Methylation analysis of the human multidrug resistance 1 gene in normal and leukemic hematopoietic cells

Expression of the human multidrug resistance 1 gene (MDR1), which encodes t he P-glycoprotein transmembrane efflux pump, has been associated with treat ment failure of some leukemias, primarily acute myeloid leukemia (AML). To elucidate the epigenetic events associated with overexpression of MDR1 in A ML, we analyzed the methylation status of a 2000 bp region within the MDR1 locus using a bisulphite genomic sequencing technique. A CpG-rich domain, a pproximately 1 kb in size, encompasses the promoter region, exon I, and int ron I. This domain was found to be relatively unmethylated in five out of s ix primary and cultured human hematopoietic cells, as well as five out of s ix AML patient samples, independent of the MDR1 phenotype. The data suggest that the methylation status of the CpG-rich domain does not act as a 'swit ch' to regulate expression of the MDR1 gene. In addition, we found an upstr eam Alu repeat sequence to be unmethylated in three out of five cultured he matopoietic cell lines, both MDR1 expressing and non-expressing. However, a nalysis of primary CD8-positive T cells and AML patient samples revealed de nse methylation of this region which is consistent with methylation of Alu repeat sequences observed in somatic tissues.