Echovirus 1 replication, not only virus binding to its receptor, VLA-2, is required for the induction of cellular immediate-early genes

Hsp70 Is a Potential Therapeutic Target for Echovirus 9 Infection

Echovirus is an important cause of viral pneumonia and encephalitis in infants, neonates, and young children worldwide. However, the exact mechanism of its pathogenesis is still not well understood. Here, we established an echovirus type 9 infection mice model, and performed two-dimensional gel electrophoresis (2DE) and tandem mass spectrometry (MS/MS)-based comparative proteomics analysis to investigate the differentially expressed host proteins in mice brain. A total of 21 differentially expressed proteins were identified by MS/MS. The annotation of the differentially expressed proteins by function using the UniProt and GO databases identified one viral protein (5%), seven cytoskeletal proteins (33%), six macromolecular biosynthesis and metabolism proteins (28%), two stress response and chaperone binding proteins (9%), and five other cellular proteins (25%). The subcellular locations of these proteins were mainly found in the cytoskeleton, cytoplasm, nucleus, mitochondria, and Golgi apparatus. The protein expression profiles and the results of quantitative RT-PCR in the detection of gene transcripts were found to complement each other. The differential protein interaction network was predicted using the STRING database. Of the identified proteins, heat shock protein 70 (Hsp70), showing consistent results in the proteomics and transcriptomic analyses, was analyzed through Western blotting to verify the reliability of differential protein expression data in this study. Further, evaluation of the function of Hsp70 using siRNA and quercetin, an inhibitor of Hsp70, showed that Hsp70 was necessary for the infection of echovirus type 9. This study revealed that echovirus infection could cause the differential expression of a series of host proteins, which is helpful to reveal the pathogenesis of viral infection and identify therapeutic drug targets. Additionally, our results suggest that Hsp70 could be a useful therapeutic host protein target for echovirus infection.

Simian varicella virus causes robust transcriptional changes in T cells that support viral replication

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T cells play a major role in varicella viruses dissemination to ganglia and skin.

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SVV infection of T cells increases the expression of cell cycle genes.

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SVV infection downregulates genes important for antigen presentation in T cells.

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SVV T cell infection disrupts expression of genes vital for metabolism and immunity.

Varicella zoster virus (VZV) causes varicella (chickenpox) during acute infection. Several studies have shown that T cells are early and preferential targets of VZV infection that play a critical role in disseminating VZV in to the skin and ganglia. However, the transcriptional changes that occur in VZV-infected T cells remain unclear due to limited access to clinical samples and robust translational animal models. In this study, we used a nonhuman primate model of VZV infection where rhesus macaques are infected with the closely related Simian Varicella Virus (SVV) to provide novel insights into VZV-T cell interactions. RNA sequencing of bronchial alveolar lavage-resident T cells isolated from infected rhesus macaques show that SVV infection alters expression of genes important for regulation of gene expression, cell cycle progression, metabolism, and antiviral immunity. These data provide insight into cellular processes that may support viral replication, facilitate SVV dissemination, and evade host defense.

Different mechanisms preserve translation of programmed cell death 8 and JunB in virus-infected endothelial cells

OBJECTIVE

Translation initiation of eukaryotic mRNAs typically occurs by cap-dependent ribosome scanning mechanism. However, certain mRNAs are translated by ribosome assembly at internal ribosome entry sites (IRESs). Whether IRES-mediated translation occurs in stressed primary human endothelial cells (ECs) is unknown.

METHODS AND RESULTS

We performed microarray analysis of polyribosomal mRNA from ECs to identify IRES-containing mRNAs. Cap-dependent translation was disabled by poliovirus (PV) infection and confirmed by loss of polysome peaks, detection of eukaryotic initiation factor (eIF) 4G cleavage, and decreased protein synthesis. We found that 87.4% of mRNAs were dissociated from polysomes in virus-infected ECs. Twelve percent of mRNAs remained associated with polysomes, and 0.6% were enriched ≥2-fold in polysome fractions from infected ECs. Quantitative reverse transcription-polymerase chain reaction confirmed the microarray findings for 31 selected mRNAs. We found that enriched polysome associations of programmed cell death 8 (PDCD8) and JunB mRNA resulted in increased protein expression in PV-infected ECs. The presence of IRESs in the 5' untranslated region of PDCD8 mRNA, but not of JunB mRNA, was confirmed by dicistronic analysis.

CONCLUSIONS

We show that microarray profiling of polyribosomal mRNA transcripts from PV-infected ECs successfully identifies mRNAs whose translation is preserved in the face of stress-induced, near complete cessation of cap-dependent initiation. Nevertheless, internal ribosome entry is not the only mechanism responsible for this privileged translation.

Effects of echovirus 1 infection on cellular gene expression

To obtain a view of the influence of enterovirus infection on host cell gene expression, multiple cellular mRNA levels were first investigated during echovirus 1 (EV1) infection in HOS palpha2AW cells using cDNA array analysis. Visible cytopathic effect and partial shut-off of host cell protein synthesis were observed 6-10 h after the EV1 infection. Simultaneously, approximately 2% of the investigated genes, among them immediate-early response genes and genes involved in apoptotic pathways and cell growth regulation, were activated over twofold and less than 0.5% of genes were downregulated. For comparison, the cellular effects of coxsackievirus B4 and poliovirus 1 infections were studied in HeLa-Ohio cells by cDNA arrays. Gene activation patterns detected in the host cells during the infection by the three enteroviruses were only partially similar.

alpha6 integrin is not the obligatory cell receptor for bovine papillomavirus type 4

Recently, alpha6 integrin has been proposed as the epithelial cell receptor for papillomavirus. This study investigated whether alpha6 integrin is the cellular receptor for bovine papillomavirus type 4 (BPV-4), which is strictly epitheliotropic and infects the mucous epithelium of the upper digestive tract. Primary bovine mucosal keratinocytes from the palate of a foetus (PalK) displayed high levels of alpha6 integrin; matched primary fibroblasts from the same biopsy (PalF) expressed almost no alpha6 integrin. However, BPV-4 bound both PalK and PalF to similar, saturable levels. Native BPV-4 virions infected PalK in vitro, as detected by RT-PCR of E7 RNA. Infection could be blocked by excess virus-like particles (VLPs) and by neutralizing antisera against L1-L2 and L1 VLPs or by denaturation of the virions, supporting the view that infection in vitro mimics the process in vivo. alpha6 integrin-negative human keratinocyte cell lines were derived from patients affected by junctional epidermolysis bullosa presenting genetic lesions in their hemidesmosomes. The level of alpha6 integrin expression was determined in these cell lines by in situ immunofluorescence and FACS. Despite the absence of alpha6 integrin expression by BO-SV cells, they were bound by BPV-4 to similar, saturable levels as normal keratinocytes, KH-SV. Furthermore, BO-SV and KH-SV cells were both infected by BPV-4 to apparently the same extent as PalK cells. These results are consistent with the conclusion that alpha6 integrin is not the obligatory receptor for a bovine mucosotropic papillomavirus.

Cleavage of RasGAP and phosphorylation of mitogen-activated protein kinase in the course of coxsackievirus B3 replication

Recently, we reported on tyrosine phosphorylation of distinct cellular proteins in the course of enterovirus infections (M. Huber, H.-C. Selinka, and R. Kandolf, J. Virol. 71:595-600, 1997). These phosphorylation events were mediated by Src-like kinases and were shown to be necessary for effective virus replication. That study is now extended by examination of the interaction of the adapter protein Sam68, a cellular target of Src-like kinases which has been shown to interact with the poliovirus 3D polypeptide, with cellular signaling proteins as well as the function of the latter during infection. Here, we report that the RNA-binding and protein-binding protein Sam68 associates with the p21(ras) GTPase-activating protein RasGAP. Remarkably, RasGAP is cleaved during infections with different strains of coxsackievirus B3 as well as with echovirus 11 and echovirus 12, yielding a 104-kDa protein fragment. This cleavage event, which cannot be prevented by the general caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone, may promote the activation of the Ras pathway, as shown by the activating dual phosphorylation of the mitogen-activated protein kinases Erk-1 and Erk-2 in the late phase of infection. Moreover, downstream targets of the mitogen-activated protein kinases, i.e., the p21(ras) exchange factor Sos-1 and cytoplasmic phospholipase A2, are phosphorylated with parallel time courses during infection. Activation or inhibition of cellular signaling pathways may play a general role in regulating effective enterovirus replication and pathogenesis, and the results of this study begin to unravel the molecular cross talk between enterovirus infection and key cellular signaling networks.

Echovirus 1 infection induces both stress- and growth-activated mitogen-activated protein kinase pathways and regulates the transcription of cellular immediate-early genes

We have previously shown that echovirus 1 (EV1) infection increases the mRNA levels of cellular immediate-early (IE) genes in host cells. Here we provide further evidence that the induction of junB, c-jun, and c-fos genes is due to active viral macromolecular synthesis rather than to the interaction of EV1 with its receptor, alpha2beta1 integrin. Nuclear run-on transcription assays indicated that differences in mRNA levels in infected and uninfected cells are brought about by regulation at the transcriptional level. EV1 infection induced the phosphorylation of both the stress-related p38 mitogen-activated protein kinase (MAPK) and the growth signal-related ERK1/2 MAPKs. Studies with selective MAPK inhibitors revealed that p38 was the main inducer of junB expression, whereas both MAPK pathways were involved in the induction of c-fos. Activation of AP-1 genes was also observed to occur during infections with other enteroviruses and with Semliki Forest A7(74) virus, suggesting that the phosphorylation of MAPKs and induction of AP-1 gene expression may be important regulators of host cell behavior during viral infections.