Methylation pattern of preferentially expressed antigen of melanoma in acute myeloid leukemia and myelodysplastic syndromes.

Preferentially expressed antigen of melanoma (PRAME), a tumor-associated antigen, is overexpressed in a variety of hematologic malignancies with a great variation in expression. The majority of patients with acute myeloid leukemia (AML) 1-eight-twenty one (ETO)+ AML and a certain number of myelodysplastic syndromes (MDS) have an abnormally high increase in PRAME expression level. The landscape of PRAME methylation requires evaluation in order to determine the most relevant sites and the exact association of its methylation with expression level and type of disease. In the present study, bone marrow samples collected from 8 AML1-ETO+ AML, 4 MDS, 3 AML1-ETO- AML and 2 normal volunteers underwent bisulfate sequencing to analyze the methylation status of all four 5'-C-phosphate-G-3' (CpG) regions within the entire PRAME gene. The median PRAME transcript level of 15 patients was 204.5% (range, 0.02-710.3%). PRAME transcript levels were inversely associated with the degree of methylation of the -389 to -146 CpG sites (r=-0.69; P=0.002) in the 3' part of the promoter region and the +132 to +363 CpG sites (r=-0.69; P=0.006) in the exon 1b region. However, not every sample strictly followed this correlation: Certain samples with high degrees of methylation demonstrated abnormally high expression levels, and vice versa. The methylation ratios of CpG sites in exon 1a were low for all samples (range, 0.0-13.8%), and those in exon 2 were similar in 16 samples (range, 72.4-93.4%), with the exception of one patient with high expression (425.2%) and significantly low degree of methylation in the PRAME gene (22.2%). MDS patients revealed similar methylation ratios in the 3' section of the promoter region, but tended to have lower methylation ratios in the exon 1b region (P=0.62 and P=0.09, respectively) compared with those observed in AML1-ETO+ patients with AML and similar degree of PRAME overexpression. Therefore, the hypomethylation of CpG sites in the 3' part of the promoter region and in exon 1b was typically found with PRAME overexpression in AML and MDS. Methylation of other CpG islands, epigenetic and genetic mechanisms, and type of disease may also be involved.