Translational control during stage conversion of Toxoplasma, an opportunistic infection of HIV/AIDS

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 DESCRIPTION (provided by applicant): This proposal addresses molecular mechanisms that are central for formation and reactivation of latent stages of Toxoplasma gondii, a protozoan parasite that causes life-threatening opportunistic infection in AIDS/HIV patients. The ability of Toxoplasma to convert from its proliferative stage (tachyzoite) to latent tissue cysts (bradyzoite) gives rise to the life-threatening chronic opportunistic disease that afflicts AIDS patients. There is a vital need for new approaches for treatment of AIDS-toxoplasmosis, but this effort has been hindered by an insufficient understanding of the mechanisms by which the latent stage develops and reactivates. We discovered that phosphorylation of the Toxoplasma alpha subunit of eukaryotic initiation factor-2 (TgIF2α) contributes to bradyzoite development. Using polysome profiling, which we adapted for use in Toxoplasma, we showed that TgIF2α phosphorylation leads to preferential translation of a subset of mRNAs that are linked to bradyzoite development. Further support that translational control has critical functions during both replicative and lateny stages comes from our new studies using the drugs salubrinal (SAL) and guanabenz (GA), which inhibit TgIF2α dephosphorylation and block the reactivation of bradyzoites. Here we show that GA also protects mice acutely infected with Toxoplasma and decreases the number of cysts in chronically infected mice. Together, our genetic, biochemical, and pharmacological experiments support our hypothesis that translational control mediated by TgIF2α phosphorylation is critical for parasite stage interconversion. Our proposed experiments will address this hypothesis and 1) establish how TgIF2α kinases coordinate conversion to bradyzoites, 2) identify translationally controlled mRNAs initiating bradyzoite development and reconversion into replicating tachyzoites, and 3) determine the mechanisms underlying TgIF2α dephosphorylation and reactivation of infection. Completion of these aims will help define the mechanics of Toxoplasma stage conversion, with an eye towards developing critically needed novel therapies for AIDS-toxoplasmosis.