Sialyltransferases in cancer

Surface display of sialyltransferase on the outer membrane of Escherichia coli and ClearColi

α2,3-Sialyltransferase from Pasteurella multocida (PmST1) is an enzyme that transfers a sialyl group of donor substrates to an acceptor substrate called N-acetyl-d-lactosamine (LacNAc). In this study PmST1 was expressed on the outer membrane of wildtype Escherichia coli (BL21) with lipopolysaccharide (LPS) and ClearColi with no LPS, and then the enzyme activity and expression level of PmST1 were compared. As the first step, the expression levels of PmST1 on the outer membranes of wildtype E. coli (BL21) and ClearColi were compared according to the IPTG induction time, and the absolute amount of surface-displayed PmST1 was calculated using densitometry of SDS-PAGE. As the next step, the influence of LPS on the PmST1 activity was estimated by analyzing Michaelis-Menten plot. The enzyme activity of PmST1 was analyzed by measuring the concentration of CMP, which was a by-product after the transfer of the sialyl group of donor compounds to the acceptor compounds. From a Michaelis-Menten plot, the enzyme activity of the surface-displayed PmST1 and the maximum rate (V_max) of ClearColi were higher than those of wildtype E. coli (BL21). However, the K_M value, which represented the concentration of substrate to reach half the maximum rate (V_max), was similar for both enzymes. These results represented such a difference in enzyme activity was occurred from the interference of LPS on the mass transport of the donor and acceptor to PmST1 for the sialyl group transfer.

Transfer of Functional Cargo in Exomeres

Exomeres are a recently discovered type of extracellular nanoparticle with no known biological function. Herein, we describe a simple ultracentrifugation-based method for separation of exomeres from exosomes. Exomeres are enriched in Argonaute 1-3 and amyloid precursor protein. We identify distinct functions of exomeres mediated by two of their cargo, the β-galactoside α2,6-sialyltransferase 1 (ST6Gal-I) that α2,6- sialylates N-glycans, and the EGFR ligand, amphiregulin (AREG). Functional ST6Gal-I in exomeres can be transferred to cells, resulting in hypersialylation of recipient cell-surface proteins including β1-integrin. AREG-containing exomeres elicit prolonged EGFR and downstream signaling in recipient cells, modulate EGFR trafficking in normal intestinal organoids, and dramatically enhance the growth of colonic tumor organoids. This study provides a simplified method of exomere isolation and demonstrates that exomeres contain and can transfer functional cargo. These findings underscore the heterogeneity of nanoparticles and should accelerate advances in determining the composition and biological functions of exomeres.

α2,6-Sialylation promotes immune escape in hepatocarcinoma cells by regulating T cell functions and CD147/MMP signaling

Altered glycosylation is a common feature of cancer cells and plays an important role in tumor progression. β-Galactoside α2-6-sialyltransferase 1 (ST6Gal-I) is the critical sialyltransferase responsible for the addition of α2-6-sialic acid to the terminal N-glycans on the cell surface. However, the functions and mechanism of ST6Gal-I in tumor immune escape remain poorly understood. Here, we found that ST6Gal-I overexpression promoted hepatocarcinoma cell proliferation, migration, and immune escape by increasing the levels of CD147, MMP9, MMP2, and MMP7. When CD8⁺ T cells were co-cultured with cell lines expressing different levels of ST6Gal-I, we found that ST6Gal-I upregulation inhibited the T cell proliferation and increased the secretion of IL-10 and TGF-β1, while secretion of IFN-γ and TNF-α was diminished. In a syngeneic tumor transplant model, ST6Gal-I upregulated Hca-P. In addition, Hepa1-6 cells formed significantly larger tumors and suppressed intratumoral penetration by CD8⁺ T cells. In combination, these results suggest that ST6Gal-I promotes the immune escape of hepatocarcinoma cells in the tumor microenvironment and highlight the importance of assessing ST6Gal-I status for immunotherapies.

Engineering of CHO cells for the production of vertebrate recombinant sialyltransferases

Background

Sialyltransferases (SIATs) are a family of enzymes that transfer sialic acid (Sia) to glycan chains on glycoproteins, glycolipids, and oligosaccharides. They play key roles in determining cell–cell and cell-matrix interactions and are important in neuronal development, immune regulation, protein stability and clearance. Most fully characterized SIATs are of mammalian origin and these have been used for in vitro and in vivo modification of glycans. Additional versatility could be achieved by the use of animal SIATs from other species that live in much more variable environments. Our aim was to generate a panel of stable CHO cell lines expressing a range of vertebrate SIATs with different physicochemical and functional properties.

Methods

The soluble forms of various animal ST6Gal and ST3Gal enzymes were stably expressed from a Gateway-modified secretion vector in CHO cells. The secreted proteins were IMAC-purified from serum-free media. Functionality of the protein was initially assessed by lectin binding to the host CHO cells. Activity of purified proteins was determined by a number of approaches that included a phosphate-linked sialyltransferase assay, HILIC-HPLC identification of sialyllactose products and enzyme-linked lectin assay (ELLA).

Results

A range of sialyltransferase from mammals, birds and fish were stably expressed in CHO Flp-In cells. The stable cell lines expressing ST6Gal1 modify the glycans on the surface of the CHO cells as detected by fluorescently labelled lectin microscopy. The catalytic domains, as isolated by Ni Sepharose from culture media, have enzymatic activities comparable to commercial enzymes. Sialyllactoses were identified by HILIC-HPLC on incubation of the enzymes from lactose or whey permeate. The enzymes also increased SNA-I labelling of asialofetuin when incubated in a plate format.

Conclusion

Stable cell lines are available that may provide options for the in vivo sialylation of glycoproteins. Proteins are active and should display a variety of biological and physicochemical properties based on the animal source of the enzyme.

Accumulation of α-2,6-sialyoglycoproteins in the Muscle Sarcoplasm Due to Trichinella Sp. Invasion

The sialylation of the glycoproteins in skeletal muscle tissue is not well investigated, even though the essential role of the sialic acids for the proper muscular function has been proven by many researchers. The invasion of the parasitic nematode Trichinella spiralis in the muscles with subsequent formation of Nurse cell-parasite complex initiates increased accumulation of sialylated glycoproteins within the affected area of the muscle fiber. The aim of this study is to describe some details of the α-2,6-sialylation in invaded muscle cells. Asynchronous invasion with infectious T. spiralis larvae was experimentally induced in mice. The areas of the occupied sarcoplasm were reactive towards α-2,6-sialic acid specific Sambucus nigra agglutinin during the whole process of transformation to a Nurse cell.The cytoplasm of the developing Nurse cell reacted with Helix pomatia agglutinin, Arachis hypogea agglutinin and Vicia villosa lectin-B4 after neuraminidase pretreatment.Up-regulation of the enzyme ST6GalNAc1 and down-regulation of the enzyme ST6GalNAc3 were detected throughout the course of this study. The results from our study assumed accumulation of sialyl-Tn-Ag, 6`-sialyl lactosamine, SiA-α-2,6-Gal-β-1,3-GalNAc-α-Ser/Thr and Gal-β-1,3-GalNAc(SiA-α-2,6-)-α-1-Ser/Thr oligosaccharide structures into the occupied sarcoplasm. Further investigations in this domain will develop the understanding about the amazing adaptive capabilities of skeletal muscle tissue.

Cancer Cell Glycocalyx and Its Significance in Cancer Progression

Cancer is a malignant tumor that threatens the health of human beings, and has become the leading cause of death in urban and rural residents in China. The glycocalyx is a layer of multifunctional glycans that covers the surfaces of a variety of cells, including vascular endothelial cells, smooth muscle cells, stem cells, epithelial, osteocytes, as well as cancer cells. The glycosylation and syndecan of cancer cell glycocalyx are unique. However, heparan sulfate (HS), hyaluronic acid (HA), and syndecan are all closely associated with the processes of cancer progression, including cell migration and metastasis, tumor cell adhesion, tumorigenesis, and tumor growth. The possible underlying mechanisms may be the interruption of its barrier function, its radical role in growth factor storage, signaling, and mechanotransduction. In the later sections, we discuss glycocalyx targeting therapeutic approaches reported in animal and clinical experiments. The study concludes that cancer cells’ glycocalyx and its role in cancer progression are beginning to be known by more groups, and future studies should pay more attention to its mechanotransduction of interstitial flow-induced shear stress, seeking promising therapeutic targets with less toxicity but more specificity.

Quantitative Analysis of Sex-Hormone-Binding Globulin Glycosylation in Liver Diseases by Liquid Chromatography-Mass Spectrometry Parallel Reaction Monitoring

Sex-hormone-binding globulin (SHBG) is a liver-secreted glycoprotein and a major regulator of steroid distribution. It has been reported that the serum concentration of SHBG changes in liver disease. To explore the involvement of SHBG in liver disease of different etiologies in greater detail, we developed a sensitive and selective liquid chromatography-mass spectrometry parallel reaction monitoring workflow to achieve quantitative analysis of SHBG glycosylation microheterogeneity. The method uses energy-optimized "soft" fragmentation to extract informative Y ions for maximal coverage of glycoforms and their quantitative comparisons. A total of 15 N-glycoforms of two N-glycosites and 3 O-glycoforms of 1 O-glycosite of this low-abundance serum protein were simultaneously analyzed in the complex samples. At the same time, we were able to partially resolve linkage isoforms of the fucosylated glycoforms and to identify and quantify SHBG N-glycoforms that were not previously reported. The results show that both core and outer-arm fucosylation of the N-glycoforms increases with liver cirrhosis but that a further increase of fucosylation is not observed with hepatocellular carcinoma (HCC). In contrast, the α-2-6 sialylated glycoform of the O-glycopeptide of SHBG increases in liver cirrhosis, and a significant 2-fold further increase is observed in HCC. In general, we do not find a significant contribution of different liver disease etiologies to the observed changes in glycosylation; however, elevation of the newly reported HexNAc(4)Hex(6) N-glycoform is associated with alcoholic liver disease.

Plasma N-glycans in colorectal cancer risk

Aberrant glycosylation has been associated with a number of diseases including cancer. Our aim was to elucidate changes in whole plasma N-glycosylation between colorectal cancer (CRC) cases and controls in one of the largest cohorts of its kind. A set of 633 CRC patients and 478 age and gender matched controls was analysed. Additionally, patients were stratified into four CRC stages. Moreover, N-glycan analysis was carried out in plasma of 40 patients collected prior to the initial diagnosis of CRC. Statistically significant differences were observed in the plasma N-glycome at all stages of CRC, this included a highly significant decrease in relation to the core fucosylated bi-antennary glycans F(6)A2G2 and F(6)A2G2S(6)1 (P < 0.0009). Stage 1 showed a unique biomarker signature compared to stages 2, 3 and 4. There were indications that at risk groups could be identified from the glycome (retrospective AUC = 0.77 and prospective AUC = 0.65). N-glycome biomarkers related to the pathogenic progress of the disease would be a considerable asset in a clinical setting and it could enable novel therapeutics to be developed to target the disease in patients at risk of progression.

Diagnostic utility of glycosyltransferase mRNA expression in gastric cancer

OBJECTIVE/BACKGROUND

Posttranslational modification of proteins, including glycosylation, is known to differ between normal and tumor cells. Altered glycosyltransferase levels have been observed in tumor tissues and their role in tumor metastasis and invasion has been implicated. In this study the role of altered glycosyltransferase messenger RNA (mRNA) levels in serum of gastric cancer patients as early markers of gastric cancer was evaluated.

METHODS

In this case control study the expression profile of ppGalNAc-T6, GlcNAcT-V, ST3Gal I, ST3 Gal IV, and ST6GalNAc-I in normal healthy control and gastric cancer patients was compared. Serum was isolated from blood samples of gastric cancer patients (n = 200) and controls (n = 200). Following RNA extraction, reverse transcription was carried out and transcript levels of glycosyltransferases were determined using real-time quantitative polymerase chain reaction and normalized against glyceraldehyde-3-phosphate dehydrogenase (GAPDH) expression. The amount of target gene, normalized to an endogenous reference gene relative to calibrator was calculated by using ΔΔCT method. Transcript levels in the serum samples of gastric cancer patients were compared with those of controls; also the same was correlated within sex and different stages of disease.

RESULTS

The mRNA expression of ppGalNAc-T6 and ST6GalNAc-I was significantly higher in serum samples of gastric cancer patients on comparison with controls (p = .008), however, there was no significant difference in mRNA expression of GlcNAcT-V, ST3Gal I, and ST3 Gal IV in serum samples of gastric cancer patients and controls (p = .097). In addition, no significant association of mRNA expression of these glycosyltransferases was found within sex and stages in this study.

CONCLUSION

This study revealed the potential of ppGalNAc-T6 and ST6GalNAc-I mRNA transcript levels in serum as markers of gastric cancer. Further studies on the wider range of glycosyltransferases in various cancers are needed to establish signature mRNA batteries as minimally invasive markers of gastric cancer.

A One-Step Chemoenzymatic Labeling Strategy for Probing Sialylated Thomsen-Friedenreich Antigen

Abnormal expression of sialylated Thomsen-Friedenreich antigen (Neu5Acα2-3Galβ1-3GalNAcα-O-Ser/Thr, sialyl-T) has a strong relationship with various types of human cancers and many other diseases. However, the size and structural complexity, and relatively lower abundance of sialyl-T have posed a significant challenge to its detection. Therefore, details about the role of sialyl-T in a variety of physiological and pathological processes are still poorly understood. Here, a one-step chemoenzymatic labeling strategy to probe sialyl-T is described. This approach enables the sensitive, selective, and rapid detection of sialyl-T, and global profiling and identification of unknown sialyl-T-attached glycoproteins, which are potential therapeutic targets or biomarkers. The use of one-step labeling strategy not only has a higher sensitivity than a typical two-step reporter strategy but also avoids undergoing an additional chemical reaction step to introduce a reporter group after the labeling reaction, making it particularly useful for detecting low-abundance glycan epitopes on living cells.

Sialyltransferase-Based Chemoenzymatic Histology for the Detection of N- and O-Glycans

Profiling specific glycans in histopathological samples is hampered by the lack of selective and sensitive tools for their detection. Here, we report on the development of chemoenzymatic histology of membrane polysaccharide (CHoMP)-based methods for the detection of O- and N-linked glycans on tissue sections via the use of sialyltransferases ST3Gal1 and ST6Gal1, respectively. Combining these two methods, we developed tandem labeling and double labeling strategies that permit the detection of unsialylated and sialylated glycans or the detection of O- and N-linked glycans on the same tissue section, respectively. We applied these methods to screen murine tissue specimens, human multiple-organ cancer arrays, and lymphoma and prostate cancer arrays. Using tandem labeling with ST6Gal1 to analyze N-glycans in a prostate cancer array, we found striking differences in expression patterns of both sialylated and unsialylated N-glycans between cancerous and healthy samples. Such differences were also observed between normal tissue from healthy donors and healthy tissue adjacent to tumors. Our double labeling technique identified significant differences in unsialylated O-glycans between B-cell and T-cell lymphomas and between B-cell lymphomas and normal adjacent lymph nodes. Remarkable differences were also detected between adjacent lymph nodes and spleen tissue samples. These new chemoenzymatic histology methods therefore provide valuable tools for the analysis of glycans in clinically relevant tissue samples.

α2,3-sialyltransferase type I regulates migration and peritoneal dissemination of ovarian cancer cells

Epithelial ovarian cancer (EOC) has the highest mortality rate among gynecologic cancers due to advanced stage presentation, peritoneal dissemination, and refractory ascites at diagnosis. We investigated the role of α2,3-sialyltransferase type I (ST3GalI) by analyzing human ovarian cancer datasets and human EOC tissue arrays. We found that high expression of ST3GalI was associated with advanced stage EOC. Transwell migration and cell invasion assays showed that high ST3GalI expression enhanced migration of EOC cells. We also observed that there was a linear relation between ST3GalI expression and epidermal growth factor receptor (EGFR) signaling in EOC patients, and that high ST3GalI expression blocked the effect of EGFR inhibitors. Co-Immunoprecipitation experiments demonstrated that ST3GalI and EGFR were present in the same protein complex. Inhibition of ST3GalI using a competitive inhibitor, Soyasaponin I (SsaI), inhibited tumor cell migration and dissemination in the in vivo mouse model with transplanted MOSEC cells. Further, SsaI synergistically enhanced the anti-tumor effects of EGFR inhibitor on EOC cells. Our study demonstrates that ST3GalI regulates ovarian cancer cell migration and peritoneal dissemination via EGFR signaling. This suggests α2,3-linked sialylation inhibitors in combination with EGFR inhibitors could be effective agents for the treatment of EOC.

LncRNA HCP5 promotes follicular thyroid carcinoma progression via miRNAs sponge

Long non-coding RNAs (lncRNAs), which are important functional regulators in cancer, have received increased attention in recent years. In this study, next-generation sequencing technology was used to identify aberrantly expressed lncRNAs in follicular thyroid carcinoma (FTC). The long non-coding RNA-HLA complex P5 (HCP5) was found to be overexpressed in FTC. The results of the qPCR analysis were consistent with the sequencing results. In addition, functional experiments showed that overexpression of HCP5 can promote the proliferation, migration, invasiveness and angiogenic ability of FTC cells. Furthermore, according to the sequencing results, HCP5 and alpha-2, 6-sialyltransferase 2 (ST6GAL2) were co-expressed in FTC. We hypothesised that ST6GAL2 may be regulated by HCP5, which would in turn mediate the activity of FTC cells. Through qPCR, immunostaining analyses and functional experiments, we determined that the expression of HCP5 was elevated and was correlated with the levels of ST6GAL2 in FTC tissues and cells. Mechanistic experiments showed that HCP5 functions as a competing endogenous RNA (ceRNA) and acts as a sponge for miR-22-3p, miR-186-5p and miR-216a-5p, which activates ST6GAL2. In summary, our study revealed that HCP5 is a tumour regulator in the development of FTC and that it may contribute to improvement of FTC diagnosis and therapy.

Oxidative damage and response to Bacillus Calmette-Guérin in bladder cancer cells expressing sialyltransferase ST3GAL1

Background

Treatment with Bacillus Calmette-Guérin (BCG) is the gold standard adjuvant immunotherapy of non-muscle invasive bladder cancer (NMIBC), although it fails in one third of the patients. NMIBC expresses two tumor-associated O-linked carbohydrates: the disaccharide (Galβ1,3GalNAc) Thomsen-Friedenreich (T) antigen, and its sialylated counterpart (Siaα2,3Galβ1,3GalNAc) sialyl-T (sT), synthesized by sialyltransferase ST3GAL1, whose roles in BCG response are unknown.

Methods

The human bladder cancer (BC) cell line HT1376 strongly expressing the T antigen, was retrovirally transduced with the ST3GAL1 cDNA or with an empty vector, yielding the cell lines HT1376_sT and HT1376_T, that express, respectively, either the sT or the T antigens. Cells were in vitro challenged with BCG. Whole gene expression was studied by microarray technology, cytokine secretion was measured by multiplex immune-beads assay. Human macrophages derived from blood monocytes were challenged with the secretome of BCG-challenged BC cells.

Results

The secretome from BCG-challenged HT1376_sT cells induced a stronger macrophage secretion of IL-6, IL-1β, TNFα and IL-10 than that of HT1376_T cells. Transcriptomic analysis revealed that ST3GAL1 overexpression and T/sT replacement modulated hundreds of genes. Several genes preserving genomic stability were down-regulated in HT1376_sT cells which, as a consequence, displayed increased sensitivity to oxidative damage. After BCG challenge, the transcriptome of HT1376_sT cells showed higher susceptibility to BCG modulation than that of HT1376_T cells.

Conclusions

High ST3GAL1 expression and T/sT replacement in BCG challenged-BC cancer cells induce a stronger macrophage response and alter the gene expression towards genomic instability, indicating a potential impact on BC biology and patient’s response to BCG.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4107-1) contains supplementary material, which is available to authorized users.

Sialylation of EGFR by the ST6Gal-I sialyltransferase promotes EGFR activation and resistance to gefitinib-mediated cell death

BACKGROUND

The ST6Gal-I sialyltransferase is upregulated in numerous cancers, and high expression of this enzyme correlates with poor patient prognosis in various malignancies, including ovarian cancer. Through its sialylation of a select cohort of cell surface receptors, ST6Gal-I modulates cell signaling to promote tumor cell survival. The goal of the present study was to investigate the influence of ST6Gal-I on another important receptor that controls cancer cell behavior, EGFR. Additionally, the effect of ST6Gal-I on cancer cells treated with the common EGFR inhibitor, gefitinib, was evaluated.

RESULTS

Using the OV4 ovarian cancer cell line, which lacks endogenous ST6Gal-I expression, a kinomics assay revealed that cells with forced overexpression of ST6Gal-I exhibited increased global tyrosine kinase activity, a finding confirmed by immunoblotting whole cell lysates with an anti-phosphotyrosine antibody. Interestingly, the kinomics assay suggested that one of the most highly activated tyrosine kinases in ST6Gal-I-overexpressing OV4 cells was EGFR. Based on these findings, additional analyses were performed to investigate the effect of ST6Gal-I on EGFR activation. To this end, we utilized, in addition to OV4 cells, the SKOV3 ovarian cancer cell line, engineered with both ST6Gal-I overexpression and knockdown, as well as the BxPC3 pancreatic cancer cell line with knockdown of ST6Gal-I. In all three cell lines, we determined that EGFR is a substrate of ST6Gal-I, and that the sialylation status of EGFR directly correlates with ST6Gal-I expression. Cells with differential ST6Gal-I expression were subsequently evaluated for EGFR tyrosine phosphorylation. Cells with high ST6Gal-I expression were found to have elevated levels of basal and EGF-induced EGFR activation. Conversely, knockdown of ST6Gal-I greatly attenuated EGFR activation, both basally and post EGF treatment. Finally, to illustrate the functional importance of ST6Gal-I in regulating EGFR-dependent survival, cells were treated with gefitinib, an EGFR inhibitor widely used for cancer therapy. These studies showed that ST6Gal-I promotes resistance to gefitinib-mediated apoptosis, as measured by caspase activity assays.

CONCLUSION

Results herein indicate that ST6Gal-I promotes EGFR activation and protects against gefitinib-mediated cell death. Establishing the tumor-associated ST6Gal-I sialyltransferase as a regulator of EGFR provides novel insight into the role of glycosylation in growth factor signaling and chemoresistance.

ST6Gal-I sialyltransferase promotes chemoresistance in pancreatic ductal adenocarcinoma by abrogating gemcitabine-mediated DNA damage

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive malignancy with a poor prognosis. Gemcitabine, as a single agent or in combination therapy, remains the frontline chemotherapy despite its limited efficacy due to de novo or acquired chemoresistance. There is an acute need to decipher mechanisms underlying chemoresistance and identify new targets to improve patient outcomes. Here, we report a novel role for the ST6Gal-I sialyltransferase in gemcitabine resistance. Utilizing MiaPaCa-2 and BxPC-3 PDAC cells, we found that knockdown (KD) of ST6Gal-I expression, as well as removal of surface α2-6 sialic acids by neuraminidase, enhances gemcitabine-mediated cell death assessed via clonogenic assays and cleaved caspase 3 expression. Additionally, KD of ST6Gal-I potentiates gemcitabine-induced DNA damage as measured by comet assays and quantification of γH2AX foci. ST6Gal-I KD also alters mRNA expression of key gemcitabine metabolic genes, RRM1, RRM2, hENT1, and DCK, leading to an increased gemcitabine sensitivity ratio, an indicator of gemcitabine toxicity. Gemcitabine-resistant MiaPaCa-2 cells display higher ST6Gal-I levels than treatment-naïve cells along with a reduced gemcitabine sensitivity ratio, suggesting that chronic chemotherapy selects for clonal variants with more abundant ST6Gal-I. Finally, we examined Suit2 PDAC cells and Suit2 derivatives with enhanced metastatic potential. Intriguingly, three metastatic and chemoresistant subclones, S2-CP9, S2-LM7AA, and S2-013, exhibit up-regulated ST6Gal-I relative to parental Suit2 cells. ST6Gal-I KD in S2-013 cells increases gemcitabine-mediated DNA damage, indicating that suppressing ST6Gal-I activity sensitizes inherently resistant cells to gemcitabine. Together, these findings place ST6Gal-I as a critical player in imparting gemcitabine resistance and as a potential target to restore PDAC chemoresponse.

E-Selectin Ligands in the Human Mononuclear Phagocyte System: Implications for Infection, Inflammation, and Immunotherapy

The mononuclear phagocyte system comprises a network of circulating monocytes and dendritic cells (DCs), and “histiocytes” (tissue-resident macrophages and DCs) that are derived in part from blood-borne monocytes and DCs. The capacity of circulating monocytes and DCs to function as the body’s first-line defense against offending pathogens greatly depends on their ability to egress the bloodstream and infiltrate inflammatory sites. Extravasation involves a sequence of coordinated molecular events and is initiated by E-selectin-mediated deceleration of the circulating leukocytes onto microvascular endothelial cells of the target tissue. E-selectin is inducibly expressed by cytokines (tumor necrosis factor-α and IL-1β) on inflamed endothelium, and binds to sialofucosylated glycan determinants displayed on protein and lipid scaffolds of blood cells. Efficient extravasation of circulating monocytes and DCs to inflamed tissues is crucial in facilitating an effective immune response, but also fuels the immunopathology of several inflammatory disorders. Thus, insights into the structural and functional properties of the E-selectin ligands expressed by different monocyte and DC populations is key to understanding the biology of protective immunity and the pathobiology of several acute and chronic inflammatory diseases. This review will address the role of E-selectin in recruitment of human circulating monocytes and DCs to sites of tissue injury/inflammation, the structural biology of the E-selectin ligands expressed by these cells, and the molecular effectors that shape E-selectin ligand cell-specific display. In addition, therapeutic approaches targeting E-selectin receptor/ligand interactions, which can be used to boost host defense or, conversely, to dampen pathological inflammatory conditions, will also be discussed.

ST6Gal-I sialyltransferase promotes tumor necrosis factor (TNF)-mediated cancer cell survival via sialylation of the TNF receptor 1 (TNFR1) death receptor

Activation of the tumor necrosis factor receptor 1 (TNFR1) death receptor by TNF induces either cell survival or cell death. However, the mechanisms mediating these distinct outcomes remain poorly understood. In this study, we report that the ST6Gal-I sialyltransferase, an enzyme up-regulated in numerous cancers, sialylates TNFR1 and thereby protects tumor cells from TNF-induced apoptosis. Using pancreatic and ovarian cancer cells with ST6Gal-I knockdown or overexpression, we determined that α2-6 sialylation of TNFR1 had no effect on early TNF-induced signaling events, including the rapid activation of NF-κB, c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase (ERK), and Akt (occurring within 15 min). However, upon extended TNF treatment (6-24 h), cells with high ST6Gal-I levels exhibited resistance to TNF-induced apoptosis, as indicated by morphological evidence of cell death and decreased activation of caspases 8 and 3. Correspondingly, at these later time points, high ST6Gal-I expressers displayed sustained activation of the survival molecules Akt and NF-κB. Additionally, extended TNF treatment resulted in the selective enrichment of clonal variants with high ST6Gal-I expression, further substantiating a role for ST6Gal-I in cell survival. Given that TNFR1 internalization is known to be essential for apoptosis induction, whereas survival signaling is initiated by TNFR1 at the plasma membrane, we examined TNFR1 localization. The α2-6 sialylation of TNFR1 was found to inhibit TNF-induced TNFR1 internalization. Thus, by restraining TNFR1 at the cell surface via sialylation, ST6Gal-I acts as a functional switch to divert signaling toward survival. These collective findings point to a novel glycosylation-dependent mechanism that regulates the cellular response to TNF and may promote cancer cell survival within TNF-rich tumor microenvironments.

miR-182 and miR-135b Mediate the Tumorigenesis and Invasiveness of Colorectal Cancer Cells via Targeting ST6GALNAC2 and PI3K/AKT Pathway

BACKGROUND

Metastasis is a leading cause of cancer-related death including colorectal cancer (CRC). MicroRNAs are known to regulate cancer pathways and to be expressed aberrantly in cancer. Aberrant sialylation is closely associated with malignant phenotype of tumor cells, including invasiveness and metastasis.

AIM

This study aimed to investigate the association of miR-182 and miR-135b with proliferation and invasion by targeting sialyltransferase ST6GALNAC2 in CRC cells and explore the potential molecular mechanism.

METHODS

We measured the levels of miR-182, miR-135b, and ST6GALNAC2 in a series of CRC cell lines and tissues using real-time PCR. Bioinformatics analysis and luciferase reporter assay were performed to test the direct binding of miR-182 and miR-135b to the target gene ST6GALNAC2. We also analyzed the possible role of miR-182/-135b on colony formation, wound healing, invasion, and tube formation.

RESULTS

The expression of miR-182 and miR-135b was higher in tumor tissues compared to adjacent noncancerous tissues of CRC patients, as well as up-regulated in SW620 cells than in SW480 cells with different metastatic potential. By applying bioinformatics analysis and luciferase reporter assay, we identified ST6GALNAC2 as the direct target of miR-182/-135b. Furthermore, miR-182/-135b inhibited significantly ST6GALNAC2 expression, and consistently, ST6GALNAC2 mediated migration, adhesion, invasion, proliferation, and tumor angiogenesis in CRC cell lines. Additionally, PI3K/AKT signaling pathway was regulated by miR-182/135b, which was partially blocked by altered level of ST6GALNAC2 in CRC.

CONCLUSIONS

The miR-182/-135b/ST6GALNAC2/PI3K/AKT axis may serve as a predictive biomarker and a potential therapeutic target in CRC treatment.

Organelle Specific O-Glycosylation Drives MMP14 Activation, Tumor Growth, and Metastasis

Cancers grow within tissues through molecular mechanisms still unclear. Invasiveness correlates with perturbed O-glycosylation, a covalent modification of cell-surface proteins. Here, we show that, in human and mouse liver cancers, initiation of O-glycosylation by the GALNT glycosyl-transferases increases and shifts from the Golgi to the endoplasmic reticulum (ER). In a mouse liver cancer model, expressing an ER-targeted GALNT1 (ER-G1) massively increased tumor expansion, with median survival reduced from 23 to 10 weeks. In vitro cell growth was unaffected, but ER-G1 strongly enabled matrix degradation and tissue invasion. Unlike its Golgi-localized counterpart, ER-G1 glycosylates the matrix metalloproteinase MMP14, a process required for tumor expansion. Together, our results indicate that GALNTs strongly promote liver tumor growth after relocating to the ER.

α2,6-linked sialic acid serves as a high-affinity receptor for cancer oncolytic virotherapy with Newcastle disease virus

PURPOSE

Newcastle disease virus (NDV) has been applied to oncolytic virotherapy for decades due to its naturally oncolytic property. In spite of the substantiation of the sialic acid receptors of NDV on host cells, knowledge of preference of sialic acid linkage in viral attachment and oncolytic effect is lacking and imperative to be elucidated.

METHODS

Surface plasmon resonance analysis and competitive inhibition with sialylated glycan receptor analogues were used to determine the affinity and the preference of sialic acid receptor. Treatments of sialyltransferase inhibitors and linkage-specific sialidases and transfection with sialyltransferase expression vector were performed to regulate sialic acids levels.

RESULTS

We demonstrated that sialic acid was essential for NDV binding and infection of tumor cells. α2,6-linked sialic acid served as a high-affinity receptor for NDV and the ST6Gal I sialyltransferase that synthesizes α2-6 linkage of sialylated N-linked glycans in CHO-K1 cells promoted NDV binding and cytopathic effect. More importantly, an enhanced antitumor effect of NDV on aggressive SW620 colorectal carcinoma cells with high-level of cell surface α2,6-sialylation, but not SW480 cells with relative low-level of α2,6-sialylation, was observed both in vitro and in vivo.

CONCLUSIONS

The study provides evidence of optimized therapeutic strategy in oncolytic virotherapy via partly defining α2,6-sialylated receptor as a "cellular marker" for NDV.

Sialic Acid-Targeted Biointerface Materials and Bio-Applications

Sialic acids (SAs) are typically found as terminal monosaccharides attached to cell surface glycoconjugates, which play crucial roles in various biological processes, and aberrant sialylation is closely associated with many diseases, particularly cancers. As SAs are overexpressed in tumor-associated glycoproteins, the recognition and specific binding of SA are crucial for monitoring, analyzing and controlling cancer cells, which would have a considerable impact on diagnostic and therapeutic application. However, both effective and selective recognition of SA on the cancer cell surface remains challenging. In recent years, SA-targeted biointerface materials have attracted great attention in various bio-applications, including cancer detection and imaging, drug delivery for cancer therapy and sialylated glycopeptide separation or enrichment. This review provides an overview of recent advances in SA-targeted biointerface materials and related bio-applications.

Cell surface N-glycan alteration in HepAD38 cell lines expressing Hepatitis B virus

Hepatitis B virus (HBV) is the smallest partially double-stranded DNA virus known to infect humans. Worldwide, more than 50% of hepatocellular carcinoma (HCC) cases are related to chronic Hepatitis B. Development of HCC from normal liver cells is characterized by changes in cell surface N-glycans, which can promote the invasive behavior of tumor cells, leading ultimately to the progression of cancer. However, little is understood about the cell surface N-glycans of HBV-infected liver cells. We try to address this by taking advantage of the HepAD38 cell line, which can replicate HBV in the absence of tetracycline [tet(-)] in growth medium. In the presence of tetracycline [tet(+)], this cell line is free from the virus due to the repression of pregenomic (pg) RNA synthesis. In culture medium without tetracycline, cells express viral pgRNA and start to secrete virions into the supernatant. Here we studied the expression of glycosyltransferases and the cell surface N-glycan composition of tet(+) and tet(-) HepAD38. Among the glycosyltransferases upregulated by the expression of HBV were GnT-II, GnT-IVa, ST6Gal1, and GnT-V, whereas GnT-I, GnT-III, β4GalT1, and FUT8 were downregulated. About one-third of the total cell surface N-glycans found on tet(-)HepAD38 were sialylated. As for tet(+)HepAD38, sialylation was 6% lower compared to the tet(-) cells. Neither treatment changed the cell surface N-glycans expression of the total complex type or the total fucosylated type, which were about 50% or 60%, respectively. Our results showed that the expression of HBV triggers higher sialylation in HepAD38 cells. Altogether, the results show that HBV expression triggered the alteration of the cell surface N-glycosylation pattern and the expression levels of glycosyltransferases of HepAD38 cells.

Epigenetic Bases of Aberrant Glycosylation in Cancer

In this review, the sugar portions of glycoproteins, glycolipids, and glycosaminoglycans constitute the glycome, and the genes involved in their biosynthesis, degradation, transport and recognition are referred to as “glycogenes“. The extreme complexity of the glycome requires the regulatory layer to be provided by the epigenetic mechanisms. Almost all types of cancers present glycosylation aberrations, giving rise to phenotypic changes and to the expression of tumor markers. In this review, we discuss how cancer-associated alterations of promoter methylation, histone methylation/acetylation, and miRNAs determine glycomic changes associated with the malignant phenotype. Usually, increased promoter methylation and miRNA expression induce glycogene silencing. However, treatment with demethylating agents sometimes results in silencing, rather than in a reactivation of glycogenes, suggesting the involvement of distant methylation-dependent regulatory elements. From a therapeutic perspective aimed at the normalization of the malignant glycome, it appears that miRNA targeting of cancer-deranged glycogenes can be a more specific and promising approach than the use of drugs, which broad target methylation/acetylation. A very specific type of glycosylation, the addition of GlcNAc to serine or threonine (O-GlcNAc), is not only regulated by epigenetic mechanisms, but is an epigenetic modifier of histones and transcription factors. Thus, glycosylation is both under the control of epigenetic mechanisms and is an integral part of the epigenetic code.

Expression of sialyl-Tn sugar antigen in bladder cancer cells affects response to Bacillus Calmette Guérin (BCG) and to oxidative damage

The sialyl-Tn (sTn) antigen is an O-linked carbohydrate chain aberrantly expressed in bladder cancer (BC), whose biosynthesis is mainly controlled by the sialyltransferase ST6GALNAC1. Treatment with Bacillus Calmette-Guérin (BCG) is the most effective adjuvant immunotherapy for superficial BC but one third of the patients fail to respond. A poorly understood correlation between the expression of sTn and BC patient's response to BCG was previously observed. By analyzing tumor tissues, we showed that patients with high ST6GALNAC1 and IL-6 mRNA expression were BCG responders. To investigate the role of sTn in BC cell biology and BCG response, we established the cell lines MCR_sTn and MCR_Nc by retroviral transduction of the BC cell line MCR with the ST6GALNAC1 cDNA or with an empty vector, respectively. Compared with MCR_Nc, BCG-stimulated MCR_sTn secreted higher levels of IL-6 and IL-8 and their secretome induced a stronger IL-6, IL-1β, and TNFα secretion by macrophages, suggesting the induction of a stronger inflammatory response. Transcriptomic analysis of MCR_Nc and MCR_sTn revealed that ST6GALNAC1/sTn expression modulates hundreds of genes towards a putative more malignant phenotype and down-regulates several genes maintaining genomic stability. Consistently, MCR_sTn cells displayed higher H₂O₂ sensitivity. In MCR_sTn,, BCG challenge induced an increased expression of several regulatory non coding RNA genes. These results indicate that the expression of ST6GALNAC1/sTn improves the response to BCG therapy by inducing a stronger macrophage response and alters gene expression towards malignancy and genomic instability, increasing the sensitivity of BC cells to the oxidizing agents released by BCG.

A standardized method for lectin microarray-based tissue glycome mapping

The significance of glycomic profiling has been highlighted by recent findings that structural changes of glycans are observed in many diseases, including cancer. Therefore, glycomic profiling of the whole body (glycome mapping) under different physiopathological states may contribute to the discovery of reliable biomarkers with disease-specific alterations. To achieve this, standardization of high-throughput and in-depth analysis of tissue glycome mapping is needed. However, this is a great challenge due to the lack of analytical methodology for glycans on small amounts of endogenous glycoproteins. Here, we established a standardized method of lectin-assisted tissue glycome mapping. Formalin-fixed, paraffin-embedded tissue sections were prepared from brain, liver, kidney, spleen, and testis of two C57BL/6J mice. In total, 190 size-adjusted fragments with different morphology were serially collected from each tissue by laser microdissection and subjected to lectin microarray analysis. The results and subsequent histochemical analysis with selected lectins were highly consistent with previous reports of mass spectrometry-based N- and/or O-glycome analyses and histochemistry. This is the first report to look at both N- and O-glycome profiles of various regions within tissue sections of five different organs. This simple and reproducible mapping approach is also applicable to various disease model mice to facilitate disease-related biomarker discovery.

Harnessing cancer cell metabolism for theranostic applications using metabolic glycoengineering of sialic acid in breast cancer as a pioneering example

Abnormal cell surface display of sialic acids - a family of unusual 9-carbon sugars - is widely recognized as distinguishing feature of many types of cancer. Sialoglycans, however, typically cannot be identified with sufficiently high reproducibility and sensitivity to serve as clinically accepted biomarkers and similarly, almost all efforts to exploit cancer-specific differences in sialylation signatures for therapy remain in early stage development. In this report we provide an overview of important facets of glycosylation that contribute to cancer in general with a focus on breast cancer as an example of malignant disease characterized by aberrant sialylation. We then describe how cancer cells experience nutrient deprivation during oncogenesis and discuss how the resulting metabolic reprogramming, which endows breast cancer cells with the ability to obtain nutrients during scarcity, constitutes an "Achilles' heel" that we believe can be exploited by metabolic glycoengineering (MGE) strategies to develop new diagnostic methods and therapeutic approaches. In particular, we hypothesize that adaptations made by breast cancer cells that allow them to efficiently scavenge sialic acid during times of nutrient deprivation renders them vulnerable to MGE, which refers to the use of exogenously-supplied, non-natural monosaccharide analogues to modulate targeted aspects of glycosylation in living cells and animals. In specific, once non-natural sialosides are incorporated into the cancer "sialome" they can be exploited as epitopes for immunotherapy or as chemical tags for targeted delivery of imaging or therapeutic agents selectively to tumors.

Quantitative Glycomics: A Combined Analytical and Bioinformatics Approach

Glycosylation is one of the most common and essential protein modifications. Glycans conjugated to biomolecules modulate the function of such molecules through both direct recognition of glycan structures and indirect mechanisms that involve the control of protein turnover rates, stability, and conformation. The biological attributes of glycans in numerous biological processes and implications in a number of diseases highlight the necessity for comprehensive characterization of protein glycosylation. This chapter reviews cutting-edge methods and tools developed to facilitate quantitative glycomics. This chapter highlights the different methods employed for the release and purification of glycans from biological samples. The most effective labeling methods developed for sensitive quantitative glycomics are also described and discussed. The chromatographic approaches that have been used effectively in glycomics are also highlighted.

Identification of novel plasma glycosylation-associated markers of aging

The pro- or anti-inflammatory activities of immunoglobulins G (IgGs) are controlled by the structure of the glycan N-linked to Asn₂₉₇ of their heavy chain. The age-associated low grade inflammation (inflammaging) is associated with increased plasmatic levels of agalactosylated IgGs terminating with N-acetylglucosamine (IgG-G0) whose biogenesis has not been fully explained. Although the biosynthesis of glycans is in general mediated by glycosyltransferases associated with internal cell membranes, the extracellular glycosylation of circulating glycoproteins mediated by plasmatic glycosyltransferases has been recently demonstrated. In this study we have investigated the relationship between plasmatic glycosyltransferases, IgG glycosylation and inflammatory and aging markers. In cohorts of individuals ranging from infancy to centenarians we determined the activity of plasmatic β4 galactosyltransferase(s) (B4GALTs) and of α2,6-sialyltransferase ST6GAL1, the glycosylation of IgG, the GlycoAge test (a glycosylation-based marker of aging) and the plasma level of inflammatory and liver damage markers. Our results show that: 1) plasmatic B4GALTs activity is a new marker of aging, showing a linear increase throughout the whole age range. 2) plasmatic ST6GAL1 was high only in children and in people above 80, showing a quadratic relationship with age. 3) Neither plasmatic glycosyltransferase correlated with markers of liver damage. 4) plasmatic ST6GAL1 showed a positive association with acute phase proteins in offspring of short lived parents, but not in centenarians or in their offspring. 5) Although the glycosylation of IgGs was not correlated with the level of the two plasmatic glycosyltransferases, it showed progressive age-associated changes consistent with a shift toward a pro-inflammatory glycotype.

Extreme Activity of Drug Nanocrystals Coated with A Layer of Non-Covalent Polymers from Self-Assembled Boric Acid

Non-covalent polymers have remarkable advantages over synthetic polymers for wide biomedical applications. In this study, non-covalent polymers from self-assembled boric acid were used as the capping reagent to replace synthetic polymers in drug crystallization. Under acidic pH, boric acid self-assembled on the surface of drug nanocrystals to form polymers with network-like structures held together by hydrogen bonds. Coating driven by boric acid self-assembly had negligible effects on drug crystallinity and structure but resulted in drug nanocrystals with excellent dispersion properties that aided in the formation of a more stable suspension. Boric acid coating improved drug stability dramatically by preventing drug molecules from undergoing water hydrolysis in a neutral environment. More importantly, the specific reactivity of orthoboric groups to diols in cell glycocalyx facilitated a rapid cross-membrane translocation of drug nanocrystals, leading to efficient intracellular drug delivery, especially on cancer cells with highly expressed sialic acids. Boric acid coated nanocrystals of camptothecin, an anticancer drug with poor aqueous solubility and stability, demonstrated extreme cytotoxic activity (IC₅₀ < 5.0 μg/mL) to cancer cells compared to synthetic polymer coated CPT nanocrystals and free CPT. Surface coating using non-covalent polymers from self-assembled boric acid will have wide biomedical applications especially in biomaterials and drug delivery field.

Circulating blood and platelets supply glycosyltransferases that enable extrinsic extracellular glycosylation

Glycosyltransferases, usually residing within the intracellular secretory apparatus, also circulate in the blood. Many of these blood-borne glycosyltransferases are associated with pathological states, including malignancies and inflammatory conditions. Despite the potential for dynamic modifications of glycans on distal cell surfaces and in the extracellular milieu, the glycan-modifying activities present in systemic circulation have not been systematically examined. Here, we describe an evaluation of blood-borne sialyl-, galactosyl- and fucosyltransferase activities that act upon the four common terminal glycan precursor motifs, GlcNAc monomer, Gal(β3)GlcNAc, Gal(β4)GlcNAc and Gal(β3)GalNAc, to produce more complex glycan structures. Data from radioisotope assays and detailed product analysis by sequential tandem mass spectrometry show that blood has the capacity to generate many of the well-recognized and important glycan motifs, including the Lewis, sialyl-Lewis, H- and Sialyl-T antigens. While many of these glycosyltransferases are freely circulating in the plasma, human and mouse platelets are important carriers for others, including ST3Gal-1 and β4GalT. Platelets compartmentalize glycosyltransferases and release them upon activation. Human platelets are also carriers for large amounts of ST6Gal-1 and the α3-sialyl to Gal(β4)GlcNAc sialyltransferases, both of which are conspicuously absent in mouse platelets. This study highlights the capability of circulatory glycosyltransferases, which are dynamically controlled by platelet activation, to remodel cell surface glycans and alter cell behavior.

RNase activity of sialic acid-binding lectin from bullfrog eggs drives antitumor effect via the activation of p38 MAPK to caspase-3/7 signaling pathway in human breast cancer cells

Sialic acid-binding lectin obtained from bullfrog eggs (SBL) induces cell death in cancer cells but not in normal cells. This antitumor effect is mediated through its ribo-nuclease (RNase) activity. However, the underlying molecular mechanisms remain unclear. We found that the p38 mitogen-activated protein kinase (MAPK) signaling pathway was activated when SBL induced cell death in three human breast cancer cell lines: SK-BR-3, MCF-7, and MDA-MB231. The suppression of p38 MAPK phosphorylation by a p38 MAPK inhibitor as well as short interference RNA knockdown of p38 MAPK expression significantly decreased cell death and increased the cell viability of SBL-treated MDA-MB231 cells. H103A, an SBL mutant lacking in RNase activity, showed decreased SBL-induced cell death compared with native SBL. However, the loss of RNase activity of SBL had no effect on its internalization into cells. The H103A mutant also displayed decreased phosphorylation of p38 MAPK. Moreover, SBL promoted caspase-3/7 activation followed by a cleavage of poly (ADP-ribose)-polymerase, whereas the SBL mutant, H103A, lost this ability. The SBL-induced caspase-3/7 activation was suppressed by the p38 MAPK inhibitor, SB203580, as well as pan-caspase inhibitor, zVAD-fmk. In the presence of zVAD-fmk, the SBL-induced cell death was decreased. In addition, the cell viability of SBL-treated MDA-MB231 cells recovered by zVAD-fmk treatment. Taken together, our results suggest that the RNase activity of SBL leads to breast cancer cell death through the activation of p38 MAPK followed by the activation of caspase-3/7.

The Tumor-Associated Glycosyltransferase ST6Gal-I Regulates Stem Cell Transcription Factors and Confers a Cancer Stem Cell Phenotype

The glycosyltransferase ST6Gal-I, which adds α2-6-linked sialic acids to substrate glycoproteins, has been implicated in carcinogenesis; however, the nature of its pathogenic role remains poorly understood. Here we show that ST6Gal-I is upregulated in ovarian and pancreatic carcinomas, enriched in metastatic tumors, and associated with reduced patient survival. Notably, ST6Gal-I upregulation in cancer cells conferred hallmark cancer stem-like cell (CSC) characteristics. Modulating ST6Gal-I expression in pancreatic and ovarian cancer cells directly altered CSC spheroid growth, and clonal variants with high ST6Gal-I activity preferentially survived in CSC culture. Primary ovarian cancer cells from patient ascites or solid tumors sorted for α2-6 sialylation grew as spheroids, while cells lacking α2-6 sialylation remained as single cells and lost viability. ST6Gal-I also promoted resistance to gemcitabine and enabled the formation of stably resistant colonies. Gemcitabine treatment of patient-derived xenograft tumors enriched for ST6Gal-I-expressing cells relative to pair-matched untreated tumors. ST6Gal-I also augmented tumor-initiating potential. In limiting dilution assays, subcutaneous tumor formation was inhibited by ST6Gal-I knockdown, whereas in a chemically induced tumor initiation model, mice with conditional ST6Gal-I overexpression exhibited enhanced tumorigenesis. Finally, we found that ST6Gal-I induced expression of the key tumor-promoting transcription factors, Sox9 and Slug. Collectively, this work highlighted a previously unrecognized role for a specific glycosyltransferase in driving a CSC state. Cancer Res; 76(13); 3978-88. ©2016 AACR.

MALDI-MS analysis of sialylated N-glycan linkage isomers using solid-phase two step derivatization method

Sialic acids usually locate at the terminal of many glycan structures in either α(2,3) or α(2,6) linkage, playing different roles in various biological and pathological processes. Several linkage specific carboxyl derivatization methods have been reported to discriminate between α(2,3) and α(2,6)-linked sialic acids by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Among them, ethyl esterification was recently reported to achieve linkage specific derivatization between α(2,3) and α(2,6)-linked sialic acids with good selectivity. However, the method suffered from the instability of the generated lactones and byproducts of the derivatives. To overcome these shortcomings, a solid-phase two step derivatization method was introduced to convert the α(2,6)-linked sialic acid into ethyl esters and the α(2,3)-inked counterparts into N-methyl amides, respectively. Under the optimized derivatization conditions, our method was able to achieve accurate relative quantification of N-glycan as well as their corresponding sialylated linkage types, superior to the ethyl esterification method. The solid phase derivatization strategy was further applied to investigate N-glycans from biosimilar antibody drug and human serum from patients and healthy volunteers. This method has the potential to be used in the biomarker discovery and pharmaceutical industry.

The Origin and Activities of IgA1-Containing Immune Complexes in IgA Nephropathy

IgA nephropathy (IgAN) is the most common primary glomerulonephritis, frequently leading to end-stage renal disease, as there is no disease-specific therapy. IgAN is diagnosed from pathological assessment of a renal biopsy specimen based on predominant or codominant IgA-containing immunodeposits, usually with complement C3 co-deposits and with variable presence of IgG and/or IgM. The IgA in these renal deposits is galactose-deficient IgA1, with less than a full complement of galactose residues on the O-glycans in the hinge region of the heavy chains. Research from the past decade led to the definition of IgAN as an autoimmune disease with a multi-hit pathogenetic process with contributing genetic and environmental components. In this process, circulating galactose-deficient IgA1 (autoantigen) is bound by antiglycan IgG or IgA (autoantibodies) to form immune complexes. Some of these circulating complexes deposit in glomeruli, and thereby activate mesangial cells and induce renal injury through cellular proliferation and overproduction of extracellular matrix components and cytokines/chemokines. Glycosylation pathways associated with production of the autoantigen and the unique characteristics of the corresponding autoantibodies in patients with IgAN have been uncovered. Complement likely plays a significant role in the formation and the nephritogenic activities of these complexes. Complement activation is mediated through the alternative and lectin pathways and probably occurs systemically on IgA1-containing circulating immune complexes as well as locally in glomeruli. Incidence of IgAN varies greatly by geographical location; the disease is rare in central Africa but accounts for up to 40% of native-kidney biopsies in eastern Asia. Some of this variation may be explained by genetically determined influences on the pathogenesis of the disease. Genome-wide association studies to date have identified several loci associated with IgAN. Some of these loci are associated with the increased prevalence of IgAN, whereas others, such as deletion of complement factor H-related genes 1 and 3, are protective against the disease. Understanding the molecular mechanisms and genetic and biochemical factors involved in formation and activities of pathogenic IgA1-containing immune complexes will enable the development of future disease-specific therapies as well as identification of non-invasive disease-specific biomarkers.

Glycomic Approaches for the Discovery of Targets in Gastrointestinal Cancer

Gastrointestinal (GI) cancer is the most common group of malignancies and many of its types are among the most deadly. Various glycoconjugates have been used in clinical practice as serum biomarker for several GI tumors, however, with limited diagnose application. Despite the good accessibility by endoscopy of many GI organs, the lack of reliable serum biomarkers often leads to late diagnosis of malignancy and consequently low 5-year survival rates. Recent advances in analytical techniques have provided novel glycoproteomic and glycomic data and generated functional information and putative biomarker targets in oncology. Glycosylation alterations have been demonstrated in a series of glycoconjugates (glycoproteins, proteoglycans, and glycosphingolipids) that are involved in cancer cell adhesion, signaling, invasion, and metastasis formation. In this review, we present an overview on the major glycosylation alterations in GI cancer and the current serological biomarkers used in the clinical oncology setting. We further describe recent glycomic studies in GI cancer, namely gastric, colorectal, and pancreatic cancer. Moreover, we discuss the role of glycosylation as a modulator of the function of several key players in cancer cell biology. Finally, we address several state-of-the-art techniques currently applied in this field, such as glycomic and glycoproteomic analyses, the application of glycoengineered cell line models, microarray and proximity ligation assay, and imaging mass spectrometry, and provide an outlook to future perspectives and clinical applications.

ST6GalNAcII mediates tumor invasion through PI3K/Akt/NF-κB signaling pathway in follicular thyroid carcinoma

Altered sialylation, closely associated with tumor progression and metastasis, has been implicated in human thyroid carcinoma. The present study investigated the alteration in expression of ST6GalNAcII involved in invasion and to clarify the possible mechanism of ST6GalNAcII in the metastasis process in human follicular thyroid carcinoma cell lines. Using real-time PCR, western blot and IHC analysis, ST6GalNAcII differed in three follicular thyroid cancer cell lines (FTC133, primary and FTC238, lung metastasis). It also showed differential expression in follicular thyroid carcinoma and tissue specimens. In addition, we analyzed the PI3K/Akt signaling pathway. The altered expression of ST6GalNAcII corresponded to changed invasive phenotype of FTC-238 and FTC-133 cells in vitro and in vivo. Further studies showed that regulating ST6GalNAcII expression markedly modulated the activity of the phosphoinositide 3-kinase (PI3K)/Akt signaling pathway. Targeting the PI3K/Akt pathway by its specific inhibitor LY294002, or by Akt small interfering RNA (siRNA) resulted in reduced capacity in invasion of FTC-238. In conclusion, taken together, our results imply that ST6GalNAcII activated the invasion in follicular thyroid cancer cells through regulating the activity of PI3K/Akt pathway.

Expression of N-Acetylglucosaminyltransferase III Suppresses α2,3-Sialylation, and Its Distinctive Functions in Cell Migration Are Attributed to α2,6-Sialylation Levels

N-Acetylglucosaminyltransferase III (GnT-III), which catalyzes the addition of the bisecting GlcNAc branch on N-glycans, is usually described as a metastasis suppressor. Overexpression of GnT-III inhibited migration in multiple types of tumor cells. However, these results seem controversial to the clinical observations for the increased expression of GnT-III in human hepatomas, glioma, and ovarian cancers. Here, we present evidence that these inconsistencies are mainly attributed to the different expression pattern of cell sialylation. In detail, we show that overexpression of GnT-III significantly inhibits α2,3-sialylation but not α2,6-sialylation. The migratory ability of cells without or with a low level of α2,6-sialylation is consistently suppressed after GnT-III overexpression. In contrast, the effects of GnT-III overexpression are variable in tumor cells that are highly α2,6-sialylated. Overexpression of GnT-III promotes the cell migration in glioma cells U-251 and hepatoma cells HepG2, although it has little influence in human breast cancer cell MDA-MB-231 and gastric cancer cell MKN-45. Interestingly, up-regulation of α2,6-sialylation by overexpressing β-galactoside α2,6-sialyltranferase 1 in the α2,6-hyposialylated HeLa-S3 cells abolishes the anti-migratory effects of GnT-III. Conversely, depletion of α2,6-sialylation by knock-out of β-galactoside α2,6-sialyltranferase 1 in α2,6-hypersialylated HepG2 cells endows GnT-III with the anti-migratory ability. Taken together, our data clearly demonstrate that high expression of α2,6-sialylation on the cell surface could affect the anti-migratory role of GnT-III, which provides an insight into the mechanistic roles of GnT-III in tumor metastasis.

miR-4299 mediates the invasive properties and tumorigenicity of human follicular thyroid carcinoma by targeting ST6GALNAC4

Altered sialylation is closely associated with tumor progression and invasiveness. Micro-RNAs endogenous regulators of gene expression have been implicated in human thyroid carcinoma invasiveness. The objective of this study is to examine the alterations of miR-4299 and ST6GALNAC family in human follicular thyroid carcinoma during metastatic process. qRT-PCR showed the differential expressional profiles of miR-4299 and ST6GALNAC family in three kinds of thyroid cell lines (FTC-133,FTC-238, Nthy-ori 3-1) and clinical tissue specimens(malignant and borderline). The altered expression levels of ST6GALNAC4 were corresponding to invasive phenotypes of FTC-133 and FTC-238 cells both in vitro and in vivo. Further date indicated that miR-4299 regulated tumor progression and invasiveness by directly targeting ST6GALNAC4. This study implies the potential therapeutic application of miR-4299 and ST6GALNAC4 in modulating the invasion and tumorigenicity of follicular thyroid carcinoma cell.

Glycomic analysis of gastric carcinoma cells discloses glycans as modulators of RON receptor tyrosine kinase activation in cancer

BACKGROUND

Terminal α2-3 and α2-6 sialylation of glycans precludes further chain elongation, leading to the biosynthesis of cancer relevant epitopes such as sialyl-Lewis X (SLe(X)). SLe(X) overexpression is associated with tumor aggressive phenotype and patients' poor prognosis.

METHODS

MKN45 gastric carcinoma cells transfected with the sialyltransferase ST3GAL4 were established as a model overexpressing sialylated terminal glycans. We have evaluated at the structural level the glycome and the sialoproteome of this gastric cancer cell line applying liquid chromatography and mass spectrometry. We further validated an identified target expression by proximity ligation assay in gastric tumors.

RESULTS

Our results showed that ST3GAL4 overexpression leads to several glycosylation alterations, including reduced O-glycan extension and decreased bisected and increased branched N-glycans. A shift from α2-6 towards α2-3 linked sialylated N-glycans was also observed. Sialoproteomic analysis further identified 47 proteins with significantly increased sialylated N-glycans. These included integrins, insulin receptor, carcinoembryonic antigens and RON receptor tyrosine kinase, which are proteins known to be key players in malignancy. Further analysis of RON confirmed its modification with SLe(X) and the concomitant activation. SLe(X) and RON co-expression was validated in gastric tumors.

CONCLUSION

The overexpression of ST3GAL4 interferes with the overall glycophenotype of cancer cells affecting a multitude of key proteins involved in malignancy. Aberrant glycosylation of the RON receptor was shown as an alternative mechanism of oncogenic activation.

GENERAL SIGNIFICANCE

This study provides novel targets and points to an integrative tumor glycomic/proteomic-profiling for gastric cancer patients' stratification. This article is part of a Special Issue entitled "Glycans in personalised medicine" Guest Editor: Professor Gordan Lauc.

Mass Spectrometry-Based N-Glycomics of Colorectal Cancer

Colorectal cancer (CRC) is one of the most prevalent cancers worldwide. An increased molecular understanding of the CRC pathology is warranted to gain insights into the underlying molecular and cellular mechanisms of the disease. Altered protein glycosylation patterns are associated with most diseases including malignant transformation. Recent advances in mass spectrometry and bioinformatics have accelerated glycomics research and present a new paradigm for cancer biomarker discovery. Mass spectrometry (MS)-based glycoproteomics and glycomics, therefore, hold considerable promise to improve the discovery of novel biomarkers with utility in disease diagnosis and therapy. This review focuses on the emerging field of glycomics to present a comprehensive review of advances in technologies and their application in studies aimed at discovering novel glycan-based biomarkers. We will also discuss some of the challenges associated with using glycans as biomarkers.

ST3GAL1-Associated Transcriptomic Program in Glioblastoma Tumor Growth, Invasion, and Prognosis

Background:

Cell surface sialylation is associated with tumor cell invasiveness in many cancers. Glioblastoma is the most malignant primary brain tumor and is highly infiltrative. ST3GAL1 sialyltransferase gene is amplified in a subclass of glioblastomas, and its role in tumor cell self-renewal remains unexplored.

Methods:

Self-renewal of patient glioma cells was evaluated using clonogenic, viability, and invasiveness assays. ST3GAL1 was identified from differentially expressed genes in Peanut Agglutinin–stained cells and validated in REMBRANDT (n = 390) and Gravendeel (n = 276) clinical databases. Gene set enrichment analysis revealed upstream processes. TGFβ signaling on ST3GAL1 transcription was assessed using chromatin immunoprecipitation. Transcriptome analysis of ST3GAL1 knockdown cells was done to identify downstream pathways. A constitutively active FoxM1 mutant lacking critical anaphase-promoting complex/cyclosome ([APC/C]-Cdh1) binding sites was used to evaluate ST3Gal1-mediated regulation of FoxM1 protein. Finally, the prognostic role of ST3Gal1 was determined using an orthotopic xenograft model (3 mice groups comprising nontargeting and 2 clones of ST3GAL1 knockdown in NNI-11 [8 per group] and NNI-21 [6 per group]), and the correlation with patient clinical information. All statistical tests on patients’ data were two-sided; other P values below are one-sided.

Results:

High ST3GAL1 expression defines an invasive subfraction with self-renewal capacity; its loss of function prolongs survival in a mouse model established from mesenchymal NNI-11 (P < .001; groups of 8 in 3 arms: nontargeting, C1, and C2 clones of ST3GAL1 knockdown). ST3GAL1 transcriptomic program stratifies patient survival (hazard ratio [HR] = 2.47, 95% confidence interval [CI] = 1.72 to 3.55, REMBRANDT P = 1.92x10^-8; HR = 2.89, 95% CI = 1.94 to 4.30, Gravendeel P = 1.05x10^-11), independent of age and histology, and associates with higher tumor grade and T2 volume (P = 1.46x10^-4). TGFβ signaling, elevated in mesenchymal patients, correlates with high ST3GAL1 (REMBRANDT glioma_cor = 0.31, P = 2.29x10^-10; Gravendeel glioma_cor = 0.50, P = 3.63x10^-20). The transcriptomic program upon ST3GAL1 knockdown enriches for mitotic cell cycle processes. FoxM1 was identified as a statistically significantly modulated gene (P = 2.25x10^-5) and mediates ST3Gal1 signaling via the (APC/C)-Cdh1 complex.

Conclusions:

The ST3GAL1-associated transcriptomic program portends poor prognosis in glioma patients and enriches for higher tumor grades of the mesenchymal molecular classification. We show that ST3Gal1-regulated self-renewal traits are crucial to the sustenance of glioblastoma multiforme growth.

Enhanced expression of polysialic acid correlates with malignant phenotype in breast cancer cell lines and clinical tissue samples

Polysialic acid (PSA) is highly expressed during embryonic development, but barely expressed during postnatal development, and may be 're-expressed' in cancer tissues. In this study, motility and migration assays were performed to compare the changes in cell behavior between non-malignant and maligant cells. Next, the expression levels of PSA were evaluated in 4 human and mouse normal breast or breast cancer (BC) cell lines using 1,2-diamino-4,5-methylenedioxybenzene-labeling HPLC technology, as well as in human clinical BC tissue samples. PSA expression was significantly higher in malignant cells (where it appeared to facilitate cell migration and motility) than in non-malignant cells. Enhanced PSA expression levels were also observed during epithelial-mesenchymal transition (EMT), a leading cause of cancer cell metastasis, which was induced in the NMuMG and MCF10A cells by treatment with transforming growth factor-β1 (TGF-β1). An increased PSA expression also correlated with the disease stage in the patients with BC (P<0.0001). Using RT-qPCR, we found that polysialyltransferase ST8SiaIV (PST) and polysialyltransferase ST8SiaII (STX), which are responsible for PSA synthesis, were differently expressed in the tested BC samples. However, PST, but not STX, was re-expressed in 14 out of 20 clinical BC samples. The findings of the present study indicate that the pathophysiology of BC involves the aberrant regulation of PSA expression and PST gene expression.

Glycosylation in cancer: mechanisms and clinical implications

Despite recent progress in understanding the cancer genome, there is still a relative delay in understanding the full aspects of the glycome and glycoproteome of cancer. Glycobiology has been instrumental in relevant discoveries in various biological and medical fields, and has contributed to the deciphering of several human diseases. Glycans are involved in fundamental molecular and cell biology processes occurring in cancer, such as cell signalling and communication, tumour cell dissociation and invasion, cell-matrix interactions, tumour angiogenesis, immune modulation and metastasis formation. The roles of glycans in cancer have been highlighted by the fact that alterations in glycosylation regulate the development and progression of cancer, serving as important biomarkers and providing a set of specific targets for therapeutic intervention. This Review discusses the role of glycans in fundamental mechanisms controlling cancer development and progression, and their applications in oncology.

p70 S6 kinase drives ovarian cancer metastasis through multicellular spheroid-peritoneum interaction and P-cadherin/b1 integrin signaling activation

Peritoneal dissemination as a manifestation of ovarian cancer is an adverse prognostic factor associated with poor clinical outcome, and is thus a potentially promising target for improved treatment. Sphere forming cells (multicellular spheroids) present in malignant ascites of patients with ovarian cancer represent a major impediment to effective treatment. p70 S6 kinase (p70^S6K), which is a downstream effector of mammalian target of rapamycin, is frequently hyperactivated in human ovarian cancer. Here, we identified p70^S6K as an important regulator for the seeding and successful colonization of ovarian cancer spheroids on the peritoneum. Furthermore, we provided evidence for the existence of a novel crosstalk between P-cadherin and β1 integrin, which was crucial for the high degree of specificity in cell adhesion. In particular, we demonstrated that the upregulation of mature β1 integrin occurred as a consequence of P-cadherin expression through the induction of the Golgi glycosyltransferase, ST6Gal-I, which mediated β1 integrin hypersialylation. Loss of p70^S6K or targeting the P-cadherin/β1-integrin interplay could significantly attenuate the metastatic spread onto the peritoneum in vivo. These findings establish a new role for p70^S6K in tumor spheroid-mesothelium communication in ovarian cancer and provide a preclinical rationale for targeting p70^S6K as a new avenue for microenvironment-based therapeutic strategy.

Noninvasive imaging of sialyltransferase activity in living cells by chemoselective recognition

To elucidate the biological and pathological functions of sialyltransferases (STs), intracellular ST activity evaluation is necessary. Focusing on the lack of noninvasive methods for obtaining the dynamic activity information, this work designs a sensing platform for in situ FRET imaging of intracellular ST activity and tracing of sialylation process. The system uses tetramethylrhodamine isothiocyanate labeled asialofetuin (TRITC-AF) as a ST substrate and fluorescein isothiocyanate labeled 3-aminophenylboronic acid (FITC-APBA) as the chemoselective recognition probe of sialylation product, both of which are encapsulated in a liposome vesicle for cellular delivery. The recognition of FITC-APBA to sialylated TRITC-AF leads to the FRET signal that is analyzed by FRET efficiency images. This strategy has been used to evaluate the correlation of ST activity with malignancy and cell surface sialylation, and the sialylation inhibition activity of inhibitors. This work provides a powerful noninvasive tool for glycan biosynthesis mechanism research, cancer diagnostics and drug development.