Disease relevance of EIF5A

• A series of truncated forms of the eIF-5A precursor protein generated by expression in E. coli of recombinant deletion constructs from the human eIF-5A cDNA were tested [1].
• The eukaryotic cofactor for the human immunodeficiency virus type 1 (HIV-1) rev protein, eIF-5A, maps to chromosome 17p12-p13: three eIF-5A pseudogenes map to 10q23.3, 17q25, and 19q13.2 [2].
• EIF5A2 is highly expressed in testis and colorectal adenocarcinoma and at moderate levels in the brain, in contrast to the ubiquitously expressed EIF5A1 gene [3].
• It has previously been shown that interaction of eukaryotic initiation factor 5A (eIF-5A) with the Rev trans-activator protein of HIV-1 mediates the transport of unspliced or incompletely spliced viral mRNAs across the nuclear envelope [4].
• Heat stress-induced loss of eukaryotic initiation factor 5A (eIF-5A) in a human pancreatic cancer cell line, MIA PaCa-2, analyzed by two-dimensional gel electrophoresis [5].

High impact information on EIF5A

• Inhibition of HIV-1 replication in lymphocytes by mutants of the Rev cofactor eIF-5A [6].
• In this study, we investigated the course of expression of the unique hypusine-containing protein eukaryotic initiation factor 5A (eIF-5A), which is part of a particular RNA nuclear export pathway, during in vitro generation of human DCs [7].
• Specific inhibition of eIF-5A and collagen hydroxylation by a single agent. Antiproliferative and fibrosuppressive effects on smooth muscle cells from human coronary arteries [8].
• Hypusine [N epsilon-(4-amino-2-hydroxybutyl)-L-lysine] is a most remarkable amino acid, occurring in all eukaryotic cells, yet occupying only a single position in one protein, eukaryotic protein synthesis initiation factor 5A (eIF-5A) [9].
• Quite unexpectedly, nuclear actin was also identified as an eIF-5A binding protein [10].

Chemical compound and disease context of EIF5A

• Proteolytic fragments (5-6 kDa) of ec-eIF-5A (the precursor form of eIF-5A produced in Escherichia coli by expression of the human eIF-5A cDNA) generated by specific cleavage by endoproteinases Arg-C, Asp-N, or Glu-C, did not act as substrates for deoxyhypusine synthesis [1].
• We examined the eIF-5A protein expression in 93 lung adenocarcinomas and 10 uninvolved lung samples using quantitative two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) analysis with identification by mass spectrometry and 2-D Western blots [11].
• The first step in hypusine biosynthesis, i.e. the formation of the intermediate, deoxyhypusine (N epsilon-(4-aminobutyl)lysine), was carried out in vitro using spermidine, deoxyhypusine synthase, and ec-eIF-4D(Lys), an eIF-4D precursor prepared by over-expression of human eIF-4D cDNA in Escherichia coli [12].
• The cloned human cDNA encoding eIF-4D was overexpressed in Escherichia coli and a precursor form lacking hypusine was purified [13].
• We have expressed an unmodified variant of eIF-5A in Escherichia coli and show that it has structural properties different from those of the native protein in terms of its near- and far-UV circular dichroism spectra and its equilibrium unfolding transition with guanidinium chloride [14].

Biological context of EIF5A

• We discuss possible cellular roles for nuclear export of eIF-5A [15].
• However, the actual function of eIF5A in apoptosis is still unknown [16].
• Upon depletion of deoxyhypusine synthase, and consequently of eIF-5A, cessation of growth was accompanied by a marked enlargement of cells, suggesting a defect in cell cycle progression or in cell division [17].
• In contrast, a point mutant of eIF5A, hypusination being abolished, was revealed to be functionally defective in p53 up-regulation [16].
• Further analysis by reverse transcription PCR showed eIF5A-activated p53 transcription [16].

Anatomical context of EIF5A

• Since eIF-5A is the only known cellular substrate for DHS and GC7 has been reported to block the proliferation of CHO cells, it has been suggested that DHS may be a novel target for anti-cancer therapy [18].
• Comparison of eIF-5A levels in the PBMCs of uninfected and HIV-1-infected donors shows a significant upregulation of eIF-5A gene expression in the PBMCs of HIV-1 patients, compatible with a possible role of eIF-5A in HIV-1 replication during T-cell activation [19].
• In contrast, eIF-5A is constitutively expressed at high levels in human cell lines as well as in various human organs [19].
• Eukaryotic initiation factor 4D (eIF-4D) was purified from human red blood cells by a simple 5-step procedure [20].
• In this study we used indirect immunofluorescence and immunogold electron microscopy to demonstrate that eIF-5A accumulates at nuclear pore-associated intranuclear filaments in mammalian cells and Xenopus oocytes [21].

Associations of EIF5A with chemical compounds

• The export signal in eIF-5A appears to be complex and to involve the hypusine modification that is unique to eIF-5A [15].
• Thus it was found that [14C]putrescine can replace eIF5A precursor protein as an acceptor of the 4-aminobutyl moiety of spermidine to form radiolabeled homospermidine [22].
• The results obtained thus far define the minimum domain of the eIF-5A precursor protein required for enzymatic deoxyhypusine synthesis as Phe30-Asp80, which corresponds to a region of high amino acid conservation in this protein throughout the eukaryotic kingdom [1].
• The biosynthesis of hypusine occurs posttranslationally in only this protein by modification of a single lysine residue (Lys50 in the human eIF-5A precursor) [1].
• The Km value for putrescine (1.12 mM) as a 4-aminobutyl acceptor, however, is much higher than that for eIF5A precursor (1.5 microM) [22].

Physical interactions of EIF5A

• Molecular evolution by change of function. Alkaloid-specific homospermidine synthase retained all properties of deoxyhypusine synthase except binding the eIF5A precursor protein [23].
• These findings support a proposed model of DOHH-eIF5A binding in which the amino group(s) of the deoxyhypusine side chain of the substrate is primarily anchored by gamma-carboxyl groups of Glu57 and Glu208 at the DOHH active site [24].

Enzymatic interactions of EIF5A

• Deoxyhypusine synthase catalyzes the formation of deoxyhypusine by conjugation of the butylamine moiety of spermidine to the epsilon-amino group of one specific lysine residue of the eukaryotic translation initiation factor 5A (eIF-5A) precursor protein [25].

Regulatory relationships of EIF5A

• These results suggest that loss of the active form of eIF-5A is an important factor in the irreversible process of heat stress-induced death of MIA PaCa-2 cells [5].

Other interactions of EIF5A

• Overexpression of eIF5A led to a p53-dependent apoptosis or sensitized cells to induction of apoptosis by chemotherapeutic agents [16].
• Our results demonstrated that eIF5A and syntenin could engage in a specific interaction both in vitro and in vivo and functioned collaboratively to regulate p53 activity [16].
• This result supports the hypothesis that the synthesis of a subset of proteins important for the S-phase progression of CHO-K1 cells might be dependent upon hypusinated eIF-5A [18].
• Here we show that the ribosomal protein L5, which is the central protein component of the 5S rRNA export system, is a cellular interaction partner of eIF-5A [4].
• We are able to show that eIF-5A interacts with the general nuclear export receptor, CRM1 [21].

Analytical, diagnostic and therapeutic context of EIF5A

• Equilibrium ultracentrifugation data further supported this 1:1 ratio and indicated a very strong interaction of the enzyme with ec-eIF5A (Kd</=0.5 nM) [26].
• Indirect immunofluorescence studies demonstrate that a significant fraction of eIF-5A localizes to the nucleus [27].
• Furthermore, microinjection studies in somatic cells revealed that eIF-5A is transported from the nucleus to the cytoplasm, and that this nuclear export is blocked by leptomycin B [21].
• The main form, which accounts for approximately 95% of the total eIF-5A, carries hypusine at position 50 and is amino-terminally acetylated as determined by amino acid composition analysis and electrospray ionization mass spectrometry [28].
• Sequence analysis revealed that the eIF-5A coding region is identical to the corresponding cDNA but interrupted by three introns [29].

References