Characterization of the ATP-Dependent LTC4Transporter in Cisplatin-Resistant Human KB Cells

Abstract

An active efflux pump forcis-diamminedichloroplatinum(II) (cisplatin) has been identified in cisplatin-resistant KCP-4 cells isolated from human epidermoid carcinoma KB-3-1 cells. The adenosine triphosphate(ATP)-dependent transport of leukotriene C4(LTC4), an endogenous substrate for the glutathione S-conjugate export pump(GS-X pump), has been found in membrane vesicles prepared from KCP-4 cells. Multidrug resistance-associated protein (MRP) has also been identified as an ATP-dependent LTC4transporter. To examine whether the GS-X pump expressed in KCP-4 cells is MRP, we investigated the expression of MRP in KCP-4 cells and compared the LTC4transporting activity of GS-X pump expressed in KCP-4 cells with that of MRP. The level ofMRPgene expression in KCP-4 cells was low and similar to that in KB-3-1 cells. MRP was not detected in membrane vesicles prepared from KB-3-1 and KCP-4 cells by immunoblot analysis. The ATP-dependent transport of LTC4in KCP-4 and C-A120 vesicles showed saturable kinetics with an apparent Km of 0.18 μM and 0.25 μM, respectively. [3H]LTC4transport in KCP-4 vesicles was more inhibited by 2,4-dinitrophenyl-S-glutathione(DNP-SG), bis-(glutathionato)-platinum(II) (GS-platinum) complex and glutathione disulfide(GS-SG) and less by LTD4compared with that in C-A120 vesicles. The character of the LTC4transporter expressed in KCP-4 vesicles is similar but not identical to that of MRP. Our results suggest that a glutathione S-conjugate export pump which is different from MRP exists in cisplatin-resistant KCP-4 cells.