Abstract 4791: Genome-wide DNA methylation maps in chronic lymphocytic leukemia cells determined by next-generation sequencing

Abstract

Abstract Chronic lymphocytic leukemia (CLL) is the most common leukemia of adults in the western world. The clinical course of CLL is highly variable. Some patients are able to live years with no need for treatment; whereas others progress rapidly requiring therapy within a short time after diagnosis. The identification and validation of prognostic molecular markers (including surface markers, cytogenetic abnormalities, and IGHV mutational status) have resulted in refinements in the approach to the management of these patients. Further discovery of biologically relevant factors that influence the heterogeneity and progression of CLL will not only promote our understanding of the disease process, but also allow us to identify rational therapeutic approaches. In this study, we conducted genome-wide DNA methylation analyses in purified CD19+ B-cells from 11 CLL patients with a range of CD38 expression using reduced representation bisulfite sequencing (RRBS). Using one lane of the Illumina sequencing data, we were able to consistently determine the methylation status of approximately 1.8 million CpGs; 45% of these CpGs are located in more than 23,000 CpG islands (CGIs), accounting for more than 80% of all annotated CGIs across the genome. We have identified a large number of CGIs that were differentially methylated between CLL cells and normal CD19+ B-cells. The promoter hypermethylation patterns of many genes previously reported in CLL, such as FOXD3, GRM7, DLEU7 etc, were determined in the 11 CLL samples. In addition, we have observed aberrant DNA methylation changes in all 4 HOX gene clusters in CLL. For instance, HOXD8, HOXD9, and HOXD11 were hypermethylated in 11 out of 11 CLL samples. In addition, we also identified a significant number of DNA methylation alterations in the WNT signaling pathway genes. One-way ANOVA analysis of DNA methylation profiles of 764,984 CpGs shared by all CLL samples identified 570 CpGs that were differentially methylated (p<0.001) between CD38high and CD38low group (with >20% CLL cells expressing CD38 as CD38high group). The cluster analysis of the 570 CpGs reveals that it is possible to separate these CLL samples into two distinct groups based on the DNA methylation profiles. The study further confirms our early findings that CLL is affected by CpG island methylation in some genes that segregate with CD38 expression levels, while most others show similar methylation patterns across all levels. The aberrant promoter hypermethylation in certain functional gene groups and pathway-associated genes that are known to be deregulated in CLL provides additional insights into the CLL methylome and epigenetic contribution to cellular dysfunction. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4791. doi:10.1158/1538-7445.AM2011-4791