Liver-Enriched Transcription Factors Regulate MicroRNA-122 That Targets CUTL1 During Liver Development

Abstract

MicroRNA-122 (miR-122) is a liver-specific microRNA whose expression is specifically turned on in the mouse liver during embryogenesis, thus it is expected to be involved in liver development. However, the role of miR-122 in liver development and its potential underlying mechanism remain unclear. Here, we show that the expression of miR-122 is closely correlated with four liver-enriched transcription factors (LETFs)-hepatocyte nuclear factor (HNF) 1a, HNF3b, HNF4a, and CCAAT/enhancer-binding protein (C/EBP) a-in the livers of developing mouse embryos and in human hepatocellular carcinoma (HCC) cell lines. Correspondingly, promoter analysis revealed that these LETFs are coordinately involved in the transcriptional regulation of miR-122, and three HNFs directly bind to the miR-122 promoter as transcriptional activators. Using a luciferase reporter system, we identified a group of miR-122 targets involved in proliferation and differentiation regulation. Among these targets, the most prominently repressed target was CUTL1, a transcriptional repressor of genes specifying terminal differentiation in multiple cell lineages, including hepatocytes. We show that CUTL1 expression is gradually silenced at the posttranscriptional level during mouse liver development. Overexpression and knockdown studies both showed that miR-122 repressed CUTL1 protein expression in HCC cell lines. Finally, we show that the stable restoration of miR-122 in HepG2 cells suppresses cellular proliferation and activates the expression of three hepatocyte functional genes, including the cholesterol-7a hydroxylase gene (CYP7A1), a known target of CUTL1 in hepatocytes. Conclusion: Our study provides a model in which miR-122 functions as an effector of LETFs and contributes to liver development by regulating the balance between proliferation and differentiation of hepatocytes, at least by targeting CUTL1. (HEPATOLOGY 2010;52:1431-1442

MiR-122 in hepatic function and liver diseases

“…These observations suggest that miR-122 may play an essential role in the regulation of hepatocyte differentiation and liver development. Direct evidence that miR-122 might be involved in liver development was first provided by Xu et al (2010), who showed in mice that four liver-enriched transcription factors including hepatocyte nuclear factor (HNF) 1α, HNF3β, HNF4α and CCAAT/enhancer-binding protein (C/EBP)α bind to miR-122 promoter and activate miR-122 expression. The increase of miR-122 leads to down-regulation of its target CUTL1, a transcriptional repressor of genes specifying terminal differentiation in hepatocytes, thereby contributing to differentiation of hepatocytes (Xu et al, 2010).…”

“…Direct evidence that miR-122 might be involved in liver development was first provided by Xu et al (2010), who showed in mice that four liver-enriched transcription factors including hepatocyte nuclear factor (HNF) 1α, HNF3β, HNF4α and CCAAT/enhancer-binding protein (C/EBP)α bind to miR-122 promoter and activate miR-122 expression. The increase of miR-122 leads to down-regulation of its target CUTL1, a transcriptional repressor of genes specifying terminal differentiation in hepatocytes, thereby contributing to differentiation of hepatocytes (Xu et al, 2010). A subsequent study further showed that as transcriptional stimulators, HNF6 and its paralog Onecut2 promote the expression of miR-122 which is required for proper progression of hepatocyte differentiation.…”

“…We also observed a marked decrease (about 50% at maximum) of the expression of miR-122 under IFN-α treatment in Huh-7 cells. Since the expression of miR-122 has been shown to be transcriptionally regulated by liver-enriched transcription factors (Xu et al, 2010), analysis of the regulation of miR-122 expression by these transcriptional factors is needed.…”

MicroRNAs in Liver Disease: Bench to Bedside

“…34 Quantitative analyses of miRs have demonstrated higher and dynamic expression in various developmental stages of liver during the fetal period. 35 MiR-30 is crucial for liver development and it is upregulated during later developmental stages, influencing known regulators of hepatic function, including epidermal growth factor receptor.…”

“…[37][38][39] It is highly expressed in hepatocytes due to its liver specific transcriptional regulation by hepatic nuclear transcription factors 34,40 and is elevated in most hepatic diseases including hepatitis C virus (HCV) and hepatitis B virus (HBV) infections as well as alcohol and drug-induced liver injury, HCC and NAFLD. 13,14,[37][38][39][40][41][42][43][44][45] There are four miR-122 binding sites in the HCV genome 42 and miR-122 may promote viral replication by direct interaction with seed-sequencebinding to two target sites, S1 and S2, in the 5 0 -UTR of the HCV genome resulting in HCV-RNA genome stabilization and enhanced viral RNA abundance.…”