Overexpression of O-GlcNAc by prostate cancer cells is significantly associated with poor prognosis of patients

Salivary metabolomics in oral potentially malignant disorders and oral cancer patients-a systematic review with meta-analysis

OBJECTIVES

The aim of this systematic review and meta-analysis is to assess the diagnostic potential of salivary metabolomics in the detection of oral potentially malignant disorders (OPMDs) and oral cancer (OC).

MATERIALS AND METHODS

A systematic review was performed in accordance with the 3rd edition of the Centre for Reviews and Dissemination (CRD) and Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) statement. Electronic searches for articles were carried out in the PubMed, Web of Science, and Scopus databases. The quality assessment of the included studies was evaluated using the Newcastle-Ottawa Quality Assessment Scale (NOS) and the new version of the QUADOMICS tool. Meta-analysis was conducted whenever possible. The effect size was presented using the Forest plot, whereas the presence of publication bias was examined through Begg's funnel plot.

RESULTS

A total of nine studies were included in the systematic review. The metabolite profiling was heterogeneous across all the studies. The expression of several salivary metabolites was found to be significantly altered in OPMDs and OCs as compared to healthy controls. Meta-analysis was able to be conducted only for N-acetylglucosamine. There was no significant difference (SMD = 0.15; 95% CI - 0.25-0.56) in the level of N-acetylglucosamine between OPMDs, OC, and the control group.

CONCLUSION

Evidence for N-acetylglucosamine as a salivary biomarker for oral cancer is lacking. Although several salivary metabolites show changes between healthy, OPMDs, and OC, their diagnostic potential cannot be assessed in this review due to a lack of data. Therefore, further high-quality studies with detailed analysis and reporting are required to establish the diagnostic potential of the salivary metabolites in OPMDs and OC.

CLINICAL RELEVANCE

While some salivary metabolites exhibit significant changes in oral potentially malignant disorders (OPMDs) and oral cancer (OC) compared to healthy controls, the current evidence, especially for N-acetylglucosamine, is inadequate to confirm their reliability as diagnostic biomarkers. Additional high-quality studies are needed for a more conclusive assessment of salivary metabolites in oral disease diagnosis.

Role of O-GlcNAcylation in cancer biology

One of the general characteristics of cancer cells is the abnormal increase of O-GlcNAcylation. Recent studies have shown that it affects the basic functions of proteins and regulates multiple phenotypes of cancer cells through key signals and metabolic pathways. O-GlcNAcylation is a covalent linkage between the β-D-N-acetylglucosamine (GlcNAc) sugar and target protein. It interacts with many other types of post-translational modifications and works together in the whole process of cancer development. For example, it regulates cell activities such as cell signal transduction, transcription, cell division, metabolism and cytoskeleton regulation. In this review, we summarized the general concept of O-GlcNAcylation and its related role in the ten major tumor phenotypes.

O-GlcNAcylation in cancer development and immunotherapy

O-linked β-D-N-acetylglucosamine (O-GlcNAc), as a posttranslational modification (PTM), is a reversible reaction that attaches β-N-GlcNAc to Ser/Thr residues on specific proteins by O-GlcNAc transferase (OGT). O-GlcNAcase (OGA) removes the O-GlcNAc from O-GlcNAcylated proteins. O-GlcNAcylation regulates numerous cellular processes, including signal transduction, the cell cycle, metabolism, and energy homeostasis. Dysregulation of O-GlcNAcylation contributes to the development of various diseases, including cancers. Accumulating evidence has revealed that higher expression levels of OGT and hyper-O-GlcNAcylation are detected in many cancer types and governs glucose metabolism, proliferation, metastasis, invasion, angiogenesis, migration and drug resistance. In this review, we describe the biological functions and molecular mechanisms of OGT- or O-GlcNAcylation-mediated tumorigenesis. Moreover, we discuss the potential role of O-GlcNAcylation in tumor immunotherapy. Furthermore, we highlight that compounds can target O-GlcNAcylation by regulating OGT to suppress oncogenesis. Taken together, targeting protein O-GlcNAcylation might be a promising strategy for the treatment of human malignancies.

HIPK2 in cancer biology and therapy: Recent findings and future perspectives

Homeodomain-interacting protein kinase 2 (HIPK2) is a serine-threonine kinase that phosphorylates and regulates a plethora of transcriptional regulators and chromatin modifiers. The heterogeneity of its interactome allows HIPK2 to modulate several cellular processes and signaling pathways, ultimately regulating cell fate and proliferation. Because of its p53-dependent pro-apoptotic activity and its downregulation in many tumor types, HIPK2 is traditionally considered a bone fide tumor suppressor gene. However, recent findings revealed that the role of HIPK2 in the pathogenesis of cancer is much more complex, ranging from tumor suppressive to oncogenic, strongly depending on the cellular context. Here, we review the very recent data emerged in the last years about the involvement of HIPK2 in cancer biology and therapy, highlighting the various alterations of this kinase (downregulation, upregulation, mutations and/or delocalization) in dependence on the cancer types. In addition, we discuss the recent advancement in the understanding the tumor suppressive and oncogenic functions of HIPK2, its role in establishing the response to cancer therapies, and its regulation by cancer-associated microRNAs. All these data strengthen the idea that HIPK2 is a key player in many types of cancer; therefore, it could represent an important prognostic marker, a factor to predict therapy response, and even a therapeutic target itself.

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.

Inhibition of O-GlcNAc transferase sensitizes prostate cancer cells to docetaxel

The expression of O-GlcNAc transferase (OGT) and its catalytic product, O-GlcNAcylation (O-GlcNAc), are elevated in many types of cancers, including prostate cancer (PC). Inhibition of OGT serves as a potential strategy for PC treatment alone or combinational therapy. PC is the second common cancer type in male worldwide, for which chemotherapy is still the first-line treatment. However, the function of inhibition of OGT on chemotherapeutic response in PC cells is still unknown. In this study, we show that inhibition of OGT by genetic knockdown using shRNA or by chemical inhibition using OGT inhibitors sensitize PC cells to docetaxel, which is the most common chemotherapeutic agent in PC chemotherapy. Furthermore, we identified that microRNA-140 (miR-140) directly binds to OGT mRNA 3' untranslated region and inhibits OGT expression. Moreover, docetaxel treatment stimulates miR-140 expression, whereas represses OGT expression in PC cells. Overexpression of miR-140 enhanced the drug sensitivity of PC cells to docetaxel, which could be reversed by overexpression of OGT. Overall, this study demonstrates miR-140/OGT axis as therapeutic target in PC treatment and provides a promising adjuvant therapeutic strategy for PC therapy.

VPRBP Functions Downstream of the Androgen Receptor and OGT to Restrict p53 Activation in Prostate Cancer

Androgen receptor (AR) is a major driver of prostate cancer initiation and progression. O-GlcNAc transferase (OGT), the enzyme that catalyzes the covalent addition of UDP-N-acetylglucosamine (UDP-GlcNAc) to serine and threonine residues of proteins, is often highly expressed in prostate cancer with its expression correlated with high Gleason score. In this study, we have identified an AR and OGT coregulated factor, Vpr (HIV-1) binding protein (VPRBP) also known as DDB1 and CUL4 Associated Factor 1 (DCAF1). We show that VPRBP is regulated by the AR at the transcript level, and stabilized by OGT at the protein level. VPRBP knockdown in prostate cancer cells led to a significant decrease in cell proliferation, p53 stabilization, nucleolar fragmentation, and increased p53 recruitment to the chromatin. In human prostate tumor samples, VPRBP protein overexpression correlated with AR amplification, OGT overexpression, a shorter time to postoperative biochemical progression and poor clinical outcome. In clinical transcriptomic data, VPRBP expression was positively correlated with the AR and also with AR activity gene signatures.

IMPLICATIONS

In conclusion, we have shown that VPRBP/DCAF1 promotes prostate cancer cell proliferation by restraining p53 activation under the influence of the AR and OGT.

The Glycobiology of Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a progressive pulmonary vascular disease of complex etiology. Cases of PAH that do not receive therapy after diagnosis have a low survival rate. Multiple reports have shown that idiopathic PAH, or IPAH, is associated with metabolic dysregulation including altered bioavailability of nitric oxide (NO) and dysregulated glucose metabolism. Multiple processes such as increased proliferation of pulmonary vascular cells, angiogenesis, apoptotic resistance, and vasoconstriction may be regulated by the metabolic changes demonstrated in PAH. Recent reports have underscored similarities between metabolic abnormalities in cancer and IPAH. In particular, increased glucose uptake and altered glucose utilization have been documented and have been linked to the aforementioned processes. We were the first to report a link between altered glucose metabolism and changes in glycosylation. Subsequent reports have highlighted similar findings, including a potential role for altered metabolism and aberrant glycosylation in IPAH pathogenesis. This review will detail research findings that demonstrate metabolic dysregulation in PAH with an emphasis on glycobiology. Furthermore, this report will illustrate the similarities in the pathobiology of PAH and cancer and highlight the novel findings that researchers have explored in the field.

Ogt Demonstrated Conspicuous Clinical Significance in Cancers, from Pan-Cancer to Small-Cell Lung Cancer

The clinical progression of small-cell lung cancer (SCLC) remains pessimistic. The aim of the present study was to promote the understanding of the clinical significance and mechanism of O-linked N-acetylglucosamine (GlcNAc) transferase (OGT) in SCLC. Wilcoxon tests, standardized mean difference (SMD), and Kruskal–Wallis tests were utilized to compare OGT level differences among the experimental and control groups. The univariate Cox regression analysis, Kaplan–Meier curves, and receiver operating characteristic curves were applied to determine OGT's clinical relevance in cancers. The Spearman correlation analysis and enrichment analysis were utilized to explore the underlying mechanisms of OGT in cancers. For the first time in the field, we provide an overview of OGT in 32 cancers using a large number of samples (n = 21,196), determining distinct OGT expression in 25 cancers and its prognosis effects in 12 cancers. Furthermore, using 950 samples from multiple sources, upregulated OGT was found in both mRNA and protein levels in SCLC (SMD = 0.93, 95% CI [0.24, 1.63]). Higher OGT levels represented a more unfavorable disease-free interval for SCLC patients (p < 0.001). The research also identified OGT expression as a potential marker for SCLC prediction (sensitivity = 0.79, specificity = 0.86, and AUC = 0.88). The high expression of OGT in SCLC may result from the positive regulation of two transcription factors—DEK and XRN2. We primarily investigated the underlying mechanisms of OGT in SCLC. Herein, based on the analyses from pan-cancer to SCLC, OGT demonstrated conspicuous clinical significance. OGT may be an underlying biomarker for the treatment and identification of some cancers, including SCLC.

O-GlcNAcylation regulates β1,4-GlcNAc-branched N-glycan biosynthesis via the OGT/SLC35A3/GnT-IV axis

N-Linked glycosylation and O-linked N-acetylglucosamine (O-GlcNAc) are important protein post-translational modifications that are orchestrated by a diverse set of gene products. Thus far, the relationship between these two types of glycosylation has remained elusive, and it is unclear whether one influences the other via UDP-GlcNAc, which is a common donor substrate. Theoretically, a decrease in O-GlcNAcylation may increase the products of GlcNAc-branched N-glycans. In this study, via examination by lectin blotting, HPLC, and mass spectrometry analysis, however, we found that the amounts of GlcNAc-branched tri-antennary N-glycans catalyzed by N-acetylglucosaminyltransferase IV (GnT-IV) and tetra-antennary N-glycans were significantly decreased in O-GlcNAc transferase knockdown cells (OGT-KD) compared with those in wild type cells. We examined this specific alteration by focusing on SLC35A3, which is the main UDP-GlcNAc transporter in mammals that is believed to modulate GnT-IV activation. It is interesting that a deficiency of SLC35A3 specifically leads to a decrease in the amounts of GlcNAc-branched tri- and tetra-antennary N-glycans. Furthermore, co-immunoprecipitation experiments have shown that SLC35A3 interacts with GnT-IV, but not with N-acetylglucosaminyltransferase V. Western blot and chemoenzymatic labeling assay have confirmed that OGT modifies SLC35A3 and that O-GlcNAcylation contributes to its stability. Furthermore, we found that SLC35A3-KO enhances cell spreading and suppresses both cell migration and cell proliferation, which is similar to the phenomena observed in the OGT-KD cells. Taken together, these data are the first to demonstrate that O-GlcNAcylation specifically governs the biosynthesis of tri- and tetra-antennary N-glycans via the OGT-SLC35A3-GnT-IV axis.

Glycosylation Changes in Prostate Cancer Progression

Prostate Cancer (PCa) is the most commonly diagnosed malignancy and second leading cause of cancer-related mortality in men. With the use of next generation sequencing and proteomic platforms, new biomarkers are constantly being developed to both improve diagnostic sensitivity and specificity and help stratify patients into different risk groups for optimal management. In recent years, it has become well accepted that altered glycosylation is a hallmark of cancer progression and that the glycan structures resulting from these mechanisms show tremendous promise as both diagnostic and prognostic biomarkers. In PCa, a wide range of structural alterations to glycans have been reported such as variations in sialylation and fucosylation, changes in branching, altered levels of Lewis and sialyl Lewis antigens, as well as the emergence of high mannose "cryptic" structures, which may be immunogenic and therapeutically relevant. Furthermore, aberrant expression of galectins, glycolipids, and proteoglycans have also been reported and associated with PCa cell survival and metastasis. In this review, we discuss the findings from various studies that have explored altered N- and O-linked glycosylation in PCa tissue and body fluids. We further discuss changes in O-GlcNAcylation as well as altered expression of galectins and glycoconjugates and their effects on PCa progression. Finally, we emphasize the clinical utility and potential impact of exploiting glycans as both biomarkers and therapeutic targets to improve our ability to diagnose clinically relevant tumors as well as expand treatment options for patients with advanced disease.

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.

Relationship Between O-GlcNAcase Expression and Prognosis of Patients With Osteosarcoma

Several studies have demonstrated a role of O-GlcNAcylation (O-GlcNAc) in tumorigenesis of various carcinomas by modification of tumor-associated proteins. However, its implication in the pathogenesis of osteosarcoma remains unclear. This study aimed to investigate the levels of O-GlcNAc and the expressions of O-linked N-acetylglucosamine transferase (OGT) and O-GlcNAcase (OGA) in human osteosarcoma tissues, by using immunohistochemistry; and to find correlations between the levels or expressions and several clinicopathologic parameters. There were 109 first diagnosed osteosarcoma patients, including Enneking stage IIB (n=70) and III (n=39). Correlations between the immunoreactive score (IRS) and clinicopathologic parameters, overall survival, and metastasis-free survival were evaluated. A positive correlation was found between the IRS of OGA and the percentage of postchemotherapeutic tumor necrosis (r=0.308; P=0.017). Univariate analysis revealed significantly lower OGA IRS in metastatic patients (P=0.020) and poor chemotherapeutic-responder patients (P=0.001). By multivariate analysis, presence of tumor metastasis (P=0.002) and lower OGA IRS (P=0.004) was significantly associated with shorter overall survival. Subgroup analysis in stage IIB osteosarcoma (n=70) demonstrated that male sex (P=0.019), presence of tumor recurrence (P=0.026), poor chemotherapeutic responder (P=0.022), and lower OGA IRS (P=0.019) were significantly correlated with short metastasis-free survival. But, lower OGA IRS was the only independent predictor for short metastasis-free survival (P=0.006). Our findings suggested that O-GlcNAc pathway, especially OGA, may involve in pathogenesis and aggressiveness of osteosarcoma. Low level of OGA expression may be used as a poor prognostic indicator.

The hexosamine biosynthetic pathway and cancer: Current knowledge and future therapeutic strategies

The hexosamine biosynthetic pathway (HBP) is a glucose metabolism pathway that results in the synthesis of a nucleotide sugar UDP-GlcNAc, which is subsequently used for the post-translational modification (O-GlcNAcylation) of intracellular proteins that regulate nutrient sensing and stress response. The HBP is carried out by a series of enzymes, many of which have been extensively implicated in cancer pathophysiology. Increasing evidence suggests that elevated activation of the HBP may act as a cancer biomarker. Inhibition of HBP enzymes could suppress tumor cell growth, modulate the immune response, reduce resistance, and sensitize tumor cells to conventional cancer therapy. Therefore, targeting the HBP may serve as a novel strategy for treating cancer patients. Here, we review the current findings on the significance of HBP enzymes in various cancers and discuss future approaches for exploiting HBP inhibition for cancer treatment.

Signalling transduction of O-GlcNAcylation and PI3K/AKT/mTOR-axis in prostate cancer

Hexosamine biosynthetic (HBP) and PI3K/AKT/mTOR pathways are found to predominate the proliferation and survival of prostate cancer cells. Both these pathways have their own specific intermediates to propagate the secondary signals in down-stream cascades and besides having their own structured network, also have shared interconnecting branches. These interconnections are either competitive or co-operative in nature depending on the microenvironmental conditions. Specifically, in prostate cancer HBP and mTOR pathways increases the expression and protein level of androgen receptor in order to support cancer cell proliferation, advancement and metastasis. Pharmacological inhibition of a single pathway is therefore insufficient to stop disease progression as the cancer cells manage to alter the signalling channel. This is one of the primary reasons for the therapeutic failure in prostate cancer and emergence of chemoresistance. Inhibition of these multiple pathways at their common junctures might prove to be of benefit in men suffering from an advanced disease state. Hence, a thorough understanding of these cellular intersecting points and their significance with respect to signal transduction mechanisms might assist in the rational designing of combinations for effective management of prostate cancer.

New Insights Into the Biology of Protein O-GlcNAcylation: Approaches and Observations

O-GlcNAcylation is a protein posttranslational modification that results in the addition of O-GlcNAc to Ser/Thr residues. Since its discovery in the 1980s, it has been shown to play an important role in a broad range of cellular functions by modifying nuclear, cytosolic, and mitochondrial proteins. The addition of O-GlcNAc is catalyzed by O-GlcNAc transferase (OGT), and its removal is catalyzed by O-GlcNAcase (OGA). Levels of protein O-GlcNAcylation change in response to nutrient availability and metabolic, oxidative, and proteotoxic stress. OGT and OGA levels, activity, and target engagement are also regulated. Together, this results in adaptive and, on occasions, detrimental responses that affect cellular function and survival, which impact a broad range of pathologies and aging. Over the past several decades, approaches and tools to aid the investigation of the regulation and consequences of protein O-GlcNAcylation have been developed and enhanced. This review is divided into two sections: 1) We will first focus on current standard and advanced technical approaches for assessing enzymatic activities of OGT and OGT, assessing the global and specific protein O-GlcNAcylation and 2) we will summarize in vivo findings of functional consequences of changing protein O-GlcNAcylation, using genetic and pharmacological approaches.

Roles of CNC Transcription Factors NRF1 and NRF2 in Cancer

Simple Summary

Although NRF1 (nuclear factor erythroid 2-like 1; NFE2L1) and NRF2 (nuclear factor erythroid 2-like 2; NFE2L2) belong to the CNC (cap‘n’collar) transcription factor family and share DNA recognition elements, their functions in vivo are substantially different. In cancer cells, while NRF2 confers therapeutic resistance via increasing antioxidant capacity and modulating glucose and glutamine metabolism, NRF1 confers therapeutic resistance via triggering proteasome bounce back response. Proteasome inhibition activates NRF1, and NRF1, in turn, activates the proteasome by inducing the transcriptional activation of proteasome subunit genes. One of the oncometabolites, UDP-GlcNAc (uridine diphosphate N-acetylglucosamine), has been found to be a key to the NRF1-mediated proteasome bounce back response. In this review, we introduce the roles of NRF1 in the cancer malignancy in comparison with NRF2.

Abstract

Cancer cells exhibit unique metabolic features and take advantage of them to enhance their survival and proliferation. While the activation of NRF2 (nuclear factor erythroid 2-like 2; NFE2L2), a CNC (cap‘n’collar) family transcription factor, is effective for the prevention and alleviation of various diseases, NRF2 contributes to cancer malignancy by promoting aggressive tumorigenesis and conferring therapeutic resistance. NRF2-mediated metabolic reprogramming and increased antioxidant capacity underlie the malignant behaviors of NRF2-activated cancer cells. Another member of the CNC family, NRF1, plays a key role in the therapeutic resistance of cancers. Since NRF1 maintains proteasome activity by inducing proteasome subunit genes in response to proteasome inhibitors, NRF1 protects cancer cells from proteotoxicity induced by anticancer proteasome inhibitors. An important metabolite that activates NRF1 is UDP-GlcNAc (uridine diphosphate N-acetylglucosamine), which is abundantly generated in many cancer cells from glucose and glutamine via the hexosamine pathway. Thus, the metabolic signatures of cancer cells are closely related to the oncogenic and tumor-promoting functions of CNC family members. In this review, we provide a brief overview of NRF2-mediated cancer malignancy and elaborate on NRF1-mediated drug resistance affected by an oncometabolite UDP-GlcNAc.

O-GlcNAcylation Enhances NUSAP1 Stability and Promotes Bladder Cancer Aggressiveness

Objective

NUSAPl and O-GlcNAcylation were reported to be hyper-activated in many kinds of cancers and involved in the advanced progression of cancers. In bladder cancer, O-GlcNAc transferase (OGT) expresses in patients' urine samples, with no expression in healthy individuals, indicating O-GlcNAcylation might involve in the occurrence and development of bladder cancer. Therefore, the present study aims to investigate the effects of O-GlcNAcylation in bladder cancer and if it can regulate NUSAP1 protein.

Materials and Methods

Western blot, immunohistochemistry, and PCR were used to evaluate the protein expression and mRNA level of NUSAP1; CCK-8 and flow cytometry used to evaluate the proliferation and inhibited the apoptosis of bladder cancer.

Results

The results showed that NUSAP1 was highly expressed in bladder cancer cells and tissue samples. NUSAP1 up-regulation significantly promoted the proliferation and inhibited the apoptosis of bladder cancer HT-1376 and T24 cells. Besides, the expression of O-GlcNAc was elevated in bladder cancer tissues and cells, and up-regulation of O-GlcNAc with GlcNAc and PuGNAc obviously increased NUSAP1 protein expression and stability. Moreover, knockdown OGT significantly inhibited the proliferation and tumorigenesis and promoted the apoptosis of bladder cancer cells, confirmed by CCK-8, in vivo xenotransplantation, and flow cytometry, whereas these roles were impaired when NUSAP1 was up-regulated.

Conclusion

Overall, our study makes clear that hyper-O-GlcNAcylation accelerates bladder cancer progression through promotion of NUSAP1 expression and its stability.

Functional Analysis of O-GlcNAcylation in Cancer Metastasis

One common and reversible type of post-translational modification (PTM) is the addition of O-linked β-N-acetylglucosamine (O-GlcNAc) modification (O-GlcNAcylation), and its dynamic balance is controlled by O-GlcNAc transferase (OGT) and glycoside hydrolase O-GlcNAcase (OGA) through the addition or removal of O-GlcNAc groups. A large amount of research data confirms that proteins regulated by O-GlcNAcylation play a pivotal role in cells. In particularly, imbalanced levels of OGT and O-GlcNAcylation have been found in various types of cancers. Recently, increasing evidence shows that imbalanced O-GlcNAcylation directly or indirectly impacts the process of cancer metastasis. This review summarizes the current understanding of the influence of O-GlcNAc-proteins on the regulation of cancer metastasis. It will provide a theoretical basis to further elucidate of the molecular mechanisms underlying cancer emergence and progression.

Altered glycosylation in cancer: A promising target for biomarkers and therapeutics

Glycosylation is a well-regulated cell and microenvironment specific post-translational modification. Several glycosyltransferases and glycosidases orchestrate the addition of defined glycan structures on the proteins and lipids. Recent advances and systemic approaches in glycomics have significantly contributed to a better understanding of instrumental roles of glycans in health and diseases. Emerging research evidence recognized aberrantly glycosylated proteins as the modulators of the malignant phenotype of cancer cells. The Cancer Genome Atlas has identified alterations in the expressions of glycosylation-specific genes that are correlated with cancer progression. However, the mechanistic basis remains poorly explored. Recent researches have shown that specific changes in the glycan structures are associated with 'stemness' and epithelial-to-mesenchymal transition of cancer cells. Moreover, epigenetic changes in the glycosylation pattern make the tumor cells capable of escaping immunosurveillance mechanisms. The deciphering roles of glycans in cancer emphasize that glycans can serve as a source for the development of novel clinical biomarkers. The ability of glycans in intervening various stages of tumor progression and the biosynthetic pathways involved in glycan structures constitute a promising target for cancer therapy. Advances in the knowledge of innovative strategies for identifying the mechanisms of glycan-binding proteins are hoped to hold great potential in cancer therapy. This review discusses the fundamental role of glycans in regulating tumorigenesis and tumor progression and provides insights into the influence of glycans in the current tactics of targeted therapies in the clinical setting.

Inhibition of O-GlcNAc Transferase Renders Prostate Cancer Cells Dependent on CDK9

O-GlcNAc transferase (OGT) is a nutrient-sensitive glycosyltransferase that is overexpressed in prostate cancer, the most common cancer in males. We recently developed a specific and potent inhibitor targeting this enzyme, and here, we report a synthetic lethality screen using this compound. Our screen identified pan-cyclin-dependent kinase (CDK) inhibitor AT7519 as lethal in combination with OGT inhibition. Follow-up chemical and genetic approaches identified CDK9 as the major target for synthetic lethality with OGT inhibition in prostate cancer cells. OGT expression is regulated through retention of the fourth intron in the gene and CDK9 inhibition blunted this regulatory mechanism. CDK9 phosphorylates carboxy-terminal domain (CTD) of RNA Polymerase II to promote transcription elongation. We show that OGT inhibition augments effects of CDK9 inhibitors on CTD phosphorylation and general transcription. Finally, the combined inhibition of both OGT and CDK9 blocked growth of organoids derived from patients with metastatic prostate cancer, but had minimal effects on normal prostate spheroids. We report a novel synthetic lethal interaction between inhibitors of OGT and CDK9 that specifically kills prostate cancer cells, but not normal cells. Our study highlights the potential of combining OGT inhibitors with other treatments to exploit cancer-specific vulnerabilities. IMPLICATIONS: The primary contribution of OGT to cell proliferation is unknown, and in this study, we used a compound screen to indicate that OGT and CDK9 collaborate to sustain a cancer cell-specific pro-proliferative program. A better understanding of how OGT and CDK9 cross-talk will refine our understanding of this novel synthetic lethal interaction.

The nutrient sensor OGT regulates Hipk stability and tumorigenic-like activities in Drosophila

Environmental cues such as nutrients alter cellular behaviors by acting on a wide array of molecular sensors inside cells. Of emerging interest is the link observed between effects of dietary sugars on cancer proliferation. Here, we identify the requirements of hexosamine biosynthetic pathway (HBP) and O-GlcNAc transferase (OGT) for Drosophila homeodomain-interacting protein kinase (Hipk)-induced growth abnormalities in response to a high sugar diet. On a normal diet, OGT is both necessary and sufficient for inducing Hipk-mediated tumor-like growth. We further show that OGT maintains Hipk protein stability by blocking its proteasomal degradation and that Hipk is O-GlcNAcylated by OGT. In mammalian cells, human HIPK2 proteins accumulate posttranscriptionally upon OGT overexpression. Mass spectrometry analyses reveal that HIPK2 is at least O-GlcNAc modified at S852, T1009, and S1147 residues. Mutations of these residues reduce HIPK2 O-GlcNAcylation and stability. Together, our data demonstrate a conserved role of OGT in positively regulating the protein stability of HIPKs (fly Hipk and human HIPK2), which likely permits the nutritional responsiveness of HIPKs.

O-GlcNAc Transferase Regulates Angiogenesis in Idiopathic Pulmonary Arterial Hypertension

Idiopathic pulmonary arterial hypertension (IPAH) is considered a vasculopathy characterized by elevated pulmonary vascular resistance due to vasoconstriction and/or lung remodeling such as plexiform lesions, the hallmark of the PAH, as well as cell proliferation and vascular and angiogenic dysfunction. The serine/threonine hydroxyl-linked N-Acetylglucosamine (O-GlcNAc) transferase (OGT) has been shown to drive pulmonary arterial smooth muscle cell (PASMC) proliferation in IPAH. OGT is a cellular nutrient sensor that is essential in maintaining proper cell function through the regulation of cell signaling, proliferation, and metabolism. The aim of this study was to determine the role of OGT and O-GlcNAc in vascular and angiogenic dysfunction in IPAH. Primary isolated human control and IPAH patient PASMCs and pulmonary arterial endothelial cells (PAECs) were grown in the presence or absence of OGT inhibitors and subjected to biochemical assessments in monolayer cultures and tube formation assays, in vitro vascular sprouting 3D spheroid co-culture models, and de novo vascularization models in NODSCID mice. We showed that knockdown of OGT resulted in reduced vascular endothelial growth factor (VEGF) expression in IPAH primary isolated vascular cells. In addition, specificity protein 1 (SP1), a known stimulator of VEGF expression, was shown to have higher O-GlcNAc levels in IPAH compared to control at physiological (5 mM) and high (25 mM) glucose concentrations, and knockdown resulted in decreased VEGF protein levels. Furthermore, human IPAH PAECs demonstrated a significantly higher degree of capillary tube-like structures and increased length compared to control PAECs. Addition of an OGT inhibitor, OSMI-1, significantly reduced the number of tube-like structures and tube length similar to control levels. Assessment of vascular sprouting from an in vitro 3D spheroid co-culture model using IPAH and control PAEC/PASMCs and an in vivo vascularization model using control and PAEC-embedded collagen implants demonstrated higher vascularization in IPAH compared to control. Blocking OGT activity in these experiments, however, altered the vascular sprouting and de novo vascularization in IPAH similar to control levels when compared to controls. Our findings in this report are the first to describe a role for the OGT/O-GlcNAc axis in modulating VEGF expression and vascularization in IPAH. These findings provide greater insight into the potential role that altered glucose uptake and metabolism may have on the angiogenic process and the development of plexiform lesions. Therefore, we believe that the OGT/O-GlcNAc axis may be a potential therapeutic target for treating the angiogenic dysregulation that is present in IPAH.

A New Classification Method of Metastatic Cancers Using a 1H-NMR-Based Approach: A Study Case of Melanoma, Breast, and Prostate Cancer Cell Lines

In this study, metastatic melanoma, breast, and prostate cancer cell lines were analyzed using a ¹H-NMR-based approach in order to investigate common features and differences of aggressive cancers metabolomes. For that purpose, ¹H-NMR spectra of both cellular extracts and culture media were combined with multivariate data analysis, bringing to light no less than 20 discriminant metabolites able to separate the metastatic metabolomes. The supervised approach succeeded in classifying the metastatic cell lines depending on their glucose metabolism, more glycolysis-oriented in the BRAF proto-oncogene mutated cell lines compared to the others. Other adaptive metabolic features also contributed to the classification, such as the increased total choline content (tCho), UDP-GlcNAc detection, and various changes in the glucose-related metabolites tree, giving additional information about the metastatic metabolome status and direction. Finally, common metabolic features detected via ¹H-NMR in the studied cancer cell lines are discussed, identifying the glycolytic pathway, Kennedy’s pathway, and the glutaminolysis as potential and common targets in metastasis, opening up new avenues to cure cancer.

Hyper-O-GlcNAcylation promotes epithelial-mesenchymal transition in endometrial cancer cells

Diabetic women have a 2–3 fold increased risk of developing endometrial cancer, however, the molecular aspects of this risk are not fully understood. This study investigated the alteration of cellular O-GlcNAcylation of proteins as the potential mechanistic connection between these two conditions. The endometrial cancer cell line (Ishikawa) was utilized to study the effect of dysregulation of O-GlcNAcylation on epithelial mesenchymal transition (EMT). Hyper-O-GlcNAcylation (via 1 μM Thiamet-G/ThmG or 25 mM Glucose) enhanced the expression of EMT-associated genes (WNT5B and FOXC2), and protein expression of the EMT adhesion molecule, N-Cadherin. Reorganization of stress filaments (actin filaments), consistent with EMT, was also noted in ThmG-treated cells. Interestingly, Hypo-O-GlcNAcylation (via 50 μM OSMI-1) also upregulated WNT5B, inferring that any disruption to O-GlcNAc cycling impacts EMT. However, Hypo-O-GlcNAcylation reduced overall cellular proliferation/migration and the expression of pro-EMT genes (AHNAK, TGFB2, FGFBP1, CALD1, TFPI2). In summary, disruption of O-GlcNAc cycling (i.e., Hyper- or Hypo-O-GlcNAcylation) promoted EMT at both the molecular and cellular levels, but only Hyper-O-GlcNAcylation provoked cellular proliferation/migration, and cytoskeletal reorganization.

High OGT activity is essential for MYC-driven proliferation of prostate cancer cells

O-GlcNAc transferase (OGT) is overexpressed in aggressive prostate cancer. OGT modifies intra-cellular proteins via single sugar conjugation (O-GlcNAcylation) to alter their activity. We recently discovered the first fast-acting OGT inhibitor OSMI-2. Here, we probe the stability and function of the chromatin O-GlcNAc and identify transcription factors that coordinate with OGT to promote proliferation of prostate cancer cells.

Methods: Chromatin immunoprecipitation (ChIP) coupled to sequencing (seq), formaldehyde-assisted isolation of regulatory elements, RNA-seq and reverse-phase protein arrays (RPPA) were used to study the importance of OGT for chromatin structure and transcription. Mass spectrometry, western blot, RT-qPCR, cell cycle analysis and viability assays were used to establish the role of OGT for MYC-related processes. Prostate cancer patient data profiled for both mRNA and protein levels were used to validate findings.

Results: We show for the first time that OGT inhibition leads to a rapid loss of O-GlcNAc chromatin mark. O-GlcNAc ChIP-seq regions overlap with super-enhancers (SE) and MYC binding sites. OGT inhibition leads to down-regulation of SE-dependent genes. We establish the first O-GlcNAc chromatin consensus motif, which we use as a bait for mass spectrometry. By combining the proteomic data from oligonucleotide enrichment with O-GlcNAc and MYC ChIP-mass spectrometry, we identify host cell factor 1 (HCF-1) as an interaction partner of MYC. Inhibition of OGT disrupts this interaction and compromises MYC's ability to confer androgen-independent proliferation to prostate cancer cells. We show that OGT is required for MYC-mediated stabilization of mitotic proteins, including Cyclin B1, and/or the increased translation of their coding transcripts. This implies that increased expression of mRNA is not always required to achieve increased protein expression and confer aggressive phenotype. Indeed, high expression of Cyclin B1 protein has strong predictive value in prostate cancer patients (p=0.000014) while mRNA does not.

Conclusions: OGT promotes SE-dependent gene expression. OGT activity is required for the interaction between MYC and HCF-1 and expression of MYC-regulated mitotic proteins. These features render OGT essential for the androgen-independent, MYC-driven proliferation of prostate cancer cells. Androgen-independency is the major mechanism of prostate cancer progression, and our study identifies OGT as an essential mediator in this process.

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.

Hexosamine Biosynthetic Pathway and Glycosylation Regulate Cell Migration in Melanoma Cells

The Hexosamine Biosynthetic Pathway (HBP) is a branch of glycolysis responsible for the production of a key substrate for protein glycosylation, UDP-GlcNAc. Cancer cells present altered glucose metabolism and aberrant glycosylation, pointing to alterations on HBP. Recently it was demonstrated that HBP influences many aspects of tumor biology, including the development of metastasis. In this work we characterize HBP in melanoma cells and analyze its importance to cellular processes related to the metastatic phenotype. We demonstrate that an increase in HBP flux, as well as increased O-GlcNAcylation, leads to decreased cell motility and migration in melanoma cells. In addition, inhibition of N- and O-glycosylation glycosylation reduces cell migration. High HBP flux and inhibition of N-glycosylation decrease the activity of metalloproteases 2 and 9. Our data demonstrates that modulation of HBP and different types of glycosylation impact cell migration.

Prostate Cancer Energetics and Biosynthesis

Cancers must alter their metabolism to satisfy the increased demand for energy and to produce building blocks that are required to create a rapidly growing tumor. Further, for cancer cells to thrive, they must also adapt to an often changing tumor microenvironment, which can present new metabolic challenges (ex. hypoxia) that are unfavorable for most other cells. As such, altered metabolism is now considered an emerging hallmark of cancer. Like many other malignancies, the metabolism of prostate cancer is considerably different compared to matched benign tissue. However, prostate cancers exhibit distinct metabolic characteristics that set them apart from many other tumor types. In this chapter, we will describe the known alterations in prostate cancer metabolism that occur during initial tumorigenesis and throughout disease progression. In addition, we will highlight upstream regulators that control these metabolic changes. Finally, we will discuss how this new knowledge is being leveraged to improve patient care through the development of novel biomarkers and metabolically targeted therapies.

O-GlcNAcylation promotes colorectal cancer progression by regulating protein stability and potential catcinogenic function of DDX5

The RNA helicase p68 (DDX5), a key player in RNA metabolism, belongs to the DEAD box family and is involved in the development of colorectal cancer. Here, we found both DDX5 and O‐GlcNAcylation are up‐regulated in colorectal cancer. In addition, DDX5 protein level is significantly positively correlated with the expression of O‐GlcNAcylation. Although it was known DDX5 protein could be regulated by post‐translational modification (PTM), how O‐GlcNAcylation modification regulated of DDX5 remains unclear. Here we show that DDX5 interacts directly with OGT in the SW480 cell line, which is the only known enzyme that catalyses O‐GlcNAcylation in humans. Meanwhile, O‐GlcNAcylation could promote DDX5 protein stability. The OGT‐DDX5 axis affects colorectal cancer progression mainly by regulating activation of the AKT/mTOR signalling pathway. Taken together, these results indicated that OGT‐mediated O‐GlcNAcylation stabilizes DDX5, promoting activation of the AKT/mTOR signalling pathway, thus accelerating colorectal cancer progression. This study not only reveals the novel functional of O‐GlcNAcylation in regulating DDX5, but also reveals the carcinogenic effect of the OGT‐DDX5 axis in colorectal cancer.

Clinical significance of bromodomain-containing protein 7 and its association with tumor progression in prostate cancer

Prostate cancer (PCa) is a common malignancy in males. The current study assessed the clinical significance of bromodomain-containing protein 7 (BRD7) and its association with PCa tumor progression. Serum and tissue expression levels of BRD7 were analyzed by reverse transcription-quantitative polymerase chain reaction. Receiver operating characteristic (ROC) analysis was used to evaluate the diagnostic value of BRD7. Kaplan-Meier survival analysis and Cox regression analysis were performed to assess the prognostic performance of BRD7. The association of BRD7 with cell behavior was investigated by transfection with a pcDNA3.1-BRD7 vector. The results revealed that serum and tissue BRD7 expression levels were significantly decreased in PCa samples compared with normal controls (P<0.001). BRD7 expression was significantly associated with the pathological stage (P=0.037), lymph node metastasis (P=0.009) and TNM stage (P=0.010). An area under the ROC curve of 0.864 was obtained, with a sensitivity and specificity of 77.0 and 83.3%, respectively. Low BRD7 expression was significantly associated with a shorter survival time in both overall survival analysis (P=0.003) and cancer-specific survival analysis (P=0.029). Furthermore, BRD7 appeared to serve as an independent prognostic factor for PCa. The proliferation, migration and invasion of PCa cells were suppressed by BRD7 overexpression. In summary, downregulation of BRD7 in PCa may be involved in tumor progression and serve as an effective diagnostic and prognostic biomarker.

Molecular underpinnings of enzalutamide resistance

Prostate cancer (PCa) is among the most common adult malignancies, and the second leading cause of cancer-related death in men. As PCa is hormone dependent, blockade of the androgen receptor (AR) signaling is an effective therapeutic strategy for men with advanced metastatic disease. The discovery of enzalutamide, a compound that effectively blocks the AR axis and its clinical application has led to a significant improvement in survival time. However, the effect of enzalutamide is not permanent, and resistance to treatment ultimately leads to development of lethal disease, for which there currently is no cure. This review will focus on the molecular underpinnings of enzalutamide resistance, bridging the gap between the preclinical and clinical research on novel therapeutic strategies for combating this lethal stage of prostate cancer.

High O-linked N-acetylglucosamine transferase expression predicts poor survival in patients with early stage lung adenocarcinoma

Tumor cell heterogeneity can make selection of appropriate interventions to lung cancer a challenge. Novel biomarkers predictive of disease risk and treatment response are needed to improve personalized treatment strategies. O-GlcNAcylation, the attachment of β-N-acetylglucosamine (O-GlcNAc) to serine or threonine residues of intracellular proteins, modulates protein functions and is implicated in cancer pathogenesis. O-GlcNAc-transferase (OGT) and O-GlcNAcase (OGA) catalyze O-GlcNAc addition and removal, respectively. We used immunohistochemistry to explore the utility of OGT, OGA, and O-GlcNAc as potential biomarkers for lung adenocarcinoma. We found that high OGT expression is associated with poor overall survival (OS) in both stage I patients (P=0.032) and those at variable stages of disease (P=0.029), and with poor recurrence-free survival (RFS) in stage I patients (P=0.035). High OGT expression is also associated with poorer OS in patients with EGFR wild-type tumors at variable stages (P=0.038). Multivariate analysis indicated that OGT expression is an independent prognostic factor for RFS (HR 2.946, 95% CI: 1.411-6.150, P=0.004) and OS (HR 2.002, 95% CI: 1.183-3.391, P=0.010) in stage I patients. Our findings indicate OGT is a promising biomarker for further classifying early stage lung adenocarcinomas.

Elevated O-GlcNAcylation promotes gastric cancer cells proliferation by modulating cell cycle related proteins and ERK 1/2 signaling

O-GlcNAc transferase (OGT) is the only enzyme in mammals that catalyzes the attachment of β-D-N-acetylglucosamine (GlcNAc) to serine or threonine residues of target proteins. Hyper-O-GlcNAcylation is becoming increasingly realized as a general feature of cancer and contributes to rapid proliferation of cancer cells. In this study, we demonstrated that O-GlcNAc and OGT levels were increased in all six gastric cancer (GC) cell lines as compared with immortal gastric epithelial cells. Downregulation of the O-GlcNAcylation level by silencing OGT inhibited cell viability and growth rate via the cdk-2, cyclin D1 and ERK 1/2 pathways. In vivo xenograft assays also demonstrated that the hyper-O-GlcNAc level markedly promoted the proliferation of tumors. Moreover, compared with noncancerous tissues, the O-GlcNAcylation level was increased in cancerous tissues. GC patients with higher levels of O-GlcNAcylation exhibited large tumor sizes (≥5 cm), deep tumor invasion (T3 and T4), high AJCC stages (stage III and IV), more lymph node metastases and lower overall survival. Notably, the phosphorylation level of ERK 1/2 was increased progressively with the increase of O-GlcNAcylation in both SGC 7901 and AGS cells. Consistently, human GC tissue arrays also revealed that ERK 1/2 signaling was positively correlated to O-GlcNAcylation (r = 0.348; P = 0.015). Taken together, here we reported that hyper-O-GlcNAcylation significantly promotes GC cells proliferation by modulating cell cycle related proteins and ERK 1/2 signaling, suggesting that inhibition of OGT may be a potential novel therapeutic target of GC.

Potential coordination role between O-GlcNAcylation and epigenetics

Dynamic changes of the post-translational O-GlcNAc modification (O-GlcNAcylation) are controlled by O-linked β-N-acetylglucosamine (O-GlcNAc) transferase (OGT) and the glycoside hydrolase O-GlcNAcase (OGA) in cells. O-GlcNAcylation often occurs on serine (Ser) and threonine (Thr) residues of the specific substrate proteins via the addition of O-GlcNAc group by OGT. It has been known that O-GlcNAcylation is not only involved in many fundamental cellular processes, but also plays an important role in cancer development through various mechanisms. Recently, accumulating data reveal that O-GlcNAcylation at histones or non-histone proteins can lead to the start of the subsequent biological processes, suggesting that O-GlcNAcylation as ‘protein code’ or ‘histone code’ may provide recognition platforms or executive instructions for subsequent recruitment of proteins to carry out the specific functions. In this review, we summarize the interaction of O-GlcNAcylation and epigenetic changes, introduce recent research findings that link crosstalk between O-GlcNAcylation and epigenetic changes, and speculate on the potential coordination role of O-GlcNAcylation with epigenetic changes in intracellular biological processes.

[O-GlcNAc glycosylation influences the biological behaviors and etoposide-induced apoptosis of Nalm-6 cells]

目的

研究O连接的N-乙酰葡萄糖胺（O-GlcNAc）糖基化及乙酰氨基葡萄糖转移酶（OGT）对Nalm-6细胞生物学行为及对依托泊苷（Vp16）诱导凋亡的影响。

方法

利用OGT抑制剂Alloxan构建低O-GlcNAc修饰的Nalm-6细胞模型，CCK-8法检测Alloxan对细胞增殖的影响，流式细胞术检测Alloxan对细胞凋亡及细胞周期的影响；以不同浓度的Vp16处理Nalm-6细胞12 h，Western blot检测O-GlcNAc糖基化修饰程度及OGT表达量的变化；以Alloxan处理Nalm-6细胞24 h后再加入Vp16（5 µg/ml）处理12 h，应用流式细胞术检测不同组别细胞凋亡，Western blot检测凋亡相关蛋白Bax和Bcl-2的表达情况。

结果

随着Vp16浓度的增加，Nalm-6细胞O-GlcNAc修饰及OGT表达均逐渐上调（P<0.05）；Alloxan可抑制Nalm-6细胞增殖，诱发Nalm-6细胞凋亡[（15.190±2.539）%对（21.910±4.105）%，P=0.007]，阻滞细胞周期[G₁期：（43.534±4.453）%对（57.322±6.091）%，P=0.003；S期：（50.747±5.937）%对（37.201±4.661）%，P=0.001]；Alloxan可抑制Vp16诱导的Nalm-6细胞凋亡[（75.195±13.845）%对（52.741±10.815）%，P=0.011]，并伴随Bax表达下调（5.496±1.998对2.950±0.703，P=0.015）、Bcl-2表达上调（0.454±0.125对0.803±0.223，P=0.013）。

结论

通过抑制OGT而改变Nalm-6细胞O-GlcNAc修饰程度可影响其增殖、凋亡、改变细胞周期并抑制Vp16诱导的细胞凋亡。

Glycosylation is a global target for androgen control in prostate cancer cells

Changes in glycan composition are common in cancer and can play important roles in all of the recognised hallmarks of cancer. We recently identified glycosylation as a global target for androgen control in prostate cancer cells and further defined a set of 8 glycosylation enzymes (GALNT7, ST6GalNAc1, GCNT1, UAP1, PGM3, CSGALNACT1, ST6GAL1 and EDEM3), which are also significantly upregulated in prostate cancer tissue. These 8 enzymes are under direct control of the androgen receptor (AR) and are linked to the synthesis of important cancer-associated glycans such as sialyl-Tn (sTn), sialyl LewisX (SLeX), O-GlcNAc and chondroitin sulfate. Glycosylation has a key role in many important biological processes in cancer including cell adhesion, migration, interactions with the cell matrix, immune surveillance, cell signalling and cellular metabolism. Our results suggest that alterations in patterns of glycosylation via androgen control might modify some or all of these processes in prostate cancer. The prostate is an abundant secretor of glycoproteins of all types, and alterations in glycans are, therefore, attractive as potential biomarkers and therapeutic targets. Emerging data on these often overlooked glycan modifications have the potential to improve risk stratification and therapeutic strategies in patients with prostate cancer.

Therapeutic Targeting of Epithelial Plasticity Programs: Focus on the Epithelial-Mesenchymal Transition

Mounting data points to epithelial plasticity programs such as the epithelial-mesenchymal transition (EMT) as clinically relevant therapeutic targets for the treatment of malignant tumors. In addition to the widely realized role of EMT in increasing cancer cell invasiveness during cancer metastasis, the EMT has also been implicated in allowing cancer cells to avoid tumor suppressor pathways during early tumorigenesis. In addition, data linking EMT to innate and acquired treatment resistance further points towards the desire to develop pharmacological therapies to target epithelial plasticity in cancer. In this review we organized our discussion on pathways and agents that can be used to target the EMT in cancer into 3 groups: (1) extracellular inducers of EMT, (2) the transcription factors that orchestrate the EMT transcriptome, and (3) the downstream effectors of EMT. We highlight only briefly specific canonical pathways known to be involved in EMT, such as the signal transduction pathways TGFβ, EFGR, and Axl-Gas6. We emphasize in more detail pathways that we believe are emerging novel pathways and therapeutic targets such as epigenetic therapies, glycosylation pathways, and immunotherapy. The heterogeneity of tumors and the dynamic nature of epithelial plasticity in cancer cells make it likely that targeting only 1 EMT-related process will be unsuccessful or only transiently successful. We suggest that with greater understanding of epithelial plasticity regulation, such as with the EMT, a more systematic targeting of multiple EMT regulatory networks will be the best path forward to improve cancer outcomes.

Selenium Protects Retinal Cells from Cisplatin-Induced Alterations in Carbohydrate Residues

BACKGROUND

Investigate alterations in the expression and localization of carbohydrate units in rat retinal cells exposed to cisplatin toxicity.

AIMS

The aim of the study was to evaluate putative protective effects of selenium on retinal cells subjected to cisplatin.

STUDY DESIGN

Animal experiment.

METHODS

Eighteen healthy Wistar rats were divided into three equal groups: 1. Control, 2. Cisplatin and 3. Cisplatin+selenium groups. After anesthesia, the right eye of each rat was enucleated.

RESULTS

Histochemically, retinal cells of control groups reacted with α-2,3-bound sialic acid-specific Maackia amurensis lectin (MAA) strongly, while cisplatin reduced the staining intensity for MAA. However, selenium administration alleviated the reducing effect of cisplatin on the binding sites for MAA in retinal cells. The staining intensity for N-acetylgalactosamine (GalNAc residues) specific Griffonia simplicifolia-1 (GSL-1) was relatively slight in control animals and cisplatin reduced this slight staining for GSL-1 further. Selenium administration mitigated the reducing effect of cisplatin on the binding sites for GSL-1. A diffuse staining for N-acetylglucosamine (GlcNAc) specific wheat germ agglutinin (WGA) was observed throughout the retina of the control animals. In particular, cells localized in the inner plexiform and photoreceptor layers are reacted strongly with WGA. Compared to the control animals, binding sites for WGA in the retina of rats given cisplatin were remarkably decreased. However, the retinal cells of rats given selenium reacted strongly with WGA.

CONCLUSION

Cisplatin reduces α-2,3-bound sialic acid, GlcNAc and GalNAc residues in certain retinal cells. However, selenium alleviates the reducing effect of cisplatin on carbohydrate residues in retinal cells.

O-GlcNAcylation in Cancer Biology: Linking Metabolism and Signaling

The hexosamine biosynthetic pathway (HBP) is highly dependent on multiple metabolic nutrients including glucose, glutamine, and acetyl-CoA. Increased flux through HBP leads to elevated post-translational addition of β-D-N-acetylglucosamine sugars to nuclear and cytoplasmic proteins. Increased total O-GlcNAcylation is emerging as a general characteristic of cancer cells, and recent studies suggest that O-GlcNAcylation is a central communicator of nutritional status to control key signaling and metabolic pathways that regulate multiple cancer cell phenotypes. This review summarizes our current understanding of changes of O-GlcNAc cycling enzymes in cancer, the role of O-GlcNAcylation in tumorigenesis, and the current challenges in targeting this pathway therapeutically.

Mechanistic insights of O-GlcNAcylation that promote progression of cholangiocarcinoma cells via nuclear translocation of NF-κB

O-GlcNAcylation, an O-linked protein glycosylation with a single molecule of N-acetylglucosamine (GlcNAc), is reversibly controlled by O-GlcNAc transferase (OGT) and N-acetyl D-glucosaminidase (OGA). Aberrant O-GlcNAcylation contributes an important role in initiation and progression of many human cancers. Elevation of O-GlcNAcylation in tumor tissues and poor prognosis of cholangiocarcinoma (CCA) patients have been reported. In this study, the role of O-GlcNAcylation in promoting tumor progression was further investigated in CCA cell lines. Suppression of O-GlcNAcylation using small interfering RNAs of OGT (siOGT) significantly reduced cell migration and invasion of CCA cells whereas siOGA treated cells exhibited opposite effects. Manipulating levels of O-GlcNAcylation did affect the nuclear translocation of NF-κB and Akt-phosphorylation together with expression of matrix-metalloproteinases (MMPs). O-GlcNAcylation and nuclear translocation of NF-κB, the upstream signaling cascade of MMP activation were shown to be important for MMP activation. Immunoprecipitation revealed the elevation of O-GlcNAc-modified NF-κB with increased cellular O-GlcNAcylation. Involvement of O-GlcNAcylation in MMP-mediated migration and invasion of CCA cells was shown to be via O-GlcNAcylation and nuclear translocation of NF-κB. This information indicates the significance of O-GlcNAcylation in controlling the metastatic ability of CCA cells, hence, O-GlcNAcylation and its products may be new targets for treatment of metastatic CCA.

Glycosylation is an Androgen-Regulated Process Essential for Prostate Cancer Cell Viability

Steroid androgen hormones play a key role in the progression and treatment of prostate cancer, with androgen deprivation therapy being the first-line treatment used to control cancer growth. Here we apply a novel search strategy to identify androgen-regulated cellular pathways that may be clinically important in prostate cancer. Using RNASeq data, we searched for genes that showed reciprocal changes in expression in response to acute androgen stimulation in culture, and androgen deprivation in patients with prostate cancer. Amongst 700 genes displaying reciprocal expression patterns we observed a significant enrichment in the cellular process glycosylation. Of 31 reciprocally-regulated glycosylation enzymes, a set of 8 (GALNT7, ST6GalNAc1, GCNT1, UAP1, PGM3, CSGALNACT1, ST6GAL1 and EDEM3) were significantly up-regulated in clinical prostate carcinoma. Androgen exposure stimulated synthesis of glycan structures downstream of this core set of regulated enzymes including sialyl-Tn (sTn), sialyl Lewis(X) (SLe(X)), O-GlcNAc and chondroitin sulphate, suggesting androgen regulation of the core set of enzymes controls key steps in glycan synthesis. Expression of each of these enzymes also contributed to prostate cancer cell viability. This study identifies glycosylation as a global target for androgen control, and suggests loss of specific glycosylation enzymes might contribute to tumour regression following androgen depletion therapy.

The role of glycans in the development and progression of prostate cancer

Prostate cancer is a unique and heterogeneous disease. Currently, a major unmet clinical need exists to develop biomarkers that enable indolent disease to be distinguished from aggressive disease. The prostate is an abundant secretor of glycoproteins of all types, and alterations in glycans are, therefore, attractive as potential biomarkers and therapeutic targets. Despite progress over the past decade in profiling the genome and proteome, the prostate cancer glycoproteome remains relatively understudied. A wide range of alterations in the glycoproteins on prostate cancer cells can occur, including increased sialylation and fucosylation, increased O-β-N-acetylglucosamine (GlcNAc) conjugation, the emergence of cryptic and high-mannose N-glycans and alterations to proteoglycans. Glycosylation can alter protein function and has a key role in many important biological processes in cancer including cell adhesion, migration, interactions with the cell matrix, immune surveillance, cell signalling and cellular metabolism; altered glycosylation in prostate cancer might modify some, or all of these processes. In the past three years, powerful tools such as glycosylation-specific antibodies and glycosylation gene signatures have been developed, which enable detailed analyses of changes in glycosylation. Thus, emerging data on these often overlooked modifications have the potential to improve risk stratification and therapeutic strategies in patients with prostate cancer.

Hijacking the Hexosamine Biosynthetic Pathway to Promote EMT-Mediated Neoplastic Phenotypes

The epithelial-mesenchymal transition (EMT) is a highly conserved program necessary for orchestrating distant cell migration during embryonic development. Multiple studies in cancer have demonstrated a critical role for EMT during the initial stages of tumorigenesis and later during tumor invasion. Transcription factors (TFs) such as SNAIL, TWIST, and ZEB are master EMT regulators that are aberrantly overexpressed in many malignancies. Recent evidence correlates EMT-related transcriptomic alterations with metabolic reprograming in cancer. Metabolic alterations may allow cancer to adapt to environmental stressors, supporting the irregular macromolecular demand of rapid proliferation. One potential metabolic pathway of increasing importance is the hexosamine biosynthesis pathway (HBP). The HBP utilizes glycolytic intermediates to generate the metabolite UDP-GlcNAc. This and other charged nucleotide sugars serve as the basis for biosynthesis of glycoproteins and other glycoconjugates. Recent reports in the field of glycobiology have cultivated great curiosity within the cancer research community. However, specific mechanistic relationships between the HBP and fundamental pathways of cancer, such as EMT, have yet to be elucidated. Altered protein glycosylation downstream of the HBP is well positioned to mediate many cellular changes associated with EMT including cell-cell adhesion, responsiveness to growth factors, immune system evasion, and signal transduction programs. Here, we outline some of the basics of the HBP and putative roles the HBP may have in driving EMT-related cancer processes. With novel appreciation of the HBP's connection to EMT, we hope to illuminate the potential for new therapeutic targets of cancer.

O-GlcNAcylation is associated with the development and progression of gastric carcinoma

INTRODUCTION

O-GlcNAcylation occurs via an O-linked β-N-acetylglucosamine (O-GlcNAc) moiety linked to the side chain hydroxyl of a serine or threonine residue on nucleocytoplasmic proteins. This reaction, which is catalyzed by O-GlcNAc-transferase (OGT), is involved in a variety of human cancers; however, its clinical significance in gastric carcinomas (GC) has been poorly investigated in vivo.

MATERIALS AND METHODS

Immunohistochemical staining for O-GlcNAcylation and OGT was performed in 64 primary GCs, 40 gastric adenomas and nonneoplastic tissues adjacent to GCs, including 31 tissues of intestinal metaplasia and 24 normal gastric tissues. Their expressions were also studied in 20 tissues of chronic gastritis according to Helicobacter pylori (H. pylori) infection.

RESULTS

O-GlcNAcylation was expressed in the nucleus and both the nuclear rim and cytoplasm. OGT was strongly expressed in the nucleus and weakly expressed in the cytoplasm. O-GlcNAcylation expression levels were significantly correlated with those of OGT. Their expression levels were progressively increased during the carcinogenesis of GC. O-GlcNAcylation expression was higher in GC with intestinal type, higher pT stage and nodal metastasis, while OGT expression was higher in GC with nodal metastasis. Nuclear O-GlcNAcylation expression was more frequently observed in tumors including GC and adenoma than in nonneoplastic tissues including intestinal metaplasia and normal tissue. Nuclear O-GlcNAcylation expression in GC was closely associated with large size, moderate and poor differentiation, higher pT stage, nodal metastasis and higher clinical stage. In addition, the expression of O-GlcNAcylation and OGT was more elevated in H. pylori-infected chronic gastritis than in chronic gastritis without H. pylori infection.

CONCLUSIONS

O-GlcNAcylation expression and its nuclear expression were associated with the carcinogenesis and progression of GC.

Mixed Lineage Leukemia 5 (MLL5) Protein Stability Is Cooperatively Regulated by O-GlcNac Transferase (OGT) and Ubiquitin Specific Protease 7 (USP7)

Mixed lineage leukemia 5 (MLL5) protein is a trithorax family histone 3 lysine 4 (H3K4) methyltransferase that regulates diverse biological processes, including cell cycle progression, hematopoiesis and cancer. The mechanisms by which MLL5 protein stability is regulated have remained unclear to date. Here, we showed that MLL5 protein stability is cooperatively regulated by O-GlcNAc transferase (OGT) and ubiquitin-specific protease 7 (USP7). Depletion of OGT in cells led to a decrease in the MLL5 protein level through ubiquitin/proteasome-dependent proteolytic degradation, whereas ectopic expression of OGT protein suppressed MLL5 ubiquitylation. We further identified deubiquitinase USP7 as a novel MLL5-associated protein using mass spectrometry. USP7 stabilized the MLL5 protein through direct binding and deubiquitylation. Loss of USP7 induced degradation of MLL5 protein. Conversely, overexpression of USP7, but not a catalytically inactive USP7 mutant, led to decreased ubiquitylation and increased MLL5 stability. Co-immunoprecipitation and co-immunostaining assays revealed that MLL5, OGT and USP7 interact with each other to form a stable ternary complex that is predominantly located in the nucleus. In addition, upregulation of MLL5 expression was correlated with increased expression of OGT and USP7 in human primary cervical adenocarcinomas. Our results collectively reveal a novel molecular mechanism underlying regulation of MLL5 protein stability and provide new insights into the functional interplay among O-GlcNAc transferase, deubiquitinase and histone methyltransferase.