ChREBP Regulates Itself and Metabolic Genes Implicated in Lipid Accumulation in β–Cell Line

Abstract

Carbohydrate response element binding protein (ChREBP) is an important transcription factor that regulates a variety of glucose-responsive genes in hepatocytes. To date, only two natural isoforms, Chrebpα and Chrebpβ, have been identified. Although ChREBP is known to be expressed in pancreatic β cells, most of the glucose-responsive genes have never been verified as ChREBP targets in this organ. We aimed to explore the impact of ChREBP expression on regulating genes linked to accumulation of lipid droplets, a typical feature of β-cell glucotoxicity. We assessed gene expression in 832/13 cells overexpressing constitutively active ChREBP (caChREBP), truncated ChREBP with nearly identical amino acid sequence to Chrebpβ, or dominant negative ChREBP (dnChREBP). Among multiple ChREBP-controlled genes, ChREBP was sufficient and necessary for regulation of Eno1, Pklr, Mdh1, Me1, Pdha1, Acly, Acaca, Fasn, Elovl6, Gpd1, Cpt1a, Rgs16, Mid1ip1,Txnip, and Chrebpβ. Expression of Chrebpα and Srebp1c were not changed by caChREBP or dnChREBP. We identified functional ChREBP binding sequences that were located on the promoters of Chrebpβ and Rgs16. We also showed that Rgs16 overexpression lead to increased considerable amounts of lipids in 832/13 cells. This phenotype was accompanied by reduction of Cpt1a expression and slight induction of Fasn and Pklr gene in these cells. In summary, we conclude that Chrebpβ modulates its own expression, not that of Chrebpα; it also regulates the expression of several metabolic genes in β-cells without affecting SREBP-1c dependent regulation. We also demonstrate that Rgs16 is one of the ChREBP-controlled genes that potentiate accumulation of lipid droplets in β-cells.

Divergent effects of glucose and fructose on hepatic lipogenesis and insulin signaling

“…However, genes involved in lipid oxidation, such as fibroblast growth factor 21 (Fgf21) (21) and carnitine palmitoyltransferase 1 (Cpt1a) (22), have only been reported to be induced by ChREBP. Indeed the expression of these genes as well as many other genes involved in fatty acid oxidation, such as carnitine palmitoyltransferase 2 (Cpt2); family member 12, medium, long, and very long chain acyl-coenzyme A dehydrogenase (Acad12, Acadm, Acadl, Acadvl); acetyl-coenzyme A acyltransferase 2 (Acaa2), and the α and β subunits of hydroxyacylcoenzyme A dehydrogenase (Hadha and Hadhb), were increased in HFD+Gluc, but not in the HFD+Fruct group (Figure 4D), confirming that many ChREBP targets were increased with glucose supplementation as compared with the downstream targets of SREBP1c, which were increased with fructose.…”

Islet ChREBP-β is increased in diabetes and controls ChREBP-α and glucose-induced gene expression via a negative feedback loop

“…As such, these studies have greatly contributed to our understanding of the detrimental effects excessive ChREBP-α can have on beta cell biology [24]. In a recent report, overexpression of this constitutively active, truncated form of ChREBP-α failed to regulate endogenous ChREBP-α [25]. While this truncated form of ChREBP-α resembles ChREBP-β in that it lacks a N-terminal domain and, therefore, can freely enter the nucleus, it lacks amino acids 1–196, resulting in a 667-amino acid protein, whereas ChREBP-β only lacks amino acids 1–176 giving rise to a 687-amino acid protein.…”

Myc and ChREBP transcription factors cooperatively regulate normal and neoplastic hepatocyte proliferation in mice

“…MondoA and ChREBP target genes have been identified in a variety of cell lines, and ChREBP-bound genes have been cataloged in liver and white adipose tissue (37,40,43,63,67,69). However, it remains unclear how many of the nearly 6,000 ChREBP-binding sites actually alter gene expression (37).…”