ChREBP, but not LXRs, is required for the induction of glucose-regulated genes in mouse liver
Pierre-Damien Denechaud, … , Jean Girard, Catherine Postic
Pierre-Damien Denechaud, … , Jean Girard, Catherine Postic
Published February 21, 2008
Citation Information: J Clin Invest. 2008;118(3):956-964. https://doi.org/10.1172/JCI34314.
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Research Article

ChREBP, but not LXRs, is required for the induction of glucose-regulated genes in mouse liver

Abstract

The transcription factor carbohydrate-responsive element–binding protein (ChREBP) has emerged as a central regulator of lipid synthesis in liver because it is required for glucose-induced expression of the glycolytic enzyme liver–pyruvate kinase (L-PK) and acts in synergy with SREBP to induce lipogenic genes such as acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS). Liver X receptors (LXRs) are also important regulators of the lipogenic pathway, and the recent finding that ChREBP is a direct target of LXRs and that glucose itself can bind and activate LXRs prompted us to study the role of LXRs in the induction of glucose-regulated genes in liver. Using an LXR agonist in wild-type mice, we found that LXR stimulation did not promote ChREBP phosphorylation or nuclear localization in the absence of an increased intrahepatic glucose flux. Furthermore, the induction of ChREBP, L-PK, and ACC by glucose or high-carbohydrate diet was similar in LXRα/β knockout compared with wild-type mice, suggesting that the activation of these genes by glucose occurs by an LXR-independent mechanism. We used fluorescence resonance energy transfer analysis to demonstrate that glucose failed to promote the interaction of LXRα/β with specific cofactors. Finally, siRNA silencing of ChREBP in LXRα/β knockout hepatocytes abrogated glucose-induced expression of L-PK and ACC, further demonstrating the central role of ChREBP in glucose signaling. Taken together, our results demonstrate that glucose is required for ChREBP functional activity and that LXRs are not necessary for the induction of glucose-regulated genes in liver.

Authors

Pierre-Damien Denechaud, Pascale Bossard, Jean-Marc A. Lobaccaro, Lesley Millatt, Bart Staels, Jean Girard, Catherine Postic

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Figure 2

Differential regulation of ChREBP by LXRs and glucose.

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Differential regulation of ChREBP by LXRs and glucose. (A) Quantitative ...
(A) Quantitative real-time RT-PCR (qRT-PCR) analysis of GK, ChREBP, L-PK, ACC, SREBP-1c, FAS, SCD1, LXRα, and ABCG1 in livers of C57BL/6J mice treated for 3 days with either vehicle or 50 mg/kg body weight of the synthetic LXR agonist T0-901317. After treatment, mice were fasted overnight or maintained in the fed state. Results are mean ± SEM (n = 6 per group). #P < 0.005 vs. fasted; *P < 0.05, **P < 0.001 vs. vehicle. (B) Total, cytosolic, and nuclear ChREBP protein in liver extracts from vehicle- and T0-901317–treated fasted and fed mice. Lamin A/C and β-actin antibodies were used as loading controls. A representative Western blot is shown (n = 6 per group). (C) Ser196 phosphorylation level of the endogenous ChREBP protein. A representative Western blot is shown (n = 6 per group). Quantification of the ratio of Ser196 ChREBP phosphorylation to total ChREBP protein content is shown. *P < 0.05 vs. fasted T0-901317–treated. ChREBP immunofluorescence analysis in liver sections from T0-901317–treated fasted and vehicle-treated fed mice. Original magnification, ×400. n = 6 per group. (D) qRT-PCR analysis of ChREBP and L-PK in mouse hepatocytes incubated in the presence of low glucose (5 mM; G5) plus DMSO (white bars) or 10 μM T0-901317 (black bars) or in the presence of high glucose concentrations (25 mM) plus 100 nM insulin (gray bars) for 24 h. Error bars represent SD (n = 4 independent cultures). *P < 0.005 vs. 5 mM glucose plus DMSO.