Beta-catenin regulates vitamin C biosynthesis and cell survival in murine liver.
Because the Wnt/beta-catenin pathway plays multiple roles in liver pathobiology, it is critical to identify gene targets that mediate such diverse effects. Here we report a novel role of beta-catenin in controlling ascorbic acid biosynthesis in murine liver through regulation of expression of regucalcin or senescence marker protein 30 and ... L-gulonolactone oxidase. Reverse transcription-PCR, Western blotting, and immunohistochemistry demonstrate decreased regucalcin expression in beta-catenin-null livers and greater expression in beta-catenin overexpressing transgenic livers, HepG2 hepatoma cells (contain constitutively active beta-catenin), regenerating livers, and in hepatocellular cancer tissues that exhibit beta-catenin activation. Interestingly, coprecipitation and immunofluorescence studies also demonstrate an association of beta-catenin and regucalcin. Luciferase reporter and chromatin immunoprecipitation assays verified a functional TCF-4-binding site located between -163 and -157 (CTTTGCA) on the regucalcin promoter to be critical for regulation by beta-catenin. Significantly lower serum ascorbate levels were observed in beta-catenin knock-out mice secondary to decreased expression of regucalcin and also of L-gulonolactone oxidase, the penultimate and last (also rate-limiting) steps in the synthesis of ascorbic acid, respectively. These mice also show enhanced basal hepatocyte apoptosis. To test if ascorbate deficiency secondary to beta-catenin loss and regucalcin decrease was contributing to apoptosis, beta-catenin-null hepatocytes or regucalcin small interfering RNA-transfected HepG2 cells were cultured, which exhibited significant apoptosis that was alleviated by the addition of ascorbic acid. Thus, through regucalcin and L-gulonolactone oxidase expression, beta-catenin regulates vitamin C biosynthesis in murine liver, which in turn may be one of the mechanisms contributing to the role of beta-catenin in cell survival.
Mesh Terms:
Animals, Antioxidants, Ascorbic Acid, Basic Helix-Loop-Helix Leucine Zipper Transcription Factors, Calcium-Binding Proteins, Carcinoma, Hepatocellular, Cell Line, Tumor, Cell Survival, DNA-Binding Proteins, Gene Expression Regulation, Hepatocytes, Humans, Intracellular Signaling Peptides and Proteins, L-Gulonolactone Oxidase, Liver, Liver Neoplasms, Mice, Mice, Inbred C57BL, Mice, Knockout, Mice, Transgenic, Promoter Regions, Genetic, RNA, Small Interfering, Transcription Factor 4, Transcription Factors, beta Catenin
Animals, Antioxidants, Ascorbic Acid, Basic Helix-Loop-Helix Leucine Zipper Transcription Factors, Calcium-Binding Proteins, Carcinoma, Hepatocellular, Cell Line, Tumor, Cell Survival, DNA-Binding Proteins, Gene Expression Regulation, Hepatocytes, Humans, Intracellular Signaling Peptides and Proteins, L-Gulonolactone Oxidase, Liver, Liver Neoplasms, Mice, Mice, Inbred C57BL, Mice, Knockout, Mice, Transgenic, Promoter Regions, Genetic, RNA, Small Interfering, Transcription Factor 4, Transcription Factors, beta Catenin
J Biol Chem
Date: Oct. 09, 2009
PubMed ID: 19690176
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