p15INK4b DNA methylation and expression in AML cell lines used in study. (A) Bisulfite sequencing of the p15INK4b exon 1 CpG island. Filled circles represent percentage of DNA methylation at CpG positions from 10 independently sequenced clones (● represents ≥ 50% methylcytosine; , 10%-49% methylcytosine). (B-C) Quantitative reverse-transcriptase (RT)–PCR analysis of p15INK4b, p14ARF, and p16INK4a expression in AML cell lines. Copies of cDNA per 100 ng of total RNA were calculated from a plasmid DNA standard curve and represent the averages of 3 independent experiments with error bars of SD.