Influence of functional MDR1 gene polymorphisms on P-glycoprotein activity in CD34+ hematopoietic stem cells.

BACKGROUND AND OBJECTIVES Expression of the multidrug resistance P-glycoprotein, a transmembrane drug transporter, is influenced by recently described polymorphisms of the human MDR1 gene. Hematopoietic cells, such as lymphocytes, and hematopoietic stem cells, express P-glycoprotein, but the effect of MDR1 gene polymorphisms on P-glycoprotein activity in stem cells is unknown. We investigated whether T-129C, G26677T and C3435T polymorphisms influence P-glycoprotein function in stem cells. DESIGN AND METHODS P-glycoprotein function was evaluated in immunomagnetically purified bone marrow CD34+ cells from 33 healthy bone marrow donors by the flow cytometric rhodamine 123-efflux assay. For T-129C and C3435T, bone marrow donors were genotyped by polymerase chain reaction amplification followed by MspA1I and DpnII digestion analyses, respectively. For the analysis of C2677T, exon 21 was sequenced. RESULTS P-glycoprotein function was not different among the C3435T genotypes (CC, 38.2 +/- 3.5%; n=17; CT, 42.2 +/- 3.3%; n=11; and TT, 45.0 +/- 5.3%; n=5) nor was it among the C2677T genotypes (CC, 39.4 +/- 2.4%; n=27; CT, 43.7 +/- 6.4%; n=5; and TT, 54.3%; n=1). Among the 33 subjects, three were heterozygotes for the 129C allele (CT) and no mutant homozygote was identified. P-glycoprotein was similar in heterozygotes (TC, 50.6 +/- 2.9%) and wild-type subjects (TT, 39.5 +/- 2.4%). INTERPRETATION AND CONCLUSIONS These findings suggest that the known functional MDR1 gene polymorphisms are not major determinants of P-glycoprotein function in hematopoietic stem cells. Other genetic variants might influence P-glycoprotein activity in this cell type.