Interaction of decay-accelerating factor with coxsackievirus B3

Many entero-, parecho-, and rhinoviruses use immunoglobulin (Ig)-like receptors that bind into the viral canyon and are required to initiate viral uncoating during infection. However, some of these viruses use an alternative or additional receptor that binds outside the canyon. Both the coxsackievirus-adenovirus receptor (CAR), an Ig-like molecule that binds into the viral canyon, and decay-accelerating factor (DAF) have been identified as cellular receptors for coxsackievirus B3 (CVB3). A cryoelectron microscopy reconstruction of a variant of CVB3 complexed with DAF shows full occupancy of the DAF receptor in each of 60 binding sites. The DAF molecule bridges the canyon, blocking the CAR binding site and causing the two receptors to compete with one another. The binding site of DAF on CVB3 differs from the binding site of DAF on the surface of echoviruses, suggesting independent evolutionary processes.     

Single amino acid modification of adeno-associated virus capsid changes transduction and humoral immune profiles

Adeno-associated virus (AAV) vectors have the potential to promote long-term gene expression. Unfortunately, humoral immunity restricts patient treatment and in addition provides an obstacle to the potential option of vector readministration. In this study, we describe a comprehensive characterization of the neutralizing antibody (NAb) response to AAV type 1 (AAV1) through AAV5 both in vitro and in vivo. These results demonstrated that NAbs generated from one AAV type are unable to neutralize the transduction of other types. We extended this observation by demonstrating that a rationally engineered, muscle-tropic AAV2 mutant containing 5 amino acid substitutions from AAV1 displayed a NAb profile different from those of parental AAV2 and AAV1. Here we found that a single insertion of Thr from AAV1 into AAV2 capsid at residue 265 preserved high muscle transduction, while also changing the immune profile. To better understand the role of Thr insertion at position 265, we replaced all 20 amino acids and evaluated both muscle transduction and the NAb response. Of these variants, 8 mutants induced higher muscle transduction than AAV2. Additionally, three classes of capsid NAb immune profile were defined based on the ability to inhibit transduction from AAV2 or mutants. While no relationship was found between transduction, amino acid properties, and NAb titer or its cross-reactivity, these studies map a critical capsid motif involved in all steps of AAV infectivity. Our results suggest that AAV types can be utilized not only as templates to generate mutants with enhanced transduction efficiency but also as substrates for repeat administration.     

Interaction with decay-accelerating factor facilitates coxsackievirus B infection of polarized epithelial cells

All coxsackie B (CB) viruses can initiate infection by attaching to the coxsackievirus and adenovirus receptor (CAR). Although some CB isolates also bind to decay-accelerating factor (DAF), the role of DAF interaction during infection remains uncertain. We recently observed that CAR in polarized epithelial cells is concentrated at tight junctions, where it is relatively inaccessible to virus. In the experiments reported here we found that, unlike CAR, DAF was present on the apical surface of polarized cells and that DAF-binding isolates of CB3 and CB5 infected polarized epithelial cells more efficiently than did isolates incapable of attaching to DAF. Virus attachment and subsequent infection of polarized cells by DAF-binding isolates were prevented in the presence of anti-DAF antibody. Serial passage on polarized cell monolayers selected for DAF-binding virus variants. Taken together, these results indicate that interaction with DAF on the apical surface of polarized epithelial cells facilitates infection by a subset of CB virus isolates. The results suggest a possible role for DAF in infection of epithelial cells at mucosal surfaces.     

Interaction with coxsackievirus and adenovirus receptor, but not with decay-accelerating factor (DAF), induces A-particle formation in a DAF-binding coxsackievirus B3 isolate

Although many coxsackie B viruses interact with decay accelerating factor (DAF), attachment to DAF by itself is not sufficient to initiate infection. We examined the early events in infection that follow virus interaction with DAF, and with the coxsackievirus and adenovirus receptor (CAR). Interaction with soluble CAR in a cell-free system, or with CAR on the surfaces of transfected cells, induced the formation of A particles; interaction with soluble or cell surface DAF did not. The results suggest that CAR, but not DAF, is capable of initiating the conformational changes in the viral capsid that lead to release of viral nucleic acid.     

Identification of a single amino acid residue in the capsid protein VP1 of coxsackievirus B4 that determines the virulent phenotype.

To identify the molecular determinants of virulence for coxsackievirus B4, a panel of recombinant, chimeric viruses were constructed from cDNA clones of a virulent virus, CB4-V, and a nonvirulent virus, CB4-P. Initial studies mapped a major determinant of virulence to the 5' end of the viral genome, which contained the 5' untranslated and the P1 regions (A. Ramsingh, A. Hixson, B. Duceman, and J. Slack, J. Virol. 64:3078-3081, 1990). To determine whether the 5' untranslated region contributed to the virulent phenotype, a chimeric virus (vCB403) containing this region of the virulent virus on an avirulent background was tested in mice. The vCB403 construct displayed a phenotype similar to that of CB4-P, suggesting that the 5' untranslated region did not significantly contribute to virulence. Analysis of the sequence data of the P1 regions of both CB4-V and CB4-P revealed five mutations that resulted in amino acid substitutions in VP1, VP2, and VP4 (A. Ramsingh, H. Araki, S. Bryant, and A. Hixson, Virus Res. 23:281-292, 1992). Analysis of individual mutations in both VP1 and VP2 revealed that a single residue (Thr-129 of VP1) determined the virulent phenotype.     

Novel role for decay-accelerating factor in coxsackievirus A21-mediated cell infectivity

Decay-accelerating factor (DAF) is involved in the cell membrane attachment of many human enteroviruses. Presently, further specific active roles of DAF in mediating productive cell infection and in the pathogenesis of natural enterovirus infection are poorly understood. In an attempt to more fully understand the role of DAF in lytic cell infection we examined the specific interactions of the prototype strain of coxsackievirus A21 (CVA21) with surface-expressed DAF. Investigations into discrete DAF-CVA21 interactions focused on viral binding; viral particle elution with respect to the parameters of time, temperature, and pH; and subsequent cell infection. Radiolabeled-virus binding assays revealed that peak elution of CVA21 from DAF occurred within 15 min of initial attachment and that the DAF-eluted virus increased in a linear fashion with respect to temperature and pH. CVA21 eluted from endogenous surface-expressed DAF was highly infectious, in contrast to CVA21 eluted from intercellular adhesion molecule 1 (ICAM-1), which retained little to no infectivity. Using an adenovirus transduction system, we demonstrate that CVA21 can remain infectious for up to 24 h after DAF binding and is capable of initiating a multicycle lytic infection upon delayed ICAM-1 surface expression. Taken together, the data suggest that a major role of DAF in cell infection by the prototype strain of CVA21 is to provide membrane concentration of infectious virions, effectively increasing viral interactions with endogenous or induced ICAM-1.     

Single amino acid changes in the Nipah and Hendra virus attachment glycoproteins distinguish ephrinB2 from ephrinB3 usage

The henipaviruses, Nipah virus (NiV) and Hendra virus (HeV), are lethal emerging paramyxoviruses. EphrinB2 and ephrinB3 have been identified as receptors for henipavirus entry. NiV and HeV share similar cellular tropisms and likely use an identical receptor set, although a quantitative comparison of receptor usage by NiV and HeV has not been reported. Here we show that (i) soluble NiV attachment protein G (sNiV-G) bound to cell surface-expressed ephrinB3 with a 30-fold higher affinity than that of sHeV-G, (ii) NiV envelope pseudotyped reporter virus (NiVpp) entered ephrinB3-expressing cells much more efficiently than did HeV pseudotyped particles (HeVpp), and (iii) NiVpp but not HeVpp entry was inhibited efficiently by soluble ephrinB3. These data underscore the finding that NiV uses ephrinB3 more efficiently than does HeV. Henipavirus G chimeric protein analysis implicated residue 507 in the G ectodomain in efficient ephrinB3 usage. Curiously, alternative versions of published HeV-G sequences show variations at residue 507 that can clearly affect ephrinB3 but not ephrinB2 usage. We further defined surrounding mutations (W504A and E505A) that diminished ephrinB3-dependent binding and viral entry without compromising ephrinB2 receptor usage and another mutation (E533Q) that abrogated both ephrinB2 and -B3 usage. Our results suggest that ephrinB2 and -B3 binding determinants on henipavirus G are distinct and dissociable. Global expression analysis showed that ephrinB3, but not ephrinB2, is expressed in the brain stem. Thus, ephrinB3-mediated viral entry and pathology may underlie the severe brain stem neuronal dysfunction seen in fatal Nipah viral encephalitis. Characterizing the determinants of ephrinB2 versus -B3 usage will further our understanding of henipavirus pathogenesis.     

A single amino acid substitution in the capsid of foot-and-mouth disease virus can increase acid resistance

Foot-and-mouth disease virus (FMDV) particles lose infectivity due to their disassembly at pH values slightly below neutrality. This acid-dependent disassembly process is required for viral RNA release inside endosomes. To study the molecular determinants of viral resistance to acid-induced disassembly, six FMDV variants with increased resistance to acid inactivation were isolated. Infection by these mutants was more sensitive to drugs that raise the endosomal pH (NH(4)Cl and concanamycin A) than was infection by the parental C-S8c1 virus, confirming that the increase in acid resistance is related to a lower pH requirement for productive uncoating. Amino acid replacement N17D at the N terminus of VP1 capsid protein was found in all six mutants. This single substitution was shown to be responsible for increased acid resistance when introduced into an infectious FMDV clone. The increased resistance of this mutant against acid-induced inactivation was shown to be due to its increased resistance against capsid dissociation into pentameric subunits. Interestingly, the N17D mutation was located close to but not at the interpentamer interfaces. The mutants described here extend the panel of FMDV variants exhibiting different pH sensitivities and illustrate the adaptive flexibility of viral quasispecies to pH variations.     

A decay-accelerating factor-binding strain of coxsackievirus B3 requires the coxsackievirus-adenovirus receptor protein to mediate lytic infection of rhabdomyosarcoma cells.

The composition of the cellular receptor complex for coxsackievirus B3 (CVB3) has been an area of much contention for the last 30 years. Recently, two individual components of a putative CVB3 cellular receptor complex have been identified as (i) decay-accelerating factor (DAF) and (ii) the coxsackievirus-adenovirus receptor protein (CAR). The present study elucidates the individual roles of DAF and CAR in cell entry of CVB3 Nancy. First, we confirm that the DAF-binding phenotype of CVB3 correlates to the presence of key amino acids located in the viral capsid protein, VP2. Second, using antibody blockade, we show that complete protection of permissive cells from infection by high input multiplicities of CVB3 requires a combination of both anti-DAF and anti-CAR antibodies. Finally, it is shown that expression of the CAR protein on the surface of nonpermissive DAF-expressing RD cells renders them highly susceptible to CVB3-mediated lytic infection. Therefore, although the majority of CVB3 Nancy attaches to the cell via DAF, only virus directly interacting with the CAR protein mediates lytic infection. The role of DAF in CVB3 cell infection may be analogous to that recently described for coxsackievirus A21 (D. R. Shafren, D. J. Dorahy, R. A. Ingham, G. F. Burns, and R. D. Barry, J. Virol. 71:4736-4743, 1997), in that DAF may act as a CVB3 sequestration site, enhancing viral presentation to the functional CAR protein.     

Coxsackievirus B3 adapted to growth in RD cells binds to decay-accelerating factor (CD55).

A coxsackievirus B3 (CB3) isolate adapted to growth in RD cells shows an alteration in cell tropism as a result of its capacity to bind a 70-kDa cell surface molecule expressed on these cells. We now show that this molecule is the complement regulatory protein, decay-accelerating factor (DAF) (CD55). Anti-DAF antibodies prevented CB3 attachment to the cell surface. Radiolabeled CB3 adapted to growth in RD cells bound to CHO cells transfected with human DAF, whereas CB3 (strain Nancy), the parental strain, did not bind to DAF transfectants. These results indicate that growth of CB3 in RD cells selected for a virus strain that uses DAF for cell surface attachment.     

Trace element changes in the myocardium during coxsackievirus B3 myocarditis in the mouse

During most infections plasma, concentrations of trace elements change, but it is unclear if this reflects changes in infected target tissues. In coxsackievirus B3 (CB3) infection, the myocardium is a target in both humans and mice. The concentrations of 12 trace elements were analyzed by inductively coupled plasma-mass spectrometry (ICP-MS) in the myocardium of sham-inoculated controls and infected A/J mice 4 and 7 d postinoculation. The size of the inflammatory lesion was positively correlated to the virus content of the heart, as estimated by histopathology and in situ hybridization, respectively. Iron, cobalt, vanadium, and selenium showed transient changes, whereas for the other elements, tendencies on d 4 were manifest on d 7. A threefold increase in calcium on d 7 suggests prestages of calcification, whereas increases in zinc, selenium, and copper may be the result of the accumulation of immune cells. The magnesium decrease may contribute to the increased sensitivity to cardiac arrhythmias in myocarditis.     

Variations of coxsackievirus B3 capsid primary structure, ligands, and stability are selected for in a coxsackievirus and adenovirus receptor-limited environment

While group B coxsackieviruses (CVB) use the coxsackievirus and adenovirus receptor (CAR) as the receptor through which they infect susceptible cells, some CVB strains are known for their acquired capacity to bind other molecules. The CVB3/RD strain that emerged from a CVB3/Nancy population sequentially passaged in the CAR-poor RD cell line binds decay-accelerating factor (DAF) (CD55) and CAR. A new strain, CVB3/RDVa, has been isolated from RD cells chronically infected with CVB3/RD and binds multiple molecules in addition to DAF and CAR. The capsid proteins of CVB3/RD differ from those of CVB3/28, a cloned strain that binds only CAR, by only four amino acids, including a glutamate/glutamine dimorphism in the DAF-binding region of the capsid. The capsid proteins of CVB3/RD and CVB3/RDVa differ by seven amino acids. The ability of CVB3/RDVa to bind ligands in addition to CAR and DAF may be attributed to lysine residues near the icosahedral 5-fold axes of symmetry. Considered with differences in the stability of the CVB3 strains, these traits suggest that in vitro selection in a CAR-limited environment selects for virus populations that can associate with molecules on the cell surface and survive until CAR becomes available to support infection.     

A subfamily of Dr adhesins of Escherichia coli bind independently to decay-accelerating factor and the N-domain of carcinoembryonic antigen

Escherichia coli expressing the Dr family of adhesins adheres to epithelial cells by binding to decay-accelerating factor (DAF) and carcinoembryonic antigen (CEA)-related cell surface proteins. The attachment of bacteria expressing Dr adhesins to DAF induces clustering of DAF around bacterial cells and also recruitment of CEA-related cell adhesion molecules. CEA, CEACAM1, and CEACAM6 have been shown to serve as receptors for some Dr adhesins (AfaE-I, AfaE-III, DraE, and DaaE). We demonstrate that AfaE-I, AfaE-V, DraE, and DaaE adhesins bind to the N-domain of CEA. To identify the residues involved in the N-CEA/DraE interaction, we performed SPR binding analyses of naturally occurring variants and a number of randomly generated mutants in DraE and N-CEA. Additionally, we used chemical shift mapping by NMR to determine the surface of DraE involved in N-CEA binding. These results show a distinct CEA binding site located primarily in the A, B, E, and D strands of the Dr adhesin. Interestingly, this site is located opposite to the beta-sheet encompassing the previously determined binding site for DAF, which implies that the adhesin can bind simultaneously to both receptors on the epithelial cell surface. The recognition of CEACAMs from a highly diverse DrCEA subfamily of Dr adhesins indicates that interaction with these receptors plays an important role in niche adaptation of E. coli strains expressing Dr adhesins.     

Sex chromosome complement contributes to sex differences in coxsackievirus B3 but not influenza A virus pathogenesis

Background

Both coxsackievirus B3 (CVB3) and influenza A virus (IAV; H1N1) produce sexually dimorphic infections in C57BL/6 mice. Gonadal steroids can modulate sex differences in response to both viruses. Here, the effect of sex chromosomal complement in response to viral infection was evaluated using four core genotypes (FCG) mice, where the Sry gene is deleted from the Y chromosome, and in some mice is inserted into an autosomal chromosome. This results in four genotypes: XX or XY gonadal females (XXF and XYF), and XX or XY gonadal males (XXM and XYM). The FCG model permits evaluation of the impact of the sex chromosome complement independent of the gonadal phenotype.

Methods

Wild-type (WT) male and female C57BL/6 mice were assigned to remain intact or be gonadectomized (Gdx) and all FCG mice on a C57BL/6 background were Gdx. Mice were infected with either CVB3 or mouse-adapted IAV, A/Puerto Rico/8/1934 (PR8), and monitored for changes in immunity, virus titers, morbidity, or mortality.

Results

In CVB3 infection, mortality was increased in WT males compared to females and males developed more severe cardiac inflammation. Gonadectomy suppressed male, but increased female, susceptibility to CVB3. Infection with IAV resulted in greater morbidity and mortality in WT females compared with males and this sex difference was significantly reduced by gonadectomy of male and female mice. In Gdx FCG mice infected with CVB3, XY mice were less susceptible than XX mice. Protection correlated with increased CD4+ forkhead box P3 (FoxP3)+ T regulatory (Treg) cell activation in these animals. Neither CD4+ interferon (IFN)γ (T helper 1 (Th1)) nor CD4+ interleukin (IL)-4+ (Th2) responses differed among the FCG mice during CVB3 infection. Infection of Gdx FCG mice revealed no effect of sex chromosome complement on morbidity or mortality following IAV infection.

Conclusions

These studies indicate that sex chromosome complement can influence pathogenicity of some, but not all, viruses.     

Single amino acid changes can influence titer, heparin binding, and tissue tropism in different adeno-associated virus serotypes

Despite the high degree of sequence homology between adeno-associated virus (AAV) serotype 1 and 6 capsids (99.2%), these viruses have different liver transduction profiles when tested as vectors. Examination of the six amino acid residues that differ between AAV1 and AAV6 revealed that a lysine-to-glutamate change (K531E) suppresses the heparin binding ability of AAV6. In addition, the same mutation in AAV6 reduces transgene expression to levels similar to those achieved with AAV1 in HepG2 cells in vitro and in mouse liver following portal vein administration. In corollary, the converse E531K mutation in AAV1 imparts heparin binding ability and increases transduction efficiency. Extraction of vector genomes from liver tissue suggests that the lysine 531 residue assists in preferential transduction of parenchymal cells by AAV6 vectors in comparison with AAV1. Lysine 531 is unique to AAV6 among other known AAV serotypes and is located in a basic cluster near the spikes that surround the icosahedral threefold axes of the AAV capsid. Similar to studies with autonomous parvoviruses, this study describes the first example of single amino acid changes that can explain differential phenotypes such as viral titer, receptor binding, and tissue tropism exhibited by closely related AAV serotypes. In particular, a single lysine residue appears to provide the critical minimum charged surface required for interacting with heparin through electrostatic interaction and simultaneously plays an unrelated yet critical role in the liver tropism of AAV6 vectors.     

Interactions between Sindbis virus RNAs and a 68 amino acid derivative of the viral capsid protein further defines the capsid binding site.

In previous studies of encapsidation of Sindbis virus RNA, we identified a 570nt fragment (nt 684-1253) from the 12 kb genome that binds to the viral capsid protein with specificity and is required for packaging of Sindbis virus defective interfering RNAs. We now show that the capsid binding activity resides in a highly structured 132nt fragment (nt 945-1076). We had also demonstrated that a 68 amino acid peptide derived from the capsid protein retained most of the binding activity of the original protein and have now developed an RNA mobility shift assay with this peptide fused to glutathione-S-transferase. We have used this assay in conjunction with the original assay in which the intact capsid protein was immobilized on nitrocellulose to analyze more extensive deletions in the 132-mer. All of the deletions led to a reduction in binding, but the binding of a 5' 67-mer was enhanced by the addition of nonspecific flanking sequences. This result suggests that the stability of a particular structure within the 132nt sequence may be important for capsid recognition.     

Morphological changes in the T=3 capsid of Flock House virus during cell entry

We report the identification and characterization of a viral intermediate formed during infection of Drosophila cells with the nodavirus Flock House virus (FHV). We observed that even at a very low multiplicity of infection, only 70% of the input virus stayed attached to or entered the cells, while the remaining 30% of the virus eluted from cells after initial binding. The eluted FHV particles did not rebind to Drosophila cells and, thus, could no longer initiate infection by the receptor-mediated entry pathway. FHV virus-like particles with the same capsid composition as native FHV but containing cellular RNA also exhibited formation of eluted particles when incubated with the cells. A maturation cleavage-defective mutant of FHV, however, did not. Compared to na?ve FHV particles, i.e., particles that had never been incubated with cells, eluted particles showed an acid-sensitive phenotype and morphological alterations. Furthermore, eluted particles had lost a fraction of the internally located capsid protein gamma. Based on these results, we hypothesize that FHV eluted particles represent an infection intermediate analogous to eluted particles observed for members of the family Picornaviridae.