Beta-catenin regulates vitamin C biosynthesis and cell survival in murine liver

J Biol Chem. 2009 Oct 9;284(41):28115-28127. doi: 10.1074/jbc.M109.047258. Epub 2009 Aug 18.

Abstract

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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antioxidants / metabolism
  • Ascorbic Acid / biosynthesis*
  • Basic Helix-Loop-Helix Leucine Zipper Transcription Factors
  • Calcium-Binding Proteins / genetics
  • Calcium-Binding Proteins / metabolism*
  • Carcinoma, Hepatocellular / genetics
  • Carcinoma, Hepatocellular / metabolism
  • Cell Line, Tumor
  • Cell Survival / physiology*
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism
  • Gene Expression Regulation
  • Hepatocytes / cytology
  • Hepatocytes / metabolism
  • Humans
  • Intracellular Signaling Peptides and Proteins / genetics
  • Intracellular Signaling Peptides and Proteins / metabolism*
  • L-Gulonolactone Oxidase / genetics
  • L-Gulonolactone Oxidase / metabolism*
  • Liver / cytology
  • Liver / metabolism*
  • Liver Neoplasms / genetics
  • Liver Neoplasms / metabolism
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Mice, Transgenic
  • Promoter Regions, Genetic
  • RNA, Small Interfering / genetics
  • RNA, Small Interfering / metabolism
  • Transcription Factor 4
  • Transcription Factors / genetics
  • Transcription Factors / metabolism
  • beta Catenin / genetics
  • beta Catenin / metabolism*

Substances

  • Antioxidants
  • Basic Helix-Loop-Helix Leucine Zipper Transcription Factors
  • Calcium-Binding Proteins
  • DNA-Binding Proteins
  • Intracellular Signaling Peptides and Proteins
  • RGN protein, human
  • RNA, Small Interfering
  • Rgn protein, mouse
  • TCF4 protein, human
  • Transcription Factor 4
  • Transcription Factors
  • beta Catenin
  • L-Gulonolactone Oxidase
  • Ascorbic Acid