Sweet Sixteenth for ChREBP: Established Roles and Future Goals Aya Abdul-Wahed, Sandra Guilmeau, Catherine Postic  Cell Metabolism  Volume 26, Issue 2, Pages 324-341 (August 2017) DOI: 10.1016/j.cmet.2017.07.004 Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 1 ChREBP Protein Structure and Regulation upon Nutritional and Hormonal Signals The full-length protein ChREBPα (∼95 kDa, 864 aa) contains several functional domains: two nuclear export signals (NES1 and 2) and a nuclear import signal (NLS), a polyproline region, and a DNA-binding basic helix-loop-helix/Zip domain, site of heterodimerization with MLX. Nuclear shuttling factors (14-3-3, CRM1, importins) bind to the NES1, NES2, and NLS motifs within the sequence of ChREBP to affect its subcellular localization (nuclear or cytosolic) in response to variations in nutritional status (carbohydrate versus fasting as indicated). The N-terminal domain of the protein contains the evolutionarily conserved domain GSM (glucose-sensing module) also known as MCR (mondo conserved region), composed of a low-glucose inhibitory domain (LID) and a transactivation domain called glucose-response activation conserved element (GRACE). The shorter ChREBP isoform, ChREBPβ (72 KDa, 687 aa), lacks most of the LID domain and hence presents features of a constitutive active isoform. The activation of ChREBP by glucose is mediated by a dynamic intramolecular inhibition between LID and GRACE. Low glucose concentrations restrain the transcriptional activity of GRACE through the LID (Inactive ChREBP), while high glucose releases this inhibition (Active ChREBP). Glucose metabolite(s) potentially bind within the GSM/MCR6 region. Post-translational modifications known to stimulate ChREBP activity (lysine acetylation on Lys672) or inhibit its activity (phosphorylation on serine [Ser196 and Ser568] or threonine [Thr666]) are indicated. Cell Metabolism 2017 26, 324-341DOI: (10.1016/j.cmet.2017.07.004) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 2 Activation of Liver De Novo Lipogenesis in Response to Carbohydrate Feeding Insulin induces the expression of Gck gene (encoding GK) via SREBP-1c, whereas the induction of Lpk gene (encoding L-PK), one of the rate-limiting enzymes of glycolysis, is exclusively dependent on ChREBP isoforms. ChREBPα is activated by several mechanisms that drive its nuclear translocation and binding to ChoRE element present on the promoter of its target genes. Glucose metabolites (G6P, X5P, and F2,6P2) were all suggested as ChREBPα-activating metabolites. ChREBPα was identified as an activator of the Chrebpβ gene expression through binding on a ChoRE element located in the Chrebpβ first exon. It remains to be determined whether both ChREBPα and ChREBPβ bind together as heterotetramers onto ChoRE elements of their target genes (encoding L-PK, ACC, FAS, and SCD1). In pancreatic β cells, ChREBPβ was shown to downregulate Chrebpα expression, thereby revealing the existence of a negative feedback loop between these two isoforms. This mechanism was not demonstrated in other sites of co-expression of ChREBPα and ChREBPβ such as liver or adipose tissue. ACC, acetyl-CoA carboxylase; FAS, fatty acid synthase; F2,6P2, fructose 2,6 bisphosphate; GK, glucokinase; G6P, glucose 6-phosphate; L-PK, liver pyruvate kinase; PPP, pentose phosphate pathway; SCD1, stearoyl-CoA desaturase 1; X5P, xylulose 5-phosphate. Cell Metabolism 2017 26, 324-341DOI: (10.1016/j.cmet.2017.07.004) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 3 Summary of the Phenotypes Associated with ChREBP Deficiency in Mice The metabolic phenotypes of ChREBP-deficient mice are illustrated under normal diet (light blue), frucose-enriched diet (light yellow), or western diet and in the context of genetic obesity (pink). HFD, high-fat diet; HSD, high-sucrose diet. Cell Metabolism 2017 26, 324-341DOI: (10.1016/j.cmet.2017.07.004) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 4 Integrative Model of ChREBP Functions in Health and Disease In health (light blue), ChREBP activity in the liver regulates glycolysis and lipogenesis in response to feeding. It also promotes the release of hepatokines, among which is FGF21, which controls sweet taste and/or alcohol preference by acting on specific regions of the brain. Local ChREBP activity in the brain may be involved in the control of satiety, although its direct contribution remains to be addressed. In adipocytes, ChREBP controls local and systemic insulin sensitivity by promoting the synthesis of adipokines and lipid species (PAHSAs, FGF21, and PPARγ ligands), as well as adipocyte differentiation (mostly demonstrated in vitro). In macrophages, ChREBP exerts anti-inflammatory effects by releasing anti-inflammatory cytokines. In disease (pink), ChREBP activity in the liver is increased and contributes to hepatic steatosis through direct stimulation of the lipogenic pathway. Enhanced hepatic ChREBP activity may also participate in the release of hepatokines (including FGF21 or PANDER), which could affect either sweet preference or local or systemic insulin resistance. Decreased ChREBP expression in adipocytes (in the context of insulin resistance or hyperglycemia) may also exacerbate the state of insulin resistance by directly affecting the release of specific adipokines and lipid species. In pancreas, kidney, and skeletal muscle, increased ChREBP activity in the context of sugar overload is associated with glucotoxicity, β cell deterioration, lipotoxicity, fibrosis, and decreased oxidative capacity. Cell Metabolism 2017 26, 324-341DOI: (10.1016/j.cmet.2017.07.004) Copyright © 2017 Elsevier Inc. Terms and Conditions