Prevalence of neutralizing antibodies to Equine rhinitis A and B virus in horses and man.

Equine rhinitis viruses (ERVs) are the causative agents of mild to severe upper respiratory infections in horses worldwide. Immunologically, four serotypes of ERVs have been identified. Equine rhinitis A virus (ERAV) and Equine rhinitis B virus 1 (ERBV1) are the most frequent serotypes in Europe. Both viruses have a broad host range in cultured cells with ERAV being able to infect humans. Since there is neither information on the seroprevalence of ERAV and ERBV1 in Austria nor on the zoonotic potential of ERBV1, we investigated 200 horse and 137 veterinary sera for the presence of neutralizing antibodies relating to ERAV and ERBV1. One hundred and eighty (90%) and 173 (86%) horse sera neutralized ERAV and ERBV1, respectively. In contrast, only four (2.7%) and five (3.6%) human sera showed weak neutralizing activity to ERAV and ERBV1, respectively. These results indicate that ERAV and ERBV1 are widespread in the Austrian horse population; however, the risk of acquiring zoonotic infection among veterinarians appears low.

2A proteinase of human rhinovirus cleaves cytokeratin 8 in infected HeLa cells.

Rhino- and enteroviruses encode two proteinases, 2A and 3C, which are responsible for the processing of the viral polyprotein and for cleavage of several cellular proteins. To identify further targets of the 2A proteinase of human rhinovirus serotype 2 (HRV2), an in vitro cleavage assay followed by two-dimensional electrophoresis was employed. Cytokeratin 8, a member of the intermediate filament group of proteins, was found to be proteolytically cleaved in vitro by the 2A proteinase of HRV2 and of coxsackievirus B4 and in vivo during HRV2 infection of HeLa cells. The cleavage results in removal of 14 amino acids from the N-terminal head domain of cytokeratin 8. However, other intermediate filament proteins (cytokeratins 7 and 18 and vimentin) were not cleaved in the course of the HRV2 infection. Compared with the processing of the eucaryotic translation initiation factors 4GI and 4GII, cleavage of cytokeratin 8 occurs late in the infection cycle at the time of the onset of the cytopathic effect.

Rhinovirus 2A proteinase mediated stimulation of rhinovirus RNA translation is additive to the stimulation effected by cellular RNA binding proteins.

The internal ribosome entry site (IRES) of enteroviruses, and especially human rhinoviruses (HRV), functions very inefficiently in rabbit reticulocyte lysates, but can be stimulated by addition of HeLa cell extracts. Two HeLa cell activities have been identified: the A-type activity is due to polypyrimidine tract binding protein and the B-type to unr. In addition HRV and enterovirus IRES function requires a third RNA binding protein, poly(rC) binding protein 2, but this is present in reticulocyte lysates in non-limiting amounts. IRES activity can also be stimulated by the cleavage of initiation factor eIF4G mediated by either HRV 2A protease, or foot-and-mouth disease virus (FMDV) L protease. This raises the question of whether this stimulation is independent of that effected by the three RNA binding proteins, or whether cleaved eIF4G functionally mimics one or more of these proteins. It is shown here that the stimulation of HRV IRES activity resulting from cleavage of eIF4G is additive with the stimulation effected by HeLa cell A- and B-type activities. It is proposed that the role of the RNA binding proteins is to maintain or attain the appropriate 3-dimensional structure of the IRES RNA element, whereas the function of eIF4G is to deliver the 40S ribosomal subunit to the correct site on the IRES, a function which, for reasons not yet fully understood, is fulfilled more efficiently by the C-terminal cleavage product of eIF4G than by the intact factor.

Human major group rhinoviruses downmodulate the accessory function of monocytes by inducing IL-10.

Human rhinoviruses (HRVs) are the predominant cause of the common cold. Although this disease is per se rather harmless, HRV infection is considered to set the stage for more dangerous pathogens in vivo. Here we demonstrate that HRV-14, a member of the major group HRV family, can efficiently inhibit antigen-induced T-cell proliferation and T-cell responses to allogeneic monocytes. HRV-14 triggered a significant downregulation of MHC class II molecules on monocytes. Moreover, supernatants from monocytes cultured in the presence of HRV-14 strongly reduced the allogeneic T-cell stimulatory property of untreated monocytes and monocyte-derived dendritic cells (md-DCs), whereas Epstein Barr virus-transformed B-lymphoblastoid cells were not sensitive. Analysis of the supernatant revealed that HRV-14 induced the production of significant amounts of the immunosuppressive cytokine IL-10. The important T-cell stimulatory cytokine IL-12 or the proinflammatory cytokines IL-1beta or TNF-alpha were not detected or were only minimally detected. Finally, monocytes pretreated with HRV-14 were greatly inhibited in their production of IL-12 upon stimulation with IFN-gamma/LPS. These observations suggest that altered cytokine production in mononuclear phagocytes upon interaction with HRV downmodulates appropriate immune responses during the viral infection.

The structure of the 2A proteinase from a common cold virus: a proteinase responsible for the shut-off of host-cell protein synthesis.

The crystal structure of the 2A proteinase from human rhinovirus serotype 2 (HRV2-2A(pro)) has been solved to 1.95 A resolution. The structure has an unusual, although chymotrypsin-related, fold comprising a unique four-stranded beta sheet as the N-terminal domain and a six-stranded beta barrel as the C-terminal domain. A tightly bound zinc ion, essential for the stability of HRV2-2A(pro), is tetrahedrally coordinated by three cysteine sulfurs and one histidine nitrogen. The active site consists of a catalytic triad formed by His18, Asp35 and Cys106. Asp35 is additionally involved in an extensive hydrogen-bonding network. Modelling studies reveal a substrate-induced fit that explains the specificity of the subsites S4, S2, S1 and S1'. The structure of HRV2-2A(pro) suggests the mechanism of the cis cleavage and its release from the polyprotein.

The eIF4G-eIF4E complex is the target for direct cleavage by the rhinovirus 2A proteinase.

The 2A proteinases (2Apro) of certain picornaviruses induce the cleavage of the eIF4G subunit of the cap-binding protein complex, eIF4F. Several reports have demonstrated that 2Apro of rhinovirus and coxsackievirus B4 cleave eIF4G directly. However, it was suggested that in poliovirus infection, the 2Apro induces the activation of a cellular proteinase which in turn cleaves eIF4G. Furthermore, it is not clear whether eIF4G is cleaved as part of the eIF4F complex or as an individual polypeptide. To address these issues, recombinant eIF4G was purified from Sf9 insect cells and tested for cleavage by purified rhinovirus 2Apro. Here we report that eIF4G alone is a relatively poor substrate for cleavage by the rhinovirus 2Apro. However, an eIF4G-eIF4E complex is cleaved efficiently by the 2Apro, suggesting that eIF4F is a preferred substrate for cleavage by rhinovirus 2Apro. Furthermore, 2Apr drastically reduced the translation of a capped mRNA. An eIF4G-eIF4E complex, but not eIF4G alone, was required to restore translation.

Human rhinovirus 2A proteinase mutant and its second-site revertants.

The 2A proteinases of human rhinoviruses are cysteine proteinases with marked similarities to serine proteinases. In the absence of a three-dimensional structure, we developed a genetical screening system for proteolytic activity and identified Phe-130 as a key residue. The mutation Phe-130-->Tyr almost completely inhibited enzyme activity at 37 degrees C; activity was, however, partially restored by the following exchanges: Ser-27-->Pro, His-135-->Arg or His-137-->Arg. To investigate this phenotypic reversion, 2A proteinases with the mutations Phe-130-->Tyr, Phe-130-->Tyr/His-135-->Arg, Phe-130-->Tyr/His-137-->Arg, His-135-->Arg or His-137-->Arg were expressed in Escherichia coli and purified. None of these mutations affected the affinity of the enzyme for a peptide substrate. However, the temperature-dependence of enzyme activity, as assayed by cleavage of a peptide substrate and by monitoring the toxicity of the proteinases towards the E. coli strain BL21(DE3), and the structural stability, as monitored by 8-anilino-I-naphthalenesulphonic acid fluorescence and CD spectrometry, were affected. The thermal transition temperatures for both the activity and the stability of the Phe-130-->Tyr 2A proteinase were reduced by about 17 degrees C compared with the wild-type enzyme. The presence of the additional mutations His-135-->Arg or His-137-->Arg in the Phe-130-->Tyr mutant increased temperature stability by 3 degrees C and 6 degrees C respectively. Thus essential interactions exist within the C-terminal domain of human rhinoviral 2A proteinases which contribute to the overall stability and integrity of the enzyme.

Equine rhinovirus serotypes 1 and 2: relationship to each other and to aphthoviruses and cardioviruses.

Equine rhinoviruses (ERVs) are picornaviruses which cause a mild respiratory infection in horses. The illness resembles the common cold brought about by rhinoviruses in humans; however, the presence of a viraemia during ERV-1 infection, the occurrence of persistent infections and the physical properties are all more reminiscent of foot-and-mouth disease virus (FMDV). cDNA cloning and sequencing of the genomes of ERV-1 and ERV-2 between the poly(C) and poly(A) tracts showed that the serotypes are heterogeneous. Nevertheless, the genomic architecture of both serotypes is most similar to that of FMDV. Indeed, a comparison of the derived protein sequences of ERV-1 shows that their identity is greatest to FMDV. In contrast, most ERV-2 proteins are more related to encephalomyocarditis virus (EMCV) proteins than they are to FMDV or ERV-1. These results place ERV-1 alongside FMDV in the aphthovirus genus of the picornavirus family and indicate that this virus may serve as a model system for examining the biology of FMDV.

Proteolytically active 2A proteinase of human rhinovirus 2 is toxic for Saccharomyces cerevisiae but does not cleave the homologues of eIF-4 gamma in vivo or in vitro.

During the replication of rhino- and enteroviruses, the translation initiation factor elF-4 gamma is specifically cleaved by the virally encoded 2 A proteinase. This cleavage has been proposed to lead to the inability of the host cell to translate its own capped mRNA and to stimulate internal initiation of protein synthesis from the viral mRNA. However, a direct causal relationship between these effects and 2A proteinase-mediated cleavage of elF-4 gamma has remained difficult to prove, mainly because of the toxicity of the 2A proteinase in mammalian expression systems. As an alternative approach, we placed the cDNA sequences for the human rhinovirus 2 2A proteinase and two mutants defective in proteolytic activity under the control of an inducible yeast Gal1-10 promoter and stably integrated them into the yeast genome. Induction of the wildtype enzyme led to changes in cellular morphology, an inhibition of cell division activity, and finally to cell death. As the yeast homologues of mammalian elF-4 gamma, p150 and p130, were shown to be refractory to cleavage by human rhinovirus 2A proteinase both in vivo and in vitro and the rate of protein synthesis was unaffected, the toxicity of the 2A proteinase toward budding yeast must be due to its interaction with at least one other cellular protein essential for viability.

Picornavirus 2A proteinase-mediated stimulation of internal initiation of translation is dependent on enzymatic activity and the cleavage products of cellular proteins.

Poliovirus and human rhinovirus 2A proteinases are known to stimulate translation initiation on the cognate viral Internal Ribosome Entry Segments (IRESes). The molecular mechanism of this translational transactivation was investigated in vitro using dicistronic mRNAs containing picornaviral IRESes as the intercistronic spacer and purified human rhinovirus type 2 and coxsackievirus B4 2A proteinases. The stimulation achieved on the HRV2 IRES in the presence of the cognate 2A proteinase at 1 microgram/ml was twofold; the maximum stimulation at 100 micrograms/ml was fivefold. The IRESes and proteinases from rhino- and enteroviruses were interchangeable; however, stimulation of translation initiation on a cardiovirus IRES by these proteinases was minimal. Studies using an inhibitor or a mutant 2A proteinase demonstrated that translation stimulation requires 2A-mediated enzymatic conversion of some cellular component(s). The HRV2 2A proteinase also stimulated translation initiation on full-length viral RNA, suggesting that 2A proteinase-mediated stimulation of IRES-driven translation has a physiological role.

Avian homologs of the mammalian low-density lipoprotein receptor family bind minor receptor group human rhinovirus.

Avian oocyte-specific very low density lipoprotein receptor specifically binds human rhinovirus of the minor receptor group on ligand blots and in solution. The solubilized receptor protects cell against infection in a dose-dependent manner.

An antibody fragment from a phage display library competes for ligand binding to the low density lipoprotein receptor family and inhibits rhinovirus infection.

Recently antibodies with a wide range of binding specificities have been isolated from large repertoires of antibody fragments displayed on filamentous phage, including those that are difficult to raise by immunization. We have used this approach to isolate an antibody fragment against chicken very low density lipoprotein (VLDL) receptor. It binds to the receptor with good affinity (Kaff = 2 x 10(8) M-1) as measured by plasmon surface resonance, and competes for binding of natural ligands (vitellogenin, VLDL, and receptor-associated protein). The antibody also binds to other members of the low density lipoprotein (LDL) receptor family including rat LDL receptor and human and rat low density lipoprotein receptor-related protein (LRP/alpha 2MR), and it competes for binding of receptor-associated protein to LRP/alpha 2MR. Moreover, the antibody fragment inhibits infection of human fibroblasts deficient in LDL-R but expressing LRP/alpha 2MR by human rhinovirus. Binding of the antibody is abolished upon reduction of the receptors and is strictly Ca2+ dependent. The phage antibody thus recognizes the ligand binding site(s) of several members of the LDL receptor family, in contrast to antibodies produced by hybridoma technology.

Rhinovirus-mediated endosomal release of transfection complexes.

Endocytosis is an efficient method for transfer of genes into mammalian cells. Incorporation of adenovirus particles into gene transfer complexes greatly enhances gene delivery, probably by the release of endocytosed DNA into the cytoplasm. We report here that two different serotypes of human rhinovirus (HRV), HRV2 and HRV14, are also able to enhance receptor-mediated gene transfer. The effect of several compounds known to inhibit viral infection on HRV2- and HRV14-enhanced transfection was examined. WIN I(s) and WIN IV, two compounds which inhibit viral uncoating, had different effects on HRV2- and HRV14-enhanced gene transfer to NIH 3T3 cells. While HRV14-enhanced gene transfer was severely reduced in the presence of these compounds, virtually no effects were observed when HRV2 was used. The use of antiviral compounds thus allowed transfection of human cells, which are normally lysed rapidly upon infection with HRV. Viral activity could be mimicked by using a peptide derived from the N terminus of VP1 of HRV2. This peptide possesses pH-dependent membrane-disrupting activity and enhances gene transfer to NIH 3T3 and HeLa cells.

Uncoating of human rhinovirus serotype 2 from late endosomes.

The internalization pathway and mechanism of uncoating of human rhinovirus serotype 2 (HRV2), a minor-group human rhinovirus, were investigated. Kinetic analysis revealed a late endosomal compartment as the site of capsid modification from D to C antigenicity. The conformational change as well as the infection was prevented by the specific V-ATPase inhibitor bafilomycin A1. A requirement for ATP was also demonstrated with purified endosomes in vitro. Capsid modifications occurred at a pH of 5.5 regardless of whether the virus was entrapped in isolated endosomes or free in solution. These findings suggest that the receptor is not directly involved in the structural modification of HRV2. Viral particles found in purified endosomes of infected cells were mostly devoid of RNA. This supports the hypothesis that uncoating of HRV2 occurs in intact endosomes rather than by a mechanism involving endosomal disruption with subsequent release of the RNA into the cytoplasm.

Members of the low density lipoprotein receptor family mediate cell entry of a minor-group common cold virus.

A protein binding to a minor-group human rhinovirus (HRV2) was purified from HeLa cell culture supernatant. The amino acid sequences of tryptic peptides showed identity with the human low density lipoprotein (LDL) receptor (LDLR). LDL and HRV2 mutually competed for binding sites on human fibroblasts. Cells down-regulated for LDLR expression yielded much less HRV2 upon infection than cells with up-regulated LDLR. Virus also bound to the large subunit of the alpha 2-macroglobulin receptor/LDLR-related protein (alpha 2MR/LRP). LDLR-deficient fibroblasts yielded considerably less virus in the presence of receptor-associated protein (RAP), providing evidence that alpha 2MR/LRP also acts as a minor group HRV receptor.

2A proteinases of coxsackie- and rhinovirus cleave peptides derived from eIF-4 gamma via a common recognition motif.

The cleavage specificities of the 2A proteinases from coxsackievirus B4 (CVB4) and human rhinovirus 2 (HRV2) on oligopeptide substrates have been determined. Comparison of the specificity of CVB4 2A proteinase with that of HRV2 2A proteinase allowed cleavable peptides to be designed using the common motif IIe/Leu-X-Thr-X*Gly; little resemblance to the viral cleavage site remained. The data also allowed the prediction of three possible cleavage sites for 2A proteinases on eIF-4 gamma; two peptides derived from these sequences were cleaved by both 2A proteinases. One of these peptides corresponds to the cleavage site for 2A proteinases mapped on eIF-4 gamma [B. J. Lamphear et al. (1993) J. Biol. Chem. 268, 19200-19203]. This supports the hypothesis that cleavage of eIF-4 gamma by picornaviral 2A proteinases occurs directly.

Rhinoviral receptor discrimination: mutational changes in the canyon regions of human rhinovirus types 2 and 14 indicate a different site of interaction.

Amino acid sequence comparisons between the capsid proteins of several human rhinovirus (HRV) serotypes identified residues potentially involved in the discrimination between the major and the minor group receptors. Amino acids conserved within minor group HRVs were substituted in a full-length cDNA clone of HRV2 for those found at equivalent positions in major group HRVs. Transfection of HeLa cells with RNAs transcribed from seven individual mutated cDNAs gave rise to only two viable viruses; growth characteristics and affinity for the minor group receptor of both were unchanged compared to wild-type. Similar mutations in HRV14 were previously shown to alter the affinity for its receptor; the contact sites between the minor group viruses and the respective receptor may therefore be different.

Mapping the cleavage site in protein synthesis initiation factor eIF-4 gamma of the 2A proteases from human Coxsackievirus and rhinovirus.

The rate-limiting step of eukaryotic protein synthesis is the binding of mRNA to the 40 S ribosomal subunit, a step which is catalyzed by initiation factors of the eIF-4 (eukaryotic initiation factor 4) group: eIF-4A, eIF-4B, eIF-4E, and eIF-4 gamma. Infection of cells with picornaviruses of the rhino- and enterovirus groups causes a shut-off in translation of cellular mRNAs but permits viral RNA translation to proceed. This change in translational specificity is thought to be mediated by proteolytic cleavage of eIF-4 gamma, which is catalyzed, directly or indirectly, by the picornaviral 2A protease. In this report we have used highly purified recombinant 2A protease from either human Coxsackievirus serotype B4 or rhinovirus serotype 2 to cleave eIF-4 gamma in vitro in the eIF-4 complex purified from rabbit reticulocytes. Neither the rate of cleavage nor fragment sizes were affected by addition of eIF-3. The NH2- and COOH-terminal fragments of eIF-4 gamma were separated by reverse phase HPLC and identified with specific antibodies, and the NH2-terminal sequence of the COOH-terminal fragment was determined by automated Edman degradation. The cleavage site for both proteases is 479GRPALSSR decreases GPPRGGPG494 in rabbit eIF-4 gamma, corresponding to 478GRTTLSTR decreases GPPRGGPG493 in human eIF-4 gamma.

Cleavage specificity on synthetic peptide substrates of human rhinovirus 2 proteinase 2A.

Proteinase 2A of human rhinovirus serotype 2 (HRV2 2A) was expressed in Escherichia coli and partially purified; the preparation was used to study various enzymatic parameters. Using a 16-amino acid peptide representing the native cleavage region of HRV2 2A, an apparent Km value of 5.4 x 10(-4) mol/liter was determined. A minimum of 9 amino acids (comprising residues P8 to P1') was necessary for cleavage to occur. Proteolysis of substituted peptides was highly tolerant toward changes at P1, P2', and P3' but an absolute requirement for glycine P1' and a high preference for threonine P2 was found. Furthermore, HRV2 2A only cleaved peptide substrates derived from other rhinovirus serotypes and poliovirus that possessed P2 Thr and P1' Gly. Thus, the sequence Thr-X-Gly may form the basis of the cellular cleavage site processed by rhinoviral 2As during viral replication. Studies with various inhibitors support the hypothesis that HRV2 2A belongs to a new class of cysteine proteinases.