Decoding the Role of O-GlcNAcylation in Hepatocellular Carcinoma.

Post-translational modifications (PTMs) influence protein functionality by modulating protein stability, localization, and interactions with other molecules, thereby controlling various cellular processes. Common PTMs include phosphorylation, acetylation, ubiquitination, glycosylation, SUMOylation, methylation, sulfation, and nitrosylation. Among these modifications, O-GlcNAcylation has been shown to play a critical role in cancer development and progression, especially in hepatocellular carcinoma (HCC). This review outlines the role of O-GlcNAcylation in the development and progression of HCC. Moreover, we delve into the underlying mechanisms of O-GlcNAcylation in HCC and highlight compounds that target O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA) to improve treatment outcomes. Understanding the role of O-GlcNAcylation in HCC will offer insights into potential therapeutic strategies targeting OGT and OGA, which could improve treatment for patients with HCC.

The non-catalytic domains of O-GlcNAc cycling enzymes present new opportunities for function-specific control.

O-GlcNAcylation is an essential protein glycosylation governed by two O-GlcNAc cycling enzymes: O-GlcNAc transferase (OGT) installs a single sugar moiety N-acetylglucosamine (GlcNAc) on protein serine and threonine residues, and O-GlcNAcase (OGA) removes them. Aberrant O-GlcNAcylation has been implicated in various diseases. However, the large repertoire of more than 1000 O-GlcNAcylated proteins and the elusive mechanisms of OGT/OGA in substrate recognition present significant challenges in targeting the dysregulated O-GlcNAcylation for therapeutic development. Recently, emerging evidence suggested that the non-catalytic domains play critical roles in regulating the functional specificity of OGT/OGA via modulating their protein interactions and substrate recognition. Here, we discuss recent studies on the structures, mechanisms, and related tools of the OGT/OGA non-catalytic domains, highlighting new opportunities for function-specific control.

O-GlcNAcase regulates pluripotency states of human embryonic stem cells.

Understanding the regulation of human embryonic stem cells (hESCs) pluripotency is critical to advance the field of developmental biology and regenerative medicine. Despite the recent progress, molecular events regulating hESC pluripotency, especially the transition between naive and primed states, still remain unclear. Here we show that naive hESCs display lower levels of O-linked N-acetylglucosamine (O-GlcNAcylation) than primed hESCs. O-GlcNAcase (OGA), the key enzyme catalyzing the removal of O-GlcNAc from proteins, is highly expressed in naive hESCs and is important for naive pluripotency. Depletion of OGA accelerates naive-to-primed pluripotency transition. OGA is transcriptionally regulated by EP300 and acts as a transcription regulator of genes important for maintaining naive pluripotency. Moreover, we profile protein O-GlcNAcylation of the two pluripotency states by quantitative proteomics. Together, this study identifies OGA as an important factor of naive pluripotency in hESCs and suggests that O-GlcNAcylation has a broad effect on hESCs homeostasis.

OGT and OGA gene-edited human induced pluripotent stem cells for dissecting the functional roles of O-GlcNAcylation in hematopoiesis.

Hematopoiesis continues throughout life to produce all types of blood cells from hematopoietic stem cells (HSCs). Metabolic state is a known regulator of HSC self-renewal and differentiation, but whether and how metabolic sensor O-GlcNAcylation, which can be modulated via an inhibition of its cycling enzymes O-GlcNAcase (OGA) and O-GlcNAc transferase (OGT), contributes to hematopoiesis remains largely unknown. Herein, isogenic, single-cell clones of OGA-depleted (OGAi) and OGT-depleted (OGTi) human induced pluripotent stem cells (hiPSCs) were successfully generated from the master hiPSC line MUSIi012-A, which were reprogrammed from CD34+ hematopoietic stem/progenitor cells (HSPCs) containing epigenetic memory. The established OGAi and OGTi hiPSCs exhibiting an increase or decrease in cellular O-GlcNAcylation concomitant with their loss of OGA and OGT, respectively, appeared normal in phenotype and karyotype, and retained pluripotency, although they may favor differentiation toward certain germ lineages. Upon hematopoietic differentiation through mesoderm induction and endothelial-to-hematopoietic transition, we found that OGA inhibition accelerates hiPSC commitment toward HSPCs and that disruption of O-GlcNAc homeostasis affects their commitment toward erythroid lineage. The differentiated HSPCs from all groups were capable of giving rise to all hematopoietic progenitors, thus confirming their functional characteristics. Altogether, the established single-cell clones of OGTi and OGAi hiPSCs represent a valuable platform for further dissecting the roles of O-GlcNAcylation in blood cell development at various stages and lineages of blood cells. The incomplete knockout of OGA and OGT in these hiPSCs makes them susceptible to additional manipulation, i.e., by small molecules, allowing the molecular dynamics studies of O-GlcNAcylation.

Dual Transcriptomic and Metabolomic Analysis of Elicited Flax Sheds Light on the Kinetics of Immune Defense Activation Against the Biotrophic Pathogen Oidium lini.

Flax (Linum usitatissimum) grown under controlled conditions displayed genotype-dependent resistance to powdery mildew (Oidium lini) following COS-OGA (comprising chitosan- and pectin-derived oligomers) elicitor application. The present study reveals a two-step immune response in plants preventively challenged with the elicitor: an initial, rapid response characterized by the transcription of defense genes whose protein products act in contact with or within the cell wall, where biotrophic pathogens initially thrive, followed by a prolonged activation of cell wall peroxidases and accumulation of secondary metabolites. Thus, dozens of genes encoding membrane receptors, pathogenesis-related proteins, and wall peroxidases were initially overexpressed. Repeated COS-OGA treatments had a transient effect on the transcriptome response while cumulatively remodeling the metabolome over time, with a minimum of two applications required for maximal metabolomic shifts. Secondary metabolites, in particular terpenoids and phenylpropanoids, emerged as major components of this secondary defense response alongside pathogenesis-related proteins and wall peroxidases. The sustained accumulation of secondary metabolites, even after cessation of elicitation, contrasted with the short-lived transcriptomic response. Wall peroxidase enzyme activity also exhibited cumulative effects, increasing strongly for weeks after a third elicitor treatment. This underscores the plasticity of the plant immune response in the face of a potential infection, and the need for repeated preventive applications to achieve the full protective potential of the elicitor.

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

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

MUC4 O-GlcNAcylation Regulates the Epithelial Phenotype in Conjunctival Epithelial Cells.

In the present study, our aim was to explore the role of MUC4 in IL-4-stimulated conjunctival epithelial cells and the underlying mechanisms. Human recombinant IL-4 was employed in human conjunctival epithelial cells (HConEpic) cells, and MUC4 shRNA (sh-MUC4) was constructed to explore the functional role of MUC4. The protein level of MUC4, O-GlcNAc transferase (OGT), O-GlcNAc hydrolase (OGA), zonula occludens 1 (ZO-1), gap junction protein beta 2 (GJB2), claudin-8 (CLDN8), and E-cadherin were detected by Western blot in HConEpic cells, the interaction between MUC4 and OGT/OGA was assessed by co-immunoprecipitation (IP) and Western blot in 293T cells. Our results showed that IL-4 significantly up-regulated MUC4 and OGT protein levels in HConEpic cells, while down-regulated OGA protein level. Also, IL-4 down-regulated ZO-1, GJB2, CLDN8, and E-cadherin protein levels in HConEpic cells, while which was markedly reversed by sh-MUC4. Additionally, OGT inhibitor significantly reduced MUC4 protein level, and elevated ZO-1, GJB2, CLDN8, and E-cadherin protein levels in HConEpic cells, while OGA inhibitor resulted in the opposite results. Furthermore, in addition to the interaction between OGT/OGA and MUC4, Co-IP and Western blot also revealed the alteration of MUC4 O-GlcNAcylation in 293T cells treated with OGT/OGA inhibitor. Above findings suggested that OGT/OGA inhibitor regulated MUC4 protein level by affecting MUC4 O-GlcNAcylation to regulate ZO-1, GJB2, CLDN8, and E-cadherin protein levels in HConEpic cells, which was achieved via inhibiting the interaction between OGT/OGA and MUC4. This study may provide a better understanding of the pathogenesis of allergic conjunctivitis (AC).

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.

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.

Improving the integrity and reproducibility of research that uses antibodies: a technical, data sharing, behavioral and policy challenge.

Antibodies are one of the most important reagents used in biomedical and fundamental research, used to identify, and quantify proteins, contribute to knowledge of disease mechanisms, and validate drug targets. Yet many antibodies used in research do not recognize their intended target, or recognize additional molecules, compromising the integrity of research findings and leading to waste of resources, lack of reproducibility, failure of research projects, and delays in drug development. Researchers frequently use antibodies without confirming that they perform as intended in their application of interest. Here we argue that the determinants of end-user antibody choice and use are critical, and under-addressed, behavioral drivers of this problem. This interacts with the batch-to-batch variability of these biological reagents, and the paucity of available characterization data for most antibodies, making it more difficult for researchers to choose high quality reagents and perform necessary validation experiments. The open-science company YCharOS works with major antibody manufacturers and knockout cell line producers to characterize antibodies, identifying high-performing renewable antibodies for many targets in neuroscience. This shows the progress that can be made by stakeholders working together. However, their work so far applies to only a tiny fraction of available antibodies. Where characterization data exists, end-users need help to find and use it appropriately. While progress has been made in the context of technical solutions and antibody characterization, we argue that initiatives to make best practice behaviors by researchers more feasible, easy, and rewarding are needed. Global cooperation and coordination between multiple partners and stakeholders will be crucial to address the technical, policy, behavioral, and open data sharing challenges. We offer potential solutions by describing our Only Good Antibodies initiative, a community of researchers and partner organizations working toward the necessary change. We conclude with an open invitation for stakeholders, including researchers, to join our cause.

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.

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.

The role of O-GlcNAcylation in RNA polymerase II transcription.

Eukaryotic RNA polymerase II (RNAPII) is responsible for the transcription of the protein-coding genes in the cell. Enormous progress has been made in discovering the protein activities that are required for transcription to occur, but the effects of post-translational modifications (PTMs) on RNAPII transcriptional regulation are much less understood. Most of our understanding relates to the cyclin-dependent kinases (CDKs), which appear to act relatively early in transcription. However, it is becoming apparent that other PTMs play a crucial role in the transcriptional cycle, and it is doubtful that any sort of complete understanding of this regulation is attainable without understanding the spectra of PTMs that occur on the transcriptional machinery. Among these is O-GlcNAcylation. Recent experiments have shown that the O-GlcNAc PTM likely has a prominent role in transcription. This review will cover the role of the O-GlcNAcylation in RNAPII transcription during initiation, pausing, and elongation, which will hopefully be of interest to both O-GlcNAc and RNAPII transcription researchers.

Regulation of protein O-GlcNAcylation by circadian, metabolic, and cellular signals.

O-linked ß-N-acetylglucosamine (O-GlcNAcylation) is a dynamic post-translational modification that regulates thousands of proteins and almost all cellular processes. Aberrant O-GlcNAcylation has been associated with numerous diseases, including cancer, neurodegenerative diseases, cardiovascular diseases, and type 2 diabetes. O-GlcNAcylation is highly nutrient-sensitive since it is dependent on UDP-GlcNAc, the end product of the hexosamine biosynthetic pathway (HBP). We previously observed daily rhythmicity of protein O-GlcNAcylation in a Drosophila model that is sensitive to the timing of food consumption. We showed that the circadian clock is pivotal in regulating daily O-GlcNAcylation rhythms given its control of the feeding-fasting cycle and hence nutrient availability. Interestingly, we reported that the circadian clock also modulates daily O-GlcNAcylation rhythm by regulating molecular mechanisms beyond the regulation of food consumption time. A large body of work now indicates that O-GlcNAcylation is likely a generalized cellular status effector as it responds to various cellular signals and conditions, such as ER stress, apoptosis, and infection. In this review, we summarize the metabolic regulation of protein O-GlcNAcylation through nutrient availability, HBP enzymes, and O-GlcNAc processing enzymes. We discuss the emerging roles of circadian clocks in regulating daily O-GlcNAcylation rhythm. Finally, we provide an overview of other cellular signals or conditions that impact O-GlcNAcylation. Many of these cellular pathways are themselves regulated by the clock and/or metabolism. Our review highlights the importance of maintaining optimal O-GlcNAc rhythm by restricting eating activity to the active period under physiological conditions and provides insights into potential therapeutic targets of O-GlcNAc homeostasis under pathological conditions.

Development of a PET Tracer for OGA with Improved Kinetics in the Living Brain.

O-GlcNAcylation is thought to play a role in the development of tau pathology in Alzheimer's disease because of its ability to modulate tau's aggregation propensity. O-GlcNAcylation is regulated by 2 enzymes: O-GlcNAc transferase and O-GlcNAcase (OGA). Development of a PET tracer would therefore be an essential tool for developing therapeutic small-molecule inhibitors of OGA, enabling clinical testing of target engagement and dose selection. Methods: A collection of small-molecule compounds was screened for inhibitory activity and high-affinity binding to OGA, as well as favorable PET tracer attributes (multidrug resistance protein 1 efflux, central nervous system PET multiparameter optimization, etc.). Two lead compounds with high affinity and selectivity for OGA were selected for further profiling, including OGA binding to tissue homogenate using a radioligand competition binding assay. In vivo pharmacokinetics were established using a microdosing approach with unlabeled compounds in rats. In vivo imaging studies were performed in rodents and nonhuman primates (NHPs) with 11C-labeled compounds. Results: Two selected candidates, BIO-735 and BIO-578, displayed promising attributes in vitro. After radiolabeling with tritium, [3H]BIO-735 and [3H]BIO-578 binding in rodent brain homogenates demonstrated dissociation constants of 0.6 and 2.3 nM, respectively. Binding was inhibited, concentration-dependently, by homologous compounds and thiamet G, a well-characterized and structurally diverse OGA inhibitor. Imaging studies in rats and NHPs showed both tracers had high uptake in the brain and inhibition of binding to OGA in the presence of a nonradioactive compound. However, only BIO-578 demonstrated reversible binding kinetics within the time frame of a PET study with a 11C-labeled molecule to enable quantification using kinetic modeling. Specificity of tracer uptake was confirmed with a 10 mg/kg blocking dose of thiamet G. Conclusion: We describe the development and testing of 2 11C PET tracers targeting the protein OGA. The lead compound BIO-578 demonstrated high affinity and selectivity for OGA in rodent and human postmortem brain tissue, leading to its further testing in NHPs. NHP PET imaging studies showed that the tracer had excellent brain kinetics, with full inhibition of specific binding by thiamet G. These results suggest that the tracer [11C]BIO-578 is well suited for further characterization in humans.

Protein O-GlcNAcylation in multiple immune cells and its therapeutic potential.

O-GlcNAcylation is a post-translational modification of proteins that involves the addition of O-GlcNAc to serine or threonine residues of nuclear or cytoplasmic proteins, catalyzed by O-GlcNAc transferase (OGT). This modification is highly dynamic and can be reversed by O-GlcNAcase (OGA). O-GlcNAcylation is widespread in the immune system, which engages in multiple physiologic and pathophysiologic processes. There is substantial evidence indicating that both the hexosamine biosynthesis pathway (HBP) and O-GlcNAcylation are critically involved in regulating immune cell function. However, the precise role of O-GlcNAcylation in the immune system needs to be adequately elucidated. This review offers a thorough synopsis of the present research on protein O-GlcNAcylation, accentuating the molecular mechanisms that control immune cells' growth, maturation, and performance via this PTM.

Adipocyte-derived exosomes promote the progression of triple-negative breast cancer through circCRIM1-dependent OGA activation.

Triple-negative breast cancer (TNBC) has an escalating morbidity and a dismal prognosis. Obesity has been reported to be strongly linked to adverse TNBC outcomes. Exosomes (Exos) transport RNA and proteins between cells and serve as intermediaries for cell-to-cell communication. Accumulated evidence suggests that adipose-secreted circular RNAs (circRNAs) can modulate protein glycosylation in TNBC to facilitate tumor cell outgrowth. Herein, exo-circCRIM1 expression was found to be elevated in TNBC patients with a high body fat percentage. Functional experiments demonstrated that by inhibiting miR-503-5p, exo-circCRIM1 enhanced TNBC evolution and metastasis while activating glycosylation hydrolase OGA. Furthermore, OGA negatively regulates FBP1 by decreasing its protein stability. Moreover, the levels of OGA and FBP1 were positively related to the infiltration level of some immune cells in TNBC. These findings indicate that exo-cirCRIM1 secreted by adipocytes contributes to TNBC progression by inhibiting miR-503-5p and activating the OGA/FBP1 signaling pathway. The findings reveal a novel intercellular signaling pathway mediated by adipose-derived exosomes and suggest that treatment targeting the secreted exosome-circCRIM1 may reverse TNBC progression.

Increasing O-GlcNAcylation Attenuates tau Hyperphosphorylation and Behavioral Impairment in rTg4510 Tauopathy Mice.

BACKGROUND: Tauopathies such as Alzheimer's disease (AD) are characterized by abnormal hyperphosphorylation of the microtubule-associated protein tau (MAPT) aggregating into neurofibrillary tangles (NFTs). O-linked ß-N-acetylglucosamine (O-GlcNAc) modifications have been suggested to regulate tau phosphorylation and aggregation and N-acetylglucosaminidase (OGA) removes GlcNAc moieties from proteins. METHODS: We investigated effects of the OGA inhibitor Thiamet G in rTg4510 primary neuronal cultures and in rTg4510 mice. The rTg4510 mice overexpress human tau harboring the P301L mutation and display an age-dependent progression of tau pathology including hyperphosphorylated tau species and NFTs. Aged rTg4510 mice exhibit a non-mnemonic behavioral defect involving a hyperactive phenotype that is associated with the progression of tau pathology. RESULTS: Thiamet G increased overall O-GlcNAc levels and crossed the blood brain barrier in rTg4510 mice. The free fraction of Thiamet G in the brain was 22-fold above the half maximal effective concentration (EC50) measured in rTg4510 primary neurons. Chronic Thiamet G treatment (18 weeks) initiated in young 6 week old rTg4510 mice increased brain O-GlcNAc levels and this corresponded with a significant reduction in soluble and insoluble hyperphosphorylated tau in aged 24 week old rTg4510 mice. Levels of normally phosphorylated P301L tau were not altered under these conditions. Reduction of hyperphosphorylated tau species by increased O-GlcNAcylation was associated with significant attenuation of hyperactivity in 24 week old rTg4510 mice. CONCLUSIONS: Our findings support the pharmacological inhibition of OGA as a potential therapeutic approach for the treatment of AD and other tauopathies.

Enzymatic assay for UDP-GlcNAc and its application in the parallel assessment of substrate availability and protein O-GlcNAcylation.

O-linked N-acetylglucosaminylation (O-GlcNAcylation) is a ubiquitous and dynamic non-canonical glycosylation of intracellular proteins. Several branches of metabolism converge at the hexosamine biosynthetic pathway (HBP) to produce the substrate for protein O-GlcNAcylation, the uridine diphosphate N-acetylglucosamine (UDP-GlcNAc). Availability of UDP-GlcNAc is considered a key regulator of O-GlcNAcylation. Yet UDP-GlcNAc concentrations are rarely reported in studies exploring the HBP and O-GlcNAcylation, most likely because the methods to measure it are restricted to specialized chromatographic procedures. Here, we introduce an enzymatic method to quantify cellular and tissue UDP-GlcNAc. The method is based on O-GlcNAcylation of a substrate peptide by O-linked N-acetylglucosamine transferase (OGT) and subsequent immunodetection of the modification. The assay can be performed in dot-blot or microplate format. We apply it to quantify UDP-GlcNAc concentrations in several mouse tissues and cell lines. Furthermore, we show how changes in UDP-GlcNAc levels correlate with O-GlcNAcylation and the expression of OGT and O-GlcNAcase (OGA).

Plant Resistance Inducers Affect Multiple Epidemiological Components of Plasmopara viticola on Grapevine Leaves.

Plant resistance inducers (PRIs) harbor promising potential for use in downy mildew (DM) control in viticulture. Here, the effects of six commercial PRIs on some epidemiological components of Plasmopara viticola (Pv) on grapevine leaves were studied over 3 years. Disease severity, mycelial colonization of leaf tissue, sporulation severity, production of sporangia on affected leaves, and per unit of DM lesion were evaluated by inoculating the leaves of PRI-treated plants at 1, 3, 6, 12, and 19 days after treatment (DAT). Laminarin, potassium phosphonate (PHO), and fosetyl-aluminium (FOS) were the most effective in reducing disease severity as well as the Pv DNA concentration of DM lesions on leaves treated and inoculated at 1 and 3 DAT; PHO and FOS also showed long-lasting effects on leaves established after treatment (inoculations at 6 to 19 DAT). PRIs also prevented the sporulation of Pv on lesions; all the PRI-treated leaves produced fewer sporangia than the nontreated control, especially in PHO-, FOS-, and cerevisane-treated leaves (>75% reduction). These results illustrate the broader and longer effect of PRIs on DM epidemics. The findings open up new perspectives for using PRIs in a defense program based on single, timely, and preventative field interventions.