Heavy metal resistance: a new role for P-glycoproteins in Leishmania

P-glycoproteins are responsible for multidrug resistance in tumor cell lines and are thought to have a physiologic role in exporting cellular metabolites. We now report that a P-glycoprotein gene in the H region of the trypanosomatid protozoan Leishmania confers resistance to heavy metals when present in multiple copies. The Leishmania H region is frequently amplified in drug-resistant lines and is associated with metal resistance. Leishmania expression vectors were used to introduce multiple copies of segments of the Leishmania major H region into wild-type L. major promastigotes. Only constructs bearing a segment of L. major DNA containing the P-glycoprotein lmpgpA conferred arsenite resistance. Deletional analysis of the arsenite-resistant construct mapped resistance to the lmpgpA protein coding region. Lines expressing lmpgpA showed resistance to arsenite and trivalent antimonials, but not to pentavalent antimonials, zinc, cadmium, or the typical multidrug-resistant P-glycoprotein substrates vinblastine and puromycin. Transfection of the Leishmania tarentolae P-glycoprotein homologue ltpgpA resulted in a similar resistance profile. Thus, these pgpAs represent a functionally distinct group of P-glycoproteins which exhibit a substrate specificity similar to prokaryotic heavy metal pumps. Additionally, several arguments suggest that pgpAs may play a role in the susceptibility of Leishmania to clinically utilized antimonials.