RESUMEN

O-GlcNAc transferase (OGT) is the sole enzyme responsible for the post-translational modification of O-GlcNAc on thousands of target nucleocytoplasmic proteins. To date, nine variants of OGT that segregate with OGT Congenital Disorder of Glycosylation (OGT-CDG) have been reported and characterized. Numerous additional variants have been associated with OGT-CDG, some of which are currently undergoing investigation. This disorder primarily presents with global developmental delay and intellectual disability (ID), alongside other variable neurological features and subtle facial dysmorphisms in patients. Several hypotheses aim to explain the etiology of OGT-CDG, with a prominent hypothesis attributing the pathophysiology of OGT-CDG to mutations segregating with this disorder disrupting the OGT interactome. The OGT interactome consists of thousands of proteins, including substrates as well as interactors that require noncatalytic functions of OGT. A key aim in the field is to identify which interactors and substrates contribute to the primarily neural-specific phenotype of OGT-CDG. In this review, we will discuss the heterogenous phenotypic features of OGT-CDG seen clinically, the variable biochemical effects of mutations associated with OGT-CDG, and the use of animal models to understand this disorder. Furthermore, we will discuss how previously identified OGT interactors causal for ID provide mechanistic targets for investigation that could explain the dysregulated gene expression seen in OGT-CDG models. Identifying shared or unique altered pathways impacted in OGT-CDG patients will provide a better understanding of the disorder as well as potential therapeutic targets.

RESUMEN

O-GlcNAc transferase (OGT) is an essential glycosylating enzyme that catalyzes the addition of N-acetylglucosamine to serine or threonine residues of nuclear and cytoplasmic proteins. The enzyme glycosylates a broad range of peptide sequences and the prediction of glycosylation sites has proven challenging. The lack of an experimentally verified set of polypeptide sequences that are not glycosylated by OGT has made prediction of legitimate glycosylation sites more difficult. Here, we tested a number of intrinsically disordered protein regions as substrates of OGT to establish a set of sequences that are not glycosylated by OGT. The negative data set suggests an amino acid compositional bias for OGT targets. This compositional bias was validated by modifying the amino acid composition of the protein fused in sarcoma (FUS) to enhance glycosylation. NMR experiments demonstrate that the tetratricopeptide repeat region of OGT can bind FUS and that glycosylation-promoting mutations enhance binding. These results provide evidence that the tetratricopeptide repeat region recognizes disordered segments of substrates with particular compositions to promote glycosylation, providing insight into the broad specificity of OGT.

Asunto(s)

N-Acetilglucosaminiltransferasas , Aminoácidos/metabolismo , Glicosilación , Mutación , N-Acetilglucosaminiltransferasas/metabolismo , Humanos , Proteínas Adaptadoras Transductoras de Señales/química , Proteínas Adaptadoras Transductoras de Señales/genética , Proteínas Adaptadoras Transductoras de Señales/metabolismo , Biología Computacional , Imagen por Resonancia Magnética

RESUMEN

O-linked-N-acetylglucosamine (O-GlcNAc) modification is a unique post-translational modification that plays a regulatory role in many cellular processes, such as transcription, intracellular signaling, endocytosis, and protein stability. Epidermal growth factor (EGF) domain-specific O-GlcNAc transferase (EOGT) is an endoplasmic reticulum (ER) resident protein which can glycosylate the residues of Ser or Thr of secreted or membrane (transmembrane) glycoproteins containing EGF domain. Notch signaling pathway is involved in cell-to-cell communication which regulates cell biological processes through interactions between adjacent cells. To date, EOGT-mediated O-GlcNAc modification has been found to be involved in many human diseases, and shown significant relation with Notch signaling pathway. However, the specific molecular mechanisms have not been fully elucidated. In this review, we briefly introduce recent studies regarding to the roles of EOGT-mediated O-GlcNAc modification and its correlation with Notch signaling pathway in human diseases.

RESUMEN

Protein O-GlcNAcylation is a nutrient and stress-sensitive protein post-translational modification (PTM). The addition of an O-GlcNAc molecule to proteins is catalyzed by O-GlcNAc transferase (OGT), whereas O-GlcNAcase (OGA) enzyme is responsible for removal of this PTM. Previous work showed that OGT is highly expressed in the pancreas, and we demonstrated that hypo-O-GlcNAcylation in ß-cells cause severe diabetes in mice. These studies show a direct link between nutrient-sensitive OGT and ß-cell health and function. In the current study, we hypothesized that hyper-O-GlcNAcylation may confer protection from ß-cell failure in high-fat diet (HFD)-induced obesity. To test this hypothesis, we generated a mouse model with constitutive ß-cell OGA ablation (ßOGAKO) to specifically increase O-GlcNAcylation in ß-cells. Under normal chow diet, young male and female ßOGAKO mice exhibited normal glucose tolerance but developed glucose intolerance with aging, relative to littermate controls. No alteration in ß-cell mass was observed between ßOGAKO and littermate controls. Total insulin content was reduced despite an increase in pro-insulin to insulin ratio in ßOGAKO islets. ßOGAKO mice showed deficit in insulin secretion in vivo and in vitro. When young animals were subjected to HFD, both male and female ßOGAKO mice displayed normal body weight gain and insulin tolerance but developed glucose intolerance that worsened with longer exposure to HFD. Comparable ß-cell mass was found between ßOGAKO and littermate controls. Taken together, these data demonstrate that the loss of OGA in ß-cells reduces ß-cell function, thereby perturbing glucose homeostasis. The findings reinforce the rheostat model of intracellular O-GlcNAcylation where too much (OGA loss) or too little (OGT loss) O-GlcNAcylation are both detrimental to the ß-cell.

Asunto(s)

Intolerancia a la Glucosa , Células Secretoras de Insulina , Ratones , Masculino , Femenino , Animales , Intolerancia a la Glucosa/etiología , Células Secretoras de Insulina/metabolismo , Homeostasis , Insulina/metabolismo , Glucosa/metabolismo

RESUMEN

Protein O-GlcNAcylation is a dynamic post-translational modification involving the attachment of N-acetylglucosamine (GlcNAc) to the hydroxyl groups of Ser/Thr residues on numerous nucleocytoplasmic proteins. Two enzymes are responsible for O-GlcNAc cycling on substrate proteins: O-GlcNAc transferase (OGT) catalyzes the addition while O-GlcNAcase (OGA) helps the removal of GlcNAc. O-GlcNAcylation modifies protein functions; therefore, dysregulation of O-GlcNAcylation affects cell physiology and contributes to pathogenesis. To maintain homeostasis of cellular O-GlcNAcylation, there exists feedback regulation of OGT and OGA expression responding to fluctuations of O-GlcNAc levels; yet, little is known about the molecular mechanisms involved. In this study, we investigated the O-GlcNAc-feedback regulation of OGT and OGA expression in lung cancer cells. Results suggest that, upon alterations in O-GlcNAcylation, the regulation of OGA expression occurs at the mRNA level and likely involves epigenetic mechanisms, while modulation of OGT expression is through translation control. Further analyses revealed that the eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1) contributes to the downregulation of OGT induced by hyper-O-GlcNAcylation; the S5A/S6A O-GlcNAcylation-site mutant of 4E-BP1 cannot support this regulation, suggesting an important role of O-GlcNAcylation. The results provide additional insight into the molecular mechanisms through which cells may fine-tune intracellular O-GlcNAc levels to maintain homeostasis.

Asunto(s)

Acetilglucosamina/química , Regulación Enzimológica de la Expresión Génica , N-Acetilglucosaminiltransferasas/metabolismo , Células A549 , Proteínas Adaptadoras Transductoras de Señales/metabolismo , Sitios de Unión , Proteínas de Ciclo Celular/metabolismo , Línea Celular Tumoral , Epigénesis Genética , Retroalimentación Fisiológica , Regulación Neoplásica de la Expresión Génica , Homeostasis , Humanos , Neoplasias Pulmonares/enzimología , Mutación , Péptidos/química , Procesamiento Proteico-Postraduccional , Ribosomas/química , beta-N-Acetilhexosaminidasas/química

RESUMEN

Caveolin-1 (Cav-1), a major structural protein of caveolae, is implicated in the vesicular uptake processes of transcytosis and cell signaling. However, its role in modulating protein glycosylation and tumor metastasis remains to be further elucidated. In the present study, it was shown that Cav-1 promotes the expression of O-GlcNAcylation and O-GlcNAc transferase (OGT), and triggers the invasion and metastasis of hepatocellular carcinoma (HCC) cells. The results of RT-qPCR, Western blot and dual lucif-erase reporter assay showed that Cav-1 negatively regulated the expression of transcription factor RUNX2 in HCC. Subsequently, this results in attenuate RUNX2-induced transcription of miR24. miR24 suppresses mouse HCC cells invasion and metastasis via directly targeting Ogt mRNA 3′UTR. This research provides evidence of Cav-1-mediated OGT expression and O-GlcNAc (O-linked N-acetylglucosamine) elevation. These data give insight into a novel mechanism of HCC occurrence and development.

RESUMEN

Stromal interaction molecule 1 (STIM1) plays a pivotal role in store-operated Ca2+ entry (SOCE), an essential mechanism in cellular calcium signaling and in maintaining cellular calcium balance. Because O-GlcNAcylation plays pivotal roles in various cellular function, we examined the effect of fluctuation in STIM1 O-GlcNAcylation on SOCE activity. We found that both increase and decrease in STIM1 O-GlcNAcylation impaired SOCE activity. To determine the molecular basis, we established STIM1-knockout HEK293 (STIM1-KO-HEK) cells using the CRISPR/Cas9 system and transfected STIM1 WT (STIM1-KO-WT-HEK), S621A (STIM1-KO-S621A-HEK), or T626A (STIM1-KO-T626A-HEK) cells. Using these cells, we examined the possible O-GlcNAcylation sites of STIM1 to determine whether the sites were O-GlcNAcylated. Co-immunoprecipitation analysis revealed that Ser621 and Thr626 were O-GlcNAcylated and that Thr626 was O-GlcNAcylated in the steady state but Ser621 was not. The SOCE activity in STIM1-KO-S621A-HEK and STIM1-KO-T626A-HEK cells was lower than that in STIM1-KO-WT-HEK cells because of reduced phosphorylation at Ser621 Treatment with the O-GlcNAcase inhibitor Thiamet G or O-GlcNAc transferase (OGT) transfection, which increases O-GlcNAcylation, reduced SOCE activity, whereas treatment with the OGT inhibitor ST045849 or siOGT transfection, which decreases O-GlcNAcylation, also reduced SOCE activity. Decrease in SOCE activity due to increase and decrease in O-GlcNAcylation was attributable to reduced phosphorylation at Ser621 These data suggest that both decrease in O-GlcNAcylation at Thr626 and increase in O-GlcNAcylation at Ser621 in STIM1 lead to impairment of SOCE activity through decrease in Ser621 phosphorylation. Targeting STIM1 O-GlcNAcylation could provide a promising treatment option for the related diseases, such as neurodegenerative diseases.

Asunto(s)

Señalización del Calcio , Calcio/metabolismo , Proteínas de Neoplasias/metabolismo , Molécula de Interacción Estromal 1/metabolismo , Acilación , Técnicas de Silenciamiento del Gen , Células HEK293 , Humanos , Proteínas de Neoplasias/genética , Fosforilación , Serina , Molécula de Interacción Estromal 1/genética

RESUMEN

Epidermal growth factor (EGF) domain-specific O-GlcNAc transferase (EOGT) is an endoplasmic reticulum (ER)-resident protein that modifies EGF repeats of Notch receptors and thereby regulates Delta-like ligand-mediated Notch signaling. Several EOGT mutations that may affect putative N-glycosylation consensus sites are recorded in the cancer database, but the presence and function of N-glycans in EOGT have not yet been characterized. Here, we identified N-glycosylation sites in mouse EOGT and elucidated their molecular functions. Three predicted N-glycosylation consensus sequences on EOGT are highly conserved among mammalian species. Within these sites, we found that Asn-263 and Asn-354, but not Asn-493, are modified with N-glycans. Lectin blotting, endoglycosidase H digestion, and MS analysis revealed that both residues are modified with oligomannose N-glycans. Loss of an individual N-glycan on EOGT did not affect its endoplasmic reticulum (ER) localization, enzyme activity, and ability to O-GlcNAcylate Notch1 in HEK293T cells. However, simultaneous substitution of both N-glycosylation sites affected both EOGT maturation and expression levels without an apparent change in enzymatic activity, suggesting that N-glycosylation at a single site is sufficient for EOGT maturation and expression. Accordingly, a decrease in O-GlcNAc stoichiometry was observed in Notch1 co-expressed with an N263Q/N354Q variant compared with WT EOGT. Moreover, the N263Q/N354Q variant exhibited altered subcellular distribution within the ER in HEK293T cells, indicating that N-glycosylation of EOGT is required for its ER localization at the cell periphery. These results suggest critical roles of N-glycans in sustaining O-GlcNAc transferase function both by maintaining EOGT levels and by ensuring its proper subcellular localization in the ER.

Asunto(s)

Retículo Endoplásmico/metabolismo , N-Acetilglucosaminiltransferasas/metabolismo , Secuencia de Aminoácidos , Animales , Sistemas CRISPR-Cas/genética , Línea Celular , Cromatografía Líquida de Alta Presión , Estrés del Retículo Endoplásmico/efectos de los fármacos , Edición Génica , Glicopéptidos/análisis , Glicosilación , Humanos , Ratones , Mutagénesis Sitio-Dirigida , N-Acetilglucosaminiltransferasas/deficiencia , N-Acetilglucosaminiltransferasas/genética , Receptor Notch1/genética , Receptor Notch1/metabolismo , Alineación de Secuencia , Espectrometría de Masas en Tándem , Tunicamicina/farmacología

RESUMEN

The role of O-linked N-acetylglucosamine (O-GlcNAc) modification in the cell cycle has been enigmatic. Previously, both O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA) disruptions have been shown to derail the mitotic centrosome numbers, suggesting that mitotic O-GlcNAc oscillation needs to be in concert with mitotic progression to account for centrosome integrity. Here, using both chemical approaches and biological assays with HeLa cells, we attempted to address the underlying molecular mechanism and observed that incubation of the cells with the OGA inhibitor Thiamet-G strikingly elevates centrosomal distances, suggestive of premature centrosome disjunction. These aberrations could be overcome by inhibiting Polo-like kinase 1 (PLK1), a mitotic master kinase. PLK1 inactivation is modulated by the myosin phosphatase targeting subunit 1 (MYPT1)-protein phosphatase 1cß (PP1cß) complex. Interestingly, MYPT1 has been shown to be abundantly O-GlcNAcylated, and the modified residues have been detected in a recent O-GlcNAc-profiling screen utilizing chemoenzymatic labeling and bioorthogonal conjugation. We demonstrate here that MYPT1 is O-GlcNAcylated at Thr-577, Ser-585, Ser-589, and Ser-601, which antagonizes CDK1-dependent phosphorylation at Ser-473 and attenuates the association between MYPT1 and PLK1, thereby promoting PLK1 activity. We conclude that under high O-GlcNAc levels, PLK1 is untimely activated, conducive to inopportune centrosome separation and disruption of the cell cycle. We propose that too much O-GlcNAc is equally deleterious as too little O-GlcNAc, and a fine balance between the OGT/OGA duo is indispensable for successful mitotic divisions.

Asunto(s)

Centrosoma/metabolismo , Mitosis , Fosfatasa de Miosina de Cadena Ligera/metabolismo , Proteína Quinasa CDC2/genética , Proteína Quinasa CDC2/metabolismo , Proteínas de Ciclo Celular/genética , Proteínas de Ciclo Celular/metabolismo , Línea Celular , Glicosilación , Humanos , Fosfatasa de Miosina de Cadena Ligera/genética , Proteínas Serina-Treonina Quinasas/genética , Proteínas Serina-Treonina Quinasas/metabolismo , Proteínas Proto-Oncogénicas/genética , Proteínas Proto-Oncogénicas/metabolismo , Quinasa Tipo Polo 1

RESUMEN

O-GlcNAcylation is an abundant post-translational modification in neurons. In mice, an increase in O-GlcNAcylation leads to defects in hippocampal synaptic plasticity and learning. O-GlcNAcylation is established by two opposing enzymes: O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA). To investigate the role of OGA in elementary learning, we generated catalytically inactive and precise knockout Oga alleles (OgaD133N and OgaKO , respectively) in Drosophila melanogaster Adult OgaD133N and OgaKO flies lacking O-GlcNAcase activity showed locomotor phenotypes. Importantly, both Oga lines exhibited deficits in habituation, an evolutionarily conserved form of learning, highlighting that the requirement for O-GlcNAcase activity for cognitive function is preserved across species. Loss of O-GlcNAcase affected a number of synaptic boutons at the axon terminals of larval neuromuscular junction. Taken together, we report behavioral and neurodevelopmental phenotypes associated with Oga alleles and show that Oga contributes to cognition and synaptic morphology in Drosophila.

Asunto(s)

Drosophila melanogaster/enzimología , Drosophila melanogaster/fisiología , beta-N-Acetilhexosaminidasas/metabolismo , Acilación , Animales , Cognición , Proteínas de Drosophila/genética , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/genética , Técnicas de Inactivación de Genes , Locomoción , Longevidad , Sinapsis/fisiología , beta-N-Acetilhexosaminidasas/genética

RESUMEN

The hexosamine biosynthesis pathway (HBP) branches from glycolysis and forms UDP-GlcNAc, the moiety for O-linked ß-GlcNAc (O-GlcNAc) post-translational modifications. An inability to directly measure HBP flux has hindered our understanding of the factors regulating protein O-GlcNAcylation. Our goals in this study were to (i) validate a LC-MS method that assesses HBP flux as UDP-GlcNAc (13C)-molar percent enrichment (MPE) and concentration and (ii) determine whether glucose availability or workload regulate cardiac HBP flux. For (i), we perfused isolated murine working hearts with [U-13C6]glucosamine (1, 10, 50, or 100 µm), which bypasses the rate-limiting HBP enzyme. We observed a concentration-dependent increase in UDP-GlcNAc levels and MPE, with the latter reaching a plateau of 56.3 ± 2.9%. For (ii), we perfused isolated working hearts with [U-13C6]glucose (5.5 or 25 mm). Glycolytic efflux doubled with 25 mm [U-13C6]glucose; however, the calculated HBP flux was similar among the glucose concentrations at ∼2.5 nmol/g of heart protein/min, representing ∼0.003-0.006% of glycolysis. Reducing cardiac workload in beating and nonbeating Langendorff perfusions had no effect on the calculated HBP flux at ∼2.3 and 2.5 nmol/g of heart protein/min, respectively. To the best of our knowledge, this is the first direct measurement of glucose flux through the HBP in any organ. We anticipate that these methods will enable foundational analyses of the regulation of HBP flux and protein O-GlcNAcylation. Our results suggest that in the healthy ex vivo perfused heart, HBP flux does not respond to acute changes in glucose availability or cardiac workload.

Asunto(s)

Acetilglucosamina/metabolismo , Glucosa/metabolismo , Miocardio/metabolismo , Procesamiento Proteico-Postraduccional/genética , Animales , Vías Biosintéticas/genética , Glucólisis/genética , Glicosilación , Corazón/efectos de los fármacos , Corazón/fisiopatología , Hexosaminas/biosíntesis , Hexosaminas/genética , Humanos , Ratones , Miocardio/patología

RESUMEN

Post-translational modifications, including O-GlcNAcylation, play fundamental roles in modulating cellular events, including transcription, signal transduction, and immune signaling. Several molecular targets of O-GlcNAcylation associated with pathogen-induced innate immune responses have been identified; however, the direct regulatory mechanisms linking O-GlcNAcylation with antiviral RIG-I-like receptor signaling are not fully understood. In this study, we found that cellular levels of O-GlcNAcylation decline in response to infection with Sendai virus. We identified a heavily O-GlcNAcylated serine-rich region between amino acids 249-257 of the mitochondrial antiviral signaling protein (MAVS); modification at this site disrupts MAVS aggregation and prevents MAVS-mediated activation and signaling. O-GlcNAcylation of the serine-rich region of MAVS also suppresses its interaction with TRAF3; this prevents IRF3 activation and production of interferon-ß. Taken together, these results suggest that O-GlcNAcylation of MAVS may be a master regulatory event that promotes host defense against RNA viruses.

Asunto(s)

Acetilglucosamina/inmunología , Proteínas Adaptadoras Transductoras de Señales/inmunología , Infecciones por Respirovirus/inmunología , Virus Sendai , Acilación , Línea Celular , Interacciones Huésped-Patógeno/inmunología , Humanos , Inmunidad Innata , Mitocondrias/inmunología , Transducción de Señal

RESUMEN

O-GlcNAcylation is a ubiquitous protein glycosylation playing different roles on variant proteins. O-GlcNAc transferase (OGT) is the unique enzyme responsible for the sugar addition to nucleocytoplasmic proteins. Recently, multiple O-GlcNAc sites have been observed on short-form OGT (sOGT) and nucleocytoplasmic OGT (ncOGT), both of which locate in the nucleus and cytoplasm in cell. Moreover, O-GlcNAcylation of Ser389 in ncOGT (1036 amino acids) affects its nuclear translocation in HeLa cells. To date, the major O-GlcNAcylation sites and their roles in sOGT remain unknown. Here, we performed LC-MS/MS and mutational analyses to seek the major O-GlcNAcylation site on sOGT. We identified six O-GlcNAc sites in the tetratricopeptide repeat domain in sOGT, with Thr12 and Ser56 being two "key" sites. Thr12 is a dominant O-GlcNAcylation site, whereas the modification of Ser56 plays a role in regulating sOGT O-GlcNAcylation, partly through Thr12In vitro activity and pulldown assays demonstrated that O-GlcNAcylation does not affect sOGT activity but does affect sOGT-interacting proteins. In HEK293T cells, S56A bound to and hence glycosylated more proteins in contrast to T12A and WT sOGT. By proteomic and bioinformatics analyses, we found that T12A and S56A differed in substrate proteins (e.g. HNRNPU and PDCD6IP), which eventually affected cell cycle progression and/or cell proliferation. These findings demonstrate that O-GlcNAcylation modulates sOGT substrate selectivity and affects its role in the cell. The data also highlight the regulatory role of O-GlcNAcylation at Thr12 and Ser56.

Asunto(s)

N-Acetilglucosaminiltransferasas/metabolismo , Serina/metabolismo , Treonina/metabolismo , Secuencia de Aminoácidos , Puntos de Control del Ciclo Celular , Núcleo Celular/metabolismo , Proliferación Celular , Cromatografía Líquida de Alta Presión , Glicopéptidos/análisis , Glicopéptidos/química , Glicosilación , Células HEK293 , Células HeLa , Humanos , Mutagénesis Sitio-Dirigida , N-Acetilglucosaminiltransferasas/antagonistas & inhibidores , N-Acetilglucosaminiltransferasas/genética , Interferencia de ARN , ARN Interferente Pequeño/metabolismo , Proteínas Recombinantes/biosíntesis , Proteínas Recombinantes/aislamiento & purificación , Especificidad por Sustrato , Espectrometría de Masas en Tándem

RESUMEN

An early hallmark of type 2 diabetes is a failure of proinsulin-to-insulin processing in pancreatic ß-cells, resulting in hyperproinsulinemia. Proinsulin processing is quite sensitive to nutrient flux, and ß-cell-specific deletion of the nutrient-sensing protein modifier OGlcNAc transferase (ßOGTKO) causes ß-cell failure and diabetes, including early development of hyperproinsulinemia. The mechanisms underlying this latter defect are unknown. Here, using several approaches, including site-directed mutagenesis, Click O-GlcNAc labeling, immunoblotting, and immunofluorescence and EM imaging, we provide the first evidence for a relationship between the O-GlcNAcylation of eukaryotic translation initiation factor 4γ1 (eIF4G1) and carboxypeptidase E (CPE)-dependent proinsulin processing in ßOGTKO mice. We first established that ßOGTKO hyperproinsulinemia is independent of age, sex, glucose levels, and endoplasmic reticulum-CCAAT enhancer-binding protein homologous protein (CHOP)-mediated stress status. Of note, OGT loss was associated with a reduction in ß-cell-resident CPE, and genetic reconstitution of CPE in ßOGTKO islets rescued the dysfunctional proinsulin-to-insulin ratio. We show that although CPE is not directly OGlcNAc modified in islets, overexpression of the suspected OGT target eIF4G1, previously shown to regulate CPE translation in ß-cells, increases islet CPE levels, and fully reverses ßOGTKO islet-induced hyperproinsulinemia. Furthermore, our results reveal that OGT O-GlcNAc-modifies eIF4G1 at Ser-61 and that this modification is critical for eIF4G1 protein stability. Together, these results indicate a direct link between nutrient-sensitive OGT and insulin processing, underscoring the importance of post-translational O-GlcNAc modification in general cell physiology.

Asunto(s)

Carboxipeptidasa H/metabolismo , Diabetes Mellitus/metabolismo , Factor 4G Eucariótico de Iniciación/metabolismo , Células Secretoras de Insulina/metabolismo , N-Acetilglucosaminiltransferasas/metabolismo , Animales , Modelos Animales de Enfermedad , Ratones , Ratones Noqueados , N-Acetilglucosaminiltransferasas/deficiencia

RESUMEN

Chronic, low-grade inflammation increases the risk for atherosclerosis, cancer, and autoimmunity in diseases such as obesity and diabetes. Levels of CD4+ T helper 17 (Th17) cells, which secrete interleukin 17A (IL-17A), are increased in obesity and contribute to the inflammatory milieu; however, the relationship between signaling events triggered by excess nutrient levels and IL-17A-mediated inflammation is unclear. Here, using cytokine, quantitative real-time PCR, immunoprecipitation, and ChIP assays, along with lipidomics and MS-based approaches, we show that increased levels of the nutrient-responsive, post-translational protein modification, O-GlcNAc, are present in naive CD4+ T cells from a diet-induced obesity murine model and that elevated O-GlcNAc levels increase IL-17A production. We also found that increased binding of the Th17 master transcription factor RAR-related orphan receptor γ t variant (RORγt) at the IL-17 gene promoter and enhancer, as well as significant alterations in the intracellular lipid microenvironment, elevates the production of ligands capable of increasing RORγt transcriptional activity. Importantly, the rate-limiting enzyme of fatty acid biosynthesis, acetyl-CoA carboxylase 1 (ACC1), is O-GlcNAcylated and necessary for production of these RORγt-activating ligands. Our results suggest that increased O-GlcNAcylation of cellular proteins may be a potential link between excess nutrient levels and pathological inflammation.

Asunto(s)

Ácidos Grasos/biosíntesis , Interleucina-17/metabolismo , Células Th17/metabolismo , Acetil-CoA Carboxilasa/metabolismo , Acilación/efectos de los fármacos , Adulto , Anciano , Anciano de 80 o más Años , Animales , Linfocitos T CD4-Positivos/citología , Linfocitos T CD4-Positivos/metabolismo , Citocinas/metabolismo , Ácidos Grasos/análisis , Femenino , Humanos , Interleucina-17/genética , Lipidómica/métodos , Masculino , Ratones , Ratones Endogámicos C57BL , Persona de Mediana Edad , Miembro 3 del Grupo F de la Subfamilia 1 de Receptores Nucleares/genética , Miembro 3 del Grupo F de la Subfamilia 1 de Receptores Nucleares/metabolismo , Obesidad/metabolismo , Obesidad/patología , Regiones Promotoras Genéticas , Unión Proteica , Piranos/farmacología , Células Th17/citología , Tiazoles/farmacología , Activación Transcripcional/efectos de los fármacos

RESUMEN

Inhibitory GABAergic transmission is required for proper circuit function in the nervous system. However, our understanding of molecular mechanisms that preferentially influence GABAergic transmission, particularly presynaptic mechanisms, remains limited. We previously reported that the ubiquitin ligase EEL-1 preferentially regulates GABAergic presynaptic transmission. To further explore how EEL-1 functions, here we performed affinity purification proteomics using Caenorhabditis elegans and identified the O-GlcNAc transferase OGT-1 as an EEL-1 binding protein. This observation was intriguing, as we know little about how OGT-1 affects neuron function. Using C. elegans biochemistry, we confirmed that the OGT-1/EEL-1 complex forms in neurons in vivo and showed that the human orthologs, OGT and HUWE1, also bind in cell culture. We observed that, like EEL-1, OGT-1 is expressed in GABAergic motor neurons, localizes to GABAergic presynaptic terminals, and functions cell-autonomously to regulate GABA neuron function. Results with catalytically inactive point mutants indicated that OGT-1 glycosyltransferase activity is dispensable for GABA neuron function. Consistent with OGT-1 and EEL-1 forming a complex, genetic results using automated, behavioral pharmacology assays showed that ogt-1 and eel-1 act in parallel to regulate GABA neuron function. These findings demonstrate that OGT-1 and EEL-1 form a conserved signaling complex and function together to affect GABA neuron function.

Asunto(s)

Proteínas de Caenorhabditis elegans/metabolismo , Caenorhabditis elegans/fisiología , Neuronas GABAérgicas/fisiología , N-Acetilglucosaminiltransferasas/metabolismo , Ubiquitina-Proteína Ligasas/metabolismo , Aldicarb/farmacología , Animales , Caenorhabditis elegans/metabolismo , Proteínas de Caenorhabditis elegans/aislamiento & purificación , Cromatografía de Afinidad , Neuronas GABAérgicas/efectos de los fármacos , Terminales Presinápticos/metabolismo , Unión Proteica , Proteómica , Transducción de Señal , Transmisión Sináptica/efectos de los fármacos , Ubiquitina-Proteína Ligasas/aislamiento & purificación

RESUMEN

Diabetes promotes the posttranslational modification of proteins by O-linked addition of GlcNAc (O-GlcNAcylation) to Ser/Thr residues of proteins and thereby contributes to diabetic complications. In the retina of diabetic mice, the repressor of mRNA translation, eIF4E-binding protein 1 (4E-BP1), is O-GlcNAcylated, and sequestration of the cap-binding protein eukaryotic translation initiation factor (eIF4E) is enhanced. O-GlcNAcylation has also been detected on several eukaryotic translation initiation factors and ribosomal proteins. However, the functional consequence of this modification is unknown. Here, using ribosome profiling, we evaluated the effect of enhanced O-GlcNAcylation on retinal gene expression. Mice receiving thiamet G (TMG), an inhibitor of the O-GlcNAc hydrolase O-GlcNAcase, exhibited enhanced retinal protein O-GlcNAcylation. The principal effect of TMG on retinal gene expression was observed in ribosome-associated mRNAs (i.e. mRNAs undergoing translation), as less than 1% of mRNAs exhibited changes in abundance. Remarkably, ∼19% of the transcriptome exhibited TMG-induced changes in ribosome occupancy, with 1912 mRNAs having reduced and 1683 mRNAs having increased translational rates. In the retina, the effect of O-GlcNAcase inhibition on translation of specific mitochondrial proteins, including superoxide dismutase 2 (SOD2), depended on 4E-BP1/2. O-GlcNAcylation enhanced cellular respiration and promoted mitochondrial superoxide levels in WT cells, and 4E-BP1/2 deletion prevented O-GlcNAcylation-induced mitochondrial superoxide in cells in culture and in the retina. The retina of diabetic WT mice exhibited increased reactive oxygen species levels, an effect not observed in diabetic 4E-BP1/2-deficient mice. These findings provide evidence for a mechanism whereby diabetes-induced O-GlcNAcylation promotes oxidative stress in the retina by altering the selection of mRNAs for translation.

Asunto(s)

Proteínas Portadoras/metabolismo , Retinopatía Diabética/metabolismo , Proteínas del Ojo/metabolismo , Mitocondrias/metabolismo , Fosfoproteínas/metabolismo , Biosíntesis de Proteínas , ARN Mensajero/metabolismo , Retina/metabolismo , Acilación , Proteínas Adaptadoras Transductoras de Señales , Animales , Proteínas Portadoras/genética , Proteínas de Ciclo Celular , Retinopatía Diabética/genética , Retinopatía Diabética/patología , Factores Eucarióticos de Iniciación , Proteínas del Ojo/genética , Femenino , Ratones , Ratones Noqueados , Mitocondrias/genética , Mitocondrias/patología , Consumo de Oxígeno/efectos de los fármacos , Fosfoproteínas/genética , Piranos/farmacología , ARN Mensajero/genética , Especies Reactivas de Oxígeno/metabolismo , Retina/patología , Tiazoles/farmacología

RESUMEN

We previously reported that iron down-regulates transcription of the leptin gene by increasing occupancy of phosphorylated cAMP response element-binding protein (pCREB) at two sites in the leptin gene promoter. Several nutrient-sensing pathways including O-GlcNAcylation also regulate leptin. We therefore investigated whether O-glycosylation plays a role in iron- and CREB-mediated regulation of leptin. We found that high iron decreases protein O-GlcNAcylation both in cultured 3T3-L1 adipocytes and in mice fed high-iron diets and down-regulates leptin mRNA and protein levels. Glucosamine treatment, which bypasses the rate-limiting step in the synthesis of substrate for glycosylation, increased both O-GlcNAc and leptin, whereas inhibition of O-glycosyltransferase (OGT) decreased O-GlcNAc and leptin. The increased leptin levels induced by glucosamine were susceptible to the inhibition by iron, but in the case of OGT inhibition, iron did not further decrease leptin. Mice with deletion of the O-GlcNAcase gene, either via whole-body heterozygous deletion or through adipocyte-targeted homozygous deletion, exhibited increased O-GlcNAc levels in adipose tissue and increased leptin levels that were inhibited by iron. Of note, iron increased the occupancy of pCREB and decreased the occupancy of O-GlcNAcylated CREB on the leptin promoter. These patterns observed in our experimental models suggest that iron exerts its effects on leptin by decreasing O-glycosylation and not by increasing protein deglycosylation and that neither O-GlcNAcase nor OGT mRNA and protein levels are affected by iron. We conclude that iron down-regulates leptin by decreasing CREB glycosylation, resulting in increased CREB phosphorylation and leptin promoter occupancy by pCREB.

Asunto(s)

Adipocitos/metabolismo , Proteína de Unión a Elemento de Respuesta al AMP Cíclico/metabolismo , Regulación hacia Abajo/efectos de los fármacos , Hierro/farmacología , Leptina/biosíntesis , Modelos Biológicos , Células 3T3-L1 , Animales , Glucosamina/metabolismo , Glicosilación/efectos de los fármacos , Hierro/metabolismo , Ratones , Regiones Promotoras Genéticas

RESUMEN

In the early 1980s, while using purified glycosyltransferases to probe glycan structures on surfaces of living cells in the murine immune system, we discovered a novel form of serine/threonine protein glycosylation (O-linked ß-GlcNAc; O-GlcNAc) that occurs on thousands of proteins within the nucleus, cytoplasm, and mitochondria. Prior to this discovery, it was dogma that protein glycosylation was restricted to the luminal compartments of the secretory pathway and on extracellular domains of membrane and secretory proteins. Work in the last 3 decades from several laboratories has shown that O-GlcNAc cycling serves as a nutrient sensor to regulate signaling, transcription, mitochondrial activity, and cytoskeletal functions. O-GlcNAc also has extensive cross-talk with phosphorylation, not only at the same or proximal sites on polypeptides, but also by regulating each other's enzymes that catalyze cycling of the modifications. O-GlcNAc is generally not elongated or modified. It cycles on and off polypeptides in a time scale similar to phosphorylation, and both the enzyme that adds O-GlcNAc, the O-GlcNAc transferase (OGT), and the enzyme that removes O-GlcNAc, O-GlcNAcase (OGA), are highly conserved from C. elegans to humans. Both O-GlcNAc cycling enzymes are essential in mammals and plants. Due to O-GlcNAc's fundamental roles as a nutrient and stress sensor, it plays an important role in the etiologies of chronic diseases of aging, including diabetes, cancer, and neurodegenerative disease. This review will present an overview of our current understanding of O-GlcNAc's regulation, functions, and roles in chronic diseases of aging.

Asunto(s)

Envejecimiento/metabolismo , Diabetes Mellitus/metabolismo , Proteínas de Neoplasias/metabolismo , Neoplasias/metabolismo , Enfermedades Neurodegenerativas/metabolismo , Nutrientes/metabolismo , Transducción de Señal , Transcripción Genética , Envejecimiento/patología , Animales , Caenorhabditis elegans/metabolismo , Proteínas de Caenorhabditis elegans/metabolismo , Enfermedad Crónica , Citoesqueleto/metabolismo , Citoesqueleto/patología , Diabetes Mellitus/patología , Glicosilación , Humanos , Ratones , Mitocondrias/metabolismo , Mitocondrias/patología , N-Acetilglucosaminiltransferasas/metabolismo , Neoplasias/patología , Enfermedades Neurodegenerativas/patología , Fosforilación

RESUMEN

The addition of a single ß-d-GlcNAc sugar (O-GlcNAc) by O-GlcNAc-transferase (OGT) and O-GlcNAc removal by O-GlcNAcase (OGA) maintain homeostatic O-GlcNAc levels on cellular proteins. Changes in protein O-GlcNAcylation regulate cellular differentiation and cell fate decisions, but how these changes affect erythropoiesis, an essential process in blood cell formation, remains unclear. Here, we investigated the role of O-GlcNAcylation in erythropoiesis by using G1E-ER4 cells, which carry the erythroid-specific transcription factor GATA-binding protein 1 (GATA-1) fused to the estrogen receptor (GATA-1-ER) and therefore undergo erythropoiesis after ß-estradiol (E2) addition. We observed that during G1E-ER4 differentiation, overall O-GlcNAc levels decrease, and physical interactions of GATA-1 with both OGT and OGA increase. RNA-Seq-based transcriptome analysis of G1E-ER4 cells differentiated in the presence of the OGA inhibitor Thiamet-G (TMG) revealed changes in expression of 433 GATA-1 target genes. ChIP results indicated that the TMG treatment decreases the occupancy of GATA-1, OGT, and OGA at the GATA-binding site of the lysosomal protein transmembrane 5 (Laptm5) gene promoter. TMG also reduced the expression of genes involved in differentiation of NB4 and HL60 human myeloid leukemia cells, suggesting that O-GlcNAcylation is involved in the regulation of hematopoietic differentiation. Sustained treatment of G1E-ER4 cells with TMG before differentiation reduced hemoglobin-positive cells and increased stem/progenitor cell surface markers. Our results show that alterations in O-GlcNAcylation disrupt transcriptional programs controlling erythropoietic lineage commitment, suggesting a role for O-GlcNAcylation in regulating hematopoietic cell fate.

Asunto(s)

Acetilglucosamina/metabolismo , Diferenciación Celular , Células Eritroides/citología , Hematopoyesis , Homeostasis , Células Mieloides/citología , N-Acetilglucosaminiltransferasas/metabolismo , Células Cultivadas , Células Eritroides/metabolismo , Factor de Transcripción GATA1/metabolismo , Humanos , Células Mieloides/fisiología