Reassembly of nucleosomes at the MLH1 promoter initiates resilencing following decitabine exposure.
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.
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
Luke B
LB
Hesson
Vibha
V
Patil
Mathew A
MA
Sloane
Andrea C
AC
Nunez
Jia
J
Liu
John E
JE
Pimanda
Robyn L
RL
Ward
D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics*; D001374:Azacitidine / Q000008:administration & dosage / Q000031:analogs & derivatives; D045744:Cell Line, Tumor; D042002:Chromatin Assembly and Disassembly / Q000235:genetics; D018899:CpG Islands / Q000235:genetics; D019175:DNA Methylation / Q000187:drug effects / Q000235:genetics*; D000077209:Decitabine; D019008:Drug Resistance, Neoplasm / Q000187:drug effects / Q000235:genetics*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D020868:Gene Silencing; D006801:Humans; D000070957:MutL Protein Homolog 1; D009687:Nuclear Proteins / Q000235:genetics*; D009707:Nucleosomes / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000187:drug effects
D048868:Adaptor Proteins, Signal Transducing; C501486:MLH1 protein, human; D009687:Nuclear Proteins; D009707:Nucleosomes; D000077209:Decitabine; D000070957:MutL Protein Homolog 1; D001374:Azacitidine