FUNCTIONAL EXPRESSION OF THE MULTIDRUG RESISTANCE-ASSOCIATED PROTEIN IN THE YEAST SACCHAROMYCES-CEREVISIAE

The multidrug resistance associated protein (MRP) is a member of the A TP binding cassette superfamily of transporters which includes the mam malian P-glycoproteins (P-gp) family, In order to facilitate the bioch emical and genetic analyses of MRP, we have expressed human MRP in the yeast Saccharomyces cerevisiae and have compared its functional prope rties to those of the mouse Mdr3 P-gp isoform, Expression of both MRP and Mdr3 in the anthracycline hypersensitive mutant VASY2563 restored cellular resistance to Adriamycin in this mutant, MRP and Mdr3 express ion produced pleiotropic effects on drug resistance in this mutant, as corresponding VASY2563 transformants also acquired resistance to the anti-fungal agent FK506 and to the K+/H+ ionophore valinomycin, The ap pearance of increased cellular resistance to the toxic effect of Adria mycin (ADM) in MRP and Mdr3 transformants was concomitant with a reduc ed intracellular accumulation of [C-14]ADM in spheroplasts prepared fr om these cells, Moreover, MRP and Mdr3, but not control spheroplasts, could mediate a time-dependent reduction in the overall cell-associate d [C-14]ADM from preloaded cells, suggesting the presence of an active ADM transport mechanism in MRP and Mdr3 transformants, Finally, human MRP was found to complement the biological activity of the yeast pept ide pheromone transporter Ste6 and partially restored mating in a ster ile ste6 null mutant, These findings suggest that despite their relati vely low level of structural homology, MRP and P-gp share similar func tional aspects, since both proteins can mediate transport of chemother apeutic drugs and the a mating peptide pheromone in yeast.