N-Glycomic and Transcriptomic Changes Associated with CDX1 mRNA Expression in Colorectal Cancer Cell Lines

Regulation of the Lewis Blood Group Antigen Expression: A Literature Review Supplemented with Computational Analysis

Background

The Lewis (Le) blood group system, unlike most other blood groups, is not defined by antigens produced internally to the erythrocytes and their precursors but rather by glycan antigens adsorbed on to the erythrocyte membrane from the plasma. These oligosaccharides are synthesized by the two fucosyltransferases FUT2 and FUT3 mainly in epithelial cells of the digestive tract and transferred to the plasma. At their place of synthesis, some Lewis blood group carbohydrate antigen variants also seem to be involved in various gastrointestinal malignancies. However, relatively little is known about the transcriptional regulation of FUT2 and FUT3.

Summary

To address this question, we screened existing literature and additionally used in silico prediction tools to identify novel candidate regulators for FUT2 and FUT3 and combine these findings with already known data on their regulation. With this approach, we were able to describe a variety of transcription factors, RNA binding proteins and microRNAs, which increase FUT2 and FUT3 transcription and translation upon interaction.

Key Messages

Understanding the regulation of FUT2 and FUT3 is crucial to fully understand the blood group system Lewis (ISBT 007 LE) phenotypes, to shed light on the role of the different Lewis antigens in various pathologies, and to identify potential new diagnostic targets for these diseases.

(Sialyl)Lewis Antigen Expression on Glycosphingolipids, N-, and O-Glycans in Colorectal Cancer Cell Lines is Linked to a Colon-Like Differentiation Program

Alterations in the glycomic profile are a hallmark of cancer, including colorectal cancer (CRC). While, the glycosylation of glycoproteins and glycolipids has been widely studied for CRC cell lines and tissues, a comprehensive overview of CRC glycomics is still lacking due to the usage of different samples and analytical methods. In this study, we compared glycosylation features of N-, O-glycans, and glycosphingolipid glycans for a set of 22 CRC cell lines, all measured by porous graphitized carbon nano-liquid chromatography-tandem mass spectrometry. An overall, high abundance of (sialyl)Lewis antigens for colon-like cell lines was found, while undifferentiated cell lines showed high expression of H blood group antigens and α2-3/6 sialylation. Moreover, significant associations of glycosylation features were found between the three classes of glycans, such as (sialyl)Lewis and H blood group antigens. Integration of the datasets with transcriptomics data revealed positive correlations between (sialyl)Lewis antigens, the corresponding glycosyltransferase FUT3 and transcription factors CDX1, ETS, HNF1/4A, MECOM, and MYB. This indicates a possible role of these transcription factors in the upregulation of (sialyl)Lewis antigens, particularly on glycosphingolipid glycans, via FUT3/4 expression in colon-like cell lines. In conclusion, our study provides insights into the possible regulation of glycans in CRC and can serve as a guide for the development of diagnostic and therapeutic biomarkers.

The Assessment of CDX1, IHH, SHH, GATA4, FOXA2, FOXF1 in Congenital Intra-Abdominal Adhesions

Congenital abdominal adhesions are a rare condition that can result in a small bowel obstruction at any age, more frequently in pediatric populations. The cause remains unknown, and the importance of aberrant congenital bands is related to the difficulty of diagnosis, and cases of death with late detection have been documented. This research examines the expression of Caudal Type Homeobox 1 (CDX1), Indian Hedgehog (IHH), Sonic Hedgehog (SHH), GATA Binding Protein 4 (GATA4), Forkhead Box A2 (FOXA2) and Forkhead Box F1 (FOXF1) gene expression in human abdominal congenital adhesion fibroblast and endothelium cells by chromogenic in situ hybridization, with the aim of elucidating their potential association with the etiology of congenital intra-abdominal adhesion band development. The potential genes' signals were examined using a semi-quantitative approach. Significant correlations were observed between the expression of CDX1 (p <.001) and SHH (p=0.032) genes in fibroblasts from congenital intra-abdominal adhesions compared to fibroblasts from control peritoneal tissue. Statistically significant very strong correlations were found between the CDX1 and IHH comparing endothelium and fibroblast cells in congenital abdominal adhesion bands. There was no statistically significant difference found in the distribution of IHH, FOXA2, GATA4, and FOXF1 between the fibroblasts and endothelium of the patients compared to the control group. The presence of notable distinctions and diverse associations suggests the potential involvement of numerous morpho-pathogenetic processes in the development of intraabdominal adhesions.

Label-Free Liquid Chromatography-Mass Spectrometry Quantitation of Relative N- and O-Glycan Concentrations in Human Milk in Japan

Human milk is abundant in carbohydrates and includes human milk oligosaccharides (HMOs) and N/O-glycans conjugated to proteins. HMO compositions and concentrations vary in individuals according to the maternal secretor status based on the fucosyltransferase 2 genotype; however, the profile of N/O-glycans remains uninvestigated because of the analytical complexity. Herein, we applied a label-free chromatography-mass spectrometry (LC-MS) technique to elucidate the variation in the composition and concentration of N/O-glycans in human milk. We used label-free LC-MS to relatively quantify 16 N-glycans and 12 O-glycans in 200 samples of Japanese human milk (1-2 months postpartum) and applied high performance anion exchange chromatography with pulsed amperometric detection to absolutely quantify the concentrations of 11 representative HMOs. Cluster analysis of the quantitative data revealed that O-glycans and several HMOs were classified according to the presence or absence of fucose linked to galactose while N-glycans were classified into a different group from O-glycans and HMOs. O-glycans and HMOs with fucose linked to galactose were more abundant in human milk from secretor mothers than from nonsecretor mothers. Thus, secretor status influenced the composition and concentration of HMOs and O-glycans but not those of N-glycans in human milk.

N-Glycomic Profiling of Microsatellite Unstable Colorectal Cancer

Aberrant glycosylation affects cancer progression and immune evasion. Approximately 15% of colorectal cancers (CRCs) demonstrate microsatellite instability (MSI) and display major differences in outcomes and therapeutic responses, as compared to corresponding microsatellite stable (MSS) tumors. We compared the N-glycan profiles of stage II and IV MSI CRC tumors, further subdivided into BRAF^V600E wild-type and mutated subgroups (n = 10 in each subgroup), with each other and with those of paired non-neoplastic mucosal samples using mass spectrometry. Further, the N-glycans of BRAF^V600E wild-type stage II MSI tumors were compared to corresponding MSS tumors (n = 9). Multiple differences in N-glycan profiles were identified between the MSI CRCs and control tissues, as well as between the stage II MSI and MSS samples. The MSI CRC tumors showed a lower relative abundance of high-mannose N-glycans than did the control tissues or the MSS CRCs. Among MSI CRC subgroups, acidic N-glycans showed tumor stage and BRAF mutation status-dependent variation. Specifically, the large, sulfated/phosphorylated, and putative terminal N-acetylhexosamine-containing acidic N-glycans differed between the MSI CRC subgroups, showing opposite changes in stages II and IV, when comparing BRAF mutated and wild-type tumors. Our results show that molecular subgroups of CRC exhibit characteristic glycan profiles that may explain certain carcinogenic properties of MSI tumors.

Human milk whey glycoprotein N-glycans varied greatly among different maternal secretor status

Human milk glycans are complex carbohydrates, which play a pivotal role in infant health and neonatal development. Maternal secretor status is known to affect free oligosaccharides in milk. Here, the milk N-glycome of secretor (Se+) and nonsecretor (Se-) individuals was qualitatively and quantitatively analyzed by hydrophilic interaction chromatography-electrospray ionization-tandem mass spectrometry. The total glycosylation, fucosylation, and sialylation of N-glycans was three times higher in the Se+ group compared to the Se- group (p < 0.001) per equal volume of milk. Importantly, 52 out of 63 N-glycans-including the eight most abundant ones-differed greatly between Se+ and Se- individuals (p < 0.05). Moreover, nine N-glycans (H5N3F1, H6N3, H3N5F1, H5N5F1, H5N5F1S1, H5N4F3S1, H6N4F2S1, H6N5F4S1, and H8N7S1) were >10 times more abundant in Se+ milk than in Se- milk. These findings lay a glycomics-basis for designing personalized nutrition supplements for infants.

In-Depth Analysis of the N-Glycome of Colorectal Cancer Cell Lines

Colorectal cancer (CRC) is the third most commonly diagnosed cancer and the second leading cause of cancer deaths worldwide. A well-known hallmark of cancer is altered glycosylation. Analyzing the N-glycosylation of CRC cell lines may provide potential therapeutic or diagnostic targets. In this study, an in-depth N-glycomic analysis of 25 CRC cell lines was conducted using porous graphitized carbon nano-liquid chromatography coupled to electrospray ionization mass spectrometry. This method allows for the separation of isomers and performs structural characterization, revealing profound N-glycomic diversity among the studied CRC cell lines with the elucidation of a number of 139 N-glycans. A high degree of similarity between the two N-glycan datasets measured on the two different platforms (porous graphitized carbon nano-liquid chromatography electrospray ionization tandem mass spectrometry (PGC-nano-LC-ESI-MS) and matrix-assisted laser desorption/ionization time of flight-mass spectrometry (MALDI-TOF-MS)) was discovered. Furthermore, we studied the associations between glycosylation features, glycosyltransferases (GTs), and transcription factors (TFs). While no significant correlations between the glycosylation features and GTs were found, the association between TF CDX1 and (s)Le antigen expression and relevant GTs FUT3/6 suggests that CDX1 contributes to the expression of the (s)Le antigen through the regulation of FUT3/6. Our study provides a comprehensive characterization of the N-glycome of CRC cell lines, which may contribute to the future discovery of novel glyco-biomarkers of CRC.

O-Glycomic and Proteomic Signatures of Spontaneous and Butyrate-Stimulated Colorectal Cancer Cell Line Differentiation

Gut microbiota of the gastrointestinal tract provide health benefits to the human host via bacterial metabolites. Bacterial butyrate has beneficial effects on intestinal homeostasis and is the preferred energy source of intestinal epithelial cells, capable of inducing differentiation. It was previously observed that changes in the expression of specific proteins as well as protein glycosylation occur with differentiation. In this study, specific mucin O-glycans were identified that mark butyrate-induced epithelial differentiation of the intestinal cell line CaCo-2 (Cancer Coli-2), by applying porous graphitized carbon nano-liquid chromatography with electrospray ionization tandem mass spectrometry. Moreover, a quantitative proteomic approach was used to decipher changes in the cell proteome. It was found that the fully differentiated butyrate-stimulated cells are characterized by a higher expression of sialylated O-glycan structures, whereas fucosylation is downregulated with differentiation. By performing an integrative approach, we generated hypotheses about the origin of the observed O-glycome changes. These insights pave the way for future endeavors to study the dynamic O-glycosylation patterns in the gut, either produced via cellular biosynthesis or through the action of bacterial glycosidases as well as the functional role of these patterns in homeostasis and dysbiosis at the gut-microbiota interface.

High Diversity of Glycosphingolipid Glycans of Colorectal Cancer Cell Lines Reflects the Cellular Differentiation Phenotype

Colorectal cancer (CRC)–associated changes of protein glycosylation have been widely studied. In contrast, the expression of glycosphingolipid (GSL) patterns in CRC has, hitherto, remained largely unexplored. Even though GSLs are major carriers of cell surface carbohydrates, they are understudied due to their complexity and analytical challenges. In this study, we provide an in-depth analysis of GSL glycans of 22 CRC cell lines using porous graphitized carbon nano–liquid chromatography coupled with electrospray ionization–mass spectrometry. Our data revealed that the GSL expression varies among different cell line classifications, with undifferentiated cell lines showing high expression of blood group A, B, and H antigens while for colon-like cell lines the most prominent GSL glycans contained (sialyl)-Lewis^A/X and Lewis^B/Y antigens. Moreover, the GSL expression correlated with relevant glycosyltransferases that are involved in their biosynthesis as well as with transcription factors (TFs) implicated in colon differentiation. Additionally, correlations between certain glycosyltransferases and TFs at mRNA expression level were found, such as FUT3, which correlated with CDX1, ETS2, HNF1A, HNF4A, MECOM, and MYB. These TFs are upregulated in colon-like cell lines pointing to their potential role in regulating fucosylation during colon differentiation. In conclusion, our study reveals novel layers of potential GSL glycans regulation relevant for future research in colon differentiation and CRC.

•

Undifferentiated cell lines showed high expression of blood group A, B, and H antigens.

•

Colon-like cell lines are high in GSLs carrying (sialyl)-Lewis^A/X and Lewis^B/Y antigens.

•

(Sialyl)-Lewis^A/X and Lewis^B/Y antigens associated with expression of FUT3 and CDX1.

•

I-branching was elevated in undifferentiated cells.

Glycosphingolipid-Glycan Signatures of Acute Myeloid Leukemia Cell Lines Reflect Hematopoietic Differentiation

Aberrant expression of certain glycosphingolipids (GSLs) is associated with the differentiation of acute myeloid leukemia (AML) cells. However, the expression patterns of GSLs in AML are still poorly explored because of their complexity, the presence of multiple isomeric structures, and tedious analytical procedures. In this study, we performed an in-depth GSL glycan analysis of 19 AML cell lines using porous graphitized carbon liquid chromatography-mass spectrometry revealing strikingly different GSL glycan profiles between the various AML cell lines. The cell lines of the M6 subtype showed a high expression of gangliosides with α2,3-sialylation and Neu5Gc, while the M2 and M5 subtypes were characterized by high expression of (neo)lacto-series glycans and Lewis A/X antigens. Integrated analysis of glycomics and available transcriptomics data revealed the association of GSL glycan abundances with the transcriptomics expression of certain glycosyltransferases (GTs) and transcription factors (TFs). In addition, correlations were found between specific GTs and TFs. Our data reveal TFs GATA2, GATA1, and RUNX1 as candidate inducers of the expression of gangliosides and sialylation via regulation of the GTs ST3GAL2 and ST8SIA1. In conclusion, we show that GSL glycan expression levels are associated with hematopoietic AML classifications and TF and GT gene expression. Further research is needed to dissect the regulation of GSL expression and its role in hematopoiesis and associated malignancies.

Towards Mapping of the Human Brain N-Glycome with Standardized Graphitic Carbon Chromatography

The brain N-glycome is known to be crucial for many biological functions, including its involvement in neuronal diseases. Although large structural studies of brain N-glycans were recently carried out, a comprehensive isomer-specific structural analysis has still not been achieved, as indicated by the recent discovery of novel structures with galactosylated bisecting GlcNAc. Here, we present a detailed, isomer-specific analysis of the human brain N-glycome based on standardized porous graphitic carbon (PGC)-LC-MS/MS. To achieve this goal, we biosynthesized glycans with substitutions typically occurring in the brain N-glycome and acquired their normalized retention times. Comparison of these values with the standardized retention times of neutral and desialylated N-glycan fractions of the human brain led to unambiguous isomer specific assignment of most major peaks. Profound differences in the glycan structures between naturally neutral and desialylated glycans were found. The neutral and sialylated N-glycans derive from diverging biosynthetic pathways and are biosynthetically finished end products, rather than just partially processed intermediates. The focus on structural glycomics defined the structure of human brain N-glycans, amongst these are HNK-1 containing glycans, a bisecting sialyl-lactose and structures with fucose and N-acetylgalactosamine on the same arm, the so-called LDNF epitope often associated with parasitic worms.

Alterations of Fucosyltransferase Genes and Fucosylated Glycans in Gastric Epithelial Cells Infected with Helicobacter pylori

Helicobacter pylori (H. pylori) adhesion to human gastric epithelial cells is closely linked with fucosylated glycans. Therefore, investigation of fucosylation in the interaction of gastric epithelial cells with H. pylori is critical. In this study we used lectin microarrays to detect the expression of fucosylated glycans in gastric epithelial cells (GES-1) infected with H. pylori strains isolated from patients with different diseases including chronic gastritis, duodenal ulcers, and gastric cancer (each containing two strains) at 4 h. In addition, we investigated the time-course expression of fucosyltransferase (FUT) 1–6 genes in GES-1 cells stimulated with H. pylori strains at 0.5–8 h. At 4 h post-infection, Lotus, AAA, BC2LCN, PA-IIL, CNL and ACG lectins had increased signals in H. pylori-infected GES-1 cells compared to uninfected cells. Higher expression of FUT1 and FUT2 was detected in all H. pylori-infected GES-1 cells within 2 h, regardless of the H. pylori strain. In particular, the expression of FUT2 was higher in H. pylori-infected GES-1 cells with a higher fold change in levels of BC2LCN lectin specific to α1-2 linked fucose (Fuc) at 4 h. The results suggest that the high levels of α1, 2-linked Fuc synthesized by FUT1/2, might play a role in the preliminary stage of H. pylori infection. This provides us with pivotal information to understand the adhesion of H. pylori to human gastric epithelial cells.

Colorectal cancer cell lines show striking diversity of their O-glycome reflecting the cellular differentiation phenotype

Alterations in protein glycosylation in colorectal cancer (CRC) have been extensively studied using cell lines as models. However, little is known about their O-glycome and the differences in glycan biosynthesis in different cell types. To provide a better understanding of the variation in O-glycosylation phenotypes and their association with other molecular features, an in-depth O-glycosylation analysis of 26 different CRC cell lines was performed. The released O-glycans were analysed on porous graphitized carbon nano-liquid chromatography system coupled to a mass spectrometer via electrospray ionization (PGC-nano-LC-ESI-MS/MS) allowing isomeric separation as well as in-depth structural characterization. Associations between the observed glycan phenotypes with previously reported cell line transcriptome signatures were examined by canonical correlation analysis. Striking differences are observed between the O-glycomes of 26 CRC cell lines. Unsupervized principal component analysis reveals a separation between well-differentiated colon-like and undifferentiated cell lines. Colon-like cell lines are characterized by a prevalence of I-branched and sialyl Lewis x/a epitope carrying glycans, while most undifferentiated cell lines show absence of Lewis epitope expression resulting in dominance of truncated α2,6-core sialylated glycans. Moreover, the expression of glycan signatures associates with the expression of glycosyltransferases that are involved in their biosynthesis, providing a deeper insight into the regulation of glycan biosynthesis in different cell types. This untargeted in-depth screening of cell line O-glycomes paves the way for future studies exploring the role of glycosylation in CRC development and drug response leading to discovery of novel targets for the development of anti-cancer antibodies.

Investigation of acidic free-glycans in urine and their alteration in cancer

Alterations to glycans in cancer patients have been used to identify novel tumor biomarkers. Most of these studies have focused on protein glycosylation but less attention has been paid to free-glycans. Here, we analyzed acidic free-glycans in the urine of cancer patients to identify novel tumor marker candidates. Specifically, urine samples were collected from patients with gastric cancer, pancreatic cancer and cholangiocarcinoma as well as normal controls. The free-glycans were extracted from creatinine-adjusted urine and fluorescently labeled with 2-aminopyridine. Initially, we performed profiling of urinary free-glycans by high-performance liquid chromatography and mass spectrometry with enzymatic and chemical degradation. More than 100 glycans, including novel structures, were identified. The chromatographic peaks suggested some of these glycans were present at elevated levels in cancer patients. To verify cancer-associated alterations, we compared the glycan levels between cancer patients and normal controls by selected reaction monitoring. Representative structures of glycans with elevated levels in cancer patients included the following: small glycans related to sialyllactose; sialyl Lewis X; lactose- and N-acetyllactosamine (LacNAc) type-II-core glycans with LacNAc (type-I or II)-extensions and modifications of α1,3/4-fucose and/or 6-sulfate on the Glc/GlcNAc; free-N-glycans containing sialylation or β1,6-branch of 6-sulfo Lewis X; novel NeuAcα2-3Galβ1-4(+/−Fucα1-3) Xylα1-3Glc glycans. Our results provide further insight into urinary free-glycans and suggest the potential utility of these compounds as tumor markers.

Resolving Isomeric Structures of Native Glycans by Nanoflow Porous Graphitized Carbon Chromatography-Mass Spectrometry

Characterization of the structural diversity of glycans by liquid chromatography-tandem mass spectrometry (LC-MS/MS) remains an analytical challenge in large-scale glycomics applications because of the presence of heterogeneous composition, ubiquitous isomers, lability of post-translational glycan modifications, and complexity of data interpretation. High-resolution separation of glycan isomers differentiating from positional, linkage, branching, and anomeric structures is often a prerequisite to ensure the comprehensive glycan identification. Here, we developed a straightforward method using self-packed capillary porous graphitic carbon (PGC) columns for nanoflow LC-MS/MS analyses of native glycans released from glycoproteins. The technique enables highly resolved chromatographic separation of over 20 high-mannose glycan isomers in ribonuclease B and a diverse range of hybrid and complex-type sialoglycoforms of fetuin. The distinct structures of anomeric glycans and linkage sialoglycan isomers, α2,3 and α2,6, were identified by the characteristic MS/MS fragment ions. A glycan sequencing strategy utilizing diagnostic ions and complementary fragments specific to branching residues was established to simplify the MS/MS data interpretation of closely related isomeric structures. To promote the PGC-LC-MS/MS-based method for glycome-wide applications, we extended analyses to native sulfoglycans from the egg-propagated and cell culture-derived influenza vaccines and demonstrate the high-resolution separation and structural characterization of underivatized neutral and anionic glycoforms including oligomannosidic glycan anomers, sialoglycan linkage isomers, and regioisomers of afucosylated and fucosylated sulfoglycans containing sulfated-6-GlcNAc and sulfated-4-GalNAc residues.

N-Glycoproteins Have a Major Role in MGL Binding to Colorectal Cancer Cell Lines: Associations with Overall Proteome Diversity

Colorectal cancer (CRC) is the second-leading cause of cancer death worldwide due in part to a high proportion of patients diagnosed at advanced stages of the disease. For this reason, many efforts have been made towards new approaches for early detection and prognosis. Cancer-associated aberrant glycosylation, especially the Tn and STn antigens, can be detected using the macrophage galactose-type C-type lectin (MGL/CLEC10A/CD301), which has been shown to be a promising tool for CRC prognosis. We had recently identified the major MGL-binding glycoproteins in two high-MGL-binding CRC cells lines, HCT116 and HT29. However, we failed to detect the presence of O-linked Tn and STn glycans on most CRC glycoproteins recognized by MGL. We therefore investigated here the impact of N-linked and O-linked glycans carried by these proteins for the binding to MGL. In addition, we performed quantitative proteomics to study the major differences in proteins involved in glycosylation in these cells. Our results showed that N-glycans have a significant, previously underestimated, importance in MGL binding to CRC cell lines. Finally, we highlighted both common and cell-specific processes associated with a high-MGL-binding phenotype, such as differential levels of enzymes involved in protein glycosylation, and a transcriptional factor (CDX-2) involved in their regulation.

Serum Protein N-Glycans in Colostrum and Mature Milk of Chinese Mothers

To study the Chinese human milk N-glycome over lactation, N-glycans were released and separated from serum proteins, purified by solid-phase extraction, and analyzed by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS). In total, 66 different putative N-glycans were found in the colostrum (week 1) and mature milk (week 4) of seven Chinese mothers. A clear difference was observed between milk of five secretor and two nonsecretor mothers, based on the type and relative amounts of the individual N-glycans. The relative levels of the total neutral nonfucosylated and the fucosylated N-glycans in milk of five secretor mothers increased and decreased over lactation, respectively. This pattern could not be observed for the milk from the two nonsecretor mothers. Overall, this was the first study that provided detailed information on individual N-glycans in milk among mothers and over time as well as that fucosylation of N-glycans in milk was associated with the mother's secretor status.

Glycomics studies using sialic acid derivatization and mass spectrometry

Proteins can undergo glycosylation during and/or after translation to afford glycoconjugates, which are often secreted by a cell or populate cell surfaces. Changes in the glycan portion can have a strong influence on a glycoconjugate and are associated with a multitude of human pathologies. Of particular interest are sialylated glycoconjugates, which exist as constitutional isomers that differ in their linkages (α2,3, α2,6, α2,8 or α2,9) between sialic acids and their neighbouring monosaccharides. In general, mass spectrometry enables the rapid and sensitive characterization of glycosylation, but there are challenges specific to identifying and (relatively) quantifying sialic acid isomers. These challenges can be addressed using linkage-specific methodologies for sialic acid derivatization, after which mass spectrometry can enable product identification. This Review is concerned with the new and important derivatization approaches reported in the past decade, which have been implemented in various mass-spectrometry-glycomics workflows and have found clinical glycomics applications. The convenience and wide applicability of the approaches make them attractive for studies of sialylation in different types of glycoconjugate.

Dynamic analysis of N-glycomic and transcriptomic changes in the development of ovarian cancer cell line A2780 to its three cisplatin-resistant variants

Background

Platinum resistance development is a dynamic process that occurs during continuous chemotherapy and contributes to high mortality in ovarian cancer. Abnormal glycosylation has been reported in platinum resistance. Many studies on platinum resistance have been performed, but few of them have investigated platinum resistance-associated glycans based on N-glycomics. Moreover, glycomic alterations during platinum resistance development in ovarian cancer are rarely reported. Therefore, the objective of this study was to determine platinum resistance-related N-glycans in ovarian cancer cells during continuous exposure to cisplatin. These glycans might be involved in the mechanism of platinum resistance and serve as biomarkers to monitor its development.

Methods

This study mimicked the development of platinum resistance in ovarian cancer by continuously exposing A2780 cells to cisplatin. Cisplatin-resistant variants were confirmed by higher half maximal inhibitory concentration (IC₅₀) values and increased P-glycoprotein (ABCB1, P-gp) expression compared to A2780 cells. Analysis of dynamic N-glycomic changes during the development of platinum resistance in cisplatin-resistant variants was performed with MALDI-time-of-flight (TOF)-MS combined with ethyl esterification derivatization, which were used to discriminate between α2,3- and α2,6-linkage N-acetylneuraminic acid. N-glycan alterations were further validated on a glycotransferase level via transcriptome sequencing and real-time PCR (RT-PCR).

Results

Compared to the A2780 cells, MS analysis indicated that α2,3-linked sialic structures and N-glycan gal-ratios were significantly higher, while fucosylated glycans were lower in three cisplatin-resistant variants. Transcriptome sequencing and RT-PCR showed that gene expression of ST3GAL6 and MGAT4A increased, while gene expression of FUT11, FUT1, GMDS, and B4GALT5 decreased in three cisplatin-resistant variants.

Conclusions

Analysis of N-glycans and glycogene expression showed that α2,3-linked sialic structures might serve as biomarkers to monitor the development of platinum resistance and to guide individualized treatment of ovarian cancer patients.