The suppressive cap-binding complex factor 4EIP is required for normal differentiation

Abstract

Trypanosoma brucei live in mammals as bloodstream forms and in the Tsetse midgut as procyclic forms. Differentiation from one form to the other proceeds via a growth-arrested stumpy form with low messenger RNA (mRNA) content and translation. The parasites have six eIF4Es and five eIF4Gs. EIF4E1 pairs with the mRNA-binding protein 4EIP but not with any EIF4G. EIF4E1 and 4EIP each inhibit expression when tethered to a reporter mRNA, but while tethered EIF4E1 suppresses only when 4EIP is present, suppression by tethered 4EIP does not require the interaction with EIF4E1. In growing bloodstream forms, 4EIP is preferentially associated with unstable mRNAs. Bloodstream- or procyclic-form trypanosomes lacking 4EIP have only a marginal growth disadvantage. Bloodstream forms without 4EIP are, however, defective in translation suppression during stumpy-form differentiation and cannot subsequently convert to growing procyclic forms. Intriguingly, the differentiation defect can be complemented by a truncated 4EIP that does not interact with EIF4E1. In contrast, bloodstream forms lacking EIF4E1 have a growth defect, stumpy formation seems normal, but they appear unable to grow as procyclic forms. We suggest that 4EIP and EIF4E1 fine-tune mRNA levels in growing cells, and that 4EIP contributes to translation suppression during differentiation to the stumpy form.

Regulation of gene expression in trypanosomatids: living with polycistronic transcription

“…Alternative names are G1-IP2 for RBP43, and G1-IP for Tb927.11.6720. References for pull-down and interaction results are as follows: T. brucei PABPs [155]; Leishmania and T. brucei EIF4E1 [168,171]; T. brucei EIF4E2 [172]; Leishmania EIF4G3 [173]; T. brucei and Leishmania EIF4E3 and EIF4E4 [168,174]; T. brucei EIF4E5 [175]; T. brucei EIF4E6 [176]. The tethering results for EIF4E5 and EIF4E6 are unpublished (L. Melo do Nascimento and C. Clayton 2019, unpublished data); note that the activities of these proteins when bound to the 5′ cap may not be the same as those seen in the tethering assay.…”

“…It interacts with a protein called 4EIP in both Leishmania [168] and T. bruce i [171]. 4EIP binds directly to mRNA [41] and, when tethered, is a suppressor even when EIF4E1 is absent [171]. By contrast, the suppressive activity of EIF4E1 depends on its interaction with 4EIP.…”

Roles of the Pumilio domain protein PUF3 inTrypanosoma bruceigrowth and differentiation

“…These results suggest that the main role of PUF3 is in modulating gene expression during differentiationpresumably in order to suppress the expression of particular proteins. Differentiation to the stumpy form is accompanied by a general decrease in translation, and even a minor delay in this can impair subsequent differentiation (Terrao et al, 2018), so it is quite feasible that abnormal translation or degradation of a particular subset of mRNAs right at the beginning of the process could prevent subsequent steps, even in monomorphic trypanosomes. Which of the PUF3 targets might be relevant is not obvious.…”

eIF4E and Interactors from Unicellular Eukaryotes

“…It has been proposed that 4E-IP allosterically destabilizes interaction of Leishmania eIF4E1 with the cap4 structure [91]. Bloodstream forms of the parasite lacking 4E-IP are defective in translational suppression and cannot develop into the procyclic form which initiates the promastigote life cycle [98].…”

“…This is probably due to their complex life cycle involving several differentiation stages. The diverse repertoire is extended by translational repressors such as 4E-IP which is used by the parasite to allow for reprogramming of protein expression when facing varying conditions in different hosts [98].…”