Effects of nuclear receptor RORα in regulation of STAT3 signaling and hepatic inflammation

Abstract

Chronic liver inflammation plays a critical role in various liver diseases. In an inflammatory region of liver, inflammtory cytokines, IL-6 and IL-22, constitutively activate signal transducer and activator of transcription 3 (STAT3) and exacerbate inflammation induced hepatocellular carcinoma. Therefore, Inhibition of STAT3 activity is important for regulation of liver malignancy. Retonoic acid receptor related orphan receptor α (RORα) is related various metabolism and inflammatory response. Recently, It is reported that RORα attenuates liver metabolic diseases, but it is unknown that RORα has relation with STAT3 activity. To investigate the relationship between RORα and STAT3 in liver inflammation, we used RORα overexpression adenovirus in primary mouse hepatocytes and HepG2 liver cancer cells. Our data showed that RORα overexpression decreased phosphorylation of STAT3 in liver cells. In contrast, RORα knockdown increased phosphorylation of STAT3. Moreover, we observed that RORα overexpression decreased STAT3 transcriptional activity. Synthetic RORα ligands, SR1078 and JC1-40, were also decreased STAT3 transcriptional activity. STAT3 downstream genes, myc and p53, expression was modulated when RORα was overexpressed in HepG2 cells. In order to find how RORα regulates STAT3 activity, we tested endogenous STAT3 regulators expression level when RORα is overexpressed in primary mouse hepatocytes. Four STAT3 regulators that are somatic mutated or downregulated in human cancers, were selected. Our data showed that RORα overexpression downregulated GRIM19 mRNA expression level in primary mouse hepatocytes. Next, we tested effects of RORα ligands in diethylnitrosamine-induced liver inflammation in vivo model. When RORα ligand, JC1-40, was treated, serum ALT and AST levels of mice were decreased and suppression of STAT3 phosphorylation was observed in mouse liver tissue. Infiltrated immune cells number were decreased when JC1-40 was administrated. Also, JC1-40 treatment reduced mRNA expression level of IL-1β and TNFα in liver tissue. In this study, we demonstrated that RORα regulates STAT3 activity by regulation of GRIM19 expression, and RORα ligand reduced STAT3 activity and inflammatory responses in diethylnitrosamine induced liver inflammation in vivo mice model. These findings revealed that RORα is a novel therapeutic target for inflammation-related liver diseases.