Mapping of the Plasmodium falciparum multidrug resistance gene 5'-upstream region, and evidence of induction of transcript levels by antimalarial drugs in chloroquine sensitive parasites.

The Plasmodium falciparum multidrug resistance gene, pfmdr1, has been shown to be involved in the mediation of the parasite's response to various antimalarial drugs. Previous studies of pfmdr1 expression have shown that transcript levels are increased in drug-resistant isolates. However, a detailed examination of the transcriptional regulation of this gene has not been completed. The aim of this study was to map the 5' UTR of pfmdr1, and to examine the transcriptional profile of the gene in sensitive parasites treated with four different antimalarial drugs. RT-PCR and 5'-RACE mapping showed that the 5' UTR has a length of 1.94 kb. A putative promoter has been identified via transient transfection. Northern analysis revealed a 2.1- to 2.7-fold increase in pfmdr1 expression in 3D7 parasites treated with 50 nM chloroquine for 6 h, confirming results from Serial Analysis of Gene Expression. 3D7 parasites were subsequently treated with experimentally derived IC50 concentrations of mefloquine, quinine and pyrimethamine. pfmdr1 transcript levels specifically increased 2.5-fold at 6 h in mefloquine-treated parasites and threefold in parasites treated with quinine for 30 min. There was no evidence of transcript induction in pyrimethamine-treated parasites. This is the first evidence of induction of pfmdr1 expression in sensitive cells; and suggests a novel method of transcriptional control for this gene.