The LABCG2 Transporter from the Protozoan Parasite Leishmania Is Involved in Antimony Resistance

Abstract

Treatment for leishmaniasis, which is caused by Leishmania protozoan parasites, currently relies on a reduced arsenal of drugs. However, the significant increase in the incidence of drug therapeutic failure and the growing resistance to first-line drugs like antimonials in some areas of Northern India and Nepal limit the control of this parasitic disease. Understanding the molecular mechanisms of resistance in Leishmania is now a matter of urgency to optimize drugs used and to identify novel drug targets to block or reverse resistant mechanisms. Some members of the family of ATP-binding cassette (ABC) transporters in Leishmania have been associated with drug resistance. In this study, we have focused our interest to characterize LABCG2's involvement in drug resistance in Leishmania. Leishmania major parasites overexpressing the ABC protein transporter LABCG2 were generated in order to assess how LABCG2 is involved in drug resistance. Assays of susceptibility to different leishmanicidal agents were carried out. Analysis of the drug resistance profile revealed that Leishmania parasites overexpressing LABCG2 were resistant to antimony, as they demonstrated a reduced accumulation of Sb III due to an increase in drug efflux. Additionally, LABCG2 was able to transport thiols in the presence of Sb III . Biotinylation assays using parasites expressing LABCG2 fused with an N-terminal green fluorescent protein tag revealed that LABCG2 is partially localized in the plasma membrane; this supports data from previous studies which suggested that LABCG2 is localized in intracellular vesicles that fuse with the plasma membrane during exocytosis. In conclusion, Leishmania LABCG2 probably confers antimony resistance by sequestering metal-thiol conjugates within vesicles and through further exocytosis by means of the parasite's flagellar pocket.

Anti-promastigote Activity of the Amazon Plants

“…The overexpressing LABCG2 reduced accumulation of Sb III due to an increased in drug efflux [3]. Due to the toxicity and the failure of many drugs available, the search for alternative therapies for leishmaniasis is urgent.…”

ABCI3 Is a New Mitochondrial ABC Transporter from Leishmania major Involved in Susceptibility to Antimonials and Infectivity

“…Additionally, biotinylation assays suggested that part of the protein is localized in the PM, where the transporter could interact with other PM transporters involved in antimony uptake, such as aquaglyceroporin (AQP1). Two ABC transporters Antimicrobial Agents and Chemotherapy described by our group, ABCI4 and ABCG2, also showed a dual localization and played a role in Sb III resistance (8,9). Several other eukaryotic ABC transporters are found in mitochondria, and most of them belong to the B subfamily of ABC transporters (40).…”

“…Considering that some ABC transporters have been implicated in drug resistance in Leishmania (8,9,17,29), we decided to analyze whether the overexpression or partial knockout of ABCI3 could confer resistance to drugs and other related molecules. Different leishmanicidal drugs, including antimonials (Sb III ), miltefosine, amphotericin B, and paromomycin, were tested, as was As III , a metal ion which has been shown to be cross-resistant to Sb III (30); Zn-protoporphyrin, a toxic porphyrin and validated heme analog (8); and H 2 O 2 , a by-product of superoxide radical formation during macrophage activation (31) ( Table 1).…”

“…The analysis of antimony resistance mechanisms in Leishmania has revealed that several mechanisms may occur simultaneously and also that different mechanisms may operate in field isolates and lab-generated resistant Leishmania parasites (4,5). One known mechanism of resistance to antimony in Leishmania involves a reduction in its accumulation by either reduced uptake or increased efflux, with the latter being mediated by different ABC transporters: ABCC3 (also known as PgpA or MRPA) (6, 7), ABCI4 (8), and ABCG2 (9).…”

“…ABCI4 is involved in susceptibility to antimony and other compounds through the efflux of conjugated thiol complexes (8). Recently, overexpression of ABCG2 was also shown to confer resistance to antimony in Leishmania major through the sequestration and efflux of metal-thiol conjugates (9).…”