Constructing Singapore : Elitism, Ethnicity and the Nation-Building Project, Michael D. Barr & Zlatko Skrbis

Michael Barr, seul ou en collaboration, est depuis une décennie l’un des auteurs les plus prolifiques et les plus reconnus sur la structuration politique et sociologique du Singapour contemporain. Longtemps attaché à l’université du Queensland (Brisbane), aujourd’hui à Flinders (Adelaide), il est assez représentatif de la nouvelle génération (singapourienne aussi bien qu’étrangère) des spécialistes de la cité-état : fermement critique, et parfois même hyper-critique, elle n’en reconnaît pas m..

O-GlcNAcylation-Inducing Treatments Inhibit Estrogen Receptor α Expression and Confer Resistance to 4-OH-Tamoxifen in Human Breast Cancer-Derived MCF-7 Cells.

PLoS OneInternational audienceO-GlcNAcylation (addition of N-acetyl-glucosamine on serine or threonine residues) is a post-translational modification that regulates stability, activity or localization of cytosolic and nuclear proteins. O-linked N-acetylgluocosmaine transferase (OGT) uses UDP-GlcNAc, produced in the hexosamine biosynthetic pathway to O-GlcNacylate proteins. Removal of O-GlcNAc from proteins is catalyzed by the β-N-Acetylglucosaminidase (OGA). Recent evidences suggest that O-GlcNAcylation may affect the growth of cancer cells. However, the consequences of O-GlcNAcylation on anti-cancer therapy have not been evaluated. In this work, we studied the effects of O-GlcNAcylation on tamoxifen-induced cell death in the breast cancer-derived MCF-7 cells. Treatments that increase O-GlcNAcylation (PUGNAc and/or glucosoamine) protected MCF-7 cells from death induced by tamoxifen. In contrast, inhibition of OGT expression by siRNA potentiated the effect of tamoxifen on cell death. Since the PI-3 kinase/Akt pathway is a major regulator of cell survival, we used BRET to evaluate the effect of PUGNAc+glucosamine on PIP3 production. We observed that these treatments stimulated PIP3 production in MCF-7 cells. This effect was associated with an increase in Akt phosphorylation. However, the PI-3 kinase inhibitor LY294002, which abolished the effect of PUGNAc+glucosamine on Akt phosphorylation, did not impair the protective effects of PUGNAc+glucosamine against tamoxifen-induced cell death. These results suggest that the protective effects of O-GlcNAcylation are independent of the PI-3 kinase/Akt pathway. As tamoxifen sensitivity depends on the estrogen receptor (ERα) expression level, we evaluated the effect of PUGNAc+glucosamine on the expression of this receptor. We observed that O-GlcNAcylation-inducing treatment significantly reduced the expression of ERα mRNA and protein, suggesting a potential mechanism for the decreased tamoxifen sensitivity induced by these treatments. Therefore, our results suggest that inhibition of O-GlcNAcylation may constitute an interesting approach to improve the sensitivity of breast cancer to anti-estrogen therapy

O-GlcNacylation Links TxNIP to Inflammasome Activation in Pancreatic β Cells

Thioredoxin interacting protein (TxNIP), which strongly responds to glucose, has emerged as a central mediator of glucotoxicity in pancreatic β cells. TxNIP is a scaffold protein interacting with target proteins to inhibit or stimulate their activity. Recent studies reported that high glucose stimulates the interaction of TxNIP with the inflammasome protein NLRP3 (NLR family, pyrin domain containing 3) to increase interleukin-1 β (IL1β) secretion by pancreatic β cells. To better understand the regulation of TxNIP by glucose in pancreatic β cells, we investigated the implication of O-linked β-N-acetylglucosamine (O-GlcNAcylation) in regulating TxNIP at the posttranslational level. O-GlcNAcylation of proteins is controlled by two enzymes: the O-GlcNAc transferase (OGT), which transfers a monosaccharide to serine/threonine residues on target proteins, and the O-GlcNAcase (OGA), which removes it. Our study shows that TxNIP is subjected to O-GlcNAcylation in response to high glucose concentrations in β cell lines. Modification of the O-GlcNAcylation pathway through manipulation of OGT or OGA expression or activity significantly modulates TxNIP O-GlcNAcylation in INS1 832/13 cells. Interestingly, expression and O-GlcNAcylation of TxNIP appeared to be increased in islets of diabetic rodents. At the mechanistic level, the induction of the O-GlcNAcylation pathway in human and rat islets promotes inflammasome activation as evidenced by enhanced cleaved IL1β. Overexpression of OGT in HEK293 or INS1 832/13 cells stimulates TxNIP and NLRP3 interaction, while reducing TxNIP O-GlcNAcylation through OGA overexpression destabilizes this interaction. Altogether, our study reveals that O-GlcNAcylation represents an important regulatory mechanism for TxNIP activity in β cells

Etude de l'homeostasie glucidique au cours de la transition allaitement-sevrage chez le rat : mise en evidence d'une resistance a l'insuline pendant la periode d'allaitement

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

O-GlcNAc glycosylation et régulation de la signalisation cellulaire

La O-GlcNAcylation correspond à l’addition de N-Acétylglucosamine sur des résidus sérine/thréonine de protéines cytosoliques ou nucléaires. Elle constitue un mode de régulation post-traductionnel réversible, analogue aux phosphorylations, qui contrôle l’activité, la stabilité ou la localisation des protéines en fonction de la disponibilité en glucose. Des perturbations de la O-GlcNAcylation des protéines pourraient jouer un rôle important dans des pathologies humaines comme le diabète de type 2. En effet, de nombreux travaux indiquent que la O-GlcNAcylation de protéines impliquées dans la signalisation de l’insuline conduit à une atténuation du signal, suggérant un mécanisme par lequel l’hyperglycémie chronique pourrait aggraver la résistance à l’insuline observée chez les patients diabétiques

Effet de la O-GlcNAcylation sur la sensibilité du tamoxifène dans le cancer du sein dérivé des cellules MCF-7

Pas de résumé en françaisOne of the hallmarks of cancer cells is to exhibit increased uptake and consumption of glucose.3-5% of the glucose entering into the cell leads to a minor pathway of the glucose metabolismknown as the hexosamine biosynthetic pathway (HBP). UDP-N-acetylglucosamine is the endproduct of HBP and is used as substrate by OGT (O-GlcNAc transferase) to modify diverserange of nuclear and cytoplasmic proteins with a recently characterized post-translationalmodification called O-GlcNAcylation. It corresponds to the addition of sugar moiety O-linked b-N-acetylglucosamine (O-GlcNAc) on serine or threonine residue of proteins. This process isantagonized by another enzyme called O-GlcNAcase (OGA). Recent studies indicated thepresence of increased O-GlcNAcylation level in several cancer cells. Moreover, inhibition ofOGT has been shown to reduce in vivo and in vitro tumor growth of breast cancer cells.However, the relationship between O-GlcNAcylation and the response to anti-cancer therapy hasnot been studied. Tamoxifen is the oldest and most prescribed selective-estrogen receptormodulator (SERM) for patients with estrogen receptor (ER)-positive breast cancer. Tamoxifen isknown to reduce tumor growth and invasion. Despite its beneficial effects de novo and acquiredresistance are great obstacles in its clinical effectiveness. We found that O-GlcNAc elevation inMCF-7 cells protected them from tamoxifen-induced cell death. Increased O-GlcNAc alsoincreased PI3-K/Akt signaling. However, the protective effect of PUGNAc+glucosamine fromtamoxifen-induced cell death is independent of PI3K/Akt pathway. Increased O-GlcNAcylationalso led to reduced ESR1 promoter activity and decreased expression of ERa at mRNA andprotein levels. The decrease in ERa expression is correlated with a reduced expression of twotamoxifen regulated genes i.e. early growth response 1 and p21 Waf1/Cip1. In conclusion, thisstudy showed for the first time the involvement of O-GlcNAcylation in reducing tamoxifen142sensitivity in MCF-7 cells. Thus, OGT can act as a novel therapeutic target for treatment oftamoxifen resistant cells.PARIS5-Bibliotheque electronique (751069902) / SudocSudocFranceF

O-GlcNAcylation and inflammation: a vast territory to explore

Mini review articleInternational audienceO-GlcNAcylation is a reversible post-translational modification that regulates the activities of cytosolic and nuclear proteins according to glucose availability.This modification appears to participate in several hyperglycemia-associated complications. An important feature of metabolic diseases such as diabetes and obesity is the presence of a low-grade chronic inflammation that causes numerous complications. Hyperglycemia associated with the metabolic syndrome is known to promote inflammatory processes through different mech-anisms including oxidative stress and abnormally elevated protein O-GlcNAcylation. How-ever, the role of O-GlcNAcylation on inflammation remains contradictory. O-GlcNAcylation associated with hyperglycemia has been shown to increase nuclear factor κB (NFκB) transcriptional activity through different mechanisms.This could contribute in inflammation-associated diabetic complications. However, in other conditions such as acute vascular injury, O-linked N-acetyl glucosamine (O-GlcNAc) also exerts anti-inflammatory effects via inhibition of the NFκB pathway, suggesting a complex regulation of inflammation by O-GlcNAc. Moreover, whereas macrophages and monocytes exposed to high glucose for a long-term period developed a pro-inflammatory phenotype, the impact of O-GlcNAcylation in these cells remains unclear. A future challenge will be to clearly establish the role of O-GlcNAcylation in pro-and anti-inflammatory functions in macrophages

Tax : une oncoprotéine virale qui aime les CREB sucrés !

International audienc

O-GlcNAc glycosylation des protéines et régulation de la signalisation cellulaire : implication en physiopathologie

La O-GlcNAcylation des protéines cytosoliques ou nucléaires est une modification post-traductionnelle réversible, dynamique, analogue à la phosphorylation, qui contrôle les activités cellulaires en fonction de la disponibilité en glucose. Deux enzymes seulement, l’OGT (O-linked N-acetyl-glucosaminyltransferase) et l’OGA (O-linkedN-acetyl-β-D glucosaminidase), régulent l’addition ou le retrait du GlcNAc (N-Acétyl glucosamine) sur les sérines ou thréonines des protéines. La O-GlcNAcylation peut moduler l’état de phosphorylation, la localisation sub-cellulaire, la stabilité ou l’activité enzymatique des protéines. Des modifications de O-GlcNAc ont été décrites dans plusieurs pathologies humaines. Une diminution de O-GlcNAc dans le cerveau semble associée à la maladie d’Alzheimer, alors qu’une augmentation de O-GlcNAcylation des protéines a été décrite dans différents types de cancers. Par ailleurs, dans les situations d’hyperglycémie chronique, une augmentation de la O-GlcNAcylation de certains facteurs de transcription et des protéines de la signalisation de l’insuline pourrait participer au phénomène de glucotoxicité, en particulier en aggravant la résistance à l’insuline et les altérations β-pancréatiques. Alors que de nombreux biologistes ignorent encore jusqu’à l’existence de cette modification, les perturbations de O-GlcNAcylation observées dans des pathologies majeures soulignent l’urgence d’une meilleure compréhension de son rôle dans le fonctionnement de la cellule