THE MDR1 (P-GLYCOPROTEIN) AND MRP (P-190) TRANSPORTERS DO NOT PLAY A MAJOR ROLE IN THE INTRINSIC MULTIPLE-DRUG RESISTANCE OF JURKAT T-LYMPHOCYTES

The response of T cells in relation to the cell cycle has not been ext ensively studied. We have attempted to address this question using Jur kat T cells treated with cytostatic drugs known to arrest cells at var ious transition points of their cycle. We tested several concentration s of drugs that act at G1/S (hydroxyurea, lovastatin, thymidine), earl y S (aphidicolin, cyclosporin A, rapamycin) or G2+M (colchicine, nocod azole) in 24 h cultures. Cytofluorimetric analyses showed that cycling Jurkat cells were equally distributed between the G1 (44.9 +/- 6.5%) and S (42.3 +/- 8.0%) phases. Cell distribution in G2+M was 12.7 +/- 2 .8%. Hydroxyurea but not lovastatin increased the percentage of cells in S phase to approximate to 60-70% and both drugs decreased it to app roximate to 30% in G1. Thymidine had no effects. Aphidicolin increased the distribution in S phase to approximate to 70% with a decrease in G1 to approximate to 30%. Cyclosporin A and rapamycin increased the pe rcentage of the cells in G1 to approximate to 70% and decreased it to approximate to 25% in S phase. Nocodazole increased cell distribution in G2+M to approximate to 60% and induced a decrease in G1 to approxim ate to 10%. The effects of the drugs were not related to their toxicit y and their limited efficiency raised the possibility that Jurkat cell s possessed an intrinsic resistance to these xenobiotics. lime-course analysis showed (scanning electron microscopy) that the early morpholo gical changes induced by colchicine were reversible. Drug efflux exper iments (vinblastine) suggested that an ATP-dependent process could be involved. However, Northern blot analyses showed a weak signal for MDR 1 (P-glycoprotein). In contrast, a probe for MRP (P-190) showed a stro ng signal in Jurkat and peripheral lymphocytes. The presence of drugs (cyclosporin A, nocodazole, thymidine) (24 h) did not upregulate its m essage and cell treatment with DL-butathione (S,R)-sulfoximine only mo derately affected the efficiency of the glutathione S-conjugate MRP tr ansporter. Our data suggest that the intrinsic multidrug resistance of leukemic Jurkat T cells does not appear to involve the MDR1 and MRP m embers of the ABC family of reverse drug transporters and these observ ations raise the possibility of the involvement of multifaceted mechan isms. (C) 1997 Elsevier Science Ltd. All rights reserved.