Dynamic DNA methylation change in the CpG island region of p15 during human myeloid development

We examined the kenetics of p15 methylation and expression during myeloid d evelopment. We treated human cord blood CD34(+) cells with either GM-CSF al one or in combination with stem cell factor and followed methylation at thi s locus using bisulfite genomic sequencing. CD34(+) cells were found to be either fully methylated or completely unmethylated at 27 CpG dinucleotide s ites in exon 1 and at 18 CpG sites in the promoter region of the p15 gene. A time-course study showed that the percentage of the allelic methylation o f p15 CpG island increased to approximately 50% to 60% until 7 days after c ytokine stimulation, then decreased to less than 10% after 21 days. The met hylation was also observed in bone marrow CD34(+) cells exposed to GM-CSF. p15 expression varied inversely with methylation. Expression was negligible or at low levels until 14 days, after which it increased substantially. Th e frequency of myeloid colony-forming cells in the progeny decreased and my eloid-specific markers increased in the later stages. Based on our observat ions on cells grown with GM-CSF and 5-aza-2'-deoxtcytidine, DNA methylation of the p15 promoter region CpG island appears to be associated with prolif eration rather than differentiation of normal human myeloid progenitors.