GSE61785
Loss of the Histone Methyltransferase EZH2 induces Resistance to Multiple Drugs in Acute Myeloid Leukemia
Poor outcome of AML patients is closely related with therapy failure or relapse after initial response. The underlying mechanisms remain largely unknown. In this study we discovered the histone methyltransferase EZH2 as a novel marker for response to chemotherapy and patients` survival. Protein levels of EZH2 and subsequently H3K27 trimethylation (H3K27me3) are reduced in chemoresistant AML cells. To analyze which genomic regions were affected by the loss of EZH2 and reduced H3K27me3 mark we performed Chromatin Immunoprecipitation followed by high-throughput DNA sequencing (ChIP-Seq). ChIP-Seq for the H3K27me3 repressive mark revealed genome-wide differences between sensitive (MV4-11) and resistant (MV4-11R) cells. Overall, 4699 genomic regions showed a more than 1.5 fold reduction of H3K27me3 around TSS ±5kb in MV4-11R compared to MV4-11cells. Promoter regions of HOX genes, classical targets of PRC2, revealed drastically reduced H3K27me3 enrichment in the MV4-11R cells. The H3K27me3 level at the transcriptional start site (TSS) of the ABCC1 promoter was decreased in resistant compared to sensitive cells (Fig. 6D) with increased levels of H3K4me3 and H3K27ac. As expected, we found H3K27me3 enrichments to be inversely correlated with gene expression whereas histone modifications H3K4me3 and H3K27ac, known as markers for active genes, positively correlated with gene expression in our analysis. Differentially regulated genes were characterized to be involved in protein modification/phosphorylation pathways and signaling and apoptosis. Overall design: Examination of histone modifiactions H3K27me3, H3K27ac and H3K4me3 in a sensitive (MV4-11) and a drug resistant (MV4-11R) AML cell line