Characterization of tumor-associated MUC1 and its glycans expressed in mucoepidermoid carcinoma

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2021-2022

The use of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry for the analysis of carbohydrates and glycoconjugates is a well-established technique and this review is the 12th update of the original article published in 1999 and brings coverage of the literature to the end of 2022. As with previous review, this review also includes a few papers that describe methods appropriate to analysis by MALDI, such as sample preparation, even though the ionization method is not MALDI. The review follows the same format as previous reviews. It is divided into three sections: (1) general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, quantification and the use of computer software for structural identification. (2) Applications to various structural types such as oligo- and polysaccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals, and (3) other general areas such as medicine, industrial processes, natural products and glycan synthesis where MALDI is extensively used. Much of the material relating to applications is presented in tabular form. MALDI is still an ideal technique for carbohydrate analysis, particularly in its ability to produce single ions from each analyte and advancements in the technique and range of applications show little sign of diminishing.

Preparation of Soluble Mucin Solutions from the Salivary Glands

Studying salivary gland mucins is important for elucidating the pathogenesis of salivary gland diseases, including tumors and xerostomia, and developing diagnostic methods for them. Classic methods for isolating mucins from salivary glands require sacrificing several animals to obtain sufficient quantities of mucin and are time-consuming. Supported molecular matrix electrophoresis (SMME) was used to characterize mucins and their glycans. With this method, mucins can be analyzed within 2 days using less than 100 mg of tissue and without using expensive equipment, such as an ultracentrifuge. This chapter describes a method for preparing mucin solutions for SMME analysis of salivary gland mucins.

Sialylation shapes mucus architecture inhibiting bacterial invasion in the colon

In the intestine, mucin 2 (Muc2) forms a network structure and prevents bacterial invasion. Glycans are indispensable for Muc2 barrier function. Among various glycosylation patterns of Muc2, sialylation inhibits bacteria-dependent Muc2 degradation. However, the mechanisms by which Muc2 creates the network structure and sialylation prevents mucin degradation remain unknown. Here, by focusing on two glycosyltransferases, St6 N-acetylgalactosaminide α-2,6-sialyltransferase 6 (St6galnac6) and β-1,3-galactosyltransferase 5 (B3galt5), mediating the generation of desialylated glycans, we show that sialylation forms the network structure of Muc2 by providing negative charge and hydrophilicity. The colonic mucus of mice lacking St6galnac6 and B3galt5 was less sialylated, thinner, and more permeable to microbiota, resulting in high susceptibility to intestinal inflammation. Mice with a B3galt5 mutation associated with inflammatory bowel disease (IBD) also showed the loss of desialylated glycans of mucus and the high susceptibility to intestinal inflammation, suggesting that the reduced sialylation of Muc2 is associated with the pathogenesis of IBD. In mucins of mice with reduced sialylation, negative charge was reduced, the network structure was disturbed, and many bacteria invaded. Thus, sialylation mediates the negative charging of Muc2 and facilitates the formation of the mucin network structure, thereby inhibiting bacterial invasion in the colon to maintain gut homeostasis.

Expression and localisation of MUC1 modified with sialylated core-2 O-glycans in mucoepidermoid carcinoma

Mucoepidermoid carcinoma (MEC) is the most frequent of the rare salivary gland malignancies. We previously reported high expression of Mucin 1 (MUC1) modified with sialylated core-2 O-glycans in MEC by using tissue homogenates. In this study, we characterised glycan structures of MEC and identified the localisation of cells expressing these distinctive glycans on MUC1. Mucins were extracted from the frozen tissues of three patients with MEC, and normal salivary glands (NSGs) extracted from seven patients, separated by supported molecular matrix electrophoresis (SMME) and the membranes stained with various lectins. In addition, formalin-fixed, paraffin-embedded sections from three patients with MEC were subjected to immunohistochemistry (IHC) with various monoclonal antibodies and analysed for C2GnT-1 expression by in situ hybridisation (ISH). Lectin blotting of the SMME membranes revealed that glycans on MUC1 from MEC samples contained α2,3-linked sialic acid. In IHC, MUC1 was diffusely detected at MEC-affected regions but was specifically detected at apical membranes in NSGs. ISH showed that C2GnT-1 was expressed at the MUC1-positive in MEC-affected regions but not in the NSG. MEC cells produced MUC1 modified with α2,3-linked sialic acid-containing core-2 O-glycans. MUC1 containing these glycans deserves further study as a new potential diagnostic marker of MEC.