LXRα Regulates ChREBPα Transactivity in a Target Gene-Specific Manner through an Agonist-Modulated LBD-LID Interaction.

Qiong Fan,Hilde Irene Nebb,Kristin Vekterud,Christian Bindesbøll,Odd Stokke Gabrielsen,Rikke Christine Nørgaard,Line Mariann Grønning-Wang,Jason Matthews,Thomas Sæther,Christin Lucas,Cecilie Maria Ness,Ivar Grytten,Helen Soedling,Stine Marie Ulven,Roza Berhanu Lemma

doi:10.3390/cells9051214

Abstract

The cholesterol-sensing nuclear receptor liver X receptor (LXR) and the glucose-sensing transcription factor carbohydrate responsive element-binding protein (ChREBP) are central players in regulating glucose and lipid metabolism in the liver. More knowledge of their mechanistic interplay is needed to understand their role in pathological conditions like fatty liver disease and insulin resistance. In the current study, LXR and ChREBP co-occupancy was examined by analyzing ChIP-seq datasets from mice livers. LXR and ChREBP interaction was determined by Co-immunoprecipitation (CoIP) and their transactivity was assessed by real-time quantitative polymerase chain reaction (qPCR) of target genes and gene reporter assays. Chromatin binding capacity was determined by ChIP-qPCR assays. Our data show that LXRα and ChREBPα interact physically and show a high co-occupancy at regulatory regions in the mouse genome. LXRα co-activates ChREBPα and regulates ChREBP-specific target genes in vitro and in vivo. This co-activation is dependent on functional recognition elements for ChREBP but not for LXR, indicating that ChREBPα recruits LXRα to chromatin in trans. The two factors interact via their key activation domains; the low glucose inhibitory domain (LID) of ChREBPα and the ligand-binding domain (LBD) of LXRα. While unliganded LXRα co-activates ChREBPα, ligand-bound LXRα surprisingly represses ChREBPα activity on ChREBP-specific target genes. Mechanistically, this is due to a destabilized LXRα:ChREBPα interaction, leading to reduced ChREBP-binding to chromatin and restricted activation of glycolytic and lipogenic target genes. This ligand-driven molecular switch highlights an unappreciated role of LXRα in responding to nutritional cues that was overlooked due to LXR lipogenesis-promoting function.

Highlights

Glucose and lipid metabolism are tightly connected and coordinately regulated in mammals to maintain whole-body energy homeostasis
Response elements (LXREs; two direct repeats AGGTCA spaced by four nucleotides, DR4 elements) in gene regulatory regions [11]. in vivo liver X receptor (LXR) transactivity is modulated by oxysterols, which bind to the ligand-binding domain (LBD) of LXR [12]
We previously demonstrated that when knocking out LXR in mice, carbohydrate responsive element-binding protein (ChREBP) loses its ability to bind to carbohydrate responsive elements (ChoREs), which affects hepatic gene expression of ChREBP-specific targets like liver pyruvate kinase (Lpk) and Chrebpβ [16]

Summary

Introduction

Glucose and lipid metabolism are tightly connected and coordinately regulated in mammals to maintain whole-body energy homeostasis. While showing high sequence homology, the two LXR subtypes differ in their distribution (reviewed in Reference [5]): LXRα is predominantly expressed in metabolically active tissues, for example, liver and adipose tissue, while LXRβ is ubiquitously expressed [6] Both isoforms heterodimerize with retinoid X receptors (RXRs) and regulate expression of genes involved in cholesterol homeostasis, lipid and glucose metabolism and inflammation [5,7,8,9,10], by binding to LXR response elements (LXREs; two direct repeats AGGTCA spaced by four nucleotides, DR4 elements) in gene regulatory regions [11]. None of these have so far reached the clinic, as one of the concerns has been LXR-induced lipogenesis [25,26]

Methods

Results

Conclusion