Parasite-specific eIF2 (eukaryotic initiation factor-2) kinase required for stress-induced translation control

Area of Science:

• Parasitology
• Molecular Biology
• Cellular Stress Response

Background:

• Toxoplasma gondii, an Apicomplexa parasite, forms dormant bradyzoite cysts that reactivate upon immune suppression.
• Bradyzoite formation is a stress-induced differentiation from the acute tachyzoite stage.
• Eukaryotic initiation factor-2 (eIF2) alpha subunit phosphorylation is a known stress response mechanism in eukaryotes.

Purpose of the Study:

• To investigate the role of eIF2 alpha subunit phosphorylation in T. gondii stress response and differentiation.
• To identify novel protein kinases involved in this pathway within T. gondii.

Main Methods:

• Characterization of Toxoplasma eIF2 alpha (TgIF2alpha).
• Discovery and characterization of a novel eIF2 protein kinase, TgIF2K-A.
• In vitro and in vivo phosphorylation assays using yeast and T. gondii systems.
• Analysis of TgIF2K-A's effect on translation in yeast.
• Stress induction experiments (heat shock, alkaline stress) in T. gondii tachyzoites.

Main Results:

• Identification of TgIF2K-A, a novel eIF2 kinase with a divergent N-terminal region.
• Demonstration that TgIF2K-A phosphorylates both yeast eIF2alpha and TgIF2alpha in vitro.
• Evidence that TgIF2K-A modulates translation in a yeast model system.
• Increased TgIF2alpha phosphorylation in T. gondii tachyzoites under heat shock and alkaline stress conditions.
• Correlation between stress conditions, TgIF2alpha phosphorylation, and parasite differentiation.

Conclusions:

• Stress-induced eIF2 kinase pathways are conserved in Apicomplexa.
• TgIF2K-A represents a novel family member potentially regulating parasite-specific stress responses.
• This pathway may control the clinically significant conversion of T. gondii into bradyzoite cysts.