Project description:The Cytoplasmic Polyadenylation Element Binding (CPEB)-family of RNA-binding proteins regulates pre-mRNA processing and translation of CPE-containing mRNAs in early embryonic development and synaptic activity. However, the specific functions of each CPEB in the adult organism are poorly understood. Here we show that CPEB4 is required to suppress high fat diet- and aging-induced endoplasmic reticulum (ER) stress, and its subsequent hepatic steatosis. Stress-activated expression of CPEB4 in the liver is controlled through a double layer of regulation. First, Cpeb4 is transcriptionally regulated by the circadian clock and then, its mRNA translation is regulated by the Unfolded Protein Response (UPR) through the upstream Open Reading Frames (uORFs) present in its 5’ UTR. Thus, CPEB4 is synthesized only upon ER-stress but the amplitude of the induction is circadian. In turn, CPEB4 activates a second wave of UPR-translation required to maintain ER and mitochondrial homeostasis. Our results suggest that combined transcriptional and translational regulation of CPEB4 generates a “circadian mediator”, which coordinates the hepatic UPR activity with periods of high ER protein-folding demand preventing non-alcoholic fatty liver disease (NAFLD).
Project description:The Cytoplasmic Polyadenylation Element Binding (CPEB)-family of RNA-binding proteins regulates pre-mRNA processing and translation of CPE-containing mRNAs in early embryonic development and synaptic activity. However, the specific functions of each CPEB in the adult organism are poorly understood. Here we show that CPEB4 is required to suppress high fat diet- and aging-induced endoplasmic reticulum (ER) stress, and its subsequent hepatic steatosis. Stress-activated expression of CPEB4 in the liver is controlled through a double layer of regulation. First, Cpeb4 is transcriptionally regulated by the circadian clock and then, its mRNA translation is regulated by the Unfolded Protein Response (UPR) through the upstream Open Reading Frames (uORFs) present in its 5’ UTR. Thus, CPEB4 is synthesized only upon ER-stress but the amplitude of the induction is circadian. In turn, CPEB4 activates a second wave of UPR-translation required to maintain ER and mitochondrial homeostasis. Our results suggest that combined transcriptional and translational regulation of CPEB4 generates a “circadian mediator”, which coordinates the hepatic UPR activity with periods of high ER protein-folding demand preventing non-alcoholic fatty liver disease (NAFLD).
Project description:Glucocorticoids (GCs) are widely prescribed effective drugs, but their clinical use is compromised by severe side effects including hyperglycemia, hyperlipidemia and obesity. They bind to the Glucocorticoid Receptor (GR), which acts as a ligand-gated transcription factor. The transcriptional activation of metabolic genes by GR is thought to underlie these undesired adverse effects. Using mouse genetics, ChIP-Seq, RNA-Seq and ChIP-MS, we found that the bHLH transcription factor E47 is required for the regulation of hepatic glucose and lipid metabolism by GR in vivo, and that loss of E47 prevents the development of hyperglycemia and hepatic steatosis in response to GCs. Here we show that E47 and GR co-occupy metabolic promoters and enhancers. E47 is needed for the efficient binding of GR to chromatin and for the adequate recruitment of coregulators such as Mediator. Taken together, our results illustrate how GR and E47 regulate hepatic metabolism, and how inhibition of E47 might provide an entry point for novel GC therapies with reduced side effect profiles. These ChIP-MS data sets show IPs for GR in both wildtype and E47 mutant mouse livers treated with the synthetic glucocorticoid Dexamethasone.