Control of Gene Expression by the Retinoic Acid-Related Orphan Receptor Alpha in HepG2 Human Hepatoma Cells

Abstract

Retinoic acid-related Orphan Receptor alpha (RORα; NR1F1) is a widely distributed nuclear receptor involved in several (patho)physiological functions including lipid metabolism, inflammation, angiogenesis, and circadian rhythm. To better understand the role of this nuclear receptor in liver, we aimed at displaying genes controlled by RORα in liver cells by generating HepG2 human hepatoma cells stably over-expressing RORα. Genes whose expression was altered in these cells versus control cells were displayed using micro-arrays followed by qRT-PCR analysis. Expression of these genes was also altered in cells in which RORα was transiently over-expressed after adenoviral infection. A number of the genes found were involved in known pathways controlled by RORα, for instance LPA, NR1D2 and ADIPOQ in lipid metabolism, ADIPOQ and PLG in inflammation, PLG in fibrinolysis and NR1D2 and NR1D1 in circadian rhythm. This study also revealed that genes such as G6PC, involved in glucose homeostasis, and AGRP, involved in the control of body weight, are also controlled by RORα. Lastly, SPARC, involved in cell growth and adhesion, and associated with liver carcinogenesis, was up-regulated by RORα. SPARC was found to be a new putative RORα target gene since it possesses, in its promoter, a functional RORE as evidenced by EMSAs and transfection experiments. Most of the other genes that we found regulated by RORα also contained putative ROREs in their regulatory regions. Chromatin immunoprecipitation (ChIP) confirmed that the ROREs present in the SPARC, PLG, G6PC, NR1D2 and AGRP genes were occupied by RORα in HepG2 cells. Therefore these genes must now be considered as direct RORα targets. Our results open new routes on the roles of RORα in glucose metabolism and carcinogenesis within cells of hepatic origin.

Developing a New Two-Step Protocol to Generate Functional Hepatocytes from Wharton’s Jelly-Derived Mesenchymal Stem Cells under Hypoxic Condition

“…Moreover, hypoxia has been shown to activate hypoxia-inducible factor 1 ( HIF-1 ) expression which has target gene asretinoic acid-receptor-related orphan receptor alpha ( Rorα ) transcripts in HepG2 [34]. The Rora upregulations are involved in controlling ADIPOQ and G6PC expressions which play roles in regulation of lipid and glucose metabolisms in hepatic cells, respectively [35]. From these data, hypoxia seems to provide appropriate environment for maintaining physiological activities including hepatic-lineage differentiation in liver cells.…”

Clock Genes and Clock-Controlled Genes in the Regulation of Metabolic Rhythms

“…The NR auxiliary loop of the clock gene machinery plays a role in glucose metabolism: REV-ERBα represses gluconeogenic gene expression in the liver and modulates hepatic glucose production in response to heme (Yin et al, 2007), whereas RORα stimulates expression of GLC-6-Pase and modulates glycogen metabolism in the liver (Chauvet et al, 2011). In particular, the SWI/SNF chromatin-remodeling complex subunit BAF60a, rhythmically expressed in mouse liver and is present near ROR response elements on the proximal Bmal1 and G6Pc promoters, activates their transcription through coactivation of RORα, and plays a critical role in the coordinated regulation of the hepatic circadian clock, glucose metabolism, and energy homeostasis (Tao et al, 2011).…”

Genetic Variants of Retinoic Acid Receptor-Related Orphan Receptor Alpha Determine Susceptibility to Type 2 Diabetes Mellitus in Han Chinese

“…RORA has been identified as controlling the transcription of genes important in the regulation of lipid and glucose metabolism, such as genes encoding apolipoproteins A1, A5 and C3, glucose 6-phosphatase, and insulin [6,7,8,9,10]. A spontaneous mutation consisting of a deletion within the RORA gene, that prevents translation of the RORA ligand-binding domain, has been identified in the staggerer mouse ( RORA sg/sg ) [11].…”