Lysine Acetylation of CREBH Regulates Fasting-Induced Hepatic Lipid Metabolism

Abstract

dCyclic AMP-responsive element-binding protein 3-like 3, hepatocyte specific (CREBH), is a hepatic transcription factor that functions as a key regulator of energy homeostasis. Here, we defined a regulatory CREBH posttranslational modification process, namely, lysine-specific acetylation, and its functional involvement in fasting-induced hepatic lipid metabolism. Fasting induces CREBH acetylation in mouse livers in a time-dependent manner, and this event is critical for CREBH transcriptional activity in regulating hepatic lipid homeostasis. The histone acetyltransferase PCAF-mediated acetylation and the deacetylase sirtuin-1-mediated deacetylation coexist to maintain CREBH acetylation states under fasting conditions. Site-directed mutagenesis and functional analyses revealed that the lysine (K) residue at position 294 (K294) within the bZIP domain of the CREBH protein is the site where fasting-induced acetylation/deacetylation occurs. Introduction of the acetylation-deficient (K294R) or acetylationmimicking (K294Q) mutation inhibited or enhanced CREBH transcriptional activity, respectively. Importantly, CREBH acetylation at lysine 294 was required for the interaction and synergy between CREBH and peroxisome proliferator-activated receptor ␣ (PPAR␣) in activating their target genes upon fasting or glucagon stimulation. Introduction of the CREBH lysine 294 mutation in the liver leads to hepatic steatosis and hyperlipidemia in animals under prolonged fasting. In summary, our study reveals a molecular mechanism by which fasting or glucagon stimulation modulates lipid homeostasis through acetylation of CREBH.T he liver is the central metabolic organ that plays primary roles in regulating lipid and glucose homeostasis upon alterations of metabolic conditions (1). Under fasting conditions, the liver boosts metabolic pathways of energy utilization, and the energy source is shifted from carbohydrates to triglycerides to meet the demands of the energy supplies. The major changes in liver metabolic pathways upon fasting include (i) glycogen utilization and gluconeogenesis to increase blood glucose levels and (ii) the catalysis of triglycerides (TG) in adipose tissue or liver to fatty acids (FA) and glycerol when the glycogen in liver is depleted. The released FA are directly oxidized as an energy source or metabolized to ketone bodies by the liver to supply energy to the brain, while glycerol is converted into glucose by the liver (2). Defects in these metabolic pathways may cause hepatic steatosis and abnormal levels of glucose and lipids in the blood. Notably, prolonged fasting results in the rapid mobilization of fat and the abnormal accumulation of FA and TG in the liver, leading to hepatic steatosis (3).Transcriptional regulation plays a major role in controlling energy metabolism. Increasing evidence suggests that the regulation of transcription factors via posttranslational modifications, such as phosphorylation, ubiquitination, glycosylation, and acetylation, plays an important role in transcriptional activity as w...

CREBH Maintains Circadian Glucose Homeostasis by Regulating Hepatic Glycogenolysis and Gluconeogenesis

“…Previously, we demonstrated that acetylation of CREBH at the lysine residue K294 is critical for CREBH-PPAR␣ interaction and optimized CREBH transcriptional activity in lipid metabolism in response to fasting (14). As shown in Fig.…”

“…5). As we demonstrated previously, CREBH is also required in order to maintain lipid homeostasis by regulating lipolysis and fatty acid oxidation during the daytime or upon fasting (7,10,14). Apparently, CREBH functions as a major transcriptional activator that drives the processes of lipid and glucose mobilization in response to energy demands.…”

“…1). Previously, we demonstrated that CREBH acetylation at lysine residue 294 is required for optimal CREBH-PPAR␣ interaction and CREBH transcriptional activity in regulating lipolysis and fatty acid oxidation in the liver upon fasting (14). Similarly, lysine acetylation of CREBH is critical for CREBH transcriptional activity in regulating the expression of PYGL for glycogenolysis as well as that of PCK1 and G6PC for gluconeogenesis (Fig.…”

“…3A). Previously, we demonstrated that a regulatory CREBH posttranslational modification process, lysine-specific acetylation, plays a critical role in CREBH transcriptional activities (14). We therefore examined CREBH lysine acetylation in the livers of mice across the circadian cycle.…”

The regulation of FGF21 gene expression by metabolic factors and nutrients

“…Fasting and glucagon increases CREBH acetylation, which is required for the formation of the CREBH-PPARα transcriptional complex [49]. In addition to regulating each other's transcription in fasted liver [47], CREBH and PPARα synergize to activate FGF21 gene expression through the binding of the CREBH-PPARα complex to a highly conserved CRE-peroxisome proliferator-activated response element (PPRE) site in the FGF21 proximal promoter [50].…”