Metabolite Regulation of Nuclear Localization of Carbohydrate-response Element-binding Protein (ChREBP)

Abstract

The carbohydrate-response element-binding protein (ChREBP) is a glucose-responsive transcription factor that plays an essential role in converting excess carbohydrate to fat storage in the liver. In response to glucose levels, ChREBP is regulated by nuclear/ cytosol trafficking via interaction with 14-3-3 proteins, CRM-1 (exportin-1 or XPO-1), or importins. Nuclear localization of ChREBP was rapidly inhibited when incubated in branchedchain ␣-ketoacids, saturated and unsaturated fatty acids, or 5-aminoimidazole-4-carboxamide ribonucleotide. Here, we discovered that protein-free extracts of high fat-fed livers contained, in addition to ketone bodies, a new metabolite, identified as AMP, which specifically activates the interaction between ChREBP and 14-3-3. The crystal structure showed that AMP binds directly to the N terminus of ChREBP-␣2 helix. Our results suggest that AMP inhibits the nuclear localization of ChREBP through an allosteric activation of ChREBP/14-3-3 interactions and not by activation of AMPK. AMP and ketone bodies together can therefore inhibit lipogenesis by restricting localization of ChREBP to the cytoplasm during periods of ketosis.

Structural Basis for the Interaction of 14-3-3<i>β</i> with Tricarboxylic Acid Cycle Intermediate Malate

“…Intriguingly, malate binding to 14-3-3β contributes to the conformation change from "close-open" state in Apo to "close-close" state in complex, raising the possibility that the alteration by malate might regulate the interaction between target proteins like ChREBP with 14-3-3s. ChREBP is a large transcription factor to activate expression of all the lipogenic Journal of Biosciences and Medicines enzymes at high glucose level, and in liver, independent to insulin effects [8]. 14-3-3β and/or importins-α binding to ChREBP play important roles in nuclear/cytosol trafficking pathway.…”

“…All isoforms recognize two phosphorylated-dependent binding motifs with phosphorylation of serine or threnine residues: RSXpSXP (model 1) and RXXXp(S/T)X[PLM] (model 2) [5]. Nevertheless, 14-3-3(s) might also interact with non-phosphorylated peptide, such as ChREBP-α2 helix [6], p190RhoGEF [7], and metabolites, such as AMP generated during fatty acid metabolism [8]. Despite the targets contain phosphorylation modification or not, they all bind to the same amphipathic groove on 14-3-3 [9].…”

“…This pathway could origin back to increased concentration of the pentose shunt intermediate xylulose 5-P (Xu5P) [19]. In addition, a new metabolite, identified as AMP, was recently reported to specifically target the interaction between ChREBP and 14-3-3β [8]. Together with ketone bodies, AMP therefore inhibits lipogenesis by restricting localization of ChREBP to the cytoplasm.…”

Czynnik transkrypcyjny ChREBP – koordynator metabolizmu węglowodanów i lipidów

“…stanie głodu, towarzyszy temu wzrost stężenia ciał ketonowych i AMP [26]. AMP wiąże się bezpośrednio do N--końca białka i poprzez oddziaływanie allosteryczne promuje powstawanie kompleksu ChREBP z białkami 14-3-3, co hamuje import ChREBP do jądra [27]. Ciała ketonowe: β-hydroksymaślan i acetylooctan, podobnie jak AMP, aktywują i stabilizują kompleks ChREBP z białkami 14-3-3, uniemożliwiając transport do jądra [28].…”

Glucose-6 Phosphate, a Central Hub for Liver Carbohydrate Metabolism

“…High glucose also stimulates ChREBP activity and affinity to ChoRE sequences through acetylation and/or O-GlcNacetylation [44,45]. Finally, during fasting periods, phosphorylation of ChREBP by AMPK, in response to glucagon or to an increase in cellular AMP, is responsible for its cytoplasmic retention and/or for its decreased binding to target promoters [46,47].…”