FXR Controls the Tumor Suppressor NDRG2 and FXR Agonists Reduce Liver Tumor Growth and Metastasis in an Orthotopic Mouse Xenograft Model

Ulrich Deuschle,Ulrich Abel,Andreas Schulz,Olaf Kinzel,Claus Kremoser,Thomas Schlüter,Julia Schüler,Chun-Ming Wong

doi:10.1371/journal.pone.0043044

Ulrich Deuschle, Ulrich Abel + Show 6 more

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https://doi.org/10.1371/journal.pone.0043044

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Abstract

The farnesoid X receptor (FXR) is expressed predominantly in tissues exposed to high levels of bile acids and controls bile acid and lipid homeostasis. FXR−/− mice develop hepatocellular carcinoma (HCC) and show an increased prevalence for intestinal malignancies, suggesting a role of FXR as a tumor suppressor in enterohepatic tissues. The N-myc downstream-regulated gene 2 (NDRG2) has been recognized as a tumor suppressor gene, which is downregulated in human hepatocellular carcinoma, colorectal carcinoma and many other malignancies.We show reduced NDRG2 mRNA in livers of FXR−/− mice compared to wild type mice and both, FXR and NDRG2 mRNAs, are reduced in human HCC compared to normal liver. Gene reporter assays and Chromatin Immunoprecipitation data support that FXR directly controls NDRG2 transcription via IR1-type element(s) identified in the first introns of the human, mouse and rat NDRG2 genes. NDRG2 mRNA was induced by non-steroidal FXR agonists in livers of mice and the magnitude of induction of NDRG2 mRNA in three different human hepatoma cell lines was increased when ectopically expressing human FXR. Growth and metastasis of SK-Hep-1 cells was strongly reduced by non-steroidal FXR agonists in an orthotopic liver xenograft tumor model. Ectopic expression of FXR in SK-Hep1 cells reduced tumor growth and metastasis potential of corresponding cells and increased the anti-tumor efficacy of FXR agonists, which may be partly mediated via increased NDRG2 expression. FXR agonists may show a potential in the prevention and/or treatment of human hepatocellular carcinoma, a devastating malignancy with increasing prevalence and limited therapeutic options.

Highlights

The Farnesoid X Receptor (FXR, NR1H4) is a member of the nuclear hormone receptor superfamily, predominantly expressed in tissues exposed to high levels of bile acids, such as the entire gastrointestinal tract, the liver, the bile duct and gallbladder
Since farnesoid X receptor (FXR) controls many hepatoprotective genes, including genes involved in detoxification of reactive oxygen species [14], loss of N-myc downstreamregulated gene 2 (NDRG2) is more likely just one of the factors mediated by loss of FXR function that contribute to the development of hepatocellular carcinoma (HCC)
Neither FXR nor NDRG2 seemed significantly down-regulated in the combined set of 13 tested non-HCC liver-disease cDNA samples originating from patients with liver cirrhosis (n = 5), fatty liver (n = 5) and chronic hepatitis (n = 3) compared to ‘‘normal’’ liver (Fig. 3C)

Summary

Introduction

The Farnesoid X Receptor (FXR, NR1H4) is a member of the nuclear hormone receptor superfamily, predominantly expressed in tissues exposed to high levels of bile acids, such as the entire gastrointestinal tract, the liver, the bile duct and gallbladder. FXR senses bile acids (such as Chenodeoxycholic acid, CDCA) as endogenous ligands, is a master regulator of bile acid homeostasis and prevents bile acid– induced liver toxicity by regulating directly and indirectly (e.g. via Small Heterodimer Partner, SHP, NR0B2) the expression of numerous genes involved in bile acid synthesis, conjugation, and transport [3,4,5,6,7]. Activation of FXR by synthetic derivatives of the natural bile acid ligands, such as 6-Ethyl-Chenodeoxycholic Acid (6-ECDCA), or by synthetic non-steroidal agonists like GW4064 [8], results in beneficial metabolic adjustments in different mouse models such as glucose lowering, insulin sensitisation, triglyceride and cholesterol lowering [9,10,11]. Activation of FXR results in hepatoprotection in mouse models of Non Alcoholic Fatty Liver Disease (NAFLD) possibly mediated via a reduction of lipid accumulation, fibrosis and inflammation [12,13,14]. Of direct clinical importance is the tumor-stage dependent reduction of both FXR mRNA and FXR protein in human colon carcinoma [20,21]

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