ST6Gal-I overexpression facilitates prostate cancer progression via the PI3K/Akt/GSK-3β/β-catenin signaling pathway

Sialylation Inhibition Can Partially Revert Acquired Resistance to Enzalutamide in Prostate Cancer Cells

Prostate cancer is a lethal solid malignancy and a leading cause of cancer-related deaths in males worldwide. Treatments, including radical prostatectomy, radiotherapy, and hormone therapy, are available and have improved patient survival; however, recurrence remains a huge clinical challenge. Enzalutamide is a second-generation androgen receptor antagonist that is used to treat castrate-resistant prostate cancer. Among patients who initially respond to enzalutamide, virtually all acquire secondary resistance, and an improved understanding of the mechanisms involved is urgently needed. Aberrant glycosylation, and, in particular, alterations to sialylated glycans, have been reported as mediators of therapy resistance in cancer, but a link between tumour-associated glycans and resistance to therapy in prostate cancer has not yet been investigated. Here, using cell line models, we show that prostate cancer cells with acquired resistance to enzalutamide therapy have an upregulation of the sialyltransferase ST6 beta-galactoside alpha-2,6-sialyltransferase 1 (ST6GAL1) and increased levels of α2,6-sialylated N-glycans. Furthermore, using the sialyltransferase inhibitor P-SiaFNEtoc, we discover that acquired resistance to enzalutamide can be partially reversed by combining enzalutamide therapy with sialic acid blockade. Our findings identify a potential role for ST6GAL1-mediated aberrant sialylation in acquired resistance to enzalutamide therapy for prostate cancer and suggest that sialic acid blockade in combination with enzalutamide may represent a novel therapeutic approach in patients with advanced disease. Our study also highlights the potential to bridge the fields of cancer biology and glycobiology to develop novel combination therapies for prostate cancer.

Sialic acid blockade inhibits the metastatic spread of prostate cancer to bone

BACKGROUND

Bone metastasis is a common consequence of advanced prostate cancer. Bisphosphonates can be used to manage symptoms, but there are currently no curative treatments available. Altered tumour cell glycosylation is a hallmark of cancer and is an important driver of a malignant phenotype. In prostate cancer, the sialyltransferase ST6GAL1 is upregulated, and studies show ST6GAL1-mediated aberrant sialylation of N-glycans promotes prostate tumour growth and disease progression.

METHODS

Here, we monitor ST6GAL1 in tumour and serum samples from men with aggressive prostate cancer and using in vitro and in vivo models we investigate the role of ST6GAL1 in prostate cancer bone metastasis.

FINDINGS

ST6GAL1 is upregulated in patients with prostate cancer with tumours that have spread to the bone and can promote prostate cancer bone metastasis in vivo. The mechanisms involved are multi-faceted and involve modification of the pre-metastatic niche towards bone resorption to promote the vicious cycle, promoting the development of M2 like macrophages, and the regulation of immunosuppressive sialoglycans. Furthermore, using syngeneic mouse models, we show that inhibiting sialylation can block the spread of prostate tumours to bone.

INTERPRETATION

Our study identifies an important role for ST6GAL1 and α2-6 sialylated N-glycans in prostate cancer bone metastasis, provides proof-of-concept data to show that inhibiting sialylation can suppress the spread of prostate tumours to bone, and highlights sialic acid blockade as an exciting new strategy to develop new therapies for patients with advanced prostate cancer.

FUNDING

Prostate Cancer Research and the Mark Foundation For Cancer Research, the Medical Research Council and Prostate Cancer UK.

PW06 suppresses cancer cell metastasis in human pancreatic carcinoma MIA PaCa-2 cells via the inhibitions of p-Akt/mTOR/NF-κB and MMP2/MMP9 signaling pathways in vitro

PW06 [(E)-3-(9-ethyl-9H-carbazol-3-yl)-1-(2,5-dimethoxyphenyl) prop-2-en-1-one], a kind of the carbazole derivative containing chalcone moiety, induced cell apoptosis in human pancreatic carcinoma in vitro. There is no investigation to show that PW06 inhibits cancer cell metastasis in human pancreatic carcinoma in vitro. Herein, PW06 (0.1-0.8 μM) significantly exists in the antimetastatic activities of human pancreatic carcinoma MIA PaCa-2 cells in vitro. Wound healing assay shows PW06 at 0.2 μM suppressed cell mobility by 7.45 and 16.55% at 6 and 24 hours of treatments. PW06 at 0.1 and 0.2 μM reduced cell mobility by 14.72 and 21.8% for 48 hours of treatment. Transwell chamber assay indicated PW06 (0.1-0.2 μM) suppressed the cell migration (decreased 26.67-35.42%) and invasion (decreased 48.51-68.66%). Atomic force microscopy assay shows PW06 (0.2 μM) significantly changed the shape of cell morphology. The gelatin zymography assay indicates PW06 decreased MMP2's and MMP9's activities at 48 hours of treatment. Western blotting assay further confirms PW06 reduced levels of MMP2 and MMP9 and increased protein expressions of EGFR, SOS1, and Ras. PW06 also increased the p-JNK, p-ERK, and p-p38. PW06 increased the expression of PI3K, PTEN, Akt, GSK3α/β, and E-cadherin. Nevertheless, results also show PW06 decreased p-Akt, mTOR, NF-κB, p-GSK3β, β-catenin, Snail, N-cadherin, and vimentin in MIA PaCa-2 cells. The confocal laser microscopy examination shows PW06 increased E-cadherin but decreased vimentin in MIA PaCa-2 cells. Together, our findings strongly suggest that PW06 inhibited the p-Akt/mTOR/NF-κB/MMPs pathways, increased E-cadherin, and decreased N-cadherin/vimentin, suppressing the migration and invasion in MIA PaCa-2 cells in vitro.

Hippo cell signaling and HS-proteoglycans regulate tissue form and function, age-dependent maturation, extracellular matrix remodeling, and repair

This review examined how Hippo cell signaling and heparan sulfate (HS)-proteoglycans (HSPGs) regulate tissue form and function. Despite being a nonweight-bearing tissue, the brain is regulated by Hippo mechanoresponsive cell signaling pathways during embryonic development. HS-proteoglycans interact with growth factors, morphogens, and extracellular matrix components to regulate development and pathology. Pikachurin and Eyes shut (Eys) interact with dystroglycan to stabilize the photoreceptor axoneme primary cilium and ribbon synapse facilitating phototransduction and neurotransduction with bipolar retinal neuronal networks in ocular vision, the primary human sense. Another HSPG, Neurexin interacts with structural and adaptor proteins to stabilize synapses and ensure specificity of neural interactions, and aids in synaptic potentiation and plasticity in neurotransduction. HSPGs also stabilize the blood-brain barrier and motor neuron basal structures in the neuromuscular junction. Agrin and perlecan localize acetylcholinesterase and its receptors in the neuromuscular junction essential for neuromuscular control. The primary cilium is a mechanosensory hub on neurons, utilized by YES associated protein (YAP)-transcriptional coactivator with PDZ-binding motif (TAZ) Hippo, Hh, Wnt, transforming growth factor (TGF)-β/bone matrix protein (BMP) receptor tyrosine kinase cell signaling. Members of the glypican HSPG proteoglycan family interact with Smoothened and Patched G-protein coupled receptors on the cilium to regulate Hh and Wnt signaling during neuronal development. Control of glycosyl sulfotransferases and endogenous protease expression by Hippo TAZ YAP represents a mechanism whereby the fine structure of HS-proteoglycans can be potentially modulated spatiotemporally to regulate tissue morphogenesis in a similar manner to how Hippo signaling controls sialyltransferase expression and mediation of cell-cell recognition, dysfunctional sialic acid expression is a feature of many tumors.

High-throughput analysis of glycan sorting into extracellular vesicles

Extracellular vesicles (EVs) are cell-released vesicles that mediate intercellular communication by transferring bioactive cargo. Protein and RNA sorting into EVs has been extensively assessed, while selective enrichment of glycans in EVs remains less explored. In this study, a mass spectrometry-based approach, glycan node analysis (GNA), was applied to broadly assess the sorting of glycan features into EVs. Two metastatic variants (lung and bone) generated in mouse modes from the MDA-MB-231 human breast cancer cell line were assessed, as these EVs are known to contain distinct organotropic biomolecules. EVs were isolated from conditioned cell culture medium by tangential flow filtration and authenticated by standard techniques. GNA analysis revealed selective enrichment of several glycan features in EVs compared to the originating cells, particularly those associated with binding to the extracellular matrix, which was also observed in EVs from the parental MDA-MB-231 cell line (human pleural metastases). The bone-tropic variant displayed enrichment of distinct EV glycan features compared to the lung-tropic one. Additionally, the metastatic variants generated in mouse models displayed reduced EV glycan sorting compared to the parental metastatic cell line. This study represents the first comprehensive assessment of differences in glycan features between EVs and originating cells and provides evidence that the diversity of EV glycan sorting is reduced upon generation of variant cell lines in mouse models. Future research is likely to uncover novel mechanisms of EV glycan sorting, shed light on glycan features for EV authentication or biomarker purposes, and assess functional roles of the EV glycocode in (patho)physiology.

Targeting aberrant sialylation and fucosylation in prostate cancer cells using potent metabolic inhibitors

Aberrant glycosylation is a hallmark of cancer and is not just a consequence, but also a driver of a malignant phenotype. In prostate cancer, changes in fucosylated and sialylated glycans are common and this has important implications for tumor progression, metastasis, and immune evasion. Glycans hold huge translational potential and new therapies targeting tumor-associated glycans are currently being tested in clinical trials for several tumor types. Inhibitors targeting fucosylation and sialylation have been developed and show promise for cancer treatment, but translational development is hampered by safety issues related to systemic adverse effects. Recently, potent metabolic inhibitors of sialylation and fucosylation were designed that reach higher effective concentrations within the cell, thereby rendering them useful tools to study sialylation and fucosylation as potential candidates for therapeutic testing. Here, we investigated the effects of global metabolic inhibitors of fucosylation and sialylation in the context of prostate cancer progression. We find that these inhibitors effectively shut down the synthesis of sialylated and fucosylated glycans to remodel the prostate cancer glycome with only minor apparent side effects on other glycan types. Our results demonstrate that treatment with inhibitors targeting fucosylation or sialylation decreases prostate cancer cell growth and downregulates the expression of genes and proteins important in the trajectory of disease progression. We anticipate our findings will lead to the broader use of metabolic inhibitors to explore the role of fucosylated and sialylated glycans in prostate tumor pathology and may pave the way for the development of new therapies for prostate cancer.

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.

Cell Membrane Sialome: Sialic Acids as Therapeutic Targets and Regulators of Drug Resistance in Human Cancer Management

A cellular sialome is a physiologically active and dynamically changing component of the cell membrane. Sialylation plays a crucial role in tumor progression, and alterations in cellular sialylation patterns have been described as modulators of chemotherapy effectiveness. However, the precise mechanisms through which altered sialylation contributes to drug resistance in cancer are not yet fully understood. This review focuses on the intricate interplay between sialylation and cancer treatment. It presents the role of sialic acids in modulating cell-cell interactions, the extracellular matrix (ECM), and the immunosuppressive processes within the context of cancer. The issue of drug resistance is also discussed, and the mechanisms that involve transporters, the tumor microenvironment, and metabolism are analyzed. The review explores drugs and therapeutic approaches that may induce modifications in sialylation processes with a primary focus on their impact on sialyltransferases or sialidases. Despite advancements in cellular glycobiology and glycoengineering, an interdisciplinary effort is required to decipher and comprehend the biological characteristics and consequences of altered sialylation. Additionally, understanding the modulatory role of sialoglycans in drug sensitivity is crucial to applying this knowledge in clinical practice for the benefit of cancer patients.

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.

ST6GAL1-mediated aberrant sialylation promotes prostate cancer progression

Aberrant glycosylation is a universal feature of cancer cells, and cancer-associated glycans have been detected in virtually every cancer type. A common change in tumour cell glycosylation is an increase in α2,6 sialylation of N-glycans, a modification driven by the sialyltransferase ST6GAL1. ST6GAL1 is overexpressed in numerous cancer types, and sialylated glycans are fundamental for tumour growth, metastasis, immune evasion, and drug resistance, but the role of ST6GAL1 in prostate cancer is poorly understood. Here, we analyse matched cancer and normal tissue samples from 200 patients and verify that ST6GAL1 is upregulated in prostate cancer tissue. Using MALDI imaging mass spectrometry (MALDI-IMS), we identify larger branched α2,6 sialylated N-glycans that show specificity to prostate tumour tissue. We also monitored ST6GAL1 in plasma samples from >400 patients and reveal ST6GAL1 levels are significantly increased in the blood of men with prostate cancer. Using both in vitro and in vivo studies, we demonstrate that ST6GAL1 promotes prostate tumour growth and invasion. Our findings show ST6GAL1 introduces α2,6 sialylated N-glycans on prostate cancer cells and raise the possibility that prostate cancer cells can secrete active ST6GAL1 enzyme capable of remodelling glycans on the surface of other cells. Furthermore, we find α2,6 sialylated N-glycans expressed by prostate cancer cells can be targeted using the sialyltransferase inhibitor P-3FAX -Neu5Ac. Our study identifies an important role for ST6GAL1 and α2,6 sialylated N-glycans in prostate cancer progression and highlights the opportunity to inhibit abnormal sialylation for the development of new prostate cancer therapeutics. © 2023 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

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.

Computational studies on glycosaminoglycan recognition of sialyl transferases

Despite decades of research, glycosaminoglycans (GAGs) have not been known to interact with sialyl transferases (STs). Using our in-house combinatorial virtual library screening (CVLS) technology, we studied seven human isoforms, including ST6GAL1, ST6GAL2, ST3GAL1, ST3GAL3, ST3GAL4, ST3GAL5, and ST3GAL6, and predicted that GAGs, especially heparan sulfate (HS), are likely to differentially bind to STs. Exhaustive CVLS and molecular dynamics studies suggested that the common hexasaccharide sequence of HS preferentially recognized ST6GAL1 in a site overlapping the binding site of the donor substrate CMP-Sia. Interestingly, CVLS did not ascribe any special role for the rare 3-O-sulfate modification of HS in ST6GAL1 recognition. The computational predictions were tested using spectrofluorimetric studies, which confirmed preferential recognition of HS over other GAGs. A classic chain length-dependent binding of GAGs to ST6GAL1 was observed with polymeric HS displaying a tight affinity of ~65 nM. Biophysical studies also confirmed a direct competition between CMP-Sia and an HS oligosaccharide and CS polysaccharide for binding to ST6GAL1. Overall, our novel observation that GAGs bind to ST6GAL1 with high affinity and compete with the donor substrate is likely to be important because modulation of sialylation of glycan substrates on cells has considerable physiological/pathological consequences. Our work also brings forth the possibility of developing GAG-based chemical probes of ST6GAL1.

A signature based on glycosyltransferase genes provides a promising tool for the prediction of prognosis and immunotherapy responsiveness in ovarian cancer

BACKGROUND

Ovarian cancer (OC) is the most fatal gynaecological malignancy and has a poor prognosis. Glycosylation, the biosynthetic process that depends on specific glycosyltransferases (GTs), has recently attracted increasing importance due to the vital role it plays in cancer. In this study, we aimed to determine whether OC patients could be stratified by glycosyltransferase gene profiles to better predict the prognosis and efficiency of immune checkpoint blockade therapies (ICBs).

METHODS

We retrieved transcriptome data across 420 OC and 88 normal tissue samples using The Cancer Genome Atlas (TCGA) and Genotype-Tissue Expression (GTEx) databases, respectively. An external validation dataset containing 185 OC samples was downloaded from the Gene Expression Omnibus (GEO) database. Knockdown and pathway prediction of B4GALT5 were conducted to investigate the function and mechanism of B4GALT5 in OC proliferation, migration and invasion.

RESULTS

A total of 50 differentially expressed GT genes were identified between OC and normal ovarian tissues. Two clusters were stratified by operating consensus clustering, but no significant prognostic value was observed. By applying the least absolute shrinkage and selection operator (LASSO) Cox regression method, a 6-gene signature was built that classified OC patients in the TCGA cohort into a low- or high-risk group. Patients with high scores had a worse prognosis than those with low scores. This risk signature was further validated in an external GEO dataset. Furthermore, the risk score was an independent risk predictor, and a nomogram was created to improve the accuracy of prognostic classification. Notably, the low-risk OC patients exhibited a higher degree of antitumor immune cell infiltration and a superior response to ICBs. B4GALT5, one of six hub genes, was identified as a regulator of proliferation, migration and invasion in OC.

CONCLUSION

Taken together, we established a reliable GT-gene-based signature to predict prognosis, immune status and identify OC patients who would benefit from ICBs. GT genes might be a promising biomarker for OC progression and a potential therapeutic target for OC.

Role of ST6GAL1 and ST6GAL2 in subversion of cellular signaling during enteroaggregative Escherichia coli infection of human intestinal epithelial cell lines

Emerging evidence have suggested that aberrant sialylation on cell-surface carbohydrate architecture may influence host-pathogen interactions. The α2,6-sialyltransferase (ST) enzymes were found to alter the glycosylation pattern of the pathogen-infected host cell-surface proteins, which could facilitate its invasion. In this study, we assessed the role of specific α2,6-ST enzymes in the regulation of enteroaggregative E. coli (EAEC)-induced cell signaling pathways in human intestinal epithelial cells. EAEC-induced expression of α2,6-ST family genes in HCT-15 and INT-407 cell lines was assessed at mRNA level by qRT-PCR. Specific esi-RNA was used to silence the target ST-gene in each of the EAEC-infected cell type. Subsequently, the role of these enzymes in regulation of EAEC-induced cell signaling pathways was unraveled by analyzing the expression of MAPkinases (ERK1/2, p38, JNK) and transcription factors (NFκB, cJun, cFos, STAT) at mRNA and protein levels by qRT-PCR and western immunoblotting, respectively, expression of selected sialoglycoproteins by western immunoblotting along with the secretory IL-8 response using sandwich ELISA. ST6GAL-1 and ST6GAL-2 were efficiently silenced in EAEC-infected HCT-15 and INT-407 cells, respectively. Significant reduction in EAEC-induced activation of MAPKs, transcription factors, sialoglycoproteins, and IL-8 secretion was noted in ST-silenced cells in comparison to the respective control cells. We propose that ST6GAL-1 and ST6GAL-2 are quintessential for EAEC-induced stimulation of MAPK-mediated pathways, resulting in activation of transcription factors, leading to an inflammatory response in the human intestinal epithelial cells. Our study may be helpful to design better therapeutic strategies to control EAEC- infection. KEY POINTS: • EAEC induces α2,6-sialyltransferase (ST) upregulation in intestinal epithelial cells • Target STs (ST6GAL-1 & ST6GAL-2) were efficiently silenced using specific esiRNAs • Expression of MAPKs, transcription factors & IL-8 was reduced in ST silenced cells.

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.

Serum α2,6-sialylated glycoform of serotransferrin as a glycobiomarker for diagnosis and prediction of clinical severity in cholangiocarcinoma

BACKGROUND

Glycoprotein sialylation changes are associated with severe development of various cancers. We previously discovered the sialylation of serotransferrin (TF) in cholangiocarcinoma (CCA) using glycoproteomics approach. However, a simple and reliable method for validating sialylation of a specific glycobiomarker is urgently needed.

METHODS

We identified the altered glycosylation in CCA tissues by glycoproteomics approach using mass spectrometry. An enzyme-linked lectin assay (ELLA) was developed for determining the serum levels of sialylated TF in CCA, hepatocellular carcinoma (HCC) and healthy controls in training and validation cohorts.

RESULTS

The nine highly sialylated glycoforms of TF were markedly abundant in CCA tumor tissues than in control. Serum SNA-TF and MAL1-TF were significantly higher in CCA patients. Under receiver operating characteristic curve, serum SNA-TF concentrations significantly differentiated CCA from healthy control. Higher SNA-TF were significantly correlated with severe tumor stages and lymph node metastasis. The combined SNA-TF, MAL1-TF, and CA19-9 as a novel glycobiomarkers panel demonstrated the highest specificity (96.2%) for distinguishing CCA from HCC patients. In CCA patients with low CA19-9 levels, SNA-TF in combination with CA19-9 achieved in 97% diagnostic accuracy.

CONCLUSIONS

Sialylated serotransferrin glycoforms could be used as a novel glycobiomarker for diagnosis and prediction of clinical severity in CCA patients.

Sialylated glycoproteins as biomarkers and drivers of progression in prostate cancer

Sialic acids have been implicated in cancer initiation, progression, and immune evasion in diverse human malignancies. Sialylation of terminal glycans on cell surface and secreted glycoproteins is a long-recognized feature of cancer cells. Recently, immune checkpoint inhibitor immunotherapy has tremendously improved the outcomes of patients with various cancers. However, available immunotherapy approaches have had limited efficacy in metastatic castration-resistant prostate cancer. Sialic acid modified glycoproteins in prostate cancers and their interaction with Siglec receptors on tumor infiltrating immune cells might underlie immunosuppressive signaling in prostate cancer. Here, we summarize the function of sialic acids and relevant glycosynthetic enzymes in cancer initiation and progression. We also discuss the possible uses of sialic acids as biomarkers in prostate cancer and the potential methods for targeting Siglec-sialic acid interactions for prostate cancer treatment.

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.

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.

Genome-Wide Association Analysis and Genomic Prediction of Thyroglobulin Plasma Levels

Thyroglobulin (Tg) is an iodoglycoprotein produced by thyroid follicular cells which acts as an essential substrate for thyroid hormone synthesis. To date, only one genome-wide association study (GWAS) of plasma Tg levels has been performed by our research group. Utilizing recent advancements in computation and modeling, we apply a Bayesian approach to the probabilistic inference of the genetic architecture of Tg. We fitted a Bayesian sparse linear mixed model (BSLMM) and a frequentist linear mixed model (LMM) of 7,289,083 variants in 1096 healthy European-ancestry participants of the Croatian Biobank. Meta-analysis with two independent cohorts (total n = 2109) identified 83 genome-wide significant single nucleotide polymorphisms (SNPs) within the ST6GAL1 gene (p<5×10-8). BSLMM revealed additional association signals on chromosomes 1, 8, 10, and 14. For ST6GAL1 and the newly uncovered genes, we provide physiological and pathophysiological explanations of how their expression could be associated with variations in plasma Tg levels. We found that the SNP-heritability of Tg is 17% and that 52% of this variation is due to a small number of 16 variants that have a major effect on Tg levels. Our results suggest that the genetic architecture of plasma Tg is not polygenic, but influenced by a few genes with major effects.

ERBB3 binding protein 1 promotes the progression of malignant melanoma through activation of the Wnt/ β-catenin signaling pathway

Background

Malignant melanoma (MM) is highly metastatic and has the highest mortality rate in patients with skin cancer. The ERBB3 binding protein 1 (Ebp1) has been linked to the onset and progression of a number of malignancies. However, the role of Ebp1 in MM has not yet been reported.

Methods

Multiple databases were analyzed for comparing the expression of Ebp1 in normal skin and MM. Ebp1 expression was knocked down in A375 and B16 cells, and the impact of Ebp1 on the cell growth was tested by CCK-8, plate clone colony, and cell cycle assays. Scratch, transwell, and in vivo caudal vein lung metastasis tests were also used to confirm the effects of Ebp1 on melanoma cells migration, invasion, and metastasis. Furthermore, the possible molecular mechanism of Ebp1 was predicted by set enrichment analysis and verified by western blotting.

Results

Ebp1 expression was substantially higher in MM than it was in normal skin, and Ebp1 was linked to the clinical stage and lymph node metastases of patients with MM. Knockdown of Ebp1 inhibited cell proliferation, migration, and invasion. In vivo experiments further verified that the knockdown of Ebp1 had an obvious inhibitory effect on lung metastasis in nude mice. Knockdown of Ebp1 reduced vimentin, N-cadherin, slug, and snail expression while increasing E-cadherin expression. Furthermore, knockdown of Ebp1 reduced the expression of β-catenin, as well as its downstream targets CyclinD1 and p-GSK3β; however, a Wnt/β-catenin agonist could reverse this effect.

Conclusion

Ebp1 may promote the proliferation and metastasis of melanoma cells through activation of the Wnt/β-catenin pathway.

Graphical Abstract

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.

Pectin Oligosaccharides Enhance α2,6-Sialylation Modification that Promotes Apoptosis of Bladder Cancer Cells by Targeting the Hedgehog Pathway

Although pectin oligosaccharide (POS) can inhibit the growth and proliferation of gastric, colon, prostate, breast, melanoma, and leukemia cells, its effect on bladder cancer remains unknown. Therefore, screening and identification of factors associated with the sensitivity of bladder cancer to drugs and elucidation of their molecular mechanisms will help provide a theoretical basis for establishing postoperative systemic chemotherapy for patients with bladder cancer. We showed that POS promoted the apoptosis of bladder cancer cells, and this finding was consistent with enhanced α2,6-sialylation post-modification. Moreover, POS activated the Hedgehog pathway, the inhibition of which regulated the tumorigenicity of bladder cancer cells in vivo. These findings were consistent with our results in vitro. We conclude that POS promotes the apoptosis of bladder cancer and offers new insights and evidence for the development of individualized treatment strategies. Schema of molecular events underlying POS-induced inhibition of bladder cancer cell proliferation.

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.

Knockdown of ST6Gal-I expression in human hepatocellular carcinoma cells inhibits their exosome-mediated proliferation- and migration-promoting effects

Abnormal sialylation is a distinctive feature of human hepatocellular carcinoma (HCC) and is closely related to its malignant properties. Exosomes have characteristic protein and lipid composition; however, the results concerning glycoprotein composition and glycosylation are scarce. In this study, liquid chromatography-tandem mass spectrometry (LC-MS/MS) identified multiple microvesicle-related sialylated proteins including CD63, a classic marker of exosomes. The silencing of α2,6-sialyltransferase I (ST6Gal-I) significantly reduced the levels of α2,6-sialylated glycoconjugates on CD63 and the surface of HCC-derived exosomes (HCC-exo). And surface glycoconjugates play important roles in exosomes biogenesis and in their interaction with other cells. Compared to exosomes derived from naive HCC cells, α2,6-sialylation degradation abolished both the proliferation-promoting and migration-promoting effects of HCC-exo. Further analysis revealed that the Akt/GSK-3β or JNK1/2 signaling mediates HCC-exo-mediated proliferation in HCC cells, while ST6Gal-I silencing deactivated this pathway. These findings suggest that a loss of α2,6-sialylation decreases HCC progression through the loss of cancer cell-derived exosomes; furthermore, it opens novel perspectives to further explore the functional role of glycans in the biology of exosomes.

CASC11 promotes aggressiveness of prostate cancer cells through miR-145/IGF1R axis

BACKGROUND

Prostate cancer (PCa) is the most common malignancy diagnosed among men after lung cancer in developed countries. Investigation of the underlying molecular mechanisms of PCa is urgently needed in order to develop better therapeutic strategies and to reveal more effective therapeutic targets. In this study, we aimed at exploring the potential functions of CASC11 in association with miR-145 and IGF1R during the malignant progression of PCa cells.

METHODS

We initially investigated the oncogenic potential of noncoding members of CASC gene family and analyzed the effects of CASC11 overexpression on proliferation, migration, and colony formation ability of DU145, LNCaP, and PC3 PCa cells. We, then, exprlored the association of CASC11, miR-145, and IGF1R expression and their impacts on PI3K/AKT/mTOR signaling pathway in in vitro models.

RESULTS

In silico analysis revealed that of the CASC family only CASC11 showed consistent results considering its differential expression as well as its association with the overall survival of patients. We demonstrated that ectopic overexpression of CASC11 significantly increased the proliferation, colony formation, and migration capacity in all three cell lines. CASC11 overexpression caused suppression of miR-145 and overexpression of IGF1R, leading to activation of PI3K/AKT/mTOR signaling pathway.

CONCLUSION

In summary, we found that CASC11 is upregulated in PCa cells and clinical tumor samples in comparison to corresponding controls and revealed that ectopic CASC11 overexpression promotes cellular phenotypes associated with PCa progression through CASC11/miR-145/IGF1R axis.

ST6GAL1 and α2-6 Sialylation Regulates IL-6 Expression and Secretion in Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is a systemic disease strongly associated with cigarette smoking, airway inflammation, and acute disease exacerbations. Changes in terminal sialylation and fucosylation of asparagine (N)-linked glycans have been documented in COPD, but the role that glycosyltransferases may play in the regulation of N-linked glycans in COPD has not been fully elucidated. Recent studies suggest that modulation of ST6GAL1 (ST6 beta-galactoside alpha-2,6-sialyltransferase-1), which catalyzes terminal α2-6 sialylation of cellular proteins, may regulate inflammation and contribute to COPD phenotype(s). Interestingly, it has been previously demonstrated that ST6GAL1, a Golgi resident protein, can be proteolytically processed by BACE1 (beta-site amyloid precursor protein cleaving enzyme-1) to a circulating form that retains activity. In this study, we showed that loss of ST6GAL1 expression increased interleukin (IL)-6 expression and secretion in human bronchial epithelial cells (HBECs). Furthermore, exposure to cigarette smoke medium/extract (CSE) or BACE1 inhibition resulted in decreased ST6GAL1 secretion, reduced α2-6 sialylation, and increased IL-6 production in HBECs. Analysis of plasma ST6GAL1 levels in a small COPD patient cohort demonstrated an inverse association with prospective acute exacerbations of COPD (AECOPD), while IL-6 was positively associated. Altogether, these results suggest that reduced ST6GAL1 and α2-6 sialylation augments IL-6 expression/secretion in HBECs and is associated with poor clinical outcomes in COPD.

Caveolin-1 facilitates cell migration by upregulating nuclear receptor 4A2/retinoid X receptor α-mediated β-galactoside α2,6-sialyltransferase I expression in human hepatocarcinoma cells

It has been reported that caveolin-1 (Cav-1) acts as a tumor promoter in hepatocellular carcinoma (HCC). Our previous studies showed that Cav-1 promoted mouse hepatocarcinoma cell adhesion to fibronectin by upregulating β-galactoside α2,6-sialyltransferase I (ST6Gal-I) expression. However, the detailed mechanism by which Cav-1 regulates ST6Gal-I is not fully understood. In this study, we found that the expression levels of Cav-1 and ST6Gal-I were increased in HCC tissues and correlated with poor prognosis. Cav-1 upregulated ST6Gal-I expression to promote the migration and invasion of HCC cells by inducing epithelial-to-mesenchymal transition. Importantly, the binding of the transcription factor nuclear receptor 4A2/retinoid X receptor alpha (NR4A2/RXRα) to the -550/-200 region of the ST6GAL1 promoter was critical for Cav-1-induced ST6GAL1 gene expression. Furthermore, Cav-1 expression activated the phosphatidylinositol 3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/AKT/mTOR) signaling pathway, followed by upregulation of NR4A2 expression and phosphorylation of RXRα, which facilitated the complex of NR4A2 and phosphorylated RXRα forming and binding to the ST6GAL1 promoter region to induce its transcription. Finally, in the diethylnitrosamine (DEN)-induced HCC murine model, the expression levels of NR4A2, p-RXRα, ST6Gal-I, and α2,6-linked sialic acid decreased in parallel in Cav-1^-/- mice compared with Cav-1^+/+ mice, which was consistent with the above in vitro results. These findings provide insight into the mechanism of ST6GAL1 gene transcription mediated by Cav-1, which may lead to the development of novel therapeutic strategies targeting metastasis in HCC.

Alginate derived functional oligosaccharides: Recent developments, barriers, and future outlooks

Alginate is a biopolymer used extensively in the food, pharmaceutical, and chemical industries. Alginate oligosaccharides (AOS) derived from alginate exhibit superior biological activities and therapeutic potential. Alginate lyases with characteristic substrate specificity can facilitate the production of a broad array of AOS with precise structure and functionality. By adopting innovative analytical tools in conjunction with focused clinical studies, the structure-bioactivity relationship of a number of AOS has been brought to light. This review covers fundamental aspects and recent developments in AOS research. Enzymatic and microbial processes involved in AOS production from brown algae and sequential steps involved in AOS structure elucidation are outlined. Biological mechanisms underlying the health benefits of AOS and their potential industrial and therapeutic applications are elaborated. Withal, various challenges in AOS research are traced out, and future directions, specifically on recombinant systems for AOS preparation, are delineated to further widen the horizon of these exceptional oligosaccharides.

Aberrant Sialylation in Cancer: Biomarker and Potential Target for Therapeutic Intervention?

Simple Summary

Sialylation is a post-translational modification that consists in the addition of sialic acid to growing glycan chains on glycoproteins and glycolipids. Aberrant sialylation is an established hallmark of several types of cancer, including breast, ovarian, pancreatic, prostate, colorectal and lung cancers, melanoma and hepatocellular carcinoma. Hypersialylation can be the effect of increased activity of sialyltransferases and results in an excess of negatively charged sialic acid on the surface of cancer cells. Sialic acid accumulation contributes to tumor progression by several paths, including stimulation of tumor invasion and migration, and enhancing immune evasion and tumor cell survival. In this review we explore the mechanisms by which sialyltransferases promote cancer progression. In addition, we provide insights into the possible use of sialyltransferases as biomarkers for cancer and summarize findings on the development of sialyltransferase inhibitors as potential anti-cancer treatments.

Abstract

Sialylation is an integral part of cellular function, governing many biological processes including cellular recognition, adhesion, molecular trafficking, signal transduction and endocytosis. Sialylation is controlled by the levels and the activities of sialyltransferases on glycoproteins and lipids. Altered gene expression of these enzymes in cancer yields to cancer-specific alterations of glycoprotein sialylation. Mounting evidence indicate that hypersialylation is closely associated with cancer progression and metastatic spread, and can be of prognostic significance in human cancer. Aberrant sialylation is not only a result of cancer, but also a driver of malignant phenotype, directly impacting key processes such as tumor cell dissociation and invasion, cell-cell and cell-matrix interactions, angiogenesis, resistance to apoptosis, and evasion of immune destruction. In this review we provide insights on the impact of sialylation in tumor progression, and outline the possible application of sialyltransferases as cancer biomarkers. We also summarize the most promising findings on the development of sialyltransferase inhibitors as potential anti-cancer treatments.

Association of ST6GAL1 and CYP19A1 polymorphisms in the 3'-UTR with astrocytoma risk and prognosis in a Chinese Han population

Background

Astrocytoma is a common type of central nervous system tumor. In this study, we investigated the correlation between ST6GAL1 and CYP19A1 polymorphisms and the risk and prognosis of astrocytoma.

Methods

A total of 365 astrocytoma patients and 379 healthy controls were genotyped using the Agena MassARRAY system. The correlation between ST6GAL1 and CYP19A1 variants and astrocytoma risk was calculated using logistic regression. The survival rate of patients with astrocytoma was analyzed to evaluate prognosis.

Results

We found that the ST6GAL1-rs2239611 significantly decreased the risk of astrocytoma in the codominant model (p = 0.044) and dominant model (p = 0.049). In stratified analyses, CYP19A1-rs2255192 might be associated with a higher risk of astrocytoma among the low-grade subgroup under recessive (p = 0.034) and additive (p = 0.030) models. However, CYP19A1-rs4646 had a risk-decreasing effect on the high-grade subgroup in the codominant model (p = 0.044). The results of Cox regression analysis showed that the CYP19A1-rs2239611 and -rs1042757 polymorphisms were significantly correlated with the prognosis of astrocytoma.

Conclusion

Our results suggest that ST6GAL1 and CYP19A1 genes may be a potential biomarker of genetic susceptibility and prognosis to astrocytoma in the Chinese Han population.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08110-1.

Post-Translational Modifications That Drive Prostate Cancer Progression

While a protein primary structure is determined by genetic code, its specific functional form is mostly achieved in a dynamic interplay that includes actions of many enzymes involved in post-translational modifications. This versatile repertoire is widely used by cells to direct their response to external stimuli, regulate transcription and protein localization and to keep proteostasis. Herein, post-translational modifications with evident potency to drive prostate cancer are explored. A comprehensive list of proteome-wide and single protein post-translational modifications and their involvement in phenotypic outcomes is presented. Specifically, the data on phosphorylation, glycosylation, ubiquitination, SUMOylation, acetylation, and lipidation in prostate cancer and the enzymes involved are collected. This type of knowledge is especially valuable in cases when cancer cells do not differ in the expression or mutational status of a protein, but its differential activity is regulated on the level of post-translational modifications. Since their driving roles in prostate cancer, post-translational modifications are widely studied in attempts to advance prostate cancer treatment. Current strategies that exploit the potential of post-translational modifications in prostate cancer therapy are presented.

Regulation of ST6GAL1 sialyltransferase expression in cancer cells

The ST6GAL1 sialyltransferase, which adds α2-6 linked sialic acids to N-glycosylated proteins, is overexpressed in a wide range of human malignancies. Recent studies have established the importance of ST6GAL1 in promoting tumor cell behaviors such as invasion, resistance to cell stress and chemoresistance. Furthermore, ST6GAL1 activity has been implicated in imparting cancer stem cell characteristics. However, despite the burgeoning interest in the role of ST6GAL1 in the phenotypic features of tumor cells, insufficient attention has been paid to the molecular mechanisms responsible for ST6GAL1 upregulation during neoplastic transformation. Evidence suggests that these mechanisms are multifactorial, encompassing genetic, epigenetic, transcriptional and posttranslational regulation. The purpose of this review is to summarize current knowledge regarding the molecular events that drive enriched ST6GAL1 expression in cancer cells.

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

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

Human La Protein: An RNA-Binding Protein Involved in Ovarian Cancer Development and Multidrug Resistance

Multidrug resistance is the main cause of chemotherapy failure and death in patients with advanced ovarian cancer. Drug resistance is a problem that must be solved to improve the survival rate of patients with advanced ovarian cancer. The RNA-binding protein La and the La-related protein family are highly expressed in various malignant tumors, including ovarian cancer. This article reviews the mechanisms of La protein in tumorigenesis, development, and drug resistance. High La protein expression in tumor cells promotes tumor proliferation, invasion, and migration; disrupts cell cycle; and inhibits tumor cell apoptosis caused by chemotherapeutic drugs through various pathways, resulting in chemotherapy resistance in ovarian cancer. Further study of the role of La protein in ovarian cancer multidrug resistance may be conducive to the development of human La protein-specific inhibitors that suppress ovarian cancer drug resistance.

Characterization of Signaling Pathways Associated with Pancreatic β-cell Adaptive Flexibility in Compensation of Obesity-linked Diabetes in db/db Mice

The onset of obesity-linked type 2 diabetes (T2D) is marked by an eventual failure in pancreatic β-cell function and mass that is no longer able to compensate for the inherent insulin resistance and increased metabolic load intrinsic to obesity. However, in a commonly used model of T2D, the db/db mouse, β-cells have an inbuilt adaptive flexibility enabling them to effectively adjust insulin production rates relative to the metabolic demand. Pancreatic β-cells from these animals have markedly reduced intracellular insulin stores, yet high rates of (pro)insulin secretion, together with a substantial increase in proinsulin biosynthesis highlighted by expanded rough endoplasmic reticulum and Golgi apparatus. However, when the metabolic overload and/or hyperglycemia is normalized, β-cells from db/db mice quickly restore their insulin stores and normalize secretory function. This demonstrates the β-cell's adaptive flexibility and indicates that therapeutic approaches applied to encourage β-cell rest are capable of restoring endogenous β-cell function. However, mechanisms that regulate β-cell adaptive flexibility are essentially unknown. To gain deeper mechanistic insight into the molecular events underlying β-cell adaptive flexibility in db/db β-cells, we conducted a combined proteomic and post-translational modification specific proteomic (PTMomics) approach on islets from db/db mice and wild-type controls (WT) with or without prior exposure to normal glucose levels. We identified differential modifications of proteins involved in redox homeostasis, protein refolding, K48-linked deubiquitination, mRNA/protein export, focal adhesion, ERK1/2 signaling, and renin-angiotensin-aldosterone signaling, as well as sialyltransferase activity, associated with β-cell adaptive flexibility. These proteins are all related to proinsulin biosynthesis and processing, maturation of insulin secretory granules, and vesicular trafficking-core pathways involved in the adaptation of insulin production to meet metabolic demand. Collectively, this study outlines a novel and comprehensive global PTMome signaling map that highlights important molecular mechanisms related to the adaptive flexibility of β-cell function, providing improved insight into disease pathogenesis of T2D.

Role of PI3K/AKT pathway in cancer: the framework of malignant behavior

Given that the PI3K/AKT pathway has manifested its compelling influence on multiple cellular process, we further review the roles of hyperactivation of PI3K/AKT pathway in various human cancers. We state the abnormalities of PI3K/AKT pathway in different cancers, which are closely related with tumorigenesis, proliferation, growth, apoptosis, invasion, metastasis, epithelial-mesenchymal transition, stem-like phenotype, immune microenvironment and drug resistance of cancer cells. In addition, we investigated the current clinical trials of inhibitors against PI3K/AKT pathway in cancers and found that the clinical efficacy of these inhibitors as monotherapy has so far been limited despite of the promising preclinical activity, which means combinations of targeted therapy may achieve better efficacies in cancers. In short, we hope to feature PI3K/AKT pathway in cancers to the clinic and bring the new promising to patients for targeted therapies.

Impact of sialyltransferase ST6GAL1 overexpression on different colon cancer cell types

Cancer-associated glycan structures can be both tumor markers and engines of disease progression. The structure Siaα2,6Galβ1,4GlcNAc (Sia6LacNAc), synthesized by sialyltransferase ST6GAL1, is a cancer-associated glycan. Although ST6GAL1/Sia6LacNAc are often overexpressed in colorectal cancer (CRC), their biological and clinical significance remains unclear. To get insights into the clinical relevance of ST6GAL1 expression in CRC, we interrogated The Cancer Genome Atlas with mRNA expression data of hundreds of clinically characterized CRC and normal samples. We found an association of low ST6GAL1 expression with microsatellite instability (MSI), BRAF mutations and mucinous phenotype but not with stage, response to therapy and survival. To investigate the impact of ST6GAL1 expression in experimental systems, we analyzed the transcriptome and the phenotype of the CRC cell lines SW948 and SW48 after retroviral transduction with ST6GAL1 cDNA. The two cell lines display the two main pathways of CRC transformation: chromosomal instability and MSI, respectively. Constitutive ST6GAL1 expression induced much deeper transcriptomic changes in SW948 than in SW48 and affected different genes in the two cell lines. ST6GAL1 expression affected differentially the tyrosine phosphorylation induced by hepatocyte growth factor, the ability to grow in soft agar, to heal a scratch wound and to invade Matrigel in the two cell lines. These results indicate that the altered expression of a cancer-associated glycosyltransferase impacts the gene expression profile, as well as the phenotype, although in a cancer subtype-specific manner.

SERPINH1 regulates EMT and gastric cancer metastasis via the Wnt/β-catenin signaling pathway

In this study, we investigated the role of SERPINH1 in gastric cancer (GC) progression. GC patient tissues show significantly higher SERPINH1 mRNA and protein levels than normal gastric mucosal tissues. GC patients with high SERPINH1 expression are associated with lymph node metastasis and poor prognosis. SERPINH1 mRNA levels negatively correlate with E-cadherin mRNA levels and positively correlate with levels of N-cadherin, MMP2, and MMP9 mRNA levels. This suggests SERPINH1 regulates epithelial to mesenchymal transition (EMT). SERPINH1 expression was significantly higher in the HGC-27, AGS, MGC-803, and SGC-7901 GC cell lines than in the GES-1 normal gastric mucosal cell line. In SERPINH1-silenced SGC-7901 cells, survival, colony formation, migration and invasion were all reduced, whereas they were all enhanced in SERPINH1-overexpressing MGC-803 cells. Levels of WNT/β-catenin signaling pathway proteins, including β-catenin, Wnt2, GSK-3β, p-GSK-3β, NF-κB P65, Snail1, Slug and TWIST, were all reduced in SERPINH1-silenced SGC-7901 cells, and increased in the SERPINH1-overexpressing MGC-803 cells. Inhibition of SERPINH1 protein using Co1003 significantly decreased survival, invasion, and migration of GC cells. SERPINH1 thus appears to regulate EMT and GC progression via the Wnt/β-catenin pathway, making SERPINH1 a potential prognostic biomarker and therapeutic target in GC patients.

Increase of MAL-II Binding Alpha2,3-Sialylated Glycan Is Associated with 5-FU Resistance and Short Survival of Cholangiocarcinoma Patients

Background and objectives: Sialylation plays important roles in tumor progression. Our present study aimed to demonstrate the alteration of sialylation and its role in cholangiocarcinoma (CCA). Materials and Methods: The α2,3- and α2,6-sialylation in CCA tissue was analyzed by lectin-histochemistry using Maackia amurensis lectin-II (MAL-II) and Sambucus nigra agglutinin (SNA). CCA cell lines were treated with the pan-sialylation inhibitor 3Fax-peracetyl-Neu5Ac (3F-Sia) followed by proliferation and chemosensitivity assays. Results: MAL-II binding α2,3-Sialylated Glycan (MAL-SG) and SNA binding α2,6-Sialylated Glycan (SNA-SG) were both elevated in CCA compared with hyperplastic/dysplastic (HP/DP) and normal bile ducts (NBD). The positive staining for MAL-SG or SNA-SG were found in 82% (61/74) of the CCA cases. Higher expression of MAL-SG in CCA was associated with shorter survival of the patients. The median survival of patients with high and low MAL-SG were 167 and 308 days, respectively, with overall survival of 233 days, suggesting the involvement of MAL-SG in CCA progression. MAL-SG expression of CCA cell lines was markedly decreased after treatment with 3F-Sia for 48 to 72 h. While proliferation of CCA cells were not affected by 3F-Sia treatment, their susceptibility to 5-fluorouracil (5-FU) was significantly enhanced. These results suggest that sialylation is involved in the development of 5-FU resistance and the sialylation inhibitor 3F-Sia can be used as a chemosensitizer for CCA. Conclusions: Sialylation is critically involved in the development of chemoresistance of CCA, and sialylation inhibitors may be used as a chemosensitizer in CCA treatment.

The HOTAIR/miR-214/ST6GAL1 crosstalk modulates colorectal cancer procession through mediating sialylated c-Met via JAK2/STAT3 cascade

Background

The regulatory non-coding RNAs, including long non-coding RNAs (lncRNAs) and microRNAs (miRNAs), emerge as pivotal markers during tumor progression. Abnormal sialylated glycoprotein often leads to the malignancy of colorectal cancer (CRC).

Methods

Differential levels of HOTAIR and ST6GAL1 are analyzed by qRT-PCR. Functionally, CRC cell proliferation, aggressiveness and apoptosis are measured through relevant experiments, including CCK8 assay, colony formation assay, transwell assay, western blot and flow cytometry. Dual-luciferase reporter gene assay and RIP assay confirm the direct interaction between HOTAIR and miR-214. The lung metastasis, liver metatstasis and xenografts nude mice models are established to show the in vivo effect of HOATIR.

Results

Here, differential levels of HOTAIR and ST6GAL1 are primarily observed in CRC samples and cells. Upregulated HOTAIR and ST6GAL1 are crucial predictors for poor CRC prognosis. Altered level of ST6GAL1 modulates CRC malignancy. Furthermore, ST6GAL1 and HOTAIR are confirmed as the direct targets of miR-214, and ST6GAL1 is regulated by HOTAIR via sponging miR-214. ST6GAL1 induces the elevated metabolic sialylation of c-Met, which is co-mediated by HOTAIR and miR-214. Sialylated c-Met affects the activity of JAK2/STAT3 pathway. The regulatory role of HOTAIR/miR-214/ST6GAL1 axis also impacts CRC procession. In addition, HOTAIR mediates lung metastasis, liver metastasis and tumorigenesis in vivo. ShHOTAIR and AMG-208 are combined to inhibit tumorigenesis for successful drug development.

Conclusion

The HOTAIR/miR-214/ST6GAL1 axis commands the CRC malignancy by modifying c-Met with sialylation and activating JAK2/STAT3 pathway. Our study presents novel insights into CRC progression and provided prospective therapeutic target for CRC.

Targeting Aberrant Sialylation to Treat Cancer

Cell surface carbohydrates (known as glycans) are often aberrantly expressed or found at atypical levels in cancer. Glycans can impact all steps in tumour progression, from malignant transformation to metastasis, and have roles in all the cancer hallmarks. An increased understanding of glycans in the metastatic cascade offers exciting new therapeutic opportunities. Glycan-based targeting strategies are currently being tested in clinical trials and are a rich and untapped frontier for development. As we learn more about cancer glycobiology, new targets will continue to emerge for drug design. One key change in tumour glycosylation is the upregulation of cancer-associated sialylated glycans. Abnormal sialylation is integral to tumour growth, metastasis and immune evasion; therefore, targeting sialic acid moieties in cancer could be of high therapeutic value. Here, we summarise the changes to sialic acid biology in cancer and discuss recent advances and technologies bringing sialic-acid targeting treatments to the forefront of cancer therapeutics.

The sialoglycan-Siglec glyco-immune checkpoint - a target for improving innate and adaptive anti-cancer immunity

Introduction: During cancer progression, tumor cells develop several mechanisms to prevent killing and to shape the immune system into a tumor-promoting environment. One of such regulatory mechanism is the overexpression of sialic acid (Sia) on carbohydrates of proteins and lipids on tumor cells. Sia-containing glycans or sialoglycans were shown to inhibit immune effector functions of NK cells and T cells by engaging inhibitory Siglec receptors on the surface of these cells. They can also modulate the differentiation of myeloid cells into tumor-promoting M2 macrophages. Areas covered: We review the role of sialoglycans in cancer and introduce the Siglecs, their expression on different immune cells and their interaction with cancer-associated sialoglycans. The targeting of this sialoglycan-Siglec glyco-immune checkpoint is discussed along with potential therapeutic approaches. Pubmed was searched for publications on Siglecs, sialic acid, and cancer. Expert opinion: The targeting of sialoglycan-Siglec interactions has become a major focus in cancer research. New approaches have been developed that directly target sialic acids in tumor lesions. Targeted sialidases that cleave sialic acid specifically in the tumor, have already shown efficacy; efforts targeting the sialoglycan-Siglec pathway for improvement of CAR T cell therapy are ongoing. The sialoglycan-Siglec immune checkpoint is a promising new target for cancer immunotherapy.

β-catenin regulates effects of miR-24 on the viability and autophagy of glioma cells

Mutations of the β-catenin gene are common in various cancer types. MicroRNA (miR)-24 suppresses gene expression during the cell cycle. However, the effects of miR-24 on the cell viability and autophagy of glioma cells, and how these biological processes are regulated by β-catenin are largely unclear. The current study aimed to investigate the role of β-catenin in regulating the effects of miR-24 on the cell viability and autophagy of glioma cells. The expression levels of microtubule-associated proteins 1A/1B light chain 3B (LC3B) and Beclin1 were detected by immunohistochemistry and western blotting. Glioma C6 cells were transfected with miR-24 mimics, miR-24 inhibitors and negative control miRNAs. C6 cells transfected with miR-24 mimics or negative control miRNAs were treated with the β-catenin inhibitor, XAV-939. An MTT assay was utilized to evaluate the viability of C6 cells. The expression of miR-24 and mRNA expression of autophagy related 4a cysteine peptidase (ATG4A) were detected by quantitative polymerase chain reaction analysis. The protein expression of LC3B and Beclin1 decreased significantly in glioma tissue and glioma C6 cells compared with normal brain tissue. Compared with the negative control group, C6 cells transfected with miR-24 mimics exhibited significantly higher cell viability at 24 and 48 h, and those transfected with miR-24 inhibitors exhibited significantly lower cell viability at 48 h. XAV-939 decreased the stimulatory effects of miR-24 mimics on the viability of C6 cells. The expression of miR-24 significantly decreased and ATG4A mRNA significantly increased in C6 cells transfected with XAV-939 compared with those transfected with the negative control miRNA. XAV-939 attenuated the miR-24-induced decrease of the protein expression of LC3B and Beclin1, and decreased the stimulatory effects of miR-24 mimics on cell viability. In addition, XAV-939 attenuated the miR-24-induced decrease of autophagy marker expression by attenuating miR-24 expression and increasing ATG4A mRNA expression in glioma C6 cells. To the best of our knowledge, the present study is the first to demonstrate whether β-catenin regulates the intracellular effects of miR-24 on the viability and autophagy of glioma cells. The results also provide some mechanistic basis to the pharmaceutical targeting of WNT signaling in high grade glial tumors.

ST6GAL1: A key player in cancer

Aberrant glycosylation is a universal feature of cancer cells and there is now overwhelming evidence that glycans can modulate pathways intrinsic to tumour cell biology. Glycans are important in all of the cancer hallmarks and there is a renewed interest in the glycomic profiling of tumours to improve early diagnosis, determine patient prognosis and identify targets for therapeutic intervention. One of the most widely occurring cancer associated changes in glycosylation is abnormal sialylation which is often accompanied by changes in sialyltransferase activity. Several sialyltransferases are implicated in cancer, but in recent years ST6 β-galactoside α-2,6-sialyltransferase 1 (ST6GAL1) has become increasingly dominant in the literature. ST6GAL1 catalyses the addition of α2,6-linked sialic acids to terminal N-glycans and can modify glycoproteins and/or glycolipids. ST6GAL1 is upregulated in numerous types of cancer (including pancreatic, prostate, breast and ovarian cancer) and can promote growth, survival and metastasis. The present review discusses ST6GAL in relation to the hallmarks of cancer, and highlights its key role in multiple mechanisms intrinsic to tumour cell biology.

Alginate oligosaccharide attenuates α2,6-sialylation modification to inhibit prostate cancer cell growth via the Hippo/YAP pathway

Chitosan oligosaccharides have been reported to inhibit various tumors. However, the water-soluble marine plant oligosaccharide alginate oligosaccharide (AOS) has only rarely been reported to have anti-cancer effects. Moreover, the inhibitory effect of AOS on prostate cancer and the underlying molecular mechanism remain unknown. This study shows that AOS inhibited cell growth, which was consistent with the attenuation of α2,6-sialylation modification. Furthermore, AOS inhibited ST6Gal-1 promoter activity and thus affected transcriptional processes. In addition, AOS could activate the Hippo/YAP pathway and block the recruitment of both the coactivator YAP and c-Jun. Furthermore, YAP interacted with the transcription factor c-Jun and regulated the transcriptional activity of the downstream target ST6Gal-1 gene. Consistent with in vitro data, AOS suppressed the tumorigenicity of prostate cancer cells via the Hippo/YAP pathway in vivo. In summary, these data indicate that AOS slows the proliferation of prostate cancer and provides a basis for the healthy function of kelp in traditional cognition.

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

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

Glycans as Biomarkers in Prostate Cancer

Prostate cancer is the most commonly diagnosed malignancy in men, claiming over350,000 lives worldwide annually. Current diagnosis relies on prostate-specific antigen (PSA)testing, but this misses some aggressive tumours, and leads to the overtreatment of non-harmfuldisease. Hence, there is an urgent unmet clinical need to identify new diagnostic and prognosticbiomarkers. As prostate cancer is a heterogeneous and multifocal disease, it is likely that multiplebiomarkers will be needed to guide clinical decisions. Fluid-based biomarkers would be ideal, andattention is now turning to minimally invasive liquid biopsies, which enable the analysis oftumour components in patient blood or urine. Effective diagnostics using liquid biopsies willrequire a multifaceted approach, and a recent high-profile review discussed combining multipleanalytes, including changes to the tumour transcriptome, epigenome, proteome, and metabolome.However, the concentration on genomics-based paramaters for analysing liquid biopsies ispotentially missing a goldmine. Glycans have shown huge promise as disease biomarkers, anddata suggests that integrating biomarkers across multi-omic platforms (including changes to theglycome) can improve the stratification of patients with prostate cancer. A wide range ofalterations to glycans have been observed in prostate cancer, including changes to PSAglycosylation, increased sialylation and core fucosylation, increased O-GlcNacylation, theemergence of cryptic and branched N-glyans, and changes to galectins and proteoglycans. In thisreview, we discuss the huge potential to exploit glycans as diagnostic and prognostic biomarkersfor prostate cancer, and argue that the inclusion of glycans in a multi-analyte liquid biopsy test forprostate cancer will help maximise clinical utility.