Terminal glycosylation and disease: influence on cancer and cystic fibrosis

Targeting protein glycosylation to regulate inflammation in the respiratory tract: novel diagnostic and therapeutic candidates for chronic respiratory diseases

Protein glycosylation is a widespread posttranslational modification that can impact the function of proteins. Dysregulated protein glycosylation has been linked to several diseases, including chronic respiratory diseases (CRDs). CRDs pose a significant public health threat globally, affecting the airways and other lung structures. Emerging researches suggest that glycosylation plays a significant role in regulating inflammation associated with CRDs. This review offers an overview of the abnormal glycoenzyme activity and corresponding glycosylation changes involved in various CRDs, including chronic obstructive pulmonary disease, asthma, cystic fibrosis, idiopathic pulmonary fibrosis, pulmonary arterial hypertension, non-cystic fibrosis bronchiectasis, and lung cancer. Additionally, this review summarizes recent advances in glycomics and glycoproteomics-based protein glycosylation analysis of CRDs. The potential of glycoenzymes and glycoproteins for clinical use in the diagnosis and treatment of CRDs is also discussed.

Fucosyltransferase 2 induces lung epithelial fucosylation and exacerbates house dust mite-induced airway inflammation

BACKGROUND

One of the pathognomonic features of asthma is epithelial hyperproduction of mucus, which is composed of a series of glycoproteins; however, it remains unclear how glycosylation is induced in lung epithelial cells from asthmatic patients and how glycan residues play a role in the pathogenesis of asthma.

OBJECTIVE

The objective of this study was to explore comprehensive epithelial glycosylation status induced by allergic inflammation and reveal its possible role in the pathogenesis of asthma.

METHODS

We evaluated the glycosylation status of lung epithelium using a lectin microarray. We next searched for molecular mechanisms underlying epithelial glycosylation. We also examined whether epithelial glycosylation is involved in induction of allergic inflammation.

RESULTS

On allergen inhalation, lung epithelial cells were heavily α(1,2)fucosylated by fucosyltransferase 2 (Fut2), which was induced by the IL-13-signal transducer and activator of transcription 6 pathway. Importantly, Fut2-deficient (Fut2-/-) mice, which lacked lung epithelial fucosylation, showed significantly attenuated eosinophilic inflammation and airway hyperresponsiveness in house dust mite (HDM)-induced asthma models. Proteome analyses and immunostaining of the HDM-challenged lung identified that complement C3 was accumulated in fucosylated areas. Indeed, Fut2-/- mice showed significantly reduced levels of C3a and impaired accumulation of C3a receptor-expressing monocyte-derived dendritic cells in the lung on HDM challenge.

CONCLUSION

Fut2 induces epithelial fucosylation and exacerbates airway inflammation in asthmatic patients in part through C3a production and monocyte-derived dendritic cell accumulation in the lung.

Intact glycopeptide characterization using mass spectrometry

Glycosylation is one of the most prominent and extensively studied protein post-translational modifications. However, traditional proteomic studies at the peptide level (bottom-up) rarely characterize intact glycopeptides (glycosylated peptides without removing glycans), so no glycoprotein heterogeneity information is retained. Intact glycopeptide characterization, on the other hand, provides opportunities to simultaneously elucidate the glycan structure and the glycosylation site needed to reveal the actual biological function of protein glycosylation. Recently, significant improvements have been made in the characterization of intact glycopeptides, ranging from enrichment and separation, mass spectroscopy (MS) detection, to bioinformatics analysis. In this review, we recapitulated currently available intact glycopeptide characterization methods with respect to their advantages and limitations as well as their potential applications.

Brachyspira hyodysenteriae Infection Regulates Mucin Glycosylation Synthesis Inducing an Increased Expression of Core-2 O-Glycans in Porcine Colon

Brachyspira hyodysenteriae causes swine dysentery (SD), leading to global financial losses to the pig industry. Infection with this pathogen results in an increase in B. hyodysenteriae binding sites on mucins, along with increased colonic mucin secretion. We predict that B. hyodysenteriae modifies the glycosylation pattern of the porcine intestinal mucus layer to optimize its host niche. We characterized the swine colonic mucin O-glycome and identified the differences in glycosylation between B. hyodysenteriae-infected and noninfected pigs. O-Glycans were chemically released from soluble and insoluble mucins isolated from five infected and five healthy colon tissues and analyzed using porous graphitized carbon liquid chromatography tandem mass spectrometry. In total, 94 O-glycans were identified, with healthy pigs having higher interindividual variation, although a larger array of glycan structures was present in infected pigs. This implied that infection induced loss of individual variation and that specific infection-related glycans were induced. The dominating structures shifted from core-4-type O-glycans in noninfected pigs toward core-2-type O-glycans in infected animals, which correlated with increased levels of the C2GnT glycosyl transferase. Overall, glycan chains from infected pigs were shorter and had a higher abundance of structures that were neutral or predominantly contained NeuGc instead of NeuAc, whereas they had a lower abundance of structures that were fucosylated, acidic, or sulfated than those from noninfected pigs. Therefore, we conclude that B. hyodysenteriae plays a major role in regulating colonic mucin glycosylation in pigs during SD. The changes in mucin O-glycosylation thus resulted in a glycan fingerprint in porcine colonic mucus that may provide increased exposure of epitopes important for host-pathogen interactions. The results from this study provide potential therapeutic targets and a platform for investigations of B. hyodysenteriae interactions with the host via mucin glycans.

Sialic Acid-Responsive Polymeric Interface Material: From Molecular Recognition to Macroscopic Property Switching

Biological systems that utilize multiple weak non-covalent interactions and hierarchical assemblies to achieve various bio-functions bring much inspiration for the design of artificial biomaterials. However, it remains a big challenge to correlate underlying biomolecule interactions with macroscopic level of materials, for example, recognizing such weak interaction, further transforming it into regulating material's macroscopic property and contributing to some new bio-applications. Here we designed a novel smart polymer based on polyacrylamide (PAM) grafted with lactose units (PAM-g-lactose0.11), and reported carbohydrate-carbohydrate interaction (CCI)-promoted macroscopic properties switching on this smart polymer surface. Detailed investigations indicated that the binding of sialic acid molecules with the grafted lactose units via the CCIs induced conformational transformation of the polymer chains, further resulted in remarkable and reversible switching in surface topography, wettability and stiffness. With these excellent recognition and response capacities towards sialic acid, the PAM-g-lactose0.11 further facilitated good selectivity, strong anti-interference and high adsorption capacity in the capture of sialylated glycopeptides (important biomarkers for cancers). This work provides some enlightenment for the development of biointerface materials with tunable property, as well as high-performance glycopeptide enrichment materials.

Biological roles of glycans

Simple and complex carbohydrates (glycans) have long been known to play major metabolic, structural and physical roles in biological systems. Targeted microbial binding to host glycans has also been studied for decades. But such biological roles can only explain some of the remarkable complexity and organismal diversity of glycans in nature. Reviewing the subject about two decades ago, one could find very few clear-cut instances of glycan-recognition-specific biological roles of glycans that were of intrinsic value to the organism expressing them. In striking contrast there is now a profusion of examples, such that this updated review cannot be comprehensive. Instead, a historical overview is presented, broad principles outlined and a few examples cited, representing diverse types of roles, mediated by various glycan classes, in different evolutionary lineages. What remains unchanged is the fact that while all theories regarding biological roles of glycans are supported by compelling evidence, exceptions to each can be found. In retrospect, this is not surprising. Complex and diverse glycans appear to be ubiquitous to all cells in nature, and essential to all life forms. Thus, >3 billion years of evolution consistently generated organisms that use these molecules for many key biological roles, even while sometimes coopting them for minor functions. In this respect, glycans are no different from other major macromolecular building blocks of life (nucleic acids, proteins and lipids), simply more rapidly evolving and complex. It is time for the diverse functional roles of glycans to be fully incorporated into the mainstream of biological sciences.

Laser microdissection of paraffin embedded tissue as a tool to estimate the sialylation status of selected cell populations

In vertebrates, sialic acids occur at the terminal end of glycans mediating numerous biological processes like cell differentiation or tumor metastasis. Consequently, the cellular sialylation status under healthy and pathological conditions is of high interest. Existing analytical strategies to determine sialylation patterns are mostly applied to tissue samples consisting of a mixture of different cell types. Alterations in the sialylation status in a distinct area of tissues or in a specific cell population may, therefore, be easily overlooked. Likewise, estimated variations in sialylation in tissue homogenates might be simply the result of a changed cell composition. To overcome these limitations, we employed laser microdissection to isolate defined cell types or functional subunits and cell populations of paraffin embedded specimens which represent the most abundant supply of human tissue associated with clinical records. For qualitative and quantitative estimation of the sialylation status, sialic acids were released, fluorescently labeled, and analyzed by an online high-performance liquid chromatography-electrospray ionization-mass spectrometry (HPLC-ESI-MS) system. As a proof of principle, this strategy was successfully applied to characterize the sialylation of the apical region of epididymal epithelial cells. Furthermore, it was possible to detect an impaired sialylation during kidney maturation in a transgenic mouse model, which was restricted to glomeruli, whereas no differences in sialylation were observed when whole kidney homogenates were used. Thus, starting from paraffin embedded tissue samples, the outlined approach offers a sensitive method to detect and quantify sialic acids on defined cell populations, which may be useful to explore novel sialic acid dependent roles during physiological and pathological processes.

Software tools for glycan profiling

We introduce three software tools, Cartoonist, GlycoWorkbench, and MultiGlycan, for N-glycan profiling of complex biological samples. Detailed instructions for using these tools are provided, and their performances are demonstrated by using real glycan profiling data.

Development of antimetastatic drugs by targeting tumor sialic acids

One-third of all cancer categories in clinics have a high incidence of neoplasm metastasis. Neoplasm metastasis is one of the leading causes of cancer deaths. However, the prevailing therapeutic approach to this pathogenic process is presently unsatisfactory. Paradoxically to our efforts and expectations, except for some antibodies, no obvious improvements and therapeutic benefits in currently used drugs have been achieved until now. Therapeutic benefits in late-stage or elderly cancer patients are especially poor and useless. One of the reasons for this, we would guess, is the lack of therapeutic targets specifically related to neoplasm metastasis. In order to enhance the therapeutic efficacy, the development of antimetastatic drugs transcending from current drug-screening pathways is urgently needed. Antimetastatic drugs targeting aberrantly sialylated in tumors have evolved for about a quarter of a century and might be a future therapeutic option other than the currently utilized antimetastatic drugs, such as antivascular and MMP inhibitors. Since neoplasm tissues often manifest high levels of sialic acids and sialyl antigens or glycoligands, some types of sialic acid analogue, such as N-glycolylneuraminic acid (Nau5Gc), occurred in most tumor tissues which is normally absent in most humans. Consequently, more attention is needed to work with new therapeutic approaches to target these changes. This review addresses and discusses the latest six types of therapeutic approaches targeting sialic acids in metastatic tissues.

Recent advances in sialic acid-focused glycomics

Recent emergences of glycobiology, glycotechnology and glycomics have been clarifying enormous roles of carbohydrates in biological recognition systems. For example, cell surface carbohydrates existing as glycoconjugates (glycolipids, glycoproteins and proteoglycans) play crucial roles in cell-cell communication, cell proliferation and differentiation, tumor metastasis, inflammatory response or viral infection. In particular, sialic acids (SAs) existing as terminal residues in carbohydrate chains on cell surface are involved in signal recognition and adhesion to ligands, antibodies, enzymes and microbes. In addition, plasma free SAs and sialoglycans have shown great potential for disease biomarker discovery. Therefore, the development of efficient analytical methods for structural and functional studies of SAs and sialylglycans are very important and highly demanded. The problems of SAs and sialylglycans analysis are vanishingly small sample amount, complicated and unstable structures, and complex mixtures. Nevertheless, in the past decade, mass spectrometry in combination with chemical derivatization and modern separation methodologies has become a powerful and versatile technique for structural analysis of SAs and sialylglycans. This review summarizes these recent advances in glycomic studies on SAs and sialylglycans. Specially, derivatization and capturing of SAs and sialylglycans combined with mass spectrometry analysis are highlighted.

Selective enrichment of sialic acid-containing glycopeptides using titanium dioxide chromatography with analysis by HILIC and mass spectrometry

The terminal monosaccharide of cell surface glycoconjugates is typically a sialic acid (SA), and aberrant sialylation is involved in several diseases. Several methodological approaches in sample preparation and subsequent analysis using mass spectrometry (MS) have enabled the identification of glycosylation sites and the characterization of glycan structures. In this paper, we describe a protocol for the selective enrichment of SA-containing glycopeptides using a combination of titanium dioxide (TiO(2)) and hydrophilic interaction liquid chromatography (HILIC). The selectivity of TiO(2) toward SA-containing glycopeptides is achieved by using a low-pH buffer that contains a substituted acid such as glycolic acid to improve the binding efficiency and selectivity of SA-containing glycopeptides to the TiO(2) resin. By combining TiO(2) enrichment of sialylated glycopeptides with HILIC separation of deglycosylated peptides, a more comprehensive analysis of formerly sialylated glycopeptides by MS can be achieved. Here we illustrate the efficiency of the method by the identification of 1,632 unique formerly sialylated glycopeptides from 817 sialylated glycoproteins. The TiO(2)/HILIC protocol requires 2 d and the entire procedure from protein isolation can be performed in <5 d, depending on the time taken to analyze data.

Exploring the Sialiome Using Titanium Dioxide Chromatography and Mass Spectrometry

Strategies for biomarker discovery increasingly focus on biofluid protein and peptide expression patterns. Post-translational modifications contribute significantly to the pattern complexity and thereby increase the likelihood of obtaining specific biomarkers for diagnostics and disease monitoring. Glycosylation is a common post-translational modification that plays a role e.g. in cell adhesion and in cell-cell and receptor-ligand interactions. Abnormal protein glycosylation has important disease associations, and the glycoproteome is therefore a target for biomarker discovery. Here we present a simple and highly selective strategy for purification of sialic acid-containing glycopeptides (the sialiome) from complex peptide mixtures. The approach utilizes a high and selective affinity of sialic acids for titanium dioxide under specific buffer conditions. In combination with mass spectrometry we used this strategy to characterize the human plasma and saliva sialiomes where 192 and 97 glycosylation sites, respectively, were identified. Furthermore we illustrate the potential of this method in biomarker discovery.

Comparative and phylogenetic analysis of alpha-L-fucosidase genes

Fucosylated glycoconjugates play a role in a wide variety of biological processes, including immune responses, signal transduction, ontogenic events and pathogenesis of several human diseases. Alpha-L-fucosidases, which are responsible for their processing, have been demonstrated to be involved in lysosomal storage disease, inflammation, cystic fibrosis, cancer development and in the interactions between gametes in vertebrates as well as invertebrates. The sequence and comparative genomic analysis of these glycosyl hydrolases and the study of their evolutionary relationships appear therefore to be of considerable interest. In this work we carried out extensive similarity searches and comparative analyses to identify sequences encoding alpha-L-fucosidases. We have identified novel alpha-L-fucosidase coding sequences in worms, insects, sea urchin, ascidians, fish, chicken, amphibians, mammals and various bacteria resulting in a total of 39 alpha-L-fucosidase sequences. Two alpha-L-fucosidases that are present in all vertebrates likely reflect a distinct biological role for paralogous genes. Comparative sequence analysis of all metazoan alpha-L-fucosidases reveals a broad conservation of features, including the aspartate residue that constitutes the catalytic nucleophile. However, a cysteine which is thought to be part of the active site is also conserved in metazoa but not in arthropods, where it is replaced by an alanine. Phylogenetic analysis suggests a gene duplication event very early in metazoan evolution with the subsequent differential loss of isoforms in various metazoan lineages.

Fucosylation in prokaryotes and eukaryotes

Fucosylated carbohydrate structures are involved in a variety of biological and pathological processes in eukaryotic organisms including tissue development, angiogenesis, fertilization, cell adhesion, inflammation, and tumor metastasis. In contrast, fucosylation appears less common in prokaryotic organisms and has been suggested to be involved in molecular mimicry, adhesion, colonization, and modulating the host immune response. Fucosyltransferases (FucTs), present in both eukaryotic and prokaryotic organisms, are the enzymes responsible for the catalysis of fucose transfer from donor guanosine-diphosphate fucose to various acceptor molecules including oligosaccharides, glycoproteins, and glycolipids. To date, several subfamilies of mammalian FucTs have been well characterized; these enzymes are therefore delineated and used as models. Non-mammalian FucTs that possess different domain construction or display distinctive acceptor substrate specificity are highlighted. It is noteworthy that the glycoconjugates from plants and schistosomes contain some unusual fucose linkages, suggesting the presence of novel FucT subfamilies as yet to be characterized. Despite the very low sequence homology, striking functional similarity is exhibited between mammalian and Helicobacter pylori alpha1,3/4 FucTs, implying that these enzymes likely share a conserved mechanistic and structural basis for fucose transfer; such conserved functional features might also exist when comparing other FucT subfamilies from different origins. Fucosyltranferases are promising tools used in synthesis of fucosylated oligosaccharides and glycoconjugates, which show great potential in the treatment of infectious and inflammatory diseases and tumor metastasis.

Elevated Golgi pH in breast and colorectal cancer cells correlates with the expression of oncofetal carbohydrate T-antigen

Altered glycosylation has turned out to be a universal feature of cancer cells, and in many cases, to correlate with altered expression or localization of relevant glycosyltransferases. However, no such correlation exists between observed enzymatic changes and the expression of the oncofetal Thomsen-Friedenreich (T)-antigen, a core 1 (Gal-beta1 --> 3-GalNAc-ser/thr) carbohydrate structure. Here we report that T-antigen expression, instead, correlates with elevated Golgi pH in cancer cells. Firstly, using a Golgi-targeted green fluorescent protein (GT-EGFP) as a probe, we show that the medial/trans-Golgi pH (pHG) in a high proportion of breast (MCF-7) and colorectal (HT-29, SW-48) cancer cells is significantly more alkaline (pHG > or = 6.75) than that of control cells (pHG 5.9-6.5). The pH gradient between the cytoplasm and the Golgi lumen is also markedly reduced in MCF-7 cells, suggesting a Golgi acidification defect. Secondly, we show that T-antigen expression is highly sensitive to changes in Golgi pH, as only a 0.2 pH unit increase was sufficient to increase T-antigen expression in control cells. Thirdly, we found that T-antigen expressing MCF-7 cells have 0.3 pH units more alkaline Golgi pH than non-expressing MCF-7 cells. Fourthly, in all cell types examined, we observed significant correlation between the number of T-antigen expressing cells and cells with a markedly elevated Golgi pH (pHG > or = 6.75). Consistent with these observations in cultured cells, cells in solid tumors also heterogenously expressed the T-antigen. Thus, elevated Golgi pH appears to be directly linked to T-antigen expression in cancer cells, but it may also act as a more general factor for altered glycosylation in cancer by affecting the distribution of Golgi-localized glycosyltransferases.

Tumor galectinology: insights into the complex network of a family of endogenous lectins

Beta-Galactosides of cell surface glycoconjugates are docking sites for endogenous lectins of the galectin family. In cancer cells, primarily galectins-1 and -3 have been studied to date. With the emergence of insights into their role in growth control, resistance to or induction of apoptosis and invasive behavior the notion is supported that they can be considered as functional tumor markers. In principle, the same might hold true for the other members of the galectin family. But their expression in tumors has hitherto been a subject of attention only to a very limited extent. Pursuing our concept to define the complexity of the galectin network in cancer cells and the degree of functional overlap/divergence with diagnostic/therapeutic implications, we have introduced comprehensive RT-PCR monitoring to map their galectin gene expression. The data on so far less appreciated galectins in this context such as galectins-4 and -8 vindicate this approach. They, too, attach value to extend the immunohistochemical panel accordingly. Our initial histopathological and cell biological studies, for example on colon cancer progression, prove the merit of this procedure. Aside from the detection of gene expression profiles by RT-PCR, the detailed molecular biological monitoring yielded further important information. We describe different levels of regulation of galectin production in colon cancer cells in the cases of the tandem-repeat-type galectins-8 and -9. Isoforms for them are present with insertions into the peptide linker sequence attributed to alternative splicing. Furthermore, variants with distinct amino acid substitutions (galectin-8, Po66-CBP, PCTA-1, CocaI/II and galectin-9/ecalectin) and generation of multiple mRNA species, notably those coding for truncated galectin-8 and -9 versions with only one lectin site, justify to portray these two family members not as distinct individuals but as groups. In aggregate, the ongoing work to thoroughly chart the galectin network and to disentangle the individual functional contributions is expected to make its mark on our understanding of the malignant phenotype in certain tumor types.

Altered terminal glycosylation and the pathophysiology of CF lung disease

Altered terminal glycosylation, with increased fucosylation and decreased sialylation, is a hallmark of the cystic fibrosis (CF) glycosylation phenotype. The glycosylation phenotype of CF airway epithelial cells has been modulated by the expression of wtCFTR. Understanding the effects of mutant CFTR on glycosylation may provide further insight into the regulation of glycoconjugate processing as well as new approaches to the therapy of CF.

Variant glycosylation: an underappreciated regulatory mechanism for β1 integrins

Although it has been known for many years that beta1 integrins undergo differential glycosylation in accordance with changes in cell phenotype, the potential role of N-glycosylation as a modulator of integrin function has received little attention. One reason for the relatively limited interest in this topic likely relates to the fact that much of the prior research was correlative in nature. However, new results now bolster the hypothesis that there is a causal relationship between variant glycosylation and altered integrin activity. In this review, the evidence for variant glycosylation as a regulatory mechanism for beta1 integrins are summarized, with particular emphasis on: (1). outlining the instances in which cell phenotypic variation is associated with differential beta1 glycosylation, (2). describing the specific alterations in glycan structure that accompany phenotypic changes and (3). presenting potential mechanisms by which variant glycosylation might regulate integrin function.

Free secretory component from cystic fibrosis sputa displays the cystic fibrosis glycosylation phenotype

Secretory IgA contributes to humoral defense mechanisms against pathogens targeting mucosal surfaces, and secretory component (SC) fulfills multiple roles in this defense. The aims of this study were to quantify total SC and to analyze the form of free SC in sputa from normal subjects, subjects with asthma, and subjects with cystic fibrosis (CF). Significantly higher levels of SC were detected in CF compared with both other groups. Gel filtration chromatography revealed that SC in CF was relatively degraded. Free SC normally binds interleukin (IL)-8 and inhibits its function. However, in CF sputa, IL-8 binding to intact SC was reduced. Analysis of the total carbohydrate content of free SC signified overglycosylation in CF compared with normal subjects and subjects with asthma. Monosaccharide composition analysis of free SC from CF subjects revealed overfucosylation and undersialylation, in agreement with the reported CF glycosylation phenotype. SC binding to IL-8 did not interfere with the binding of IL-8 to heparin, indicating distinct binding sites on IL-8 for negative regulation of function by SC and heparin. We suggest that defective structure and function of SC contribute to the characteristic sustained inflammatory response in the CF airways.

Terminal glycosylation in cystic fibrosis (CF): a review emphasizing the airway epithelial cell

Altered terminal glycosylation, with increased fucosylation and decreased sialylation is a hallmark of the cystic fibrosis (CF) glycosylation phenotype. Oligosaccharides purified from the surface membrane glycoconjugates of CF airway epithelial cells have the Lewis x, selectin ligand in terminal positions. This review is focused on the investigations of the glycoconjugates of the CF airway epithelial cell surface. Two of the major bacterial pathogens in CF, Pseudomonas aeruginosa and Haemophilus influenzae, have binding proteins which recognize fucose in alpha-1,3 linkage and asialoglycoconjugates. Therefore, consideration has been given to the possibility that the altered terminal glycosylation of airway epithelial glycoproteins in CF contributes to both the chronic infection and the robust, but ineffective, inflammatory response in the CF lung. Since the glycosylation phenotype of CF airway epithelial cells have been modulated by the expression of wtCFTR, the hypotheses which have been proposed to relate altered function of CFTR to the regulation of the glycosyltransferases are discussed. Understanding the effects of mutant CFTR on glycosylation may provide further insight into the regulation of glycoconjugate processing as well as new approaches to the therapy of CF.

Glycosylation and the cystic fibrosis transmembrane conductance regulator

The cystic fibrosis transmembrane conductance regulator (CFTR) has been known for the past 11 years to be a membrane glycoprotein with chloride channel activity. Only recently has the glycosylation of CFTR been examined in detail, by O'Riordan et al in Glycobiology. Using cells that overexpress wild-type (wt)CFTR, the presence of polylactosamine was noted on the fully glycosylated form of CFTR. In the present commentary the results of that work are discussed in relation to the glycosylation phenotype of cystic fibrosis (CF), and the cellular localization and processing of DeltaF508 CFTR. The significance of the glycosylation will be known when endogenous CFTR from primary human tissue is examined.