OBJECTIVETo investigate the underlying mechanism and clinical significance of PU.1 down-expression in chronic myeloid leukemia (CML) patients.

METHODSDifferent methylation status of PU.1 promoter region containing 20 CpG islands in normal individuals, CML chronic phase and blast crisis patients, complete cytogenetic remission patients after imatinib treatment, and blast crisis bone marrow K562 CML cells was detected by bisulfite sequencing. Semi-quantitative PCR was used to detect the PU.1 mRNA expression in normal controls, CML chronic phase and blast crisis patients, and blast crisis bone marrow K562 CML cells. Indirect immune fluorescence and Western blot were used to analyze the exprtession of PU.1 protein in normal individuals, CML chronic phase and blast crisis patients, and blast crisis bone marrow K562 CML cells.

RESULTSAberrant methylation in the promoter region of transcription factor PU.1 was found in both CML chronic phase and blast crisis phase bone marrow cells, as well as in CML blast K562 cells. Down-expression of PU.1 mRNA and protein levels was found in above cells. No methylation in the promoter region of PU.1 was observed in normal individuals, and the PU.1 mRNA and protein expressions were not reduced at all. Furthermore, high methylation status of bone marrow cells was even observed in the CML patients who acquired complete cytogenetic remission.

CONCLUSIONSThe results of our study indicate that the epigenetic modification of PU.1 in CML patients and K562 cell line might be responsible for the down-expression of PU.1. The data suggest that aberrant methylation of PU.1 plays a role in CML pathogenesis, therefore, it might serve as a useful biomarker and potential target in therapy for chronic myeloid leukemia.