Cancer metabolism and elevated O-GlcNAc in oncogenic signaling

O-GlcNAcylation of RBM14 contributes to elevated cellular O-GlcNAc through regulation of OGA protein stability

Dysregulation of O-GlcNAcylation has emerged as a potential biomarker for several diseases, particularly cancer. The role of OGT (O-GlcNAc transferase) in maintaining O-GlcNAc homeostasis has been extensively studied; nevertheless, the regulation of OGA (O-GlcNAcase) in cancer remains elusive. Here, we demonstrated that the multifunctional protein RBM14 is a regulator of cellular O-GlcNAcylation. By investigating the correlation between elevated O-GlcNAcylation and increased RBM14 expression in lung cancer cells, we discovered that RBM14 promotes ubiquitin-dependent proteasomal degradation of OGA, ultimately mediating cellular O-GlcNAcylation levels. In addition, RBM14 itself is O-GlcNAcylated at serine 521, regulating its interaction with the E3 ligase TRIM33, consequently affecting OGA protein stability. Moreover, we demonstrated that mutation of serine 521 to alanine abrogated the oncogenic properties of RBM14. Collectively, our findings reveal a previously unknown mechanism for the regulation of OGA and suggest a potential therapeutic target for the treatment of cancers with dysregulated O-GlcNAcylation.

Salivary Metabolites Produced by Oral Microbes in Oral Diseases and Oral Squamous Cell Carcinoma: A Review

In recent years, salivary metabolome studies have provided new biological information and salivary biomarkers to diagnose different diseases at early stages. The saliva in the oral cavity is influenced by many factors that are reflected in the salivary metabolite profile. Oral microbes can alter the salivary metabolite profile and may express oral inflammation or oral diseases. The released microbial metabolites in the saliva represent the altered biochemical pathways in the oral cavity. This review highlights the oral microbial profile and microbial metabolites released in saliva and its use as a diagnostic biofluid for different oral diseases. The importance of salivary metabolites produced by oral microbes as risk factors for oral diseases and their possible relationship in oral carcinogenesis is discussed.

Subcellular imaging of lipids and sugars using genetically encoded proximity sensors

Live cell imaging of lipids and other metabolites is a long-standing challenge in cell biology. Bioorthogonal labeling tools allow for the conjugation of fluorophores to several phospholipid classes, but cannot discern their trafficking between adjacent organelles or asymmetry across individual membrane leaflets. Here we present fluorogen-activating coincidence sensing (FACES), a chemogenetic tool capable of quantitatively imaging subcellular lipid pools and reporting their transbilayer orientation in living cells. FACES combines bioorthogonal chemistry with genetically encoded fluorogen-activating proteins (FAPs) for reversible proximity sensing of conjugated molecules. We first validate this approach for quantifying discrete phosphatidylcholine pools in the ER and mitochondria that are trafficked by lipid transfer proteins. We then show that transmembrane domain-containing FAPs can be used to reveal the membrane asymmetry of multiple lipid classes that are generated in the trans-Golgi network. Lastly, we demonstrate that FACES is a generalizable tool for subcellular bioorthogonal imaging by measuring changes in mitochondrial N -acetylhexosamine levels. These results demonstrate the use of fluorogenic tags for spatially-defined molecular imaging.

Metabolic reprogramming regulated by TRAF6 contributes to the leukemia progression

TNF receptor associated factor 6 (TRAF6) is an E3 ubiquitin ligase that has been implicated in myeloid malignancies. Although altered TRAF6 expression is observed in human acute myeloid leukemia (AML), its role in the AML pathogenesis remains elusive. In this study, we showed that the loss of TRAF6 in AML cells significantly impairs leukemic function in vitro and in vivo, indicating its functional importance in AML subsets. Loss of TRAF6 induces metabolic alterations, such as changes in glycolysis, TCA cycle, and nucleic acid metabolism as well as impaired mitochondrial membrane potential and respiratory capacity. In leukemic cells, TRAF6 expression shows a positive correlation with the expression of O-linked N-acetylglucosamine (O-GlcNAc) transferase (OGT), which catalyzes the addition of O-GlcNAc to target proteins involved in metabolic regulation. The restoration of growth capacity and metabolic activity in leukemic cells with TRAF6 loss, achieved through either forced expression of OGT or pharmacological inhibition of O-GlcNAcase (OGA) that removes O-GlcNAc, indicates the significant role of O-GlcNAc modification in the TRAF6-related cellular and metabolic dynamics. Our findings highlight the oncogenic function of TRAF6 in leukemia and illuminate the novel TRAF6/OGT/O-GlcNAc axis as a potential regulator of metabolic reprogramming in leukemogenesis.

Relevance of glyco-biomakers and glycan profiles in cancer stem cells

Altered and aberrant glycosylation signatures have been linked to being a hallmark in a variety of human disorders including cancer. Cancer stem cells (CSCs), capable of self-renewal and differentiation, have recently been credited with a unique notion of disease genesis and implicated as the cause for initiation and recurrence of the disease in a new regime of neoplastic transformations hypothesis. Many biomarkers relating to diagnostic and prognostic intents have been discovered using the ubiquitous and abundant surface glycan patterns on CSCs. Various technological advancements have been developed to identify and determine concerns with glycosylation structure. However, the nature and purpose of the glycan moiety on these glycosylation pattern have not yet been thoroughly investigated. This review, thus, summarizes the process of glycosylation in CSCs, variations in glycosylation patterns in various stem cells, aberrant glycosylation patterns in cancer, the role of glycosylation in tumor cell adhesion, cell-matrix interactions, and signaling, as well as cancer detection and treatment. The function of carbohydrates as prospective serum biomarkers, some clinically authorized biomarkers, and potential novel biomarkers relating to cancer disease diagnosis and prognosis are also discussed in the review.

Breast cancer therapy: from the perspective of glucose metabolism and glycosylation

Breast cancer is a leading cause of mortality and the most prevalent form of malignant tumor among women worldwide. Breast cancer cells exhibit an elevated glycolysis and altered glucose metabolism. Moreover, these cells display abnormal glycosylation patterns, influencing invasion, proliferation, metastasis, and drug resistance. Consequently, targeting glycolysis and mitigating abnormal glycosylation represent key therapeutic strategies for breast cancer. This review underscores the importance of protein glycosylation and glucose metabolism alterations in breast cancer. The current research efforts in developing effective interventions targeting glycolysis and glycosylation are further discussed.

NMR Metabolomics of Primary Ovarian Cancer Cells in Comparison to Established Cisplatin-Resistant and -Sensitive Cell Lines

Cancer cell lines are frequently used in metabolomics, such as in vitro tumor models. In particular, A2780 cells are commonly used as a model for ovarian cancer to evaluate the effects of drug treatment. Here, we compare the NMR metabolomics profiles of A2780 and cisplatin-resistant A2780 cells with those of cells derived from 10 patients with high-grade serous ovarian carcinoma (collected during primary cytoreduction before any chemotherapeutic treatment). Our analysis reveals a substantial similarity among all primary cells but significant differences between them and both A2780 and cisplatin-resistant A2780 cells. Notably, the patient-derived cells are closer to the resistant A2780 cells when considering the exo-metabolome, whereas they are essentially equidistant from A2780 and A2780-resistant cells in terms of the endo-metabolome. This behavior results from dissimilarities in the levels of several metabolites attributable to the differential modulation of underlying biochemical pathways. The patient-derived cells are those with the most pronounced glycolytic phenotype, whereas A2780-resistant cells mainly diverge from the others due to alterations in a few specific metabolites already known as markers of resistance.

Review: Protein O-GlcNAcylation regulates DNA damage response: A novel target for cancer therapy

The DNA damage response (DDR) safeguards the stable genetic information inheritance by orchestrating a complex protein network in response to DNA damage. However, this mechanism can often hamper the effectiveness of radiotherapy and DNA-damaging chemotherapy in destroying tumor cells, causing cancer resistance. Inhibiting DDR can significantly improve tumor cell sensitivity to radiotherapy and DNA-damaging chemotherapy. Thus, DDR can be a potential target for cancer treatment. Post-translational modifications (PTMs) of DDR-associated proteins profoundly affect their activity and function by covalently attaching new functional groups. O-GlcNAcylation (O-linked-N-acetylglucosaminylation) is an emerging PTM associated with adding and removing O-linked N-acetylglucosamine to serine and threonine residues of proteins. It acts as a dual sensor for nutrients and stress in the cell and is sensitive to DNA damage. However, the explanation behind the specific role of O-GlcNAcylation in the DDR remains remains to be elucidated. To illustrate the complex relationship between O-GlcNAcylation and DDR, this review systematically describes the role of O-GlcNAcylation in DNA repair, cell cycle, and chromatin. We also discuss the defects of current strategies for targeting O-GlcNAcylation-regulated DDR in cancer therapy and suggest potential directions to address them.

Single cell and bulk RNA expression analyses identify enhanced hexosamine biosynthetic pathway and O-GlcNAcylation in acute myeloid leukemia blasts and stem cells

Introduction

Acute myeloid leukemia (AML) is the most common acute leukemia in adults with an overall poor prognosis and high relapse rate. Multiple factors including genetic abnormalities, differentiation defects and altered cellular metabolism contribute to AML development and progression. Though the roles of oxidative phosphorylation and glycolysis are defined in AML, the role of the hexosamine biosynthetic pathway (HBP), which regulates the O-GlcNAcylation of cytoplasmic and nuclear proteins, remains poorly defined.

Methods

We studied the expression of the key enzymes involved in the HBP in AML blasts and stem cells by RNA sequencing at the single-cell and bulk level. We performed flow cytometry to study OGT protein expression and global O-GlcNAcylation. We studied the functional effects of inhibiting O-GlcNAcylation on transcriptional activation in AML cells by Western blotting and real time PCR and on cell cycle by flow cytometry.

Results

We found higher expression levels of the key enzymes in the HBP in AML as compared to healthy donors in whole blood. We observed elevated O-GlcNAc Transferase (OGT) and O-GlcNAcase (OGA) expression in AML stem and bulk cells as compared to normal hematopoietic stem and progenitor cells (HSPCs). We also found that both AML bulk cells and stem cells show significantly enhanced OGT protein expression and global O-GlcNAcylation as compared to normal HSPCs, validating our in silico findings. Gene set analysis showed substantial enrichment of the NF-κB pathway in AML cells expressing high OGT levels. Inhibition of O-GlcNAcylation decreased NF-κB nuclear translocation and the expression of selected NF-κB-dependent genes controlling cell cycle. It also blocked cell cycle progression suggesting a link between enhanced O-GlcNAcylation and NF-κB activation in AML cell survival and proliferation.

Discussion

Our study suggests the HBP may prove a potential target, alone or in combination with other therapeutic approaches, to impact both AML blasts and stem cells. Moreover, as insufficient targeting of AML stem cells by traditional chemotherapy is thought to lead to relapse, blocking HBP and O-GlcNAcylation in AML stem cells may represent a novel promising target to control relapse.

Increased O-GlcNAcylation by Upregulation of Mitochondrial O-GlcNAc Transferase (mOGT) Inhibits the Activity of Respiratory Chain Complexes and Controls Cellular Bioenergetics

O-linked β-N-acetylglucosamine (O-GlcNAc) is a reversible post-translational modification involved in the regulation of cytosolic, nuclear, and mitochondrial proteins. The interplay between O-GlcNAcylation and phosphorylation is critical to control signaling pathways and maintain cellular homeostasis. The addition of O-GlcNAc moieties to target proteins is catalyzed by O-linked N-acetylglucosamine transferase (OGT). Of the three splice variants of OGT described, one is destined for the mitochondria (mOGT). Although the effects of O-GlcNAcylation on the biology of normal and cancer cells are well documented, the role of mOGT remains poorly understood. In this manuscript, the effects of mOGT on mitochondrial protein phosphorylation, electron transport chain (ETC) complex activity, and the expression of VDAC porins were investigated. We performed studies using normal and breast cancer cells with upregulated mOGT or its catalytically inactive mutant. Proteomic approaches included the isolation of O-GlcNAc-modified proteins of the electron transport chain, followed by their analysis using mass spectrometry. We found that mitochondrial OGT regulates the activity of complexes I-V of the respiratory chain and identified a group of 19 ETC components as mOGT substrates in mammary cells. Furthermore, we observed that the upregulation of mOGT inhibited the interaction of VDAC1 with hexokinase II. Our results suggest that the deregulation of mOGT reprograms cellular energy metabolism via interaction with and O-GlcNAcylation of proteins involved in ATP production in mitochondria and its exchange between mitochondria and the cytosol.

Protein O-GlcNAcylation: The sweet hub in liver metabolic flexibility from a (patho)physiological perspective

O-GlcNAcylation is a dynamic, reversible and atypical O-glycosylation that regulates various cellular physiological processes via conformation, stabilisation, localisation, chaperone interaction or activity of target proteins. The O-GlcNAcylation cycle is precisely controlled by collaboration between O-GlcNAc transferase and O-GlcNAcase. Uridine-diphosphate-N-acetylglucosamine, the sole donor of O-GlcNAcylation produced by the hexosamine biosynthesis pathway, is controlled by the input of glucose, glutamine, acetyl coenzyme A and uridine triphosphate, making it a sensor of the fluctuation of molecules, making O-GlcNAcylation a pivotal nutrient sensor for the metabolism of carbohydrates, amino acids, lipids and nucleotides. O-GlcNAcylation, particularly prevalent in liver, is the core hub for controlling systemic glucose homeostasis due to its nutritional sensitivity and precise spatiotemporal regulation of insulin signal transduction. The pathology of various liver diseases has highlighted hepatic metabolic disorder and dysfunction, and abnormal O-GlcNAcylation also plays a specific pathological role in these processes. Therefore, this review describes the unique features of O-GlcNAcylation and its dynamic homeostasis maintenance. Additionally, it explains the underlying nutritional sensitivity of O-GlcNAcylation and discusses its mechanism of spatiotemporal modulation of insulin signal transduction and liver metabolic homeostasis during the fasting and feeding cycle. This review emphasises the pathophysiological implications of O-GlcNAcylation in nonalcoholic fatty liver disease, nonalcoholic steatohepatitis and hepatic fibrosis, and focuses on the adverse effects of hyper O-GlcNAcylation on liver cancer progression and metabolic reprogramming.

A novel CSN5/CRT O-GlcNAc/ER stress regulatory axis in platinum resistance of epithelial ovarian cancer

Background: High levels of COP9 signalosome subunit 5 (CSN5) in epithelial ovarian cancer (EOC) are associated with poor prognosis and are implicated in mediating platinum resistance in EOC cells. The underlying mechanisms, however, remained undefined. This study aimed to elucidate the molecular process and identify potential therapeutic targets. Methods: RNA-sequencing was used to investigate differentially expressed genes between platinum-resistant EOC cells with CSN5 knockdown and controls. O-GlcNAc proteomics were employed to identify critical modulators downstream of CSN5. The omics findings were confirmed through qRT-PCR and immunoblotting. In vitro and in vivo experiments assessed the sensitivity of resistant EOCs to platinum. Results: We demonstrated an involvement of aberrant O-GlcNAc and endoplasmic reticulum (ER) stress disequilibrium in CSN5-mediated platinum resistance of EOC. Genetic or pharmacologic inhibition of CSN5 led to tumor regression and surmounted the intrinsic EOC resistance to platinum both in vitro and in vivo. Integration of RNA-sequencing and O-GlcNAc proteomics pinpointed calreticulin (CRT) as a potential target of aberrant O-GlcNAc modification. CSN5 upregulated O-GlcNAc-CRT at T346 to inhibit ER stress-induced cell death. Blocking T346 O-GlcNAc-CRT through CSN5 deficiency or T346A mutation resulted in Ca2+ disturbances, followed by ER stress overactivation, mitochondrial dysfunction, and ultimately cell apoptosis. Conclusion: This study reveals that CSN5-mediated aberrant O-GlcNAc-CRT acts as a crucial ER stress checkpoint, governing cell fate response to stress, and emphasizes an unrecognized role for the CSN5/CRT O-GlcNAc/ER stress axis in platinum resistance of EOC.

Sialic Acid-Modified O-GlcNAc Transferase Inhibitor Liposome Presents Antitumor Effect in Hepatocellular Carcinoma

O-linked-N-acetylglucosaminylation (O-GlcNAcylation) plays a key role in hepatocellular carcinoma (HCC) development, and the inhibition of O-GlcNAcylation has therapeutic potential. To decrease the systemic adverse events and increase targeting, we used sialic acid (SA)-decorated liposomes loaded with OSMI-1, an inhibitor of the O-GlcNAcylation, to further improve the anti-HCC effect. Fifty pairs of HCC tissue samples and the cancer genome atlas database were used to analyze the expression of O-GlcNAc transferase (OGT) and its effects on prognosis and immune cell infiltration. OSMI-1 cells were treated with SA and liposomes. Western blotting, immunofluorescence, cell proliferation assay, flow cytometry, enzyme-linked immunosorbent assay, immunohistochemistry, and tumorigenicity assays were used to investigate the antitumor effect of SA-modified OSMI-1 liposomes in vitro and in vivo. OGT was highly expressed in HCC tissues, negatively correlated with the degree of tumor infiltration of CD8+ and CD4+T cells and prognosis, and positively correlated with the degree of Treg cell infiltration. SA-modified OSMI-1 liposome (OSMI-1-SAL) was synthesized with stable hydrodynamic size distribution. Both in vitro and in vivo, OSMI-1-SAL exhibited satisfactory biosafety and rapid uptake by HCC cells. Compared to free OSMI-1, OSMI-1-SAL had a stronger capacity for suppressing the proliferation and promoting the apoptosis of HCC cells. Moreover, OSMI-1-SAL effectively inhibited tumor initiation and development in mice. OSMI-1-SAL also promoted the release of damage-associated molecular patterns, including anticalreticulin, high-mobility-group protein B1, and adenosine triphosphate, from HCC cells and further promoted the activation and proliferation of the CD8+ and CD4+T cells. In conclusion, the OSMI-1-SAL synthesized in this study can target HCC cells, inhibit tumor proliferation, induce tumor immunogenic cell death, enhance tumor immunogenicity, and promote antitumor immune responses, which has the potential for clinical application in the future.

Fucosyltransferase 3 and 8 promote the metastatic capacity of cancer stem-like cells via CD15s and E-cadherin in esophageal cancer

Objectives

Esophageal cancer stem cells (ECSCs) have been identified as the subset of cells within esophageal squamous cell carcinoma that possess tumorigenic, invasive, and metastatic properties. One important aspect of cancer metastasis is the binding of sialyl-Lewis X (CD15s) with E- or P-selectin, which facilitates the adhesion and migration of cancer cells to distant sites. This study was conducted to investigate the impact of fucosylation processes on the metastatic behavior of ECSCs.

Materials and Methods

The esophageal cancer cell line (KYSE-30) was cultured and divided into control and 2F-peracetyl fucose (2F-PerAcFuc) treated groups. Spheres were harvested from these cultures. Cell invasion assay and qPCR were conducted to examine migration and marker expression in both groups. Cancer cell line-derived xenografts were established in nude mice to validate findings in vivo.

Results

Our results initially indicated that the addition of 2F-PerAcFuc, an inhibitor of fucosylation, resulted in the down-regulation of the Fut3/CD15s pathway in both cancer stem-like cells and the xenograft model. Measurements of subcutaneous xenograft tumor volume revealed a significant decrease in tumor size among nude mice after treatment with 2F-PerAcFuc. Additionally, a reduction in Fut8/E-cadherin levels was observed in the xenograft model of nude mice. Furthermore, the administration of 2F-PerAcFuc lowered the levels of fucosylated glycoconjugates in nude mice.

Conclusion

Our data suggest that inhibition of fucosyltransferase 3 and 8 can reduce the metastatic capacity of cancer stem-like cells by down-regulating CD15s and E-cadherin in a mouse model of esophageal cancer.

Desmin and its molecular chaperone, the αB-crystallin: How post-translational modifications modulate their functions in heart and skeletal muscles?

Maintenance of the highly organized striated muscle tissue requires a cell-wide dynamic network through protein-protein interactions providing an effective mechanochemical integrator of morphology and function. Through a continuous and complex trans-cytoplasmic network, desmin intermediate filaments ensure this essential role in heart and in skeletal muscle. Besides their role in the maintenance of cell shape and architecture (permitting contractile activity efficiency and conferring resistance towards mechanical stress), desmin intermediate filaments are also key actors of cell and tissue homeostasis. Desmin participates to several cellular processes such as differentiation, apoptosis, intracellular signalisation, mechanotransduction, vesicle trafficking, organelle biogenesis and/or positioning, calcium homeostasis, protein homeostasis, cell adhesion, metabolism and gene expression. Desmin intermediate filaments assembly requires αB-crystallin, a small heat shock protein. Over its chaperone activity, αB-crystallin is involved in several cellular functions such as cell integrity, cytoskeleton stabilization, apoptosis, autophagy, differentiation, mitochondria function or aggresome formation. Importantly, both proteins are known to be strongly associated to the aetiology of several cardiac and skeletal muscles pathologies related to desmin filaments disorganization and a strong disturbance of desmin interactome. Note that these key proteins of cytoskeleton architecture are extensively modified by post-translational modifications that could affect their functional properties. Therefore, we reviewed in the herein paper the impact of post-translational modifications on the modulation of cellular functions of desmin and its molecular chaperone, the αB-crystallin.

Targeting Breast Cancer with N-Acetyl-D-Glucosamine: Integrating Machine Learning and Cellular Assays for Promising Results

BACKGROUND

Breast cancer is a common cancer with high mortality rates. Early diagnosis is crucial for reducing the prognosis and mortality rates. Therefore, the development of alternative treatment options is necessary.

OBJECTIVE

This study aimed to investigate the inhibitory effect of N-acetyl-D-glucosamine (D-GlcNAc) on breast cancer using a machine learning method. The findings were further confirmed through assays on breast cancer cell lines.

METHODS

MCF-7 and 4T1 cell lines (ATCC) were cultured in the presence and absence of varying concentrations of D-GlcNAc (0.5 mM, 1 mM, 2 mM, and 4 mM) for 72 hours. A xenograft mouse model for breast cancer was established by injecting 4T1 cells into mammary glands. D-GlcNAc (2 mM) was administered intraperitoneally to mice daily for 28 days, and histopathological effects were evaluated at pre-tumoral and post-tumoral stages.

RESULTS

Treatment with 2 mM and 4 mM D-GlcNAc significantly decreased cell proliferation rates in MCF-7 and 4T1 cell lines and increased Fas expression. The number of apoptotic cells was significantly higher than untreated cell cultures (p < 0.01 - p < 0.0001). D-GlcNAc administration also considerably reduced tumour size, mitosis, and angiogenesis in the post-treatment group compared to the control breast cancer group (p < 0.01 - p < 0.0001). Additionally, molecular docking/dynamic analysis revealed a high binding affinity of D-GlcNAc to the marker protein HER2, which is involved in tumour progression and cell signalling.

CONCLUSION

Our study demonstrated the positive effect of D-GlcNAc administration on breast cancer cells, leading to increased apoptosis and Fas expression in the malignant phenotype. The binding affinity of D-GlcNAc to HER2 suggests a potential mechanism of action. These findings contribute to understanding D-GlcNAc as a potential anti-tumour agent for breast cancer treatment.

Identification of salivary metabolic biomarker signatures for oral tongue squamous cell carcinoma

OBJECTIVE

To identify the salivary metabolites associated with squamous cell carcinoma of the tongue to develop easy and non-invasive potential biomarkers for disease diagnosis.

DESIGN

Initially, the study utilized untargeted metabolomics to analyze 20 samples of tongue squamous cell carcinoma and 10 control samples. The objective was to determine the salivary metabolites that exhibited differential expression in tongue squamous cell carcinoma. Then the selected metabolites were validated using targeted metabolomics in saliva samples of 100 patients diagnosed with squamous cell carcinoma of the tongue, as well as 30 healthy control individuals.

RESULTS

From the analysis of untargeted metabolomics, 10 metabolites were selected as potential biomarkers. In the subsequent targeted metabolomics study on these selected metabolites, it was observed that N-Acetyl-D-glucosamine, L-Pipecolic acid, L-Carnitine, Phosphorylcholine, and Deoxyguanosine exhibited significant differences. The receiver operating characteristic curve analysis indicates a combination of three important metabolites such as N-Acetyl-D-glucosamine, L-Pipecolic acid and L-Carnitine provided the best prediction with an area under the curve of 0.901.

CONCLUSIONS

The present result reveals that the N-Acetyl-D-glucosamine, L-Pipecolic acid and L-Carnitine are the signature diagnostic biomarkers for oral tongue squamous cell carcinoma. These findings can be used to develop a rapid and non-invasive method for disease monitoring and prognosis in oral tongue cancer.

On a sugar high: Role of O-GlcNAcylation in cancer

Recent advances in the understanding of the molecular mechanisms underlying cancer progression have led to the development of novel therapeutic targeting strategies. Aberrant glycosylation patterns and their implication in cancer have gained increasing attention as potential targets due to the critical role of glycosylation in regulating tumor-specific pathways that contribute to cancer cell survival, proliferation, and progression. A special type of glycosylation that has been gaining momentum in cancer research is the modification of nuclear, cytoplasmic, and mitochondrial proteins, termed O-GlcNAcylation. This protein modification is catalyzed by an enzyme called O-GlcNAc transferase (OGT), which uses the final product of the Hexosamine Biosynthetic Pathway (HBP) to connect altered nutrient availability to changes in cellular signaling that contribute to multiple aspects of tumor progression. Both O-GlcNAc and its enzyme OGT are highly elevated in cancer and fulfill the crucial role in regulating many hallmarks of cancer. In this review, we present and discuss the latest findings elucidating the involvement of OGT and O-GlcNAc in cancer.

Post-translational modifications and their implications in cancer

Post-translational modifications (PTMs) are crucial regulatory mechanisms that alter the properties of a protein by covalently attaching a modified chemical group to some of its amino acid residues. PTMs modulate essential physiological processes such as signal transduction, metabolism, protein localization, and turnover and have clinical relevance in cancer and age-related pathologies. Majority of proteins undergo post-translational modifications, irrespective of their occurrence in or after protein biosynthesis. Post-translational modifications link to amino acid termini or side chains, causing the protein backbone to get cleaved, spliced, or cyclized, to name a few. These chemical modifications expand the diversity of the proteome and regulate protein activity, structure, locations, functions, and protein-protein interactions (PPIs). This ability to modify the physical and chemical properties and functions of proteins render PTMs vital. To date, over 200 different protein modifications have been reported, owing to advanced detection technologies. Some of these modifications include phosphorylation, glycosylation, methylation, acetylation, and ubiquitination. Here, we discuss about the existing as well as some novel post-translational protein modifications, with their implications in aberrant states, which will help us better understand the modified sites in different proteins and the effect of PTMs on protein functions in core biological processes and progression in cancer.

Chromatin-associated OGT promotes the malignant progression of hepatocellular carcinoma by activating ZNF263

Reversible and dynamic O-GlcNAcylation regulates vast networks of highly coordinated cellular and nuclear processes. Although dysregulation of the sole enzyme O-GlcNAc transferase (OGT) was shown to be associated with the progression of hepatocellular carcinoma (HCC), the mechanisms by which OGT controls the cis-regulatory elements in the genome and performs transcriptional functions remain unclear. Here, we demonstrate that elevated OGT levels enhance HCC proliferation and metastasis, in vitro and in vivo, by orchestrating the transcription of numerous regulators of malignancy. Diverse transcriptional regulators are recruited by OGT in HCC cells undergoing malignant progression, which shapes genome-wide OGT chromatin cis-element occupation. Furthermore, an unrecognized cooperation between ZNF263 and OGT is crucial for activating downstream transcription in HCC cells. We reveal that O-GlcNAcylation of Ser662 is responsible for the chromatin association of ZNF263 at candidate gene promoters and the OGT-facilitated HCC malignant phenotypes. Our data establish the importance of aberrant OGT activity and ZNF263 O-GlcNAcylation in the malignant progression of HCC and support the investigation of OGT as a therapeutic target for HCC.

Synergistic apoptosis by combination of metformin and an O-GlcNAcylation inhibitor in colon cancer cells

BACKGROUND

Although autophagy is an important mediator of metformin antitumor activity, the role of metformin in the crosstalk between autophagy and apoptosis remains unclear. The aim was to confirm the anticancer effect by inducing apoptosis by co-treatment with metformin and OSMI-1, an inhibitor of O-GlcNAcylation, in colon cancer cells.

METHODS

Cell viability was measured by MTT in colon cancer cell lines HCT116 and SW620 cells. Co-treatment with metformin and OSMI-1 induced autophagy and apoptosis, which was analyzed using western blot, reverse transcription-polymerase chain reaction (RT-PCR) analysis, and fluorescence-activated cell sorting (FACS). Combined treatment with metformin and OSMI-1 synergistically inhibit the growth of HCT116 was confirmed by xenograft tumors.

RESULTS

We showed that metformin inhibited mammalian target of rapamycin (mTOR) activity by inducing high levels of C/EBP homologous protein (CHOP) expression through endoplasmic reticulum (ER) stress and activating adenosine monophosphate-activated protein kinase (AMPK) to induce autophagy in HCT116 cells. Interestingly, metformin increased O-GlcNAcylation and glutamine:fructose-6-phosphate amidotransferase (GFAT) levels in HCT116 cells. Thus, metformin also blocks autophagy by enhancing O-GlcNAcylation, whereas OSMI-1 increases autophagy via ER stress. In contrast, combined metformin and OSMI-1 treatment resulted in continuous induction of autophagy and disruption of O-GlcNAcylation homeostasis, resulting in excessive autophagic flux, which synergistically induced apoptosis. Downregulation of Bcl2 promoted apoptosis via the activation of c-Jun N-terminal kinase (JNK) and CHOP overexpression, synergistically inducing apoptosis. The activation of IRE1α/JNK signaling by OSMI-1 and PERK/CHOP signaling by metformin combined to inhibit Bcl2 activity, ultimately leading to the upregulation of cytochrome c release and activation of caspase-3.

CONCLUSIONS

In conclusion, combinatorial treatment of HCT116 cells with metformin and OSMI-1 resulted in more synergistic apoptosis being induced by enhancement of signal activation through ER stress-induced signaling rather than the cell protective autophagy function. These results in HCT116 cells were also confirmed in xenograft models, suggesting that this combination strategy could be utilized for colon cancer treatment.

Glycosylation in breast cancer progression and mammary development: Molecular connections and malignant transformations

INTRODUCTION

The cellular behavior in normal mammary gland development and the progression of breast cancer is like the relationship between an object and its mirror image: they may appear similar, but their essence is completely different. Breast cancer can be considered as temporal and spatial aberrations of normal development in mammary gland. Glycans have been shown to regulate key pathophysiological steps during mammary development and breast cancer progression, and the glycoproteins that play a key role in both processes can affect the normal differentiation and development of mammary cells, and even cause malignant transformation or accelerate tumorigenesis due to differences in their type and level of glycosylation.

KEY FINDINGS

In this review, we summarize the roles of glycan alterations in essential cellular behaviors during breast cancer progression and mammary development, and also highlight the importance of key glycan-binding proteins such as epidermal growth factor receptor, transforming growth factor β receptors and other proteins, which are pivotal in the modulation of cellular signaling in mammary gland. Our review takes an overall view of the molecular interplay, signal transduction and cellular behaviors in mammary gland development and breast cancer progression from a glycobiological perspective.

SIGNIFICANCE

This review will give a better understanding of the similarities and differences in glycosylation between mammary gland development and breast cancer progression, laying the foundation for elucidating the key molecular mechanisms of glycobiology underlying the malignant transformation of mammary cells.

O-GlcNAcylation promotes tumor immune evasion by inhibiting PD-L1 lysosomal degradation

Programmed-death ligand 1 (PD-L1) and its receptor programmed cell death 1 (PD-1) mediate T cell-dependent immunity against tumors. The abundance of cell surface PD-L1 is a key determinant of the efficacy of immune checkpoint blockade therapy targeting PD-L1. However, the regulation of cell surface PD-L1 is still poorly understood. Here, we show that lysosomal degradation of PD-L1 is regulated by O-linked N-acetylglucosamine (O-GlcNAc) during the intracellular trafficking pathway. O-GlcNAc modifies the hepatocyte growth factor-regulated tyrosine kinase substrate (HGS), a key component of the endosomal sorting machinery, and subsequently inhibits its interaction with intracellular PD-L1, leading to impaired lysosomal degradation of PD-L1. O-GlcNAc inhibition activates T cell-mediated antitumor immunity in vitro and in immune-competent mice in a manner dependent on HGS glycosylation. Combination of O-GlcNAc inhibition with PD-L1 antibody synergistically promotes antitumor immune response. We also designed a competitive peptide inhibitor of HGS glycosylation that decreases PD-L1 expression and enhances T cell-mediated immunity against tumor cells. Collectively, our study reveals a link between O-GlcNAc and tumor immune evasion, and suggests strategies for improving PD-L1-mediated immune checkpoint blockade therapy.

Astragalus Polysaccharide Promotes Doxorubicin-Induced Apoptosis by Reducing O-GlcNAcylation in Hepatocellular Carcinoma

The toxicity and side effects of chemotherapeutic drugs remain a crucial obstacle to the clinical treatment of hepatocellular carcinoma (HCC). Identifying combination therapy from Chinese herbs to enhance the sensitivity of tumors to chemotherapeutic drugs is of particular interest. Astragalus polysaccharide (APS), one of the natural active components in Astragalus membranaceus, has been reported to exhibit anti-tumor properties in diverse cancer cell lines. The aim of this study was to determine the effect of APS on Doxorubicin (Dox)-induced apoptosis in HCC and the underlying mechanism. The results showed that APS dose-dependently promoted Dox-induced apoptosis and enhanced endoplasmic reticulum (ER) stress. Additionally, APS decreased the mRNA level and protein stability of O-GlcNAc transferase (OGT), and increased the O-GlcNAcase (OGA) expression. Furthermore, OGT lentiviral transfection or PugNAc (OGA inhibitor) treatment reversed the ER stress and apoptosis induced by the combination of Dox and APS. A xenograft tumor mouse model confirmed that the combination of APS and Dox showed an advantage in inhibiting tumor growth in vivo. These findings suggested that APS promoted Dox-induced apoptosis in HCC cells through reducing the O-GlcNAcylation, which led to the exacerbation of ER stress and activation of apoptotic pathways.

The role of O-GlcNAcylation in innate immunity and inflammation

O-linked β-N-acetylglucosaminylation (O-GlcNAcylation) is a highly dynamic and widespread post-translational modification (PTM) that regulates the activity, subcellular localization, and stability of target proteins. O-GlcNAcylation is a reversible PTM controlled by two cycling enzymes: O-linked N-acetylglucosamine transferase and O-GlcNAcase. Emerging evidence indicates that O-GlcNAcylation plays critical roles in innate immunity, inflammatory signaling, and cancer development. O-GlcNAcylation usually occurs on serine/threonine residues, where it interacts with other PTMs, such as phosphorylation. Thus, it likely has a broad regulatory scope. This review discusses the recent research advances regarding the regulatory roles of O-GlcNAcylation in innate immunity and inflammation. A more comprehensive understanding of O-GlcNAcylation could help to optimize therapeutic strategies regarding inflammatory diseases and cancer.

Small Molecule-Activated O-GlcNAcase for Spatiotemporal Removal of O-GlcNAc in Live Cells

The nutrient sensor O-linked N-acetylglucosamine (O-GlcNAc) is a post-translational modification found on thousands of nucleocytoplasmic proteins. O-GlcNAc levels in cells dynamically respond to environmental cues in a temporal and spatial manner, leading to altered signal transduction and functional effects. The spatiotemporal regulation of O-GlcNAc levels would accelerate functional interrogation of O-GlcNAc and manipulation of cell behaviors for desired outcomes. Here, we report a strategy for spatiotemporal reduction of O-GlcNAc in live cells by designing an O-GlcNAcase (OGA) fused to an intein triggered by 4-hydroxytamoxifen (4-HT). After rational protein engineering and optimization, we identified an OGA-intein variant whose deglycosidase activity can be triggered in the desired subcellular compartments by 4-HT in a time- and dose-dependent manner. Finally, we demonstrated that 4-HT activation of the OGA-intein fusion can likewise potentiate inhibitory effects in breast cancer cells by virtue of the reduction of O-GlcNAc. The spatiotemporal control of O-GlcNAc through the chemically activatable OGA-intein fusion will facilitate the manipulation and functional understanding of O-GlcNAc in live cells.

Improved antitumor activity against prostate cancer via synergistic targeting of Myc and GFAT-1

Inhibition of Myc promotes the regression of many types of tumors, including prostate cancer. However, the success of anti-Myc therapy is hampered by the lack of a strategy to effectively deliver the inhibitors to the tumor site and by the feedback mechanisms that cancer cells use to adapt to metabolic reprogramming. Methods: The effects of Myc inhibitors (10074-G5 or 10058-F4), alone or in combination with 6-diazo-5-oxo-L-norleucine (DON), were evaluated in cultured human or murine prostate cancer cells by cell viability assay, qRT-PCR and Western blot. To facilitate the in vivo therapeutic evaluation, a prodrug conjugate of 10074-G4 and DON (10074-DON) was developed, which could be effectively loaded into a polysaccharide-based nanocarrier (PS). Results: The treatment with Myc inhibitors led to significant induction of glutamine: fructose-6-phosphate amidotransferase-1 (GFAT1) and enhanced protein glycosylation. Mechanistically, Myc inhibition triggered GFAT1 induction through the IREα-Xbp1s pathway. The combination use of Myc inhibitors and GFAT1 inhibitor DON led to a synergistic effect in inhibiting the proliferation and migration of prostate cancer cells. Enhanced in vivo delivery of 10074-DON via the PS nanocarrier led to a significant inhibition of tumor growth along with an improvement in tumor immune microenvironment in several PCa animal models. Conclusion: Simultaneous targeting of Myc and GFAT-1 may represent a novel strategy for the treatment of prostate cancer.

O-GlcNAcylation: an important post-translational modification and a potential therapeutic target for cancer therapy

O-linked β-d-N-acetylglucosamine (O-GlcNAc) is an important post-translational modification of serine or threonine residues on thousands of proteins in the nucleus and cytoplasm of all animals and plants. In eukaryotes, only two conserved enzymes are involved in this process. O-GlcNAc transferase is responsible for adding O-GlcNAc to proteins, while O-GlcNAcase is responsible for removing it. Aberrant O-GlcNAcylation is associated with a variety of human diseases, such as diabetes, cancer, neurodegenerative diseases, and cardiovascular diseases. Numerous studies have confirmed that O-GlcNAcylation is involved in the occurrence and progression of cancers in multiple systems throughout the body. It is also involved in regulating multiple cancer hallmarks, such as metabolic reprogramming, proliferation, invasion, metastasis, and angiogenesis. In this review, we first describe the process of O-GlcNAcylation and the structure and function of O-GlcNAc cycling enzymes. In addition, we detail the occurrence of O-GlcNAc in various cancers and the role it plays. Finally, we discuss the potential of O-GlcNAc as a promising biomarker and novel therapeutic target for cancer diagnosis, treatment, and prognosis.

Mass Spectrometry-Based Proteomics of Human Milk to Identify Differentially Expressed Proteins in Women with Breast Cancer versus Controls

It is thought that accurate risk assessment and early diagnosis of breast cancer (BC) can help reduce cancer-related mortality. Proteomics analysis of breast milk may provide biomarkers of risk and occult disease. Our group works on the analysis of human milk samples from women with BC and controls to investigate alterations in protein patterns of milk that could be related to BC. In the current study, we used mass spectrometry (MS)-based proteomics analysis of 12 milk samples from donors with BC and matched controls. Specifically, we used one-dimensional (1D)-polyacrylamide gel electrophoresis (PAGE) coupled with nanoliquid chromatography tandem MS (nanoLC-MS/MS), followed by bioinformatics analysis. We confirmed the dysregulation of several proteins identified previously in a different set of milk samples. We also identified additional dysregulations in milk proteins shown to play a role in cancer development, such as Lactadherin isoform A, O-linked N-acetylglucosamine (GlcNAc) transferase, galactosyltransferase, recoverin, perilipin-3 isoform 1, histone-lysine methyltransferase, or clathrin heavy chain. Our results expand our current understanding of using milk as a biological fluid for identification of BC-related dysregulated proteins. Overall, our results also indicate that milk has the potential to be used for BC biomarker discovery, early detection and risk assessment in young, reproductively active women.

Connexins and Glucose Metabolism in Cancer

Connexins are a family of transmembrane proteins that regulate diverse cellular functions. Originally characterized for their ability to mediate direct intercellular communication through the formation of highly regulated membrane channels, their functions have been extended to the exchange of molecules with the extracellular environment, and the ability to modulate numerous channel-independent effects on processes such as motility and survival. Notably, connexins have been implicated in cancer biology for their context-dependent roles that can both promote or suppress cancer cell function. Moreover, connexins are able to mediate many aspects of cellular metabolism including the intercellular coupling of nutrients and signaling molecules. During cancer progression, changes to substrate utilization occur to support energy production and biomass accumulation. This results in metabolic plasticity that promotes cell survival and proliferation, and can impact therapeutic resistance. Significant progress has been made in our understanding of connexin and cancer biology, however, delineating the roles these multi-faceted proteins play in metabolic adaptation of cancer cells is just beginning. Glucose represents a major carbon substrate for energy production, nucleotide synthesis, carbohydrate modifications and generation of biosynthetic intermediates. While cancer cells often exhibit a dependence on glycolytic metabolism for survival, cellular reprogramming of metabolic pathways is common when blood perfusion is limited in growing tumors. These metabolic changes drive aggressive phenotypes through the acquisition of functional traits. Connections between glucose metabolism and connexin function in cancer cells and the surrounding stroma are now apparent, however much remains to be discovered regarding these relationships. This review discusses the existing evidence in this area and highlights directions for continued investigation.

O-GlcNAcylation: An Emerging Protein Modification Regulating the Hippo Pathway

Simple Summary

The contact point between the Hippo pathway, which serves as a central hub for various external environments, and O-GlcNAcylation, which is a non-canonical glycosylation process acting as a dynamic regulator in various signal transduction pathways, has recently been identified. This review aims to summarize the function of O-GlcNAcylation as an intrinsic and extrinsic regulator of the Hippo pathway.

Abstract

The balance between cellular proliferation and apoptosis and the regulation of cell differentiation must be established to maintain tissue homeostasis. These cellular responses involve the kinase cascade-mediated Hippo pathway as a crucial regulator. Hence, Hippo pathway dysregulation is implicated in diverse diseases, including cancer. O-GlcNAcylation is a non-canonical glycosylation that affects multiple signaling pathways through its interplay with phosphorylation in the nucleus and cytoplasm. An abnormal increase in the O-GlcNAcylation levels in various cancer cells is a potent factor in Hippo pathway dysregulation. Intriguingly, Hippo pathway dysregulation also disrupts O-GlcNAc homeostasis, leading to a persistent elevation of O-GlcNAcylation levels, which is potentially pathogenic in several diseases. Therefore, O-GlcNAcylation is gaining attention as a protein modification that regulates the Hippo pathway. This review presents a framework on how O-GlcNAcylation regulates the Hippo pathway and forms a self-perpetuating cycle with it. The pathological significance of this self-perpetuating cycle and clinical strategies for targeting O-GlcNAcylation that causes Hippo pathway dysregulation are also discussed.

O-GlcNAcylation: The Underestimated Emerging Regulators of Skeletal Muscle Physiology

O-GlcNAcylation is a highly dynamic, reversible and atypical glycosylation that regulates the activity, biological function, stability, sublocation and interaction of target proteins. O-GlcNAcylation receives and coordinates different signal inputs as an intracellular integrator similar to the nutrient sensor and stress receptor, which target multiple substrates with spatio-temporal analysis specifically to maintain cellular homeostasis and normal physiological functions. Our review gives a brief description of O-GlcNAcylation and its only two processing enzymes and HBP flux, which will help to better understand its physiological characteristics of sensing nutrition and environmental cues. This nutritional and stress-sensitive properties of O-GlcNAcylation allow it to participate in the precise regulation of skeletal muscle metabolism. This review discusses the mechanism of O-GlcNAcylation to alleviate metabolic disorders and the controversy about the insulin resistance of skeletal muscle. The level of global O-GlcNAcylation is precisely controlled and maintained in the “optimal zone”, and its abnormal changes is a potential factor in the pathogenesis of cancer, neurodegeneration, diabetes and diabetic complications. Although the essential role of O-GlcNAcylation in skeletal muscle physiology has been widely studied and recognized, it still is underestimated and overlooked. This review highlights the latest progress and potential mechanisms of O-GlcNAcylation in the regulation of skeletal muscle contraction and structural properties.

Inhibition of O-GlcNAcylation Decreases the Cytotoxic Function of Natural Killer Cells

Natural killer (NK) cells mediate killing of malignant and virus-infected cells, a property that is explored as a cell therapy approach in the clinic. Various cell intrinsic and extrinsic factors affect NK cell cytotoxic function, and an improved understanding of the mechanism regulating NK cell function is necessary to accomplish better success with NK cell therapeutics. Here, we explored the role of O-GlcNAcylation, a previously unexplored molecular mechanism regulating NK cell function. O-GlcNAcylation is a post-translational modification mediated by O-GlcNAc transferase (OGT) that adds the monosaccharide N-acetylglucosamine to serine and threonine residues on intracellular proteins and O-GlcNAcase (OGA) that removes the sugar. We found that stimulation of NK cells with the cytokines interleukin-2 (IL-2) and IL-15 results in enhanced O-GlcNAcylation of several cellular proteins. Chemical inhibition of O-GlcNAcylation using OSMI-1 was associated with a decreased expression of NK cell receptors (NKG2D, NKG2A, NKp44), cytokines [tumor necrosis factor (TNF)-α, interferon (IFN-γ)], granulysin, soluble Fas ligand, perforin, and granzyme B in NK cells. Importantly, inhibition of O-GlcNAcylation inhibited NK cell cytotoxicity against cancer cells. However, increases in O-GlcNAcylation following OGA inhibition using an OGA inhibitor or shRNA-mediated suppression did not alter NK cell cytotoxicity. Finally, we found that NK cells pretreated with OSMI-1 to inhibit O-GlcNAcylation showed compromised cytotoxic activity against tumor cells in vivo in a lymphoma xenograft mouse model. Overall, this study provides the seminal insight into the role of O-GlcNAcylation in regulating NK cell cytotoxic function.

Demystifying the O-GlcNAc Code: A Systems View

Post-translational modification with O-linked β-N-acetylglucosamine (O-GlcNAc), a process referred to as O-GlcNAcylation, occurs on a vast variety of proteins. Mounting evidence in the past several decades has clearly demonstrated that O-GlcNAcylation is a unique and ubiquitous modification. Reminiscent of a code, protein O-GlcNAcylation functions as a crucial regulator of nearly all cellular processes studied. The primary aim of this review is to summarize the developments in our understanding of myriad protein substrates modified by O-GlcNAcylation from a systems perspective. Specifically, we provide a comprehensive survey of O-GlcNAcylation in multiple species studied, including eukaryotes (e.g., protists, fungi, plants, Caenorhabditis elegans, Drosophila melanogaster, murine, and human), prokaryotes, and some viruses. We evaluate features (e.g., structural properties and sequence motifs) of O-GlcNAc modification on proteins across species. Given that O-GlcNAcylation functions in a species-, tissue-/cell-, protein-, and site-specific manner, we discuss the functional roles of O-GlcNAcylation on human proteins. We focus particularly on several classes of relatively well-characterized human proteins (including transcription factors, protein kinases, protein phosphatases, and E3 ubiquitin-ligases), with representative O-GlcNAc site-specific functions presented. We hope the systems view of the great endeavor in the past 35 years will help demystify the O-GlcNAc code and lead to more fascinating studies in the years to come.

Path to Clonal Theranostics in Luminal Breast Cancers

Integrating tumor heterogeneity in the drug discovery process is a key challenge to tackle breast cancer resistance. Identifying protein targets for functionally distinct tumor clones is particularly important to tailor therapy to the heterogeneous tumor subpopulations and achieve clonal theranostics. For this purpose, we performed an unsupervised, label-free, spatially resolved shotgun proteomics guided by MALDI mass spectrometry imaging (MSI) on 124 selected tumor clonal areas from early luminal breast cancers, tumor stroma, and breast cancer metastases. 2868 proteins were identified. The main protein classes found in the clonal proteome dataset were enzymes, cytoskeletal proteins, membrane-traffic, translational or scaffold proteins, or transporters. As a comparison, gene-specific transcriptional regulators, chromatin related proteins or transmembrane signal receptor were more abundant in the TCGA dataset. Moreover, 26 mutated proteins have been identified. Similarly, expanding the search to alternative proteins databases retrieved 126 alternative proteins in the clonal proteome dataset. Most of these alternative proteins were coded mainly from non-coding RNA. To fully understand the molecular information brought by our approach and its relevance to drug target discovery, the clonal proteomic dataset was further compared to the TCGA breast cancer database and two transcriptomic panels, BC360 (nanoString^®) and CDx (Foundation One^®). We retrieved 139 pathways in the clonal proteome dataset. Only 55% of these pathways were also present in the TCGA dataset, 68% in BC360 and 50% in CDx. Seven of these pathways have been suggested as candidate for drug targeting, 22 have been associated with breast cancer in experimental or clinical reports, the remaining 19 pathways have been understudied in breast cancer. Among the anticancer drugs, 35 drugs matched uniquely with the clonal proteome dataset, with only 7 of them already approved in breast cancer. The number of target and drug interactions with non-anticancer drugs (such as agents targeting the cardiovascular system, metabolism, the musculoskeletal or the nervous systems) was higher in the clonal proteome dataset (540 interactions) compared to TCGA (83 interactions), BC360 (419 interactions), or CDx (172 interactions). Many of the protein targets identified and drugs screened were clinically relevant to breast cancer and are in clinical trials. Thus, we described the non-redundant knowledge brought by this clone-tailored approach compared to TCGA or transcriptomic panels, the targetable proteins identified in the clonal proteome dataset, and the potential of this approach for drug discovery and repurposing through drug interactions with antineoplastic agents and non-anticancer drugs.

The Beginner’s Guide to O-GlcNAc: From Nutrient Sensitive Pathway Regulation to Its Impact on the Immune System

The addition of N-acetyl glucosamine (GlcNAc) on the hydroxy group of serine/threonine residues is known as O-GlcNAcylation (OGN). The dynamic cycling of this monosaccharide on and off substrates occurs via O-linked β-N-acetylglucosamine transferase (OGT) and O-linked β-N-acetylglucosaminase (OGA) respectively. These enzymes are found ubiquitously in eukaryotes and genetic knock outs of the ogt gene has been found to be lethal in embryonic mice. The substrate scope of these enzymes is vast, over 15,000 proteins across 43 species have been identified with O-GlcNAc. OGN has been known to play a key role in several cellular processes such as: transcription, translation, cell signaling, nutrient sensing, immune cell development and various steps of the cell cycle. However, its dysregulation is present in various diseases: cancer, neurodegenerative diseases, diabetes. O-GlcNAc is heavily involved in cross talk with other post-translational modifications (PTM), such as phosphorylation, acetylation, and ubiquitination, by regulating each other’s cycling enzymes or directly competing addition on the same substrate. This crosstalk between PTMs can affect gene expression, protein localization, and protein stability; therefore, regulating a multitude of cell signaling pathways. In this review the roles of OGN will be discussed. The effect O-GlcNAc exerts over protein-protein interactions, the various forms of crosstalk with other PTMs, and its role as a nutrient sensor will be highlighted. A summary of how these O-GlcNAc driven processes effect the immune system will also be included.

Comparative O-GlcNAc Proteomic Analysis Reveals a Role of O-GlcNAcylated SAM68 in Lung Cancer Aggressiveness

Simple Summary

Lung cancer claims the most lives annually among cancers; to date, invasion and metastasis still pose challenges to effective treatment. O-GlcNAcylation, an enzymatic modification of proteins after biosynthesis, modulates the functions of many proteins. Aberrant O-GlcNAcylation is linked to pathogenic mechanisms of cancer, including invasion and metastasis. However, little is known about the profile of O-GlcNAcylated proteins involved in cancer aggressiveness. Here, by comparing profiles of O-GlcNAcylated proteins from two lung cancer cell lines different in their invasive potential, we identified candidates for O-GlcNAcylated proteins that may be involved in cancer aggressiveness. One of these candidates, SAM68, was further characterized. Results confirmed O-GlcNAcylation of SAM68; functional analyses on SAM68 with mutations at O-GlcNAcylation sites suggested a role of O-GlcNAcylated SAM68 in modulating lung cancer cell migration/invasion. Future elucidation of the functional significance of differential O-GlcNAcylation of proteins identified in this study may provide new insights into mechanisms of lung cancer progression.

Abstract

O-GlcNAcylation is a reversible and dynamic post-translational protein modification catalyzed by O-GlcNAc transferase (OGT). Despite the reported association of O-GlcNAcylation with cancer metastasis, the O-GlcNAc proteome profile for cancer aggressiveness remains largely uncharacterized. Here, we report our comparative O-GlcNAc proteome profiling of two differentially invasive lung adenocarcinoma cell lines, which identified 158 down-regulated and 106 up-regulated candidates in highly invasive cells. Among these differential proteins, a nuclear RNA-binding protein, SAM68 (SRC associated in mitosis of 68 kDa), was further investigated. Results showed that SAM68 is O-GlcNAcylated and may interact with OGT in the nucleus. Eleven O-GlcNAcylation sites were identified, and data from mutant analysis suggested that multiple serine residues in the N-terminal region are important for O-GlcNAcylation and the function of SAM68 in modulating cancer cell migration and invasion. Analysis of clinical specimens found that high SAM68 expression was associated with late cancer stages, and patients with high-OGT/high-SAM68 expression in their tumors had poorer overall survival compared to those with low-OGT/low-SAM68 expression. Our study revealed an invasiveness-associated O-GlcNAc proteome profile and connected O-GlcNAcylated SAM68 to lung cancer aggressiveness.

Upregulation of O-GlcNAc transferase is involved in the pathogenesis of acute myeloid leukemia

BACKGROUND

Acute myeloid leukemia (AML) is the most common acute leukemia in adults. Patients have a low survival rate and a high recurrence rate, and AML is a highly heterogeneous disease without an effective and specific targeted therapy.

AIMS

Therefore, it is urgent to explore new AML markers to enable early diagnosis and find drug targets for individualized treatment.

RESULTS

Herein, we demonstrate that O-linked-N-acetylglucosamine transferase (OGT) is significantly upregulated in AML tissues compared with normal tissues. The high level of OGT expression is significantly related to poor overall survival (OS) in AML. Inhibition of OGT can inhibit AML cell proliferation and promote AML cell apoptosis.

CONCLUSION

These results suggest that OGT plays an important role in the pathogenesis of AML, and may become a potential biomarker and molecular drug target for precision therapy for AML.

O-GlcNAcylation links oncogenic signals and cancer epigenetics

Prevalent dysregulation of epigenetic modifications plays a pivotal role in cancer. Targeting epigenetic abnormality is a new strategy for cancer therapy. Understanding how conventional oncogenic factors cause epigenetic abnormality is of great basic and translational value. O-GlcNAcylation is a protein modification which affects physiology and pathophysiology. In mammals, O-GlcNAcylation is catalyzed by one single enzyme OGT and removed by one single enzyme OGA. O-GlcNAcylation is affected by the availability of the donor, UDP-GlcNAc, generated by the serial enzymatic reactions in the hexoamine biogenesis pathway (HBP). O-GlcNAcylation regulates a wide spectrum of substrates including many proteins involved in epigenetic modification. Like epigenetic modifications, abnormality of O-GlcNAcylation is also common in cancer. Studies have revealed substantial impact on HBP enzymes and OGT/OGA by oncogenic signals. In this review, we will first summarize how oncogenic signals regulate HBP enzymes, OGT and OGA in cancer. We will then integrate this knowledge with the up to date understanding how O-GlcNAcylation regulates epigenetic machinery. With this, we propose a signal axis from oncogenic signals through O-GlcNAcylation dysregulation to epigenetic abnormality in cancer. Further elucidation of this axis will not only advance our understanding of cancer biology but also provide new revenues towards cancer therapy.

O-GlcNAcylation increases PYGL activity by promoting phosphorylation

O-GlcNAcylation is a post-translational modification that links metabolism with signal transduction. High O-GlcNAcylation appears to be the general characteristic of cancer cells. It promotes the invasion, metastasis, proliferation and survival of tumor cells, and alters many metabolic pathways. Glycogen metabolism increases in a wide variety of tumors, suggesting that it is an important aspect of cancer pathophysiology. Herein we focused on the O-GlcNAcylation of liver glycogen phosphorylase (PYGL), an important catabolism enzyme in the glycogen metabolism pathway. PYGL expressed in both HEK 293 T and HCT116 were modified by O-GlcNAc. And both PYGL O-GlcNAcylation and phosphorylation of Ser15 (pSer15) were decreased under glucose and insulin, while increased under glucagon and Na2S2O4 (hypoxia) conditions. Then, we identified the major O-GlcNAcylation site to be Ser430, and demonstrated that pSer15 and Ser430 O-GlcNAcylation were mutually reinforced. Lastly, we found that Ser430 O-GlcNAcylation was fundamental for PYGL activity. Thus, O-GlcNAcylation of PYGL positively regulated pSer15 and therefore its enzymatic activity. Our results provided another molecular insight into the intricate post-translational regulation network of PYGL.

Role and Function of O-GlcNAcylation in Cancer

Simple Summary

Despite the rapid advancement in immunotherapy and targeted agents, many patients diagnosed with cancer have poor prognosis with dismal overall survival. One of the key hallmarks of cancer is the ability of cancer cells to reprogram their energy metabolism. O-GlcNAcylation is an emerging potential mechanism for cancer cells to induce proliferation and progression of tumor cells and resistance to chemotherapy. This review summarizes the mechanism behind O-GlcNAcylation and discusses the role of O-GlcNAcylation, including its function with receptor tyrosine kinase and chemo-resistance in cancer, and immune response to cancer and as a prognostic factor. Further pre-clinical studies on O-GlcNAcylation are warranted to assess the clinical efficacy of agents targeting O-GlcNAcylation.

Abstract

Cancer cells are able to reprogram their glucose metabolism and retain energy via glycolysis even under aerobic conditions. They activate the hexosamine biosynthetic pathway (HBP), and the complex interplay of O-linked N-acetylglucosaminylation (O-GlcNAcylation) via deprivation of nutrients or increase in cellular stress results in the proliferation, progression, and metastasis of cancer cells. Notably, cancer is one of the emerging diseases associated with O-GlcNAcylation. In this review, we summarize studies that delineate the role of O-GlcNAcylation in cancer, including its modulation in metastasis, function with receptor tyrosine kinases, and resistance to chemotherapeutic agents, such as cisplatin. In addition, we discuss the function of O-GlcNAcylation in eliciting immune responses associated with immune surveillance in the tumor microenvironment. O-GlcNAcylation is increasingly accepted as one of the key players involved in the activation and differentiation of T cells and macrophages. Finally, we discuss the prognostic role of O-GlcNAcylation and potential therapeutic agents such as O-linked β-N-acetylglucosamine-transferase inhibitors, which may help overcome the resistance mechanism associated with the reprogramming of glucose metabolism.

Regulation of Nuclear Factor-kappaB Function by O-GlcNAcylation in Inflammation and Cancer

Nuclear factor-kappaB (NF-κB) is a pleiotropic, evolutionarily conserved transcription factor family that plays a central role in regulating immune responses, inflammation, cell survival, and apoptosis. Great strides have been made in the past three decades to understand the role of NF-κB in physiological and pathological conditions. Carcinogenesis is associated with constitutive activation of NF-κB that promotes tumor cell proliferation, angiogenesis, and apoptosis evasion. NF-κB is ubiquitously expressed, however, its activity is under tight regulation by inhibitors of the pathway and through multiple posttranslational modifications. O-GlcNAcylation is a dynamic posttranslational modification that controls NF-κB-dependent transactivation. O-GlcNAcylation acts as a nutrient-dependent rheostat of cellular signaling. Increased uptake of glucose and glutamine by cancer cells enhances NF-κB O-GlcNAcylation. Growing evidence indicates that O-GlcNAcylation of NF-κB is a key molecular mechanism that regulates cancer cell proliferation, survival and metastasis and acts as link between inflammation and cancer. In this review, we are attempting to summarize the current understanding of the cohesive role of NF-κB O-GlcNAcylation in inflammation and cancer.

Upregulation of OGT by Caveolin-1 promotes hepatocellular carcinoma cell migration and invasion

Caveolin-1 (CAV1), a major structural protein of caveolae, is reported to exert a positive regulatory effect on tumor growth and to play a crucial role in hepatocellular carcinoma (HCC) cell metastasis by regulating glycosyltransferase expression and cellular glycosylation. However, the role of CAV1 in modulating protein glycosylation and tumor metastasis remains to be further elucidated. In the present study, we showed that CAV1 promoted the expression of O-GlcNAc transferase (OGT), which catalyzed the addition of O-GlcNAc residues to a variety of nuclear and cytoplasmic proteins. In human HCC cell lines with different metastatic potentials, high levels of OGT and cellular O-GlcNAcylation were associated with CAV1 expression and cell metastasis. Overexpression of CAV1 increased the levels of OGT and O-GlcNAcylation, and cell migration was also increased. Furthermore, CAV1 was found to reduce the expression of Runt-related transcription factor 2 (RUNX2) in HCC cells. Subsequently, this effect resulted in the attenuation of the RUNX2-induced transcription of microRNA24 (miR24), a microRNA previously shown to suppress OGT mRNA expression by targeting its 3' untranslated regions (UTR). Finally, we demonstrated that CAV1 induced cellular O-GlcNAcylation and HCC cell invasion. This study provides evidence of CAV1-mediated increases in OGT expression and O-GlcNAcylation. These data provide insight into a novel mechanism underlying HCC metastasis and suggest a novel strategy for the treatment of HCC.

RANBP2 Activates O-GlcNAcylation through Inducing CEBPα-Dependent OGA Downregulation to Promote Hepatocellular Carcinoma Malignant Phenotypes

O-GlcNAcylation is an important post-translational modification (PTM) jointly controlled by O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA). Aberrant hyper-O-GlcNAcylation is reported to yield hepatocellular carcinoma (HCC) malignancy, but the underlying mechanisms of the OGT/OGA imbalance responsible for HCC tumorigenesis remain largely unknown. Here, we report that RAN-binding protein 2 (RANBP2), one of the small ubiquitin-like modifier (SUMO) E3 ligases, contributed to malignant phenotypes in HCC. RANBP2 was found to facilitate CCAAT/enhancer-binding protein alpha (CEBPα) SUMOylation and degradation by direct interplay with CEBPα. As a transcriptional factor, CEBPα was verified to augment OGA transcription, and further experiments demonstrated that RANBP2 enhanced the O-GlcNAc level by downregulating OGA transcription while not affecting OGT expression. Importantly, we provided in vitro and in vivo evidence of HCC malignant phenotypes that RANBP2 triggered through an imbalance of OGT/OGA and subsequent higher O-GlcNAcylation events for oncogenic proteins such as peroxisome proliferative-activated receptor gamma coactivator 1 alpha (PGC1α) in a CEBPα-dependent manner. Altogether, our results show a novel molecular mechanism whereby RANBP2 regulates its function through CEBPα-dependent OGA downregulation to induce a global change in the hyper-O-GlcNAcylation of genes, such as PGC1α, encouraging the further study of promising implications for HCC therapy.

Machine Learning-Enabled Renal Cell Carcinoma Status Prediction Using Multiplatform Urine-Based Metabolomics

Renal cell carcinoma (RCC) is diagnosed through expensive cross-sectional imaging, frequently followed by renal mass biopsy, which is not only invasive but also prone to sampling errors. Hence, there is a critical need for a noninvasive diagnostic assay. RCC exhibits altered cellular metabolism combined with the close proximity of the tumor(s) to the urine in the kidney, suggesting that urine metabolomic profiling is an excellent choice for assay development. Here, we acquired liquid chromatography-mass spectrometry (LC-MS) and nuclear magnetic resonance (NMR) data followed by the use of machine learning (ML) to discover candidate metabolomic panels for RCC. The study cohort consisted of 105 RCC patients and 179 controls separated into two subcohorts: the model cohort and the test cohort. Univariate, wrapper, and embedded methods were used to select discriminatory features using the model cohort. Three ML techniques, each with different induction biases, were used for training and hyperparameter tuning. Assessment of RCC status prediction was evaluated using the test cohort with the selected biomarkers and the optimally tuned ML algorithms. A seven-metabolite panel predicted RCC in the test cohort with 88% accuracy, 94% sensitivity, 85% specificity, and 0.98 AUC. Metabolomics Workbench Study IDs are ST001705 and ST001706.

O-GlcNAcylation in early stages of chronic lymphocytic leukemia; protocol development for flow cytometry

BACKGROUND

Recent studies proved that metabolic changes in malignant disorders have an impact on protein glycosylation, however, only a few attempts have been made so far to use O-GlcNAc analysis as a prognostic tool. Glucose metabolism is reported to be altered in hematological malignancies thus, we hypothesized that monitoring intracellular O-GlcNAc levels in Rai stage 0-I (Binet A) CLL patients could give deeper insights regarding subtle metabolic changes of progression which are not completely detected by the routine follow-up procedures.

OBJECTIVE

In this proof of concept study we established a flow cytometric detection method for the assessment of O-GlcNAcylation as a possible prognostic marker in CLL malignancy which was supported by fluorescence microscopy.

METHODS

Healthy volunteers and CLL patients were recruited for this study. Lymphocytes were isolated, fixed and permeabilised by various methods to find the optimal experimental condition for O-GlcNAc detection by flow cytometry. O-GlcNAc levels were measured and compared to lymphocyte count and various blood parameters including plasma glucose level.

RESULTS

The protocol we developed includes red blood cell lysis, formalin fixation, 0.1% Tween 20 permeabilisation and employs standardized cell number per sample and unstained controls. We have found significant correlation between O-GlcNAc levels and WBC (R2= 0.8535, p< 0.0029) and lymphocyte count (R2= 0.9225, p< 0.0006) in CLL patients. Interestingly, there was no such correlation in healthy individuals (R2= 0.05664 for O-GlcNAc vs WBC and R2= 0.04379 for O-GlcNAc vs lymphocytes).

CONCLUSION

Analyzing O-GlcNAc changes in malignant disorders, specifically in malignant hematologic diseases such as CLL, could be a useful tool to monitor the progression of the disease.

Detection and Analysis of Proteins Modified by O-Linked N-Acetylglucosamine

O-GlcNAc is a common post-translational modification of nuclear, mitochondrial, and cytoplasmic proteins that regulates normal physiology and the cell stress response. Dysregulation of O-GlcNAc cycling is implicated in the etiology of type II diabetes, heart failure, hypertension, and Alzheimer's disease, as well as cardioprotection. These protocols cover simple and comprehensive techniques for detecting proteins modified by O-GlcNAc and studying the enzymes that add or remove O-GlcNAc. © 2021 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Increasing the stoichiometry of O-GlcNAc on proteins before analysis Basic Protocol 2: Detection of proteins modified by O-GlcNAc using antibodies Basic Protocol 3: Detection of proteins modified by O-GlcNAc using the lectin sWGA Support Protocol 1: Control for O-linked glycosylation Basic Protocol 4: Detection and enrichment of proteins using WGA-agarose Support Protocol 2: Digestion of proteins with hexosaminidase Alternate Protocol: Detection of proteins modified by O-GlcNAc using galactosyltransferase Support Protocol 3: Autogalactosylation of galactosyltransferase Support Protocol 4: Assay of galactosyltransferase activity Basic Protocol 5: Characterization of labeled glycans by β-elimination and chromatography Basic Protocol 6: Detection of O-GlcNAc in 96-well plates Basic Protocol 7: Assay for OGT activity Support Protocol 5: Desalting of O-GlcNAc transferase Basic Protocol 8: Assay for O-GlcNAcase activity.