Trypanosoma brucei EIF4E2 cap-binding protein binds a homolog of the histone-mRNA stem-loop-binding protein
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Trypanosomatids are parasitic protozoans characterized by several unique structural and metabolic processes that include exquisite mechanisms associated with gene expression and regulation. During the initiation of protein synthesis, for instance, mRNA selection for translation seems to be mediated by different eIF4F-like complexes, which may play a significant role in parasite adaptation to different hosts. In eukaryotes, the heterotrimeric eIF4F complex (formed by eIF4E, eIF4G, and eIF4A) mediates mRNA recognition and ribosome binding and participates in various translation regulatory events. Six eIF4Es and five eIF4Gs have been described in trypanosomatids with several of these forming different eIF4F-like complexes. This has raised questions about their role in differential mRNA translation. Here we have studied further TbEIF4E2, the least known eIF4E homologue from Trypanosoma brucei, and found that it is not associated with an eIF4G homolog. It is, however, associated with mature mRNAs and binds to a histone mRNA stem-loop-binding protein (SLBP), one of two Trypanosoma SLBP homologs (TbSLBP1 and TbSLBP2). TbSLBP1 is more similar to the mammalian counterpart while TbSLBP2 is exclusive to trypanosomatids and related organisms. TbSLBP2 binds to TbEIF4E2 through a conserved central region missing in other SLBP homologs. Both SLBPs, as well as TbEIF4E2, were found to localize to the cytoplasm. TbEIF4E2 and TbSLBP2 are differentially expressed during cell culture, being more abundant in early-log phase, with TbSLBP2 also showing cell-cycle dependent expression. The new data reinforce unique aspects of the trypanosomatid eIF4Es, with the TbEIF4E2–TbSLBP complex possibly having a role in differential selection of mRNAs containing stem-loop structures.
KeywordsSLBP Kinetoplastid mRNA cap SLBP Translation initiation factor
The authors thank Dr. Mark Carrington, from University of Cambridge (UK), and Dr. Steve Kelly, from Department of Plant Sciences, University of Oxford (UK) for providing the SLBP protein sequences from Euglena gracilis. We also thank Dr. Cássia Docena from the Núcleo de Plataformas Tecnológicas (NPT), Instituto Aggeu Magalhães, Fiocruz-PE, for the assistance in obtaining Immunofluorescence images. The anti-BiP and anti-TY antibodies were kind gifts from Jay Bangs and Keith Gull, respectively. This work was supported by a UCLA Stein-Oppenheimer award (D. C.), the National Institutes of Health (Grant numbers AI056034, AI073806, TW009035 to D. C. and N. S., Grant number GM089778 to J. W.), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq-Brazil, Grant number 401282/2014-7) and Fundação Oswaldo Cruz-Fiocruz (Brazil). Funding was provided by Fogarty International Center (PAR-08-222).
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Conflict of interest
No potential conflicts of interest were disclosed.
- de Melo Neto OP, da Costa Lima TDC, Xavier CC et al (2015) The unique Leishmania EIF4E4 N-terminus is a target for multiple phosphorylation events and participates in critical interactions required for translation initiation. RNA Biol 12:1209–1221. https://doi.org/10.1080/15476286.2015.1086865 CrossRefPubMedPubMedCentralGoogle Scholar
- de Melo Neto OPOP., Reis CRS, Moura DMNDMN et al (2016) Unique and conserved features of the protein synthesis apparatus in parasitic trypanosomatid (Trypanosoma and Leishmania) species. In: Hernández G, Jagus R (eds) Evolution of the protein synthesis machinery and its regulation. Springer International Publishing, Cham, pp 435–475CrossRefGoogle Scholar
- Ebenezer TE, Carrington M, Lebert M et al (2017) Euglena gracilis genome and transcriptome: organelles, nuclear genome assembly strategies and initial features. Adv Exp Med Biol 979:125–140Google Scholar
- Freire ER, Vashisht AA, Malvezzi AM et al (2014b) eIF4F-like complexes formed by cap-binding homolog TbEIF4E5 with TbEIF4G1 or TbEIF4G2 are implicated in post-transcriptional regulation in Trypanosoma brucei. RNA 20:1272–1286. https://doi.org/10.1261/rna.045534.114 CrossRefPubMedPubMedCentralGoogle Scholar
- Hill KL, Hutchings NR, Russell DG, Donelson JE (1999) A novel protein targeting domain directs proteins to the anterior cytoplasmic face of the flagellar pocket in African trypanosomes. J Cell Sci 112 Pt 18:3091–3101Google Scholar
- Kramer S, Bannerman-Chukualim B, Ellis L et al (2013) Differential localization of the two T. brucei poly(A) binding proteins to the nucleus and RNP granules suggests binding to distinct mRNA pools. PLoS One 8:e54004. https://doi.org/10.1371/journal.pone.0054004 CrossRefPubMedPubMedCentralGoogle Scholar
- Pereira MMC, Malvezzi AM, Nascimento LM et al (2013) The eIF4E subunits of two distinct trypanosomatid eIF4F complexes are subjected to differential post-translational modifications associated to distinct growth phases in culture. Mol Biochem Parasitol 190:82–86. https://doi.org/10.1016/j.molbiopara.2013.06.008 CrossRefPubMedGoogle Scholar
- Urbaniak MD, Martin DMA, Ferguson MAJ (2013) Global quantitative SILAC phosphoproteomics reveals differential phosphorylation is widespread between the procyclic and bloodstream form lifecycle stages of Trypanosoma brucei. J Proteome Res 12:2233–2244. https://doi.org/10.1021/pr400086y CrossRefPubMedPubMedCentralGoogle Scholar
- Zheng L, Dominski Z, Yang X-C et al (2003) Phosphorylation of stem-loop binding protein (SLBP) on two threonines triggers degradation of SLBP, the sole cell cycle-regulated factor required for regulation of histone mRNA processing, at the end of S phase. Mol Cell Biol 23:1590–1601CrossRefPubMedPubMedCentralGoogle Scholar