Clockwork orange-mediated control of sugar responsive transcription [ChIP-seq]

Feeding on high sugar diet reprograms metabolism, partially mediated through a gene regulatory network controlled by intracellular sugar sensor Mondo/ChREBP-Mlx. Sugar-induced gene expression changes include activation of genes encoding enzymes of glycolysis, pentose phosphate pathways, and de novo lipogenesis, collectively driving the flux of sugar-derived carbon into triacylglycerides. These sugar-induced metabolic changes are likely to trigger compensatory responses to avoid depletion of necessary metabolites, but they remain poorly characterized. Through a global temporal clustering analysis of sugar-induced gene expression in Drosophila we identify new gene expression programs controlled by sugar feeding. These include rapid and transient downregulation of ribosome biogenesis genes, known targets of transcription factor Myc. Through in silico motif predictions and experimental validation, we identify transcriptional repressor Clockwork orange (CWO) as a mediator of this response. CWO expression is directly activated by Mondo-Mlx and it counteracts Myc through repression of its expression as well as through binding to overlapping regulatory regions of ribosome biogenesis genes. Loss of CWO function leads to depletion of UDP-GlcNAc pools and impaired viability on high sugar diet. Analysis of CWO orthologs, BHLHE40 and BHLHE41, in mouse hepatocytes revealed a conserved role for BHLHE41 in repressing ribosome biogenesis genes. Collectively, our data uncover a gene regulatory circuit balancing the activities of lipid and protein biosynthesis to maintain homeostasis during high sugar feeding. Overall design: Chromatin immunoprecipitation DNA-sequencing (ChIP-seq) for ChREBP and Dec1 in mice fed a standard diet.