A strategy to reveal potential glycan markers from serum glycoproteins associated with breast cancer progression

Linkage specific fucosylation of alpha-1-antitrypsin in liver cirrhosis and cancer patients: implications for a biomarker of hepatocellular carcinoma

Background

We previously reported increased levels of protein-linked fucosylation with the development of liver cancer and identified many of the proteins containing the altered glycan structures. One such protein is alpha-1-antitrypsin (A1AT). To advance these studies, we performed N-linked glycan analysis on the five major isoforms of A1AT and completed a comprehensive study of the glycosylation of A1AT found in healthy controls, patients with hepatitis C- (HCV) induced liver cirrhosis, and in patients infected with HCV with a diagnosis of hepatocellular carcinoma (HCC).

Methodology/Principal Findings

Patients with liver cirrhosis and liver cancer had increased levels of triantennary glycan-containing outer arm (α-1,3) fucosylation. Increases in core (α-1,6) fucosylation were observed only on A1AT from patients with cancer. We performed a lectin fluorophore-linked immunosorbent assay using Aleuria Aurantia lectin (AAL), specific for core and outer arm fucosylation in over 400 patients with liver disease. AAL-reactive A1AT was able to detect HCC with a sensitivity of 70% and a specificity of 86%, which was greater than that observed with the current marker of HCC, alpha-fetoprotein. Glycosylation analysis of the false positives was performed; results indicated that these patients had increases in outer arm fucosylation but not in core fucosylation, suggesting that core fucosylation is cancer specific.

Conclusions/Significance

This report details the stepwise change in the glycosylation of A1AT with the progression from liver cirrhosis to cancer and identifies core fucosylation on A1AT as an HCC specific modification.

A quantitative investigation of fucosylated serum glycoproteins with application to esophageal adenocarcinoma

Although glycoproteomic studies provide unique opportunities for cancer research, it has been necessary to develop specific methods for analysis of oncologically interesting glycoproteins. We describe a general, multimethodological approach for quantitative glycoproteomic analysis of fucosylated glycoproteins in human blood serum. A total of 136 putative fucosylated glycoproteins were identified with very high confidence in three clinically relevant sample pools (N=5 for each), with a mean CV of 3.1% observed for replicate analyses. Two samples were collected from subjects diagnosed with esophagus disease states, high-grade dysplasia plus esophageal adenocarcinoma, while the third sample was representative of a disease-free condition. Some glycoproteins, observed to be significantly upregulated in esophageal adenocarcinoma, i.e. more than twofold higher than in the disease-free condition, are briefly discussed. Further investigation will be necessary to validate these findings; however, the method itself is demonstrated to be an effective tool for quantitative glycoproteomics of clinical samples.

Levels of specific glycans significantly distinguish lymph node-positive from lymph node-negative breast cancer patients

One of the most urgent requirements in breast cancer is the development of a blood-based test for early detection and prognosis. Previously published results found a significant difference between specific glycan levels in patients with advanced breast cancer and healthy controls. The aim of this investigation was to address a more clinically relevant problem, i.e., whether the measurement of specific glycans could identify women with aggressive disease at an early stage. In order to reduce potential bias in this study, blood samples from patients were collected, stored and analyzed in a similar manner. Agalactosyl biantennary glycans (FA2) and glycans containing the sialyl Lewis x epitope (A3F1G1 and A2F1G1) were measured using high throughput normal-phase high-performance liquid chromatography in combination with exoglycosidase digestions in sera from 52 patients with early breast cancer (21 with lymph node-negative and 20 with lymph node-positive disease) and 134 women with benign breast disease. The combined levels of the glycans were significantly higher in patients with lymph node metastases compared to women without these metastases. Lymph node status is the single most important determinant of survival in early stage breast cancer. As high levels of these glycans were associated with nodal metastases, their measurement may provide a new non-invasive approach to determining prognosis in women with newly diagnosed breast cancer.

Chip-based reversed-phase liquid chromatography-mass spectrometry of permethylated N-linked glycans: a potential methodology for cancer-biomarker discovery

The study of protein glycosylation in biological fluids and tissues has substantial medical importance, as changes in glycan structures have now been associated with a number of diseases. Quantification of glycomic-profile changes is becoming increasingly important in the search for disease biomarkers. Here, we report a highly reproducible combination of a glycomic sample preparation/solid-phase derivatization of glycoprotein-derived N-linked glycans with their subsequent microchip-based separation and mass-spectrometric (MS) measurements. Following our previously described reductive beta-elimination for O-linked glycans with ammonia-borane complex to reduce N-linked structures, the N-linked alditol structures are effectively methylated in dimethylformamide medium to avoid artefacts in MS measurements. Reversed-phase microfluidic liquid chromatography (LC) of methylated N-linked oligosaccharide alditols resolved some closely related structures into regular retention increments, aiding in their structural assignments. Optimized LC gradients, together with nanospray MS, have been applied here in the quantitative measurements of N-linked glycans in blood serum, distinguishing breast cancer patients from control individuals.

Tumour-associated carbohydrate antigens in breast cancer

Glycosylation changes that occur in cancer often lead to the expression of tumour-associated carbohydrate antigens. In breast cancer, these antigens are usually associated with a poor prognosis and a reduced overall survival. Cellular models have shown the implication of these antigens in cell adhesion, migration, proliferation and tumour growth. The present review summarizes our current knowledge of glycosylation changes (structures, biosynthesis and occurrence) in breast cancer cell lines and primary tumours, and the consequences on disease progression and aggressiveness. The therapeutic strategies attempted to target tumour-associated carbohydrate antigens in breast cancer are also discussed.

Glycomic analysis of sialic acid linkages in glycans derived from blood serum glycoproteins

A number of alterations to the normal glycomic profile have been previously described for a number of diseases and disorders, thus underscoring the medical importance of studying the glycans associated with proteins present in biological samples. An important alteration in cancer progression is an increased level of alpha2,6-sialylation, which aids in increasing the metastatic potential of tumor cells. Here we report a glycomic method that selectively amidates alpha2,6-linked sialic acids, while those that are alpha2,3-linked undergo spontaneous lactonization. Following subsequent permethylation, MALDI-TOF MS analysis revealed that many sialylated glycans present on glycoproteins found in blood serum featured increased levels of alpha2,6-sialylation in breast cancer samples. On the basis of the altered ratios of alpha2,3-linked to alpha2,6-linked sialic acids, many of these glycans became diagnostically relevant when they did not act as such indicators when based on traditional glycomic profiling alone.

Identification of breast cancer biomarkers in transgenic mouse models: A proteomics approach

PURPOSE

Transgenic mouse models for cancer circumvent many challenges that hamper human studies aimed at biomarker discovery. Lower biological variances among mice combined with controllable factors such as food uptake and health status may enable the detection of more subtle protein expression differences. This is envisioned to result in the identification of biomarkers better discriminating cancer cases from controls.

EXPERIMENTAL DESIGN

The current study used two innovative mouse models for breast-cancer to identify new serum biomarkers. Multi-analyte profiling technique was used to analyze 70 proteins in individual serum samples of non-tumor and mammary tumor-bearing Tg.NK (MMTV/c-neu) mice.

RESULTS

A small set of proteins fully differentiated tumor samples from controls. These comprised osteopontin, interleukin-18, cystatin C and CD40 antigen. Comparison of protein expression in another breast-cancer mouse model, the humanized p53.R270H mice, showed common discriminatory expression of osteopontin. However, other biomarkers showed distinct expression in the two different breast-cancer models, indicating that different mammary tumor sub-types with respect to molecular and estrogen receptor status reveal divergent serum biomarker sets.

CONCLUSIONS AND CLINICAL RELEVANCE

The current study supports the concept that serum proteins can discriminate mammary tumor cases from controls, and yielded interesting biomarkers that need further testing and validation in human studies.

Alterations of insulin-like growth factor binding protein 3 (IGFBP-3) glycosylation in patients with breast tumours

OBJECTIVES

Insulin-like growth factor binding protein-3 (IGFBP-3) is an important modulator of development and progression of breast cancer as it regulates the amount of free, physiologically active IGF-I and IGF-II. Changes in the glycosylation pattern within IGFBP-3 may affect its interaction with ligands. The aim of this study was to investigate whether such changes occur during disease progression.

DESIGN AND METHODS

IGFBP-3 in serum samples from healthy women and from women with breast tumours was characterised in terms of its concentration (IRMA), glycosylation moiety (lectin-affinity chromatography) and distribution of molecular species (immunoblotting).

RESULTS

In patients with benign tumours the concentration and carbohydrate content of IGFBP-3 was unaltered compared to healthy women. In patients with malignant tumours in most cases these two parameters were unchanged, but there were women whose concentration of IGFBP-3 was reduced and its structure was altered. In non-surviving cancer patients the concentration of IGFBP-3 was significantly reduced and these molecules contained a greater amount of biantennary complex type N-glycans having more mannose, fucose, bisecting GlcNAc and terminal sialic acid residues.

CONCLUSION

Our results showed that breast cancer progression causes alterations of IGFBP-3 glycosylation. The extent of changes increases with breast cancer severity.

Consequences of the expression of sialylated antigens in breast cancer

Changes in cell surface glycosylation are common modifications that occur during oncogenesis, leading to the over-expression of tumour-associated carbohydrate antigens (TACA). Most of these antigens are sialylated and the increase of sialylation is a well-known feature of transformed cells. In breast cancer, expression of TACA such as sialyl-Lewis(x) or sialyl-Tn is usually associated with a poor prognosis and a decreased overall survival of patients. However, the specific role of these sialylated antigens in breast tumour development and aggressiveness is not clearly understood. These glycosylation changes result from the modification of the expression of genes encoding specific glycosyltransferases involved in glycan biosynthesis and the level of expression of sialyltransferase genes has been proposed to be a prognostic marker for the follow-up of breast cancer patients. Several human cellular models have been developed in order to explain the mechanisms by which carbohydrate antigens can reinforce breast cancer progression and aggressiveness. TACA expression is associated with changes in cell adhesion, migration, proliferation and tumour growth. In addition, recent data on glycolipid biosynthesis indicate an important role of G(D3) synthase expression in breast cancer progression. The aim of this review is to summarize our current knowledge of sialylation changes that occur in breast cancer and to describe the cellular models developed to analyze the consequences of these changes on disease progression and aggressiveness.

Glycosylation of liver acute-phase proteins in pancreatic cancer and chronic pancreatitis

PURPOSE

Glycosylation of acute-phase proteins (APP), which is partially regulated by cytokines, may be distinct in disease and provide useful tumour markers. Thus, we have examined the glycosylation of major serum APP in pancreatic cancer (PaC), chronic pancreatitis (CP) and control patients.

EXPERIMENTAL DESIGN

Using a specific anti-sialyl Lewis X antibody and N-glycan sequencing, we have determined glycosylation changes on α-1-acid glycoprotein (AGP), haptoglobin (HPT), fetuin (FET), α-1-antitrypsin (AT) and transferrin (TRF).

RESULTS

Increased levels of sialyl Lewis X (SLe(x) ) were detected on AGP in advanced PaC and CP and on HPT, FET, AT and TRF in CP. An increase in N-glycan branching was detected on AGP and HPT in the advanced stage of PaC and CP and on FET and TRF in the CP. A core fucosylated structure was increased on AGP and HPT only in the advanced PaC patients.

CONCLUSIONS AND CLINICAL RELEVANCE

Changes in APP SLe(x) and branching are probably associated with an inflammatory response because they were detected in both advanced PaC and CP patients and these conditions give rise to inflammation. On the contrary, the increase in APP core fucosylation could be cancer associated and the presence of this glycoform may give an advantage to the tumour.

Liver proteins as sensor of human malignancies and inflammation

In this review we would like to highlight the importance of acute-phase proteins as sensor of diseases. Both acute-phase protein levels and glycosylation have been reported to be altered in inflammation and other diseases including cancer. Factors that promote acute-phase protein synthesis and enhance the expression of specific glycosyltransferases, such as sialyltransferases and fucosyltransferases, may be up-regulated in some tumours and would explain the changes in acute-phase protein levels and the specific N-glycosylation modifications of some acute-phase proteins in cancer. However, further studies are required to define the potential clinical application of these acute-phase protein cancer-specific modifications as possible cancer diagnostic or monitoring tools.

Glycomics and disease markers

Glycomics is the comprehensive study of all glycans expressed in biological systems. The biosynthesis of glycan relies on a number of highly competitive processes involving glycosyl transferases. Glycosylation is therefore highly sensitive to the biochemical environment and has been implicated in many diseases including cancer. Recently, interest in profiling the glycome has increased owing to the potential of glycans for disease markers. In this regard, mass spectrometry is emerging as a powerful technique for profiling the glycome. Global glycan profiling of human serum based on mass spectrometry has already led to several potentially promising markers for several types of cancer and diseases.

N-glycosylation status of beta-haptoglobin in sera of patients with colon cancer, chronic inflammatory diseases and normal subjects

N-glycosylation status of purified beta-haptoglobin from sera of 17 patients, and from sera of 14 healthy volunteer subjects, was compared by blotting with various lectins and antibodies. Patients in this study were diagnosed as having colon cancer through histological examination of each tumor tissue by biopsy. Blotting index of serum beta-haptoglobin with Aleuria aurantia lectin (AAL) was clearly higher for cancer patients than for healthy subjects. No such distinction was observed for blotting with three other lectins and two monoclonal antibodies. To determine tumor-associated reactivity of AAL binding as compared to inflammatory processes in colonic tissues, beta-haptoglobin separated from sera of 5 patients with Crohn's disease (CD), and 4 patients with ulcerative colitis (UC), was studied. All these cases, except one case of UC, showed AAL index lower than that in cancer cases, similarly to healthy subjects. The higher AAL binding of beta-haptoglobin in colon cancer patients than in healthy subjects appeared to be due to alpha-L-fucosyl residue, since it was eliminated by bovine kidney alpha-fucosidase treatment. N-linked glycans of serum haptoglobin from colon cancer patients vs. healthy subjects were released by N-glycanase, fluorescence-labeled, and subjected to normal-phase high performance liquid chromatography (NP-HPLC). Glycan structures were determined based on glucose unit (GU) values and their changes upon sequential treatment with various exoglycosidases. Glycosyl sequences and their branching status of glycans from 14 cases of serum beta-haptoglobin were characterized. The identified glycans were sialylated or nonsialylated, bi-antennary or tri-antennary structures, with or without terminal fucosylation.

Protein modifications as potential biomarkers in breast cancer

A variety of post-translational protein modifications (PTMs) are known to be altered as a result of cancer development. Thus, these PTMs are potentially useful biomarkers for breast cancer. Mass spectrometry, antibody microarrays and immunohistochemistry techniques have shown promise for identifying changes in PTMs. In this review, we summarize the current literature on PTMs identified in the plasma and tumor tissue of breast-cancer patients or in breast cell lines. We also discuss some of the analytical techniques currently being used to evaluate PTMs.

Multiplexed antibody arrays for the discovery and validation of glycosylated protein biomarkers

Protein glycosylation, the enzymatic linkage of mono- and poly-saccharides to proteins, is a critical determinant of protein function; however, there is a lack of tools for studying the glycosylation of specific proteins in complex samples. A new type of antibody–lectin sandwich assay enables the measurement of the glycosylation of specific proteins that have been captured from complex samples using antibody arrays combined with lectin-based detection probes. Antibody–lectin sandwich arrays have the potential to expand our understanding of the role of glycans and protein glycosylation in disease and to identify and investigate new biomarkers for early detection, disease prognosis and therapeutic response prediction. While antibody–lectin sandwich arrays yield less-detailed structural information regarding protein glycosylation than other available methods, they do provide a simple and reproducible method for investigating changes in protein abundance and glycosylation of multiple proteins and can be easily applied to large or small sample sets. By profiling protein and glycan variations, new disease-associated glycan alterations can be identified and validated for use as biomarkers.

Glycomic analysis: an array of technologies

Carbohydrates encode biological information necessary for cellular function. The structural diversity and complexity of these sugar residues have necessitated the creation of novel methodologies for their study. This review highlights recent technological advancements that are starting to unravel the intricate web of carbohydrate biology. New methods for the analysis of both glycoconjugates and glycan structures are discussed. With the use of these innovative tools, the field of glycobiology is poised to take center-stage in the postgenomic era of modern biology and medicine.

The development of an integrated platform to identify breast cancer glycoproteome changes in human serum

Protein glycosylation represents one of the major post-translational modifications and can have significant effects on protein function. Moreover, changes in the carbohydrate structure are increasingly being recognized as an important modification associated with cancer etiology. In this report, we describe the development of a proteomics approach to identify breast cancer related changes in either concentration and/or the carbohydrate structures of glycoprotein(s) present in blood samples. Diseased and healthy serum samples were processed by an optimized sample preparation protocol using multiple lectin affinity chromatography (M-LAC) that partitions serum proteins based on glycan characteristics. Subsequently, three separate procedures, 1D SDS-PAGE, isoelectric focusing and an antibody microarray, were applied to identify potential candidate markers for future study. The combination of these three platforms is illustrated in this report with the analysis of control and cancer glycoproteomic fractions. Firstly, a molecular weight based separation of glycoproteins by 1D SDS-PAGE was performed, followed by protein, glycoprotein staining, lectin blotting and LC-MS analysis. To refine or confirm the list of interesting glycoproteins, isoelectric focusing (targeting sialic acid changes) and an antibody microarray (used to detect neutral glycan shifts) were selected as the orthogonal methods. As a result, several glycoproteins including alpha-1B-glycoprotein, complement C3, alpha-1-antitrypsin and transferrin were identified as potential candidates for further study.

Towards an integrated proteomic and glycomic approach to finding cancer biomarkers

Advances in mass spectrometry have had a great impact on the field of proteomics. A major challenge of proteomic analysis has been the elucidation of glycan modifications of proteins in complex proteomes. Glycosylation is the most structurally elaborate and diverse type of protein post-translational modification and, because of this, proteomics and glycomics have largely developed independently. However, given that such a large proportion of proteins contain glycan modifications, and that these may be important for their function or may produce biologically relevant protein variation, a convergence of the fields of glycomics and proteomics would be highly desirable. Here we review the current status of glycoproteomic efforts, focusing on the identification of glycoproteins as cancer biomarkers.