Cross talk between O-GlcNAcylation and phosphorylation: roles in signaling, transcription, and chronic disease

Systematic Evaluation of Affinity Enrichment Methods for O-GlcNAc Proteomics

O-Linked β-N-acetylglucosamine (O-GlcNAc) modification (i.e., O-GlcNAcylation) on proteins plays critical roles in the regulation of diverse biological processes. However, protein O-GlcNAcylation analysis, especially at a large scale, has been a challenge. So far, a number of enrichment materials and methods have been developed for site-specific O-GlcNAc proteomics in different biological settings. Despite the presence of multiple methods, their performance for the O-GlcNAc proteomics is largely unclear. In this work, by using the lysates of PANC-1 cells (a pancreatic cancer cell line), we provided a head-to-head comparison of three affinity enrichment methods and materials (i.e., antibody, lectin AANL6, and an OGA mutant) for site-specific O-GlcNAc proteomics. The enriched peptides were analyzed by HCD product-dependent EThcD (i.e., HCD-pd-EThcD) mass spectrometry. The resulting data files were processed by three different data analysis packages (i.e., Sequest HT, Byonic, and FragPipe). Our data suggest that each method captures a subpopulation of the O-GlcNAc proteins. Besides the enrichment methods, we also observe complementarity between the different data analysis tools. Thus, combining different approaches holds promise for enhanced coverage of O-GlcNAc proteomics.

Type 2 diabetes mellitus in adults: pathogenesis, prevention and therapy

Type 2 diabetes (T2D) is a disease characterized by heterogeneously progressive loss of islet β cell insulin secretion usually occurring after the presence of insulin resistance (IR) and it is one component of metabolic syndrome (MS), and we named it metabolic dysfunction syndrome (MDS). The pathogenesis of T2D is not fully understood, with IR and β cell dysfunction playing central roles in its pathophysiology. Dyslipidemia, hyperglycemia, along with other metabolic disorders, results in IR and/or islet β cell dysfunction via some shared pathways, such as inflammation, endoplasmic reticulum stress (ERS), oxidative stress, and ectopic lipid deposition. There is currently no cure for T2D, but it can be prevented or in remission by lifestyle intervention and/or some medication. If prevention fails, holistic and personalized management should be taken as soon as possible through timely detection and diagnosis, considering target organ protection, comorbidities, treatment goals, and other factors in reality. T2D is often accompanied by other components of MDS, such as preobesity/obesity, metabolic dysfunction associated steatotic liver disease, dyslipidemia, which usually occurs before it, and they are considered as the upstream diseases of T2D. It is more appropriate to call "diabetic complications" as "MDS-related target organ damage (TOD)", since their development involves not only hyperglycemia but also other metabolic disorders of MDS, promoting an up-to-date management philosophy. In this review, we aim to summarize the underlying mechanism, screening, diagnosis, prevention, and treatment of T2D, especially regarding the personalized selection of hypoglycemic agents and holistic management based on the concept of "MDS-related TOD".

AMPK and O-GlcNAcylation: interplay in cardiac pathologies and heart failure

Heart failure (HF) represents a multifaceted clinical syndrome characterized by the heart's inability to pump blood efficiently to meet the body's metabolic demands. Despite advances in medical management, HF remains a major cause of morbidity and mortality worldwide. In recent years, considerable attention has been directed toward understanding the molecular mechanisms underlying HF pathogenesis, with a particular focus on the role of AMP-activated protein kinase (AMPK) and protein O-GlcNAcylation. This review comprehensively examines the current understanding of AMPK and O-GlcNAcylation signalling pathways in HF, emphasizing their interplay and dysregulation. We delve into the intricate molecular mechanisms by which AMPK and O-GlcNAcylation contribute to cardiac energetics, metabolism, and remodelling, highlighting recent preclinical and clinical studies that have explored novel therapeutic interventions targeting these pathways.

High glucose promotes lipopolysaccharide-induced macrophage pyroptosis through GSDME O-GlcNAcylation

AIM

The high glucose (HG) environment in diabetic periodontitis aggravates the damage of periodontal tissue. Pyroptosis has been shown to be positively correlated with the severity of periodontitis, including macrophage pyroptosis. O-GlcNAcylation is a posttranslational modification that is involved in the pathogenesis of periodontitis. However, whether HG regulates macrophage pyroptosis through O-GlcNAcylation remains uncertain. This study aimed to investigate the effect of HG on the O-GlcNAcylation level of a pyroptosis regulator GSDME in macrophages to further probe the mechanisms of diabetic periodontitis.

METHODS

Blood samples were collected from patients with diabetic periodontitis. THP-1 monocytes were induced to differentiate into macrophages by phorbol 12-myristate 13-acetate and then treated with HG to simulate periodontitis in vitro. GSDME expression of blood samples and macrophages was measured by quantitative real-time PCR. Pyroptosis was assessed by propidium iodide staining, measurement of cell viability, cytotoxicity, protein levels of inflammation factors, and pyroptosis-related proteins. O-GlcNAcylation of GSDME was analyzed using co-immunoprecipitation (co-IP), IP, and western blot.

RESULTS

The results showed that GSDME expression was elevated in patients with periodontitis and HG-treated macrophages. HG inhibited cell viability but increased LDH content, levels of IL-1β, IL-18, TNF-α, NLRP3, GSDMD, and Caspase-1, indicating that HG promoted pyroptosis of macrophages, which was reversed by GSDME knockdown. HG treatment increased O-GlcNAcylation in macrophages. Mechanically, GSDME interacted with OGT, and OGT knockdown suppressed O-GlcNAcylation of GSDME at Ser (S)339 site. Knockdown of OGT inhibited pyroptosis in HG-treated macrophages, while GSDME overexpression partially reversed this inhibition.

CONCLUSION

HG treatment enhanced OGT-mediated GSDME O-GlcNAcylation, thereby augmenting pyroptosis in LPS-induced macrophages. These results may provide a novel sight for the treatment of periodontitis.

GFPT2: A novel biomarker in mesothelioma for diagnosis and prognosis and its molecular mechanism in malignant progression

BACKGROUND

Mesothelioma (MESO) is an insidious malignancy with a complex diagnosis and a poor prognosis. Our study unveils Glutamine-Fructose-6-Phosphate Transaminase 2 (GFPT2) as a valuable diagnostic and prognostic marker for MESO, exploring its role in MESO pathogenesis.

METHODS

We utilised tissue samples and clinicopathologic data to evaluate the diagnostic and prognostic significance of GFPT2 as a biomarker for MESO. The role of GFPT2 in the malignant progression of MESO was investigated through in vitro and in vivo experiments. The activation of NF-κB-p65 through O-GlcNAcylation at Ser75 was elucidated using experiments like HPLC-QTRAP-MS/MS and mass spectrometry analysis.

RESULTS

The study demonstrates that GFPT2 exhibits a sensitivity of 92.60% in diagnosing MESO. Overexpression of it has been linked to an unfavourable prognosis. Through rigorous verification, we have confirmed that elevated GFPT2 levels drive malignant proliferation, invasiveness, and metastasis in MESO. At the molecular level, GFPT2 augments p65 O-GlcNAcylation, orchestrating its nuclear translocation and activating the NF-κB signalling pathway.

CONCLUSIONS

Our insights suggest GFPT2's potential as a distinctive biomarker for MESO diagnosis and prognosis, and as an innovative therapeutic target, offering a new horizon for identification and treatment strategies in MESO management.

O-GlcNAc informatics: advances and trends

As a post-translational modification, protein glycosylation is critical in health and disease. O-Linked β-N-acetylglucosamine (O-GlcNAc) modification (O-GlcNAcylation), as an intracellular monosaccharide modification on proteins, was discovered 40 years ago. Thanks to technological advances, the physiological and pathological significance of O-GlcNAcylation has been gradually revealed and widely appreciated, especially in recent years. O-GlcNAc informatics has been quickly evolving. Clearly, O-GlcNAc informatics tools have not only facilitated O-GlcNAc functional studies, but also provided us a unique perspective on protein O-GlcNAcylation. In this article, we review O-GlcNAc-focused software tools and servers that have been developed for O-GlcNAc research over the past four decades. Specifically, we will (1) survey bioinformatics tools that have facilitated O-GlcNAc proteomics data analysis, (2) introduce databases/servers for O-GlcNAc proteins/sites that have been experimentally identified by individual research labs, (3) describe software tools that have been developed to predict O-GlcNAc sites, and (4) introduce platforms cataloging proteins that interact with the O-GlcNAc cycling enzymes (i.e., O-GlcNAc transferase and O-GlcNAcase). We hope these resources will provide useful information to both experienced researchers and new incomers to the O-GlcNAc field. We anticipate that this review provides a framework to stimulate the future development of more sophisticated informatic tools for O-GlcNAc research.

O-GlcNAcylation: Crosstalk between Hemostasis, Inflammation, and Cancer

O-linked β-N-acetylglucosamine (O-GlcNAc, O-GlcNAcylation) is a post-translational modification of serine/threonine residues of proteins. Alterations in O-GlcNAcylation have been implicated in several types of cancer, regulation of tumor progression, inflammation, and thrombosis through its interaction with signaling pathways. We aim to explore the relationship between O-GlcNAcylation and hemostasis, inflammation, and cancer, which could serve as potential prognostic tools or clinical predictions for cancer patients' healthcare and as an approach to combat cancer. We found that cancer is characterized by high glucose demand and consumption, a chronic inflammatory state, a state of hypercoagulability, and platelet hyperaggregability that favors thrombosis; the latter is a major cause of death in these patients. Furthermore, we review transcription factors and pathways associated with O-GlcNAcylation, thrombosis, inflammation, and cancer, such as the PI3K/Akt/c-Myc pathway, the nuclear factor kappa B pathway, and the PI3K/AKT/mTOR pathway. We also review infectious agents associated with cancer and chronic inflammation and potential inhibitors of cancer cell development. We conclude that it is necessary to approach both the diagnosis and treatment of cancer as a network in which multiple signaling pathways are integrated, and to search for a combination of potential drugs that regulate this signaling network.

14-3-3ε augments OGT stability by binding with S20-phosphorylated OGT

The relationship between O-linked N-acetylglucosamine (O-GlcNAc) transferase (OGT) and mitosis is intertwined. Besides the numerous mitotic OGT substrates that have been identified, OGT itself is also a target of the mitotic machinery. Previously, our investigations have shown that Checkpoint kinase 1 (Chk1) phosphorylates OGT at Ser-20 to increase OGT levels during cytokinesis, suggesting that OGT levels oscillate as mitosis progresses. Herein we studied its underlying mechanism. We set out from an R17C mutation of OGT, which is a uterine carcinoma mutation in The Cancer Genome Atlas. We found that R17C abolishes the S20 phosphorylation of OGT, as it lies in the Chk1 phosphorylating consensus motif. Consistent with our previous report that pSer-20 is essential for OGT level increases during cytokinesis, we further demonstrate that the R17C mutation renders OGT less stable, decreases vimentin phosphorylation levels and results in cytokinesis defects. Based on bioinformatic predictions, pSer-20 renders OGT more likely to interact with 14-3-3 proteins, the phospho-binding signal adaptor/scaffold protein family. By screening the seven isoforms of 14-3-3 family, we show that 14-3-3ε specifically associates with Ser-20-phosphorylated OGT. Moreover, we studied the R17C and S20A mutations in xenograft models and demonstrated that they both inhibit uterine carcinoma compared to wild-type OGT, probably due to less cellular reproduction. Our work is a sequel of our previous report on pS20 of OGT and is in line with the notion that OGT is intricately regulated by the mitotic network.

Comprehensive Glycomic and Glycoproteomic Analyses of Human Programmed Cell Death Protein 1 Extracellular Domain

Human programmed cell death protein 1 (hPD-1) is an essential receptor in the immune checkpoint pathway. It has played an important role in cancer therapy. However, not all patients respond positively to the PD-1 antibody treatment, and the underlying mechanism remains unknown. PD-1 is a transmembrane glycoprotein, and its extracellular domain (ECD) is reported to be responsible for interactions and signal transduction. This domain contains 4 N-glycosylation sites and 25 potential O-glycosylation sites, which implicates the importance of glycosylation. The structure of hPD-1 has been intensively studied, but the glycosylation of this protein, especially the glycan on each glycosylation site, has not been comprehensively illustrated. In this study, hPD-1 ECD expressed by human embryonic kidney 293 (HEK 293) and Chinese hamster ovary (CHO) cells was analyzed; not only N- and O-glycosylation sites but also the glycans on these sites were comprehensively analyzed using mass spectrometry. In addition, hPD-1 ECD binding to different anti-hPD-1 antibodies was tested, and N-glycans were found functioned differently. All of this glycan information will be beneficial for future PD-1 studies.

Modulation of extrinsic apoptotic pathway by intracellular glycosylation

The importance of post-translational modifications (PTMs), particularly O-GlcNAcylation, of cytoplasmic proteins in apoptosis has been neglected for quite a while. Modification of cytoplasmic proteins by a single N-acetylglucosamine sugar is a dynamic and reversible PTM exhibiting properties more like phosphorylation than classical O- and N-linked glycosylation. Due to the sparse information existing, we have only limited understanding of how GlcNAcylation affects cell death. Deciphering the role of GlcNAcylation in cell fate may provide further understanding of cell fate decisions. This review focus on the modulation of extrinsic apoptotic pathway via GlcNAcylation carried out by O-GlcNAc transferase (OGT) or by other bacterial effector proteins.

The OGT-c-Myc-PDK2 axis rewires the TCA cycle and promotes colorectal tumor growth

Deregulated glucose metabolism termed the "Warburg effect" is a fundamental feature of cancers, including the colorectal cancer. This is typically characterized with an increased rate of glycolysis, and a concomitant reduced rate of the tricarboxylic acid (TCA) cycle metabolism as compared to the normal cells. How the TCA cycle is manipulated in cancer cells remains unknown. Here, we show that O-linked N-acetylglucosamine (O-GlcNAc) regulates the TCA cycle in colorectal cancer cells. Depletion of OGT, the sole transferase of O-GlcNAc, significantly increases the TCA cycle metabolism in colorectal cancer cells. Mechanistically, OGT-catalyzed O-GlcNAc modification of c-Myc at serine 415 (S415) increases c-Myc stability, which transcriptionally upregulates the expression of pyruvate dehydrogenase kinase 2 (PDK2). PDK2 phosphorylates pyruvate dehydrogenase (PDH) to inhibit the activity of mitochondrial pyruvate dehydrogenase complex, which reduces mitochondrial pyruvate metabolism, suppresses reactive oxygen species production, and promotes xenograft tumor growth. Furthermore, c-Myc S415 glycosylation levels positively correlate with PDK2 expression levels in clinical colorectal tumor tissues. This study highlights the OGT-c-Myc-PDK2 axis as a key mechanism linking oncoprotein activation with deregulated glucose metabolism in colorectal cancer.

Management of Microcomplications of Diabetes Mellitus: Challenges, Current Trends, and Future Perspectives in Treatment

Diabetes mellitus is a chronic metabolic disorder characterized by high blood sugar levels, which can lead to severe health issues if not managed effectively. Recent statistics indicate a significant global impact, with 463 million adults diagnosed worldwide and this projected to rise to 700 million by 2045. Type 1 diabetes is an autoimmune disorder where the immune system attacks pancreatic beta cells, reducing insulin production. Type 2 diabetes is primarily due to insulin resistance. Both types of diabetes are linked to severe microvascular and macrovascular complications if unmanaged. Microvascular complications, such as diabetic retinopathy, nephropathy, and neuropathy, result from damage to small blood vessels and can lead to organ and tissue dysfunction. Chronic hyperglycemia plays a central role in the onset of these complications, with prolonged high blood sugar levels causing extensive vascular damage. The emerging treatments and current research focus on various aspects, from insulin resistance to the intricate cellular damage induced by glucose toxicity. Understanding and intervening in these pathways are critical for developing effective treatments and managing diabetes long term. Furthermore, ongoing health initiatives, such as increasing awareness, encouraging early detection, and improving treatments, are in place to manage diabetes globally and mitigate its impact on health and society. These initiatives are a testament to the collective effort to combat this global health challenge.

Neuro-protective effects of increased O-GlcNAcylation by glucosamine in an optic tectum traumatic brain injury model of adult zebrafish

This study investigated the behavioral and molecular changes in the telencephalon following needle stab-induced injury in the optic tectum of adult zebrafish. At 3 days post-injury (dpi), there was noticeable structural damage to brain tissue and reduced neuronal proliferation in the telencephalon that persisted until 30 dpi. Neurobehavioral deficits observed at 3 dpi included decreased exploratory and social activities and impaired learning and memory (L/M) functions; all of these resolved by 7 dpi. The injury led to a reduction in telencephalic phosphorylated cAMP response element-binding protein and O-GlcNAcylation, both of which were restored by 30 dpi. There was an increase in GFAP expression and nuclear translocation of NF-κB p65 at 3 dpi, which were not restored by 30 dpi. The injury caused decreased O-GlcNAc transferase and increased O-GlcNAcase levels at 3 dpi, normalizing by 30 dpi. Glucosamine (GlcN) treatment at 3 dpi significantly restored O-GlcNAcylation levels and L/M function, also reducing GFAP activation. Glucose treatment recovered L/M function by 7 dpi, but inhibition of the hexosamine biosynthetic pathway by 6-diazo-5-oxo-L-norleucine blocked this recovery. These findings suggest that the O-GlcNAc pathway is a potential therapeutic target for addressing L/M impairment following traumatic brain injury in zebrafish.

A protein O-GlcNAc glycosyltransferase regulates the antioxidative response in Yersinia pestis

Post-translational addition of O-linked N-acetylglucosamine (O-GlcNAc) to proteins is commonly associated with a variety of stress responses and cellular processes in eukaryotes, but its potential roles in bacteria are unclear. Here, we show that protein HmwC acts as an O-GlcNAc transferase (OGT) responsible for O-GlcNAcylation of multiple proteins in Yersinia pestis, a flea-borne pathogen responsible for plague. We identify 64 O-GlcNAcylated proteins (comprising 65 sites) with differential abundance under conditions mimicking the mammalian host (Mh) and flea vector (Fv) environments. Deletion of hmwC, encoding a putative OGT, structurally distinct from any existing member of the GT41 family, results in reduced O-GlcNAcylation, reduced growth, and alterations in virulence properties and survival under stress. Purified HmwC can modify target proteins in vitro using UDP-GlcNAc as sugar donor. One of the target proteins, OsdY, promotes Y. pestis survival under oxidative stress conditions. Thus, our results support that regulation of antioxidative responses through O-GlcNAcylation may be a conserved process shared by prokaryotes and eukaryotes.

Manipulating mannose metabolism as a potential anticancer strategy

Cancer cells acquire metabolic advantages over their normal counterparts regarding the use of nutrients for sustained cell proliferation and cell survival in the tumor microenvironment. Notable among the metabolic traits in cancer cells is the Warburg effect, which is a reprogrammed form of glycolysis that favors the rapid generation of ATP from glucose and the production of biological macromolecules by diverting glucose into various metabolic intermediates. Meanwhile, mannose, which is the C-2 epimer of glucose, has the ability to dampen the Warburg effect, resulting in slow-cycling cancer cells that are highly susceptible to chemotherapy. This anticancer effect of mannose appears when its catabolism is compromised in cancer cells. Moreover, de novo synthesis of mannose within cancer cells has also been identified as a potential target for enhancing chemosensitivity through targeting glycosylation pathways. The underlying mechanisms by which alterations in mannose metabolism induce cancer cell vulnerability are just beginning to emerge. This review summarizes the current state of our knowledge of mannose metabolism and provides insights into its manipulation as a potential anticancer strategy.

Post-translational modification by the Pgf glycosylation machinery modulates Streptococcus mutans OMZ175 physiology and virulence

Streptococcus mutans is commonly associated with dental caries and the ability to form biofilms is essential for its pathogenicity. We recently identified the Pgf glycosylation machinery of S. mutans, responsible for the post-translational modification of the surface-associated adhesins Cnm and WapA. Since the four-gene pgf operon (pgfS-pgfM1-pgfE-pgfM2) is part of the S. mutans core genome, we hypothesized that the scope of the Pgf system goes beyond Cnm and WapA glycosylation. In silico analyses and tunicamycin sensitivity assays suggested a functional overlap between the Pgf machinery and the rhamnose-glucose polysaccharide synthesis pathway. Phenotypic characterization of pgf mutants (ΔpgfS, ΔpgfE, ΔpgfM1, ΔpgfM2, and Δpgf) revealed that the Pgf system is important for biofilm formation, surface charge, membrane stability, and survival in human saliva. Moreover, deletion of the entire pgf operon (Δpgf strain) resulted in significantly impaired colonization in a rat oral colonization model. Using Cnm as a model, we showed that Cnm is heavily modified with N-acetyl hexosamines but it becomes heavily phosphorylated with the inactivation of the PgfS glycosyltransferase, suggesting a crosstalk between these two post-translational modification mechanisms. Our results revealed that the Pgf machinery contributes to multiple aspects of S. mutans pathobiology that may go beyond Cnm and WapA glycosylation.

Mineralocorticoid receptor overactivation in diabetes mellitus: role of O-GlcNAc modification

Hypertension is a significant risk factor for microangiopathy and cardiovascular complications in diabetic patients. The efficacy of mineralocorticoid receptor (MR) antagonists in impeding the advancement of diabetic nephropathy, along with the reduction in active renin concentration observed in diabetic retinopathy, strongly implies the involvement of MR overactivation in diabetic complications. This review provides a comprehensive review of various mechanisms proposed for MR overactivation in diabetes mellitus. In particular, it focuses on post-translational MR modifications, including O-linked N-acetylglucosamine modification and phosphorylation, which have been implicated in MR protein stabilization and overactivation under conditions of high glucose. Given the role of MR overactivation in hyperglycemia, it emerges as a promising therapeutic target for preventing diabetic complications. Post-translational modifications (PTMs), such as O-GlcNAcylation and phosphorylation, are related to MR overactivation in diabetes and metabolic syndrome. Aldosterone binding promotes the proteasomal degradation of MR. Under conditions of high glucose, O-GlcNAcylation, and PKCβ-mediated MR phosphorylation are increased. Salt loading and oxidative stress also increase MR phosphorylation through the EGER/ERK pathway. PTMs inhibit ubiquitin attachment to the MR and interfere with the receptor's aldosterone-induced proteasomal degradation. Consequently, they increase the sensitivity of the MR to aldosterone and exacerbate aldosterone-associated complications.

Hyperglycemia-driven signaling bridges between diabetes and cancer

Growing epidemiological evidence indicates an association between obesity, type 2 diabetes, and certain cancers, suggesting the existence of common underlying mechanisms in these diseases. Frequent hyperglycemias in type 2 diabetes promote pro-inflammatory responses and stimulate intracellular metabolic flux which rewires signaling pathways and influences the onset and advancement of different types of cancers. Here, we review the provocative impact of hyperglycemia on a subset of interconnected signalling pathways that regulate (i) cell growth and survival, (ii) metabolism adjustments, (iii) protein function modulation in response to nutrient availability (iv) and cell fate and proliferation and which are driven respectively by PI3K (Phosphoinositide 3-kinase), AMPK (AMP-activated protein kinase), O-GlcNAc (O-linked N-acetylglucosamine) and Wnt/β-catenin. Specifically, we will elaborate on their involvement in glucose metabolism, inflammation, and cell proliferation, highlighting their interplay in the pathogenesis of diabetes and cancer. Furthermore, the influence of antineoplastic and antidiabetic drugs on the unbridled cellular pathways will be examined. This review aims to inspire the next molecular studies to understand how type 2 diabetes may lead to certain cancers. This will contribute to personalized medicine and direct better prevention strategies.

Sex-specific effect of antenatal Zika virus infection on murine fetal growth, placental nutrient transporters, and nutrient sensor signaling pathways

Maternal Zika virus (ZIKV) infection during pregnancy has been associated with severe intrauterine growth restriction (IUGR), placental damage, metabolism disturbances, and newborn neurological abnormalities. Here, we investigated the impact of maternal ZIKV infection on placental nutrient transporters and nutrient-sensitive pathways. Immunocompetent (C57BL/6) mice were injected with Low (103 PFU-ZIKVPE243) or High (5 × 107 PFU-ZIKVPE243) ZIKV titers at gestational day (GD) 12.5, and tissue was collected at GD18.5 (term). Fetal-placental growth was impaired in male fetuses, which exhibited higher placental expression of the ZIKV infective marker, eukaryotic translation initiation factor 2 (eIF2α), but lower levels of phospho-eIF2α. There were no differences in fetal-placental growth in female fetuses, which exhibited no significant alterations in placental ZIKV infective markers. Furthermore, ZIKV promoted increased expression of glucose transporter type 1 (Slc2a1/Glut1) and decreased levels of glucose-6-phosphate in female placentae, with no differences in amino acid transport potential. In contrast, ZIKV did not impact glucose transporters in male placentae but downregulated sodium-coupled neutral amino acid 2 (Snat2) transporter expression. We also observed sex-dependent differences in the hexosamine biosynthesis pathway (HBP) and O-GlcNAcylation in ZIKV-infected pregnancies, showing that ZIKV can disturb placental nutrient sensing. Our findings highlight molecular alterations in the placenta caused by maternal ZIKV infection, shedding light on nutrient transport, sensing, and availability. Our results also suggest that female and male placentae employ distinct coping mechanisms in response to ZIKV-induced metabolic changes, providing insights into therapeutic approaches for congenital Zika syndrome.

Thermodynamic coupling of the tandem RRM domains of hnRNP A1 underlie its pleiotropic RNA binding functions

The functional properties of RNA binding proteins (RBPs) require allosteric regulation through interdomain communication. Despite the importance of allostery to biological regulation, only a few studies have been conducted to describe the biophysical nature by which interdomain communication manifests in RBPs. Here, we show for hnRNP A1 that interdomain communication is vital for the unique stability of its amino-terminal domain, which consists of two RNA recognition motifs (RRMs). These RRMs exhibit drastically different stability under pressure. RRM2 unfolds as an individual domain but remains stable when appended to RRM1. Variants that disrupt interdomain communication between the tandem RRMs show a significant decrease in stability. Carrying these mutations over to the full-length protein for in vivo experiments revealed that the mutations affected the ability of the disordered carboxyl-terminal domain to engage in protein-protein interactions and influenced the protein's RNA binding capacity. Collectively, this work reveals that thermodynamic coupling between the tandem RRMs of hnRNP A1 accounts for its allosteric regulatory functions.

O-GlcNAcylation of MITF regulates its activity and CDK4/6 inhibitor resistance in breast cancer

Cyclin-dependent kinases 4 and 6 (CDK4/6) play a pivotal role in cell cycle and cancer development. Targeting CDK4/6 has demonstrated promising effects against breast cancer. However, resistance to CDK4/6 inhibitors (CDK4/6i), such as palbociclib, remains a substantial challenge in clinical settings. Using high-throughput combinatorial drug screening and genomic sequencing, we find that the microphthalmia-associated transcription factor (MITF) is activated via O-GlcNAcylation by O-GlcNAc transferase (OGT) in palbociclib-resistant breast cancer cells and tumors. Mechanistically, O-GlcNAcylation of MITF at Serine 49 enhances its interaction with importin α/β, thus promoting its translocation to nuclei, where it suppresses palbociclib-induced senescence. Inhibition of MITF or its O-GlcNAcylation re-sensitizes resistant cells to palbociclib. Moreover, clinical studies confirm the activation of MITF in tumors from patients who are palbociclib-resistant or undergoing palbociclib treatment. Collectively, our studies shed light on the mechanism regulating palbociclib resistance and present clinical evidence for developing therapeutic approaches to treat CDK4/6i-resistant breast cancer patients.

The ubiquitin E3 ligase APC/CCdc20 mediates mitotic degradation of OGT

O-linked β-N-acetylglucosamine (O-GlcNAc) transferase (OGT) is the sole enzyme that catalyzes all O-GlcNAcylation reactions intracellularly. Previous investigations have found that OGT levels oscillate during the cell division process. Specifically, OGT abundance is downregulated during mitosis, but the underlying mechanism is lacking. Here we demonstrate that OGT is ubiquitinated by the ubiquitin E3 ligase, anaphase promoting complex/cyclosome (APC/C)-cell division cycle 20 (Cdc20). We show that APC/CCdc20 interacts with OGT through a conserved destruction box (D-box): Arg-351/Leu-354, the abrogation of which stabilizes OGT. As APC/CCdc20-substrate binding is often preceded by a priming ubiquitination event, we also used mass spectrometry and mapped OGT Lys-352 to be a ubiquitination site, which is a prerequisite for OGT association with APC/C subunits. Interestingly, in The Cancer Genome Atlas, R351C is a uterine carcinoma mutant, suggesting that mutations of the D-box are linked with tumorigenesis. Paradoxically, we found that both R351C and the D-box mutants (R351A/L354A) inhibit uterine carcinoma in mouse xenograft models, probably due to impaired cell division and proliferation. In sum, we propose a model where OGT Lys-352 ubiquitination primes its binding with APC/C, and then APC/CCdc20 partners with OGT through the D-box for its mitotic destruction. Our work not only highlights the key mechanism that regulates OGT during the cell cycle, but also reveals the mutual coordination between glycosylation and the cell division machinery.

N-terminal cysteine acetylation and oxidation patterns may define protein stability

Oxygen homeostasis is maintained in plants and animals by O2-sensing enzymes initiating adaptive responses to low O2 (hypoxia). Recently, the O2-sensitive enzyme ADO was shown to initiate degradation of target proteins RGS4/5 and IL32 via the Cysteine/Arginine N-degron pathway. ADO functions by catalysing oxidation of N-terminal cysteine residues, but despite multiple proteins in the human proteome having an N-terminal cysteine, other endogenous ADO substrates have not yet been identified. This could be because alternative modifications of N-terminal cysteine residues, including acetylation, prevent ADO-catalysed oxidation. Here we investigate the relationship between ADO-catalysed oxidation and NatA-catalysed acetylation of a broad range of protein sequences with N-terminal cysteines. We present evidence that human NatA catalyses N-terminal cysteine acetylation in vitro and in vivo. We then show that sequences downstream of the N-terminal cysteine dictate whether this residue is oxidised or acetylated, with ADO preferring basic and aromatic amino acids and NatA preferring acidic or polar residues. In vitro, the two modifications appear to be mutually exclusive, suggesting that distinct pools of N-terminal cysteine proteins may be acetylated or oxidised. These results reveal the sequence determinants that contribute to N-terminal cysteine protein modifications, with implications for O2-dependent protein stability and the hypoxic response.

Glycosylation editing: an innovative therapeutic opportunity in precision oncology

Cancer is still one of the most arduous challenges in the human society, even though humans have found many ways to try to conquer it. With our incremental understandings on the impact of sugar on human health, the clinical relevance of glycosylation has attracted our attention. The fact that altered glycosylation profiles reflect and define different health statuses provide novel opportunities for cancer diagnosis and therapeutics. By reviewing the mechanisms and critical enzymes involved in protein, lipid and glycosylation, as well as current use of glycosylation for cancer diagnosis and therapeutics, we identify the pivotal connection between glycosylation and cellular redox status and, correspondingly, propose the use of redox modulatory tools such as cold atmospheric plasma (CAP) in cancer control via glycosylation editing. This paper interrogates the clinical relevance of glycosylation on cancer and has the promise to provide new ideas for laboratory practice of cold atmospheric plasma (CAP) and precision oncology therapy.

Sitetack: A Deep Learning Model that Improves PTM Prediction by Using Known PTMs

Post-translational modifications (PTMs) increase the diversity of the proteome and are vital to organismal life and therapeutic strategies. Deep learning has been used to predict PTM locations. Still, limitations in datasets and their analyses compromise success. Here we evaluate the use of known PTM sites in prediction via sequence-based deep learning algorithms. Specifically, PTM locations were encoded as a separate amino acid before sequences were encoded via word embedding and passed into a convolutional neural network that predicts the probability of a modification at a given site. Without labeling known PTMs, our model is on par with others. With labeling, however, we improved significantly upon extant models. Moreover, knowing PTM locations can increase the predictability of a different PTM. Our findings highlight the importance of PTMs for the installation of additional PTMs. We anticipate that including known PTM locations will enhance the performance of other proteomic machine learning algorithms.

ULK1-dependent phosphorylation of PKM2 antagonizes O-GlcNAcylation and regulates the Warburg effect in breast cancer

Pyruvate kinase M2 (PKM2) is a central metabolic enzyme driving the Warburg effect in tumor growth. Previous investigations have demonstrated that PKM2 is subject to O-linked β-N-acetylglucosamine (O-GlcNAc) modification, which is a nutrient-sensitive post-translational modification. Here we found that unc-51 like autophagy activating kinase 1 (ULK1), a glucose-sensitive kinase, interacts with PKM2 and phosphorylates PKM2 at Ser333. Ser333 phosphorylation antagonizes PKM2 O-GlcNAcylation, promotes its tetramer formation and enzymatic activity, and decreases its nuclear localization. As PKM2 is known to have a nuclear role in regulating c-Myc, we also show that PKM2-S333 phosphorylation inhibits c-Myc expression. By downregulating glucose consumption and lactate production, PKM2 pS333 attenuates the Warburg effect. Through mouse xenograft assays, we demonstrate that the phospho-deficient PKM2-S333A mutant promotes tumor growth in vivo. In conclusion, we identified a ULK1-PKM2-c-Myc axis in inhibiting breast cancer, and a glucose-sensitive phosphorylation of PKM2 in modulating the Warburg effect.

O-GlcNAcylation and immune cell signaling: A review of known and a preview of unknown

The dynamic and reversible modification of nuclear and cytoplasmic proteins by O-GlcNAcylation significantly impacts the function and dysfunction of the immune system. O-GlcNAcylation plays crucial roles under both physiological and pathological conditions in the biochemical regulation of all immune cell functions. Three and a half decades of knowledge acquired in this field is merely sufficient to perceive that what we know is just the prelude. This review attempts to mark out the known regulatory roles of O-GlcNAcylation in key signal transduction pathways and specific protein functions in the immune system and adumbrate ensuing questions toward the unknown functions.

Exploration of potential novel drug targets for diabetic retinopathy by plasma proteome screening

The aim of this study is to identify novel potential drug targets for diabetic retinopathy (DR). A bidirectional two-sample Mendelian randomization (MR) analysis was performed using protein quantitative trait loci (pQTL) of 734 plasma proteins as the exposures and clinically diagnosed DR as the outcome. Genetic instruments for 734 plasma proteins were obtained from recently published genome-wide association studies (GWAS), and external plasma proteome data was retrieved from the Icelandic Decoding Genetics Study and UK Biobank Pharma Proteomics Project. Summary-level data of GWAS for DR were obtained from the Finngen Consortium, comprising 14,584 cases and 202,082 population controls. Steiger filtering, Bayesian co-localization, and phenotype scanning were used to further verify the causal relationships calculated by MR. Three significant (p < 6.81 × 10-5) plasma protein-DR pairs were identified during the primary MR analysis, including CFH (OR = 0.8; 95% CI 0.75-0.86; p = 1.29 × 10-9), B3GNT8 (OR = 1.09; 95% CI 1.05-1.12; p = 5.9 × 10-6) and CFHR4 (OR = 1.11; 95% CI 1.06-1.16; p = 1.95 × 10-6). None of the three proteins showed reverse causation. According to Bayesian colocalization analysis, CFH (coloc.abf-PPH4 = 0.534) and B3GNT8 (coloc.abf-PPH4 = 0.638) in plasma shared the same variant with DR. All three identified proteins were validated in external replication cohorts. Our research shows a cause-and-effect connection between genetically determined levels of CFH, B3GNT8 and CFHR4 plasma proteins and DR. The discovery implies that these proteins hold potential as drug target in the process of developing drugs to treat DR.

O-GlcNAcylation: roles and potential therapeutic target for bone pathophysiology

O-linked N-acetylglucosamine (O-GlcNAc) protein modification (O-GlcNAcylation) is a critical post-translational modification (PTM) of cytoplasmic and nuclear proteins. O-GlcNAcylation levels are regulated by the activity of two enzymes, O-GlcNAc transferase (OGT) and O‑GlcNAcase (OGA). While OGT attaches O-GlcNAc to proteins, OGA removes O-GlcNAc from proteins. Since its discovery, researchers have demonstrated O-GlcNAcylation on thousands of proteins implicated in numerous different biological processes. Moreover, dysregulation of O-GlcNAcylation has been associated with several pathologies, including cancers, ischemia-reperfusion injury, and neurodegenerative diseases. In this review, we focus on progress in our understanding of the role of O-GlcNAcylation in bone pathophysiology, and we discuss the potential molecular mechanisms of O-GlcNAcylation modulation of bone-related diseases. In addition, we explore significant advances in the identification of O-GlcNAcylation-related regulators as potential therapeutic targets, providing novel therapeutic strategies for the treatment of bone-related disorders.

O-GlcNAcylation in ischemic diseases

Protein glycosylation is an extensively studied field, with the most studied forms being oxygen or nitrogen-linked N-acetylglucosamine (O-GlcNAc or N-GlcNAc) glycosylation. Particular residues on proteins are targeted by O-GlcNAcylation, which is among the most intricate post-translational modifications. Significantly contributing to an organism's proteome, it influences numerous factors affecting protein stability, function, and subcellular localization. It also modifies the cellular function of target proteins that have crucial responsibilities in controlling pathways related to the central nervous system, cardiovascular homeostasis, and other organ functions. Under conditions of acute stress, changes in the levels of O-GlcNAcylation of these proteins may have a defensive function. Nevertheless, deviant O-GlcNAcylation nullifies this safeguard and stimulates the advancement of several ailments, the prognosis of which relies on the cellular milieu. Hence, this review provides a concise overview of the function and comprehension of O-GlcNAcylation in ischemia diseases, aiming to facilitate the discovery of new therapeutic targets for efficient treatment, particularly in patients with diabetes.

O-GlcNAc transferase regulates collagen deposition and fibrosis resolution in idiopathic pulmonary fibrosis

Background

Idiopathic pulmonary fibrosis (IPF) is a chronic pulmonary disease that is characterized by an excessive accumulation of extracellular matrix (ECM) proteins (e.g. collagens) in the parenchyma, which ultimately leads to respiratory failure and death. While current therapies exist to slow the progression, no therapies are available to resolve fibrosis.

Methods

We characterized the O-linked N-Acetylglucosamine (O-GlcNAc) transferase (OGT)/O-GlcNAc axis in IPF using single-cell RNA-sequencing (scRNA-seq) data and human lung sections and isolated fibroblasts from IPF and non-IPF donors. The underlying mechanism(s) of IPF were further investigated using multiple experimental models to modulate collagen expression and accumulation by genetically and pharmacologically targeting OGT. Furthermore, we hone in on the transforming growth factor-beta (TGF-β) effector molecule, Smad3, by co-expressing it with OGT to determine if it is modified and its subsequent effect on Smad3 activation.

Results

We found that OGT and O-GlcNAc levels are upregulated in patients with IPF compared to non-IPF. We report that the OGT regulates collagen deposition and fibrosis resolution, which is an evolutionarily conserved process demonstrated across multiple species. Co-expression of OGT and Smad3 showed that Smad3 is O-GlcNAc modified. Blocking OGT activity resulted in decreased phosphorylation at Ser-423/425 of Smad3 attenuating the effects of TGF-β1 induced collagen expression/deposition.

Conclusion

OGT inhibition or knockdown successfully blocked and reversed collagen expression and accumulation, respectively. Smad3 is discovered to be a substrate of OGT and its O-GlcNAc modification(s) directly affects its phosphorylation state. These data identify OGT as a potential target in pulmonary fibrosis resolution, as well as other diseases that might have aberrant ECM/collagen accumulation.

OGT and OGA: Sweet guardians of the genome

The past 4 decades have witnessed tremendous efforts in deciphering the role of O-GlcNAcylation in a plethora of biological processes. Chemists and biologists have joined hand in hand in the sweet adventure to unravel this unique and universal yet uncharted post-translational modification, and the recent advent of cutting-edge chemical biology and mass spectrometry tools has greatly facilitated the process. Compared with O-GlcNAc, DNA damage response (DDR) is a relatively intensively studied area that could be traced to before the elucidation of the structure of DNA. Unexpectedly, yet somewhat expectedly, O-GlcNAc has been found to regulate various DDR pathways: homologous recombination, nonhomologous end joining, base excision repair, and translesion DNA synthesis. In this review, we first cover the recent structural studies of the O-GlcNAc transferase and O-GlcNAcase, the elegant duo that "writes" and "erases" O-GlcNAc modification. Then we delineate the intricate roles of O-GlcNAc transferase and O-GlcNAcase in DDR. We envision that this is only the beginning of our full appreciation of how O-GlcNAc regulates the blueprint of life-DNA.

Functional significance of O-linked N-acetylglucosamine protein modification in regulating autophagy

Autophagy is a core molecular pathway that preserves cellular and organismal homeostasis. Being susceptible to nutrient availability and stress, eukaryotic cells recycle or degrade internal components via membrane transport pathways to provide sustainable biological molecules and energy sources. The dysregulation of this highly conserved physiological process has been strongly linked to human disease. Post-translational modification, a mechanism that regulates protein function, plays a crucial role in autophagy regulation. O-linked N-acetylglucosamine protein modification (O-GlcNAcylation), a monosaccharide post-translational modification of intracellular proteins, is essential in nutritional and stress regulatory mechanisms. O-GlcNAcylation has emerged as an essential regulatory mechanism of autophagy. It regulates autophagy throughout its lifetime by targeting the core components of the autophagy regulatory network. This review provides an overview of the O-GlcNAcylation of autophagy-associated proteins and their regulation and function in the autophagy pathway. Therefore, this article may contribute to further understanding of the role of O-GlcNAc-regulated autophagy and provide new perspectives for the treatment of human diseases.

Post-translational modifications in diabetic cardiomyopathy

The increasing attention towards diabetic cardiomyopathy as a distinctive complication of diabetes mellitus has highlighted the need for standardized diagnostic criteria and targeted treatment approaches in clinical practice. Ongoing research is gradually unravelling the pathogenesis of diabetic cardiomyopathy, with a particular emphasis on investigating various post-translational modifications. These modifications dynamically regulate protein function in response to changes in the internal and external environment, and their disturbance of homeostasis holds significant relevance for the development of chronic ailments. This review provides a comprehensive overview of the common post-translational modifications involved in the initiation and progression of diabetic cardiomyopathy, including O-GlcNAcylation, phosphorylation, methylation, acetylation and ubiquitination. Additionally, the review discusses drug development strategies for targeting key post-translational modification targets, such as agonists, inhibitors and PROTAC (proteolysis targeting chimaera) technology that targets E3 ubiquitin ligases.

O-GlcNAcylation mediates H2O2-induced apoptosis through regulation of STAT3 and FOXO1

The O-linked-β-N-acetylglucosamine (O-GlcNAc) glycosylation (O-GlcNAcylation) is a critical post-translational modification that couples the external stimuli to intracellular signal transduction networks. However, the critical protein targets of O-GlcNAcylation in oxidative stress-induced apoptosis remain to be elucidated. Here, we show that treatment with H2O2 inhibited O-GlcNAcylation, impaired cell viability, increased the cleaved caspase 3 and accelerated apoptosis of neuroblastoma N2a cells. The O-GlcNAc transferase (OGT) inhibitor OSMI-1 or the O-GlcNAcase (OGA) inhibitor Thiamet-G enhanced or inhibited H2O2-induced apoptosis, respectively. The total and phosphorylated protein levels, as well as the promoter activities of signal transducer and activator of transcription factor 3 (STAT3) and Forkhead box protein O 1 (FOXO1) were suppressed by OSMI-1. In contrast, overexpressing OGT or treating with Thiamet-G increased the total protein levels of STAT3 and FOXO1. Overexpression of STAT3 or FOXO1 abolished OSMI-1-induced apoptosis. Whereas the anti-apoptotic effect of OGT and Thiamet-G in H2O2-treated cells was abolished by either downregulating the expression or activity of endogenous STAT3 or FOXO1. These results suggest that STAT3 or FOXO1 are the potential targets of O-GlcNAcylation involved in the H2O2-induced apoptosis of N2a cells.

Neurodevelopmental defects in a mouse model of O-GlcNAc transferase intellectual disability

The addition of O-linked β-N-acetylglucosamine (O-GlcNAc) to proteins (referred to as O-GlcNAcylation) is a modification that is crucial for vertebrate development. O-GlcNAcylation is catalyzed by O-GlcNAc transferase (OGT) and reversed by O-GlcNAcase (OGA). Missense variants of OGT have recently been shown to segregate with an X-linked syndromic form of intellectual disability, OGT-linked congenital disorder of glycosylation (OGT-CDG). Although the existence of OGT-CDG suggests that O-GlcNAcylation is crucial for neurodevelopment and/or cognitive function, the underlying pathophysiologic mechanisms remain unknown. Here we report a mouse line that carries a catalytically impaired OGT-CDG variant. These mice show altered O-GlcNAc homeostasis with decreased global O-GlcNAcylation and reduced levels of OGT and OGA in the brain. Phenotypic characterization of the mice revealed lower body weight associated with reduced body fat mass, short stature and microcephaly. This mouse model will serve as an important tool to study genotype-phenotype correlations in OGT-CDG in vivo and for the development of possible treatment avenues for this disorder.

Ethylene insensitive 2 (EIN2) destiny shaper: The post-translational modification

PTMs (Post-Translational Modifications) of proteins facilitate rapid modulation of protein function in response to various environmental stimuli. The EIN2 (Ethylene Insensitive 2) protein is a core regulatory of the ethylene signaling pathway. Recent findings have demonstrated that PTMs, including protein phosphorylation, ubiquitination, and glycosylation, govern EIN2 trafficking, subcellular localization, stability, and physiological roles. The cognition of multiple PTMs in EIN2 underscores the stringent regulation of protein. Consequently, a thorough review of the regulatory role of PTMs in EIN2 functions will improve our profound comprehension of the regulation mechanism and various physiological processes of EIN2-mediated signaling pathways. This review discusses the evolution, functions, structure and characteristics of EIN2 protein in plants. Additionally, this review sheds light on the progress of protein ubiquitination, phosphorylation, O-Glycosylation in the regulation of EIN2 functions, and the unresolved questions and future perspectives.

SECRET AGENT O-GlcNAcylates Hundreds of Proteins Involved in Diverse Cellular Processes in Arabidopsis

O-GlcNAcylation is a critical post-translational modification of proteins observed in both plants and animals and plays a key role in growth and development. While considerable knowledge exists about over 3000 substrates in animals, our understanding of this modification in plants remains limited. Unlike animals, plants possess two putative homologs: SECRET AGENT (SEC) and SPINDLY, with SPINDLY also exhibiting O-fucosylation activity. To investigate the role of SEC as a major O-GlcNAc transferase in plants, we utilized lectin-weak affinity chromatography enrichment and stable isotope labeling in Arabidopsis labeling, quantifying at both MS1 and MS2 levels. Our findings reveal a significant reduction in O-GlcNAc levels in the sec mutant, indicating the critical role of SEC in mediating O-GlcNAcylation. Through a comprehensive approach, combining higher-energy collision dissociation and electron-transfer high-energy collision dissociation fragmentation with substantial fractionations, we expanded our GlcNAc profiling, identifying 436 O-GlcNAc targets, including 227 new targets. The targets span diverse cellular processes, suggesting broad regulatory functions of O-GlcNAcylation. The expanded targets also enabled exploration of crosstalk between O-GlcNAcylation and O-fucosylation. We also examined electron-transfer high-energy collision dissociation fragmentation for site assignment. This report advances our understanding of O-GlcNAcylation in plants, facilitating further research in this field.

O-GlcNAcylation stimulates the deubiquitination activity of USP16 and regulates cell cycle progression

Histone 2A monoubiquitination (uH2A) underscores a key epigenetic regulation of gene expression. In this report, we show that the deubiquitinase for uH2A, ubiquitin-specific peptidase 16 (USP16), is modified by O-linked N-acetylglucosamine (O-GlcNAc). O-GlcNAcylation involves the installation of the O-GlcNAc moiety to Ser/Thr residues. It crosstalks with Ser/Thr phosphorylation, affects protein-protein interaction, alters enzyme activity or protein folding, and changes protein subcellular localization. In our study, we first confirmed that USP16 is glycosylated on Thr203 and Ser214, as reported in a previous chemoenzymatic screen. We then discovered that mutation of the O-GlcNAcylation site Thr203, which is adjacent to deubiquitination-required Cys204, reduces the deubiquitination activity toward H2AK119ub in vitro and in cells, while mutation on Ser214 had the opposite effects. Using USP16 Ser552 phosphorylation-specific antibodies, we demonstrated that O-GlcNAcylation antagonizes cyclin-dependent kinase 1-mediated phosphorylation and promotes USP16 nuclear export. O-GlcNAcylation of USP16 is also required for deubiquitination of Polo-like kinase 1, a mitotic master kinase, and the subsequent chromosome segregation and cytokinesis. In summary, our study revealed that O-GlcNAcylation of USP16 at Thr203 and Ser214 coordinates deubiquitination of uH2A and Polo-like kinase 1, thus ensuring proper cell cycle progression.

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.

Hexosamine biosynthesis and related pathways, protein N-glycosylation and O-GlcNAcylation: their interconnection and role in plants

N-Acetylglucosamine (GlcNAc), a fundamental amino sugar moiety, is essential for protein glycosylation, glycolipid, GPI-anchor protein, and cell wall components. Uridine diphosphate-GlcNAc (UDP-GlcNAc), an active form of GlcNAc, is synthesized through the hexosamine biosynthesis pathway (HBP). Although HBP is highly conserved across organisms, the enzymes involved perform subtly distinct functions among microbes, mammals, and plants. A complete block of HBP normally causes lethality in any life form, reflecting the pivotal role of HBP in the normal growth and development of organisms. Although HBP is mainly composed of four biochemical reactions, HBP is exquisitely regulated to maintain the homeostasis of UDP-GlcNAc content. As HBP utilizes substrates including fructose-6-P, glutamine, acetyl-CoA, and UTP, endogenous nutrient/energy metabolites may be integrated to better suit internal growth and development, and external environmental stimuli. Although the genes encoding HBP enzymes are well characterized in microbes and mammals, they were less understood in higher plants in the past. As the HBP-related genes/enzymes have largely been characterized in higher plants in recent years, in this review we update the latest advances in the functions of the HBP-related genes in higher plants. In addition, HBP's salvage pathway and GlcNAc-mediated two major co- or post-translational modifications, N-glycosylation and O-GlcNAcylation, are also included in this review. Further knowledge on the function of HBP and its product conjugates, and the mechanisms underlying their response to deleterious environments might provide an alternative strategy for agricultural biofortification in the future.

A Metabolic Axis of Immune Intractability

Immune cells in the tumor niche robustly influence disease progression. Remarkably, in cancer, developmental pathways are reenacted. Many parallels between immune regulation of embryonic development and immune regulation of tumor progression can be drawn, with evidence clearly supporting an immune-suppressive microenvironment in both situations. In these ecosystems, metabolic and bioenergetic circuits guide and regulate immune cell differentiation, plasticity, and functional properties of suppressive and inflammatory immune subsets. As such, there is an emerging pattern of intersection across the dynamic process of ontogeny and the ever-evolving tumor neighborhood. In this article, we focus on the convergence of immune programming during ontogeny and in the tumor microenvironment. Exemplifying dysregulation of Hedgehog (Hh) activity, a key player during ontogeny, we highlight a critical convergence of these fields and the metabolic axis of the nutrient sensing hexosamine biosynthetic pathway (HBP) that integrates glucose, glutamine, amino acids, acetyl CoA, and uridine-5'-triphosphate (UTP), culminating in the synthesis of UDP-GlcNAc, a metabolite that functions as a metabolic and bioenergetic sensor. We discuss an emerging pattern of immune regulation, orchestrated by O-GlcNAcylation of key transcriptional regulators, spurring suppressive activity of dysfunctional immune cells in the tumor microenvironment.

Insights into cAMP-dependent molecular mechanisms regulating expression and function of LGALS16 gene in choriocarcinoma JEG-3 cells

The human choriocarcinoma cell line JEG-3 offers a valuable model to study galectin-16 gene (LGALS16) expression and functions in the context of placental cell differentiation and cancer cell biology. Recent evidence indicates that cAMP-mediated signaling pathways might be responsible for the upregulation of LGALS16; however, the underlying mechanisms are unknown. Here, we employed biochemical inhibitors of the cAMP cascade and CRISPR/Cas9 engineered cells to assess regulatory patterns and associations between cAMP-induced trophoblast differentiation and LGALS16 expression in JEG-3 cells. The expression of LGALS16 was significantly upregulated in parallel with human chorionic gonadotropin beta (CGB), a biomarker of syncytiotrophoblast differentiation, in response to 8-Br-cAMP. Inhibition of p38 MAPK and EPAC significantly altered LGALS16 expression during differentiation, while PKA inhibition failed to change LGALS16 and CGB3/5 expression in our cell model. The CRISPR/Cas9 LGALS16 knockout cell pool expressed a significantly lower amount of CGB3/5, a reduced level of CGB protein, and an unaltered cell growth rate in response to 8-Br-cAMP in comparison with wild-type JEG-3 cells. Collectively, these findings suggest that LGALS16 is required for the trophoblast-like differentiation of JEG-3 cells, and its expression is mediated through p38 MAPK and EPAC signaling pathway branches.

O-GlcNAc of STING mediates antiviral innate immunity

BACKGROUND

O-GlcNAcylation modification affects multiple physiological and pathophysiolocal functions of cells. Altered O-GlcNAcylation was reported to participate in antivirus response. Stimulator of interferon genes (STING) is an adaptor mediating DNA virus-induced innate immune response. Whether STING is able to be modified by O-GlcNAcylation and how O-GlcNAcylation affects STING-mediated anti-DNA virus response remain unknown.

METHODS

Metabolomics analysis was used for detecting metabolic alterations in HSV-1 infection cells. Succinylated wheat germ agglutinin (sWGA), co-immunoprecipitation, and pull-down assay were employed for determining O-GlcNAcylation. Mutagenesis PCR was applied for the generation of STING mutants. WT and Sting1-/- C57BL/6 mice (KOCMP-72512-Sting1-B6NVA) were infected with HSV-1 and treated with O-GlcNAcylation inhibitor for validating the role of STING O-GlcNAcylation in antiviral response.

RESULTS

STING was functionally activated by O-GlcNAcylation in host cells challenged with HSV-1. We demonstrated that this signaling event was initiated by virus infection-enhanced hexosamine biosynthesis pathway (HBP). HSV-1 (or viral DNA mimics) promotes glucose metabolism of host cells with a marked increase in HBP, which provides donor glucosamine for O-GlcNAcylation. STING was O-GlcNAcylated on threonine 229, which led to lysine 63-linked ubiquitination of STING and activation of antiviral immune responses. Mutation of STING T229 to alanine abrogated STING activation and reduced HSV-1 stimulated production of interferon (IFN). Application of 6-diazo-5-oxonorleucine (DON), an agent that blocks the production of UDP-GlcNAc and inhibits O-GlcNAcylation, markedly attenuated the removal of HSV-1 in wild type C57BL/6 mice, leading to an increased viral retention, elevated infiltration of inflammatory cells, and worsened tissue damages to those displayed in STING gene knockout mice. Together, our data suggest that STING is O-GlcNAcylated in HSV-1, which is crucial for an effective antiviral innate immune response.

CONCLUSION

HSV-1 infection activates the generation of UDP-Glc-NAc by upregulating the HBP metabolism. Elevated UDP-Glc-NAc promotes the O-GlcNAcylation of STING, which mediates the anti-viral function of STING. Targeting O-GlcNAcylation of STING could be a useful strategy for antiviral innate immunity.

O-glycosylation in viruses: A sweet tango

O-glycosylation is an ancient yet underappreciated protein posttranslational modification, on which many bacteria and viruses heavily rely to perform critical biological functions involved in numerous infectious diseases or even cancer. But due to the innate complexity of O-glycosylation, research techniques have been limited to study its exact role in viral attachment and entry, assembly and exit, spreading in the host cells, and the innate and adaptive immunity of the host. Recently, the advent of many newly developed methodologies (e.g., mass spectrometry, chemical biology tools, and molecular dynamics simulations) has renewed and rekindled the interest in viral-related O-glycosylation in both viral proteins and host cells, which is further fueled by the COVID-19 pandemic. In this review, we summarize recent advances in viral-related O-glycosylation, with a particular emphasis on the mucin-type O-linked α-N-acetylgalactosamine (O-GalNAc) on viral proteins and the intracellular O-linked β-N-acetylglucosamine (O-GlcNAc) modifications on host proteins. We hope to provide valuable insights into the development of antiviral reagents or vaccines for better prevention or treatment of infectious diseases.

Diet-inducing hypercholesterolemia show decreased O-GlcNAcylation of liver proteins through modulation of AMPK

O-GlcNAcylation, a nutritionally driven, post-translational modification of proteins, is gaining importance because of its health implications. Changes in O-GlcNAcylation are observed in various disease conditions. Changes in O-GlcNAcylation by diet that causes hypercholesterolemia are not critically looked into in the liver. To address it, both in vitro and in vivo approaches were employed. Hypercholesterolemia was induced individually by feeding cholesterol (H)/high-fat (HF) diet. Global O-GlcNAcylation levels and modulation of AMPK activation in both preventive and curative approaches were looked into. Diet-induced hypercholesterolemia resulted in decreased O-GlcNAcylation of liver proteins which was associated with decreased O-linked N-acetylglucosaminyltransferase (OGT) and Glutamine fructose-6-phosphate amidotransferase-1 (GFAT1). Activation of AMPK by metformin in preventive mode restored the O-GlcNAcylation levels; however, metformin treatment of HepG2 cells in curative mode restored O-GlcNAcylation levels in HF but failed to in H condition (at 24 h). Further, maternal faulty diet resulted in decreased O-GlcNAcylation in pup liver despite feeding normal diet till adulthood. A faulty diet modulates global O-GlcNAcylation of liver proteins which is accompanied by decreased AMPK activation which could exacerbate metabolic syndromes through fat accumulation in the liver.

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.

Progress of fluorescent probes for protein phosphorylation and glycosylation in atherosclerosis

Exploring the post-translational modification (PTM) of proteins in the course of atherosclerotic disease has important guiding significance for the early warning of atherosclerotic plaque, the development of targeted drugs and the treatment of disease. The advancement advanced detection and imaging methods for phosphorylated and glycosylated proteins is an important tool to further reveal the levels of protein phosphorylation and glycosylation during atherosclerotic plaque formation. We present research strategies for detecting protein phosphorylation and glycosylation from the perspective of fluorescent probes, and discuss the feasibility and future direction of the development of these methods for detecting and imaging phosphorylated and glycosylated proteins in atherosclerotic disease.

Cell and tissue-specific glycosylation pathways informed by single-cell transcriptomics

While single cell studies have made significant impacts in various subfields of biology, they lag in the Glycosciences. To address this gap, we analyzed single-cell glycogene expressions in the Tabula Sapiens dataset of human tissues and cell types using a recent glycosylation-specific gene ontology (GlycoEnzOnto). At the median sequencing (count) depth, ~40-50 out of 400 glycogenes were detected in individual cells. Upon increasing the sequencing depth, the number of detectable glycogenes saturates at ~200 glycogenes, suggesting that the average human cell expresses about half of the glycogene repertoire. Hierarchies in glycogene and glycopathway expressions emerged from our analysis: nucleotide-sugar synthesis and transport exhibited the highest gene expressions, followed by genes for core enzymes, glycan modification and extensions, and finally terminal modifications. Interestingly, the same cell types showed variable glycopathway expressions based on their organ or tissue origin, suggesting nuanced cell- and tissue-specific glycosylation patterns. Probing deeper into the transcription factors (TFs) of glycogenes, we identified distinct groupings of TFs controlling different aspects of glycosylation: core biosynthesis, terminal modifications, etc. We present webtools to explore the interconnections across glycogenes, glycopathways, and TFs regulating glycosylation in human cell/tissue types. Overall, the study presents an overview of glycosylation across multiple human organ systems.