Viral stimuli trigger exaggerated thymic stromal lymphopoietin expression by chronic obstructive pulmonary disease epithelium: role of endosomal TLR3 and cytosolic RIG-I-like helicases

BACKGROUND

Rhinovirus (RV)-induced chronic obstructive pulmonary disease (COPD) exacerbations exhibit TH(2)-like inflammation. We hypothesized that RV-infected bronchial epithelial cells (BEC) overproduce TH(2)-switching hub cytokine, thymic stromal lymphopoietin (TSLP) in COPD.

METHODS

Primary BEC from healthy (HBEC) and from COPD donors (COPD-BEC) were grown in 12-well plates, infected with RV16 (0.5-5 MOI) or stimulated with agonists for either toll-like receptor (TLR) 3 (dsRNA, 0.1-10 μg/ml) or RIG-I-like helicases (dsRNA-LyoVec, 0.1-10 μg/ml). Cytokine mRNA and protein were determined (RTqPCR; ELISA).

RESULTS

dsRNA dose-dependently evoked cytokine gene overproduction of TSLP, CXCL8 and TNF-α in COPD-BEC compared to HBEC. This was confirmed using RV16 infection. IFN-β induction did not differ between COPD-BEC and HBEC. Endosomal TLR3 inhibition by chloroquine dose-dependently inhibited dsRNA-induced TSLP generation and reduced generation of CXCL8, TNF-α, and IFN-β. Stimulation of cytosolic viral sensors (RIG-I-like helicases) with dsRNA-LyoVec increased production of CXCL8, TNF-α, and IFN-β, but not TSLP.

CONCLUSIONS

Endosomal TLR3-stimulation, by dsRNA or RV16, induces overproduction of TSLP in COPD-BEC. dsRNA- and RV-induced overproduction of TNF-α and CXCL8 involves endosomal TLR3 and cytosolic RIG-I-like helicases and so does the generation of IFN-β in COPD-BEC. RV16 and dsRNA-induced epithelial TSLP may contribute to pathogenic effects at exacerbations and development of COPD.

Engineered picornavirus VPg-RNA substrates: analysis of a tyrosyl-RNA phosphodiesterase activity

Using poliovirus, the prototypic member of Picornaviridae, we have further characterized a host cell enzymatic activity found in uninfected cells, termed "unlinkase," that recognizes and cleaves the unique 5' tyrosyl-RNA phosphodiester bond found at the 5' end of picornavirus virion RNAs. This bond connects VPg, a viral-encoded protein primer essential for RNA replication, to the viral RNA; it is cleaved from virion RNA prior to its engaging in protein synthesis as mRNA. Due to VPg retention on nascent RNA strands and replication templates, but not on viral mRNA, we hypothesize that picornaviruses utilize unlinkase activity as a means of controlling the ratio of viral RNAs that are translated versus those that either serve as RNA replication templates or are encapsidated. To test our hypothesis and further characterize this enzyme, we have developed a novel assay to detect unlinkase activity. We demonstrate that unlinkase activity can be detected using this assay, that this unique activity remains unchanged over the course of a poliovirus infection in HeLa cells, and that unlinkase activity is unaffected by the presence of exogenous VPg or anti-VPg antibodies. Furthermore, we have determined that unlinkase recognizes and cleaves a human rhinovirus-poliovirus chimeric substrate with the same efficiency as the poliovirus substrate.

The human rhinovirus: human-pathological impact, mechanisms of antirhinoviral agents, and strategies for their discovery

As the major etiological agent of the common cold, human rhinoviruses (HRV) cause millions of lost working and school days annually. Moreover, clinical studies proved an association between harmless upper respiratory tract infections and more severe diseases e.g. sinusitis, asthma, and chronic obstructive pulmonary disease. Both the medicinal and socio-economic impact of HRV infections and the lack of antiviral drugs substantiate the need for intensive antiviral research. A common structural feature of the approximately 100 HRV serotypes is the icosahedrally shaped capsid formed by 60 identical copies of viral capsid proteins VP1-4. The capsid protects the single-stranded, positive sense RNA genome of about 7,400 bases in length. Both structural as well as nonstructural proteins produced during the viral life cycle have been identified as potential targets for blocking viral replication at the step of attachment, entry, uncoating, RNA and protein synthesis by synthetic or natural compounds. Moreover, interferon and phytoceuticals were shown to protect host cells. Most of the known inhibitors of HRV replication were discovered as a result of empirical or semi-empirical screening in cell culture. Structure-activity relationship studies are used for hit optimization and lead structure discovery. The increasing structural insight and molecular understanding of viral proteins on the one hand and the advent of innovative computer-assisted technologies on the other hand have facilitated a rationalized access for the discovery of small chemical entities with antirhinoviral (anti-HRV) activity. This review will (i) summarize existing structural knowledge about HRV, (ii) focus on mechanisms of anti-HRV agents from synthetic and natural origin, and (iii) demonstrate strategies for efficient lead structure discovery.

Cytoplasmic relocalization of heterogeneous nuclear ribonucleoprotein A1 controls translation initiation of specific mRNAs

Heterogeneous nuclear ribonucleoprotein (hnRNP) A1 is a nucleocytoplasmic shuttling protein that regulates gene expression through its action on mRNA metabolism and translation. The cytoplasmic redistribution of hnRNP A1 is a regulated process during viral infection and cellular stress. Here, we show that hnRNP A1 is an internal ribosome entry site (IRES) trans-acting factor that binds specifically to the 5' untranslated region of both the human rhinovirus-2 and the human apoptotic peptidase activating factor 1 (apaf-1) mRNAs, thereby regulating their translation. Furthermore, the cytoplasmic redistribution of hnRNP A1 after rhinovirus infection leads to enhanced rhinovirus IRES-mediated translation, whereas the cytoplasmic relocalization of hnRNP A1 after UVC irradiation limits the UVC-triggered translational activation of the apaf-1 IRES. Therefore, this study provides a direct demonstration that IRESs behave as translational enhancer elements regulated by specific trans-acting mRNA binding proteins in given physiological conditions. Our data highlight a new way to regulate protein synthesis in eukaryotes through the subcellular relocalization of a nuclear mRNA-binding protein.

A diverse group of previously unrecognized human rhinoviruses are common causes of respiratory illnesses in infants

Background

Human rhinoviruses (HRVs) are the most prevalent human pathogens, and consist of 101 serotypes that are classified into groups A and B according to sequence variations. HRV infections cause a wide spectrum of clinical outcomes ranging from asymptomatic infection to severe lower respiratory symptoms. Defining the role of specific strains in various HRV illnesses has been difficult because traditional serology, which requires viral culture and neutralization tests using 101 serotype-specific antisera, is insensitive and laborious.

Methods and Findings

To directly type HRVs in nasal secretions of infants with frequent respiratory illnesses, we developed a sensitive molecular typing assay based on phylogenetic comparisons of a 260-bp variable sequence in the 5' noncoding region with homologous sequences of the 101 known serotypes. Nasal samples from 26 infants were first tested with a multiplex PCR assay for respiratory viruses, and HRV was the most common virus found (108 of 181 samples). Typing was completed for 101 samples and 103 HRVs were identified. Surprisingly, 54 (52.4%) HRVs did not match any of the known serotypes and had 12–35% nucleotide divergence from the nearest reference HRVs. Of these novel viruses, 9 strains (17 HRVs) segregated from HRVA, HRVB and human enterovirus into a distinct genetic group (“C”). None of these new strains could be cultured in traditional cell lines.

Conclusions

By molecular analysis, over 50% of HRV detected in sick infants were previously unrecognized strains, including 9 strains that may represent a new HRV group. These findings indicate that the number of HRV strains is considerably larger than the 101 serotypes identified with traditional diagnostic techniques, and provide evidence of a new HRV group.

Replication of poliovirus requires binding of the poly(rC) binding protein to the cloverleaf as well as to the adjacent C-rich spacer sequence between the cloverleaf and the internal ribosomal entry site

The 5' nontranslated region of poliovirus RNA contains two highly structured regions, the cloverleaf (CL) and the internal ribosomal entry site (IRES). A cellular protein, the poly(rC) binding protein (PCBP), has been reported to interact with the CL either alone or in combination with viral protein 3CD(pro). The formation of the ternary complex is essential for RNA replication and, hence, viral proliferation. PCBP also interacts with stem-loop IV of the IRES, an event critical for the initiation of cap-independent translation. Until recently, no special function was assigned to a spacer region (nucleotides [nt] 89 to 123) located between the CL and the IRES. However, on the basis of our discovery that this region strongly affects the neurovirulent phenotype of poliovirus, we have embarked upon genetic and biochemical analyses of the spacer region, focusing on two clusters of C residues (C(93-95) and C(98-100)) that are highly conserved among entero- and rhinoviruses. Replacement of all six C residues with A residues had no effect on translation in vitro but abolished RNA replication, leading to a lethal growth phenotype of the virus in HeLa cells. Mutation of the first group of C residues (C(93-95)) resulted in slower viral growth, whereas the C(98-100)A change had no significant effect on viability. Genetic analyses of the C-rich region by extensive mutagenesis and analyses of revertants revealed that two consecutive C residues (C(94-95)) were sufficient to promote normal growth of the virus. However, there was a distinct position effect of the preferred C residues. A 142-nt-long 5'-terminal RNA fragment including the CL and spacer sequences efficiently bound PCBP, whereas no PCBP binding was observed with the CL (nt 1 to 88) alone. Binding of PCBP to the 142-nt fragment was completely ablated after the two C clusters in the spacer were mutated to A clusters. In contrast, the same mutations had no effect on the binding of 3CD(pro) to the 142-nt RNA fragment. Stepwise replacement of the C residues with A residues resulted in impaired replication that covaried with weaker binding of PCBP in vitro. We conclude that PCBP has little, if any, binding affinity for the CL itself (nt 1 to 88) but requires additional nucleotides downstream of the CL for its function as an essential cofactor in poliovirus RNA replication. These data reveal a new essential function of the spacer between the CL and the IRES in poliovirus proliferation.

Pocket factors are unlikely to play a major role in the life cycle of human rhinovirus

Human rhinovirus 14 (HRV14) is a member of the rhinovirus genus, which belongs to the picornavirus family, which includes clinically and economically important members, such as poliovirus, foot-and-mouth disease virus, and endomyocarditis virus. Capsid stability plays an important role in the viral infection process, in that it needs to be stable enough to move from cell to cell and yet be able to release its genetic material upon the appropriate environmental cues from the host cell. It has been suggested that certain host cell molecules, "pocket factors," bind to the WIN drug-binding cavity beneath the canyon floor and provide transient stability to a number of the picornaviruses. To directly test this hypothesis, HRV14 was mutated in (V1188M, C1199W, and V1188M/C1199W) and around (S1223G) the drug-binding pocket. Infectivity, limited proteolysis, and matrix-assisted laser desorption ionization analyses indicate that filling the drug-binding pocket with bulky side chains is not deleterious to the viral life cycle and lends some stabilization to the capsid. In contrast, studies with the S1223G mutant suggest that this mutation at least partially overcomes WIN drug-mediated inhibition of cell attachment and capsid breathing. Finally, HRV16, which is inherently more stable than HRV14 in a number of respects, was found to "breathe" only at 37 degrees C and did not tolerate stabilizing mutations in the drug-binding cavity. These results suggest that it is the drug-binding cavity itself and not the putative pocket factor that is crucial for the capsid dynamics, which is, in turn, necessary for infection.

Corticosteroids and beta2 agonists differentially regulate rhinovirus-induced interleukin-6 via distinct Cis-acting elements

Interleukin-6 (IL-6) is a proinflammatory cytokine up-regulated by rhinovirus infection during acute exacerbations of asthma and chronic obstructive pulmonary disease. The role of IL-6 during exacerbations is unclear; however, it is believed IL-6 could contribute to airway and systemic inflammation. In this study we investigate the effects of common asthma treatments fluticasone propionate and beta(2) agonists salmeterol and salbutamol on IL-6 production in BEAS-2B and primary bronchial epithelial cells. Salmeterol and salbutamol enhanced rhinovirus- and IL-1beta-induced IL-6 production; however, fluticasone treatment caused a reduction of IL-6 protein and mRNA. Combined activity of salmeterol and fluticasone at equimolar concentrations had no effect on rhinovirus or IL-1beta induction of IL-6. The induction of IL-6 by salmeterol was dependent upon the beta(2) receptor and could also be induced by cAMP or cAMP-elevating agents forskolin and rolipram. Using transfection of IL-6 promoter reporter constructs, dominant negative mutants, and electromobility shift assays, it was found that NF-kappaB was the only transcription factor required for rhinovirus induction of IL-6 gene expression. Salmeterol caused an augmentation of rhinovirus-induced promoter activation via a mechanism dependent upon the c/EBP and/or CRE (cyclic AMP response element) cis-acting sites. The suppressive effect of FP was dependent upon distinct glucocorticoid response element sequences proximal to the transcriptional start site within the IL-6 promoter. The data demonstrate that beta(2) agonists can augment IL-6 expression by other stimuli in an additive manner via cyclic AMP and that the negative effect of steroids is mediated by glucocorticoid response elements within the IL-6 promoter.

Human rhinovirus type 54 infection via heparan sulfate is less efficient and strictly dependent on low endosomal pH

K-type major-group human rhinoviruses (HRVs) (including HRV54) share a prominent lysine residue in the HI surface loop of VP1 with all minor-group HRVs. Despite the presence of this residue, they cannot use members of the low-density lipoprotein receptor family for productive infection. Reexamining all K-type viruses for receptor usage, we noticed that HRV54 is able to replicate in RD cells that lack the major-group receptor intercellular adhesion molecule 1 (ICAM-1). By using receptor blocking assays, inhibition of sulfation, enzymatic digestion, and proteoglycan-deficient cell lines, we show here that wild-type HRV54, without any adaptation, uses heparan sulfate (HS) proteoglycan as an alternate receptor. However, infection via HS is less efficient than infection via ICAM-1. Moreover, HRV54 has an acid lability profile similar to that of the minor-group virus HRV2. In ICAM-1-deficient cells its replication is completely blocked by the H(+)-ATPase inhibitor bafilomycin A1, whereas in ICAM-1-expressing cells it replicates in the presence of the drug. Thus, use of a "noncatalytic" receptor requires the virus to be highly unstable at low pH.

Graph-Based Molecular Alignment (GMA)

We describe a combined 2D/3D approach for the superposition of flexible chemical structures, which is based on recent progress in the efficient identification of common subgraphs and a gradient-based torsion space optimization algorithm. The simplicity of the approach is reflected in its generality and computational efficiency: the suggested approach neither requires precalculated statistics on the conformations of the molecules nor does it make simplifying assumptions on the topology of the molecules being compared. Furthermore, graph-based molecular alignment produces alignments that are consistent with the chemistry of the molecules as well as their general structure, as it depends on both the local connectivities between atoms and the overall topology of the molecules. We validate this approach on benchmark sets taken from the literature and show that it leads to good results compared to computationally and algorithmically more involved methods. The results suggest that, for most practical purposes, graph-based molecular alignment is a viable alternative to molecular field alignment with respect to structural superposition and leads to structures of comparable quality in a fraction of the time.

The cold case: are rhinoviruses perfectly adapted pathogens?

Rhinoviruses, which cause common cold, belong to the Picornaviridae family, small non-enveloped viruses (diameter 15-30 nm) containing a single-stranded RNA genome (about 7 kb). Over 100 different rhinoviral serotypes have been identified thus far, establishing rhinoviruses as the most diverse group of Picornaviridae. Based on receptor binding properties, rhinoviruses are divided into two classes: the major group binding to intracellular adhesion molecule-1 and the minor group binding to the very low density lipoprotein receptors. Interactions between virus and the receptor molecules cause a conformational change in the capsid, which is a prerequisite for viral uptake. Rhinoviruses trigger a chemokine response upon infection that may lead to exacerbation of the symptoms of common cold, i.e. asthma and inflammation. The following review aims to summarize the knowledge about rhinoviral infections and discusses therapeutical approaches against this almost perfectly adapted pathogen.

Transforming growth factor-beta expression induced by rhinovirus infection in respiratory epithelial cells

Rhinovirus infection of the lower airways is now a recognized disease, associated with bronchiolitis and asthma. The bronchial epithelial cells are the host cells when rhinovirus infection occurs in the airway. It was hypothesized that a pro-fibrotic growth factor response may occur in these infected cells, leading to production of a key transforming growth factor, TGF-beta-1. Bronchial epithelial cells were inoculated with human rhinovirus and compared at day 1, 3 and 5 to control non-infected cells. Cell culture supernatant fluid and cellular RNA were isolated. The amount of released TGF-beta protein was measured by enzyme-linked immunosorbent assay (ELISA). Expression of TGF-beta at the level of transcription was measured by polymerase chain reaction (PCR) and gel electrophoresis. The results show that at all time points studied, TGF-beta production is greater in the infected cells, as demonstrated by ELISA (P<0.05) and by semi-quantitative PCR analysis. It was concluded that bronchial epithelial cells infected with common cold virus and rhinovirus, showed higher levels of TGF-beta. The production of TGF-beta may be indicative of a normal repair mechanism to counter inflammation, or in the setting of persistent asthma, could potentially lead to increased fibrosis and collagen deposition.

Nonneutralizing human rhinovirus serotype 2-specific monoclonal antibody 2G2 attaches to the region that undergoes the most dramatic changes upon release of the viral RNA

The monoclonal antibody 2G2 has been used extensively for detection and quantification of structural changes of human rhinovirus serotype 2 during infection. It recognizes exclusively A and B subviral particles, not native virus. We have elucidated the basis of this selectivity by determining the footprint of 2G2. Since viral escape mutants obviously cannot be obtained, the structures of complexes between Fab fragments of 2G2 and 80S subviral B particles were determined by cryoelectron microscopy. The footprint of the antibody corresponds to the capsid region that we predicted would undergo the most dramatic changes upon RNA release.

Role of deficient type III interferon-lambda production in asthma exacerbations

Rhinoviruses are the major cause of asthma exacerbations, and asthmatics have increased susceptibility to rhinovirus and risk of invasive bacterial infections. Here we show deficient induction of interferon-lambdas by rhinovirus in asthmatic primary bronchial epithelial cells and alveolar macrophages, which was highly correlated with severity of rhinovirus-induced asthma exacerbation and virus load in experimentally infected human volunteers. Induction by lipopolysaccharide in asthmatic macrophages was also deficient and correlated with exacerbation severity. These results identify previously unknown mechanisms of susceptibility to infection in asthma and suggest new approaches to prevention and/or treatment of asthma exacerbations.

The double-stranded RNA binding protein 76:NF45 heterodimer inhibits translation initiation at the rhinovirus type 2 internal ribosome entry site

Poliovirus (PV) plus-strand RNA genomes initiate translation in a cap-independent manner via an internal ribosome entry site (IRES) in their 5' untranslated region. Viral translation is codetermined by cellular IRES trans-acting factors, which can influence viral propagation in a cell-type-specific manner. Engineering of a poliovirus recombinant devoid of neuropathogenic properties but highly lytic in malignant glioma cells was accomplished by exchange of the cognate poliovirus IRES with its counterpart from human rhinovirus type 2 (HRV2), generating PV-RIPO. Neuroblast:glioma heterokaryon analyses revealed that loss of neurovirulence is due to trans-dominant repression of PV-RIPO propagation in neuronal cells. The double-stranded RNA binding protein 76 (DRBP76) was previously identified to bind to the HRV2 IRES in neuronal cells and to inhibit PV-RIPO translation and propagation (M. Merrill, E. Dobrikova, and M. Gromeier, J. Virol. 80:3347-3356, 2006). The results of size exclusion chromatography indicate that DRBP76 heterodimerizes with nuclear factor of activated T cells, 45 kDa (NF45), in neuronal but not in glioma cells. The DRBP76:NF45 heterodimer binds to the HRV2 IRES in neuronal but not in glioma cells. Ribosomal profile analyses show that the heterodimer preferentially associates with the translation apparatus in neuronal cells and arrests translation at the HRV2 IRES, preventing PV-RIPO RNA assembly into polysomes. Results of this study suggest that the DRBP76:NF45 heterodimer selectively blocks HRV2 IRES-driven translation initiation in neuron-derived cells.

Age-dependent poliovirus replication in the mouse central nervous system is determined by internal ribosome entry site-mediated translation

Mouse cells are not permissive for the replication of human rhinovirus type 2 (HRV2). To determine the role of the HRV2 internal ribosome entry site (IRES) in determining species specificity, a recombinant poliovirus (P1/HRV2) was constructed by substituting the poliovirus IRES with the IRES from HRV2. This recombinant virus replicated in all human and murine cell lines examined, demonstrating that the HRV2 IRES does not limit viral replication in transformed murine cells. P1/HRV2 replicated in the brain and spinal cord in neonatal but not adult mice transgenic for the poliovirus receptor, CD155. Passage of P1/HRV2 in mice led to selection of a virus that caused paralysis in neonatal mice. To determine the relationship between HRV2 IRES-mediated translation and replication of P1/HRV2 in mice, recombinant human adenoviruses were used to express bicistronic mRNAs in murine organs. The results demonstrate that the HRV2 IRES mediates translation in organs of neonatal but not adult mice. These findings show that HRV2 IRES-mediated translation is a determinant of virus replication in the murine brain and spinal cord and suggest that the IRES determines the species specificity of HRV2 infection.

Rhinoviral infections activate p38MAP-kinases via membrane rafts and RhoA

Rhinoviral infections belong to the most frequent human infections characterized by common cold, chronic bronchitis, exacerbations of asthma, otitis media and sinusitis. Here, we define molecular mechanisms that mediate infections of human epithelial cells with human rhinovirus strain 14 (RV14). We demonstrate that RV14 activates p38-MAPKinase (p38-K) in a biphasic time course. Early stimulation of p38-K by RV14 was observed a few minutes after initiation of the infection, while the late increase of p38-K activity occurred 7-12 hrs upon infection. The stimulation of p38-K was mediated by the small G-protein RhoA,which was activated by RV14. Transfection of a genetic construct preventing RhoA activation blocked RV14-induced p38-K activation. Further, integrity of cholesterol and sphingolipid-enriched membrane domains was required for RV14-mediated p38-K activation, which was inhibited by destruction of membrane rafts. The data indicate that RV employs a signaling cascade from membrane rafts via the small G-protein RhoA to p38-K to infect human cells.

Carbocisteine inhibits rhinovirus infection in human tracheal epithelial cells

The aim of the study was to examine the effects of a mucolytic drug, carbocisteine, on rhinovirus (RV) infection in the airways. Human tracheal epithelial cells were infected with a major-group RV, RV14. RV14 infection increased virus titres and the cytokine content of supernatants. Carbocisteine reduced supernatant virus titres, the amount of RV14 RNA in cells, cell susceptibility to RV infection and supernatant cytokine concentrations, including interleukin (IL)-6 and IL-8, after RV14 infection. Carbocisteine reduced the expression of mRNA encoding intercellular adhesion molecule (ICAM)-1, the receptor for the major group of RVs. It also reduced the supernatant concentration of a soluble form of ICAM-1, the number and fluorescence intensity of acidic endosomes in the cells before RV infection, and nuclear factor-kappaB activation by RV14. Carbocisteine also reduced the supernatant virus titres of the minor group RV, RV2, although carbocisteine did not reduce the expression of mRNA encoding a low density lipoprotein receptor, the receptor for RV2. These results suggest that carbocisteine inhibits rhinovirus 2 infection by blocking rhinovirus RNA entry into the endosomes, and inhibits rhinovirus 14 infection by the same mechanism as well as by reducing intercellular adhesion molecule-1 levels. Carbocisteine may modulate airway inflammation by reducing the production of cytokines in rhinovirus infection.

A mutation in the first ligand-binding repeat of the human very-low-density lipoprotein receptor results in high-affinity binding of the single V1 module to human rhinovirus 2

Minor group human rhinoviruses (HRVs) bind members of the low-density lipoprotein receptor family for cell entry. The ligand-binding domains of these membrane proteins are composed of various numbers of direct repeats of about 40 amino acids in length. Residues involved in binding of module 3 (V3) of the very-low-density lipoprotein receptor (VLDLR) to HRV2 have been identified by X-ray crystallography (N. Verdaguer, I. Fita, M. Reithmayer, R. Moser, and D. Blaas, Nat. Struct. Mol. Biol. 11:429-434, 2004). Sequence comparisons of the eight repeats of VLDLR with respect to the residues implicated in the interaction between V3 and HRV2 suggested that (in addition to V3) V1, V2, V5, and V6 also fulfill the requirements for interacting with the virus. Using a highly sensitive binding assay employing phage display, we demonstrate that single modules V2, V3, and V5 indeed bind HRV2. However, V1 does not. A single mutation from threonine 17 to proline converted the nonbinding wild-type form of V1 into a very strong binder. We interpret the dramatic increase in affinity by the generation of a hydrophobic patch between virus and receptor; in the presence of threonine, the contact area might be disturbed. This demonstrates that the interaction between virus and its natural receptors can be strongly enhanced by mutation.

Rhinoviruses promote internalisation of Staphylococcus aureus into non-fully permissive cultured pneumocytes

Respiratory viruses, including rhinoviruses, frequently promote bacterial opportunistic infections, through mechanisms that still deserve to be investigated in detail. This work was aimed at understanding how a viral infection mostly affecting the upper respiratory tract, such as the common cold, can repeatedly promote opportunistic infections in the lower airways, a site where viral replication is limited. The adhesivity and invasivity of Staphylococcus aureus were evaluated, in permissive and non-permissive cells, infected with Rhinovirus-1b. The role of inflammatory cytokines, and of ICAM-1 overexpression in the Rhinovirus-S. aureus cooperation was evaluated. Rhinovirus-1b enhanced the efficiency of internalisation of S. aureus irrespective of cellular permissivity, even when very low viral multiplicities of infection were used. Experiments performed with UV inactivated and heat inactivated viral particles suggested that this enhancement does not depend upon viral replication, but requires viral adhesion. Experimental data suggest that Rhinovirus-1b can significantly increase the ability of S. aureus to internalise into pneumocytes with a mechanism that involves the virus induced release of IL-6 and IL-8, and the overexpression of ICAM-1. Overall data disclose a possible mechanism through which rhinoviruses can promote bacterial infections in the lower respiratory tract.

The role of p38 MAPK in rhinovirus-induced monocyte chemoattractant protein-1 production by monocytic-lineage cells

Viral respiratory infections are a major cause of asthma exacerbations and can contribute to the pathogenesis of asthma. Major group human rhinovirus enters cells by binding to the cell surface molecule ICAM-1 that is present on epithelial and monocytic lineage cells. The focus of the resulting viral infection is in bronchial epithelia. However, previous studies of the cytokine dysregulation that follows rhinovirus infection have implicated monocytic lineage cells in establishing the inflammatory environment even though productive infection is not a result. We have determined that human alveolar macrophages and human peripheral blood monocytes release MCP-1 upon exposure to human rhinovirus 16 (HRV16). Indeed, we have found p38 MAPK activation in human alveolar macrophages within 15 min of exposure to HRV16, and this activation lasts up to 1 h. The targets of p38 MAPK activation include transcriptional activators of the MCP-1 promoter. The transcription factor ATF-2, a p38 MAPK substrate, is phosphorylated 45 min after HRV16 exposure. Furthermore, IkappaBalpha, the inhibitor of the transcription factor NF-kappaB, is degraded. Prevention of HRV16 binding was effective in blocking p38 MAPK activation, ATF-2 phosphorylation, and MCP-1 release. This is the first report of a relationship between HRV16 exposure, MCP-1 release and monocytic-lineage cells suggesting that MCP-1 plays a role in establishing the inflammatory microenvironment initiated in the human airway upon exposure to rhinovirus.

2-Ethoxybenzoxazole as a bioisosteric replacement of an ethyl benzoate group in a human rhinovirus (HRV) capsid binder

A series of pyridazinylpiperidinyl capsid-binding compounds with novel bicyclic substituents were synthesized and screened against human rhinovirus (HRV). Several 2-alkoxy- and 2-alkylthio-benzoxazole and benzothiazole derivatives showed excellent anti-HRV activity. When tested against a panel of 16 representative HRV types the 2-ethoxybenzoxazole derivative 13 was found to have superior HRV activity (median EC(50) 3.88ng/mL) to known capsid-binders Pleconaril and Pirodavir. Compound 13 illustrates that a 2-alkoxybenzoxazole group can be an effective bioisostere for a benzoate ester or benzaldehyde oxime ether functionality.

The minor receptor group of human rhinovirus (HRV) includes HRV23 and HRV25, but the presence of a lysine in the VP1 HI loop is not sufficient for receptor binding

Like all 10 minor receptor group human rhinoviruses (HRVs), HRV23 and HRV25, previously classified as major group viruses, are neutralized by maltose binding protein (MBP)-V33333 (a soluble recombinant concatemer of five copies of repeat 3 of the very-low-density lipoprotein receptor fused to MBP), bind to low-density lipoprotein receptor in virus overlay blots, and replicate in intercellular adhesion molecule 1 (ICAM-1)-negative COS-7 cells. From phylogenetic analysis of capsid protein VP1-coding sequences, they are also known to cluster together with other minor group strains. Therefore, they belong to the minor group; there are now 12 minor group and 87 major group HRV serotypes. Sequence comparison of the VP1 capsid proteins of all HRVs revealed that the lysine in the HI loop, strictly conserved in the 12 minor group HRVs, is also present in 9 major group serotypes that are neutralized by soluble ICAM-1. Despite the presence of this lysine, they are not neutralized by MBP-V33333 and fail to replicate in COS-7 cells and in HeLa cells in the presence of an ICAM-1-blocking antibody. These nine serotypes are therefore "true" major group viruses.

Dissociation of an antiviral compound from the internal pocket of human rhinovirus 14 capsid

WIN antiviral compounds bind human rhinovirus, as well as enterovirus and parechovirus, in an internal cavity located within the viral protein capsid. Access to the buried pocket necessitates deviation from the average viral protein structure identified by crystallography. We investigated the dissociation of WIN 52084 from the pocket in human rhinovirus 14 by using an adiabatic, biased molecular dynamics simulation method. Multiple dissociation trajectories are used to characterize the pathway. WIN 52084 exits between the polypeptide chain near the ends of betaC and betaH in a series of steps. Small, transient packing defects in the protein are sufficient for dissociation. A number of torsion-angle transitions of the antiviral compound are involved, which suggests that flexibility in antiviral compounds is important for binding. It is interesting to note that dissociation is associated with an increase in the conformational fluctuations of residues never in direct contact with WIN 52084 over the course of dissociation. These residues are N-terminal residues in the viral proteins VP3 and VP4 and are located in the interior of the capsid near the icosahedral 5-fold axis. The observed changes in dynamics may be relevant to structural changes associated with virion uncoating and its inhibition by antiviral compounds.

Rhinoviruses infect human epithelial cells via ceramide-enriched membrane platforms

The cell membrane contains very small distinct membrane domains enriched of sphingomyelin and cholesterol that are named rafts. We have shown that the formation of ceramide via activation of the acid sphingomyelinase transforms rafts into ceramide-enriched membrane platforms. These platforms are required for infection of mammalian cells with Pseudomonas aeruginosa, Staphylococcus aureus, or Neisseriae gonorrhoeae. In the present study we determined whether the acid sphingomyelinase, ceramide, and ceramide-enriched membrane platforms are also involved in the infection of human cells with pathogenic rhinoviruses. We demonstrate that infection of human epithelial cells with several rhinovirus strains triggers a rapid activation of the acid sphingomyelinase correlating with microtubules- and microfilament-mediated translocation of the enzyme from an intracellular compartment onto the extracellular leaflet of the cell membrane. The activity of the acid sphingomyelinase results in the formation of ceramide in the cell membrane and, finally, large ceramide-enriched membrane platforms. Rhinoviruses colocalize with ceramide-enriched membrane platforms during the infection. The significance of ceramide-enriched membrane platforms for rhinoviral uptake is demonstrated by the finding that genetic deficiency or pharmacological inhibition of the acid sphingomyelinase prevented infection of human epithelial cells by rhinoviruses. The data identify the acid sphingomyelinase and ceramide as key molecules for the infection of human cells with rhinoviruses.