ChREBP•Mlx Is the Principal Mediator of Glucose-induced Gene Expression in the Liver

摘要

In mammals, glucose-regulated gene expression has been best characterized in the liver, where increased glucose metabolism induces transcription of genes encoding enzymes involved in de novo lipogenesis. ChREBP and Mlx dimerize and function together as a glucose-responsive transcription factor to regulate target genes, such as liver-type pyruvate kinase, acetyl-CoA carboxylase 1, and fatty acid synthase. To identify additional glucose-responsive genes in the liver, we used microarray analysis to compare gene expression patterns in low and high glucose conditions in hepatocytes. Target genes of ChREBP·Mlx were simultaneously identified by gene profiling in the presence or absence of a dominant negative Mlx. Of 224 genes that are induced by glucose, 139 genes (62%) were also inhibited by the dominant negative Mlx. Lipogenic enzyme genes involved in the entire pathway of de novo lipogenesis were found to be glucose-responsive target genes of ChREBP·Mlx. Genes encoding enzymes in other metabolic pathways and numerous regulators of metabolism were also identified. To determine if any of these genes are direct targets of ChREBP·Mlx, we searched for ChoRE-like sequences in the 5′-flanking regions of several genes that responded rapidly to glucose. ChoRE sequences that bound to ChREBP·Mlx and supported a glucose response were identified in two additional genes. Combining all of the known ChoRE sequences, we generated a modified ChoRE consensus sequence, CAYGNGN5CNCRTG. In summary, ChREBP·Mlx is the principal transcription factor regulating glucose-responsive genes in the liver and coordinately regulates a family of genes required for glucose utilization and energy storage. In mammals, glucose-regulated gene expression has been best characterized in the liver, where increased glucose metabolism induces transcription of genes encoding enzymes involved in de novo lipogenesis. ChREBP and Mlx dimerize and function together as a glucose-responsive transcription factor to regulate target genes, such as liver-type pyruvate kinase, acetyl-CoA carboxylase 1, and fatty acid synthase. To identify additional glucose-responsive genes in the liver, we used microarray analysis to compare gene expression patterns in low and high glucose conditions in hepatocytes. Target genes of ChREBP·Mlx were simultaneously identified by gene profiling in the presence or absence of a dominant negative Mlx. Of 224 genes that are induced by glucose, 139 genes (62%) were also inhibited by the dominant negative Mlx. Lipogenic enzyme genes involved in the entire pathway of de novo lipogenesis were found to be glucose-responsive target genes of ChREBP·Mlx. Genes encoding enzymes in other metabolic pathways and numerous regulators of metabolism were also identified. To determine if any of these genes are direct targets of ChREBP·Mlx, we searched for ChoRE-like sequences in the 5′-flanking regions of several genes that responded rapidly to glucose. ChoRE sequences that bound to ChREBP·Mlx and supported a glucose response were identified in two additional genes. Combining all of the known ChoRE sequences, we generated a modified ChoRE consensus sequence, CAYGNGN5CNCRTG. In summary, ChREBP·Mlx is the principal transcription factor regulating glucose-responsive genes in the liver and coordinately regulates a family of genes required for glucose utilization and energy storage. One of the primary organs responsible for controlling energy homeostasis in mammals is the liver. In fasting conditions, the liver produces glucose through glycogenolysis and gluconeogenesis to maintain glucose homeostasis and meet the energy requirements of other tissues. In times of severe energy shortage, liver will supply alternative energy sources in the form of ketone bodies. After food intake, it is a major site for carbohydrate storage in the form of glycogen. In addition, triglycerides, the major energy storage form in mammals, are synthesized in the liver for packaging into very low density lipo