Reassembly of nucleosomes at the MLH1 promoter initiates resilencing following decitabine exposure

Luke B Hesson; Vibha Patil; Mathew A Sloane; Andrea C Nunez; Jia Liu; John E Pimanda; Robyn L Ward

doi:10.1371/journal.pgen.1003636

Reassembly of nucleosomes at the MLH1 promoter initiates resilencing following decitabine exposure

PLoS Genet. 2013;9(7):e1003636. doi: 10.1371/journal.pgen.1003636. Epub 2013 Jul 25.

Authors

Luke B Hesson¹, Vibha Patil, Mathew A Sloane, Andrea C Nunez, Jia Liu, John E Pimanda, Robyn L Ward

Affiliation

¹ Adult Cancer Program, Lowy Cancer Research Centre and Prince of Wales Clinical School, University of New South Wales, Sydney, New South Wales, Australia. l.hesson@unsw.edu.au

Abstract

Hypomethylating agents reactivate tumor suppressor genes that are epigenetically silenced in cancer. Inevitably these genes are resilenced, leading to drug resistance. Using the MLH1 tumor suppressor gene as a model, we showed that decitabine-induced re-expression was dependent upon demethylation and eviction of promoter nucleosomes. Following decitabine withdrawal, MLH1 was rapidly resilenced despite persistent promoter demethylation. Single molecule analysis at multiple time points showed that gene resilencing was initiated by nucleosome reassembly on demethylated DNA and only then was followed by remethylation and stable silencing. Taken together, these data establish the importance of nucleosome positioning in mediating resilencing of drug-induced gene reactivation and suggest a role for therapeutic targeting of nucleosome assembly as a mechanism to overcome drug resistance.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Adaptor Proteins, Signal Transducing / genetics*
Azacitidine / administration & dosage
Azacitidine / analogs & derivatives
Cell Line, Tumor
Chromatin Assembly and Disassembly / genetics
CpG Islands / genetics
DNA Methylation / drug effects
DNA Methylation / genetics*
Decitabine
Drug Resistance, Neoplasm / drug effects
Drug Resistance, Neoplasm / genetics*
Gene Expression Regulation, Neoplastic / drug effects
Gene Silencing
Humans
MutL Protein Homolog 1
Nuclear Proteins / genetics*
Nucleosomes / genetics*
Nucleosomes / metabolism
Promoter Regions, Genetic / drug effects

Substances

Adaptor Proteins, Signal Transducing
MLH1 protein, human
Nuclear Proteins
Nucleosomes
Decitabine
MutL Protein Homolog 1
Azacitidine

Grants and funding

LBH is supported by a Cancer Institute New South Wales Career Development Fellowship (Grant number: 09CDF226; www.cancerinstitute.org.au). This work was also supported by funding from the Cancer Council NSW (www.cancercouncil.com.au) and Cancer Australia (http://canceraustralia.gov.au). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.