EXPRESSION OF THE PLASMODIAL PFMDR1 GENE IN MAMMALIAN-CELLS IS ASSOCIATED WITH INCREASED SUSCEPTIBILITY TO CHLOROQUINE

Chloroquine (CQ)-resistant (CQR) Plasmodium falciparum malaria parasit es show a strong decrease in CQ accumulation in comparison with chloro quine-sensitive parasites. Controversy exists over the role of the pla smodial pfmdr1 gene in the CQR phenotype. pfmdr1 is a member of the su perfamily of ATP-binding cassette transporters. Other members of this family are the mammalian multidrug resistance genes and the CFTR gene. We have expressed the pfmdr1-encoded protein, Pgh1, in CHO cells and Xenopus oocytes. CHO cells expressing the Pgh1 protein demonstrated an increased, verapamil-insensitive susceptibility to CQ. Conversely, no increase in drug susceptibility to primaquine, quinine, adriamycin, o r colchicine was observed in Pgh1-expressing cells. CQ uptake experime nts revealed an increased, ATP-dependent accumulation of CQ in Pgh1-ex pressing cells over the level in nonexpressing control cells. The incr eased CQ accumulation in Pgh1-expressing cells coincided with an enhan ced in vivo inhibition of lysosomal alpha-galactosidase by CQ. CHO cel ls expressing Pgh1 carrying two of the CQR-associated Pgh1 amino acid changes (S1034C and N1042D) did not display an increased CQ sensitivit y. Immunofluorescence experiments revealed an intracellular localizati on of both mutant and wild-type forms of Pgh1. We conclude from our re sults that wild-type Pgh1 protein can mediate an increased intracellul ar accumulation of CQ and that this function is impaired in CQR-associ ated mutant forms of the protein. We speculate that the Pgh1 protein p lays an important role in CQ import in CQ-sensitive malaria parasites.