Phosphorylation of translation initiation factor 2 alpha in Leishmania donovani under stress is necessary for parasite survival.

The transformation of Leishmonio donovani from a promastigote to an amastigote during mammalian host infection displays the immense adaptability of the parasite to survival under stress. Induction of translation initiation factor 2-alpha (eIF2 alpha) phosphorylation by stress-specific eIF2 alpha kinases is the basic stress-perceiving signal in eukaryotes to counter stress. Here, we demonstrate that elevated temperature and acidic pH induce the phosphorylation of Leishmania donovani elF2 alpha (LdelF2 alpha). In vitro inhibition experiments suggest that interference of LdelF2 alpha phosphorylation under conditions of elevated temperature and acidic pH debilitates parasite differentiation and reduces parasite viability (P < 0.05). Furthermore, inhibition of LdelF2 alpha phosphorylation significantly reduced the infection rate (P < 0.05), emphasizing its deciding role in successful invasion and infection establishment. Notably, our findings suggested the phosphorylation of LdelF2 alpha under H2O2-induced oxidative stress. Inhibition of H2O2-induced LdelF2 alpha phosphorylation hampered antioxidant balance by impaired redox homeostasis gene expression, resulting in increased reactive oxygen species accumulation (P < 0.05) and finally leading to decreased parasite viability (P < 0.05). Interestingly, exposure to sodium antimony glucamate and amphotericin B induces LdelF2 alpha phosphorylation, indicating its possible contribution to protection against antileishmanial drugs in common use. Overall, the results strongly suggest that stress-induced LdelF2a alpha phosphorylation is a necessary event for the parasite life cycle under stressed conditions for survival.