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Selective variegated methylation of the p15 CpG island in acute myeloid leukemia

Both p15and p16are tumor suppressor genes that have 5′ CpG islands; aberrant cytosine methylation of these islands has been associated with silencing of their expression. Deoxycytidine kinase (dCK) converts prodrugs to their cytotoxic form, has a 5′ CpG island and is a candidate gene for inactivation by hypermethylation. In our study, we used sodium bisulfite sequencing to generate high resolution maps of 5‐methylcytosine in the CpG islands associated with p15, p16 and dCK in normal human bone marrow (BM), peripheral blood lymphocytes (PBL) and cytosine arabinoside (ara‐C)‐resistant acute myeloid leukemia (AML) patients, and established human hematopoietic tumor cell lines. In normal cells the p15, p16and dCK CpG islands were largely unmethylated. The p16 and dCK CpG islands were also unmethylated in the 8 AML specimens. In contrast, the p15CpG island was aberrantly methylated in 6 of the 8 AML specimens. Furthermore, bisulfite sequencing revealed that the p15CpG island is heterogeneously methylated in AML, with large intra‐individual and inter‐individual variability.Int. J. Cancer 78:561–567, 1998. © 1998 Wiley‐Liss, Inc.