A newly identified Leishmania IF4E-interacting protein, Leish4E-IP2, modulates the activity of cap-binding protein paralogs.

Ayelet Gilad,Gerhard Wagner,Michal Shapira,Mélissa Léger-Abraham,Nitin Tupperwar,Nofar Baron,Rohit Shrivastava,Shimi Meleppattu

doi:10.1093/nar/gkaa173

Abstract

Translation of most cellular mRNAs in eukaryotes proceeds through a cap-dependent pathway, whereby the cap-binding complex, eIF4F, anchors the preinitiation complex at the 5′ end of mRNAs and regulates translation initiation. The requirement of Leishmania to survive in changing environments can explain why they encode multiple eIF4E (LeishIF4Es) and eIF4G (LeishIF4Gs) paralogs, as each could be assigned a discrete role during their life cycle. Here we show that the expression and activity of different LeishIF4Es change during the growth of cultured promastigotes, urging a search for regulatory proteins. We describe a novel LeishIF4E-interacting protein, Leish4E-IP2, which contains a conserved Y(X)4LΦ IF4E-binding-motif. Despite its capacity to bind several LeishIF4Es, Leish4E-IP2 was not detected in m7GTP-eluted cap-binding complexes, suggesting that it could inhibit the cap-binding activity of LeishIF4Es. Using a functional assay, we show that a recombinant form of Leish4E-IP2 inhibits the cap-binding activity of LeishIF4E-1 and LeishIF4E-3. Furthermore, we show that transgenic parasites expressing a tagged version of Leish4E-IP2 also display reduced cap-binding activities of tested LeishIF4Es, and decreased global translation. Given its ability to bind more than a single LeishIF4E, we suggest that Leish4E-IP2 could serve as a broad-range repressor of Leishmania protein synthesis.

Highlights

Leishmania parasites cycle between invertebrate vectors and mammalian hosts
We further found that Leish4E-IP1 represses the capbinding activity of LeishIF4E-1 in promastigotes [36]
It is still unclear how the LeishIF4E1/Leish4E-IP1 complex relates to the translation process and whether additional proteins are involved in modulating the activity of the different cap-binding proteins in the different Leishmania life forms

Summary

Introduction

Leishmania parasites cycle between invertebrate vectors and mammalian hosts. Amastigotes exist within phagolysosomal vacuoles of macrophages and other cells of the immune system. During their life cycle, a developmental program of gene expression enables the parasites to adapt to different environmental conditions, including temperature, pH and variations in nutrient supplies. In Opisthokonts, cap-dependent translation initiation is the default pathway for protein synthesis. EIF4F comprises the cap-binding protein eIF4E, the DEAD-box RNA helicase eIF4A, and the scaffold protein eIF4G. EIF4G interacts with eIF4E, through a consensus binding motif, Y(X)4L (where X is any amino acid and is a hydrophobic residue). Protein synthesis can be inhibited by the binding of hypo-phosphorylated 4E-BPs to eIF4E. Since the identification of 4E-BP1, many other eIF4E regulatory proteins have been identified in several organisms

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Conclusion