymph nodes, and play critical roles in lymphocyte homing and immune surveillance. More recent studies using GlcNAc6ST-2-deficeint mice revealed that GlcNAc6ST-2 is expressed not only in lymph node HEVs but also in the colonic epithelial cells in mice, and has protective function in experimental colitis in mice by catalyzing sulfation of the colonic mucins. In this review, the two distinct functions of sulfation of mucins or mucin-like glycoproteins by sulfotransferases in lymph nodes and colon will be discussed.
Mucins are high molecular weight proteins that are highly O-glycosylated. Tumor-produced mucins are detected in tumor tissues and/or the bloodstream of cancer patients, and thus have been used as tumor markers. It has been reported that patients with higher amounts of mucins in their bloodstreams exhibit a lower 5-year survival rate, suggesting that mucins have some biological effect in cancer patients. Since mucins have a variety of sugar chains, it is possible that mucins in the bloodstream interact with some lectins on endothelial cells and/or immune cells. Recent reports suggested that tumor-produced mucins suppress immune function. Here we mainly describe the immunosuppressive effect on B cells through the ligation of mucins with Siglec-2.
The explosive progress of glycobiology in the past few decades has revealed that fucose is indispensable in various organisms and is involved in many biological events. Many researchers have spent a lot of time in order to unveil the mysterious functions of fucosylation. However, the findings which have ever been clarified are not sufficient to explain all fucosylation-related biological events. In the field of oncology, although several fucosylated molecules have been reported to be increased in cancer and have been used as cancer biomarkers, it remains unknown how dynamic changes of fucosylation are associated with cancer biology. Recently, we found that fucosylation is involved in NK cell-mediated tumor immune surveillance through regulation of the susceptibility to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), which is an apoptosis-inducing molecule. In this review, we describe the relationship between cancer biology and fucosylation, according to our recent findings.
Epidermal growth factor (EGF) domains are posttranslationally modified with unique O-linked glycans. The classical types of O-glycans on EGF domains are O-fucose and O-glucose glycans, found on many plasma glycoproteins and signaling molecules, whose biological functions have been demonstrated especially in the context of the Notch signaling pathway. We recently discovered O-GlcNAc modification as a new modification of the EGF domain that occurs on the conserved Ser/Thr residue located between the fifth and sixth cysteine residues within the EGF domains of Notch receptors in Drosophila. Isolation of the unidentified enzyme responsible for the extracellular O-GlcNAcylation and characterization of the O-GlcNAc transferase gene will reveal the new biological roles for O-GlcNAcylation in secreted and membrane glycoproteins and the extracellular environment.