O-GlcNAc modification regulates MTA1 transcriptional activity during breast cancer cell genotoxic adaptation

Targeting O-GlcNAcylation in cancer therapeutic resistance: The sugar Saga continues

O-linked-N-acetylglucosaminylation (O-GlcNAcylation), a dynamic post-translational modification (PTM), holds profound implications in controlling various cellular processes such as cell signaling, metabolism, and epigenetic regulation that influence cancer progression and therapeutic resistance. From the therapeutic perspective, O-GlcNAc modulates drug efflux, targeting and metabolism. By integrating signals from glucose, lipid, amino acid, and nucleotide metabolic pathways, O-GlcNAc acts as a nutrient sensor and transmits signals to exerts its function on genome stability, epithelial-mesenchymal transition (EMT), cell stemness, cell apoptosis, autophagy, cell cycle. O-GlcNAc also attends to tumor microenvironment (TME) and the immune response. At present, several strategies aiming at targeting O-GlcNAcylation are under mostly preclinical evaluation, where the newly developed O-GlcNAcylation inhibitors markedly enhance therapeutic efficacy. Here we systematically outline the mechanisms through which O-GlcNAcylation influences therapy resistance and deliberate on the prospects and challenges associated with targeting O-GlcNAcylation in future cancer treatments.

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.

O-GlcNAcylation: A Crucial Regulator in Cancer-Associated Biological Events

O-GlcNAcylation, a recently discovered post-translational modification of proteins, plays a crucial role in regulating protein structure and function, and is closely associated with multiple diseases. Research has shown that O-GlcNAcylation is abnormally upregulated in most cancers, promoting disease progression. To elucidate the roles of O-GlcNAcylation in cancer, this review summarizes various cancer-associated biological events regulated by O-GlcNAcylation and the corresponding signaling pathways. This work may provide insights for future studies on the function or underlying mechanisms of O-GlcNAcylation in cancer.

FOXA1 O-GlcNAcylation-mediated transcriptional switch governs metastasis capacity in breast cancer

FOXA1, a transcription factor involved in epigenetic reprogramming, is crucial for breast cancer progression. However, the mechanisms by which FOXA1 achieves its oncogenic functions remain elusive. Here, we demonstrate that the O-linked β-N-acetylglucosamine modification (O-GlcNAcylation) of FOXA1 promotes breast cancer metastasis by orchestrating the transcription of numerous metastasis regulators. O-GlcNAcylation at Thr432, Ser441, and Ser443 regulates the stability of FOXA1 and promotes its assembly with chromatin. O-GlcNAcylation shapes the FOXA1 interactome, especially triggering the recruitment of the transcriptional repressor methyl-CpG binding protein 2 and consequently stimulating FOXA1 chromatin-binding sites to switch to chromatin loci of adhesion-related genes, including EPB41L3 and COL9A2. Site-specific depletion of O-GlcNAcylation on FOXA1 affects the expression of various downstream genes and thus inhibits breast cancer proliferation and metastasis both in vitro and in vivo. Our data establish the importance of aberrant FOXA1 O-GlcNAcylation in breast cancer progression and indicate that targeting O-GlcNAcylation is a therapeutic strategy for metastatic breast 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.

O-GlcNAc transferase contributes to sex-specific placental deregulation in gestational diabetes

INTRODUCTION

Gestational diabetes (GDM) is traditionally thought to emerge from placental endocrine dysregulations, but recent evidence suggests that fetal sex can also impact GDM development. Understanding the molecular mechanisms through which sex modulates placenta physiology can help identify novel molecular targets for future clinical care. Thus, we investigated the nutrient-sensing O-GlcNAc pathway as a potential mediator of sex-specific placenta dysfunction in GDM.

METHODS

Expression levels of O-GlcNAc enzymes were measured in male and female (n = 9+/gender) human placentas based on the maternal diagnosis of GDM. We then simulated the observed differences in both BeWo cells and human syncytiotrophoblasts primary cells (SCT) from male and female origins (n = 6/gender). RNA sequencing and targeted qPCR were performed to characterize the subsequent changes in the placenta transcriptome related to gestational diabetes.

RESULTS

O-GlcNAc transferase (OGT) expression was significantly reduced only in male placenta collected from mothers with GDM compared to healthy controls. Similar downregulation of OGT in trophoblast-like BeWo male cells demonstrated significant gene expression deregulations that overlapped with known GDM-related genes. Notably, placental growth hormone (GH) production was significantly elevated, while compensatory factors against GH-related insulin resistance were diminished. Inflammatory and immunologic factors with toxic effects on pancreatic β cell mass were also increased, altogether leaning toward a decompensatory diabetic profile. Similar changes in hormone expression were confirmed in male human primary SCTs transfected with siOGT. However, down-regulating OGT in female primary SCTs did not impact hormone production.

CONCLUSION

Our study demonstrated the significant deregulation of placental OGT levels in mothers with GDM carrying a male fetus. When simulated in vitro, such deregulation impacted hormonal production in BeWo trophoblast cells and primary SCTs purified from male placentas. Interestingly, female placentas were only modestly impacted by OGT downregulation, suggesting that the sex-specific presentation observed in gestational diabetes could be related to O-GlcNAc-mediated regulation of placental hormone production.

The Emerging Roles of Protein Interactions with O-GlcNAc Cycling Enzymes in Cancer

The dynamic O-GlcNAc modification of intracellular proteins is an important nutrient sensor for integrating metabolic signals into vast networks of highly coordinated cellular activities. Dysregulation of the sole enzymes responsible for O-GlcNAc cycling, O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), and the associated cellular O-GlcNAc profile is a common feature across nearly every cancer type. Many studies have investigated the effects of aberrant OGT/OGA expression on global O-GlcNAcylation activity in cancer cells. However, recent studies have begun to elucidate the roles of protein-protein interactions (PPIs), potentially through regions outside of the immediate catalytic site of OGT/OGA, that regulate greater protein networks to facilitate substrate-specific modification, protein translocalization, and the assembly of larger biomolecular complexes. Perturbation of OGT/OGA PPI networks makes profound changes in the cell and may directly contribute to cancer malignancies. Herein, we highlight recent studies on the structural features of OGT and OGA, as well as the emerging roles and molecular mechanisms of their aberrant PPIs in rewiring cancer networks. By integrating complementary approaches, the research in this area will aid in the identification of key protein contacts and functional modules derived from OGT/OGA that drive oncogenesis and will illuminate new directions for anti-cancer drug development.

O-GlcNAcylation regulation of cellular signaling in cancer

O-GlcNAcylation is a post-translational modification occurring on serine/threonine residues of nuclear and cytoplasmic proteins, mediated by the enzymes OGT and OGA which catalyze the addition or removal of the UDP-GlcNAc moieties, respectively. Structural changes brought by this modification lead to alternations of protein stability, protein-protein interactions, and phosphorylation. Importantly, O-GlcNAcylation is a nutrient sensor by coupling nutrient sensing with cellular signaling. Elevated levels of OGT and O-GlcNAc have been reported in a variety of cancers and has been linked to regulation of multiple cancer signaling pathways. In this review, we discuss the most recent findings on the role of O-GlcNAcylation as a metabolic sensor in signaling pathways and immune response in cancer.

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.

Breast cancer glycan biomarkers: their link to tumour cell metabolism and their perspectives in clinical practice

INTRODUCTION

Breast cancer (BCa) is the most common cancer type diagnosed in women and 5^th most common cause of deaths among all cancer deaths despite the fact that screening program is at place. This is why novel diagnostics approaches are needed in order to decrease number of BCa cases and disease mortality.

AREAS COVERED

In this review paper, we aim to cover some basic aspects regarding cellular metabolism and signalling in BCa behind altered glycosylation. We also discuss novel exciting discoveries regarding glycan-based analysis, which can provide useful information for better understanding of the disease. The final part deals with clinical usefulness of glycan-based biomarkers and the clinical performance of such biomarkers is compared to already approved BCa biomarkers and diagnostic tools based on imaging.

EXPERT OPINION

Recent discoveries suggest that glycan-based biomarkers offer high accuracy for possible BCa diagnostics in blood, but also for better monitoring and management of BCa patients. The review article was written using Web of Science search engine to include articles published between 2019 and 2021.

Molecular Mechanisms and Animal Models of HBV-Related Hepatocellular Carcinoma: With Emphasis on Metastatic Tumor Antigen 1

Hepatocellular carcinoma (HCC) is an important cause of cancer death worldwide, and hepatitis B virus (HBV) infection is a major etiology, particularly in the Asia-Pacific region. Lack of sensitive biomarkers for early diagnosis of HCC and lack of effective therapeutics for patients with advanced HCC are the main reasons for high HCC mortality; these clinical needs are linked to the molecular heterogeneity of hepatocarcinogenesis. Animal models are the basis of preclinical and translational research in HBV-related HCC (HBV-HCC). Recent advances in methodology have allowed the development of several animal models to address various aspects of chronic liver disease, including HCC, which HBV causes in humans. Currently, multiple HBV-HCC animal models, including conventional, hydrodynamics-transfection-based, viral vector-mediated transgenic, and xenograft mice models, as well as the hepadnavirus-infected tree shrew and woodchuck models, are available. This review provides an overview of molecular mechanisms and animal models of HBV-HCC. Additionally, the metastatic tumor antigen 1 (MTA1), a cancer-promoting molecule, was introduced as an example to address the importance of a suitable animal model for studying HBV-related hepatocarcinogenesis.