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

The retinoic acid receptor-related orphan receptor alpha (ROR alpha) 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 ROR alpha 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 ROR alpha response element (RORE) in the promoter of the CS gene. ChIP analysis demonstrates ROR alpha occupancy of the CS promoter and a putative RORE binds to ROR alpha effectively in an electrophoretic mobility shift assay and confers ROR alpha 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 ROR alpha. protein. Furthermore, we found that SR1001 a ROR alpha inverse agonist eliminated the circadian pattern of expression of CS mRNA in mice. These data suggest that CS is a direct ROR alpha target gene and one mechanism by which ROR alpha regulates lipid metabolism is via regulation of CS expression.