Perspectives on the significance of altered glycosylation of glycoproteins in cancer

Precise structural analysis of O-linked oligosaccharides in human serum

O-glycans are suitable targets as novel and useful tumor markers. The structures of O-glycans in human sera from four healthy controls were precisely analyzed to obtain the reference O-glycan database. O-glycans were prepared from sera by hydrazine treatment followed by fluorescent labeling with aminopyridine and identified using two-dimensional mapping, enzymatic digestion and mass spectrometry (MS) together with methanolysis and the use of newly synthesized sulfated oligosaccharides as standards. O-glycans, present at more than 0.01% of the total O-glycans, were analyzed, and 18 kinds of acidic and 2 kinds of neutral glycans were identified. NeuAcα2-3Galβ1-3N-acetylgalactosamine (GalNAc) (61-64%), NeuAcα2-3Galβ1-3(NeuAcα2-6)GalNAc (15-26%) and Galβ1-3GalNAc (6-14%) were major components while other sialylated glycans, Galβ1-3(NeuAcα2-6)GalNAc, Galβ1-4GlcNAcβ1-6(NeuAcα2-3Galβ1-3)GalNAc and NeuAcα2-3Galβ1-4GlcNAcβ1-6(NeuAcα2-3Galβ1-3)GalNAc were relatively minor components, accounting for ∼1-2%. Very minor glycans accounting for ∼0.01-0.1% of the total include (i) the neutral glycan, Galβ1-4GlcNAcβ1-6(Galβ1-3)GalNAc, (ii) sialylated glycans, having sialyl Tn antigen, agalacto and trisialylated structures, (iii) fucosylated glycans forming blood type H antigen, blood type A antigen, blood type B antigen, Lewis X antigen and sialyl Lewis X antigen and (iv) sulfated glycans, having 6-sulfo and 3'-sulfo structures. Two kinds of clinically applied tumor markers namely sialyl Tn antigen and sialyl Lewis X antigen in healthy controls sera were revealed to be present at ∼0.1-0.2% of the total. However, other markers such as CA19-9 and DU-PAN-2 were not found, suggesting the relative amounts of these glycans to be <0.01%. These detailed O-glycan profiles will help to find novel carbohydrate tumor markers.

Anticancer effect of bromelain with and without cisplatin or 5-FU on malignant peritoneal mesothelioma cells

Malignant peritoneal mesothelioma (MPM) is a rare neoplasm of the peritoneum, causally related to asbestos exposure. Nonspecific symptoms with a late diagnosis results in poor survival (<1 year). Treatment with cytoreductive surgery and hyperthermic intraperitoneal chemotherapy has improved survival in some patients (median 3-5 years). Hence, new therapies are urgently needed. MUC1 is a glycosylation-dependent protein that confers tumours with invasiveness, metastasis and chemoresistance. Bromelain (cysteine proteinase) hydrolyses glycosidic bonds. Therefore, we investigated the antitumour effect of bromelain on MUC1-expressing MPM cell lines. MUC1 expressions in cells were assessed using immunofluorescent probes with cells grown on cover slips and western blot analysis on cell lysates. The cell lines were treated with various concentrations of bromelain and after 4 and 72 h, their viability was assessed using standard sulforhodamine assays. The cells were also treated with combinations of bromelain and cytotoxic drugs (cisplatin or 5-FU) and their viability was assessed at 72 h. Finally, with western blotting, the effects of bromelain on cellular survival proteins were investigated. PET cells expressed more MUC1 compared with YOU cells. The cell viability of both PET and YOU cells was adversely affected by bromelain, with PET cells being slightly resistant. The addition of bromelain increased the cytotoxicity of cisplatin significantly in both cell lines. However, 5-FU with bromelain did not show any significant increase in cytotoxicity. Bromelain-induced cell death is by apoptosis and autophagy. Bromelain has the potential of being developed as a therapeutic agent in MPM.

Altered tumor-cell glycosylation promotes metastasis

Malignant transformation of cells is associated with aberrant glycosylation presented on the cell-surface. Commonly observed changes in glycan structures during malignancy encompass aberrant expression and glycosylation of mucins; abnormal branching of N-glycans; and increased presence of sialic acid on proteins and glycolipids. Accumulating evidence supports the notion that the presence of certain glycan structures correlates with cancer progression by affecting tumor-cell invasiveness, ability to disseminate through the blood circulation and to metastasize in distant organs. During metastasis tumor-cell-derived glycans enable binding to cells in their microenvironment including endothelium and blood constituents through glycan-binding receptors – lectins. In this review, we will discuss current concepts how tumor-cell-derived glycans contribute to metastasis with the focus on three types of lectins: siglecs, galectins, and selectins. Siglecs are present on virtually all hematopoietic cells and usually negatively regulate immune responses. Galectins are mostly expressed by tumor cells and support tumor-cell survival. Selectins are vascular adhesion receptors that promote tumor-cell dissemination. All lectins facilitate interactions within the tumor microenvironment and thereby promote cancer progression. The identification of mechanisms how tumor glycans contribute to metastasis may help to improve diagnosis, prognosis, and aid to develop clinical strategies to prevent metastasis.

Glycans in immune recognition and response

Glycans at the forefront of cells facilitate immune recognition processes. Cancer cells commonly present altered cell surface glycosylation, especially manifested in the expression of sialic acid at the termini of glycolipids and glycoproteins. Although tumor-associated carbohydrate antigens (TACAs) result in expression of altered-self, most such carbohydrates do not elicit strong humoral responses. Various strategies had been devised to elicit increased immunogenicity of such TACA aiming for potent immunotherapeutic antibodies or cancer vaccines. However some carbohydrates are immunogenic in humans and hold potential for novel glycotherapies. N-Glycolylneuraminic acid (Neu5Gc) is a foreign immunogenic sugar in humans originating from the diet (e.g., red meat) and subsequently expressed on the cell surface, especially accumulating on carcinoma. Consequently, the human immune system detects this non-self carbohydrate generating a broad anti-Neu5Gc antibody response. The co-existence of Neu5Gc/anti-Neu5Gc within humans spurs chronic inflammation mediated disease, including cancer. Concurrently, anti-Neu5Gc antibodies hold potential for novel targeted therapy. αGal is another foreign immunogenic carbohydrate antigen in humans and all humans have circulating anti-Gal antibodies. This review aims to describe the immunogenicity of Neu5Gc and its implications for human diseases, highlighting differences and similarities with αGal and its potential for novel targeted theranostics.

Investigating biomolecular recognition at the cell surface using atomic force microscopy

Probing the interaction forces that drive biomolecular recognition on cell surfaces is essential for understanding diverse biological processes. Force spectroscopy has been a widely used dynamic analytical technique, allowing measurement of such interactions at the molecular and cellular level. The capabilities of working under near physiological environments, combined with excellent force and lateral resolution make atomic force microscopy (AFM)-based force spectroscopy a powerful approach to measure biomolecular interaction forces not only on non-biological substrates, but also on soft, dynamic cell surfaces. Over the last few years, AFM-based force spectroscopy has provided biophysical insight into how biomolecules on cell surfaces interact with each other and induce relevant biological processes. In this review, we focus on describing the technique of force spectroscopy using the AFM, specifically in the context of probing cell surfaces. We summarize recent progress in understanding the recognition and interactions between macromolecules that may be found at cell surfaces from a force spectroscopy perspective. We further discuss the challenges and future prospects of the application of this versatile technique.

Lipopolysaccharide induces the interactions of breast cancer and endothelial cells via activated monocytes

The adhesion of circulating cancer cells to vascular endothelium is a key step in hematogenous metastasis. Cancer cell-endothelium interactions are mediated by cell adhesion molecules that can also be involved in the arrest of monocytes and other circulating leukocytes on endothelium in inflammation. Static and microfluidic flow adhesion assays as well as flow cytometry were conducted in this study to elucidate the role of monocytes, bacterial lipopolysaccharide (LPS), and histamine in breast cancer cell adhesion to vascular endothelial cells. Tumor necrosis factor-α (TNF-α) released from LPS-treated monocytes triggered the expression of intercellular cell adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) on endothelial cells. Histamine augmented the TNF-α effect, leading to a high number of arrested breast cancer cells under both static and shear flow conditions. LPS-treated monocytes were shown to enhance the arrest of breast cancer cells by anchoring the cancer cells to activated endothelial cells. This anchorage was achieved by binding cancer cell ICAM-1 to monocyte β2 integrins and binding endothelial ICAM-1 and VCAM-1 to monocyte β1 and β2 integrins. The results of this study imply that LPS is an important risk factor for cancer metastasis and that the elevated serum level of histamine further increases the risk of LPS-induced cancer metastasis. Preventing bacterial infections is essential in cancer treatment, and it is particularly vital for cancer patients affected by allergy.

Metastatic growth progression caused by PSGL-1-mediated recruitment of monocytes to metastatic sites

Tumor cell-derived selectin ligands mediate contact to the endothelium, platelets, and leukocytes through binding to selectins that facilitates metastasis. Here, we describe the mechanism of how endogenous (non-tumor derived) selectin ligands contribute to metastasis using α(1,3)fucosyltransferase 7 (Fuc-TVII(-/-))-deficient mice. Experimental metastasis of MC-38GFP and Lewis lung (3LL) carcinoma cells was attenuated in Fuc-TVII(-/-) mice, which express minimal amount of selectin ligands. We show that metastasis is dependent on selectin ligands carried on hematopoietic cells. P-selectin glycoprotein ligand-1 (PSGL-1) was identified as the major ligand facilitating monocyte accumulation at metastatic sites. Reduced recruitment of monocytes to metastasizing tumor cells in Fuc-TVII(-/-) mice correlated with attenuated metastasis. Adoptive transfer of Fuc-T7(+) monocytes rescued metastasis in Fuc-TVII(-/-) mice, indicating that selectin ligand-dependent recruitment of monocytes is required for cancer progression. Cytokine analysis in metastatic lungs revealed high expression of CCL2 in C57BL/6 mice that was significantly lower in Fuc-TVII(-/-) mice. The absence of monocyte recruitment in Fuc-TVII(-/-) mice correlated with increased apoptosis of tumor cells. Thus, the recruitment of monocytes to metastasizing tumor cells is facilitated by endogenous selectin ligands on monocytes that enable efficient tumor cell survival, extravasation, and metastasis.

Quantitative analysis of site-specific N-glycans on sera haptoglobin β chain in liver diseases

The site-specific characterization of N-glycans in glycoproteins with the potential of clinical application is important. In our previous report, the overall N-glycans of sera haptoglobin (Hp) β chain were found to be different in liver diseases. Hp β chain contains four potential sites of N-glycosylation. In this study, we investigated the potential change of N-glycans on Hp β chain in a site-specific fashion. Sera Hp β chain in healthy individuals as well as patients with hepatitis B virus (HBV), liver cirrhosis (LC) and hepatocellular carcinoma (HCC) were purified, digested and subjected to liquid chromatography-electrospray ionization-higher energy collision dissociation mass spectrometry, which allowed identification and structure determination of the glycopeptide, as well as the relative quantification of glycans present on each glycopeptide. The quantitative results revealed that the sialylation of NLFLN(207)HSEN(211)ATAK and the fucosylated structure at all glycopeptides increased significantly in LC and HCC patients compared with those in HBV patients and healthy individuals. A set of different N-glycan patterns of Hp β chain in various liver diseases has been determined. Thus, the sialylated and fucosylated glycoforms of Hp β chain might be related to early hepatocarcinogenesis and also might be useful as novel differential markers for LC and HCC patients.

Using a cell line breast cancer progression system to identify biomarker candidates

Secreted and plasma membrane glycoproteins are considered excellent candidates for disease biomarkers. Herein we describe the identification of secreted and plasma membrane glycoproteins that are differentially expressed among a family of three breast cancer cell lines that models the progression of breast cancer. Using two-dimensional liquid chromatography-tandem mass spectrometry we identified more than 40 glycoproteins that were differentially expressed in either the premalignant (MCF10AT) or the fully malignant (MCF10CA1a) cell lines of this model system. Comparative analysis revealed that the differentially expressed breast cancer progression-associated glycoproteins were among the most highly expressed in the malignant (MCF10CA1a) breast cancer cell line; a subset of these was detected only in the malignant line; and others were detected in the malignant line at levels 25 to 50 times greater than in the benign (MCF10A) line. Using the results from this model cell system as a guide, we then carried out glycoproteomic analyses of normal and cancerous breast tissue lysates. Eleven of the glycoproteins differentially expressed in the breast cell lines were identified in the tissue lysates. Among these glycoproteins, collagen alpha-1 (XII) chain was expressed at dramatically higher (~10-fold) levels in breast cancer than in normal tissue.

BIOLOGICAL SIGNIFICANCE

Identifying glycoproteins differentially expressed during cancer progression results in information on the biological processes and key pathways associated with cancer. In addition, new hypotheses and potential biomarkers result from these glycoproteomic studies. Our glycoproteomic analysis of this model of breast cancer provides a roadmap for future experimental interventions to further tease apart critical components of tumor progression.

Cell surface-specific N-glycan profiling in breast cancer

Aberrant changes in specific glycans have been shown to be associated with immunosurveillance, tumorigenesis, tumor progression and metastasis. In this study, the N-glycan profiling of membrane proteins from human breast cancer cell lines and tissues was detected using modified DNA sequencer-assisted fluorophore-assisted carbohydrate electrophoresis (DSA-FACE). The N-glycan profiles of membrane proteins were analyzed from 7 breast cancer cell lines and MCF 10A, as well as from 100 pairs of breast cancer and corresponding adjacent tissues. The results showed that, compared with the matched adjacent normal tissue samples, two biantennary N-glycans (NA2 and NA2FB) were significantly decreased (p <0.0001) in the breast cancer tissue samples, while the triantennary glycan (NA3FB) and a high-mannose glycan (M8) were dramatically increased (p = 0.001 and p <0.0001, respectively). Moreover, the alterations in these specific N-glycans occurred through the oncogenesis and progression of breast cancer. These results suggested that the modified method based on DSA-FACE is a high-throughput detection technology that is suited for analyzing cell surface N-glycans. These cell surface-specific N-glycans may be helpful in recognizing the mechanisms of tumor cell immunologic escape and could be potential targets for new breast cancer drugs.

Glycophenotype evaluation in cutaneous tumors using lectins labeled with acridinium ester

Background. Tumor cells show alterations in their glycosylation patterns when compared to normal cells. Lectins can be used to evaluate these glycocode changes. Chemiluminescence assay is an effective technique for quantitative analysis of proteins, nucleic acids, and carbohydrates due to its high sensitivity, specificity, and rapid testing. Objective. To use histochemiluminescence based on lectin conjugated to acridinium ester (AE) for the investigation of glycophenotype changes in cutaneous tumors. Methods. Concanavalin A (Con A), Peanut agglutinin (PNA), Ulex europaeus agglutinin-I (UEA-I), and Maackia amurensis agglutinin (MAA) were conjugated to acridinium ester. Biopsies of cutaneous tumors and normal skin were incubated with the lectins-AE, and chemiluminescence was quantified and expressed as Relative Light Units (RLU). Results. Actinic keratosis (AK), keratoacanthoma (KA), squamous cell carcinoma (SCC), and basal cell carcinoma (BCC) showed lower expression of α-D-glucose/mannose and α-L-fucose residues compared to normal tissue. Cutaneous tumors displayed higher expression of Gal-β(1-3)-GalNAc residues than normal tissue. AK and SCC exhibited higher expression of Neu5Ac-α(2,3)Gal residues than normal epidermis. KA and BCC showed equivalent RLU values compared to normal tissue. Conclusions. Lectin histochemiluminescence allowed quantitative assessment of the carbohydrate expression in cutaneous tissues, contributing to eliminate the subjectivity of conventional techniques used in the histopathological diagnosis.

α2,3-Sialyltransferase ST3Gal IV promotes migration and metastasis in pancreatic adenocarcinoma cells and tends to be highly expressed in pancreatic adenocarcinoma tissues

Sialyltransferases have received much attention recently as they are frequently up-regulated in cancer cells. However, the role played by each sialyltransferase in tumour progression is still unknown. α2,3-Sialyltransferases ST3Gal III and ST3Gal IV are involved in sialyl-Lewis(x) (SLe(x)) synthesis. Given that the role of ST3Gal III in pancreatic adenocarcinoma cells has been previously reported, in this study we have focused on investigating the role of ST3Gal IV in the acquisition of adhesive, migratory and metastatic capabilities and, secondly, in analyzing the expression of ST3Gal III and ST3Gal IV in pancreatic adenocarcinoma tissues versus control tissues. ST3Gal IV overexpressing pancreatic adenocarcinoma MDAPanc-28 cell lines were generated. They showed a heterogeneous increase in SLe(x), and enhanced E-selectin adhesion and migration. Furthermore, when injected into nude mice, increased metastasis and decreased survival were found in comparison with controls. The behaviour of MDAPanc-28 ST3Gal IV overexpressing cells in these processes was similar to the already reported MDAPanc-28 ST3Gal III overexpressing cells. Furthermore, pancreatic adenocarcinoma tissues tended to express high levels of ST3Gal III and ST3Gal IV together with other fucosyltransferase genes FUT3 and FUT6, all involved in the last steps of sialyl-Lewis(x) biosynthesis. In conclusion, both α2,3-sialyltransferases are involved in key steps of pancreatic tumour progression processes and are highly expressed in most pancreatic adenocarcinoma tissues.

Autoantibodies targeting tumor-associated antigens in metastatic cancer: Sialylated IgGs as candidate anti-inflammatory antibodies

In addition to the well-established effector functions of IgGs, including direct cytotoxicity and antibody-dependent cellular cytotoxicity, some populations of IgGs may exert anti-inflammatory effects. Here, we describe a population of antibodies that form in the natural course of metastatic cancer and contain glycans that terminate with sialic acid. We demonstrate that both the titer of these antibodies and their level of sialylation are relatively stable throughout the progression of metastatic melanoma. The sialylation pattern of these antibodies somehow correlates with their specificity for tumor-associated antigens, as IgGs targeting several antigens associated with infectious agents are relatively poor of sialic acid. We also show that some antibodies targeting the melanoma-associated antigen NY-ESO-1 bind to the human C-type lectin CD209 (DC-SIGN). We propose that these antibodies are candidate anti-inflammatory antibodies. The presence of anti-inflammatory antibodies in cancer patients may explain, at least in part, why tumors persist and spread in the host despite strong tumor-specific humoral responses. The elucidation of the cellular and molecular pathways involved in the induction of anti-inflammatory antibodies specific for tumor-associated antigens and their function may yield important insights into how tumors evade immune detection and progress.

Quantum dot nanometal surface energy transfer based biosensing of sialic acid compositions and linkages in biological samples

Current methods for analyzing sialic acid diversity in modifications and linkages require multistep processing, derivatization, and chromatographic analyses. We here report a single-step optical method for identification and quantification of different compositions of sialoglycans on glycoproteins and in serum. This was achieved by measuring and quantifying nanometal surface energy transfer (NSET) signals between quantum dots and gold nanoparticles bound to specific sialic acid binding proteins (SBPs) and sialic acid moieties, respectively. The biosensing process is based on the NSET turn-on by external sialic acid species that compete for binding to the SBPs. Selectivity of the biosensor toward sialoglycans can be designed to detect the total amount, glycosylation linkages (α2-6 vs α2-3), and modifications (9-O-acetyl and N-glycolyl groups) in the samples. This nanobiosensor is a prototype expected to achieve limits of the detection down to the micromolar range for high-throughput quantification and analysis of different compositions of sialoglycans present in biological or biomedical samples.

Glycoproteomic analysis of tissues from patients with colon cancer using lectin microarrays and nanoLC-MS/MS

The current study evaluated the glycoproteomic profile of tissues from colon cancer patients. The lectin microarray was first performed to compare the glycoprotein profiles between colon cancer and matched normal tissues. Level of N-acetylglucosamine (GlcNAc) that Solanum tuberosum lectin (STL) bound was found to be elevated in colon cancer, which was verified through lectin histochemistry. The subsequent glycoproteomic analysis based on STL enrichment of glycoproteins followed by label-free quantitative nano liquid chromatography-mass spectrometry/mass spectrometry (nanoLC-MS/MS) analysis identified 72 proteins in high confidence. Among these proteins, 17 were exclusively detected in cancer tissues, and 14 were significantly upregulated in tumor tissues. Annexin A1 and HSP90β were chosen for further investigation by immunoprecipitation coupled with lectin blots, western blots and tissue microarrays. Both Annexin A1 and HSP90β were GlcNAcylated, and their protein expressions were elevated in colon cancer, compared to normal tissues. Moreover, specific changes of GlcNAc abundances in Annexin A1 and HSP90β suggested that tumor-specific glycan patterns could serve as candidate biomarkers of colon cancer for distinguishing cancer patients from healthy individuals.

Anticancer property of bromelain with therapeutic potential in malignant peritoneal mesothelioma

Bromelain is a mixture of proteolytic enzymes that is capable of hydrolyzing glycosidic linkages in glycoprotein. Glycoprotein's are ubiquitously distributed throughout the body and serve a variety of physiologic functions. Faulty glycosylation of proteins may lead to cancer. Antitumor properties of bromelain have been demonstrated in both, in vitro and in vivo studies, along with scanty anecdotal human studies. Various mechanistic pathways have been proposed to explain the anticancer properties of bromelain. However, proteolysis by bromelain has been suggested as a main pathway by some researchers. MUC1 is a glycoprotein that provides tumor cells with invasive, metastatic, and chemo-resistant properties. To date, there is no study that examines the effect of bromelain on MUC1. However, the viability of MUC1 expressing pancreatic and breast cancer cells are adversely affected by bromelain. Further, the efficacy of cisplatin and 5-FU are enhanced by adjuvant treatment with bromelain, indicating that the barrier function of MUC1 may be affected. Other studies have also indicated that there is a greater accumulation of 5-FU in the cell compartment on treatment with 5-FU and bromelain. Malignant peritoneal mesothelioma (MPM) expresses MUC1 and initial studies have shown that the viability of MPM cells is adversely affected by exposure to bromelain. Further, bromelain in combination with either 5-FU or cisplatin, the efficacy of the chemotherapeutic drug is enhanced. Hence, current evidence indicates that bromelain may have the potential of being developed into an effective anticancer agent for MPM.

Mass spectrometric analysis of sialylated glycans with use of solid-phase labeling of sialic acids

The analysis of sialylated glycans is critical for understanding the role of sialic acid in normal biological processes as well as in disease. However, the labile nature of sialic acid typically renders routine analysis of this monosaccharide by mass spectrometric methods difficult. To overcome this difficulty we pursued derivatization methodologies, extending established acetohydrazide approaches to aniline-based methods, and finally to optimized p-toluidine derivatization. This new quantitative glycoform profiling method with use of MALDI-TOF in positive ion mode was validated by first comparing N-glycans isolated from fetuin and serum and was then exploited to analyze the effects of increased metabolic flux through the sialic acid pathway in SW1990 pancreatic cancer cells by using a colabeling strategy with light and heavy toluidine. The latter results established that metabolic flux, in a complementary manner to the more well-known impact of sialyltransferase expression, can critically modulate the sialylation of specific glycans while leaving others virtually unchanged.

Multivalent presentation of a hydrolytically stable GM(3) lactone mimetic as modulator of melanoma cells motility and adhesion

A hydrolytically stable mimetic of the tumour antigen GM(3) lactone is used to decorate multivalent scaffolds. Two of them positively interfere on melanoma cell adhesion, migration and resistance to apoptosis (anoikis). Notably, their ability to hamper melanoma-cells adhesion and reduce the metastatic potential is enhanced when the two scaffolds, presenting a different shape, are used in combination.

Isomer-specific chromatographic profiling yields highly sensitive and specific potential N-glycan biomarkers for epithelial ovarian cancer

Aberrant glycosylation has been observed for decades in essentially all types of cancer, and is now well established as an indicator of carcinogenesis. Mining the glycome for biomarkers, however, requires analytical methods that can rapidly separate, identify, and quantify isomeric glycans. We have developed a rapid-throughput method for chromatographic glycan profiling using microfluidic chip-based nanoflow liquid chromatography (nano-LC)/mass spectrometry. To demonstrate the utility of this method, we analyzed and compared serum samples from epithelial ovarian cancer cases (n=46) and healthy control individuals (n=48). Over 250 N-linked glycan compound peaks with over 100 distinct N-linked glycan compositions were identified. Statistical testing identified 26 potential glycan biomarkers based on both compositional and structure-specific analyses. Using these results, an optimized model was created incorporating the combined abundances of seven potential glycan biomarkers. The receiver operating characteristic (ROC) curve of this optimized model had an area under the curve (AUC) of 0.96, indicating robust discrimination between cancer cases and healthy controls. Rapid-throughput chromatographic glycan profiling was found to be an effective platform for structure-specific biomarker discovery.

Mucin-type O-glycosylation during development

Mucin-type O-glycosylation is an evolutionarily conserved protein modification present on membrane-bound and secreted proteins. Aberrations in O-glycosylation are responsible for certain human diseases and are associated with disease risk factors. Recent studies have demonstrated essential roles for mucin-type O-glycosylation in protein secretion, stability, processing, and function. Here, we summarize our current understanding of the diverse roles of mucin-type O-glycosylation during eukaryotic development. Appreciating how this conserved modification operates in developmental processes will provide insight into its roles in human disease and disease susceptibilities.

Glycocapture-based proteomics for secretome analysis

Protein glycosylation represents the most abundant extracellular posttranslational modification in multicellular organisms. These glycoproteins unequivocally comprise the major biomolecules involved in extracellular processes, such as growth factors, signaling proteins for cellular communication, enzymes, and proteases for on- and off-site processing. It is now known that altered protein glycosylation is a hallmark event in many different pathologies. Glycoproteins are found mostly in the so-called secretome, which comprises classically and nonclassically secreted proteins and protein fragments that are released from the cell surface through ectodomain shedding. Due to biological complexity and technical difficulty, comparably few studies have taken an in-depth investigation of cellular secretomes using system-wide approaches. The cellular secretomes are considered to be a valuable source of therapeutic targets and novel biomarkers. It is not surprising that many existing biomarkers, including biomarkers for breast, ovarian, prostate, and colorectal cancers are glycoproteins. Focused analysis of secreted glycoproteins could thus provide valuable information for early disease diagnosis, and surveillance. Furthermore, since most secreted proteins are glycosylated and glycosylation predominantly targets secreted proteins, the glycan/sugar moiety itself can be used as a chemical "handle" for the targeted analysis of cellular secretomes, thereby reducing sample complexity and allowing detection of low abundance proteins in proteomic workflows. This review will focus on various glycoprotein enrichment strategies that facilitate proteomics-based technologies for the quantitative analysis of cell secretomes and cell surface proteomes.

Nanoscale reversed-phase liquid chromatography-mass spectrometry of permethylated N-glycans

Reversed-phase liquid chromatography on the nanoscale coupled to electrospray tandem mass spectrometry was used to analyse a mixture of four commercial glycan standards, and the method was further adapted to N-glycans enzymatically released from alpha-1-acid glycoprotein and immunoglobulin gamma. Glycans were permethylated to enable their separation by reversed-phase chromatography and to facilitate interpretation of fragmentation data. Prior to derivatization of glycans by permethylation, they were reduced to cancel anomerism because, although feasible, it was not desired to separate α- and β-anomers. The effect of supplementing chromatographic solvent with sodium hydroxide to guide adduct formation was investigated. Raising the temperature in which the separation was performed improved chromatographic resolution and affected retention times as expected. It was shown by using the tetrasaccharides sialyl Lewis X and sialyl Lewis A that reversed-phase chromatography could achieve the separation of methylated isobaric glycan analytes. Isobaric glycans were detected among the N-glycans of immunoglobulin gamma and further analysed by tandem mass spectrometry.

Active Targeting to Osteosarcoma Cells and Apoptotic Cell Death Induction by the Novel Lectin Eucheuma serra Agglutinin Isolated from a Marine Red Alga

Previously, we demonstrated that the novel lectin Eucheuma serra agglutinin from a marine red alga (ESA) induces apoptotic cell death in carcinoma. We now find that ESA induces apoptosis also in the case of sarcoma cells. First, propidium iodide assays with OST cells and LM8 cells showed a decrease in cell viability after addition of ESA. With 50 μg/ml ESA, the viabilities after 24 hours decreased to 54.7 ± 11.4% in the case of OST cells and to 41.7 ± 12.3% for LM8 cells. Second, using fluorescently labeled ESA and flow cytometric and fluorescence microscopic measurements, it could be shown that ESA does not bind to cells that were treated with glycosidases, indicating importance of the carbohydrate chains on the surface of the cells for efficient ESA-cell interactions. Third, Span 80 vesicles with surface-bound ESA as active targeting ligand were shown to display sarcoma cell binding activity, leading to apoptosis and complete OST cell death after 48 hours at 2 μg/ml ESA. The findings indicate that Span 80 vesicles with surface-bound ESA are a potentially useful drug delivery system not only for the treatment of carcinoma but also for the treatment of osteosarcoma.

Hypoxia modulates A431 cellular pathways association to tumor radioresistance and enhanced migration revealed by comprehensive proteomic and functional studies

Tumor hypoxia induces cancer cell angiogenesis, invasiveness, treatment resistance, and contributes to poor clinical outcome. However, the molecular mechanism by which tumor hypoxia exerts a coordinated effect on different molecular pathways to enhance tumor growth and survival and lead to poor clinical outcome is not fully understood. In this study, we attempt to elucidate the global protein expression and functional changes in A431 epithelial carcinoma cells induced by hypoxia and reoxygenation using iTRAQ quantitative proteomics and biochemical functional assays. Quantitative proteomics results showed that 4316 proteins were quantified with FDR<1%, in which over 1200 proteins were modulated >1.2 fold, and DNA repair, glycolysis, integrin, glycoprotein turnover, and STAT1 pathways were perturbed by hypoxia and reoxygenation-induced oxidative stress. For the first time, hypoxia was shown to up-regulate the nonhomologous end-joining pathway, which plays a central role in DNA repair of irradiated cells, thereby potentially contributing to the radioresistance of hypoxic A431 cells. The up-regulation of Ku70/Ku80 dimer, a key molecular complex in the nonhomologous end-joining pathway, was confirmed by Western blot and liquid chromatography/tandem mass spectrometry-MRM methods. Functional studies confirmed that up-regulation of glycolysis, integrin, glycoprotein synthesis, and down-regulation of STAT1 pathways during hypoxia enhanced metastastic activity of A431 cells. Migration of A431 cells was dramatically repressed by glycolysis inhibitor (2-Deoxy-d-glucose), glycoprotein synthesis inhibitor (1-Deoxynojirimycin Hydrochloride), and STAT1α overexpression that enhanced the integrin-mediated cell adhesion. These results revealed that hypoxia induced several biological processes involved in tumor migration and radioresistance and provided potential new targets for tumor therapy.

6-alkynyl fucose is a bioorthogonal analog for O-fucosylation of epidermal growth factor-like repeats and thrombospondin type-1 repeats by protein O-fucosyltransferases 1 and 2

Protein O-fucosyltransferase 1 (Pofut1) and protein O-fucosyltransferase 2 (Pofut2) add O-linked fucose at distinct consensus sequences in properly folded epidermal growth factor (EGF)-like repeats and thrombospondin type-1 (TSR) repeats, respectively. Glycan chain elongation past O-fucose can occur to yield a tetrasaccharide on EGF repeats and a disaccharide on TSRs. Elimination of Pofut1 in mice causes embryonic lethality with Notch-like phenotypes demonstrating that O-fucosylation of Notch is essential for its function. Similarly, elimination of Pofut2 results in an early embryonic lethal phenotype in mice, although the molecular mechanism for the lethality is unknown. The recent development of sugar analogs has revolutionized the study of glycans by providing a convenient method for labeling and tracking glycosylation. In order to study O-fucosylation, we took advantage of the recently developed reporter, 6-alkynyl fucose. Using the Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC), or "click" reaction, azido-biotin allows tagging and detection of 6AF-modified proteins. Here we examine whether proteins containing EGF repeats or TSRs with O-fucose consensus sequences are specifically modified with 6AF in cell culture. Using mass spectrometry (MS), we demonstrate that 6AF is efficiently incorporated onto the appropriate consensus sequences on EGF repeats and TSRs. Furthermore, the elongation of the O-fucose monosaccharide on EGF repeats and TSRs is not hampered when 6AF is used. These results show that 6AF is efficiently utilized in a truly bioorthogonal manner by Pofut1, Pofut2 and the enzymes that elongate O-fucose, providing evidence that 6AF is a significant new tool in the study of protein O-fucosylation.

Carbohydrate biomarker recognition using synthetic lectin mimics

Carbohydrate biomarkers play very important roles in a wide range of biological and pathological processes. Compounds that can specifically recognize a carbohydrate biomarker are useful for targeted delivery of imaging agents and for development of new diagnostics. Furthermore, such compounds could also be candidates for the development of therapeutic agents. A tremendous amount of active work on synthetic lectin mimics has been reported in recent years. Amongst all the synthetic lectins, boronic-acid-based lectins (boronolectins) have shown great promise. Along this line, four classes of boronolectins including peptide-, nucleic-acid-, polymer-, and small-molecule-based ones are discussed with a focus on the design principles and recent advances. We hope that by presenting the potentials of this field, this review will stimulate more research in this area.

Anticancer activity of small amphipathic β²,²-amino acid derivatives

We report the anticancer activity from screening of a series of synthetic β(2,2)-amino acid derivatives that were prepared to confirm the pharmacophore model of short cationic antimicrobial peptides with high anti-Staphylococcal activity. The most potent derivatives against human Burkitt's lymphoma (Ramos) cells displayed IC(50) values below 8 μM, and low toxicity against human red blood cells (EC(50) > 200 μM). A more than 5-fold preference for Ramos cancer cells compared to human lung fibroblasts (MRC-5 cells) was also obtained for the most promising β(2,2)-amino acid derivative 3-amino-N-(2-aminoethyl)-2,2-bis(naphthalen-2-ylmethyl)propanamide (5c). Screening of 5c at the National Cancer Institute (NCI, USA) confirmed its anticancer potency and revealed a very broad range of anticancer activity with IC(50) values of 0.32-3.89 μM against 59 different cancer cell lines. Highest potency was obtained against the colon cancer cell lines, a non-small cell lung cancer, a melanoma, and three leukemia cell lines included in the NCI screening panel. The reported β(2,2)-amino acid derivatives constitute a promising new class of anticancer agents based on their high anticancer potency, ease of synthesis, mode-of-action, and optimized pharmacokinetic properties compared to much larger antimicrobial peptides.

Golgi pH, its regulation and roles in human disease

Most organelles within the exocytic and endocytic pathways typically acidify their interiors, a phenomenon that is known to be crucial for their optimal functioning in eukaryotic cells. This review highlights recent advances in our understanding of how Golgi acidity is maintained and regulated, and how its misregulation contributes to organelle dysfunction and disease. Both its biosynthetic products (glycans) and protein-sorting events are highly sensitive to changes in Golgi luminal pH and are affected in certain human disease states such as cancers and cutis laxa. Other potential disease states that are caused by, or are associated with, Golgi pH misregulation will also be discussed.

Pardaxin, a fish antimicrobial peptide, exhibits antitumor activity toward murine fibrosarcoma in vitro and in vivo

The antitumor activity of pardaxin, a fish antimicrobial peptide, has not been previously examined in in vitro and in vivo systems for treating murine fibrosarcoma. In this study, the antitumor activity of synthetic pardaxin was tested using murine MN-11 tumor cells as the study model. We show that pardaxin inhibits the proliferation of MN-11 cells and reduces colony formation in a soft agar assay. Transmission electron microscopy (TEM) showed that pardaxin altered the membrane structure similar to what a lytic peptide does, and also produced apoptotic features, such as hollow mitochondria, nuclear condensation, and disrupted cell membranes. A qRT-PCR and ELISA showed that pardaxin induced apoptosis, activated caspase-7 and interleukin (IL)-7r, and downregulated caspase-9, ATF 3, SOCS3, STAT3, cathelicidin, p65, and interferon (IFN)-γ suggesting that pardaxin induces apoptosis through the death receptor/nuclear factor (NF)-κB signaling pathway after 14 days of treatment in tumor-bearing mice. An antitumor effect was observed when pardaxin (25 mg/kg; 0.5 mg/day) was used to treat mice for 14 days, which caused significant inhibition of MN-11 cell growth in mice. Overall, these results indicate that pardaxin has the potential to be a novel therapeutic agent to treat fibrosarcomas.

Accumulation of free Neu5Ac-containing complex-type N-glycans in human pancreatic cancers

We have analyzed the structures of glycosphingolipids and intracellular free glycans in human cancers. In our previous study, trace amounts of free N-acetylneuraminic acid (Neu5Ac)-containing complex-type N-glycans with a single GlcNAc at each reducing terminus (Gn1 type) was found to accumulate intracellularly in colorectal cancers, but were undetectable in most normal colorectal epithelial cells. Here, we used cancer glycomic analyses to reveal that substantial amounts of free Neu5Ac-containing complex-type N-glycans, almost all of which were α2,6-Neu5Ac-linked, accumulated in the pancreatic cancer cells from three out of five patients, but were undetectable in normal pancreatic cells from all five cases. These molecular species were mostly composed of five kinds of glycans having a sequence Neu5Ac-Gal-GlcNAc-Man-Man-GlcNAc and one with the following sequence Neu5Ac-Gal-GlcNAc-Man-(Man-)Man-GlcNAc. The most abundant glycan was Neu5Acα2-6Galβ1-4GlcNAcβ1-2Manα1-3Manβ1-4GlcNAc, followed by Neu5Acα2-6Galβ1-4GlcNAcβ1-2Manα1-6Manβ1-4GlcNAc. This is the first study to show unequivocal evidence for the occurrence of free Neu5Ac-linked N-glycans in human cancer tissues. Our findings suggest that free Neu5Ac-linked glycans may serve as a useful tumor marker.

Clinical application of serum tumor associated material (TAM) from non-small cell lung cancer patients

OBJECTIVE

To explore the associations of serum tumor associated material (TAM) with other common tumor markers like carcinoembryonic antigen (CEA), carbohydrate antigen 125 (CA125), carbohydrate antigen19-9 (CA19-9) and its clinical application in non-small cell lung cancer (NSCLC) patients.

METHODS

A total of 87 patients were enrolled into this study, all with histologically or cytologically confirmed NSCLC. With the method of chemical colorimetry, the level of TAM was determined and compared, while chemiluminescence was used to measure the levels of common tumor markers.

RESULTS

The level of TAM decreased after chemotherapy compared with before chemotherapy when CT or MRI scans showed disease control. Furthermore, it increased when disease progressed and there was no statistically significant difference in monitoring of TAM and common tumor markers (P>0.05).

CONCLUSIONS

Detecting TAM in NSCLC patients has a higher sensitivity and specificity, so it can be used as an indicator for clinical monitoring of lung cancer chemotherapy.

Separation of kallikrein 6 glycoprotein subpopulations in biological fluids by anion-exchange chromatography coupled to ELISA and identification by mass spectrometry

Kallikrein 6 (KLK6) has been shown to be aberrantly glycosylated in ovarian cancer. Here, we report a novel HPLC anion exchange method, coupled to a KLK6-specific ELISA, capable of differentiating KLK6 glycoform subgroups in biological fluids. Biological fluids were fractionated using anion exchange and resulting fractions were analyzed for KLK6 content by ELISA producing a four-peak elution profile. Using this assay, the KLK6 elution profile and distribution across peaks of a set (n = 7) of ovarian cancer patient matched serum and ascites fluid samples was found to be different than the profile of serum and cerebrospinal fluid (CSF) of normal individuals (n = 7). Glycosylation patterns of recombinant KLK6 (rKLK6) were characterized using tandem mass spectrometry (MS/MS), and found to consist of a highly heterogeneous KLK6 population. This protein was found to contain all of the four diagnostic KLK6 peaks present in the previously assayed biological fluids. The rKLK6 glycoform composition of each peak was assessed by lectin affinity and MS/MS based glycopeptide quantification by product ion monitoring. The combined results showed an increase in terminal alpha 2-6 linked sialic acid in the N-glycans found on KLK6 from ovarian cancer serum and ascites, as opposed to CSF and serum of normal individuals.

Sialofucosylated podocalyxin is a functional E- and L-selectin ligand expressed by metastatic pancreatic cancer cells

Selectin-mediated interactions in the vasculature promote metastatic spread by facilitating circulating tumor cell binding to selectin-expressing host cells. Therefore, identifying the selectin ligand(s) on tumor cells is critical to the prevention of blood-borne metastasis. A current challenge is to distinguish between structures expressed by circulating tumor cells that can bind selectins in vitro from the functional ligands whose depletion suppresses selectin-dependent binding under flow in vivo. Interestingly, podocalyxin (PODXL), which can bind E- and L-selectin, is upregulated in a number of cancers, including those of the breast, colon, and pancreas. In this work, we show that metastatic pancreatic cancer cells overexpress PODXL compared with nonmalignant pancreatic epithelial cells. We further demonstrate via tissue microarray that 69% of pancreatic ductal adenocarcinomas stain positive for PODXL. In cases of focal expression, positive staining is restricted to the invasive front of primary tumors. By combining immunoblot, immunodepletion, short-hairpin RNA-mediated gene silencing, and flow-based adhesion assays, we evaluated the functional role of sialofucosylated PODXL in selectin-mediated adhesion under flow. Our data indicate that sialofucosylated PODXL is a functional E- and L-selectin ligand expressed by metastatic pancreatic cancer cells, as specific depletion of this molecule from the cell surface significantly interferes with selectin-dependent interactions. Cumulatively, these data support a correlation between sialofucosylated PODXL expression and enhanced binding to selectins by metastatic pancreatic cancer cells and offer additional perspective on the upregulation of PODXL in aggressive cancers.

Cancer-associated carbohydrate antigens as potential biomarkers for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common human malignancies. Therefore, developing the early, high-sensitivity diagnostic biomarkers to prevent HCC is urgently needed. Serum a-fetoprotein (AFP), the clinical biomarker in current use, is elevated in only ∼60% of patients with HCC; therefore, identification of additional biomarkers is expected to have a significant impact on public health. In this study, we used glycan microarray analysis to explore the potential diagnostic value of several cancer-associated carbohydrate antigens (CACAs) as biomarkers for HCC. We used glycan microarray analysis with 58 different glycan analogs for quantitative comparison of 593 human serum samples (293 HCC samples; 133 chronic hepatitis B virus (HBV) infection samples, 134 chronic hepatitis C virus (HCV) infection samples, and 33 healthy donor samples) to explore the diagnostic possibility of serum antibody changes as biomarkers for HCC. Serum concentrations of anti-disialosyl galactosyl globoside (DSGG), anti-fucosyl GM1 and anti-Gb2 were significantly higher in patients with HCC than in chronic HBV infection individuals not in chronic HCV infection patients. Overall, in our study population, the biomarker candidates DSGG, fucosyl GM1 and Gb2 of CACAs achieved better predictive sensitivity than AFP. We identified potential biomarkers suitable for early detection of HCC. Glycan microarray analysis provides a powerful tool for high-sensitivity and high-throughput detection of serum antibodies against CACAs, which may be valuable serum biomarkers for the early detection of persons at high risk for HCC.

N-Glycosylation Pattern of Human Placental Insulin-Like Growth Factor and Insulin Receptors in Well-Controlled Pregestational Diabetes Mellitus

Diabetes mellitus is a complex disease that leads to alterations in the glycosylation of proteins. Insulin-like growth factor and insulin receptors are involved in the regulation of fetal and placental growth and development. In this work the N-glycans of these receptors, originating from placentas obtained from pregnancies complicated by pregestational insulin dependent diabetes mellitus, were studied. Diabetic mothers were under regular insulin therapy. Solubilised membrane samples from healthy and diabetic placentas were analysed using lectin-affinity chromatography. N-glycans bound to insulin-like growth factor and insulin receptors were studied in terms of their interaction with eleven agarose-immobilised lectins: wheat germ agglutinin, succinylated wheat germ agglutinin,Ricinus communisagglutinin I,Sambucus nigraagglutinin,Erythrina cristagallilectin,Ulex europaeusagglutinin,Lens culinarisagglutinin,Canavalia ensiformislectin,Phaseolus vulgariserythro- and leukoagglutinin andMaackia amurensisagglutinin. A very similar type of N-glycans and content of the terminal saccharide residues were found in both groups of placentas. The results of this work suggest that the tight glycemic control may prevent alterations in the glycosylation of insulin-like growth factor and insulin receptors, thus maintaining physiological homeostasis during pregnancy and fetal growth.

Identification of compounds that augment the lectin-sensitivity of Chinese Hamster Ovary cells

Glycosylation is now recognized as one of the most important modifications of eukaryotic proteins. In cancer biology, alterations in cell surface glycosylation have been exploited as valuable biomarkers, and the relationship of this modification to the metastatic characteristics of cancer cells has also been well-documented. Chemicals that can alter cell surface glycosylation patterns will therefore become attractive lead compounds for controlling the metastatic characteristics of cancer cells, one of the critical factors in their malignancy and prognosis of the disease. In this study, we established a system for screening compounds that have the potential to alter cell surface glycosylation by taking advantage of the susceptibility of cells toward various lectins. Through our screening of a chemical library, we were able to identify two compounds that augment the sensitivity of Chinese Hamster Ovary (CHO-K1) cells against the L4-PHA lectin. Surprisingly, these compounds did not result in alterations in cell surface glycan structures. Instead, they appeared to render the cells to be more sensitive to various lectins with distinct carbohydrate specificities. These compounds promise to be valuable, not only as tools for providing insights into the intracellular signaling of lectin-mediated growth arrest, but also as potential lead compounds for use as therapeutic, anti-cancer drugs.

Development of antimetastatic drugs by targeting tumor sialic acids

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

Boronic Acid functionalized core-shell polymer nanoparticles prepared by distillation precipitation polymerization for glycopeptide enrichment

The boronic acid-functionalized core-shell polymer nanoparticles, poly(N,N-methylenebisacrylamide-co-methacrylic acid)@4-vinylphenylboronic acid (poly(MBA-co-MAA)@VPBA), were successfully synthesized for enriching glycosylated peptides. Such nanoparticles were composed of a hydrophilic polymer core prepared by distillation precipitation polymerization (DPP) and a boronic acid-functionalized shell designed for capturing glycopeptides. Owing to the relatively large amount of residual vinyl groups introduced by DPP on the core surface, the VPBA monomer was coated with high efficiency, working as the shell. Moreover, the overall polymerization route, especially the use of DPP, made the synthesis of nanoparticles facile and time-saving. With the poly(MBA-co-MAA)@VPBA nanoparticles, 18 glycopeptides from horseradish peroxidase (HRP) digest were captured and identified by MALDI-TOF mass spectrometric analysis, relative to eight glycopeptides enriched by using commercially available meta-aminophenylboronic acid agarose under the same conditions. When the concentration of the HRP digest was decreased to as low as 5 nmol, glycopeptides could still be selectively isolated by the prepared nanoparticles. Our results demonstrated that the synthetic poly(MBA-co-MAA)@VPBA nanoparticles might be a promising selective enrichment material for glycoproteome analysis.