Eukaryotic translation initiation factor 5A induces apoptosis in colon cancer cells and associates with the nucleus in response to tumour necrosis factor alpha signalling

Proteome changes in human bronchoalveolar cells following styrene exposure indicate involvement of oxidative stress in the molecular-response mechanism

Styrene is a volatile organic compound that is widely used as an intermediate in many industrial settings. There are known adverse health effects at environmentally significant concentrations, but little is known about the molecular effect of exposure to styrene at sub-acute toxic concentrations. We exposed human lung epithelial cells, at a wide range of concentrations (1 mg/m(3)-10 g/m(3)), to styrene and analyzed the effects on the proteome level by 2-DE, where 1380 proteins spots were detected and 266 were identified unambiguously by MS. A set of 16 protein spots were found to be significantly altered due to exposure to styrene at environmentally significant concentrations of 1-10 mg/m(3) (0.2-2.3 ppm). Among these, superoxide dismutase as well as biliverdin reductase A could be correlated with the molecular pathway of oxidative stress, while eukaryotic translation initiation factor 5A-1, ezrin, lamin B2 and voltage-dependent anion channel 2 have been reported to be involved in apoptosis. Treatment with styrene also caused the formation of styrene oxide-protein adducts, specifically for thioredoxin reductase 1. These results underline the relevance of oxidative stress as a primary molecular response mechanism of lung epithelial cells to styrene exposure at indoor-relevant concentrations.

Housekeeping genes in prostate tumorigenesis

Housekeeping (HK) genes are involved in basic cellular functions and tend to be constitutively expressed across various tissues and conditions. A number of studies have analyzed the value of HK genes as an internal standard for assessing gene expression, but the role of HK genes in cancer development has never been specifically addressed. In this study, we sought to evaluate the expression of HK genes during prostate tumorigenesis. We performed a meta-analysis of gene expression during the transition from normal prostate (NP) to localized prostate cancer (LPC) (i.e., NP > LPC) and from localized to metastatic prostate cancer (MPC) (i.e., LPC > MPC). We found that HK genes are more likely to be differentially expressed during prostate tumorigenesis than is the average gene in the human genome, suggesting that prostate tumorigenesis is driven by modulation of the expression of HK genes. Cell-cycle genes and proliferation markers were up-regulated in both NP > LPC and LPC > MPC transitions. We also found that the genes encoding ribosomal proteins were up-regulated in the NP > LPC and down-regulated in the LPC > MPC transition. The expression of heat shock proteins was up-regulated during the LPC > MPC transition, suggesting that in its advanced stages, prostate tumor is under cellular stress. The results of these analyses suggest that during prostate tumorigenesis, there is a period when the tumor is under cellular stress and, therefore, may be the most vulnerable and responsive to treatment.

Identification of distinctive protein expression patterns in colorectal adenoma

PURPOSE

As a pre-malignant precursor, adenoma provides an ideal tissue for proteome profiling to investigate early colorectal cancer development and provide possible targets for preventive interventions. The aim of this study was to identify patterns of differential protein expression that distinguish colorectal adenoma from normal tissue.

EXPERIMENTAL DESIGN

Twenty paired samples of adenoma and normal mucosa were analysed by 2-DE and MALDI-TOF/TOF MS to detect proteins with ≥2-fold differential expression.

RESULTS

Four proteins were up-regulated in adenoma (Annexin A3, S100A11, S100P and eIF5A-1) and three were down-regulated (Galectin-1, S100A9 and FABPL). S100P, galectin-1, S100A9 and FABPL expression was localised by immunohistochemistry.

CONCLUSIONS AND CLINICAL RELEVANCE

Distinctive patterns of in vivo protein expression in colorectal adenoma were identified for the first time. These proteins have important functions in cell differentiation, proliferation and metabolism, and may play a crucial role in early colorectal carcinogenesis. The ability to recognise premalignant lesions may have important applications in cancer prevention.

Inhibition of HIV-1 gene expression by Ciclopirox and Deferiprone, drugs that prevent hypusination of eukaryotic initiation factor 5A

BACKGROUND

Eukaryotic translation initiation factor eIF5A has been implicated in HIV-1 replication. This protein contains the apparently unique amino acid hypusine that is formed by the post-translational modification of a lysine residue catalyzed by deoxyhypusine synthase and deoxyhypusine hydroxylase (DOHH). DOHH activity is inhibited by two clinically used drugs, the topical fungicide ciclopirox and the systemic medicinal iron chelator deferiprone. Deferiprone has been reported to inhibit HIV-1 replication in tissue culture.

RESULTS

Ciclopirox and deferiprone blocked HIV-1 replication in PBMCs. To examine the underlying mechanisms, we investigated the action of the drugs on eIF5A modification and HIV-1 gene expression in model systems. At early times after drug exposure, both drugs inhibited substrate binding to DOHH and prevented the formation of mature eIF5A. Viral gene expression from HIV-1 molecular clones was suppressed at the RNA level independently of all viral genes. The inhibition was specific for the viral promoter and occurred at the level of HIV-1 transcription initiation. Partial knockdown of eIF5A-1 by siRNA led to inhibition of HIV-1 gene expression that was non-additive with drug action. These data support the importance of eIF5A and hypusine formation in HIV-1 gene expression.

CONCLUSION

At clinically relevant concentrations, two widely used drugs blocked HIV-1 replication ex vivo. They specifically inhibited expression from the HIV-1 promoter at the level of transcription initiation. Both drugs interfered with the hydroxylation step in the hypusine modification of eIF5A. These results have profound implications for the potential therapeutic use of these drugs as antiretrovirals and for the development of optimized analogs.

An update on the mouse liver proteome

BACKGROUND

Decoding of the liver proteome is subject of intense research, but hampered by methodological constraints. We recently developed an improved protocol for studying rat liver proteins based on 2-DE-MALDI-TOF-MS peptide mass finger printing.This methodology was now applied to develop a mouse liver protein database.

RESULTS

Liver proteins were extracted by two different lysis buffers in sequence followed by a liquid-phase IEF pre-fractionation and separation of proteins by 2 DE at two different pH ranges, notably 5-8 and 7-10. Based on 9600 in gel digests a total of 643 mouse liver proteins with high sequence coverage (> 20 peptides per protein) could be identified by MALDI-TOF-MS peptide mass finger printing. Notably, 255 proteins are novel and have not been reported so far by conventional two-dimensional electrophoresis proteome mapping. Additionally, the results of the present findings for mouse liver were compared to published data of the rat proteome to compile as many proteins as possible in a rodent liver database.

CONCLUSION

Based on 2-DE MALDI-TOF-MS a significantly improved proteome map of mouse liver was obtained. We discuss some prominent members of newly identified proteins for a better understanding of liver biology.

Spermidine is indispensable in differentiation of 3T3-L1 fibroblasts to adipocytes

Impaired adipogenesis has been shown to predispose to disturbed adipocyte function and development of metabolic abnormalities. Previous studies indicate that polyamines are essential in the adipogenesis in 3T3-L1 fibroblasts. However, the specific roles of individual polyamines during adipogenesis have remained ambiguous as the natural polyamines are readily interconvertible inside the cells. Here, we have defined the roles of spermidine and spermine in adipogenesis of 3T3-L1 cells by using (S’)- and (R’)- isomers of α-methylspermidine and (S,S’)-, (R,S)- and (R,R’)-diastereomers of α,ω-bismethylspermine. Polyamine depletion caused by α-difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase, prevented adipocyte differentiation by suppressing the expression of its key regulators, peroxisome proliferator-activated receptor γ and CCAAT/enhancer binding protein α. Adipogenesis was restored by supplementation of methylspermidine isomers but not of bismethylspermine diastereomers. Although both spermidine analogues supported adipocyte differentiation only (S)-methylspermidine was able to fully support cell growth after extended treatment with α-DFMO. The distinction between the spermidine analogues in maintaining growth was found to be in their different capability to maintain functional hypusine synthesis. However, the differential ability of spermidine analogues to support hypusine synthesis did not correlate with their ability to support differentiation. Our results show that spermidine, but not spermine, is essential for adipogenesis and that the requirement of spermidine for adipogenesis is not strictly associated with hypusine modification. The involvement of polyamines in the regulation of adipogenesis may offer a potential application for the treatment of dysfunctional adipocytes in patients with obesity and metabolic syndrome.

The effect of hypusine modification on the intracellular localization of eIF5A

Eukaryotic translation initiation factor 5A (eIF5A) is a highly conserved protein essential for eukaryotic cell proliferation and is the only protein containing hypusine, [N(epsilon)-(4-amino-2-hydroxybutyl)lysine]. eIF5A is activated by the post-translational synthesis of hypusine. eIF5A also undergoes an acetylation at specific Lys residue(s). In this study, we have investigated the effect of hypusine modification and acetylation on the subcellular localization of eIF5A. Immunocytochemical analyses showed differences in the distribution of non-hypusinated eIF5A precursor and the hypusine-containing mature eIF5A. While the precursor is found in both cytoplasm and nucleus, the hypusinated eIF5A is primarily localized in cytoplasm. eIF5A mutant proteins, defective in hypusine modification (K50A, K50R) were localized in a similar manner to the eIF5A precursor, whereas hypusine-modified mutant proteins (K47A, K47R, K68A) were localized mainly in the cytoplasm. These findings provide strong evidence that the hypusine modification of eIF5A dictates its localization in the cytoplasmic compartment where it is required for protein synthesis.

Thermal killing of human colon cancer cells is associated with the loss of eukaryotic initiation factor 5A

Heat-induced cell death appears to be a cell-specific event. Chronic heat stress was lethal to human colon cancer cells (Caco-2, HT29, and HCT116), but not to normal diploid fibroblasts and other cancer cells (BJ-T, WI38, HeLa, ovarian 2008, WI38VA). Acute heat stress (45-51 degrees C, 30 min) caused cell death of colon cancer cells during recovery at physiological temperature. Thermal killing of Caco-2 cells was not mediated via oxidative stress since Caco-2 cells were much more resistant than HeLa and other cancer cells to H(2)O(2)-induced cell death. Acute heat stress caused a striking loss of eukaryotic initiation factor 5A (eIF5A) in colon cancer cells, but not in HeLa and other normal or transformed human fibroblasts. The heat-induced loss of eIF5A is likely to be due to changes in the protein stability. The half-life of eIF5A was changed from >20 h to less than 30 min during the acute heat stress. Sequence analysis of the eIF5A gene from Caco-2 and HeLa cells did not reveal any difference, suggesting that the change in stability in Caco-2 cells was not due to any eIF5A mutation. Pretreatment of cells with protease inhibitors such as phenylmethyl sulfonyl fluoride (PMSF) partially blocked the heat-induced loss of eIF5A and prevented heat-induced cell death. In light of the essential role of eIF5A in cell survival and proliferation, our results suggest that the stability of eIF5A may have an important role in determining the fate of the particular cell type after severe heat stress.

Dimerization of the yeast eukaryotic translation initiation factor 5A requires hypusine and is RNA dependent

Post-translational modification of the highly conserved K51 residue of the Saccharomyces cerevisiae eukaryotic translation initiation factor 5A (eIF5A) to form hypusine, is essential for its many functions including the binding of specific mRNAs. We characterized hypusinated yeast eIF5A by size-exclusion chromatography and native PAGE, showing that the protein exists as a homodimer. A K51R mutant, which was not functional in vivo eluted as a monomer and inhibition of hypusination abolished dimerization. Furthermore, treatment of dimeric eIF5A with RNase A resulted in disruption of the dimer, leading us to conclude that RNA binding is also required for dimerization of eIF5A. We present a model of dimerization, based on the Neurospora crassa structural analogue, HEX-1.

Eukaryotic translation initiation factor 5A small interference RNA-liposome complexes reduce inflammation and increase survival in murine models of severe sepsis and acute lung injury

BACKGROUND

Many novel therapeutics have failed to reduce all-cause mortality associated with severe sepsis. Eukaryotic translation initiation factor 5A (eIF5A) is a regulator of apoptosis as well as inflammatory cell activation, making it a potential target for sepsis therapy.

METHODS

In a murine model of severe sepsis, mice were intraperitoneally challenged with lipopolysaccharide (LPS). Mice were treated both before and after LPS challenge with liposome complexes containing either an eIF5A-specific or control small interference RNA (siRNA), and both survival and serum concentrations of inflammatory cytokines were monitored. The ability of eIF5A siRNA to reduce inflammatory cytokines was also tested in a model of acute lung injury established by intranasal administration of LPS to mice.

RESULTS

There was a statistically significant increase in the rate of survival for mice intraperitoneally challenged with LPS that received eIF5A siRNA, compared with that noted for mice that received control siRNA (71% vs. 5%; P< .001), as well as a reduction in cytokine expression in serum. Concentrations of proinflammatory cytokines were also reduced in the lung homogenates and serum of mice that were intranasally challenged with LPS and received eIF5A siRNA (P< or = .05).

CONCLUSIONS

eIF5A siRNA-liposome complexes reduced inflammation and contributed to increased survival in a model of severe sepsis, decreased inflammation in a model of acute lung injury, and should be considered for clinical use.

Insights on eukaryotic translation initiation factor 5A (eIF5A) in the brain and aging

Long-term memory, a persistent form of synaptic plasticity, requires translation of a subset of mRNA present in neuronal dendrites during a short and critical period through a mechanism not yet fully elucidated. Western blotting analysis revealed a high content of eukaryotic translation initiation factor 5A (eIF5A) in the brain of neonatal rats, a period of intense neurogenesis rate, differentiation and synaptic establishment, when compared to adult rats. Immunohistochemistry analysis revealed that eIF5A is present in the whole brain of adult rats showing a variable content among the cells from different areas (e.g. cortex, hippocampus and cerebellum). A high content of eIF5A in the soma and dendrites of Purkinje cells, key neurons in the control of motor long-term memory in the cerebellum, was observed. Detection of high eIF5A content was revealed in dendritic varicosities of Purkinje cells. Evidence is presented herein that a reduction of eIF5A content is associated to brain aging.

Synthetic lethality between eIF5A and Ypt1 reveals a connection between translation and the secretory pathway in yeast

The putative translation initiation factor 5A (eIF5A) is a small protein, highly conserved and essential in all organisms from archaea to mammals. Although the involvement of eIF5A in translation initiation has been questioned, new evidence reestablished the connection between eIF5A and this cellular process. In order to better understand the function of elF5A, a screen for synthetic lethal gene using the tif51A-3 mutant was carried out and a new mutation (G80D) was found in the essential gene YPT1, encoding a protein involved in vesicular trafficking. The precursor form of the vacuolar protein CPY is accumulated in the ypt1-G80D mutant at the nonpermissive temperature, but this defect in vesicular trafficking did not occur in the tif51A mutants tested. Overexpression of eIF5A suppresses the growth defect of a series of ypt1 mutants, but this suppression does not restore correct CPY sorting. On the other hand, overexpression of YPT1 does not suppress the growth defect of tif51A mutants. Further, it was revealed that eIF-5A is present in both soluble and membrane fractions, and its membrane association is ribosome-dependent. Finally, we demonstrated that the ypt1 and other secretion pathway mutants are sensitive to paromomycin. These results confirm the link between translation and vesicular trafficking and reinforce the implication of eIF5A in protein synthesis.

Synthesis, chaperoning, and metabolism of proteins are regulated by NT-3/TrkC signaling in the medulloblastoma cell line DAOY

The human medulloblastoma cell line DAOY was transfected with Tropomyosin receptor kinase (TrkC), a marker for good prognostic outcome. Following TrkC-activation by its ligand neurotrophin-3, protein extracts from DAOY cells were run on 2DE with subsequent MALDI-TOF-TOF analysis and quantification in order to detect downstream effectors. Protein levels of translational, splicing, processing, chaperone, protein handling, and metabolism machineries were shown to depend on neurotrophin-3-induced TrkC activation probably representing pharmacological targets.

Role of hypusinated eukaryotic translation initiation factor 5A in polyamine depletion-induced cytostasis

We have earlier shown that alpha-methylated spermidine and spermine analogues rescue cells from polyamine depletion-induced growth inhibition and maintain pancreatic integrity under severe polyamine deprivation. However, because alpha-methylspermidine can serve as a precursor of hypusine, an integral part of functional eukaryotic translation initiation factor 5A required for cell proliferation, and because alpha, omega-bismethylspermine can be converted to methylspermidine, it is not entirely clear whether the restoration of cell growth is actually attributable to hypusine formed from these polyamine analogues. Here, we have used optically active isomers of methylated spermidine and spermine and show that polyamine depletion-induced acute cytostasis in cultured cells could be reversed by all the isomers of the methylpolyamines irrespective of whether they served or not as precursors of hypusine. In transgenic rats with activated polyamine catabolism, all the isomers similarly restored liver regeneration and reduced plasma alpha-amylase activity associated with induced pancreatitis. Under the above experimental conditions, the (S, S)- but not the (R, R)-isomer of bismethylspermine was converted to methylspermidine apparently through the action of spermine oxidase strongly preferring the (S, S)-isomer. Of the analogues, however, only (S)-methylspermidine sustained cell growth during prolonged (more than 1 week) inhibition of polyamine biosynthesis. It was also the only isomer efficiently converted to hypusine, indicating that deoxyhypusine synthase likewise possesses hidden stereospecificity. Taken together, the results show that growth inhibition in response to polyamine depletion involves two phases, an acute and a late hypusine-dependent phase.