Translation initiation factor eIF-5A, the hypusine-containing protein, is phosphorylated on serine and tyrosine and O-glycosylated in Trichomonas vaginalis

Unveiling EIF5A2: A multifaceted player in cellular regulation, tumorigenesis and drug resistance

The eukaryotic initiation factor 5A2 gene (EIF5A2) is a highly conserved and multifunctional gene that significantly influences various cellular processes, including translation elongation, RNA binding, ribosome binding, protein binding and post-translational modifications. Overexpression of EIF5A2 is frequently observed in multiple cancers, where it functions as an oncoprotein. Additionally, EIF5A2 is implicated in drug resistance through the regulation of various molecular pathways. In the review, we describe the structure and functions of EIF5A2 in normal cells and its role in tumorigenesis. We also elucidate the molecular mechanisms associated with EIF5A2 in the context of tumorigenesis and drug resistance. We propose that the biological roles of EIF5A2 in regulating diverse cellular processes and tumorigenesis are clinically significant and warrant further investigation.

Eukaryotic translation initiation factor 5A and its posttranslational modifications play an important role in proliferation and potentially in differentiation of the human enteric protozoan parasite Entamoeba histolytica

The eukaryotic translation initiation factor 5A (eIF5A) is a highly conserved protein and is 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 in Entamoeba histolytica, the protozoan parasite responsible for amoebic dysentery and liver abscess in humans. E. histolytica encodes two isotypes of eIF5A and two isotypes of enzymes, deoxyhypusine synthase (DHS), responsible for their PTM. Both of the two eIF5A isotypes are functional, whereas only one DHS (EhDHS1, but not EhDHS2), is catalytically active. The DHS activity increased ~2000-fold when EhDHS1 was co-expressed with EhDHS2 in Escherichia coli, suggesting that the formation of a heteromeric complex is needed for full enzymatic activity. Both EhDHS1 and 2 genes were required for in vitro growth of E. histolytica trophozoites, indicated by small antisense RNA-mediated gene silencing. In trophozoites, only eIF5A2, but not eIF5A1, gene was actively transcribed. Gene silencing of eIF5A2 caused compensatory induction of expression of eIF5A1 gene, suggesting interchangeable role of the two eIF5A isotypes and also reinforcing the importance of eIF5As for parasite proliferation and survival. Furthermore, using a sibling species, Entamoeba invadens, we found that eIF5A1 gene was upregulated during excystation, while eIF5A2 was downregulated, suggesting that eIF5A1 gene plays an important role during differentiation. Taken together, these results have underscored the essentiality of eIF5A and DHS, for proliferation and potentially in the differentiation of this parasite, and suggest that the hypusination associated pathway represents a novel rational target for drug development against amebiasis.

Proteomic profile approach of effect of putrescine depletion over Trichomonas vaginalis

Infection with Trichomonas vaginalis produces a malodorous seropurulent vaginal discharge due to several chemicals, including polyamines. The presence of 1,4-diamino-2-butanone (DAB) reduces the amount of intracellular putrescine by 90%, preventing the cotransport of exogenous spermine. DAB-treated parasites present morphological changes, which are restored by adding exogenous putrescine into the culture medium. However, the effect of polyamines over the trichomonad proteomic profile is unknown. In this study, we used a proteomic approach to analyze the polyamine-depletion and restoration effect by exogenous putrescine on T. vaginalis proteome. In the presence of inhibitor DAB, we obtained 369 spots in polyamine-depleted condition and observed 499 spots in the normal culture media. With DAB treatment, the intensity of 43 spots was increased but was found to be reduced in 39 spots, as compared to normal conditions. Interestingly, in DAB-treated parasites restored with a medium with added exogenous putrescine, 472 spots were found, of which 33 were upregulated and 63 were downregulated in protein intensity. Some of these downregulated proteins in DAB-treated parasites are involved in several cellular pathways such as glycolysis, glycolytic fermentation, arginine dihydrolase pathway, redox homeostasis, host cell binding mediated by carbohydrate, chaperone function, and cytoskeletal remodeling. Interestingly, the intensity of some of the proteins was restored by adding exogenous putrescine. In conclusion, the presence of DAB altered the proteomic profile of T. vaginalis, resulting in a decrease in the intensity of 130 proteins and an increase in the intensity of 43 proteins that was restored by the addition of putrescine.

Eukaryotic translation initiation factors and cancer

Recent technological advancements have shown tremendous mechanistic accomplishments in our understanding of the mechanism of messenger RNA translation in eukaryotic cells. Eukaryotic messenger RNA translation is very complex process that includes four phases (initiation, elongation, termination, and ribosome recycling) and diverse mechanisms involving protein and non-protein molecules. Translation regulation is principally achieved during initiation step of translation, which is organized by multiple eukaryotic translation initiation factors. Eukaryotic translation initiation factor proteins help in stabilizing the formation of the functional ribosome around the start codon and provide regulatory mechanisms in translation initiation. Dysregulated messenger RNA translation is a common feature of tumorigenesis. Various oncogenic and tumor suppressive genes affect/are affected by the translation machinery, making the components of the translation apparatus promising therapeutic targets for the novel anticancer drug. This review provides details on the role of eukaryotic translation initiation factors in messenger RNA translation initiation, their contribution to onset and progression of tumor, and how dysregulated eukaryotic translation initiation factors can be used as a target to treat carcinogenesis.

Recombinant Trichomonas vaginalis eIF-5A protein expressed from a eukaryotic system binds specifically to mammalian and putative trichomonal eIF-5A response elements (EREs)

Trichomonas vaginalis eIF-5A-like protein (TveIF-5A) belongs to the highly conserved eIF-5A family of proteins that contains a unique polyamine-derived amino acid, hypusine. Recently, we determined that the polyamine putrescine is required for tveif-5a mRNA stability, and it is necessary for stability and maturation of the TveIF-5A protein. Eukaryotic eIF-5A is known to be involved in mRNA turnover and is capable of sequence-specific RNA binding to eIF-5A response elements (EREs). These ERE sequences are present in diverse mammalian mRNAs, including human cyclooxygenase-2 (cox-2). Here, we cloned the complete coding sequence of TveIF-5A and overexpressed it in a eukaryotic system. The recombinant protein (rTveIF-5A) was purified in soluble form using size-exclusion chromatography. Because of the polyamine-dependent regulation of TvCP39 (a protease of T. vaginalis) at the protein and RNA messenger (mRNA) levels, we looked for an ERE-like structure in the 3' region of tvcp39 mRNA. In RNA gel-shift assays, rTveIF-5A bound to transcripts at the EREs of cox-2 or tvcp39 mRNAs. This work shows the eIF-5A/ERE-like interaction in T. vaginalis.

Bifunctional activity of deoxyhypusine synthase/hydroxylase from Trichomonas vaginalis

The Trichomonas vaginalis genome analysis suggested the presence of a putative deoxyhypusine synthase (TvDHS) that catalyzes the posttranslational modification of eIF-5A. Herein, we expressed and purified the recombinant TvDHS (rTvDHS) protein (43 kDa) and the recombinant TveIF-5A (rTveIF-5A) precursor protein (46 kDa). A 41 kDa band of the native TvDHS was recognized by western blot analysis in T. vaginalis total protein extract by a mouse polyclonal anti-rTvDHS antibody. The enzymatic activity of rTvDHS was determined by in vitro rTveIF-5A precursor modification. The modification reaction was performed by using ((3)H)-spermidine, and the biochemical analysis showed that rTvDHS exhibited Km value of 0.6 μM. The rTvDHS activity was inhibited by the spermidine analog, N″-guanyl-1,7-diamino-heptane (GC7). Native gel electrophoresis analysis showed two bands corresponding to an rTvDHS-rTveIF-5A complex and an intermediate form of rTveIF-5A. The two forms were subsequently separated by ion exchange chromatography to identify the hypusine residue by MS/MS analysis. Moreover, mutations in TvDHS showed that the putative HE motif present in this enzyme is involved in the hydroxylation of TveIF-5A. We observed that only hypusine-containing TveIF-5A was bound to an RNA hairpin ERE structure from the cox-2 gene, which contains the AAAUGUCACAC consensus sequence. Interestingly, 2DE-WB assays, using parasites that were grown in DAB-culture conditions and transferred to exogenous putrescine, showed the new isoform of TveIF-5A. In summary, our results indicate that T. vaginalis contains an active TvDHS capable of modifying the precursor TveIF-5A protein, which subsequently exhibits RNA binding activity.

Identification of the phosphorylated residues in TveIF5A by mass spectrometry

The initiation factor eIF5A in Trichomonas vaginalis (TveIF5A) is previously shown to undergo hypusination, phosphorylation and glycosylation. Three different pI isoforms of TveIF5A have been reported. The most acidic isoform (pI 5.2) corresponds to the precursor TveIF5A, whereas the mature TveIF5A appears to be the most basic isoform (pI 5.5). In addition, the intermediary isoform (pI 5.3) is found only under polyamine-depleted conditions and restored with exogenous putrescine. We propose that differences in PI are due to phosphorylation of the TveIF5A isoforms. Here, we have identified phosphorylation sites using mass spectrometry. The mature TveIF5A contains four phosphorylated residues (S3, T55, T78 and T82). Phosphorylation at S3 and T82 is also identified in the intermediary TveIF5A, while no phosphorylated residues are found in the precursor TveIF5A. It has been demonstrated that eIF5A proteins from plants and yeast are phosphorylated by a casein kinase 2 (CK2). Interestingly, a gene encoding a protein highly similar to CK2 (TvCK2) is found in T. vaginalis, which might be involved in the phosphorylation of TveIF5A in T. vaginalis.

Upregulation of eIF-5A1 in the paralyzed muscle after spinal cord transection associates with spontaneous hindlimb locomotor recovery in rats by upregulation of the ErbB, MAPK and neurotrophin signal pathways

It is well known that trauma is frequently accompanied by spontaneous functional recovery after spinal cord injury (SCI), but the underlying mechanisms remain elusive. In this study, BBB scores showed a gradual return of locomotor functions after SCT. Proteomics analysis revealed 16 differential protein spots in the gastrocnemius muscle between SCT and normal rats. Of these differential proteins, eukaryotic translation initiation factor 5A1 (elf-5A1), a highly conserved molecule throughout eukaryotes, exhibited marked upregulation in the gastrocnemius muscle after SCT. To study the role of eIF-5A1 in the restoration of hindlimb locomotor functions following SCT, we used siRNA to downregulate the mRNA level of eIF-5A1. Compared with untreated SCT control rats, those subjected to eIF-5A1 knockdown exhibited impaired functional recovery. Moreover, gene expression microarrays and bioinformatic analysis showed high correlation between three main signal pathways (ErbB, MAPK and neurotrophin signal pathways) and eIF-5A1. These signal pathways regulate cell proliferation, differentiation and neurocyte growth. Consequently, eIF-5A1 played a pivotal role via these signal pathways in hindlimb locomotor functional recovery after SCT, which could pave the way for the development of a new strategy for the treatment of spinal cord injury in clinical trials.

TvMP50 is an immunogenic metalloproteinase during male trichomoniasis

Trichomonas vaginalis, a human urogenital tract parasite, is capable of surviving in the male microenvironment, despite of the presence of Zn(2+). Concentrations > 1.6 mM of Zn(2+) have a trichomonacidal effect; however, in the presence of ≤1.6 mM Zn(2+), several trichomonad proteins are up- or down-regulated. Herein, we analyzed the proteome of a T. vaginalis male isolate (HGMN01) grown in the presence of Zn(2+) and found 32 protein spots that were immunorecognized by male trichomoniasis patient serum. Using mass spectrometry (MS), the proteins were identified and compared with 23 spots that were immunorecognized in the proteome of a female isolate using the same serum. Interestingly, we found a 50-kDa metallopeptidase (TvMP50). Unexpectedly, this proteinase was immunodetected by the serum of male trichomoniasis patients but not by the female patient serum or sera from healthy men and women. We analyzed the T. vaginalis genome and localized the mp50 gene in locus TVAG_403460. Using an RT-PCR assay, we amplified a 1320-bp mp50 mRNA transcript that was expressed in the presence of Zn(2+) in the HGMN01 and CNCD147 T. vaginalis isolates. According to a Western blot assay, native TvMP50 was differentially expressed in the presence of Zn(2+). The TvMP50 proteolytic activity increased in the presence of Zn(2+) in both isolates and was inhibited by EDTA but not by ptosyl-L-lysine chloromethyl ketone (TLCK), E64, leupeptin, or phenylmethane sulfonyl fluoride. Furthermore, the recombinant TvMP50 had proteolytic activity that was inhibited by EDTA. These data suggested that TvMP50 is immunogenic during male trichomoniasis, and Zn(2+) induces its expression.