Quantitative determination of the human MRP1 and MRP2 mRNA expression in FACS-sorted peripheral blood CD4+, CD8+, CD19+, and CD56+ cells

Objectives: ATP-binding cassette (ABC) transporters extrude a wide variety of endogenous and exogenous compounds. In cancer cells, they are known to confer multidrug resistance. The aim of the present study was to determine the expression of the multidrug resistance-associated protein 1 (MRP1) and 2 (MRP2), which are members of the subfamily C of the ABC transporters family, in human hematopoietic cells. Methods: CD4(+) , CD8(+) , CD19(+) , and CD56(+) cells were isolated from whole blood by FACS-sort in 20 healthy volunteers. MRP1 and MRP2 mRNA levels were quantified using real-time reverse transcriptase-polymerase chain reaction (RT-PCR) assays on a LightCycler(TM) (Roche, Mannheim, Germany). Results: The MRP1 mRNA exhibited the highest abundance in CD4(+) cells (7.4 x 10(3) +/- 3.19 x 10(3) molecules/ng of total RNA), followed by CD8(+) > CD19(+) > CD56(+) cells. The MRP2 mRNA expression was highest in CD4(+) cells (6.7 x 10(2) +/- 2.84 x 10(2) ), followed by CD8(+) > CD56(+) > CD19(+) cells. No correlation between the MRP1 and MRP2 mRNA expression was observed. Interestingly, beta 2-microglobulin mRNA expression in CD19(+) cells was found to be twofold lower in comparison with other cells. Conclusions: On an mRNA level both MRP1 and MRP2 were expressed in peripheral blood cells, with more than sevenfold higher MRP1 expression in all cell populations investigated. The impact of the MRP1 and MRP2 transcription in these cells remains to study. The use of beta 2-microglobulin as a housekeeping gene could have a critical impact on the interpretation of RT-PCR data.