Control of gene expression by the Retinoic acid-related Orphan Receptor alpha in HepG2 human hepatoma cells

Retinoic acid-related Orphan Receptor alpha (RORalpha; NR1F1) is a nuclear receptor involved in several physiological and patho-physiological functions including lipid metabolism, inflammation, angiogenesis, and circadian rythm. It is widely distributed. In order to better understand the role of this nuclear receptor in liver, we aimed at displaying genes controlled by RORalpha in liver cells. HepG2 human hepatoma cells stably over-expressing RORalpha were designed. Genes whose expression was altered in these cells versus control cells were displayed using micro-arrays and qRT-PCR. Expression of these genes was also altered in cells in which RORalpha was transiently over-expressed after adenoviral infection. Some genes are involved in functions controlled by RORalpha. This is the case for 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 RORalpha. Lastly, SPARC, involved in cell growth and adhesion and associated with liver carcinogenesis, was up-regulated by RORalpha. It is a new direct RORalpha target gene since it possesses, in its promoter, a functional RORE as evidenced by EMSAs and transfection experiments. It is likely the case for most of the other genes we found regulated by RORalpha contain putative ROREs in their regulatory regions. These results open new routes to think about the role of RORalpha in glucose metabolism and carcinogenesis within cells of hepatic origin. Keywords: Comparison of HepG2 cells expressing RORalpha or control HepG2 cells cultured in 20% oxygen or 2% oxygen during 24h. RNAs were extracted from HepG2 cells transfected by pCMX-hRORa1 and expressing RORalpha or from control HepG2 cells transfected by pCMX (empty vector). Before the extraction, these cells were cultured in 20% oxygen or 2% oxygen (hypoxic treatment) during 24h. Each sample was hybridized on Human Whole Genome Oligonucleotides Microarrays 44k (G4112F).