Sialylation of the Fas death receptor by ST6Gal-I provides protection against Fas-mediated apoptosis in colon carcinoma cells

A review on the development of sialyltransferase inhibitors

Sialylation of terminal glycoconjugates is involved in many important physiological and pathological processes such as tumor metastasis, drug resistance, organismal immunity, and viral infections. Sialyltransferases are enzymes responsible for sialylation modification in organisms, and potent sialyltransferase inhibitors can not only serve as probes for glycobiology studies, but also hold great promise to become agents for tumor therapy and viral infection control in the clinic. This review summarizes the latest progress in the development and application of various sialyltransferase inhibitors. The current challenges and development trends are also discussed.

Aberrant Sialylation in Ovarian Cancer: Orchestrating Progression, Metastasis, and Therapeutic Hurdles

Ovarian cancer (OC), a highly lethal gynaecological malignancy, is often diagnosed at advanced stages, resulting in a poor prognosis. Sialylation, an important form of glycosylation, significantly contributes to the progression of various solid tumours, including OC. Aberrant sialylation promotes tumour progression and metastasis by altering the structure and function of glycoproteins. Although its role in several solid tumours is well documented, the role of abnormal sialylation in OC and its potential as a therapeutic target remain poorly understood. This review highlights sialylation as a key regulator of the progression, metastasis, and drug resistance of OC. A deeper understanding of altered sialylation can contribute to the identification of novel therapeutic strategies for OC.

Aberrant protein glycosylation in the colon adenoma-cancer sequence: Colorectal cancer mechanisms and clinical implications

Colorectal cancer (CRC) is a leading contributor to global cancer-related morbidity and mortality. Glycosylation is a common post-translational protein modification. Aberrant protein glycosylation is a hallmark of cancer, affecting biological processes and driving malignant CRC phenotypes. Specifically, abnormal N-glycosylation manifests as structural alterations in high mannose, sialylated, and fucosylated structures, collectively promoting cancer stemness and invasiveness. Concurrently, O-GlcNAcylation facilitates tumorigenesis through metabolic reprogramming and oncogene activation. Dysregulated mucin-type O-glycans (e.g., Core-1/Core-3 imbalance) and elevated SLex/SLea antigen expression are significantly correlated with tumor adhesion, metastatic dissemination, and adverse clinical outcomes. Furthermore, protein glycosylation contributes to chemoresistance through anti-apoptotic mechanisms, aberrant signaling activation, and pro-angiogenic pathways. This review systematically examines the dynamic evolution of protein glycosylation during CRC progression from normal mucosa to adenoma to adenocarcinoma. It also evaluates the CRC diagnostic and therapeutic implications of glycoproteins and glycans. This review can provide a molecular understanding for advancing CRC diagnostics and treatment.

Acetylated Dendrobium huoshanense polysaccharide: a novel inducer of apoptosis in colon cancer cells via Fas-FasL pathway activation and metabolic reprogramming

Introduction

Not all polysaccharides function as antitumor drugs, nor do they universally possess the same advantages regarding safety and biocompatibility. Those polysaccharides that are effective antitumor agents typically demonstrate superior safety profiles and biocompatibility compared to synthetic anticancer drugs, which can exhibit high toxicity and harmful side effects. Dendrobium huoshanense polysaccharide (DHP) has been recognized for its potential bioactive properties, particularly in anti-tumor treatment. This study investigates the effects of DHP on the proliferation and apoptosis of HCT116 colon cancer cells.

Methods

DHP was extracted according to previously published experimental methods. The inhibitory effects of DHP were evaluated using IEC6, Caco-2, and HCT116 cell lines, with changes in cell morphology observed via transmission electron microscopy. After establishing the conditions for DHP administration, flow cytometry was employed to assess its effects on apoptosis, reactive oxygen species (ROS), and mitochondrial membrane potential of HCT116 cells. Additionally, immunoprecipitation, quantitative real-time polymerase chain reaction (qRT-PCR), Western blotting, and biomarker detection were utilized to investigate the mechanisms underlying DHP's inhibition of HCT116 cells and its impact on metabolic reprogramming.

Results

In the present study, we observed that DHP treatment at 600 μg/ml for 24 h reduced HCT116 cell viability to 54.87%. In contrast, the inhibitory effect of DHP on the viability of IEC6 and Caco-2 cells was relatively mild. The specific mechanism involves DHP activating the mitochondrial apoptotic pathway leading to the downregulation of key metabolic intermediates and enzymes such as uridine diphosphate N-acetylglucosamine (UDP-GlcNAc) and ST6Gal-I. By inhibiting ST6Gal-I activity, DHP activates the Fas/FasL signaling pathway. Additionally, DHP-induced ROS production effectively triggers apoptosis in HCT116 cells.

Conclusion

Our study demonstrates that DHP effectively inhibits the proliferation and induces apoptosis in HCT116 colon cancer cells through the activation of the Fas-FasL signaling pathway and metabolic reprogramming. The selective inhibitory effect of DHP on HCT116 cells, the activation of both death receptor and mitochondrial apoptotic pathways, and the modulation of metabolic reprogramming provide novel insights into the potential therapeutic strategies for colon cancer.

Apoptotic signaling by TNFR1 is inhibited by the α2-6 sialylation, but not α2-3 sialylation, of the TNFR1 N-glycans

The TNF-TNFR1 signaling pathway plays a pivotal role in regulating the balance between cell survival and cell death. Upon binding to TNF, plasma membrane-localized TNFR1 initiates survival signaling, whereas TNFR1 internalization promotes caspase-mediated apoptosis. We previously reported that the α2-6 sialylation of TNFR1 by the tumor-associated sialyltransferase ST6GAL1 diverts signaling toward survival by inhibiting TNFR1 internalization. In the current investigation, we interrogated the mechanisms underlying sialylation-dependent regulation of TNFR1 and uncovered a novel role for α2-6 sialylation, but not α2-3 sialylation, in mediating apoptosis-resistance. Our studies utilized HEK293 cells with deletion of sialyltransferases that modify N-glycans with either α2-3-linked sialic acids (ST3GAL3/4/6) or α2-6-linked sialic acids (ST6GAL1/2). Additionally, ST6GAL1 was re-expressed in cells with ST6GAL1/2 deletion to restore α2-6 sialylation. Using total internal reflection fluorescence (TIRF) microscopy and BS3 cross-linking, we determined that, under basal conditions, cells expressing TNFR1 devoid of α2-6 sialylation displayed enhanced TNFR1 oligomerization, an event that poises cells for activation by TNF. Moreover, upon stimulation with TNF, greater internalization of TNFR1 was observed via time-lapse TIRF and flow cytometry, and this correlated with increased caspase-dependent apoptosis. These effects were reversed by ST6GAL1 re-expression. Conversely, eliminating α2-3 sialylation did not significantly alter TNFR1 clustering, internalization or apoptosis. We also evaluated the Fas receptor, given its structural similarity to TNFR1. As with TNFR1, α2-6 sialylation had a selective effect in protecting cells against Fas-mediated apoptosis. These results collectively suggest that ST6GAL1 may serve a unique function in shielding cancer cells from apoptotic stimuli within the tumor microenvironment.

When a negative (charge) is not a positive: sialylation and its role in cancer mechanics and progression

Sialic acids and sialoglycans are critical actors in cancer progression and metastasis. These terminal sugar residues on glycoproteins and glycolipids modulate key cellular processes such as immune evasion, cell adhesion, and migration. Aberrant sialylation is driven by overexpression of sialyltransferases, resulting in hypersialylation on cancer cell surfaces as well as enhancing tumor aggressiveness. Sialylated glycans alter the structure of the glycocalyx, a protective barrier that fosters cancer cell detachment, migration, and invasion. This bulky glycocalyx also increases membrane tension, promoting integrin clustering and downstream signaling pathways that drive cell proliferation and metastasis. They play a critical role in immune evasion by binding to Siglecs, inhibitory receptors on immune cells, which transmit signals that protect cancer cells from immune-mediated destruction. Targeting sialylation pathways presents a promising therapeutic opportunity to understand the complex roles of sialic acids and sialoglycans in cancer mechanics and progression, which is crucial for developing novel diagnostic and therapeutic strategies that can disrupt these processes and improve cancer treatment outcomes.

The pro-inflammatory cytokines IL-1β and IL-6 promote upregulation of the ST6GAL1 sialyltransferase in pancreatic cancer cells

The ST6GAL1 sialyltransferase is overexpressed in multiple cancers, including pancreatic ductal adenocarcinoma (PDAC). ST6GAL1 adds an α2-6-linked sialic acid to N-glycosylated membrane receptors, which consequently modulates receptor structure and function. While many studies have investigated the effects of ST6GAL1 on cell phenotype, there is a dearth of knowledge regarding mechanisms that regulate ST6GAL1 expression. In the current study, we evaluated the regulation of ST6GAL1 by two pro-inflammatory cytokines, IL-1β and IL-6, which are abundant within the PDAC tumor microenvironment. Cytokine activity was monitored using the Suit-2 PDAC cell line and two Suit-2-derived metastatic subclones, S2-013 and S2-LM7AA. For all three cell models, treatment with IL-1β or IL-6 increased the expression of ST6GAL1 protein and mRNA. Specifically, IL-1β and IL-6 induced expression of the ST6GAL1 YZ mRNA isoform, which is driven by the P3 promoter. The ST6GAL1 H and X isoforms were not detected. Promoter reporter assays confirmed that IL-1β and IL-6 activated transcription from the P3 promoter. We then examined downstream signaling mechanisms. IL-1β is known to signal through the NFκB transcription factor, whereas IL-6 signals through the STAT3 transcription factor. CUT&RUN experiments revealed that IL-1β promoted the binding of NFκB to the ST6GAL1 P3 promoter, and IL-6 induced the binding of STAT3 to the P3 promoter. Finally, we determined that inhibitors of NFκB and STAT3 blocked the upregulation of ST6GAL1 stimulated by IL-1β and IL-6, respectively. Together, these results highlight a novel molecular pathway by which cytokines within the tumor microenvironment stimulate the upregulation of ST6GAL1 in PDAC cells.

Anticancer approach by targeted activation of a global inhibitor of sialyltransferases with acrolein

Cells are covered with a thick layer of sugar molecules known as glycans. Abnormal glycosylation is a hallmark of cancer, and hypersialylation increases tumor metastasis by promoting immune evasion and inducing tumor cell invasion and migration. Inhibiting sialylation is thus a potential anticancer treatment strategy. However, targeting sialic acids is difficult because of the lack of selective delivery tools. Here, we present a prodrug strategy for selectively releasing the global inhibitor of sialylation peracetylated 3Fax-Neu5Ac (PFN) in cancer cells using the reaction between phenyl azide and endogenous acrolein, which is overproduced in most cancer cells. The prodrug significantly suppressed tumor growth in mice as effectively as PFN without causing kidney dysfunction, which is associated with PFN. The use of sialylated glycans as immune checkpoints is gaining increasing attention, and the proposed method for precisely targeting aberrant sialylation provides a novel avenue for expanding current cancer treatments.

Specific sialylation of N-glycans and its novel regulatory mechanism

Altered glycosylation is a common feature of cancer cells. Some subsets of glycans are found to be frequently enriched on the tumor cell surface and implicated in different tumor phenotypes. Among these, changes in sialylation have long been associated with metastatic cell behaviors such as invasion and enhanced cell survival. Sialylation typically exists in three prominent linkages: α2,3, α2,6, and α2,8, catalyzed by a group of sialyltransferases. The aberrant expression of all three linkages has been related to cancer progression. The increased α2,6 sialylation on N-glycans catalyzed by β-galactoside α2,6 sialyltransferase 1 (ST6Gal1) is frequently observed in many cancers. In contrast, functions of α2,3 sialylation on N-glycans catalyzed by at least three β-galactoside α2,3-sialyltransferases, ST3Gal3, ST3Gal4, and ST3Gal6 remain elusive due to a possibility of compensating for one another. In this minireview, we briefly describe functions of sialylation and recent findings that different α2,3 sialyltransferases specifically modify target proteins, as well as sialylation regulatory mechanisms vis a complex formation among integrin α3β1, Golgi phosphoprotein 3 (GOLPH3), phosphatidylinositol 4-kinase IIα (PI4KIIα), focal adhesion kinase (FAK) and sialyltransferase, which suggests a new concept for the regulation of glycosylation in cell biology.

Novel regulatory mechanisms of N-glycan sialylation: Implication of integrin and focal adhesion kinase in the regulation

BACKGROUND

Sialylation of glycoproteins, including integrins, is crucial in various cancers and diseases such as immune disorders. These modifications significantly impact cellular functions and are associated with cancer progression. Sialylation, catalyzed by specific sialyltransferases (STs), has traditionally been considered to be regulated at the mRNA level.

SCOPE OF REVIEW

Recent research has expanded our understanding of sialylation, revealing ST activity changes beyond mRNA level variations. This includes insights into COPI vesicle formation and Golgi apparatus maintenance and identifying specific target proteins of STs that are not predictable through recombinant enzyme assays.

MAJOR CONCLUSIONS

This review summarizes that Golgi-associated pathways largely influence the regulation of STs. GOLPH3, GORAB, PI4K, and FAK have become critical elements in sialylation regulation. Some STs have been revealed to possess specificity for specific target proteins, suggesting the presence of additional, enzyme-specific regulatory mechanisms.

GENERAL SIGNIFICANCE

This study enhances our understanding of the molecular interplay in sialylation regulation, mainly focusing on the role of integrin and FAK. It proposes a bidirectional system where sialylations might influence integrins and vice versa. The diversity of STs and their specific linkages offer new perspectives in cancer research, potentially broadening our understanding of cellular mechanisms and opening avenues for new therapeutic approaches in targeting sialylation pathways.

Sialylated glycoproteins and sialyltransferases in digestive cancers: Mechanisms, diagnostic biomarkers, and therapeutic targets

Sialic acid (SA), as the ultimate epitope of polysaccharides, can act as a cap at the end of polysaccharide chains to prevent their overextension. Sialylation is the enzymatic process of transferring SA residues onto polysaccharides and is catalyzed by a group of enzymes known as sialyltransferases (SiaTs). It is noteworthy that the sialylation level of glycoproteins is significantly altered when digestive cancer occurs. And this alteration exhibits a close correlation with the progression of these cancers. In this review, from the perspective of altered SiaTs expression levels and changed glycoprotein sialylation patterns, we summarize the pathogenesis of gastric cancer (GC), colorectal cancer (CRC), pancreatic ductal adenocarcinoma (PDAC), and hepatocellular carcinoma (HCC). Furthermore, we propose potential early diagnostic biomarkers and prognostic indicators for different digestive cancers. Finally, we summarize the therapeutic value of sialylation in digestive system cancers.

ST6GAL1 is associated with poor response to chemoradiation in rectal cancer

INTRODUCTION

Colorectal cancer is the third most common cause of cancer death. Rectal cancer makes up a third of all colorectal cases. Treatment for locally advanced rectal cancer includes chemoradiation followed by surgery. We have previously identified ST6GAL1 as a cause of resistance to chemoradiation in vitro and hypothesized that it would be correlated with poor response in human derived models and human tissues.

METHODS

Five organoid models were created from primary human rectal cancers and ST6GAL1 was knocked down via lentivirus transduction in one model. ST6GAL1 and Cleaved Caspase-3 (CC3) were assessed after chemoradiation via immunostaining. A tissue microarray (TMA) was created from twenty-six patients who underwent chemoradiation and had pre- and post-treatment specimens of rectal adenocarcinoma available at our institution. Immunohistochemistry was performed for ST6GAL1 and percent positive cancer cell staining was assessed and correlation with pathological grade of response was measured.

RESULTS

Organoid models were treated with chemoradiation and both ST6GAL1 mRNA and protein significantly increased after treatment. The organoid model targeted with ST6GAL1 knockdown was found to have increased CC3 after treatment. In the tissue microarray, 42 percent of patient samples had an increase in percent tumor cell staining for ST6GAL1 after treatment. Post-treatment percent staining was associated with a worse grade of treatment response (p = 0.01) and increased staining post-treatment compared to pre-treatment was also associated with a worse response (p = 0.01).

CONCLUSION

ST6GAL1 is associated with resistance to treatment in human rectal cancer and knockdown in an organoid model abrogated resistance to apoptosis caused by chemoradiation.

N-linked α2,6-sialylation of integrin β1 by the sialyltransferase ST6Gal1 promotes cell proliferation and stemness in gestational trophoblastic disease

INTRODUCTION

Gestational trophoblastic disease (GTD) encompasses a spectrum of rare pre-malignant and malignant entities originating from trophoblastic tissue, including partial hydatidiform mole, complete hydatidiform mole and choriocarcinoma. β-galactoside α2,6 sialyltransferase 1 (ST6Gal1), the primary sialyltransferase responsible for the addition of α2,6 sialic acids, is strongly associated with the occurrence and development of several tumor types. However, the role of ST6Gal1/α2,6 -sialylation of trophoblast cells in GTD is still not well understood.

METHODS

The expression of ST6Gal1 was investigated in GTD and human immortalized trophoblastic HTR-8/SVneo cells and human gestational choriocarcinoma JAR cells. We evaluated the effect of ST6Gal1 on proliferation and stemness of trophoblastic cells. We also examined the effect of internal miR-199a-5p on ST6Gal1 expression. The role of ST6Gal1 in regulating α2,6-sialylated integrin β1 and its significance in the activation of integrin β1/focal adhesion kinase (FAK) signaling pathway were also explored.

RESULTS

ST6Gal1 was observed to be highly expressed in GTD. Overexpression of ST6Gal1 promoted the proliferation and stemness of HTR-8/SVneo cells, whereas knockdown of ST6Gal1 suppressed the viability and stemness of JAR cells. MiR-199a-5p targeted and inhibited the expression of ST6Gal1 in trophoblastic cells. In addition, we revealed integrin β1 was highly α2,6-sialylated in JAR cells. Inhibition of ST6Gal1 reduced α2,6-sialylation on integrin β1 and suppressed the integrin β1/FAK pathway in JAR cells, thereby affecting its biological functions.

DISCUSSION

This study demonstrated that ST6Gal1 plays important roles in promoting proliferation and stemness through the integrin β1 signaling pathway in GTD. Therefore, ST6Gal1 may have a potential role in the occurrence and development of GTD.

TNF-Related Apoptosis-Inducing Ligand: Non-Apoptotic Signalling

TNF-related apoptosis-inducing ligand (TRAIL or Apo2 or TNFSF10) belongs to the TNF superfamily. When bound to its agonistic receptors, TRAIL can induce apoptosis in tumour cells, while sparing healthy cells. Over the last three decades, this tumour selectivity has prompted many studies aiming at evaluating the anti-tumoral potential of TRAIL or its derivatives. Although most of these attempts have failed, so far, novel formulations are still being evaluated. However, emerging evidence indicates that TRAIL can also trigger a non-canonical signal transduction pathway that is likely to be detrimental for its use in oncology. Likewise, an increasing number of studies suggest that in some circumstances TRAIL can induce, via Death receptor 5 (DR5), tumour cell motility, potentially leading to and contributing to tumour metastasis. While the pro-apoptotic signal transduction machinery of TRAIL is well known from a mechanistic point of view, that of the non-canonical pathway is less understood. In this study, we the current state of knowledge of TRAIL non-canonical signalling.

Role of ST6GAL1 in Thyroid Cancers: Insights from Tissue Analysis and Genomic Datasets

Thyroid cancer is the predominant endocrine-related malignancy. ST6 β-galactoside α2,6-sialyltransferase 1 (ST6GAL1) has been studied in various types of cancers; however, the expression and function of ST6GAL1 in thyroid cancer has not been investigated so far. Previously, we conducted two genome-wide association studies and have identified the association of the ST6GAL1 gene with plasma thyroglobulin (Tg) levels. Since Tg levels are altered in thyroid pathologies, in the current study, we wanted to evaluate the expression of ST6GAL1 in thyroid cancer tissues. We performed an immunohistochemical analysis using human thyroid tissue from 89 patients and analyzed ST6GAL1 protein expression in papillary thyroid cancer (including follicular variant and microcarcinoma) and follicular thyroid cancer in comparison to normal thyroid tissue. Additionally, ST6GAL1 mRNA levels from The Cancer Genome Atlas (TCGA, n = 572) and the Genotype-Tissue Expression (GTEx) project (n = 279) were examined. The immunohistochemical analysis revealed higher ST6GAL1 protein expression in all thyroid tumors compared to normal thyroid tissue. TCGA data revealed increased ST6GAL1 mRNA levels in both primary and metastatic tumors versus controls. Notably, the follicular variant of papillary thyroid cancer exhibited significantly higher ST6GAL1 mRNA levels than classic papillary thyroid cancer. High ST6GAL1 mRNA levels significantly correlated with lymph node metastasis status, clinical stage, and reduced survival rate. ST6GAL1 emerges as a potential cancer-associated glycosyltransferase in thyroid malignancies, offering valuable insights into its diagnostic and prognostic significance.

ST6GAL1 sialyltransferase promotes acinar to ductal metaplasia and pancreatic cancer progression

The role of aberrant glycosylation in pancreatic ductal adenocarcinoma (PDAC) remains an under-investigated area of research. In this study, we determined that ST6 β-galactoside α2,6 sialyltransferase 1 (ST6GAL1), which adds α2,6-linked sialic acids to N-glycosylated proteins, was upregulated in patients with early-stage PDAC and was further increased in advanced disease. A tumor-promoting function for ST6GAL1 was elucidated using tumor xenograft experiments with human PDAC cells. Additionally, we developed a genetically engineered mouse (GEM) model with transgenic expression of ST6GAL1 in the pancreas and found that mice with dual expression of ST6GAL1 and oncogenic KRASG12D had greatly accelerated PDAC progression compared with mice expressing KRASG12D alone. As ST6GAL1 imparts progenitor-like characteristics, we interrogated ST6GAL1's role in acinar to ductal metaplasia (ADM), a process that fosters neoplasia by reprogramming acinar cells into ductal, progenitor-like cells. We verified ST6GAL1 promotes ADM using multiple models including the 266-6 cell line, GEM-derived organoids and tissues, and an in vivo model of inflammation-induced ADM. EGFR is a key driver of ADM and is known to be activated by ST6GAL1-mediated sialylation. Importantly, EGFR activation was dramatically increased in acinar cells and organoids from mice with transgenic ST6GAL1 expression. These collective results highlight a glycosylation-dependent mechanism involved in early stages of pancreatic neoplasia.

Sialylation of EGFR by ST6GAL1 induces receptor activation and modulates trafficking dynamics

Aberrant glycosylation is a hallmark of a cancer cell. One prevalent alteration is an enrichment in α2,6-linked sialylation of N-glycosylated proteins, a modification directed by the ST6GAL1 sialyltransferase. ST6GAL1 is upregulated in many malignancies including ovarian cancer. Prior studies have shown that the addition of α2,6 sialic acid to the epidermal growth factor receptor (EGFR) activates this receptor, although the mechanism was largely unknown. To investigate the role of ST6GAL1 in EGFR activation, ST6GAL1 was overexpressed in the OV4 ovarian cancer line, which lacks endogenous ST6GAL1, or knocked-down in the OVCAR-3 and OVCAR-5 ovarian cancer lines, which have robust ST6GAL1 expression. Cells with high expression of ST6GAL1 displayed increased activation of EGFR and its downstream signaling targets, AKT and NFκB. Using biochemical and microscopy approaches, including total internal reflection fluorescence microscopy, we determined that the α2,6 sialylation of EGFR promoted its dimerization and higher order oligomerization. Additionally, ST6GAL1 activity was found to modulate EGFR trafficking dynamics following EGF-induced receptor activation. Specifically, EGFR sialylation enhanced receptor recycling to the cell surface following activation while simultaneously inhibiting lysosomal degradation. 3D widefield deconvolution microscopy confirmed that in cells with high ST6GAL1 expression, EGFR exhibited greater colocalization with Rab11 recycling endosomes and reduced colocalization with LAMP1-positive lysosomes. Collectively, our findings highlight a novel mechanism by which α2,6 sialylation promotes EGFR signaling by facilitating receptor oligomerization and recycling.

Comprehensive serum N-glycan profiling identifies a biomarker panel for early diagnosis of non-small-cell lung cancer

Aberrant serum N-glycan profiles have been observed in multiple cancers including non-small-cell lung cancer (NSCLC), yet the potential of N-glycans in the early diagnosis of NSCLC remains to be determined. In this study, serum N-glycan profiles of 275 NSCLC patients and 309 healthy controls were characterized by MALDI-TOF-MS. The levels of serum N-glycans and N-glycosylation patterns were compared between NSCLC and control groups. In addition, a panel of N-glycan biomarkers for NSCLC diagnosis was established and validated using machine learning algorithms. As a result, a total of 54 N-glycan structures were identified in human serum. Compared with healthy controls, 29 serum N-glycans were increased or decreased in NSCLC patients. N-glycan abundance in different histological types or clinical stages of NSCLC presented differentiated changes. Furthermore, an optimal biomarker panel of eight N-glycans was constructed based on logistic regression, with an AUC of 0.86 in the validation set. Notably, this model also showed a desirable capacity in distinguishing early-stage patients from healthy controls (AUC = 0.88). In conclusion, our work highlights the abnormal N-glycan profiles in NSCLC and provides supports potential application of N-glycan biomarker panel in clinical NSCLC detection.

Dynamic Glycoprotein Hyposialylation Promotes Chemotherapy Evasion and Metastatic Seeding of Quiescent Circulating Tumor Cell Clusters in Breast Cancer

Most circulating tumor cells (CTC) are detected as single cells, whereas a small proportion of CTCs in multicellular clusters with stemness properties possess 20- to 100-times higher metastatic propensity than the single cells. Here we report that CTC dynamics in both singles and clusters in response to therapies predict overall survival for breast cancer. Chemotherapy-evasive CTC clusters are relatively quiescent with a specific loss of ST6GAL1-catalyzed α2,6-sialylation in glycoproteins. Dynamic hyposialylation in CTCs or deficiency of ST6GAL1 promotes cluster formation for metastatic seeding and enables cellular quiescence to evade paclitaxel treatment in breast cancer. Glycoproteomic analysis reveals newly identified protein substrates of ST6GAL1, such as adhesion or stemness markers PODXL, ICAM1, ECE1, ALCAM1, CD97, and CD44, contributing to CTC clustering (aggregation) and metastatic seeding. As a proof of concept, neutralizing antibodies against one newly identified contributor, PODXL, inhibit CTC cluster formation and lung metastasis associated with paclitaxel treatment for triple-negative breast cancer.

SIGNIFICANCE

This study discovers that dynamic loss of terminal sialylation in glycoproteins of CTC clusters contributes to the fate of cellular dormancy, advantageous evasion to chemotherapy, and enhanced metastatic seeding. It identifies PODXL as a glycoprotein substrate of ST6GAL1 and a candidate target to counter chemoevasion-associated metastasis of quiescent tumor cells. This article is featured in Selected Articles from This Issue, p. 1949.

Hyper α2,6-Sialylation Promotes CD4+ T-Cell Activation and Induces the Occurrence of Ulcerative Colitis

α2,6-sialylation, catalyzed by α2,6-sialyltransferase (ST6GAL1), plays a pivotal role in immune responses. However, the role of ST6GAL1 in the pathogenesis of ulcerative colitis (UC) remains unknown. ST6GAL1 mRNA is highly expressed in UC tissues compared with the corresponding adjacent normal tissues, and α2,6-sialylation is significantly increased in the colon tissues of patients with UC. The expression of ST6GAL1 and proinflammatory cytokines, such as interleukin (IL)-2, IL-6, IL-17, and interferon-gamma, is also increased. The number of CD4+ T cells increases in UC patients. St6gal1 gene knockout (St6gal1-/- ) rats are established by clustered regularly interspaced short palindromic repeats (CRISPR)-associated gene knockout system. St6gal1 deficiency reduces the levels of pro-inflammatory cytokines and alleviates colitis symptoms in UC model rats. Ablation of α2,6-sialylation inhibits the transport of the TCR to lipid rafts and suppresses CD4+ T-cell activation. The attenuation of TCR signaling downregulates the expression of NF-κB in ST6GAL1-/- CD4+ T-cells. Moreover, NF-κB could bind to the ST6GAL1 promoter to increase its transcription. Ablation of ST6GAL1 downregulates the expression of NF-κB and reduces the production of proinflammatory cytokines to relieve UC pathogenesis, which is a potential novel target for the clinical treatment of UC.

The role of sialylation in gynecologic cancers

Sialic acids (SA) are a kind of nine-carbon backbone sugars, serving as important molecules in cell-to-cell or cell-to-extra-cellular matrix interaction mediated by either O-linked glycosylation or N-linked glycosylation to attach the terminal end of glycans, glycoproteins, and glycolipids. All processes need a balance between sialylation by sialyltransferase (STs) and desialylation by sialidases (also known as neuraminidases, NEU). Although there is much in uncertainty whether the sialyation plays in cancer development and progression, at least four mechanisms are proposed, including surveillance of immune system, modification of cellular apoptosis and cell death, alteration of cellular surface of cancer cells and tumor associated microenvironment responsible carcinogenesis, growth and metastases. The current review focuses on the role of glycosylation in gynecologic organ-related cancers, such as ovarian cancer, cervical and endometrial cancer. Evidence shows that sialylation involving in the alternation of surface components of cells (tumor and cells in the microenvironment of host) plays an important role for carcinogenesis (escape from immunosurveillance) and dissemination (metastasis) (sloughing from the original site of cancer, migration into the circulation system, extravasation from the circulatory system to the distant site and finally deposition and establishment on the new growth lesion to complete the metastatic process). Additionally, modification of glycosylation can enhance or alleviate the aggressive characteristics of the cancer behaviors. All suggest that more understandings of glycosylation on cancers may provide a new therapeutic field to assist the cancer treatment in the near future.

Recent advances in the development of sialyltransferase inhibitors to control cancer metastasis: A comprehensive review

Metastasis accounts for the majority of cancer-associated mortalities, representing a huge health and economic burden. One of the mechanisms that enables metastasis is hypersialylation, characterized by an overabundance of sialylated glycans on the tumor surface, which leads to repulsion and detachment of cells from the original tumor. Once the tumor cells are mobilized, sialylated glycans hijack the natural killer T-cells through self-molecular mimicry and activatea downstream cascade of molecular events that result in inhibition of cytotoxicity and inflammatory responses against cancer cells, ultimately leading to immune evasion. Sialylation is mediated by a family of enzymes known as sialyltransferases (STs), which catalyse the transfer of sialic acid residue from the donor, CMP-sialic acid, onto the terminal end of an acceptor such as N-acetylgalactosamine on the cell-surface. Upregulation of STs increases tumor hypersialylation by up to 60% which is considered a distinctive hallmark of several types of cancers such as pancreatic, breast, and ovarian cancer. Therefore, inhibiting STs has emerged as a potential strategy to prevent metastasis. In this comprehensive review, we discuss the recent advances in designing novel sialyltransferase inhibitors using ligand-based drug design and high-throughput screening of natural and synthetic entities, emphasizing the most successful approaches. We analyse the limitations and challenges of designing selective, potent, and cell-permeable ST inhibitors that hindered further development of ST inhibitors into clinical trials. We conclude by analysing emerging opportunities, including advanced delivery methods which further increase the potential of these inhibitors to enrich the clinics with novel therapeutics to combat metastasis.

Integrating Bulk and Single-Cell RNA Sequencing Reveals Heterogeneity, Tumor Microenvironment, and Immunotherapeutic Efficacy Based on Sialylation-Related Genes in Bladder Cancer

Background

As known abnormal sialylation exerts crucial roles in the growth, metastasis, and immune evasion of cancers, but the molecular characteristics and roles in bladder cancer (BLCA) remain unclear. This study intends to establish BLCA risk stratification based on sialylation-related genes and elucidate its role in prognosis, tumor microenvironment, and immunotherapy of BLCA.

Methods

Bulk RNA-seq and scRNA-seq data were downloaded from open-access databases. The scRNA-seq data were processed using the R package "Seurat" to identify the core cell types. The tumor sub-typing of BLCA samples was performed by the R package "ConsensusClusterPlus" in the bulk RNA-seq data. Signature genes were identified by the R package "limma" and univariate regression analysis to calculate risk scores using the R package "GSVA" and establish risk stratification of BLCA patients. Finally, the differences in clinicopathological characteristics, tumor microenvironment, and immunotherapy efficacy between the different groups were investigated.

Results

5 core cell types were identified in the scRNA-seq dataset, with monocytes and macrophages presenting the greatest percentage, sialylation-related gene expression, and sialylation scores. The bulk RNA-seq samples were classified into 3 tumor subtypes based on 19 prognosis-related sialylation genes. The 10 differential expressed genes (DEGs) with the smallest p-values were collected as signature genes, and the risk score was calculated, with the samples divided into high and low-risk score groups. The results showed that patients in the high-risk score group exhibited worse survival outcomes, higher tumor grade, more advanced stage, more frequency of gene mutations, higher expression levels of immune checkpoints, and lower immunotherapy response.

Conclusion

We established a novel risk stratification of BLCA from a glycomics perspective, which demonstrated good accuracy in determining the prognostic outcome, clinicopathological characteristics, immune microenvironment, and immunotherapy efficacy of patients, and we are proposing to apply it to direct the choice of clinical treatment options for patients.

Transcription of human β-galactoside α2,6-sialyltransferase (hST6Gal I) is downregulated by curcumin through AMPK signaling in human colon carcinoma HCT116 cells

BACKGROUND

In this study, we observed that in human colon carcinoma HCT116 cells mRNA level of the human β-galactoside α2,6-sialyltransferase (hST6Gal I) was decreased by curcumin. FACS analysis using the α2,6-sialyl-specific lectin (SNA) also showed a noticeable decrease in binding to SNA by curcumin.

OBJECTIVE

To investigate the mechanism for curcumin-triggered downregulation of hST6Gal I transcription.

METHODS

The mRNA levels of nine kinds of hST genes were assessed by RT-PCR after curcumin was treated in HCT116 cells. The level of hST6Gal I product on cell surface was examined by flow cytometry analysis. Luciferase reporter plasmids with 5'-deleted constructs and mutants of the hST6Gal I promoter were transiently transfected into HCT116 cells, and the luciferase activity was measured after treatment with curcumin.

RESULTS

Curcumin led to significant transcriptional repression of the hST6Gal I promoter. Promoter analysis using deletion mutants proved that the - 303 to - 189 region of the hST6Gal I promoter is required for transcriptional repression in response to curcumin. Among putative binding sites for transcription factors IK2, GATA1, TCF12, TAL1/E2A, SPT, and SL1 in this region, by site-directed mutagenesis analysis the TAL/E2A binding site (nucleotides - 266/- 246) was proved to be crucial for curcumin-triggered downregulation of hST6Gal I transcription in HCT116 cells. The transcription activity of hST6Gal I gene in HCT116 cells was markedly suppressed by compound C, an AMP-activated protein kinase (AMPK) inhibitor.

CONCLUSION

These indicate that gene expression of hST6Gal I in HCT116 cells is controlled through AMPK/TAL/E2A signal pathway.

Early in vitro evidence indicates that deacetylated sialic acids modulate multi-drug resistance in colon and lung cancers via breast cancer resistance protein

Cancers utilize sugar residues to engage in multidrug resistance. The underlying mechanism of action involving glycans, specifically the glycan sialic acid (Sia) and its various functional group alterations, has not been explored. ATP-binding cassette (ABC) transporter proteins, key proteins utilized by cancers to engage in multidrug resistant (MDR) pathways, contain Sias in their extracellular domains. The core structure of Sia can contain a variety of functional groups, including O-acetylation on the C6 tail. Modulating the expression of acetylated-Sias on Breast Cancer Resistance Protein (BCRP), a significant ABC transporter implicated in MDR, in lung and colon cancer cells directly impacted the ability of cancer cells to either retain or efflux chemotherapeutics. Via CRISPR-Cas-9 gene editing, acetylation was modulated by the removal of CAS1 Domain-containing protein (CASD1) and Sialate O-Acetyl esterase (SIAE) genes. Using western blot, immunofluorescence, gene expression, and drug sensitivity analysis, we confirmed that deacetylated Sias regulated a MDR pathway in colon and lung cancer in early in vitro models. When deacetylated Sias were expressed on BCRP, colon and lung cancer cells were able to export high levels of BCRP to the cell's surface, resulting in an increased BCRP efflux activity, reduced sensitivity to the anticancer drug Mitoxantrone, and high proliferation relative to control cells. These observations correlated with increased levels of cell survival proteins, BcL-2 and PARP1. Further studies also implicated the lysosomal pathway for the observed variation in BCRP levels among the cell variants. RNASeq data analysis of clinical samples revealed higher CASD1 expression as a favorable marker of survival in lung adenocarcinoma. Collectively, our findings indicate that deacetylated Sia is utilized by colon and lung cancers to engage in MDR via overexpression and efflux action of BCRP.

Sialylation of EGFR by ST6GAL1 induces receptor activation and modulates trafficking dynamics

Aberrant glycosylation is a hallmark of a cancer cell. One prevalent alteration is an enrichment in α2,6-linked sialylation of N-glycosylated proteins, a modification directed by the ST6GAL1 sialyltransferase. ST6GAL1 is upregulated in many malignancies including ovarian cancer. Prior studies have shown that the addition of α2,6 sialic acid to the Epidermal Growth Factor Receptor (EGFR) activates this receptor, although the mechanism was largely unknown. To investigate the role of ST6GAL1 in EGFR activation, ST6GAL1 was overexpressed in the OV4 ovarian cancer line, which lacks endogenous ST6GAL1, or knocked down in the OVCAR-3 and OVCAR-5 ovarian cancer lines, which have robust ST6GAL1 expression. Cells with high expression of ST6GAL1 displayed increased activation of EGFR and its downstream signaling targets, AKT and NFκB. Using biochemical and microscopy approaches, including Total Internal Reflection Fluorescence (TIRF) microscopy, we determined that the α2,6 sialylation of EGFR promoted its dimerization and higher order oligomerization. Additionally, ST6GAL1 activity was found to modulate EGFR trafficking dynamics following EGF-induced receptor activation. Specifically, EGFR sialylation enhanced receptor recycling to the cell surface following activation while simultaneously inhibiting lysosomal degradation. 3D widefield deconvolution microscopy confirmed that in cells with high ST6GAL1 expression, EGFR exhibited greater co-localization with Rab11 recycling endosomes and reduced co-localization with LAMP1-positive lysosomes. Collectively, our findings highlight a novel mechanism by which α2,6 sialylation promotes EGFR signaling by facilitating receptor oligomerization and recycling.

Forced expression of α2,3-sialyltransferase IV rescues impaired heart development in α2,6-sialyltransferase I-deficient medaka

Sialic acids (Sias) are often linked to galactose (Gal) residues by α2,6- and α2,3-linkages in glycans of glycoproteins. Sias are indispensable for vertebrate development, because organisms deficient in some enzymes in the Sia synthetic pathway are lethal during the development. However, it remains unknown if the difference of Siaα2,6Gal or α2,3Gal linkage has a critical meaning. To find a clue to understand significance of the linkage difference at the organism level, medaka was used as a vertebrate model. In embryos, Siaα2,6Gal epitopes recognized by Sambucus nigra lectin (SNA) and Siaα2,3Gal epitopes recognized by Maackia amurensis lectin (MAA) were enriched in the blastodisc and the yolk sphere, respectively. When these lectins were injected in the perivitelline space, SNA, but not MAA, impaired embryo body formation at 1 day post-fertilization (dpf). Most Siaα2,6Gal epitopes occurred on N-glycans owing to their sensitivity to peptide:N-glycanase. Of knockout-medaka (KO) for either of two β-galactoside:α2,6-sialyltransferase genes, ST6Gal I and ST6Gal II, only ST6Gal I-KO showed severe cardiac abnormalities at 7-16 dpf, leading to lethality at 14-18 dpf. Interestingly, however, these cardiac abnormalities of ST6Gal I-KO were rescued not only by forced expression of ST6Gal I, but also by that of ST6Gal II and the β-galactoside:α2,3-sialyltransferase IV gene (ST3Gal IV). Taken together, the Siaα2,6Gal linkage synthesized by ST6Gal I are critical in heart development; however, it can be replaced by the linkages synthesized by ST6Gal II and ST3Gal IV. These data suggest that sialylation itself is more important than its particular linkage for the heart development.

ST6GAL1 inhibits metastasis of hepatocellular carcinoma via modulating sialylation of MCAM on cell surface

The poor prognosis of hepatocellular carcinoma (HCC) is mainly because of its high rate of metastasis. Thus, elucidation of the molecular mechanisms underlying HCC metastasis is of great significance. Glycosylation is an important post-translational modification that is closely associated with tumor progression. Altered glycosylation including the altered sialylation resulting from aberrant expression of β-galactoside α2,6 sialyltransferase 1 (ST6GAL1) has long been considered as an important feature of cancer cells. However, there is limited information on the roles of ST6GAL1 and α2,6 sialylation in HCC metastasis. Here, we found that ST6GAL1 and α2,6 sialylation were negatively correlated with the metastatic potentials of HCC cells. Moreover, ST6GAL1 overexpression inhibited migration and invasion of HCC cells in vitro and suppressed HCC metastasis in vivo. Using a metabolic labeling-based glycoproteomic strategy, we identified a list of sialylated proteins that may be regulated by ST6GAL1. In particular, an increase in α2,6 sialylation of melanoma cell adhesion molecule (MCAM) inhibited its interaction with galectin-3 and decreased its expression on cell surface. In vitro and in vivo analysis showed that ST6GAL1 exerted its function in HCC metastasis by regulating MCAM expression. Finally, we found the relative intensity of sialylated MCAM was negatively correlated with tumor malignancy in HCC patients. Taken together, these results demonstrate that ST6GAL1 may be an HCC metastasis suppressor by affecting sialylation of MCAM on cell surface, which provides a novel insight into the roles of ST6GAL1 in HCC progression and supports the functional complexity of ST6GAL1 in a cancer type- and tissue type-specific manner.

Glycobiology of cellular expiry: Decrypting the role of glycan-lectin regulatory complex and therapeutic strategies focusing on cancer

Often the outer leaflets of living cells bear a coat of glycosylated proteins, which primarily regulates cellular processes. Glycosylation of such proteins occurs as part of their post-translational modification. Within the endoplasmic reticulum, glycosylation enables the attachment of specific oligosaccharide moieties such as, 'glycan' to the transmembrane receptor proteins which confers precise biological information for governing the cell fate. The nature and degree of glycosylation of cell surface receptors are regulated by a bunch of glycosyl transferases and glycosidases which fine-tune attachment or detachment of glycan moieties. In classical death receptors, upregulation of glycosylation by glycosyl transferases is capable of inducing cell death in T cells, tumor cells, etc. Thus, any deregulated alternation at surface glycosylation of these death receptors can result in life-threatening disorder like cancer. In addition, transmembrane glycoproteins and lectin receptors can transduce intracellular signals for cell death execution. Exogenous interaction of lectins with glycan containing death receptors signals for cell death initiation by modulating downstream signalings. Subsequently, endogenous glycan-lectin interplay aids in the customization and implementation of the cell death program. Lastly, the glycan-lectin recognition system dictates the removal of apoptotic cells by sending accurate signals to the extracellular milieu. Since glycosylation has proven to be a biomarker of cellular death and disease progression; glycans serve as specific therapeutic targets of cancers. In this context, we are reviewing the molecular mechanisms of the glycan-lectin regulatory network as an integral part of cell death machinery in cancer to target them for successful therapeutic and clinical approaches.

Sialyltransferases and Neuraminidases: Potential Targets for Cancer Treatment

Cancers are the leading cause of death, causing around 10 million deaths annually by 2020. The most common cancers are those affecting the breast, lungs, colon, and rectum. However, it has been noted that cancer metastasis is more lethal than just cancer incidence and accounts for more than 90% of cancer deaths. Thus, early detection and prevention of cancer metastasis have the capability to save millions of lives. Finding novel biomarkers and targets for screening, determination of prognosis, targeted therapies, etc., are ways of doing so. In this review, we propose various sialyltransferases and neuraminidases as potential therapeutic targets for the treatment of the most common cancers, along with a few rare ones, on the basis of existing experimental and in silico data. This compilation of available cancer studies aiming at sialyltransferases and neuraminidases will serve as a guide for scientists and researchers working on possible targets for various cancers and will also provide data about the existing drugs which inhibit the action of these enzymes.

α2,6 Sialylation mediated by ST6GAL1 promotes glioblastoma growth

One of the least-investigated areas of brain pathology research is glycosylation, which is a critical regulator of cell surface protein structure and function. β-Galactoside α2,6-sialyltransferase (ST6GAL1) is the primary enzyme that α2,6 sialylates N-glycosylated proteins destined for the plasma membrane or secretion, thereby modulating cell signaling and behavior. We demonstrate a potentially novel, protumorigenic role for α2,6 sialylation and ST6GAL1 in the deadly brain tumor glioblastoma (GBM). GBM cells with high α2,6 sialylation exhibited increased in vitro growth and self-renewal capacity and decreased mouse survival when orthotopically injected. α2,6 Sialylation was regulated by ST6GAL1 in GBM, and ST6GAL1 was elevated in brain tumor-initiating cells (BTICs). Knockdown of ST6GAL1 in BTICs decreased in vitro growth, self-renewal capacity, and tumorigenic potential. ST6GAL1 regulates levels of the known BTIC regulators PDGF Receptor β (PDGFRB), Activated Leukocyte Cell Adhesion Molecule, and Neuropilin, which were confirmed to bind to a lectin-recognizing α2,6 sialic acid. Loss of ST6GAL1 was confirmed to decrease PDGFRB α2,6 sialylation, total protein levels, and the induction of phosphorylation by PDGF-BB. Thus, ST6GAL1-mediated α2,6 sialylation of a select subset of cell surface receptors, including PDGFRB, increases GBM growth.

Role of tumor cell sialylation in pancreatic cancer progression

Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest malignancies and is currently the third leading cause of cancer death. The aggressiveness of PDAC stems from late diagnosis, early metastasis, and poor efficacy of current chemotherapies. Thus, there is an urgent need for effective biomarkers for early detection of PDAC and development of new therapeutic strategies. It has long been known that cellular glycosylation is dysregulated in pancreatic cancer cells, however, tumor-associated glycans and their cognate glycosylating enzymes have received insufficient attention as potential clinical targets. Aberrant glycosylation affects a broad range of pathways that underpin tumor initiation, metastatic progression, and resistance to cancer treatment. One of the prevalent alterations in the cancer glycome is an enrichment in a select group of sialylated glycans including sialylated, branched N-glycans, sialyl Lewis antigens, and sialylated forms of truncated O-glycans such as the sialyl Tn antigen. These modifications affect the activity of numerous cell surface receptors, which collectively impart malignant characteristics typified by enhanced cell proliferation, migration, invasion and apoptosis-resistance. Additionally, sialic acids on tumor cells engage inhibitory Siglec receptors on immune cells to dampen anti-tumor immunity, further promoting cancer progression. The goal of this review is to summarize the predominant changes in sialylation occurring in pancreatic cancer, the biological functions of sialylated glycoproteins in cancer pathogenesis, and the emerging strategies for targeting sialoglycans and Siglec receptors in cancer therapeutics.

Aberrant Sialylation in Cancer: Therapeutic Opportunities

The surface of every eukaryotic cell is coated in a thick layer of glycans that acts as a key interface with the extracellular environment. Cancer cells have a different ‘glycan coat’ to healthy cells and aberrant glycosylation is a universal feature of cancer cells linked to all of the cancer hallmarks. This means glycans hold huge potential for the development of new diagnostic and therapeutic strategies. One key change in tumour glycosylation is increased sialylation, both on N-glycans and O-glycans, which leads to a dense forest of sialylated structures covering the cell surface. This hypersialylation has far-reaching consequences for cancer cells, and sialylated glycans are fundamental in tumour growth, metastasis, immune evasion and drug resistance. The development of strategies to inhibit aberrant sialylation in cancer represents an important opportunity to develop new therapeutics. Here, I summarise recent advances to target aberrant sialylation in cancer, including the development of sialyltransferase inhibitors and strategies to inhibit Siglecs and Selectins, and discuss opportunities for the future.

ST6Gal1: Oncogenic signaling pathways and targets

The Golgi-sialyltransferase ST6Gal1 (βgalactosidase α2,6 sialyltransferase 1), adds the negatively charged sugar, sialic acid, to the terminal galactose of N-glycosylated proteins. Upregulation of ST6Gal1 is observed in many malignancies, and a large body of research has determined that ST6Gal1-mediated α2,6 sialylation impacts cancer hallmarks. ST6Gal1 affects oncogenic behaviors including sustained proliferation, enhanced self-renewal, epithelial-to-mesenchymal transition, invasion, and chemoresistance. However, there are relatively few ST6GaL1 related signaling pathways that are well-established to mediate these biologies: greater delineation of specific targets and signaling mechanisms that are orchestrated by ST6Gal1 is needed. The aim of this review is to provide a summary of our current understanding of select oncogenic signaling pathways and targets affected by ST6Gal1.

Glycosylation in Renal Cell Carcinoma: Mechanisms and Clinical Implications

Renal cell carcinoma (RCC) is one of the most prevalent malignant tumors of the urinary system, accounting for around 2% of all cancer diagnoses and deaths worldwide. Clear cell RCC (ccRCC) is the most prevalent and aggressive histology with an unfavorable prognosis and inadequate treatment. Patients' progression-free survival is considerably improved by surgery; however, 30% of patients develop metastases following surgery. Identifying novel targets and molecular markers for RCC prognostic detection is crucial for more accurate clinical diagnosis and therapy. Glycosylation is a critical post-translational modification (PMT) for cancer cell growth, migration, and invasion, involving the transfer of glycosyl moieties to specific amino acid residues in proteins to form glycosidic bonds through the activity of glycosyltransferases. Most cancers, including RCC, undergo glycosylation changes such as branching, sialylation, and fucosylation. In this review, we discuss the latest findings on the significance of aberrant glycans in the initiation, development, and progression of RCC. The potential biomarkers of altered glycans for the diagnosis and their implications in RCC have been further highlighted.

Sialic acids on B cells are crucial for their survival and provide protection against apoptosis

Sialic acids (Sias) on the B cell membrane are involved in cell migration, in the control of the complement system and, as sialic acid-binding immunoglobulin-like lectin (Siglec) ligands, in the regulation of cellular signaling. We studied the role of sialoglycans on B cells in a mouse model with B cell-specific deletion of cytidine monophosphate sialic acid synthase (CMAS), the enzyme essential for the synthesis of sialoglycans. Surprisingly, these mice showed a severe B cell deficiency in secondary lymphoid organs. Additional depletion of the complement factor C3 rescued the phenotype only marginally, demonstrating a complement-independent mechanism. The B cell survival receptor BAFF receptor was not up-regulated, and levels of activated caspase 3 and processed caspase 8 were high in B cells of Cmas-deficient mice, indicating ongoing apoptosis. Overexpressed Bcl-2 could not rescue this phenotype, pointing to extrinsic apoptosis. These results show that sialoglycans on the B cell surface are crucial for B cell survival by counteracting several death-inducing pathways.

Bringing to Light the Risk of Colorectal Cancer in Inflammatory Bowel Disease: Mucosal Glycosylation as a Key Player

Colitis-associated cancer is a major complication of inflammatory bowel disease remaining an important clinical challenge in terms of diagnosis, screening, and prognosis. Inflammation is a driving factor both in inflammatory bowel disease and cancer, but the mechanism underlying the transition from colon inflammation to cancer remains to be defined. Dysregulation of mucosal glycosylation has been described as a key regulatory mechanism associated both with colon inflammation and colorectal cancer development. In this review, we discuss the major molecular mechanisms of colitis-associated cancer pathogenesis, highlighting the role of glycans expressed at gut epithelial cells, at lamina propria T cells, and in serum proteins in the regulation of intestinal inflammation and its progression to colon cancer, further discussing its potential clinical and therapeutic applications.

Glycosylation-Dependent Induction of Programmed Cell Death in Murine Adenocarcinoma Cells

Altered surface glycosylation is a major hallmark of tumor cells associated with aggressive phenotype and poor prognosis. By recognizing specific carbohydrate motifs, lectins can be applied to distinguish tumor from healthy cells based on the expression of glycosylation-dependent markers. Through their ability to bind to specific carbohydrates, lectins induce cell agglutination and cross-link surface glycoproteins, thereby mediating mitogenic and death-inducing effects in various cell types. The carbohydrate-selective cytotoxic effect of lectins also enables their possible application in therapies targeting cancer cells. To clarify the intracellular pathways mediating cell death induced by a group of plant and fungal lectins, we investigated mouse adenocarcinoma MC-38 cells harboring inactive genes involved in apoptosis, necroptosis and pyroptosis. Treatment of MC-38 cells with wheat germ agglutinin, Maackia amurensis lectin I, and Aleuria aurantia lectin induced multiple cell death pathways through reactions that relied on the autophagy machinery without depending on caspase activation. Furthermore, inhibition of de novo protein synthesis by cycloheximide strongly decreased the cytotoxic response, indicating that the lectins investigated induced cell death via effector molecules that are not expressed under normal circumstances and supporting the non-apoptotic nature of cell death. The broad cytotoxic response to lectins can be beneficial for the development of combination therapies targeting tumor cells. Given that tumors acquire resistance to various cytotoxic treatments because of mutations in cell death pathways, compounds inducing broad cytotoxic responses, such as lectins, represent potent sensitizers to promote tumor cell killing.

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.

Therapeutic approaches targeting CD95L/CD95 signaling in cancer and autoimmune diseases

Cell death plays a pivotal role in the maintenance of tissue homeostasis. Key players in the controlled induction of cell death are the Death Receptors (DR). CD95 is a prototypic DR activated by its cognate ligand CD95L triggering programmed cell death. As a consequence, alterations in the CD95/CD95L pathway have been involved in several disease conditions ranging from autoimmune diseases to inflammation and cancer. CD95L-induced cell death has multiple roles in the immune response since it constitutes one of the mechanisms by which cytotoxic lymphocytes kill their targets, but it is also involved in the process of turning off the immune response. Furthermore, beyond the canonical pro-death signals, CD95L, which can be membrane-bound or soluble, also induces non-apoptotic signaling that contributes to its tumor-promoting and pro-inflammatory roles. The intent of this review is to describe the role of CD95/CD95L in the pathophysiology of cancers, autoimmune diseases and chronic inflammation and to discuss recently patented and emerging therapeutic strategies that exploit/block the CD95/CD95L system in these diseases.

Sialyltransferase ST6GAL-1 mediates resistance to chemoradiation in rectal cancer

Locally advanced rectal cancer is typically treated with chemoradiotherapy followed by surgery. Most patients do not display a complete response to chemoradiotherapy, but resistance mechanisms are poorly understood. ST6GAL-1 is a sialyltransferase that adds the negatively charged sugar, sialic acid (Sia), to cell surface proteins in the Golgi, altering their function. We therefore hypothesized that ST6GAL-1 could mediate resistance to chemoradiation in rectal cancer by inhibiting apoptosis. Patient-derived xenograft and organoid models of rectal cancer and rectal cancer cell lines were assessed for ST6GAL-1 protein with and without chemoradiation treatment. ST6GAL-1 mRNA was assessed in untreated human rectal adenocarcinoma by PCR assays. Samples were further assessed by Western blotting, Caspase-Glo apoptosis assays, and colony formation assays. The presence of functional ST6GAL-1 was assessed via flow cytometry using the Sambucus nigra lectin, which specifically binds cell surface α2,6-linked Sia, and via lectin precipitation. In patient-derived xenograft models of rectal cancer, we found that ST6GAL-1 protein was increased after chemoradiation in a subset of samples. Rectal cancer cell lines demonstrated increased ST6GAL-1 protein and cell surface Sia after chemoradiation. ST6GAL-1 was also increased in rectal cancer organoids after treatment. ST6GAL-1 knockdown in rectal cancer cell lines resulted in increased apoptosis and decreased survival after treatment. We concluded that ST6GAL-1 promotes resistance to chemoradiotherapy by inhibiting apoptosis in rectal cancer cell lines. More research will be needed to further elucidate the importance and mechanism of ST6GAL-1-mediated resistance.

In Situ N-glycosylation Signatures of Epithelial Ovarian Cancer Tissue as Defined by MALDI Mass Spectrometry Imaging

The particularly high mortality of epithelial ovarian cancer (EOC) is in part linked to limited understanding of its molecular signatures. Although there are data available on in situ N-glycosylation in EOC tissue, previous studies focused primarily on neutral N-glycan species and, hence, still little is known regarding EOC tissue-specific sialylation. In this proof-of-concept study, we implemented MALDI mass spectrometry imaging (MALDI-MSI) in combination with sialic acid derivatization to simultaneously investigate neutral and sialylated N-glycans in formalin-fixed paraffin-embedded tissue microarray specimens of less common EOC histotypes and non-malignant borderline ovarian tumor (BOT). The applied protocol allowed detecting over 50 m/z species, many of which showed differential tissue distribution. Most importantly, it could be demonstrated that α2,6- and α2,3-sialylated N-glycans are enriched in tissue regions corresponding to tumor and adjacent tumor-stroma, respectively. Interestingly, analogous N-glycosylation patterns were observed in tissue cores of BOT, suggesting that regio-specific N-glycan distribution might occur already in non-malignant ovarian pathologies. All in all, our data provide proof that the combination of MALDI-MSI and sialic acid derivatization is suitable for delineating regio-specific N-glycan distribution in EOC and BOT tissues and might serve as a promising strategy for future glycosylation-based biomarker discovery studies.

ST3GAL2 knock-down decreases tumoral character of colorectal cancer cells in vitro and in vivo

Tumor cells have a modified glycosylation profile that promotes their evolution and/or their maintenance in the tumor. Sialylation is a type of glycosylation that is often altered in cancers. RNA-Seq database analysis revealed that the sialyltransferase gene ST3GAL2 is significantly overexpressed at all stages of colorectal cancer (CRC). ST3GAL2 sialylates both glycoproteins and glycolipids. The aim of this work was to investigate the involvement of ST3GAL2 in CRC. Using the HT29 tumor cell line derived from a stage II of CRC, we decreased the expression of ST3GAL2 by specific shRNA, and then characterized these cells by performing functional tests. We found that ST3GAL2 knock down (KD) significantly decreases tumor cell proliferation, cell migration and invasiveness properties in vitro. The cell cycle of these cells is affected with a change in cell cycle distribution and an increase of cell apoptosis. The effect of ST3GAL2 KD was then studied in vivo, following xenografts into nude mice, in which the tumor progression was significantly reduced. This work demonstrates that ST3GAL2 is a major player in the behavior of colorectal tumor cells, by modifying the sialylation state of glycoproteins and glycolipids which remain to be specifically identified.

The Distinct Roles of Sialyltransferases in Cancer Biology and Onco-Immunology

Aberrant glycosylation is a key feature of malignant transformation. Hypersialylation, the enhanced expression of sialic acid-terminated glycoconjugates on the cell surface, has been linked to immune evasion and metastatic spread, eventually by interaction with sialoglycan-binding lectins, including Siglecs and selectins. The biosynthesis of tumor-associated sialoglycans involves sialyltransferases, which are differentially expressed in cancer cells. In this review article, we provide an overview of the twenty human sialyltransferases and their roles in cancer biology and immunity. A better understanding of the individual contribution of select sialyltransferases to the tumor sialome may lead to more personalized strategies for the treatment of cancer.

Glycation Interferes with the Expression of Sialyltransferases in Meningiomas

Meningiomas are the most common non-malignant intracranial tumors and prefer, like most tumors, anaerobic glycolysis for energy production (Warburg effect). This anaerobic glycolysis leads to an increased synthesis of the metabolite methylglyoxal (MGO) or glyoxal (GO), which is known to react with amino groups of proteins. This reaction is called glycation, thereby building advanced glycation end products (AGEs). In this study, we investigated the influence of glycation on sialylation in two meningioma cell lines, representing the WHO grade I (BEN-MEN-1) and the WHO grade III (IOMM-Lee). In the benign meningioma cell line, glycation led to differences in expression of sialyltransferases (ST3GAL1/2/3/5/6, ST6GAL1/2, ST6GALNAC2/6, and ST8SIA1/2), which are known to play a role in tumor progression. We could show that glycation of BEN-MEN-1 cells led to decreased expression of ST3Gal5. This resulted in decreased synthesis of the ganglioside GM3, the product of ST3Gal5. In the malignant meningioma cell line, we observed changes in expression of sialyltransferases (ST3GAL1/2/3, ST6GALNAC5, and ST8SIA1) after glycation, which correlates with less aggressive behavior.

Synthesis and biological evaluation of selective phosphonate-bearing 1,2,3-triazole-linked sialyltransferase inhibitors

The critical role of sialyltransferase (ST) enzymes in tumour cell growth and metastasis, as well as links to multi-drug and radiation resistance, has seen STs emerge as a target for potential antimetastatic cancer treatments. One promising class of ST inhibitors that improve upon the pharmacokinetic issues of previous inhibitors is the 1,2,3-triazole-linked transition-state analogues. Herein, we present the design and synthesis of a new generation of 1,2,3-triazole-linked sialyltransferase inhibitors, along with their biological evaluation demonstrating increased potency for phosphonate bearing compounds. The six most promising inhibitors presented in this work exhibited a greater number of binding modes for hST6Gal I over hST3Gal I, with K _i ranging from 3-55 μM. This work highlights phosphonate bearing triazole-linked compounds as a promising class of synthetically accessible ST inhibitors that warrant further investigation.

Re-Expression of Poly/Oligo-Sialylated Adhesion Molecules on the Surface of Tumor Cells Disrupts Their Interaction with Immune-Effector Cells and Contributes to Pathophysiological Immune Escape

Glycans linked to surface proteins are the most complex biological macromolecules that play an active role in various cellular mechanisms. This diversity is the basis of cell-cell interaction and communication, cell growth, cell migration, as well as co-stimulatory or inhibitory signaling. Our review describes the importance of neuraminic acid and its derivatives as recognition elements, which are located at the outermost positions of carbohydrate chains linked to specific glycoproteins or glycolipids. Tumor cells, especially from solid tumors, mask themselves by re-expression of hypersialylated neural cell adhesion molecule (NCAM), neuropilin-2 (NRP-2), or synaptic cell adhesion molecule 1 (SynCAM 1) in order to protect themselves against the cytotoxic attack of the also highly sialylated immune effector cells. More particularly, we focus on α-2,8-linked polysialic acid chains, which characterize carrier glycoproteins such as NCAM, NRP-2, or SynCam-1. This characteristic property correlates with an aggressive clinical phenotype and endows them with multiple roles in biological processes that underlie all steps of cancer progression, including regulation of cell-cell and/or cell-extracellular matrix interactions, as well as increased proliferation, migration, reduced apoptosis rate of tumor cells, angiogenesis, and metastasis. Specifically, re-expression of poly/oligo-sialylated adhesion molecules on the surface of tumor cells disrupts their interaction with immune-effector cells and contributes to pathophysiological immune escape. Further, sialylated glycoproteins induce immunoregulatory cytokines and growth factors through interactions with sialic acid-binding immunoglobulin-like lectins. We describe the processes, which modulate the interaction between sialylated carrier glycoproteins and their ligands, and illustrate that sialic acids could be targets of novel therapeutic strategies for treatment of cancer and immune diseases.

Integrated Systems Analysis of the Murine and Human Pancreatic Cancer Glycomes Reveals a Tumor-Promoting Role for ST6GAL1

Pancreatic ductal adenocarcinoma (PDAC) is the third leading cause of cancer death in the United States. Glycans, such as carbohydrate antigen 19-9, are biomarkers of PDAC and are emerging as important modulators of cancer phenotypes. Herein, we used a systems-based approach integrating glycomic analysis of the well-established KC mouse, which models early events in transformation, and analysis of samples from human pancreatic cancer patients to identify glycans with potential roles in cancer formation. We observed both common and distinct patterns of glycosylation in pancreatic cancer across species. Common alterations included increased levels of α-2,3-sialic acid and α-2,6-sialic acid, bisecting GlcNAc and poly-N-acetyllactosamine. However, core fucose, which was increased in human PDAC, was not seen in the mouse, indicating that not all human glycomic changes are observed in the KC mouse model. In silico analysis of bulk and single-cell sequencing data identified ST6 beta-galactoside alpha-2,6-sialyltransferase 1, which underlies α-2,6-sialic acid, as overexpressed in human PDAC, concordant with histological data showing higher levels of this enzyme at the earliest stages. To test whether ST6 beta-galactoside alpha-2,6-sialyltransferase 1 promotes pancreatic cancer, we created a novel mouse in which a pancreas-specific genetic deletion of this enzyme overlays the KC mouse model. The analysis of our new model showed delayed cancer formation and a significant reduction in fibrosis. Our results highlight the importance of a strategic systems approach to identifying glycans whose functions can be modeled in mouse, a crucial step in the development of therapeutics targeting glycosylation in pancreatic cancer.

Sialyltransferase Inhibitors for the Treatment of Cancer Metastasis: Current Challenges and Future Perspectives

Potent, cell-permeable, and subtype-selective sialyltransferase inhibitors represent an attractive family of substances that can potentially be used for the clinical treatment of cancer metastasis. These substances operate by specifically inhibiting sialyltransferase-mediated hypersialylation of cell surface glycoproteins or glycolipids, which then blocks the sialic acid recognition pathway and leads to deterioration of cell motility and invasion. A vast amount of evidence for the in vitro and in vivo effects of sialyltransferase inhibition or knockdown on tumor progression and tumor cell metastasis or colonization has been accumulated over the past decades. In this regard, this review comprehensively discusses the results of studies that have led to the recent discovery and development of sialyltransferase inhibitors, their potential biomedical applications in the treatment of cancer metastasis, and their current limitations and future opportunities.

Sweet modification and regulation of death receptor signalling pathway

Death receptors, members of the tumour necrosis factor receptor (TNFR) superfamily, are characterized by the presence of a death domain in the cytosolic region. TNFR1, Fas and TNF-related apoptosis-inducing ligand receptors, which are prototypical death receptors, exert pleiotropic functions in cell death, inflammation and immune surveillance. Hence, they are involved in several human diseases. The activation of death receptors and downstream intracellular signalling is regulated by various posttranslational modifications, such as phosphorylation, ubiquitination and glycosylation. Glycosylation is one of the most abundant and versatile modifications to proteins and lipids, and it plays a critical role in the development and physiology of organisms, as well as the pathology of many human diseases. Glycans control a number of cellular events, such as receptor activation, signal transduction, endocytosis, cell recognition and cell adhesion. It has been demonstrated that oligo- and monosaccharides modify death receptors and intracellular signalling proteins and regulate their functions. Here, we review the current understanding of glycan modifications of death receptor signalling and their impact on signalling activity.