Epigenetic changes mediated by polycomb repressive complex 2 and E2a are associated with drug resistance in a mouse model of lymphoma.
BACKGROUND
The genetic origins of chemotherapy resistance are well established; however, the role of epigenetics in drug resistance is less well understood. To investigate mechanisms of drug resistance, we performed systematic genetic, epigenetic, and transcriptomic analyses of an alkylating agent-sensitive murine lymphoma cell line and a series of resistant lines derived by drug dose escalation.


METHODS
Dose escalation of the alkylating agent mafosfamide was used to create a series of increasingly drug-resistant mouse Burkitt's lymphoma cell lines. Whole genome sequencing, DNA microarrays, reduced representation bisulfite sequencing, and chromatin immunoprecipitation sequencing were used to identify alterations in DNA sequence, mRNA expression, CpG methylation, and H3K27me3 occupancy, respectively, that were associated with increased resistance.


RESULTS
Our data suggest that acquired resistance cannot be explained by genetic alterations. Based on integration of transcriptional profiles with transcription factor binding data, we hypothesize that resistance is driven by epigenetic plasticity. We observed that the resistant cells had H3K27me3 and DNA methylation profiles distinct from those of the parental lines. Moreover, we observed DNA methylation changes in the promoters of genes regulated by E2a and members of the polycomb repressor complex 2 (PRC2) and differentially expressed genes were enriched for targets of E2a. The integrative analysis considering H3K27me3 further supported a role for PRC2 in mediating resistance. By integrating our results with data from the Immunological Genome Project (Immgen.org), we showed that these transcriptional changes track the B-cell maturation axis.


CONCLUSIONS
Our data suggest a novel mechanism of drug resistance in which E2a and PRC2 drive changes in the B-cell epigenome; these alterations attenuate alkylating agent treatment-induced apoptosis.
['Flinders|Colin|C|', 'Lam|Larry|L|', 'Rubbi|Liudmilla|L|', 'Ferrari|Roberto|R|', 'Fitz-Gibbon|Sorel|S|', 'Chen|Pao-Yang|PY|', 'Thompson|Michael|M|', 'Christofk|Heather|H|', 'B Agus|David|D|', 'Ruderman|Daniel|D|', 'Mallick|Parag|P|', 'Pellegrini|Matteo|M|']
D000818:Animals D000970:Antineoplastic Agents D051792:Basic Helix-Loop-Helix Transcription Factors D002051:Burkitt Lymphoma D045744:Cell Line, Tumor D003520:Cyclophosphamide D019175:DNA Methylation D019008:Drug Resistance, Neoplasm D044127:Epigenesis, Genetic D006657:Histones D006801:Humans D051379:Mice D063151:Polycomb Repressive Complex 2 D025341:Principal Component Analysis D011401:Promoter Regions, Genetic
Epigenetics Resistance Mafosfamide Methylation Burkitt’s lymphoma Histone