A genome-wide screen for beta-catenin binding sites identifies a downstream enhancer element that controls c-Myc gene expression.
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.
Yochum
Gregory S
GS
Vollum Institute and Department of Medicine, Oregon Health and Science University, 3181 SW Sam Jackson Park Rd., Portland, OR 97239, USA. yochumg@ohsu.edu
Cleland
Ryan
R
Goodman
Richard H
RH
D000818:Animals; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000235:genetics / Q000378:metabolism; D004742:Enhancer Elements, Genetic; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D000090063:Proto-Oncogene Mas; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000378:metabolism; D051820:TCF Transcription Factors / Q000235:genetics / Q000378:metabolism; D058118:Transcription Factor 7-Like 2 Protein; D014158:Transcription, Genetic; D051176:beta Catenin / Q000235:genetics / Q000378:metabolism*
C000715470:MAS1 protein, human; D000090063:Proto-Oncogene Mas; D016271:Proto-Oncogene Proteins c-myc; D051820:TCF Transcription Factors; C544894:TCF7L2 protein, human; D058118:Transcription Factor 7-Like 2 Protein; D051176:beta Catenin; D048031:JNK Mitogen-Activated Protein Kinases