Pteridine salvage throughout the Leishmania infectious cycle: implications for antifolate chemotherapy.
Protozoan parasites of the trypanosomatid genus Leishmania are pteridine auxotrophs, and have evolved an elaborate and versatile pteridine salvage network capable of accumulating and reducing pteridines. This includes biopterin and folate transporters (BT1 and FT1), pteridine reductase (PTR1), and dihydrofolate reductase-thymidylate synthase (DHFR-TS). Notably, PTR1 is a novel alternative pteridine reductase whose activity is resistant to inhibition by standard antifolates. In cultured promastigote parasites, PTR1 can function as a metabolic by-pass under conditions of DHFR inhibition and thus reduce the efficacy of chemotherapy. To test whether pteridine salvage occurred in the infectious stage of the parasite, we examined several pathogenic species of Leishmania and the disease-causing amastigote stage that resides within human macrophages. To accomplish this we developed a new sensitive HPLC-based assay for PTR1 activity. These studies established the existence of the pteridine salvage pathway throughout the infectious cycle of Leishmania, including amastigotes. In general, activities were not well correlated with RNA transcript levels, suggesting the occurrence of at least two different modes of post-transcriptional regulation. Thus, pteridine salvage by amastigotes may account for the clinical inefficacy of antifolates against leishmaniasis, and ultimately provide insights into how this may be overcome in the future.
Cunningham
M L
ML
Department of Molecular Microbiology, Washington University School of Medicine, St Louis, MO 63110, USA.
Beverley
S M
SM
D000818:Animals; D001708:Biopterins / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D005492:Folic Acid / Q000378:metabolism; D005493:Folic Acid Antagonists / Q000627:therapeutic use; D018507:Gene Expression Regulation, Developmental; D006801:Humans; D007891:Leishmania / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development* / Q000378:metabolism; D007896:Leishmaniasis / Q000188:drug therapy; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000235:genetics / Q000378:metabolism; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D015800:Protozoan Proteins; D011621:Pteridines / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics / Q000378:metabolism; D013940:Thymidylate Synthase / Q000235:genetics / Q000378:metabolism
D002352:Carrier Proteins; D005493:Folic Acid Antagonists; D026901:Membrane Transport Proteins; D009097:Multienzyme Complexes; D015800:Protozoan Proteins; D011621:Pteridines; D012333:RNA, Messenger; C424383:biopterin transporter 1 protein, Leishmania; C056930:thymidylate synthase-dihydrofolate reductase; D001708:Biopterins; D005492:Folic Acid; D010088:Oxidoreductases; C085592:pteridine reductase; D013762:Tetrahydrofolate Dehydrogenase; D013940:Thymidylate Synthase