mRNA cap-binding protein eIF4E1 is a novel regulator ofToxoplasma gondiilatency

Abstract

The protozoan parasiteToxoplasma gondiicauses serious opportunistic disease due to its ability to persist in patients as latent tissue cysts. The molecular mechanisms coordinating conversion between proliferative parasites (tachyzoites) and dormant cysts (bradyzoites) are not fully understood. We previously showed that phosphorylation of eIF2α accompanies bradyzoite formation, suggesting that this clinically relevant process involves regulation of mRNA translation. In this study, we investigated the composition and role of eIF4F multi-subunit complexes in translational control. Using CLIPseq, we find that the cap-binding subunit, eIF4E1, localizes to the 5’-end of all tachyzoite mRNAs, many of which show evidence of stemming from heterogenous transcriptional start sites. We further show that eIF4E1 operates as the predominant cap-binding protein in two distinct eIF4F complexes. Using genetic and pharmacological approaches, we found that eIF4E1 deficiency triggers efficient spontaneous formation of bradyzoites without stress induction. Consistent with this result, we also show that stress-induced bradyzoites exhibit reduced eIF4E1 expression. Overall, our findings establish a novel role for eIF4F in translational control required for parasite latency and microbial persistence.SignificanceToxoplasma gondiiis an opportunistic pathogen of importance to global human and animal health. There are currently no chemotherapies targeting the encysted form of the parasite. Consequently, a better understanding of the mechanisms controlling encystation are required. Here we show that the mRNA cap-binding protein, eIF4E1, is involved in regulating the encystation process. Encysted parasites reduce eIF4E1 levels and depletion of eIF4E1 decreases the translation of ribosome-associated machinery and drivesToxoplasmaencystation. Together, these data reveal a new layer of mRNA translational control that regulates parasite encystation and latency.

TheToxoplasma gondiimitochondrial transporter ABCB7 is essential for cytosolic iron-sulfur cluster biogenesis and protein translation

“…Another possibility, given the decreased abundance of many proteins involved in translation in the ABCB7 mutant, is that a block in translational could induce the parasite to begin differentiation. Previous studies have shown translational control to be an important aspect of initiating differentiation (61)(62)(63)(64)(65). More work needs to be done to understand how stress and metabolic deficiencies influence a parasite's decision to initiate conversion.…”

RNA triphosphatase-mediated mRNA capping is essential for maintaining transcript homeostasis and the survival of Toxoplasma gondii

“…Similarly, we wanted to test whether in vitro-generated capped RNA could be recognized by eIF4E-like protein and productively translated into protein in Toxoplasma. BLASTP search using Plasmodium 50 and human 51 eIF4E revealed three eIF4E-like homologues (TGME49_223410, TGME49_315150, and TGME49_312560) in T. gondii genome 52 . Of these three homologue, TGME49_223410 showed highest amino acid similarity, including conserved residues required for m 7 G interaction with Plasmodium (e score: 1e-69) and human protein (e score: 1e-14) (Supplementary Fig.…”

Translation initiation factor eIF1.2 promotesToxoplasmastage conversion by regulating levels of key differentiation factors

“…The phosphorylation of eIF2α has been demonstrated as crucial for stage conversions in Leishmania 27 , Plasmodium 28,29 , Trypanosoma 30 , and T. gondii 31 . Recently, it has also been reported that the absence of eIF4E1, a key player in the cap recognition step of translation initiation, can trigger T. gondii differentiation 32 . With eIF4E1’s function in differentiation working in parallel with that of eIF2α, the translation-directed regulatory landscape of differentiation is likely more complex than previously acknowledged.…”