Expression of the Plasmodial pfmdr1 Gene in Mammalian Cells Is Associated with Increased Susceptibility to Chloroquine

Abstract

Chloroquine (CQ)-resistant (CQR) Plasmodium falciparum malaria parasites show a strong decrease in CQ accumulation in comparison with chloroquine-sensitive parasites. Controversy exists over the role of the plasmodial pfmdr1 gene in the CQR phenotype. pfmdr1 is a member of the superfamily 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, or colchicine was observed in Pgh1-expressing cells. CQ uptake experiments revealed an increased, ATP-dependent accumulation of CQ in Pgh1-expressing cells over the level in nonexpressing control cells. The increased CQ accumulation in Pgh1-expressing cells coincided with an enhanced in vivo inhibition of lysosomal alpha-galactosidase by CQ. CHO cells expressing Pgh1 carrying two of the CQR-associated Pgh1 amino acid changes (S1034C and N1042D) did not display an increased CQ sensitivity. Immunofluorescence experiments revealed an intracellular localization of both mutant and wild-type forms of Pgh1. We conclude from our results that wild-type Pgh1 protein can mediate an increased intracellular accumulation of CQ and that this function is impaired in CQR-associated mutant forms of the protein. We speculate that the Pgh1 protein plays an important role in CQ import in CQ-sensitive malaria parasites.

Mechanistic basis for multidrug resistance and collateral drug sensitivity conferred to the malaria parasite by polymorphisms in PfMDR1 and PfCRT

“…Attempts to characterize PfMDR1 in heterologous expression systems have not provided robust results and/or direct measurements of its transport activity [ 1 ]. For example, an attempt to express PfMDR1 in Xenopus oocytes resulted in a poor transport signal-to-background ratio [ 37 ], and other efforts did not make direct measurements of drug transport and thus only made inferences about PfMDR1’s function from ATPase activity [ 38 – 41 ] (and one study was subsequently retracted [ 42 ]).…”