A genome-wide screen for beta-catenin binding sites identifies a downstream enhancer element that controls c-Myc gene expression

Mol Cell Biol. 2008 Dec;28(24):7368-79. doi: 10.1128/MCB.00744-08. Epub 2008 Oct 13.

Abstract

Mutations in components of the Wnt signaling pathway initiate colorectal carcinogenesis by deregulating the beta-catenin transcriptional coactivator. beta-Catenin activation of one target in particular, the c-Myc proto-oncogene, is required for colon cancer pathogenesis. beta-Catenin is known to regulate c-Myc expression via sequences upstream of the transcription start site. Here, we report that a more robust beta-catenin binding region localizes 1.4 kb downstream from the c-Myc transcriptional stop site. This site was discovered using a genome-wide method for identifying transcription factor binding sites termed serial analysis of chromatin occupancy. Chromatin immunoprecipitation-scanning assays demonstrate that the 5' enhancer and the 3' binding element are the only beta-catenin and TCF4 binding regions across the c-Myc locus. When placed downstream of a simian virus 40-driven promoter-luciferase construct, the 3' element activated luciferase transcription when introduced into HCT116 cells. c-Myc transcription is negligible in quiescent HCT116 cells but is induced when cells reenter the cell cycle after the addition of mitogens. Using these cells, we found that beta-catenin and TCF4 occupancy at the 3' enhancer precede occupancy at the 5' enhancer. Association of c-Jun, beta-catenin, and TCF4 specifically with the downstream enhancer underlies mitogen stimulation of c-Myc transcription. Our findings indicate that a downstream enhancer element provides the principal regulation of c-Myc expression.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Base Sequence
  • Binding Sites / genetics
  • Cell Line, Tumor
  • Colorectal Neoplasms / genetics
  • Colorectal Neoplasms / metabolism
  • Enhancer Elements, Genetic*
  • Gene Expression Regulation*
  • Genes, Reporter
  • Humans
  • JNK Mitogen-Activated Protein Kinases / genetics
  • JNK Mitogen-Activated Protein Kinases / metabolism
  • Molecular Sequence Data
  • Promoter Regions, Genetic
  • Proto-Oncogene Mas
  • Proto-Oncogene Proteins c-myc* / genetics
  • Proto-Oncogene Proteins c-myc* / metabolism
  • TCF Transcription Factors / genetics
  • TCF Transcription Factors / metabolism
  • Transcription Factor 7-Like 2 Protein
  • Transcription, Genetic
  • beta Catenin / genetics
  • beta Catenin / metabolism*

Substances

  • MAS1 protein, human
  • Proto-Oncogene Mas
  • Proto-Oncogene Proteins c-myc
  • TCF Transcription Factors
  • TCF7L2 protein, human
  • Transcription Factor 7-Like 2 Protein
  • beta Catenin
  • JNK Mitogen-Activated Protein Kinases