Effect of acidic pH on heat shock gene expression in Leishmania

Temperature and pH shifts trigger differential gene expression and stage transformation in Leishmania. The parasites encounter dramatic fluctuations in the extra-cellular pH between the mid-gut of the sand fly (pH>8) and the phagolysosomal vacuole of mammalian macrophages (pH<6). The authors examined the effect of pH shifts on heat shock gene expression in Leishmania amazonensis and Leishmania donovani promastigotes. Acidic pH resulted in preferential stability of the hsp83 transcripts at 26 degrees C, but hsp transcripts were not preferentially translated as observed during heat shock. Pre-conditioning of promastigotes to acidic pH did not alter the temperature threshold for hsp synthesis but lead to an increase in hsp synthesis mainly in L. donovani at 37 degrees C, and to a slight decrease in the arrest of tubulin synthesis in L. amazonensis. The stage specific morphological alterations that take place in vitro correlated with the arrest in tubulin synthesis and occurred at different temperatures in L. donovani and L. amazonensis.