Role of P-glycoprotein in human natural killer-like cell line-mediated cytotoxicity

Natural killer (NK) cells express the highest amount of P-glycoprotein (Pgp ), a product of the multidrug resistance (MDR) 1 gene, among lymphoid cells , and our previous studies demonstrated that Pgp is required for NK cell-me diated cytotoxicity, In this study we examined the role of Pgp in NK cell-m ediated cytotoxicity using a human NK-like cell line, i.e., YTN cells and t wo MDR reversing agents, nicardipine and its structural analog, AHC-93. The se two agents inhibited the Pgp function (rhodamine-las excretion) as well as cell-mediated cytotoxicity, confirming that; Pgp is critical for Mt cell -mediated cytotoxicity, As revealed by video-rate ultraviolet laser-scannin g confocal microscopy, AHC-93 did not inhibit the increase in the intracell ular calcium concentration upon binding to target cells, whereas nicardipin e did, as reported previously. These two reagents relocated acridine orange dye from lysosomes to the cytoplasm at concentrations similar to those req uired for the inhibition of cell-mediated cytotoxicity. These results sugge st that Pgp is directly or indirectly involved in pH regulation in lysosome s, but not in calcium homeostasis. (C) 1999 Academic Press.