The BRAF oncoprotein functions through the transcriptional repressor MAFG to mediate the CpG Island Methylator phenotype

Minggang Fang; Jianhong Ou; Lloyd Hutchinson; Michael R Green

doi:10.1016/j.molcel.2014.08.010

The BRAF oncoprotein functions through the transcriptional repressor MAFG to mediate the CpG Island Methylator phenotype

Mol Cell. 2014 Sep 18;55(6):904-915. doi: 10.1016/j.molcel.2014.08.010. Epub 2014 Sep 11.

Authors

Minggang Fang¹, Jianhong Ou², Lloyd Hutchinson³, Michael R Green⁴

Affiliations

¹ Howard Hughes Medical Institute, University of Massachusetts Medical School, Worcester, MA 01605, USA; Programs in Gene Function and Expression and Molecular Medicine, University of Massachusetts Medical School, Worcester, MA 01605, USA.
² Programs in Gene Function and Expression and Molecular Medicine, University of Massachusetts Medical School, Worcester, MA 01605, USA.
³ Department of Pathology, University of Massachusetts Medical School, Worcester, MA 01605, USA.
⁴ Howard Hughes Medical Institute, University of Massachusetts Medical School, Worcester, MA 01605, USA; Programs in Gene Function and Expression and Molecular Medicine, University of Massachusetts Medical School, Worcester, MA 01605, USA. Electronic address: michael.green@umassmed.edu.

Abstract

Most colorectal cancers (CRCs) containing activated BRAF (BRAF[V600E]) have a CpG island methylator phenotype (CIMP) characterized by aberrant hypermethylation of many genes, including the mismatch repair gene MLH1. MLH1 silencing results in microsatellite instability and a hypermutable phenotype. Through an RNAi screen, here we identify the transcriptional repressor MAFG as the pivotal factor required for MLH1 silencing and CIMP in CRCs containing BRAF(V600E). In BRAF-positive human CRC cell lines and tumors, MAFG is bound at the promoters of MLH1 and other CIMP genes, and recruits a corepressor complex that includes its heterodimeric partner BACH1, the chromatin remodeling factor CHD8, and the DNA methyltransferase DNMT3B, resulting in hypermethylation and transcriptional silencing. BRAF(V600E) increases BRAF/MEK/ERK signaling resulting in phosphorylation and elevated levels of MAFG, which drives DNA binding. Analysis of transcriptionally silenced CIMP genes in KRAS-positive CRCs indicates that different oncoproteins direct the assembly of distinct repressor complexes on common promoters.

Publication types

Research Support, N.I.H., Extramural

MeSH terms

Adaptor Proteins, Signal Transducing / genetics*
Animals
Basic-Leucine Zipper Transcription Factors / metabolism
Cell Line, Tumor
Colorectal Neoplasms / genetics*
Colorectal Neoplasms / pathology
CpG Islands / genetics*
DNA (Cytosine-5-)-Methyltransferases / metabolism
DNA Methylation
DNA Methyltransferase 3B
DNA-Binding Proteins / metabolism
Fanconi Anemia Complementation Group Proteins / metabolism
Gene Expression Regulation, Neoplastic
HEK293 Cells
Humans
MafG Transcription Factor / metabolism*
Mice, Inbred BALB C
MutL Protein Homolog 1
Mutation
Neoplasms, Experimental
Nuclear Proteins / genetics*
Phenotype
Promoter Regions, Genetic
Proto-Oncogene Proteins B-raf / genetics
Proto-Oncogene Proteins B-raf / metabolism*
Repressor Proteins / metabolism*
Signal Transduction
Transcription Factors / metabolism

Substances

Adaptor Proteins, Signal Transducing
BACH1 protein, human
Basic-Leucine Zipper Transcription Factors
CHD8 protein, human
DNA-Binding Proteins
Fanconi Anemia Complementation Group Proteins
MAFG protein, human
MLH1 protein, human
MafG Transcription Factor
Nuclear Proteins
Repressor Proteins
Transcription Factors
DNA (Cytosine-5-)-Methyltransferases
BRAF protein, human
Proto-Oncogene Proteins B-raf
MutL Protein Homolog 1

Abstract

Publication types

MeSH terms

Substances

Grants and funding