Addition Of Sialic Acid Research Articles

The Role of NEU1 in Coronavirus Infection and Pathogenesis

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused the coronavirus disease 2019 (COVID-19) pandemic, resulting in millions of infections and deaths worldwide. Although vaccines are available, they appear to be less efficacious against newly emerging variants of the virus. Thus, therapeutic modalities are urgently needed. The coronavirus genome encodes four major structural proteins: the spike (S) protein, nucleocapsid (N) protein, membrane (M) protein, and envelope (E) protein, all of which are required to produce a structurally complete viral particle. N protein is one of the most abundant structural proteins, participates in the regulation of viral replication and virion assembly, and is a major immunogen in coronavirus infection-induced disease. Sialylation is the addition of sialic acids to the terminal glycans of glycoproteins and glycolipids, which act as key components for biological functions of glycoproteins or glycolipids. Sialidases (or neuraminidases) are glycosidases that remove sialic acid residues (desialylation) from glycan portions of glycoproteins or glycolipids. Through desialylation, sialidases modulate the functionality of sialic acid-containing molecules and are involved in both physiological and pathological pathways. This review aims to explore the current understanding of NEU1's involvement in coronavirus infection and pathogenesis, synthesizing available research and identifying areas for future investigation.

Limited impact of cancer-derived gangliosides on anti-tumor immunity in colorectal cancer.

Aberrant glycosylation is a key mechanism employed by cancer cells to evade immune surveillance, induce angiogenesis and metastasis, among other hallmarks of cancer. Sialic acids, distinctive terminal glycan structures located on glycoproteins or glycolipids, are prominently upregulated across various tumor types, including colorectal cancer (CRC). Sialylated glycans modulate anti-tumor immune responses through their interactions with Siglecs, a family of glycan-binding receptors with specificity for sialic acid-containing glycoconjugates, often resulting in immunosuppression. In this paper, we investigated the immunomodulatory function of ST3Gal5, a sialyltransferase that catalyzes the addition of α2-3 sialic acids to glycosphingolipids, since lower expression of ST3Gal5 is associated with better survival of CRC patients. We employed CRISPR/Cas9 to knock out the ST3Gal5 gene in two murine CRC cell lines MC38 and CT26. Glycomics analysis confirmed the removal of sialic acids on glycolipids, with no discernible impact on glycoprotein sialylation. Although knocking out ST3Gal5 in both cell lines did not affect in vivo tumor growth, we observed enhanced levels of regulatory T cells in CT26 tumors lacking ST3Gal5. Moreover, we demonstrate that the absence of ST3Gal5 affected size and blood vessel density only in MC38 tumors. In summary, we ascertain that sialylation of glycosphingolipids has a limited influence on the anti-tumor immune response in CRC, despite detecting alterations in the tumor microenvironment, possibly due to a shift in ganglioside abundance.

Abstract 336: Role of ST6GAL1 sialyltransferase in early stages of pancreatic cancer development

Abstract Increased cell surface sialylation is a prevalent feature of tumor cells. The addition of sialic acid (a negatively-charged sugar) to select surface receptors modulates the structure and function of these receptors, leading to changes in intracellular signaling and gene expression. Increased tumor cell sialylation occurs, in part, through the upregulation of sialyltransferases such as ST6GAL1, an enzyme that adds an α2-6 linked sialic acid to N-glycosylated proteins. ST6GAL1 is overexpressed in numerous malignancies, including pancreatic ductal adenocarcinoma (PDAC), and high expression correlates with a poor prognosis. Our group has shown that ST6GAL1 plays a causal role in promoting PDAC initiation and progression in tumor xenograft and genetically-engineered mouse (GEM) models. As one example, we developed a GEM model with conditional ST6GAL1 expression in the pancreas and crossed this line to the “KC” PDAC model, which expresses oncogenic Kras (KrasG12D). Mice with dual expression of ST6GAL1 and KrasG12D (”KSC” mice) exhibit greatly accelerated PDAC initiation, progression, and mortality when compared with KC mice. In light of ST6GAL1's known role in conferring progenitor-like cell characteristics, we postulated that ST6GAL1 activity contributes to PDAC initiation by fostering acinar to ductal metaplasia (ADM). During ADM, pancreatic acinar cells de-differentiate into ductal-like, progenitor cells and acquire greater proliferative potential as well as apoptosis resistance. Cells undergoing ADM are particularly vulnerable to Kras-dependent transformation. Using a variety of approaches and model systems including GEM organoids, 3D acinar cultures, acinar-like cell lines, and an in vivo assay for ADM, we uncovered a novel function for ST6GAL1 in promoting ADM. We further determined that high ST6GAL1 activity in acinar cells cooperates with KrasG12D to drive neoplasia. Finally, our studies suggest that the tumor-promoting effects of ST6GAL1 are mediated, at least in part, by ST6GAL1-mediated sialylation of EGFR. These collective results highlight a novel glycosylation-dependent mechanism involved in early stages of PDAC development. Citation Format: Susan L. Bellis, Asmi Chakraborty, Nikita Bhalerao, Michael Marciel, Jihye Hwang, Austin Silva. Role of ST6GAL1 sialyltransferase in early stages of pancreatic cancer development [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 336.

Abstract 6301: Post-translational modifications regulate sensitivity to Polatuzumab Vedotin in DLBCL

Abstract Diffuse Large B-Cell Lymphoma (DLBCL) is an aggressive malignancy of which one-third of diagnosed patients ultimately relapse and die. New treatment paradigms for relapsed-refractory patients are needed. Most DLBCL tumors are reliant on signaling through their cell surface B-cell receptor (BCR) mediated by ITAMs on CD79A and CD79B to drive anti-apoptotic NF-kB and PI3 kinase signaling. In order to understand how surface BCR is regulated, we performed whole genome CRISPR screens in 9 DLBCL cell lines in which we sorted for high and low surface CD79B or added the CD79B targeted antibody-drug conjugate Polatuzumab-Vedotin (POLA-V). Strikingly, independent of genetic or cell of origin subtype, sgRNAs encoding the entire N-linked glycosylation pathway and specific sugar modification by addition of galactose and sialic acid were found to be enriched in high CD79B fractions and depleted in POLA-V treated samples compared to control. Further testing showed that removing sialic acid by treating with a small molecule inhibitor of sialic acid, genetic perturbation of golgi sugar transporters SLC35A1 and SLC35A2, or the a2,6 sialyltransferase ST6GAL1 resulted in more surface CD79B antibody binding with no significant change in CD79B protein abundance. The specificity of the effect of sialic acid loss on POLA antibody binding was confirmed by removing cell surface sialic acid with exogenous sialidase and observing increased binding of POLA, but not other therapeutic antibodies like Rituximab or CD19 FMC-63. Loss of SLC35A1, SLC35A2, and ST6GAL1 synergized with POLA-V but not the drug conjugate MMAE alone, showing a BCR dependent mechanism of sialic acid loss on POLA-V sensitization. In a further cell of origin subtype analysis of the germinal center B-cell (GCB) DLBCL cell lines, loss of the E3 ligase KLHL6 was found to synergize with POLA-V. Importantly, KLHL6 is heavily mutated across all germinal center derived malignancies, is more highly expressed in germinal center B-cells than other members of the B-cell lineage, and plays an unknown role in the development of autoimmune diseases. Further work will give evidence for the target of KLHL6 mediated ubiquitination and will show how this gene can drive lymphoma and autoimmune disease development in the germinal center. Citation Format: Sean R. Corcoran, Louis M. Staudt, Daniel Hodson. Post-translational modifications regulate sensitivity to Polatuzumab Vedotin in DLBCL [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6301.

Sialylation regulates migration in chronic lymphocytic leukemia.

Sialylation is the terminal addition of sialic acid to underlying glycans. It plays a prominent role in cell adhesion and immune regulation. Sialylated structures found on adhesion molecules, such as CD49d, mediate the interactions between cancer cells and the microenvironment, facilitating metastatic seeding in target organs. Chronic lymphocytic leukemia (CLL) is a clonal B-cell malignancy characterized by the accumulation of CD5-positive B cells in the peripheral blood, bone marrow and lymph nodes. CLL cells proliferate mainly in the lymph node "proliferation centers", where the microenvironment provides pro-survival signals. Thus, migration and homing into these protective niches play a crucial role in CLL biology. In recent years, therapeutic strategies aimed at inducing the egress of CLL cells from the lymph nodes and bone marrow into the circulation have been highly successful. In this study, the sialylation status of 79 untreated and 24 ibrutinib-treated CLL patients was characterized by flow cytometry. Moreover, the effect of sialic acid removal on migration was tested by a transwell assay. Finally, we examined the sialylation status of CD49d by Western blot analysis. We found that CLL cells are highly sialylated, particularly those characterized by an "activated" immune phenotype. Notably, sialylation regulates CLL migration through the post-translational modification of CD49d. Finally, we showed that therapeutic agents that induce CLL mobilization from their protective niches, such as ibrutinib, modulate sialic acid levels. We propose that sialylation is an important regulator of CLL trafficking and may represent a novel target to further improve CLL therapy.

Photoproximity Labeling of Sialylated Glycoproteins (GlycoMap) Reveals Sialylation-Dependent Regulation of Ion Transport.

Sialylation, the addition of sialic acid to glycans, is a crucial post-translational modification of proteins, contributing to neurodevelopment, oncogenesis, and immune response. In cancer, sialylation is dramatically upregulated. Yet, the functional biochemical consequences of sialylation remain mysterious. Here, we establish a μMap proximity labeling platform that utilizes metabolically inserted azidosialic acid to introduce iridium-based photocatalysts on sialylated cell-surface glycoproteins as a means to profile local microenvironments across the sialylated proteome. In comparative experiments between primary cervical cells and a cancerous cell line (HeLa), we identify key differences in both the global sialome and proximal proteins, including solute carrier proteins that regulate metabolite and ion transport. In particular, we show that cell-surface interactions between receptors trafficking ethanolamine and zinc are sialylation-dependent and impact intracellular metabolite levels. These results establish a μMap method for interrogating proteoglycan function and support a role for sialylated glycoproteins in regulating cell-surface transporters.

Alpha2,3 sialic acid processing enzymes expression in gastric cancer tissues reveals that ST3Gal3 but not Neu3 are associated with Lauren's classification, angiolymphatic invasion and histological grade.

Gastric cancer (GC) is one of the leading causes of cancer-related deaths worldwide. Despite progress in the last decades, there are still no reliable biomarkers for the diagnosis of and prognosis for GC. Aberrant sialylation is a widespread critical event in the development of GC. Neuraminidases (Neu) and sialyltransferases (STs) regulate the ablation and addition of sialic acid during glycoconjugates biosynthesis, and they are a considerable source of biomarkers in various cancers. This study retrospectively characterized Neu3 and ST3Gal3 expression by immunohistochemistry in 71 paraffin-embedded GC tissue specimens and analyzed the relationship between their expression and the clinicopathological parameters. Neu3 expression was markedly increased in GC tissues compared with non-tumoral tissues (p<0.0001). Intratumoral ST3Gal3 staining was significantly associated with intestinal subtype (p=0.0042) and was negatively associated with angiolymphatic invasion (p=0.0002) and higher histological grade G3 (p=0.0066). Multivariate analysis revealed that ST3Gal3 positivity is able to predict Lauren's classification. No associations were found between Neu3 staining and clinical parameters. The in silico analysis of mRNA expression in GC validation cohorts corroborates the significant ST3Gal3 association with higher histological grade observed in our study. These findings suggest that ST3Gal3 expression may be an indicator for aggressiveness of primary GC.

Pan-cancer analysis of altered glycosyltransferases confers poor clinical outcomes.

Pan-cancer analysis of altered glycosyltransferases confers poor clinical outcomes.

Hypersialylation of Tumor Cells Promotes Pancreatic Cancer Progression

Tumor cells are well‐known to have elevated levels of sialylated surface glycoproteins. The addition of sialic acid (a negatively‐charged sugar) to select surface receptors modulates the structure and function of such receptors, leading to changes in intracellular signaling and gene expression. Increased tumor cell sialylation occurs, in part, through the upregulation of sialyltransferases such as ST6GAL1, an enzyme that adds an α2‐6 linked sialic acid to N‐glycosylated proteins. ST6GAL1 is overexpressed in numerous malignancies, including pancreatic ductal adenocarcinoma (PDAC), and high expression correlates with a poor prognosis. Prior work from our group revealed that ST6GAL1 confers a cancer stem cell phenotype, typified by invasiveness and apoptosis‐resistance, through the sialylation‐dependent activation of receptors such as EGFR. In the current investigation we used human Suit2 PDAC cells, as well as two metastatic Suit2 subclones, to show that ST6GAL1 activity promotes tumor progression and metastasis in tumor xenograft models. Moreover, high ST6GAL1 expression in this isogenic cell series induces EGFR activation and epithelial to mesenchymal transition. To complement tumor xenograft experiments, we developed a genetically‐engineered mouse (GEM) model with conditional ST6GAL1 expression in the pancreas (termed, “SC” mice) and crossed this line to the “KC” PDAC model, which expresses oncogenic Kras (KrasG12D) in the pancreas. Mice with dual expression of ST6GAL1 and KrasG12D (”KSC” mice) exhibit greatly accelerated PDAC initiation, progression, and mortality when compared with KC mice. In light of ST6GAL1's known role in conferring stem/progenitor properties, we hypothesized that ST6GAL1 activity contributes to PDAC initiation by fostering acinar to ductal metaplasia (ADM). During ADM, pancreatic acinar cells de‐differentiate into ductal‐like, progenitor cells and acquire greater proliferative potential as well as apoptosis resistance. Cells undergoing ADM are particularly vulnerable to oncogenic transformation. To interrogate whether ST6GAL1 promotes ADM, we compared SC mice with control, wild‐type littermates. Using a variety of analyses and model systems including RNA‐Seq of GEM pancreata, organoid lines derived from GEM pancreata, the canonical 266‐6 ADM cell model, and in vivo model of inflammation‐induced ADM, we determined that high expression of ST6GAL1 in acinar cells imparts an ADM‐like phenotype, as evidenced by the upregulation of stem and ductal genes and downregulation of genes associated with differentiated acinar cells. Furthermore, GEM tissues and organoids with ectopic ST6GAL1 expression display strikingly elevated levels of activated EGFR. Given that activation of EGFR is one the major drivers of ADM, these data suggest a potential mechanism by which ST6GAL1‐mediated sialylation facilitates ADM. Collectively these results point to a critical role for ST6GAL1 in both early and late stages of pancreatic malignancy.

Sialylation of CD44 by ST8sia6 is required for recognition by the inhibitory receptor Siglec-7

Abstract Glycans decorate almost all proteins and lipids on the cell surface, and they play a critical role in cell-cell interactions. Terminal sialic acid addition to glycans helps the immune system distinguish between “self” and “non-self.” The enzyme ST8sia6 adds alpha-2,8 disialic acids to cell surface receptors, and this sialic acid addition promotes binding to the inhibitory receptor Siglec-E. We have previously shown ST8sia6 overexpression in tumors accelerates tumor growth in a Siglec-E dependent manner. Proteomic analysis in murine tumor lines identified CD44 as a target for ST8sia6. CD44 expression on tumors is associated with metastasis and chemoresistance. Since humans and mice have different sialic acid structures, we examined whether ST8sia6 makes CD44 a ligand to the ortholog of Siglec-E in human cells, Siglec-7. When HEK293T cells overexpress ST8sia6 and CD44 together, Siglec-7 binding was significantly increased compared to ST8sia6 or CD44 overexpression alone. Thus, ST8sia6 has a conserved role from mouse to human in decorating CD44 with sialic acid. Our study proposes that ST8sia6 sialylation of CD44 could suppress immune responses and enables cancer progression in human. Supported by grant: 2T32AI007425-23 to DJF and R01 CA243545-01S1 to V.S.S.

Enhanced anti-tumor immunity in ST8Sia6 knockout mice

Abstract Inhibitory receptors have a critical role in the regulation of immunity. Siglecs are a family of primarily inhibitory receptors expressed by immune cells, which recognize specific sialic acid modifications on cell surface glycans. Sialyltransferases are the enzymes that catalyzing the addition of sialic acids onto glycoproteins and glycolipids. Siglec-E binds to α2,8-linked disialic acids, generated by the enzyme ST8Sia6 on O-linked glycoproteins and functions to inhibit activation of innate immune cells. Many tumors have increased sialic acid incorporation. Overexpression of the sialyltransferase ST8Sia6 on tumors led to altered macrophage polarization and increased tumor growth through engagement of ligands generated by ST8Sia6 with Siglec-E. Here, we examine the role of ST8Sia6 on immune cells in regulating anti-tumor immunity. The loss of ST8Sia6 in tumor bearing mice reduced tumor growth, increased survival, and altered the immune response as compared to ST8Sia6 sufficient tumor bearing mice. Using MC38, B16, and B16-OVA flank tumor mouse models, tumor growth was decreased in ST8Sia6 KO mice as compared to C57Bl/6 mice. Within the tumor microenvironment of tumors present in ST8Sia6 KO mice compared to tumors present in C57Bl/6 mice, macrophages and dendritic cells altered their phenotype towards enhanced immune activation. Tregs from tumors in ST8Sia6 KO mice also displayed an increase in RORγt and a reduction in TNFRII, suggesting a possible shift to a less suppressive Treg. These alterations in the immune response to tumors were due to the loss of ST8Sia6 in macrophages and dendritic cells and not T-cells. Thus, ST8Sia6 generates ligands for Siglecs that dampen anti-tumor immunity. Supported by grants from NIH (R01CA243545, 2T32AI007425) and Mayo Clinic Center of Biomedical Discovery

Exo-Enzymatic Addition of Diazirine-Modified Sialic Acid to Cell Surfaces Enables Photocrosslinking of Glycoproteins.

Glycan binding often mediates extracellular macromolecular recognition events. Accurate characterization of these binding interactions can be difficult because of dissociation and scrambling that occur during purification and analysis steps. Use of photocrosslinking methods has been pursued to covalently capture glycan-dependent interactions in situ; however, use of metabolic glycan engineering methods to incorporate photocrosslinking sugar analogs is limited to certain cell types. Here, we report an exo-enzymatic labeling method to add a diazirine-modified sialic acid (SiaDAz) to cell surface glycoconjugates. The method involves the chemoenzymatic synthesis of diazirine-modified CMP-sialic acid (CMP-SiaDAz), followed by sialyltransferase-catalyzed addition of SiaDAz to desialylated cell surfaces. Cell surface SiaDAzylation is compatible with multiple cell types and is facilitated by endogenous extracellular sialyltransferase activity present in Daudi B cells. This method for extracellular addition of α2-6-linked SiaDAz enables UV-induced crosslinking of CD22, demonstrating the utility for covalent capture of glycan-mediated binding interactions.

Multi-Faceted Effects of ST6Gal1 Expression on Precursor B-Lineage Acute Lymphoblastic Leukemia.

Normal early human B-cell development from lymphoid progenitors in the bone marrow depends on instructions from elements in that microenvironment that include stromal cells and factors secreted by these cells including the extracellular matrix. Glycosylation is thought to play a key role in such interactions. The sialyltransferase ST6Gal1, with high expression in specific hematopoietic cell types, is the only enzyme thought to catalyze the terminal addition of sialic acids in an α2-6-linkage to galactose on N-glycans in such cells. Expression of ST6Gal1 increases as B cells undergo normal B-lineage differentiation. B-cell precursor acute lymphoblastic leukemias (BCP-ALLs) with differentiation arrest at various stages of early B-cell development have widely different expression levels of ST6GAL1 at diagnosis, with high ST6Gal1 in some but not in other relapses. We analyzed the consequences of increasing ST6Gal1 expression in a diagnosis sample using lentiviral transduction. NSG mice transplanted with these BCP-ALL cells were monitored for survival. Compared to mice transplanted with leukemia cells expressing original ST6Gal1 levels, increased ST6Gal1 expression was associated with significantly reduced survival. A cohort of mice was also treated for 7 weeks with vincristine chemotherapy to induce remission and then allowed to relapse. Upon vincristine discontinuation, relapse was detected in both groups, but mice transplanted with ST6Gal1 overexpressing BCP-ALL cells had an increased leukemia burden and shorter survival than controls. The BCP-ALL cells with higher ST6Gal1 were more resistant to long-term vincristine treatment in an ex vivo tissue co-culture model with OP9 bone marrow stromal cells. Gene expression analysis using RNA-seq showed a surprisingly large number of genes with significantly differential expression, of which approximately 60% increased mRNAs, in the ST6Gal1 overexpressing BCP-ALL cells. Pathways significantly downregulated included those involved in immune cell migration. However, ST6Gal1 knockdown cells also showed increased insensitivity to chemotherapy. Our combined results point to a context-dependent effect of ST6Gal1 expression on BCP-ALL cells, which is discussed within the framework of its activity as an enzyme with many N-linked glycoprotein substrates.

ST6Gal-I–mediated sialylation of the epidermal growth factor receptor modulates cell mechanics and enhances invasion

Heterogeneity within the glycocalyx influences cell adhesion mechanics and signaling. However, the role of specific glycosylation subtypes in influencing cell mechanics via alterations of receptor function remains unexplored. It has been shown that the addition of sialic acid to terminal glycans impacts growth, development, and cancer progression. In addition, the sialyltransferase ST6Gal-I promotes epidermal growth factor receptor (EGFR) activity, and we have shown EGFR is an ‘allosteric mechano-organizer’ of integrin tension. Here, we investigated the impact of ST6Gal-I on cell mechanics. Using DNA-based tension gauge tether probes of variable thresholds, we found that high ST6Gal-I activity promotes increased integrin forces and spreading in Cos-7 and OVCAR3, OVCAR5, and OV4 cancer cells. Further, employing inhibitors and function-blocking antibodies against β1, β3, and β5 integrins and ST6Gal-I targets EGFR, tumor necrosis factor receptor, and Fas cell surface death receptor, we validated that the observed phenotypes are EGFR-specific. We found that while tension, contractility, and adhesion are extracellular-signal-regulated kinase pathway-dependent, spreading, proliferation, and invasion are phosphoinositide 3-kinase-Akt serine/threonine kinase dependent. Using total internal reflection fluorescence microscopy and flow cytometry, we also show that high ST6Gal-I activity leads to sustained EGFR membrane retention, making it a key regulator of cell mechanics. Our findings suggest a novel sialylation-dependent mechanism orchestrating cellular mechanics and enhancing cell motility via EGFR signaling.

Sialylation of IgG inhibits the formation of galactose-deficient IgA1-containing immune complexes and protects mesangial cells from injury in IgA nephropathy

BackgroundThe addition of sialic acid alters IgG from a pro-inflammatory state to an anti-inflammatory state. However, there is a lack of research on the changes of IgG sialylation in IgA nephropathy (IgAN).MethodsThis study included a total of 184 IgAN patients. The sialylated IgG (SA-IgG), IgG-galactose-deficient IgA1 complex (IgG-Gd-IgA1-IC), IL-6, TNF-α, and TGF-β were detected using commercial ELISA kits. SA-IgG, non-sialylated IgG (NSA-IgG), sialylated IgG-IgA1 complex (SA-IgG-IgA1), and non-sialylated IgG-IgA1 complex (NSA-IgG-IgA1) were purified from IgAN patients and healthy controls (HCs).ResultsThe mean SA-IgG levels in plasma and B lymphocytes in IgAN patients were significantly higher than those of healthy controls. A positive correlation was found between SA-IgG levels in plasma and B lymphocytes. In vitro, the results showed that the release of IgG-Gd-IgA1-IC was significantly decreased in peripheral blood mononuclear cells (PBMCs) cultured with SA-IgG from both IgAN patients and healthy controls. The proliferation ability and the release of IL-6, TNF-α, and TGF-β in human mesangial cells (HMCs) were measured after stimulating with SA-IgG-IgA1-IC and NSA-IgG-IgA1-IC. The mesangial cell proliferation levels induced by NSA-IgG-IgA1-IC derived from IgAN patients were significantly higher than those caused by SA-IgG-IgA1-IC derived from IgAN patients and healthy controls. Compared with NSA-IgG-IgA1 from healthy controls, IgAN-NSA-IgG-IgA1 could significantly upregulate the expression of IL-6 and TNF-α in mesangial cells. The data showed that there weren’t any significant differences in the levels of IL-6, TNF-α, and TGF-β when treated with IgAN-SA-IgG-IgA1 and HC-NSA-IgG-IgA1.ConclusionsThe present study demonstrated that the sialylation of IgG increased in patients with IgA nephropathy. It exerted an inhibitory effect on the formation of Gd-IgA1-containing immune complexes in PBMCs and the proliferation and inflammation activation in mesangial cells.

ST6GalNAc-I promotes lung cancer metastasis by altering MUC5AC sialylation.

Lung cancer (LC) is the leading cause of cancer‐related mortality. However, the molecular mechanisms associated with the development of metastasis are poorly understood. Understanding the biology of LC metastasis is critical to unveil the molecular mechanisms for designing targeted therapies. We developed two genetically engineered LC mouse models KrasG12D/+; Trp53R172H/+; Ad‐Cre (KPA) and KrasG12D/+; Ad‐Cre (KA). Survival analysis showed significantly (P = 0.0049) shorter survival in KPA tumor‐bearing mice as compared to KA, suggesting the aggressiveness of the model. Our transcriptomic data showed high expression of N‐acetylgalactosaminide alpha‐2, 6‐sialyltransferase 1 (St6galnac‐I) in KPA compared to KA tumors. ST6GalNAc‐I is an O‐glycosyltransferase, which catalyzes the addition of sialic acid to the initiating GalNAc residues forming sialyl Tn (STn) on glycoproteins, such as mucins. Ectopic expression of species‐specific p53 mutants in the syngeneic mouse and human LC cells led to increased cell migration and high expression of ST6GalNAc‐I, STn, and MUC5AC. Immunoprecipitation of MUC5AC in the ectopically expressing p53R175H cells exhibited higher affinity toward STn. In addition, ST6GalNAc‐I knockout (KO) cells also showed decreased migration, possibly due to reduced glycosylation of MUC5AC as observed by low STn on the glycoprotein. Interestingly, ST6GalNAc‐I KO cells injected mice developed less liver metastasis (P = 0.01) compared to controls, while colocalization of MUC5AC and STn was observed in the liver metastatic tissues of control mice. Collectively, our findings support the hypothesis that mutant p53R175H mediates ST6GalNAc‐I expression, leading to the sialyation of MUC5AC, and thus contribute to LC liver metastasis.

Aberrant sialylation in a patient with a HNF1α variant and liver adenomatosis

SummaryGlycosylation is a fundamental post-translational modification of proteins that boosts their structural diversity providing subtle and specialized biological properties and functions. All those genetic diseases due to a defective glycan biosynthesis and attachment to the nascent glycoproteins fall within the wide area of congenital disorders of glycosylation (CDG), mostly causing multisystem involvement. In the present paper, we detailed the unique serum N-glycosylation of a CDG-candidate patient with an unexplained neurological phenotype and liver adenomatosis harboring a recurrent pathogenic HNF1α variant. Serum transferrin isoelectric focusing showed a surprising N-glycosylation pattern consisting on hyposialylation, as well as remarkable hypersialylation. Mass spectrometry-based glycomic analyses of individual serum glycoproteins enabled to unveil hypersialylated complex N-glycans comprising up to two sialic acids per antenna. Further advanced MS analysis showed the additional sialic acid is bonded through an α2-6 linkage to the peripheral N-acetylglucosamine residue.

Addition of Sialic Acid to Insulin Confers Superior Physical Properties and Bioequivalence

Native insulin is susceptible to biophysical aggregation and fibril formation, promoted by manual agitation and elevated temperatures. The safety of the drug and its application to alternative forms of administration could be enhanced through the identification of chemical modifications that strengthen its physical stability without compromising its biological properties. Complex polysialic acids (PSAs) exist naturally and provide a means to enhance the physical properties of peptide therapeutics. A set of insulin analogues site-specifically derivatized with sialic acid were prepared in an overall yield of 50-60%. Addition of a single or multiple sialic acids conferred remarkable enhancement to the biophysical stability of human insulin while maintaining its potency. The time to the onset of fibrillation was extended by more than 10-fold relative to that of the native hormone. These results demonstrate that simplified sialic acid conjugates represent a viable alternative to complex natural PSAs in increasing the stability of therapeutic peptides.

Aberrant sialylation in ovarian cancers.

Sialylation (the covalent addition of sialic acid to the terminal end of glycoproteins or glycans), tightly regulated cell- and microenvironment-specific process and orchestrated by sialyltransferases and sialidases (neuraminidases) family, is one of the posttranslational modifications, which plays an important biological role in the maintenance of normal physiology and involves many pathological dysfunctions. Glycans have roles in all the cancer hallmarks, referring to capabilities acquired during all steps of cancer development to initiate malignant transformation (a driver of a malignant genotype), enable cancer cells to survive, proliferate, and metastasize (a consequence of a malignant phenotype), which includes sustaining proliferative signaling, evading growth suppressor, resisting cell apoptosis, enabling replicative immortality, inducing angiogenesis, reprogramming of energy metabolism, evading tumor destruction, accumulating inflammatory microenvironment, and activating invasion and accelerating metastases. Regarding the important role of altered sialylation of cancers, further knowledge about the initiation and the consequences of altered sialylation pattern in tumor cells is needed, because all may offer a better chance for developing novel therapeutic strategy. In this review, we would like to update alteration of sialylation in ovarian cancers.

Aberrant Sialylation in a Patient with a &lt;i&gt;HNF1α&lt;/i&gt; Variant and Liver Adenomatosis

Glycosylation is a fundamental post-translational modification of proteins that boosts their structural diversity providing subtle and specialized biological properties and functions. All those genetic diseases due to a defective glycan biosynthesis and attachment to the nascent glycoproteins fall within the wide area of congenital disorders of glycosylation (CDG), mostly causing multisystem involvement. In the present paper we detailed the unique serum N- glycosylation of a CDG-candidate patient with an unexplained neurological phenotype and liver adenomatosis harbouring a recurrent pathogenic HNF1α variant. Serum transferrin IEF showed a surprising N-glycosylation pattern consisting on hyposialylation as well as remarkable hypersialylation. Mass spectrometry-based glycomic analyses of individual serum glycoproteins enabled to unveil hypersialylated complex N-glycans comprising up to two sialic acids per antenna. Further advanced MS analysis showed the additional sialic acid is bonded through an α2-6 linkage to the peripheral N-acetylglucosamine residue, giving rise to disialo-epitopes never described in human N-glycoproteins.