Abstract
Ammonium is a metabolic waste product mainly detoxified by the liver. Hepatic dysfunction can lead to cytotoxic accumulation of circulating ammonium and to subsequent encephalopathy. Transmembrane ammonium transport is a widely spread process ensured by the highly conserved proteins of the Mep-Amt-Rh superfamily, including the mammalian Rhesus (Rh) factors. The regulatory mechanisms involved in the control of RH genes expression remain poorly studied. Here we addressed the expression regulation of one of these factors, RHBG. We identify HepG2 hepatocellular carcinoma cells and SW480 colon adenocarcinoma cells as expressing RHBG and show that its expression relies on β-catenin signaling. siRNA-mediated β-catenin knockdown resulted in significant reduction of RHBG mRNA in both cell lines. Pharmaceutical inhibition of the TCF4/β-catenin interaction or knockdown of the transcription factor TCF4 also downregulated RHBG expression. We identify a minimal RHBG regulatory sequence displaying a promoter activity and show that β-catenin and TCF4 bind to this fragment in vivo. We finally characterize the role of potential TCF4 binding sites in RHBG regulation. Taken together, our results indicate RHBG expression as a direct target of β-catenin regulation, a pathway frequently deregulated in many cancers and associated with tumorigenesis.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Adenocarcinoma / genetics
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Ammonium Compounds / metabolism
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Basic Helix-Loop-Helix Leucine Zipper Transcription Factors / genetics
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Carcinogenesis / genetics
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Carcinoma, Hepatocellular / genetics
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Cell Line
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Cell Line, Tumor
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Colonic Neoplasms / genetics
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Down-Regulation / genetics
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Gene Expression Regulation, Neoplastic / genetics*
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Glycoproteins / genetics*
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HEK293 Cells
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Hep G2 Cells
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Humans
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Liver Neoplasms / genetics
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Membrane Transport Proteins / genetics*
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Promoter Regions, Genetic / genetics
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Protein Binding / genetics
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Transcription Factor 4
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Transcription Factors / genetics
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Wnt Signaling Pathway / genetics*
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beta Catenin / genetics*
Substances
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Ammonium Compounds
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Basic Helix-Loop-Helix Leucine Zipper Transcription Factors
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Glycoproteins
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Membrane Transport Proteins
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RHBG protein, human
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TCF4 protein, human
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Transcription Factor 4
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Transcription Factors
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beta Catenin
Grants and funding
This work was supported by grants from the Belgian Fonds de la Recherche Scientifique F.R.S.-FNRS (F.R.S.M. 3.4633.09, M.I.S. F.4.521.10.F), the Fédération Wallonie-Bruxelles (Action de Recherche Concertée), the International Brachet Stiftung, the Jean Brachet and the Alice et David Van Buuren foundations. A.M. is a scientific research worker supported by a Télévie grant, C.D. was a scientific research worker of the F.R.S.-FNRS, JVA was supported by a da Vinci program, and A.M.M. is a senior research associate of the F.R.S.-FNRS. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.