Eukaryotic translation initiation factor 5A and its hypusination play an important role in proliferation and differentiation of the human enteric protozoan parasiteEntamoeba histolytica
Authors: Jeelani Ghulam , Nozaki Tomoyoshi 
Published: August 2020

The eukaryotic translation initiation factor 5A (eIF5A) is highly conserved and essential in all eukaryotes. However, the specific roles of eIF5A in translation and in other biological processes remain elusive. In the present study, we described the role of eIF5A, its posttranslational modifications (PTM), and the biosynthetic pathway needed for the PTM inEntamoeba histolytica, the protozoan parasite responsible for amoebic dysentery and liver abscess in humans.E. histolyticaencodes two isotypes of eIF5A and two isotypes of enzymes, deoxyhypusine synthase (DHS), responsible for their PTM. Both of the two eIF5A are functional, whereas only one DHS (EhDHS1), but not EhDHS2, is catalytically active. The DHS activity increased ∽2000 fold when EhDHS1 was coexpressed with EhDHS2 inEscherichia coli, suggesting that the formation of a heteromeric complex is needed for full enzymatic activity. BothEhDHS1and2genes were required forin vitrogrowth ofE. histolyticatrophozoites, indicated by small antisense RNA-mediated gene silencing. In trophozoites, onlyeIF5A2, but noteIF5A1, gene was actively transcribed. Gene silencing of eIF5A2 caused compensatory induction of expression ofeIF5A1gene, suggesting interchangeable role of two eIF5A isotypes and also reinforcing the importance of eIF5As for parasite proliferation and survival. Furthermore, using a sibling species,Entamoeba invadens, we found thateIF5A1gene was upregulated during excystation, whileeIF5A2was downregulated, suggesting thateIF5A1gene plays an important role during differentiation. Taken together, these results have underscored the essentiality of eIF5A and DHS, for proliferation and differentiation of this parasite, and suggest that the hypusination associated pathway represents a novel rational target for drug development against amebiasis.

Author summary

Eukaryotic initiation factor 5A is a ubiquitous protein that is essential for cell proliferation. We examined the maturation, regulation, and function of eIF5A inE. histolytica. We found by small antisense RNA-mediated gene silencing that EhDHS1/2 and EheIF5A2 are essential for growth ofE. histolyticatrophozoites. We further found that only one eIF5A, EheIF5A2, of two isotypes was constitutively expressed in the trophozoites stage and silencing ofEheIF5A2gene caused overexpression of the other eIF5A isotype (EheIF5A1) to partially rescue the growth defect in this parasites. Furthermore, we found that transcription ofeIF5A1gene was stage-specifically upregulated during excystation inE. invadens. Taken together, we have demonstrated for the first time that the two eIF5As play important and distinct roles inEntamoebabiology. This study has also provided an answer to a long standing conundrum on the biological importance of polyamines: spermidine is essential for eIF5A hypusination essential for protein translation inEntamoeba. Our work should also help our understanding of the physiological significance of eIF5A and its post-translational modifications in other pathogenic eukaryotes and potentially lead to formulation of control measures against parasitic diseases.