TY - JOUR
T1 - Substrate depletion upregulates uptake of myo-inositol, glucose and adenosine in Leishmania
AU - Seyfang, Andreas
AU - Landfear, Scott M.
N1 - Funding Information:
This work was supported by NIH grant AI25920 and Research Career Development Award AI01162 to SML. SML is a recipient of a Burroughs Wellcome Fund Scholar Award in Molecular Parasitology. AS was supported by an Alexander von Humboldt Fellowship and the American Heart Association, Oregon Chapter.
PY - 1999/10/25
Y1 - 1999/10/25
N2 - Leishmania flagellates undergo a digenetic life cycle in the gut of the sandfly insect vector and in macrophage phagolysosomes of the mammalian host. This involves vast changes of the environment to which the parasite has to adapt, including temperature, pH and concentration of nutrients between different types of meals of the insect vector or within the enclosed intracellular environment of the phagolysosome. The regulation of transporters for important organic substrates in Leishmania donovani, Leishmania mexicana and Leishmania enriettii has been investigated. A pronounced upregulation of inositol (25-fold), adenosine (11-fold) or glucose (5-fold) uptake activities was found when cells were depleted of the respective substrates during culture. Inositol-depleted cells showed a half- maximal uptake rate at nanomolar inositol concentration. Depletion of inositol only affected inositol uptake but did not affect uptake of glucose analog or proline in control experiments, indicating the specificity of the mechanism(s) underlying transport regulation. Adenosine-depleted cells showed an approximately 10-fold increase in both adenosine and uridine uptake, both mediated by the L. donovani nucleoside transporter 1 (LdNT1), but no change in guanosine uptake, which is mediated by the L. donovani nucleoside transporter 2 (LdNT2). These results suggest that extracellular adenosine concentration specifically regulates LdNT1 transport activity and does not affect LdNT2. The data imply that upregulation of transport activities by substrate depletion is a general phenomenon in protozoan flagellates, which is in remarkable contrast to bacteria where upregulation typically follows an increase of extracellular organic substrate. Hence, the parasites can maximize the uptake of important nutrients from the host even under limiting conditions, whereas bacteria often have dormant stages (spores) to overcome unfavorable environmental conditions or are heterotrophic for organic substrates.
AB - Leishmania flagellates undergo a digenetic life cycle in the gut of the sandfly insect vector and in macrophage phagolysosomes of the mammalian host. This involves vast changes of the environment to which the parasite has to adapt, including temperature, pH and concentration of nutrients between different types of meals of the insect vector or within the enclosed intracellular environment of the phagolysosome. The regulation of transporters for important organic substrates in Leishmania donovani, Leishmania mexicana and Leishmania enriettii has been investigated. A pronounced upregulation of inositol (25-fold), adenosine (11-fold) or glucose (5-fold) uptake activities was found when cells were depleted of the respective substrates during culture. Inositol-depleted cells showed a half- maximal uptake rate at nanomolar inositol concentration. Depletion of inositol only affected inositol uptake but did not affect uptake of glucose analog or proline in control experiments, indicating the specificity of the mechanism(s) underlying transport regulation. Adenosine-depleted cells showed an approximately 10-fold increase in both adenosine and uridine uptake, both mediated by the L. donovani nucleoside transporter 1 (LdNT1), but no change in guanosine uptake, which is mediated by the L. donovani nucleoside transporter 2 (LdNT2). These results suggest that extracellular adenosine concentration specifically regulates LdNT1 transport activity and does not affect LdNT2. The data imply that upregulation of transport activities by substrate depletion is a general phenomenon in protozoan flagellates, which is in remarkable contrast to bacteria where upregulation typically follows an increase of extracellular organic substrate. Hence, the parasites can maximize the uptake of important nutrients from the host even under limiting conditions, whereas bacteria often have dormant stages (spores) to overcome unfavorable environmental conditions or are heterotrophic for organic substrates.
KW - Adenosine
KW - Environmental adaptation
KW - Glucose
KW - Leishmania
KW - Nutrient starvation
KW - Transporter regulation
KW - myo-Inositol
UR - http://www.scopus.com/inward/record.url?scp=0032732044&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0032732044&partnerID=8YFLogxK
U2 - 10.1016/S0166-6851(99)00138-3
DO - 10.1016/S0166-6851(99)00138-3
M3 - Article
C2 - 10589986
AN - SCOPUS:0032732044
SN - 0166-6851
VL - 104
SP - 121
EP - 130
JO - Molecular and Biochemical Parasitology
JF - Molecular and Biochemical Parasitology
IS - 1
ER -