Epigenetic Dysregulation Of Candidate Cis-Regulatory Sequences In Hematological Malignancies.

Epigenetic changes (in particular, altered cytosine methylation) have been described in a variety of tumors. The CpG Island Methylator Phenotype (CIMP) is a well-known instance of this phenomenon wherein cytosine methylation is markedly dysregulated (normally hypomethylated loci shift to a methylated state). CIMP has been demonstrated in a number of different cancer types including hematological malignancies like AML. While methylation status has been studied predominantly at CpG islands, we used a novel assay (HELP; Khulan et al., Genome Res. 2006) to look for changes in cytosine methylation in large contiguous regions of the genome. We assessed global patterns of cytosine methylation by HELP analysis in a variety of tumor samples including leukemias and lymphomas. We found significant changes in the global methylation patterns of malignant cells, confirming prior observations of epigenetic dysregulation in these tumor types. We also discovered that the majority of the changes in cytosine methylation are occurring not at CpG islands but at other loci in the genome, including constitutively hypomethylated loci that we are finding to be candidate cis-regulatory sequences. We conclude that cytosine methylation changes in cancer occur much more extensively than analysis of CpG islands alone would indicate, and that the epigenetic dysregulation in cancer may be predominantly targeted to cis-regulatory sequences rather than to promoters.