O-GlcNAcylation Increases ChREBP Protein Content and Transcriptional Activity in the Liver

Abstract

OBJECTIVECarbohydrate-responsive element–binding protein (ChREBP) is a key transcription factor that mediates the effects of glucose on glycolytic and lipogenic genes in the liver. We have previously reported that liver-specific inhibition of ChREBP prevents hepatic steatosis in ob/ob mice by specifically decreasing lipogenic rates in vivo. To better understand the regulation of ChREBP activity in the liver, we investigated the implication of O-linked β-N-acetylglucosamine (O-GlcNAc or O-GlcNAcylation), an important glucose-dependent posttranslational modification playing multiple roles in transcription, protein stabilization, nuclear localization, and signal transduction.RESEARCH DESIGN AND METHODSO-GlcNAcylation is highly dynamic through the action of two enzymes: the O-GlcNAc transferase (OGT), which transfers the monosaccharide to serine/threonine residues on a target protein, and the O-GlcNAcase (OGA), which hydrolyses the sugar. To modulate ChREBPOG in vitro and in vivo, the OGT and OGA enzymes were overexpressed or inhibited via adenoviral approaches in mouse hepatocytes and in the liver of C57BL/6J or obese db/db mice.RESULTSOur study shows that ChREBP interacts with OGT and is subjected to O-GlcNAcylation in liver cells. O-GlcNAcylation stabilizes the ChREBP protein and increases its transcriptional activity toward its target glycolytic (L-PK) and lipogenic genes (ACC, FAS, and SCD1) when combined with an active glucose flux in vivo. Indeed, OGT overexpression significantly increased ChREBPOG in liver nuclear extracts from fed C57BL/6J mice, leading in turn to enhanced lipogenic gene expression and to excessive hepatic triglyceride deposition. In the livers of hyperglycemic obese db/db mice, ChREBPOG levels were elevated compared with controls. Interestingly, reducing ChREBPOG levels via OGA overexpression decreased lipogenic protein content (ACC, FAS), prevented hepatic steatosis, and improved the lipidic profile of OGA-treated db/db mice.CONCLUSIONSTaken together, our results reveal that O-GlcNAcylation represents an important novel regulation of ChREBP activity in the liver under both physiological and pathophysiological conditions.

O-GlcNAcase deficiency suppresses skeletal myogenesis and insulin sensitivity in mice through the modulation of mitochondrial homeostasis

“…Previous reports have shown that the loss of OGA in mice leads to defects in metabolic homeostasis, culminating in obesity and insulin resistance [26], and that the overexpression of OGA in db/db mice significantly improves the lipid profile in liver [45]. Consistently, we found impaired insulin signalling and glucose uptake capacity in myotubes after OGA knockdown or treatment with PUGNAc or D-GlcNAc, with concurrent increased O-GlcNAcylation and mitochondrial dysfunction.…”

Cancer Metabolism and Elevated O-GlcNAc in Oncogenic Signaling

“…Moreover, carbohydrate-responsive element-binding protein (ChREBP) contributes to metabolic reprogramming in tumors through inhibition of mitochondrial respiration and up-regulation of aerobic glycolysis, de novo lipogenesis, and nucleotide biosynthesis (39). ChREBP O-GlcNAcylation stabilizes the protein, leading to increased transcription of ChREBP glycolytic and lipogenic target genes L-type pyruvate kinase, acetyl-CoA carboxylase, and fatty acid synthase (40,41). O-GlcNAcylation of the transcription factor Sp1 activates a cholesterolgenic program through transcriptionally increasing the expression of the SREBP1 (sterol response element-binding protein 1) and 3-hydroxy-3-methylglutaryl-coenzyme A reductase (42).…”

Le facteur de transcription ChREBP

“…Des études récentes ont également permis de montrer que l'activité de ChREBP pouvait être modulée par des modifications post-traductionnelles comme la O-GlcNAcylation ou l'acétylation [15][16][17]. En réponse au glucose, la protéine ChREBP est acétylée sur la lysine 672 (résidu localisé dans le domaine de liaison à l'ADN) Figure 1A) [23].…”

“…Par la suite, notre laboratoire a montré une interaction directe entre ChREBP et l'OGT dans des hépatocytes en culture primaire et dans le foie in vivo. La O-GlcNAcylation qui en résulte conduit à la stabilisation de ChREBP et à l'augmentation de son activité transcriptionnelle sur ses gènes cibles [16]. Outre ChREBP, des régulateurs clefs du métabolisme énergétique, Un rôle controversé pour ChREBP dans la sensibilité à l'insuline hépatique L'importance du facteur de transcription ChREBP dans le contrôle de l'homéostasie énergétique a été mise en évidence par la caractérisa-tion phénotypique de plusieurs modèles animaux [5,[25][26][27].…”