Increased transport of pteridines compensates for mutations in the high affinity folate transporter and contributes to methotrexate resistance in the protozoan parasite Leishmania tarentolae

  • Kündig C
  • Haimeur A
  • Légaré D
 et al. 
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Functional cloning led to the isolation of a novel methotrexate (MTX) resistance gene in the protozoan parasite Leishmania. The gene corresponds to orfG, an open reading frame (ORF) of the LD1/CD1 genomic locus that is frequently amplified in several Leishmania stocks. A functional ORF G-green fluorescence protein fusion was localized to the plasma membrane. Transport studies indicated that ORF G is a high affinity biopterin transporter. ORF G also transports folic acid, with a lower affinity, but does not transport the drug analog MTX. Disruption of both alleles of orfG led to a mutant strain that became hypersensitive to MTX and had no measurable biopterin transport. Leishmania tarentolae MTX-resistant cells without their high affinity folate transporters have a rearranged orfG gene and increased orfG RNA levels. Overexpression of orfG leads to increased biopterin uptake and, in folate-rich medium, to increased folate uptake. MTX-resistant cells compensate for mutations in their high affinity folate/MTX transporter by overexpressing ORF G, which increases the uptake of pterins and selectively increases the uptake of folic acid, but not MTX.

Author-supplied keywords

  • Biopterin
  • Drug resistance
  • Folate transport
  • Leishmania
  • Methotrexate

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  • Christoph Kündig

  • Anass Haimeur

  • Danielle Légaré

  • Barbara Papadopoulou

  • Marc Ouellette

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