Cell surface-specific N-glycan profiling in breast cancer

In silico discovery and anti-tumor bioactivities validation of an algal lectin from Kappaphycus alvarezii genome

Lectins are proteins that bind specifically and reversibly to carbohydrates, and some of them have significant anti-tumor activities. Compared to those of lectins from land plants, there are far fewer studies on algal lectins, despite of the high biodiversity of algae. However, canonical strategies based on chromatographic feature-oriented screening cannot satisfy the requirement for algal lectin discovery. In this study, prospecting for novel OAAH family lectins throughout 358 genomes of red algae and cyanobacteria was conducted. Then 35 candidate lectins and 1843 of their simulated mutated forms were virtually screened based on predicted binding specificities to characteristic carbohydrates on cancer cells inferred by a deep learning model. A new lectin, named Siye, was discovered in Kappaphycus alvarezii genome and further verified on different cancer cells. Without causing agglutination of erythrocytes, Siye showed significant cytotoxicity to four human cancer cell lines (IC50 values ranging from 0.11 to 3.95 μg/mL), including breast adenocarcinoma HCC1937, lung carcinoma A549, liver cancer HepG2 and romyelocytic leukemia HL60. And the cytotoxicity was induced through promoting apoptosis by regulating the caspase and the p53 pathway within 24 h. This study testifies the feasibility and efficiency of the genome mining guided by evolutionary theory and artificial intelligence in the discovery of algal lectins.

Towards Biomimetic Recognition of Glycans by Synthetic Receptors

Carbohydrates are abundant in Nature, where they are mostly assembled within glycans as free polysaccharides or conjugated to a variety of biological molecules such as proteins and lipids. Glycans exert several functions, including protein folding, stability, solubility, resistance to proteolysis, intracellular traffic, antigenicity, and recognition by carbohydrate-binding proteins. Interestingly, misregulation of their biosynthesis that leads to changes in glycan structures is frequently recognized as a mark of a disease state. Because of glycan ubiquity, carbohydrate binding agents (CBAs) targeting glycans can lead to a deeper understanding of their function and to the development of new diagnostic and prognostic strategies. Synthetic receptors selectively recognizing specific carbohydrates of biological interest have been developed over the past three decades. In addition to the success obtained in the effective recognition of monosaccharides, synthetic receptors recognizing more complex guests have also been developed, including di- and oligosaccharide fragments of glycans, shedding light on the structural and functional requirements necessary for an effective receptor. In this review, the most relevant achievements in molecular recognition of glycans and their fragments will be summarized, highlighting potentials and future perspectives of glycan-targeting synthetic receptors.

Chromatograms and Mass Spectra of High-Mannose and Paucimannose N-Glycans for Rapid Isomeric Identifications

N-Linked glycosylation is one of the most essential post-translational modifications of proteins. However, N-glycan structural determination remains challenging because of the small differences in structures between isomers. In this study, we constructed a database containing collision-induced dissociation MSn mass spectra and chromatograms of high-performance liquid chromatography for the rapid identification of high-mannose and paucimannose N-glycan isomers. These N-glycans include isomers by breaking of arbitrary numbers of glycosidic bonds at arbitrary positions of canonical Man9GlcNAc2 N-glycans. In addition, some GlcMannGlcNAc2 N-glycan isomers were included in the database. This database is particularly useful for the identification of the N-glycans not in conventional N-glycan standards. This study demonstrated the application of the database to structural assignment for high-mannose N-glycans extracted from bovine whey proteins, soybean proteins, human mammary epithelial cells, and human breast carcinoma cells. We found many N-glycans that are not expected to be generated by conventional biosynthetic pathways of multicellular eukaryotes.

N-glycan profiling of tissue samples to aid breast cancer subtyping

Breast cancer is a highly heterogeneous disease. Its intrinsic subtype classification for diagnosis and choice of therapy traditionally relies on the presence of characteristic receptors. Unfortunately, this classification is often not sufficient for precise prediction of disease prognosis and treatment efficacy. The N-glycan profiles of 145 tumors and 10 healthy breast tissues were determined using Matrix-Assisted Laser Desorption-Ionization Time-of-Flight Mass Spectrometry. The tumor samples were classified into Mucinous, Lobular, No-Special-Type, Human Epidermal Growth Factor 2 + , and Triple-Negative Breast Cancer subtypes. Statistical analysis was conducted using the reproducibility-optimized test statistic software package in R, and the Wilcoxon rank sum test with continuity correction. In total, 92 N-glycans were detected and quantified, with 59 consistently observed in over half of the samples. Significant variations in N-glycan signals were found among subtypes. Mucinous tumor samples exhibited the most distinct changes, with 28 significantly altered N-glycan signals. Increased levels of tri- and tetra-antennary N-glycans were notably present in this subtype. Triple-Negative Breast Cancer showed more N-glycans with additional mannose units, a factor associated with cancer progression. Individual N-glycans differentiated Human Epidermal Growth Factor 2 + , No-Special-Type, and Lobular cancers, whereas lower fucosylation and branching levels were found in N-glycans significantly increased in Luminal subtypes (Lobular and No-Special-Type tumors). Clinically normal breast tissues featured a higher abundance of signals corresponding to N-glycans with bisecting moiety. This research confirms that histologically distinct breast cancer subtypes have a quantitatively unique set of N-glycans linked to clinical parameters like tumor size, proliferative rate, lymphovascular invasion, and metastases to lymph nodes. The presented results provide novel information that N-glycan profiling could accurately classify human breast cancer samples, offer stratification of patients, and ongoing disease monitoring.

Reliable N-Glycan Analysis-Removal of Frequently Occurring Oligosaccharide Impurities by Enzymatic Degradation

Glycosylation, especially N-glycosylation, is one of the most common protein modifications, with immense importance at the molecular, cellular, and organismal level. Thus, accurate and reliable N-glycan analysis is essential in many areas of pharmaceutical and food industry, medicine, and science. However, due to the complexity of the cellular glycosylation process, in-depth glycoanalysis is still a highly challenging endeavor. Contamination of samples with oligosaccharide impurities (OSIs), typically linear glucose homo-oligomers, can cause further complications. Due to their physicochemical similarity to N-glycans, OSIs produce potentially overlapping signals, which can remain unnoticed. If recognized, suspected OSI signals are usually excluded in data evaluation. However, in both cases, interpretation of results can be impaired. Alternatively, sample preparation can be repeated to include an OSI removal step from samples. However, this significantly increases sample amount, time, and effort necessary. To overcome these issues, we investigated the option to enzymatically degrade and thereby remove interfering OSIs as a final sample preparation step. Therefore, we screened ten commercially available enzymes concerning their potential to efficiently degrade maltodextrins and dextrans as most frequently found OSIs. Of these enzymes, only dextranase from Chaetomium erraticum and glucoamylase P from Hormoconis resinae enabled a degradation of OSIs within only 30 min that is free of side reactions with N-glycans. Finally, we applied the straightforward enzymatic degradation of OSIs to N-glycan samples derived from different standard glycoproteins and various stem cell lysates.

Niosomes Functionalized with a Synthetic Carbohydrate Binding Agent for Mannose-Targeted Doxorubicin Delivery

Niosomes are a potential tool for the development of active targeted drug delivery systems (DDS) for cancer therapy because of their excellent behaviour in encapsulating antitumorals and the possibility to easily functionalise their surface with targeting agents. Recently, some of us developed a synthetic carbohydrate binding agent (CBA) able to target the mannosidic residues of high-mannose-type glycans overexpressed on the surface of several cancer cell lines, promoting their apoptosis. In this article, we modified the structure of this mannose receptor to obtain an amphiphilic analogue suitable for the functionalization of doxorubicin-based niosomes. Several niosomal formulations and preparation methods were investigated deeply to finally obtain functionalized niosomes suitable for parental administration, which were stable for over six months and able to encapsulate up to 85% of doxorubicin (DOXO). In vitro studies, carried out towards triple-negative cancer cells (MDA-MB231), overexpressing high-mannose-type glycans, showed a cytotoxic activity comparable to that of DOXO but with an appreciable increment in apoptosis given by the CBA. Moreover, niosomal formulation was observed to reduce doxorubicin-induced cytotoxicity towards normal cell lines of rat cardiomyocytes (H9C2). This study is propaedeutic to further in vivo investigations that can aim to shed light on the antitumoral activity and pharmacokinetics of the developed active targeted DDS.

Mass Spectrometry-Based Glycoproteomic Workflows for Cancer Biomarker Discovery

Glycosylation has a clear role in cancer initiation and progression, with numerous studies identifying distinct glycan features or specific glycoproteoforms associated with cancer. Common findings include that aggressive cancers tend to have higher expression levels of enzymes that regulate glycosylation as well as glycoproteins with greater levels of complexity, increased branching, and enhanced chain length1. Research in cancer glycoproteomics over the last 50-plus years has mainly focused on technology development used to observe global changes in glycosylation. Efforts have also been made to connect glycans to their protein carriers as well as to delineate the role of these modifications in intracellular signaling and subsequent cell function. This review discusses currently available techniques utilizing mass spectrometry-based technologies used to study glycosylation and highlights areas for future advancement.

Triggering of the immune response to MCF7 cell line using conjugated antibody with bacterial antigens: In-vitro and in-vivo study

The current study intended to trigger the immune response to cancer cells by using antibodies conjugated with bacterial antigens. The protein membrane of the MCF7 cell line was extracted and specific antibodies against cell membrane antigens was produced in rabbits. The specific antibodies were purified using chromatography methods and linked to E. coli antigens or doxorubicin using Diethylenetriamine pentaacetate (DTPA) linker. After confirmation of the conjugation process using SDS-PAGE and ATR-FTIR methods, the MCF7 and HUVEC cells were treated with various concentrations of the prepared conjugated antibodies along with human serum. The toxicity of each treatment against MCF7 and HUVEC cells was evaluated using the MTT assay. Also, polylactic acid scaffolds that contain 10×10⁴ MCF7 cells were surgically placed in the peritoneal cavity of the rats. After treatment of each group, induction of the inflammatory responses was evaluated on stained histological sections of the scaffolds. The lowest cytotoxic doses of the antigen conjugated-antibody, doxorubicin-conjugated-antibody was 4 and 1 μg/mL, respectively. Doxorubicin conjugated antibodies displayed greater toxicity on both MCF7 and HUVEC cells. The in vivo finding revealed that the inflammatory cells were significantly higher in treating animals with antigen conjugated-antibody. The current synthetic agent stimulated the serum toxicity and induced an inflammatory response to MCF7 cell lines. Targeting of the bacterial antigens on tumor sites by immune system elements, could limit the growth of the tumor cells.

Antitumor activity of a lectibody targeting cancer-associated high-mannose glycans

Aberrant protein glycosylation is a hallmark of cancer, but few drugs targeting cancer glycobiomarkers are currently available. Here, we showed that a lectibody consisting of the high-mannose glycan-binding lectin Avaren and human immunoglobulin G1 (IgG1) Fc (AvFc) selectively recognizes a range of cell lines derived from lung, breast, colon, and blood cancers at nanomolar concentrations. Binding of AvFc to the non-small cell lung cancer (NSCLC) cell lines A549 and H460 was characterized in detail. Co-immunoprecipitation proteomics analysis revealed that epidermal growth factor receptor (EGFR) and insulin-like growth factor 1 receptor (IGF1R) are among the lectibody's common targets in these cells. AvFc blocked the activation of EGFR and IGF1R by their respective ligands in A549 cells and inhibited the migration of A549 and H460 cells upon stimulation with EGF and IGF1. Furthermore, AvFc induced potent Fc-mediated cytotoxic effects and significantly restricted A549 and H460 tumor growth in severe combined immunodeficiency (SCID) mice. Immunohistochemistry analysis of primary lung tissues from NSCLC patients demonstrated that AvFc preferentially binds to tumors over adjacent non-tumor tissues. Our findings provide evidence that increased abundance of high-mannose glycans in the glycocalyx of cancer cells can be a druggable target, and AvFc may provide a new tool to probe and target this tumor-associated glycobiomarker.

Knockdown of Oligosaccharyltransferase Subunit Ribophorin 1 Induces Endoplasmic-Reticulum-Stress-Dependent Cell Apoptosis in Breast Cancer

Ribophorin 1 (RPN1) is a major part of Oligosaccharyltransferase (OST) complex, which is vital for the N-linked glycosylation. Though it has been verified that the abnormal glycosylation is closely related to the development of breast cancer, the detail role of RPN1 in breast cancer remains unknown. In this study, we explored the public databases to investigate the relationship between the expression levels of OST subunits and the prognosis of breast cancer. Then, we focused on the function of RPN1 in breast cancer and its potential mechanisms. Our study showed that the expression of several OST subunits including RPN1, RPN2, STT3A STT3B, and DDOST were upregulated in breast cancer samples. The protein expression level of RPN1 was also upregulated in breast cancer. Higher expression of RPN1 was correlated with worse clinical features and poorer prognosis. Furthermore, knockdown of RPN1 suppressed the proliferation and invasion of breast cancer cells in vitro and induced cell apoptosis triggered by endoplasmic reticulum stress. Our results identified the oncogenic function of RPN1 in breast cancer, implying that RPN1 might be a potential biomarker and therapeutic target for breast cancer.

Trends in oligomannosylation and α1,2-mannosidase expression in human cancers

Aberrant protein glycosylation is a prominent cancer feature. While many tumour-associated glycoepitopes have been reported, advances in glycoanalytics continue to uncover new associations between glycosylation and cancer. Guided by a comprehensive literature survey suggesting that oligomannosylation (Man_5–9 GlcNAc₂) is a widespread and often regulated glycosignature in human cancers, we here revisit a valuable compilation of nearly 500 porous graphitized carbon LC-MS/MS N-glycomics datasets acquired across 11 human cancer types to systematically test for oligomannose-cancer associations. Firstly, the quantitative glycomics data obtained across 34 cancerous cell lines demonstrated that oligomannosylation is a pan-cancer feature spanning in a wide abundance range. In keeping with literature, our quantitative glycomics data of tumour and matching control tissues and new MALDI-MS imaging data of tissue microarrays showed a strong cancer-associated elevation of oligomannosylation in both basal cell (p = 1.78 × 10^–12) and squamous cell (p = 1.23 × 10^–11) skin cancer and colorectal cancer (p = 8.0 × 10^–4). The glycomics data also indicated that some cancer types including gastric and liver cancer exhibit unchanged or reduced oligomannose levels, observations also supported by literature and MALDI-MS imaging data. Finally, expression data from public cancer repositories indicated that several α1,2-mannosidases are regulated in tumour tissues suggesting that these glycan-processing enzymes may contribute to the cancer-associated modulation of oligomannosylation. This omics-centric study has compiled robust glycomics and enzyme expression data revealing interesting molecular trends that open avenues to better understand the role of oligomannosylation in human cancers.

Oligomannose N-Glycans 3D Architecture and Its Response to the FcγRIIIa Structural Landscape

Oligomannoses are evolutionarily the oldest class of N-glycans, where the arms of the common pentasaccharide unit, i.e., Manα(1-6)-[Manα(1-3)]-Manβ(1-4)-GlcNAcβ(1-4)-GlcNAcβ1-Asn, are functionalized exclusively with branched arrangements of mannose (Man) monosaccharide units. In mammalian species oligomannose N-glycans can have up to 9 Man; meanwhile structures can grow to over 200 units in yeast mannan. The highly dynamic nature, branching complexity, and 3D structure of oligomannoses have been recently highlighted for their roles in immune escape and infectivity of enveloped viruses, such as HIV-1 and SARS-CoV2. The architectural features that allow these N-glycans to perform their functions are yet unclear, due to their intrinsically disordered nature that hinders their structural characterization. In this work we will discuss the results of over 54 μs of cumulative sampling by molecular dynamics (MD) simulations of differently processed, free (not protein-linked) oligomannose N-glycans common in vertebrates. We then discuss the effects of a protein surface on their structural equilibria based on over 4 μs cumulative MD sampling of the fully glycosylated CD16a Fc γ receptor (FcγRIIIa), where the type of glycosylation is known to modulate its binding affinity for IgG1s, regulating the antibody-dependent cellular cytotoxicity (ADCC). Our results show that the protein's structural constraints shift the oligomannoses conformational ensemble to promote conformers that satisfy the steric requirements and hydrogen bonding networks demanded by the protein's surface landscape. More importantly, we find that the protein does not actively distort the N-glycans into structures not populated in the unlinked forms in solution. Ultimately, the highly populated conformations of the Man5 linked glycans support experimental evidence of high levels of hybrid complex forms at N45 and show a specific presentation of the arms at N162, which may be involved in mediating binding affinity to the IgG1 Fc.

Serum N-glycan profiling as a diagnostic biomarker for the identification and assessment of psoriasis

Background

Glycosylation is an important post‐translational modification of protein. The change in glycosylation is involved in the occurrence and development of various diseases, and this study verified that N‐glycan markers might be a diagnostic marker in psoriasis.

Methods

A total of 76 psoriasis patients were recruited. We used Psoriasis Area Severity Index (PASI) scores to evaluate the state of psoriasis, 41 of whom were divided into three subgroups: mild, moderate, and severe. At the same time, 76 healthy subjects were enrolled as a control group. We used DNA sequencer–assisted fluorophore‐assisted carbohydrate electrophoresis (DSA‐FACE) to analyze serum N‐glycan profiling.

Results

Compared with the healthy controls, the relative abundance of structures in peaks 5(NA2), 9(NA3Fb), 11(NA4), and 12(NA4Fb) was elevated (p < .05), while that in peaks 3(NG1A2F), 4(NG1A2F), 6(NA2F), and 7(NA2FB) was decreased (p < .05) in the psoriasis group. The abundance of peak 5 (NA2) increased gradually with the aggravation of disease severity though there was no statistically significant, was probably correlated with the disease severity. The best area under the receiver operating characteristic (ROC) curve (AUC) of the logistic regression model (PglycoA) to diagnose psoriasis was 0.867, with a sensitivity of 72.37%, a specificity of 85.53%, a positive predictive value(PPV) of 83.33%, a negative predictive value(NPV) of 75.58%, and an accuracy of 78.95%.

Conclusions

Our study indicated that the N‐glycan–based diagnostic model would be a new, valuable, and noninvasive alternative for diagnosing psoriasis. Furthermore, the characteristic distinctive N‐glycan marker might be correlated with the severity gradation of the psoriasis disease.

The Repertoire of Glycan Alterations and Glycoproteins in Human Cancers

Cancer as the leading cause of death worldwide has many issues that still need to be addressed. Since the alterations on the glycan compositions or/and structures (i.e., glycosylation, sialylation, and fucosylation) are common features of tumorigenesis, glycomics becomes an emerging field examining the structure and function of glycans. In the past, cancer studies heavily relied on genomics and transcriptomics with relatively little exploration of the glycan alterations and glycoprotein biomarkers among individuals and populations. Since glycosylation of proteins increases their structural complexity by several orders of magnitude, glycome studies resulted in highly dynamic biomarkers that can be evaluated for cancer diagnosis, prognosis, and therapy. Glycome not only integrates our genetic background with past and present environmental factors but also offers a promise of more efficient patient stratification compared with genetic variations. Therefore, studying glycans holds great potential for better diagnostic markers as well as developing more efficient treatment strategies in human cancers. While recent developments in glycomics and associated technologies now offer new possibilities to achieve a high-throughput profiling of glycan diversity, we aim to give an overview of the current status of glycan research and the potential applications of the glycans in the scope of the personalized medicine strategies for cancer.

Differential N-glycosylation profiling of formalin-fixed paraffin-embedded (FFPE) invasive ductal carcinoma tissues using MALDI-TOF-MS

Invasive ductal carcinoma (IDC) is the most common type of breast cancer. As dynamic changes of the glycome are closely associated with complex diseases, they have become a focal point of cancer research involving predictive and prognostic markers. Formalin-fixed paraffin-embedded (FFPE) clinical specimens are representative of the tumor environment and are thus utilized in studies on cancer related research and biomarker discovery. Further studies on differential N-glycosylation profiling of IDC cancer tissues are necessary in order to understand the biological role of glycans in cancer and to evaluate their predictive ability. In this study, matrix assisted laser desorption ionization-mass spectrometry (MALDI-MS)-based analyses were conducted for determining differential N-glycosylation patterns of IDC. Two different derivatization methods, namely, 2-aminobenzoic acid (2-AA) labeling and linkage-specific sialic acid esterification, were used for the analysis of N-glycans. Forty-seven 2-AA labeled and fifty ethyl esterified N-glycans were identified by MALDI-MS. In statistical analyses conducted for 2-AA-labeled N-glycans, the relative amounts of 32 N-glycans and prevalence of 15 N-glycan traits showed significant (p < 0.05) differences between cancer and normal tissues; and in such analyses for the ethyl-esterified N-glycans, the relative amounts of 27 N-glycans and prevalence of 17 N-glycan traits showed significant (p < 0.05) differences between them. It was found that mainly high mannose N-glycans, including H5N2, H6N2, and H7N2, and two fucosylated compositions (H3N3F1 and H5N5F1) showed strong discrimination between IDC and controls. In addition, compared with the controls, high mannose N-glycans were observed to be up-regulated in IDC whereas bisecting N-glycans were down-regulated.

Structure and anticancer activity of a new lectin from the cultivated red alga, Kappaphycus striatus

The red alga Kappaphycus striatus is economically important food species and extensively cultivated throughout most tropical parts of the world as a source of carrageenan. In this note, the primary structure of a new lectin KSL from this alga was elucidated by the rapid amplification method of complementary DNA (cDNA) ends, which consists of 267 amino acid residues distributed in four tandem-repeated domains of about 67 amino acids and sharing 43% of identity. The calculated molecular mass from the deduced sequence was consistent with that of natural KSL (27,826 Da) determined by electron spray ionization-mass spectrometry. The primary structure of KSL showed high similarity to those of the high mannose N-glycan specific lectins from marine red algae, ESA-2 from Eucheuma serra, EDA-2 from Eucheuma denticulatum, KSA-2 from Kappaphycus striatum, KAAs from Kappaphycus alvarezii and SfLs from Solieria filiformis, and from microorganisms, BOA from Burkholderia oklahomensis, MBHA from Myxococcus xanthus, OAA from Oscillatoria agardhii and PFL from Pseudomonas fluorescens. Furthermore, KSL showed anticancer effects against five carcinoma cell lines, HT29, Hela, MCF-7, SK-LU-1 and AGS, in a dose-dependent manner with the IC₅₀ values of 0.80-1.94 µM, whereas its inhibition activities on cancer cells were not detected in the presence of yeast mannan, an inhibitor against lectin KSL. The cultivated red alga K. striatus could also be a good source of functional lectin(s) for application as anticancer agents.

Molecular signatures of tumor progression in myxoid liposarcoma identified by N-glycan mass spectrometry imaging

Myxoid liposarcoma (MLS) is the second most common subtype of liposarcoma, accounting for ~6% of all sarcomas. MLS is characterized by a pathognomonic FUS-DDIT3, or rarely EWSR1-DDIT3, gene fusion. The presence of ≥5% hypercellular round cell areas is associated with a worse prognosis for the patient and is considered high grade. The prognostic significance of areas with moderately increased cellularity (intermediate) is currently unknown. Here we have applied matrix-assisted laser desorption/ionization mass spectrometry imaging to analyze the spatial distribution of N-linked glycans on an MLS microarray in order to identify molecular markers for tumor progression. Comparison of the N-glycan profiles revealed that increased relative abundances of high-mannose type glycans were associated with tumor progression. Concomitantly, an increase of the average number of mannoses on high-mannose glycans was observed. Although overall levels of complex-type glycans decreased, an increase of tri- and tetra-antennary N-glycans was observed with morphological tumor progression and increased tumor histological grade. The high abundance of tri-antennary N-glycan species was also associated with poor disease-specific survival. These findings mirror recent observations in colorectal cancer, breast cancer, ovarian cancer, and cholangiocarcinoma, and are in line with a general role of high-mannose glycans and higher-antennary complex-type glycans in cancer progression.

Bisecting N-Acetylglucosamine on EGFR Inhibits Malignant Phenotype of Breast Cancer via Down-Regulation of EGFR/Erk Signaling

Glycosylation, the most prevalent and diverse post-translational modification of protein, plays crucial biological roles in many physiological and pathological events. Alteration of N-glycan has been detected during breast cancer progression. Among the specific N-glycan structures, bisecting N-Acetylglucosamine (GlcNAc) is a β1,4-linked GlcNAc attached to the core β-mannose residue, and is catalyzed by glycosyltransferase MGAT3. Bisecting GlcNAc levels were commonly dysregulated in different types of cancer. In this study, we utilized mass spectrometry and lectin microarray analysis to investigate aberrant N-glycans in breast cancer cells. Our data showed the decreased levels of bisecting GlcNAc and down-regulated expression of MGAT3 in breast cancer cells than normal epithelial cells. Using PHA-E (a plant lectin recognizing and combining bisecting GlcNAc) based enrichment coupled with nanoLC-MS/MS, we analyzed the glycoproteins bearing bisecting GlcNAc in various breast cancer cells. Among the differentially expressed glycoproteins, levels of bisecting GlcNAc on EGFR were significantly decreased in breast cancer cells, confirmed by immunostaining and immunoprecipitation. We overexpressed MGAT3 in breast cancer MDA-MB-231 cells, and overexpression of MGAT3 significantly enhanced the bisecting N-GlcNAc on EGFR and suppressed the EGFR/Erk signaling, which further resulted in the reduction of migratory ability, cell proliferation, and clonal formation. Taken together, we conclude that bisecting N-GlcNAc on EGFR inhibits malignant phenotype of breast cancer via down-regulation of EGFR/Erk signaling.

Comparative Membrane N-Glycomics of Different Breast Cancer Cell Lines To Understand Breast Cancer Brain Metastasis

The mechanism of brain metastatic breast cancer has gained attention because of its increased incidence rate and its low survival rate. Aberrant protein glycosylation is thought to be a contributing factor in this metastatic mechanism, in which metastatic cancer cells can pass through the blood-brain barrier (BBB). The cell membrane is the outermost layer of a cell and in direct contact with the environment and with other cells, making membrane glycans especially important in many biological processes that include mediating cell-cell adhesion, cell signaling, and interactions. Thus, membrane glycomics has attracted more interest for a variety of disease studies in recent years. To reveal the role that membrane N-glycans play in breast cancer brain metastasis, in this study, membrane enrichment was achieved by ultracentrifugation. Liquid chromatography-tandem mass spectrometry was employed to analyze enriched membrane N-glycomes from five breast cancer cell lines and one brain cancer cell line. Relative quantitative glycomic data from each cell line were compared to MDA-MB-231BR, which is the brain-seeking cell line. The higher sialylation level observed in MDA-MB-231BR suggested the importance of sialylation as it might assist with cell invasion and the penetration of the BBB. Some highly sialylated N-glycans, such as HexNAc₅Hex₆DeoxyHex₁NeuAc₃ and HexNAc₆Hex₇DeoxyHex₁NeuAc₃, exhibited higher abundances in 231BR, indicating their possible contributions to breast cancer brain metastasis as well as their potential to be indicators for the breast cancer brain metastasis.

Engineering of a Lectibody Targeting High-Mannose-Type Glycans of the HIV Envelope

High-mannose-type glycans (HMGs) are aberrantly enriched on HIV envelope glycoproteins. However, there is currently no drug selectively targeting HIV-associated HMGs. Here, we describe a novel HMG-targeting "lectibody," a recombinant Fc-fusion protein comprising human IgG1 Fc and a novel actinohivin lectin variant (Avaren) obtained by structure-guided modifications for improved overall surface charge properties (AvFc). AvFc was engineered and produced using a rapid and scalable plant-based transient overexpression system. The lectibody exhibited potent antiviral activity against HIV-1 groups M and O primary viruses, as well as HIV-2 and simian immunodeficiency virus (SIV) strains, without affecting normal human blood cells. Furthermore, the lectibody induced Fc-mediated cell killing activity against HIV-1-infected cells and selectively recognized SIVmac239-infected macaque mesenteric lymph node cells in vitro. AvFc showed an extended serum half-life in rats and rhesus macaques, while no discernible toxicity was observed upon repeated systemic dosing in mice. These results highlight AvFc's potential as a biotherapeutic targeting HIV-associated HMGs of cell-free virions, as well as productively infected cells, providing a foundation for new anti-HIV strategies. Efficient and cost-effective bioproduction in greenhouse facilities may open unique possibilities for further development of AvFc.

Glycosylation and its implications in breast cancer

Introduction: For decades, the role of glycans and glycoproteins in the progression of breast cancer and other cancers have been evaluated. Through extensive studies focused on elucidating the biological functions of glycosylation, researchers have been able to implicate alterations in these functions to tumor formation and metastasis. Areas covered: In this review, we summarize how changes in glycosylation are associated with tumorigenesis, with emphasis on breast cancers. An overview of the changes in N-linked and O-linked glycans associated with breast cancer tumors and biofluids are described. Recent advances in glycomics are emphasized in the context of continuing to decipher the glycosylation changes associated with breast cancer progression. Expert opinion: While changes in glycosylation have been studied in breast cancer for many years, the clinical relevance of these studies has been limited. This reflects the inherent biological and clinical heterogeneity of breast cancers. Glycomics analysis lags behind the advances in genomics and proteomics, but new approaches are emerging. A summary of known glycosylation changes associated with breast cancer is necessary to implement new findings in the context of clinical outcomes and therapeutic strategies. A better understanding of the dynamics of tumor and immune glycosylation is critical to improving emerging immunotherapeutic treatments.

Mannose-Specific Lectins from Marine Algae: Diverse Structural Scaffolds Associated to Common Virucidal and Anti-Cancer Properties

To date, a number of mannose-specific lectins have been isolated and characterized from seaweeds, especially from red algae. In fact, man-specific seaweed lectins consist of different structural scaffolds harboring a single or a few carbohydrate-binding sites which specifically recognize mannose-containing glycans. Depending on the structural scaffold, man-specific seaweed lectins belong to five distinct structurally-related lectin families, namely (1) the griffithsin lectin family (β-prism I scaffold); (2) the Oscillatoria agardhii agglutinin homolog (OAAH) lectin family (β-barrel scaffold); (3) the legume lectin-like lectin family (β-sandwich scaffold); (4) the Galanthus nivalis agglutinin (GNA)-like lectin family (β-prism II scaffold); and, (5) the MFP2-like lectin family (MFP2-like scaffold). Another algal lectin from Ulva pertusa, has been inferred to the methanol dehydrogenase related lectin family, because it displays a rather different GlcNAc-specificity. In spite of these structural discrepancies, all members from the five lectin families share a common ability to specifically recognize man-containing glycans and, especially, high-mannose type glycans. Because of their mannose-binding specificity, these lectins have been used as valuable tools for deciphering and characterizing the complex mannose-containing glycans from the glycocalyx covering both normal and transformed cells, and as diagnostic tools and therapeutic drugs that specifically recognize the altered high-mannose N-glycans occurring at the surface of various cancer cells. In addition to these anti-cancer properties, man-specific seaweed lectins have been widely used as potent human immunodeficiency virus (HIV-1)-inactivating proteins, due to their capacity to specifically interact with the envelope glycoprotein gp120 and prevent the virion infectivity of HIV-1 towards the host CD4+ T-lymphocyte cells in vitro.

Development and characterization of a stable bovine intestinal sub-epithelial myofibroblast cell line from ileum of a young calf

Intestinal sub-epithelial myofibroblasts (ISEMFs) are mesenchymal cells that do not express cytokeratin but express α-smooth muscle actin and vimentin. Despite being cells with diverse functions, there is a paucity of knowledge about their origin and functions primarily due to the absence of a stable cell line. Although myofibroblast in vitro models for human, mouse, and pig are available, there is no ISEMF cell line available from young calves. We isolated and developed an ileal ISEMF cell line from a 2-d-old calf that expressed α-smooth muscle actin and vimentin but no cytokeratin indicating true myofibroblast cells. To overcome replicative senescence, we immortalized primary cells with SV40 large T antigen. We characterized and compared both primary and immortalized ileal ISEMF cells for surface glycan and Toll-like-receptor (TLR) expression by lectin-binding assay and real-time quantitative PCR (RT-qPCR) assay respectively. SV40 immortalization significantly decreased surface lectin binding for lectins GSL-I, PHA-L, ECL, Jacalin, Con-A, LCA, and LEL. Both cell types expressed TLRs 1-9 and showed no significant differences in TLR expression. Thus, these cells can be useful in vitro model to study ISEMF's origin, physiology, and functions.

Comprehensive N-Glycome Profiling of Cells and Tissues for Breast Cancer Diagnosis

Aberrant protein glycosylation is observed in the progression of many types of diseases, including different cancers. In this study, we assess differential N-glycan patterns of human breast cancer cells and tissues by PGC-ESI-MS/MS. Compared with mammary epithelial cells, high-mannose glycans were significantly elevated in breast cancer cells. However, the alteration of N-glycans in tissues was more obvious than that in cells. Sixty-three kinds of different N-glycans were stably identified, and 38 types of them exhibited significant differences between para-carcinoma and breast cancer tissues. High-mannose glycans and core-fucosylated glycans were increased in the breast cancer tissues, while bisected glycans and sialylated glycans were decreased. Moreover, a total of 27 types of N-glycans displayed evident differences between benign breast tumor and breast cancer tissues, and most of them including bisected and sialylated glycans exhibited decreased relative abundances in cancer tissues. Overall, three high-mannose N-glycans (F0H6N2S0, F0H7N2S0, F0H8N2S0) exhibited significant diagnostic accuracy in both breast cancer cells and tissues, suggesting their potential role in biomarkers. Furthermore, a negative correlation between sialylated glycans and age of patients was identified. In conclusion, our results may be beneficial to understand the role that N-glycan plays on the progression of breast cancer and propose potential diagnostic biomarkers.

Metabolic profiling analysis upon acylcarnitines in tissues of hepatocellular carcinoma revealed the inhibited carnitine shuttle system caused by the downregulated carnitine palmitoyltransferase 2

The carnitine shuttle system (CSS) plays a crucial role in the transportation of fatty acyls during fatty acid β-oxidation for energy supplementation, especially in cases of high energy demand, such as in cancer. In this study, to systematically characterize alterations of the CSS in hepatocellular carcinoma (HCC), acylcarnitine metabolic profiling was carried out on 80 pairs of HCC tissues and adjacent noncancerous tissues (ANTs) by using ultra-performance liquid chromatography coupled to mass spectrometry. Twenty-four acylcarnitines classified into five categories were identified and characterized between HCCs and ANTs. Notably, increased saturated long-chain acylcarnitines (LCACs) and decreased short- and medium-chain acylcarnitines (S/MCACs) were simultaneously observed in HCC samples. Subsequent correlation network and heatmap analysis indicated low correlations between LCACs and S/MCACs. The mRNA and protein expressions of carnitine palmitoyltransferase 2 (CPT2) was significantly downregulated in HCC samples, whereas CPT1A expression was not significantly changed. Correspondingly, the relative levels of S/MCACs were reduced and those of LCACs were increased in BEL-7402/CPT2-knockdown cells compared to negative controls. Both results suggested that decreased shuttling efficiency in HCC might be associated with downregulation of CPT2. In addition, decreases in the mRNA expression of acetyl-CoA acyltransferase 2 were also observed in HCC tissues and BEL-7402/CPT2-knockdown cells, suggesting potential low β-oxidation efficiency, which was consistent with the increased expression of stearoyl-CoA desaturase 1 in both samples. The systematic strategy applied in our study illustrated decreased shuttling efficiency of the carnitine shuttle system in HCC and can provide biologists with an in-depth understanding of β-oxidation in HCC.

Comparative Glycomics Study of Cell-Surface N-Glycomes of HepG2 versus LO2 Cell Lines

Cell-surface N-glycans play important roles in both inter- and intracellular processes, including cell adhesion and development, cell recognition, as well as cancer development and metastasis; detailed structural characterization of these N-glycans is thus paramount. Here we report our comparative N-glycomics study of cell-surface N-glycans of the hepatocellular carcinoma (HCC) HepG2 cells vs the normal liver LO2 cells. With sequential trypsin digestion of proteins, C18 depletion of peptides without glycosylation, PNGase F digestion of N-glycopeptides, PGC enrichment of N-glycans, CH₃I permethylation of the enriched N-glycans, cell-surface N-glycomes of the HepG2 and LO2 cells were analyzed using C18-RPLC-MS/MS (HCD). With spectrum-level FDR no bigger than 1%, 351 and 310 N-glycans were identified for HepG2 and LO2, respectively, with comprehensive structural information (not only monosaccharide composition, but also sequence and linkage) by N-glycan database search engine GlySeeker. The percentage of hybrid N-glycans with tetra-antennary structures was substantially increased in the HepG2 cells. This comprehensive discovery study of differentially expressed cell-surface N-glycans in HepG2 vs LO2 serves as a solid reference for future validation study of glycosylation markers in HCC.

Extracellular Processing of Lysyl Oxidase-like 2 and Its Effect on Amine Oxidase Activity

Overexpression of lysyl oxidase-like 2 (LOXL2) is associated with several hepatic and vascular fibrotic diseases and tumor progression in some aggressive cancers. Secreted LOXL2 promotes extracellular matrix cross-linking by catalyzing the oxidative deamination of peptidyl lysine. A great deal remains to be learned about the post-translational modifications of LOXL2, including whether such modifications modulate enzymatic and disease-promoting activities; such knowledge would inform the development of potential therapies. We discovered that upon secretion in cell culture, LOXL2 undergoes proteolytic processing of the first two of four scavenger receptor cysteine-rich domains at the N-terminus. A similar pattern of processing was also evident in tissue extracts from an invasive ductal carcinoma patient. Processing occurred at ³¹⁴Arg-³¹⁵Phe-³¹⁶Arg-³¹⁷Lys↓-³¹⁸Ala-, implicating proprotein convertases. siRNA-mediated knockdown of proprotein convertases (furin, PACE4, and PC5/6), as well as incubation with their recombinant forms, showed that PACE4 is the major protease that acts on extracellular LOXL2. Unlike LOX, which requires cleavage of its propeptide for catalytic activation, cleavage of LOXL2 was not essential for tropoelastin oxidation or for cross-linking of collagen type IV in vitro. However, in the latter case, processing enhanced the extent of collagen cross-linking ∼2-fold at ≤10 nM LOXL2. These results demonstrate an important difference in the regulatory mechanisms for LOX and LOXL2 catalytic activity. Moreover, they pave the way for further studies of potential differential functions of LOXL2 isoforms in fibrosis and tumor progression.

Tunicamycin enhances the suppressive effects of cisplatin on lung cancer growth through PTX3 glycosylation via AKT/NF-κB signaling pathway

Long pentraxin-3 (PTX3) is an inflammatory molecule related to cancer proliferation, invasion, and metastasis. Many studies have highlighted the significance of glycosylated molecules in immune modulation, inflammation and cancer progression. Moreover, aberrant glycosylation of cancer cells is linked to chemoresistance. This study aimed to develop effective therapeutic strategies for deglycosylation of PTX3 (dePTX3) in order to enhance chemosensitivity to cisplatin (Cis) in lung cancer treatment. The A549 and SPCA1 cells were used to determine the role of PTX3 glycosylation in lung cancer growth. Our results revealed that PTX3 was higher in both human lung cancer tissues and serum in comparison with control. Furthermore, we found that deglycosylated PTX3 (dePTX3) by tunicamycin (TM), which is N-glycan precursor biosynthesis blocker, and PNGase F significantly reduced the survival and migration of lung cancer cells. To further confirm this, we also generated glycosylation-site mutant of PTX3 (mPTX3) to characterize the loss of glyco-function. dePTX3 and TM enhanced the suppressive effects of Cis on lung cancer cell growth, migration and invasion compared to individual treatment. Treatment with a combination of TM and Cis significantly inactivated AKT/NF-κB signaling pathway and induced apoptosis. In conclusion, these findings suggest that PTX3 is an important mediator of lung cancer progression, and dePTX3 by TM enhances the anticancer effects of Cis. The deglycosylation in chemotherapy may represent a potential novel therapeutic strategy against lung cancer.

Glycosylation and metastases

The change of cellular glycosylation is one of the key events in malignant transformation and neoplastic progression, and tumor-related glycosylation alterations are promising targets in both tumor diagnosis and therapy. Both malignant transformation and neoplastic progression are the consequence of gene expression alterations and alterations in protein expression. Micro environmental factors such as extracellular matrix (ECM) also play an important role in their growth and metastasis. Tumor-associated glycans are important biomarker candidates for cancer diagnosis and prognosis, and analytical methods for their detection were developed recently. Glycoproteomics that use mass spectrometry for identification of cancer antigens and structural analysis of glycans play a key role in the investigation of changes of glycosylation during malignant transformation and tumor development and metastasis. Deep understanding of glycan remodeling in cancer and the role of glycosyltransferases that are involved in this process will require a detailed profiling of glycosylation patterns of tumor cells, and corresponding analytical methods for their detection were developed.

Reduced mannosidase MAN1A1 expression leads to aberrant N-glycosylation and impaired survival in breast cancer

BACKGROUND

Alterations in protein glycosylation have been related to malignant transformation and tumour progression. We recently showed that low mRNA levels of Golgi alpha-mannosidase MAN1A1 correlate with poor prognosis in breast cancer patients.

METHODS

We analysed the role of MAN1A1 on a protein level using western blot analysis (n=105) and studied the impact of MAN1A1-related glycosylation on the prognostic relevance of adhesion molecules involved in breast cancer using microarray data (n=194). Functional consequences of mannosidase inhibition using the inhibitor kifunensine or MAN1A1 silencing were investigated in breast cancer cells in vitro.

RESULTS

Patients with low/moderate MAN1A1 expression in tumours showed significantly shorter disease-free intervals than those with high MAN1A1 levels (P=0.005). Moreover, low MAN1A1 expression correlated significantly with nodal status, grading and brain metastasis. At an mRNA level, membrane proteins ALCAM and CD24 were only significantly prognostic in tumours with high MAN1A1 expression. In vitro, reduced MAN1A1 expression or mannosidase inhibition led to a significantly increased adhesion of breast cancer cells to endothelial cells.

CONCLUSIONS

Our study demonstrates the prognostic role of MAN1A1 in breast cancer by affecting the adhesive properties of tumour cells and the strong influence of this glycosylation enzyme on the prognostic impact of some adhesion proteins.

Increased expression of the high-mannose M6N2 and NeuAc3H3N3M3N2F tri-antennary N-glycans in cholangiocarcinoma

Changes in protein glycosylation have been reported in various types of cancer, including cholangiocarcinoma (CCA). Nanospray ionization-linear ion trap mass spectrometry (NSI-MSⁿ) was used in the present study to determine the comparative structural glycomics of the N-linked glycans in the serum of patients with CCA compared with healthy controls. A total of 5 high-mannose and 4 complex N-linked glycans were detected. Mannose₇-N-acetyl-glucosamine₂ was the most abundant structure among the high-mannose types (control 12.12±2.54 vs. CCA 9.27±2.66%), whereas NeuAc2H2N2M3N2 predominated the complex types (control 61.17±2.55 vs. CCA 64.68±4.23%). The expression of 3 different N-glycans differed significantly between the CCA cases and controls. These included mannose₆-N-acetyl-glucosamine₂ (P=0.044), mannose₉-N-acetyl-glucosamine₂ (Ρ=0.030) and NeuAc3H3N3M3N2F (Ρ=0.002). These three glycan structures may therefore be associated with tumor progression in CCA and may be useful for its diagnosis.

High mannose N-glycan binding lectin from Remusatia vivipara (RVL) limits cell growth, motility and invasiveness of human breast cancer cells

Breast cancer known for its high metastatic potential is responsible for large mortality rate amongst women; hence it is imperative to search for effective anti-metastatic molecules despite anticancer drugs. The current study describes the potential of Remusatia vivipara lectin (RVL), inducing apoptosis in breast cancer cells there by limiting motility and invasiveness. RVL binds to the cell surface glycans of MDA-MB-468 and MCF-7 cells, exhibiting strong glycan mediated cytotoxic effect, but show marginal effect on non-tumorigenic MCF-10A cells. RVL elicits increased cellular stress, apoptotic vacuoles and nuclear disintegration in both MDA-MB-468 and MCF-7 cells accompanied by depletion of G0/G1, S and G2/M phases. Lectin interaction induced production of reactive oxygen species through altering mitochondrial membrane potential progressing to apoptosis. Further, RVL strongly elicited reproductive cell death in MDA-MB-468 cells and showed strong inhibitory effect on neovascularization demonstrated in chorioallantoic membrane assay. Treatment of MDA-MB-468 cells with RVL, suppress the motility and invasive property as shown by scratch wound heal and Boyden chamber transwell assays respectively. These results provide an insight into significance of interaction of RVL with specific cell surface high mannose N-glycans resulting in curtailing the metastatic ability of cancer cells.

Role of protein glycosylation in cancer metastasis

Although altered glycosylation has been detected in human cancer cells decades ago, only investigations in the last years have enormously increased our knowledge about the details of protein glycosylation and its role in tumour progression. Many proteins, which are heavily glycosylated, i.e. adhesion proteins or proteases, play an important role in cancer metastasis that represents the crucial and frequently life-threatening step in progression of most tumour types. Compared to normal tissue, tumour cells often show altered glycosylation patters with appearance of new tumour-specific antigens. In this review, we give an overview about the role of glycosylation in tumour metastasis, describing recent results about O-glycans, N-glycans and glycosaminoglycans. We show that glycan structures, glycosylated proteins and glycosylation enzymes have influence on different steps of the metastatic process, including epithelial-mesenchymal transition (EMT), migration, invasion/intravasation and extravasation of tumour cells. Regarding the important role of cancer metastasis for patients survival, further knowledge about the consequences of altered glycosylation patterns in tumour cells is needed which might eventually lead to the development of novel therapeutic approaches.

Identifying N-Glycan Biomarkers in Colorectal Cancer by Mass Spectrometry

Colorectal cancer (CRC) is one of the most prevalent cancers worldwide. Delineating biological markers (biomarkers) for early detection, when treatment is most effective, is key to prevention and long-term survival of patients. Development of reliable biomarkers requires an increased understanding of the CRC biology and the underlying molecular and cellular mechanisms of the disease. With recent advances in new technologies and approaches, tremendous efforts have been put in proteomics and genomics fields to deliver detailed analysis of the two major biomolecules, genes and proteins, to gain a more complete understanding of cellular systems at both genomic and proteomic levels, allowing a mechanistic understanding of the human diseases, including cancer, and opening avenues for identification of novel gene and protein based prognostic and therapeutic markers. Although the importance of glycosylation in modulating protein function has long been appreciated, glycan analysis has been complicated by the diversity of the glycan structures and the large number of potential glycosylation combinations. Driven by recent technological advances, LC-MS/MS based glycomics is gaining momentum in cancer research and holds considerable potential to deliver new glycan-based markers. In our laboratory, we investigated alterations in N-glycosylation associated with CRC malignancy in a panel of CRC cell lines and CRC patient tissues. In an initial study, LC-MS/MS-based N-glycomics were utilized to map the N-glycome landscape associated with a panel of CRC cell lines (LIM1215, LIM1899, and LIM2405). These studies were subsequently extended to paired tumor and nontumorigenic CRC tissues to validate the findings in the cell line. Our studies in both CRC cell lines and tissues identified a strong representation of high mannose and α2,6-linked sialylated complex N-glycans, which corroborate findings from previous studies in CRC and other cancers. In addition, certain unique glycan determinants such as bisecting β1,4-GlcNAcylation and α2,3-sialylation, identified in the metastatic (LIM1215) and aggressive (LIM2405) CRC cell lines, respectively, were shown to be associated with epidermal growth factor receptor (EGFR) expression status. In this Account, we will describe the mass spectrometry based N-glycomics approach utilized in our laboratory to accurately profile the cell- and tissue-specific N-glycomes associated with CRC. We will highlight altered N-glycosylation observed by our studies, consistent with findings from other cancer studies, and discuss how the observed alterations can provide insights into CRC pathogenesis, opening new avenues to identify novel disease-associated glycan markers.

Emerging roles of protein mannosylation in inflammation and infection

Proteins are frequently modified by complex carbohydrates (glycans) that play central roles in maintaining the structural and functional integrity of cells and tissues in humans and lower organisms. Mannose forms an essential building block of protein glycosylation, and its functional involvement as components of larger and diverse α-mannosidic glycoepitopes in important intra- and intercellular glycoimmunological processes is gaining recognition. With a focus on the mannose-rich asparagine (N-linked) glycosylation type, this review summarises the increasing volume of literature covering human and non-human protein mannosylation, including their structures, biosynthesis and spatiotemporal expression. The review also covers their known interactions with specialised host and microbial mannose-recognising C-type lectin receptors (mrCLRs) and antibodies (mrAbs) during inflammation and pathogen infection. Advances in molecular mapping technologies have recently revealed novel immuno-centric mannose-terminating truncated N-glycans, termed paucimannosylation, on human proteins. The cellular presentation of α-mannosidic glycoepitopes on N-glycoproteins appears tightly regulated; α-mannose determinants are relative rare glycoepitopes in physiological extracellular environments, but may be actively secreted or leaked from cells to transmit potent signals when required. Simultaneously, our understanding of the molecular basis on the recognition of mannosidic epitopes by mrCLRs including DC-SIGN, mannose receptor, mannose binding lectin and mrAb is rapidly advancing, together with the functional implications of these interactions in facilitating an effective immune response during physiological and pathophysiological conditions. Ultimately, deciphering these complex mannose-based receptor-ligand interactions at the detailed molecular level will significantly advance our understanding of immunological disorders and infectious diseases, promoting the development of future therapeutics to improve patient clinical outcomes.

Elevated level of serum glycoprotein bifucosylation and prognostic value in Chinese breast cancer

Aberrant glycosylation is highly associated with cancer progression. The aim of this study was to compare bifucosylated N-glycans in sera obtained from healthy controls and breast cancer patients, with the goal of identifying a potential indicator for monitoring the recurrence and metastasis of breast cancer. A unique structural pattern of bifucosylated N-glycan, with both core and antennary fucosylation, was identified in breast cancer patients. The spectrum of antennary fucosylation was a composite of the standard spectra of Lewis X and H2, indicating a mixture of the two epitopes. Permethylated N-glycans of the glycoproteins extracted from 91 breast cancer patients and 43 healthy controls were detected using linear ion-trap quadrupole-electrospray ionization mass spectrometry, which appeared to be a highly sensitive and useful approach in the detection and identification of N-glycans. To evaluate MS profile data, several statistical tools were applied, including Student'st-test, partial least squares discriminant analysis and receiver-operating characteristic curve. The results showed that the measurement of bifucosylation degree and CEA levels had an improved diagnostic performance compared with that of CEA alone. We compared the potential of bifucosylated N-glycan as an indicator of breast cancer recurrence with the current clinical biomarkers, i.e., CEA, CA 15-3 and CA125. The result revealed that, compared with CEA, CA 15-3 and CA125, the bifucosylation degree of N-glycans could be a more reliable indicator of breast cancer recurrence.

Preeclampsia transforms membrane N-glycome in human placenta

Posttranslational modifications (PTM) which accompany pathological conditions affect protein structure, characteristics and modulate its activity. Glycosylation is one of the most frequent PTM influencing protein folding, localisation and function. Hypertension is a common gestational complication, which can lead to foetal growth restriction (IUGR) and even to foetal or maternal death. In this work we focused on the impact of preeclampsia complicated with IUGR on placental membrane N-glycome. Results have shown that preeclampsia reduced fucosylation of placental glycans, increased the appearance of paucimannosidic and mannosidic structures with lower number of mannose residues and decreased the amount of glycans with more mannose residues. Since preeclampsia is tightly connected to IUGR, glycosylation changes were investigated also on the functional membrane receptors responsible for growth: insulin receptor and the type 1 insulin-like growth factor receptor (IR and IGF1R). It was found that IR present in the IUGR placenta contained significantly less α2,6-Sia. Therefore, glycans on placental membranes alter due to preeclampsia, but changes seen at the level of the entire N-glycome may be different from the changes detected at the level of a specific glycoprotein. The difference recorded due to pathology in one membrane molecule (IR) was not found in another homologous molecule (IGF1R). Thus, besides studying the glycosylation pattern of the entire placental membrane due to preeclampsia, it is inevitable to study directly glycoprotein of interest, as no general assumptions or extrapolations can be made.

Specific N-glycans of Hepatocellular Carcinoma Cell Surface and the Abnormal Increase of Core-α-1, 6-fucosylated Triantennary Glycan via N-acetylglucosaminyltransferases-IVa Regulation

Glycosylation alterations of cell surface proteins are often observed during the progression of malignancies. The specific cell surface N-glycans were profiled in hepatocellular carcinoma (HCC) with clinical tissues (88 tumor and adjacent normal tissues) and the corresponding serum samples of HCC patients. The level of core-α-1,6-fucosylated triantennary glycan (NA3Fb) increased both on the cell surface and in the serum samples of HCC patients (p < 0.01). Additionally, the change of NA3Fb was not influenced by Hepatitis B virus (HBV)and cirrhosis. Furthermore, the mRNA and protein expression of N-acetylglucosaminyltransferase IVa (GnT-IVa), which was related to the synthesis of the NA3Fb, was substantially increased in HCC tissues. Knockdown of GnT-IVa leads to a decreased level of NA3Fb and decreased ability of invasion and migration in HCC cells. NA3Fb can be regarded as a specific cell surface N-glycan of HCC. The high expression of GnT-IVa is the cause of the abnormal increase of NA3Fb on the HCC cell surface, which regulates cell migration. This study demonstrated the specific N-glycans of the cell surface and the mechanisms of altered glycoform related with HCC. These findings lead to better understanding of the function of glycan and glycosyltransferase in the tumorigenesis, progression and metastasis of HCC.

Integrated Transcriptomic and Glycomic Profiling of Glioma Stem Cell Xenografts

Bone marrow-derived human mesenchymal stem cells (BM-hMSCs) have the innate ability to migrate or home toward and engraft in tumors such as glioblastoma (GBM). Because of this unique property of BM-hMSCs, we have explored their use for cell-mediated therapeutic delivery for the advancement of GBM treatment. Extravasation, the process by which blood-borne cells—such as BM-hMSCs—enter the tissue, is a highly complex process but is heavily dependent upon glycosylation for glycan-glycan and glycan-protein adhesion between the cell and endothelium. However, in a translationally significant preclinical glioma stem cell xenograft (GSCX) model of GBM, BM-hMSCs demonstrate unequal tropism toward these tumors. We hypothesized that there may be differences in the glycan compositions between the GSCXs that elicit homing ("attractors") and those that do not ("non-attractors") that facilitate or impede the engraftment of BM-hMSCs in the tumor. In this study, glycotranscriptomic analysis revealed significant heterogeneity within the attractor phenotype and the enrichment of high mannose type N-glycan biosynthesis in the non-attractor phenotype. Orthogonal validation with topical PNGase F deglycosylation on the tumor regions of xenograft tissue, followed by nLC-ESI-MS, confirmed the presence of increased high mannose type N-glycans in the non-attractors. Additional evidence provided by our glycomic study revealed the prevalence of terminal sialic acid-containing N-glycans in non-attractors and terminal galactose and N-acetyl-glucosamine N-glycans in attractors. Our results provide the first evidence for differential glycomic profiles in attractor and non-attractor GSCXs and extend the scope of molecular determinates in BM-hMSC homing to glioma.

N-glycosylation controls the function of junctional adhesion molecule-A

Junctional adhesion molecule-A (JAM-A) is an adherens and tight junction protein expressed by endothelial and epithelial cells. JAM-A serves many roles and contributes to barrier function and cell migration and motility, and it also acts as a ligand for the leukocyte receptor LFA-1. JAM-A is reported to contain N-glycans, but the extent of this modification and its contribution to the protein's functions are unknown. We show that human JAM-A contains a single N-glycan at N185 and that this residue is conserved across multiple mammalian species. A glycomutant lacking all N-glycans, N185Q, is able to reach the cell surface but exhibits decreased protein half-life compared with the wild- type protein. N-glycosylation of JAM-A is required for the protein's ability to reinforce barrier function and contributes to Rap1 activity. We further show that glycosylation of N185 is required for JAM-A-mediated reduction of cell migration. Finally, we show that N-glycosylation of JAM-A regulates leukocyte adhesion and LFA-1 binding. These findings identify N-glycosylation as critical for JAM-A's many functions.

Tandem mass spectrometry of isomeric aniline-labeled N-glycans separated on porous graphitic carbon: Revealing the attachment position of terminal sialic acids and structures of neutral glycans

RATIONALE

Quantitative monitoring of changes in the N-glycome upon disease has gained significance in the context of biomarker discovery. Separation and quantification of isobaric glycan isomers can be attained by using high-performance liquid chromatography/electrospray ionization mass spectrometry (HPLC/ESI-MS). Collision-induced dissociation (CID)-based fragmentation of separated isobaric glycans is evaluated in respect to its potential of providing fragment ions specific for the linkage positions of terminal sialic acids and the presence of intersecting GlcNAc moieties, respectively.

METHODS

N-Glycans were labeled via reductive amination using (12)C6-aniline and (13)C6-aniline as isotope-coded labeling reagents. The differently labeled glycans were merged and separated into various species using a porous graphitic carbon (PGC) stationary phase. Identification of structural features of separated isobaric isomers was performed by CID-based tandem mass spectrometry (MS/MS) carried out in a quadrupole time-of-flight (QqTOF) or a quadrupole ion-trap (IT) mass spectrometer.

RESULTS

Working in the negative ion mode, new diagnostic CID fragment ions could be found that are indicative for the α2,6-type linkage of sialic acids. Other diagnostic ions, identified before as being indicative for the substitution of the 6-antenna, could be confirmed as being of relevance also in the case of aniline labeling. In the positive ion mode, CID fragment ions indicative for the structure of short neutral N-glycans were identified.

CONCLUSIONS

One new diagnostic ion specific for the linkage position of the terminal sialic acids and one for the presence of bisecting GlcNAc in N-glycans were identified. The aniline label introduced for improved relative quantitation in MS(1) was found not to significantly alter the CID fragmentation patterns that were reported previously by other authors for unlabeled/reduced glycans or for glycans with more polar labels.

Biosynthetic Machinery Involved in Aberrant Glycosylation: Promising Targets for Developing of Drugs Against Cancer

Cancer cells depend on altered metabolism and nutrient uptake to generate and keep the malignant phenotype. The hexosamine biosynthetic pathway is a branch of glucose metabolism that produces UDP-GlcNAc and its derivatives, UDP-GalNAc and CMP-Neu5Ac and donor substrates used in the production of glycoproteins and glycolipids. Growing evidence demonstrates that alteration of the pool of activated substrates might lead to different glycosylation and cell signaling. It is already well established that aberrant glycosylation can modulate tumor growth and malignant transformation in different cancer types. Therefore, biosynthetic machinery involved in the assembly of aberrant glycans are becoming prominent targets for anti-tumor drugs. This review describes three classes of glycosylation, O-GlcNAcylation, N-linked, and mucin type O-linked glycosylation, involved in tumor progression, their biosynthesis and highlights the available inhibitors as potential anti-tumor drugs.

In-depth N-glycome profiling of paired colorectal cancer and non-tumorigenic tissues reveals cancer-, stage- and EGFR-specific protein N-glycosylation

Glycomics may assist in uncovering the structure-function relationships of protein glycosylation and identify glycoprotein markers in colorectal cancer (CRC) research. Herein, we performed label-free quantitative glycomics on a carbon-liquid chromatography-tandem mass spectrometry-based analytical platform to accurately profile the N-glycosylation changes associated with CRC malignancy. N-Glycome profiling was performed on isolated membrane proteomes of paired tumorigenic and adjacent non-tumorigenic colon tissues from a cohort of five males (62.6 ± 13.1 y.o.) suffering from colorectal adenocarcinoma. The CRC tissues were typed according to their epidermal growth factor receptor (EGFR) status by western blotting and immunohistochemistry. Detailed N-glycan characterization and relative quantitation identified an extensive structural heterogeneity with a total of 91 N-glycans. CRC-specific N-glycosylation phenotypes were observed including an overrepresentation of high mannose, hybrid and paucimannosidic type N-glycans and an under-representation of complex N-glycans (P < 0.05). Sialylation, in particular α2,6-sialylation, was significantly higher in CRC tumors relative to non-tumorigenic tissues, whereas α2,3-sialylation was down-regulated (P < 0.05). CRC stage-specific N-glycosylation was detected by high α2,3-sialylation and low bisecting β1,4-GlcNAcylation and Lewis-type fucosylation in mid-late relative to early stage CRC. Interestingly, a novel link between the EGFR status and the N-glycosylation was identified using hierarchical clustering of the N-glycome profiles. EGFR-specific N-glycan signatures included high bisecting β1,4-GlcNAcylation and low α2,3-sialylation (both P < 0.05) relative to EGFR-negative CRC tissues. This is the first study to correlate CRC stage and EGFR status with specific N-glycan features, thus advancing our understanding of the mechanisms causing the biomolecular deregulation associated with CRC.

Comprehensive N-glycome profiling of cultured human epithelial breast cells identifies unique secretome N-glycosylation signatures enabling tumorigenic subtype classification

The secreted cellular sub-proteome (secretome) is a rich source of biologically active glycoproteins. N-Glycan profiling of secretomes of cultured cancer cells provides an opportunity to investigate the link between protein N-glycosylation and tumorigenesis. Utilizing carbon-LC-ESI-CID-MS/MS of protein released native N-glycans, we accurately profiled the secretome N-glycosylation of six human epithelial breast cells including normal mammary epithelial cells (HMEC) and breast cancer cells belonging to luminal A subtype (MCF7), HER2-overexpressing subtype (SKBR3), and basal B subtype (MDA-MB157, MDA-MB231, HS578T). On the basis of intact molecular mass, LC retention time, and MS/MS fragmentation, a total of 74 N-glycans were confidently identified and quantified. The secretomes comprised significant levels of highly sialylated and fucosylated complex type N-glycans, which were elevated in all cancer cells relative to HMEC (57.7-87.2% vs 24.9%, p < 0.0001 and 57.1-78.0% vs 38.4%, p < 0.0001-0.001, respectively). Similarly, other glycan features were found to be altered in breast cancer secretomes including paucimannose and complex type N-glycans containing bisecting β1,4-GlcNAc and LacdiNAc determinants. Subtype-specific glycosylation were observed, including the preferential expression of α2,3-sialylation in the basal B breast cancer cells. Pathway analysis indicated that the regulated N-glycans were biosynthetically related. Tight clustering of the breast cancer subtypes based on N-glycome signatures supported the involvement of N-glycosylation in cancer. In conclusion, we are the first to report on the secretome N-glycosylation of a panel of breast epithelial cell lines representing different subtypes. Complementing proteome and lipid profiling, N-glycome mapping yields important pieces of structural information to help understand the biomolecular deregulation in breast cancer development and progression, knowledge that may facilitate the discovery of candidate cancer markers and potential drug targets.

Differential site accessibility mechanistically explains subcellular-specific N-glycosylation determinants

Glycoproteins perform extra- and intracellular functions in innate and adaptive immunity by lectin-based interactions to exposed glyco-determinants. Herein, we document and mechanistically explain the formation of subcellular-specific N-glycosylation determinants on glycoproteins trafficking through the shared biosynthetic machinery of human cells. LC-MS/MS-based quantitative glycomics showed that the secreted glycoproteins of eight human breast epithelial cells displaying diverse geno- and phenotypes consistently displayed more processed, primarily complex type, N-glycans than the high-mannose-rich microsomal glycoproteins. Detailed subcellular glycome profiling of proteins derived from three breast cell lines (MCF7/MDA468/MCF10A) demonstrated that secreted glycoproteins displayed significantly more α-sialylation and α1,6-fucosylation, but less α-mannosylation, than both the intermediately glycan-processed cell-surface glycoproteomes and the under-processed microsomal glycoproteomes. Subcellular proteomics and gene ontology revealed substantial presence of endoplasmic reticulum resident glycoproteins in the microsomes and confirmed significant enrichment of secreted and cell-surface glycoproteins in the respective subcellular fractions. The solvent accessibility of the glycosylation sites on maturely folded proteins of the 100 most abundant putative N-glycoproteins observed uniquely in the three subcellular glycoproteomes correlated with the glycan type processing thereby mechanistically explaining the formation of subcellular-specific N-glycosylation. In conclusion, human cells have developed mechanisms to simultaneously and reproducibly generate subcellular-specific N-glycosylation using a shared biosynthetic machinery. This aspect of protein-specific glycosylation is important for structural and functional glycobiology and discussed here in the context of the spatio-temporal interaction of glyco-determinants with lectins central to infection and immunity.