B4GALNT2 Controls Sda and SLex Antigen Biosynthesis in Healthy and Cancer Human Colon

Carbohydrate-active enzymes from Akkermansia muciniphila break down mucin O-glycans to completion

Akkermansia muciniphila is a human microbial symbiont residing in the mucosal layer of the large intestine. Its main carbon source is the highly heterogeneous mucin glycoprotein, and it uses an array of carbohydrate-active enzymes and sulfatases to access this complex energy source. Here we describe the biochemical characterization of 54 glycoside hydrolases, 11 sulfatases and 1 polysaccharide lyase from A. muciniphila to provide a holistic understanding of their carbohydrate-degrading activities. This was achieved using a variety of liquid chromatography techniques, mass spectrometry, enzyme kinetics and thin-layer chromatography. These results are supported with A. muciniphila growth and whole-cell assays. We find that these enzymes can act synergistically to degrade the O-glycans on the mucin polypeptide to completion, down to the core N-acetylgalactosaime. In addition, these enzymes can break down human breast milk oligosaccharide, ganglioside and globoside glycan structures, showing their capacity to target a variety of host glycans. These data provide a resource to understand the full degradative capability of the gut microbiome member A. muciniphila.

Transcription factor FOXD1 and miRNA-204-5p play a major role in B4GALNT2 downregulation in colon cancer

The β1,4-N-acetylgalactosaminyltransferase 2 (B4GALNT2) which synthesizes the histo-blood group antigen Sda is highly expressed by normal colon, but it is dramatically down-regulated in colorectal cancer (CRC). High B4GALNT2 expression in CRC tissues is a marker of longer survival. The molecular bases of B4GALNT2 inhibition in CRC are largely obscure. A key role may be played by transcription factors and miRNA. Through an in silico analysis of The Cancer Genome Atlas and of the Cancer Cell Line Encyclopedia, we identified the transcription factors FOXD1, FOXF2 and PGR as well as mir-204-5p as potential inhibitory agents. Their transient transfection in the cell line GP2d, whose B4GALNT2 is closer to that of a normal mucosa, confirmed their inhibitory activity with a crucial role for FOXD1. The latter inhibited B4GALNT2 also in the middle B4GALNT2 expresser cell line Caco2. Deletion experiments of the putative FOXD1 binding sites in the ~ 2800 bp sequence upstream of the B4GALNT2 transcriptional start site cloned in frame with the luciferase reporter gene, confirmed the regulatory role of FOXD1. Finally, FOXD1 knock down in the non-B4GALNT2 expresser cell line SW948 stimulated B4GALNT2. Thus, FOXD1 and miR-204-5p emerged as crucial new player of B4GALNT2 down-regulation in CRC.

Non-targeted N-glycome profiling reveals multiple layers of organ-specific diversity in mice

N-glycosylation is one of the most common protein modifications in eukaryotes, with immense importance at the molecular, cellular, and organismal level. Accurate and reliable N-glycan analysis is essential to obtain a systems-wide understanding of fundamental biological processes. Due to the structural complexity of glycans, their analysis is still highly challenging. Here we make publicly available a consistent N-glycome dataset of 20 different mouse tissues and demonstrate a multimodal data analysis workflow that allows for unprecedented depth and coverage of N-glycome features. This highly scalable, LC-MS/MS data-driven method integrates the automated identification of N-glycan spectra, the application of non-targeted N-glycome profiling strategies and the isomer-sensitive analysis of glycan structures. Our delineation of critical sub-structural determinants and glycan isomers across the mouse N-glycome uncovered tissue-specific glycosylation patterns, the expression of non-canonical N-glycan structures and highlights multiple layers of N-glycome complexity that derive from organ-specific regulations of glycobiological pathways.

(Sialyl)Lewis Antigen Expression on Glycosphingolipids, N-, and O-Glycans in Colorectal Cancer Cell Lines is Linked to a Colon-Like Differentiation Program

Alterations in the glycomic profile are a hallmark of cancer, including colorectal cancer (CRC). While, the glycosylation of glycoproteins and glycolipids has been widely studied for CRC cell lines and tissues, a comprehensive overview of CRC glycomics is still lacking due to the usage of different samples and analytical methods. In this study, we compared glycosylation features of N-, O-glycans, and glycosphingolipid glycans for a set of 22 CRC cell lines, all measured by porous graphitized carbon nano-liquid chromatography-tandem mass spectrometry. An overall, high abundance of (sialyl)Lewis antigens for colon-like cell lines was found, while undifferentiated cell lines showed high expression of H blood group antigens and α2-3/6 sialylation. Moreover, significant associations of glycosylation features were found between the three classes of glycans, such as (sialyl)Lewis and H blood group antigens. Integration of the datasets with transcriptomics data revealed positive correlations between (sialyl)Lewis antigens, the corresponding glycosyltransferase FUT3 and transcription factors CDX1, ETS, HNF1/4A, MECOM, and MYB. This indicates a possible role of these transcription factors in the upregulation of (sialyl)Lewis antigens, particularly on glycosphingolipid glycans, via FUT3/4 expression in colon-like cell lines. In conclusion, our study provides insights into the possible regulation of glycans in CRC and can serve as a guide for the development of diagnostic and therapeutic biomarkers.

An Identification of Functional Genetic Variants in B4GALNT2 Gene and Their Association with Growth Traits in Goats

β-1,4-N-acetylgalactosamine transferase 2 (B4GALNT2) is a vital candidate gene that affects the growth traits in sheep. However, whether it has the same function in goats remains to be investigated further. This study selected 348 Nanjiang Yellow goats, screened all exons, and conserved non-coding regions of the B4GALNT2 gene for single-nucleotide polymorphisms (SNPs). Our results revealed the presence of a synonymous mutation, rs672215506, within the exon of the B4GALNT2 gene in the Nanjiang Yellow goat population. The mutation resulted in a decrease in the mRNA stability of the B4GALNT2 gene. The results of SNP detection of the conserved non-coding region of the B4GALNT2 gene showed five potential regulatory SNPs in the Nanjiang Yellow goat population. Except for rs66095343, the ~500 bp fragments of the other four SNPs (rs649127714, rs649573228, rs652899012, and rs639183528) significantly increased the luciferase activity both in goat skeletal muscle satellite cells (MuSCs) and 293T cells. The genetic diversity indexes indicated low or intermediate levels for all six SNPs analyzed, and the genotype frequencies were in Hardy-Weinberg equilibrium. Association analysis showed that rs660965343, rs649127714, and rs649573228 significantly correlate with growth traits in the later stage of growth and development of Nanjiang Yellow goats. The haplotype combinations of H2H3 and H2H2 had higher body weight and greater body size. Moreover, H2H2 haplotype combinations significantly correlated with the litter size of the Nanjiang Yellow goats. The results of our study demonstrate the potential role of the B4GALNT2 gene as a functional genetic marker in the breeding programs of Nanjiang Yellow goats.

N-Glycan on the Non-Consensus N-X-C Glycosylation Site Impacts Activity, Stability, and Localization of the Sda Synthase B4GALNT2

The Sd^a carbohydrate epitope and its biosynthetic B4GALNT2 enzyme are expressed in the healthy colon and down-regulated to variable extents in colon cancer. The human B4GALNT2 gene drives the expression of a long and a short protein isoform (LF-B4GALNT2 and SF-B4GALNT2) sharing identical transmembrane and luminal domains. Both isoforms are trans-Golgi proteins and the LF-B4GALNT2 also localizes to post-Golgi vesicles thanks to its extended cytoplasmic tail. Control mechanisms underpinning Sd^a and B4GALNT2 expression in the gastrointestinal tract are complex and not fully understood. This study reveals the existence of two unusual N-glycosylation sites in B4GALNT2 luminal domain. The first atypical N-X-C site is evolutionarily conserved and occupied by a complex-type N-glycan. We explored the influence of this N-glycan using site-directed mutagenesis and showed that each mutant had a slightly decreased expression level, impaired stability, and reduced enzyme activity. Furthermore, we observed that the mutant SF-B4GALNT2 was partially mislocalized in the endoplasmic reticulum, whereas the mutant LF-B4GALNT2 was still localized in the Golgi and post-Golgi vesicles. Lastly, we showed that the formation of homodimers was drastically impaired in the two mutated isoforms. An AlphaFold2 model of the LF-B4GALNT2 dimer with an N-glycan on each monomer corroborated these findings and suggested that N-glycosylation of each B4GALNT2 isoform controlled their biological activity.

The story of the Sda antigen and of its cognate enzyme B4GALNT2: What is new?

The structure Siaα2,3(GalNAcβ1,4)Gal- is the epitope of the Sda antigen, which is expressed on the erythrocytes and secretions of the vast majority of Caucasians, carried by N- and O-linked chains of glycoproteins, as well as by glycolipids. Sda is very similar, but not identical, to ganglioside GM2 [Siaα2,3(GalNAcβ1,4)Galβ1,4Glc-Cer]. The Sda synthase β1,4 N-acetylgalactosaminyl transferase 2 (B4GALNT2) exists in a short and a long form, diverging in the aminoterminal domain. The latter has a very long cytoplasmic tail and displays a Golgi- as well as a post-Golgi localization. The biosynthesis of Sda is mutually exclusive with that of the cancer-associated sialyl Lewis antigens, whose structure is Siaα2,3Galβ1,3/4(Fucα1,4/3)GlcNAc-. B4GALNT2 is down-regulated in colon cancer but patients with higher expression survive longer. In experimental systems, B4GALNT2 inhibits colon cancer progression,not only through inhibition of sialyl Lewis antigen biosynthesis. By contrast, in breast cancer B4GALNT2 is associated with malignancy. In colon cancer, the B4GALNT2 gene is regulated by multiple mechanisms, which include miRNA and transcription factor expression, as well as CpG methylation. In addition, Sda/B4GALNT2 regulates the susceptibility to infectious agents, the protection from muscle dystrophy, the activity of immune system in pregnancy and the immune rejection in xenotransplantation.

ABO blood group antigens and differential glycan expression: Perspective on the evolution of common human enzyme deficiencies

Enzymes catalyze biochemical reactions and play critical roles in human health and disease. Enzyme variants and deficiencies can lead to variable expression of glycans, which can affect physiology, influence predilection for disease, and/or directly contribute to disease pathogenesis. Although certain well-characterized enzyme deficiencies result in overt disease, some of the most common enzyme deficiencies in humans form the basis of blood groups. These carbohydrate blood groups impact fundamental areas of clinical medicine, including the risk of infection and severity of infectious disease, bleeding risk, transfusion medicine, and tissue/organ transplantation. In this review, we examine the enzymes responsible for carbohydrate-based blood group antigen biosynthesis and their expression within the human population. We also consider the evolutionary selective pressures, e.g. malaria, that may account for the variation in carbohydrate structures and the implications of this biology for human disease.

CAR-Ts: new perspectives in cancer therapy

Chimeric antigen receptor (CAR)-T-cell therapy is a promising anticancer treatment that exploits the host's immune system to fight cancer. CAR-T cell therapy relies on immune cells being modified to express an artificial receptor targeting cancer-specific markers, and infused into the patients where they will recognize and eliminate the tumour. Although CAR-T cell therapy has produced encouraging outcomes in patients with haematologic malignancies, solid tumours remain challenging to treat, mainly due to the lack of cancer-specific molecular targets and the hostile, often immunosuppressive, tumour microenvironment. CAR-T cell therapy also depends on the quality of the injected product, which is closely connected to CAR design. Here, we explain the technology of CAR-Ts, focusing on the composition of CARs, their application, and limitations in cancer therapy, as well as on the current strategies to overcome the challenges encountered. We also address potential future targets to overcome the flaws of CAR-T cell technology in the treatment of cancer, emphasizing glycan antigens, the aberrant forms of which attain high tumour-specific expression, as promising targets for CAR-T cell therapy.