Leukemia research
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p15 and p16 are tumor suppressor genes that have 5' CpG islands and both are subject to hypermethylation associated with their transcriptional inactivation in hematological malignancies. In this study, we used sodium bisulfite sequencing to obtain a complete map of the 5-methylcytosine status of 80 CpGs covering approximately 900 bp in the 5' p15 CpG island, and 53 CpGs covering approximately 700 bp in the 5' p16 CpG island in the hematopoietic cell lines HL60, KG-1, and KG-1a, two normal human bone marrow samples (NBM), and eight cytosine arabinoside (ara-C)-resistant adult acute myeloid leukemia (AML) patients. We found methylation of the p15 CpG island in 75% of the AML cases studied spread throughout the 5' region analyzed but only minimal methylation of p15 in NBM. ⋯ Both KG-1 and KG-1a had no detectable p15 mRNA or protein. These results demonstrate that rather than continuous increases in p15 methylation, surprisingly two punctuated modes of aberrant p15 methylation, variegated and complete, were observed in vitro and in vivo. Thus aberrant methylation of tumor suppressor genes is not a binary switch but in the case of p15 occurs in two independent and stable states.