Regulation of Expression of Citrate Synthase by the Retinoic Acid Receptor-Related Orphan Receptor α (RORα)

Abstract

The retinoic acid receptor-related orphan receptor α (RORα) is a member of the nuclear receptor superfamily of transcription factors that plays an important role in regulation of the circadian rhythm and metabolism. Mice lacking a functional RORα display a range of metabolic abnormalities including decreased serum cholesterol and plasma triglycerides. Citrate synthase (CS) is a key enzyme of the citric acid cycle that provides energy for cellular function. Additionally, CS plays a critical role in providing citrate derived acetyl-CoA for lipogenesis and cholesterologenesis. Here, we identified a functional RORα response element (RORE) in the promoter of the CS gene. ChIP analysis demonstrates RORα occupancy of the CS promoter and a putative RORE binds to RORα effectively in an electrophoretic mobility shift assay and confers RORα responsiveness to a reporter gene in a cotransfection assay. We also observed a decrease in CS gene expression and CS enzymatic activity in the staggerer mouse, which has a mutation of in the Rora gene resulting in nonfunctional RORα protein. Furthermore, we found that SR1001 a RORα inverse agonist eliminated the circadian pattern of expression of CS mRNA in mice. These data suggest that CS is a direct RORα target gene and one mechanism by which RORα regulates lipid metabolism is via regulation of CS expression.

Retinoic acid-related orphan receptors α and γ: key regulators of lipid/glucose metabolism, inflammation, and insulin sensitivity

“…Data demonstrating that the circadian pattern of expression of a number of metabolic genes are regulated by clock proteins and RORs and observations showing that circadian expression of RORγ1 is controlled by the clock machinery suggested that RORs might function as downstream mediators in the mechanism by which clock proteins regulate the circadian expression of metabolic genes (Sato et al, 2004; Akashi and Takumi, 2005; Guillaumond et al, 2005; Ueda et al, 2005; Crumbley et al, 2010; Duez and Staels, 2010; Takeda et al, 2011, 2012). This is supported by observations showing that RORs regulate the circadian pattern of expression of a number of genes involved in the lipid/glucose homeostasis, including Plin2 , sulfotransferase Sul1E1 , the vasopressin receptor Avpr1a , and citrate synthase ( CS ), which exhibit roles in lipogenesis, glycogenolysis, and/or cholesterogenesis (Kang et al, 2007; Crumbley et al, 2012; Takeda et al, 2012). Thus, RORs appear to be part of the mechanism that links the circadian clock to its regulation of lipid/glucose homeostasis, inflammation, and insulin resistance ( Figure 2 ).…”

Circadian gene variants in cancer

“…The cancer risk of mice lacking Rorα or γ ( Rorα −/− or Rorγ −/− ) has not been carefully studied. However, these mice are immune-deficient (265, 266) and show adipocyte hyperplasia (267–269). Deregulation of Rorα, and/or γ is also associated with accelerated aging and neurodegeneration in mice (270, 271).…”

Interaction between Retinoid Acid Receptor-Related Orphan Receptor Alpha (RORA) and Neuropeptide S Receptor 1 (NPSR1) in Asthma

“…RORA is a transcription factor that belongs to the nuclear hormone-receptor superfamily (NR1) and binds as monomers to specific hormone response elements (RORE) in DNA. By interacting with co-activators and co-repressors [3], RORA might enhance or repress the transcription of target genes [4]–[10]. RORA is mostly known for its functions as a regulator of circadian rhythms, metabolism, as well as mood disorders, and its role in the immune system and asthma has gained attention only recently [3], [11].…”