RING Finger Protein 4 (RNF4) Derepresses Gene Expression from DNA Methylation

Yu Wang

doi:10.1074/jbc.c114.611558

Abstract

RNF4 is an E3 ubiquitin ligase originally identified as a transcription co-activator. The mechanism by which RNF4 promotes transcription remains unclear. In this study, I found that RNF4 antagonizes transcriptional repression mediated by DNA methylation. RNF4 does not promote DNA demethylation, but mediates the ubiquitination of MeCP2, a methyl-CpG-binding domain (MBD) protein. Removal of MeCP2 from gene promoters activates transcription. This study thus not only uncovers how RNF4 functions as a transcription activator, but also reveals the mechanism by which MeCP2 protein stability is regulated.

Highlights

RNF4 is a transcription activator, yet the mechanism is unknown
I found that RNF4 significantly derepresses the expression of an imprinted gene H19, as well as P16 and LINE1 known to be regulated by DNA methylation, but not genes that are constitutively expressed such as CAPN1 (Calpain1) and thymine-DNA glycosylase (TDG)
These data suggest that RNF4 derepresses gene expression caused by DNA methylation, and the Ring finger domain is important for this activity

Summary

Background

RNF4 is a transcription activator, yet the mechanism is unknown. Results: RNF4 mediates ubiquitination and turnover of MeCP2 and derepresses transcription from DNA methylation. RNF4 does not promote DNA demethylation, but mediates the ubiquitination of MeCP2, a methyl-CpG-binding domain (MBD) protein. This study uncovers how RNF4 functions as a transcription activator, and reveals the mechanism by which MeCP2 protein stability is regulated. 2 The abbreviations used are: MBD, methyl cytosine-binding domains; TET, Ten-eleven translocation; 5caC, 5-carboxylcytosine; TDG, thymine-DNA glycosylase; SIM, SUMO-interacting motif; SUMO, small ubiquitin-like modifier; qPCR, quantitative PCR; MeCP2, methyl CpG-binding protein 2; MeGFP, methylated GFP. A study revealed that RNF4 modulates DNA demethylation by activating the base excision repair machinery [14], the precise mechanism remains unclear. Rather than promoting DNA demethylation, I found that RNF4 mediates the ubiquitination and turnover of MeCP2, an MBD protein that represses transcription

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION