Genomic and phylogenetic characterization of coxsackievirus B2 prototype strain Ohio-1

Pathogenesis of coxsackievirus B2 in mice: characterization of clinical isolates of the coxsackievirus B2 from patients with myocarditis and aseptic meningitis in Korea

Group B coxsackieviruses (CVBs) are a group of common human pathogens producing various clinical symptoms. Although the virology of CVB is well known, there is limited information on viral pathogenesis and the relationship between clinical symptoms and viral phenotype, particularly for CVB type 2 (CVB2). In 2004 in Korea, two CVB2 strains were isolated: CB2/04/279 from stool of an acute myocarditis patient with heart failure and CB2/04/243 from an aseptic meningitis patient. In this study, a high degree of homology was observed between the CB2/04/279 and CB2/04/243 full genome sequences. The two Korean CVB2 isolates had 93.1% homology compared to 82.1%-82.5% nucleotide sequence identity with the cardiovirulence-associated reference CVB strain Ohio-1 (CVB/O). CVB2-induced pathogenesis was analyzed, focusing on virus-induced pathology of various tissues in 4-week-old BALB/c inbred male mice. Myocarditis developed and extensive pancreatic inflammation was observed in all mice infected with CB2/04/279 or CVB/O, but not in animals infected with CB2/04/243. This is the first report of the full-genomic sequence and pathogenesis of the CVB2 strain isolated from an acute myocarditis patient in Korea.

Study of Coxsackie B viruses interactions with Coxsackie Adenovirus receptor and Decay-Accelerating Factor using Human CaCo-2 cell line

Background

Decay Accelerating Factor (DAF) and Coxsackievirus-Adenovirus Receptor (CAR) have been identified as cellular receptors for Coxsackie B viruses (CV-B). The aim of this study is to elucidate the different binding properties of CV-B serotypes and to find out if there are any amino acid changes that could be associated to the different phenotypes.

Twenty clinical CV-B isolates were tested on CaCo-2 cell line using anti-DAF (BRIC216) and anti-CAR (RmcB) antibodies. CV-B3 Nancy prototype strain and a recombinant strain (Rec, CV-B3/B4) were tested in parallel. The P1 genomic region of 12 CV-B isolates from different serotypes was sequenced and the Trans-Epithelial Electrical Resistance (TEER) along with the virus growth cycle was measured.

Results

Infectivity assays revealed clear differences between CV-B isolates with regard to their interactions with DAF and CAR. All tested CV-B isolates showed an absolute requirement for CAR but varied in their binding to DAF. We also reported that for some isolates of CV-B, DAF attachment was not adapted. Genetic analysis of the P1 region detected multiple differences in the deduced amino acid sequences.

Conclusion

Within a given serotype, variations exist in the capacity of virus isolates to bind to specific receptors, and variants with different additional ligands may arise during infection in humans as well as in tissue culture.

A single coxsackievirus B2 capsid residue controls cytolysis and apoptosis in rhabdomyosarcoma cells

Coxsackievirus B2 (CVB2), one of six human pathogens of the group B coxsackieviruses within the enterovirus genus of Picornaviridae, causes a wide spectrum of human diseases ranging from mild upper respiratory illnesses to myocarditis and meningitis. The CVB2 prototype strain Ohio-1 (CVB2O) was originally isolated from a patient with summer grippe in the 1950s. Later on, CVB2O was adapted to cytolytic replication in rhabdomyosarcoma (RD) cells. Here, we present analyses of the correlation between the adaptive mutations of this RD variant and the cytolytic infection in RD cells. Using reverse genetics, we identified a single amino acid change within the exposed region of the VP1 protein (glutamine to lysine at position 164) as the determinant for the acquired cytolytic trait. Moreover, this cytolytic virus induced apoptosis, including caspase activation and DNA degradation, in RD cells. These findings contribute to our understanding of the host cell adaptation process of CVB2O and provide a valuable tool for further studies of virus-host interactions.

5' terminal deletions in the genome of a coxsackievirus B2 strain occurred naturally in human heart

Enteroviruses can induce human myocarditis, which can be modeled in mice inoculated with group B coxsackieviruses (CVB) and in which CVB evolve to produce defective, terminally deleted genomes. The 5' non-translated region (NTR) was enzymatically amplified from heart tissue of a fatal case of enterovirus-associated myocarditis in Japan in 2002. While no intact 5' viral genomic termini were detected, 5' terminal deletions ranged in size from 22 to 36 nucleotides. Sequence of the 5' third of this viral genome is of a modern strain, closely related to CVB2 strains isolated in Japan in 2002. A CVB3 chimera containing the 5' NTR with a 22 nt deletion produced progeny virus upon transfection of HeLa cells. When the 5' 22 nucleotide deletion was repaired, the virus induced myocarditis in mice and replicated like wild type virus in murine heart cells. This is the first report of these naturally-occurring defective enteroviral genomes in human myocarditis.

Replication of Ljungan virus in cell culture: The genomic 5′-end, infectious cDNA clones and host cell response to viral infections

Ljungan virus (LV) is a picornavirus recently isolated from bank voles (Clethrionomys glareolus). The previously uncharacterised 5'-end sequence of the LV genome was determined. Infectious cDNA clones were constructed of the wild type LV prototype strain 87-012 and of the cytolytically replicating cell culture adapted variant 87-012G. Virus generated from cDNA clones showed identical growth characteristics as uncloned virus stocks. Cell culture adapted LV, 87-012G, showed a clear cytopathic effect (CPE) at 3-4 days post-infection (p.i.). Virus titers, determined by plaque titration, increased however only within the first 18h p.i. Replication of LV (+) strand RNA was determined by real-time PCR and corresponded in time with increasing titers. In contrast, the amounts of the replication intermediate, the (-) strand, continued to increase until the cells showed CPE. This indicates separate controlling mechanisms for replication of LV (+) and (-) genome strands. Replication was also monitored by immunofluorescence (IF) staining. IF staining of both prototype 87-012 and the CPE causing 87-012G showed groups of 5-25 infected cells at 48h p.i., suggesting a, for picornaviruses, not previously described direct cell-to-cell transmission.

Cytolytic replication of coxsackievirus B2 in CAR-deficient rhabdomyosarcoma cells

The six coxsackievirus B serotypes (CVB1-6) use the coxsackie- and adenovirus receptor (CAR) for host cell entry. Four of these serotypes, CVB1, 3, 5 and 6, have also shown the capacity to replicate and cause cytolysis in rhabdomyosarcoma (RD) cells, a CAR-deficient cell line. This extended tropism has been associated with an acquired ability to bind decay accelerating factor (DAF). In this study, we have adapted the CVB2 prototype strain Ohio-1 (CVB2/O) to replicate in RD cells. Two types of infection were identified: (I) an enterovirus-typical, lytic infection, and (II) a non-lytic infection. Both CVB2/O-RD variants retained the prototype-ability to cause cytopathic effect in HeLa cells using CAR as receptor. Phenotypic and genotypic changes in the CVB2/O-RD-variants were determined and compared to the prototype cultured in HeLa cells. Inhibition studies using antibodies against CAR and DAF revealed a maintained ability of the CVB2/O-RD-variants to bind CAR, but no binding to DAF was observed. In addition, neither the prototype nor the CVB2/O-RD-variants were able to cause hemagglutination in human red blood cells, an enterovirus feature associated with affinity for DAF. Sequence analysis of the CVB2/O-RD-variants showed acquired mutations in the capsid region, suggesting extended receptor usage towards an alternative, yet unidentified, receptor for CVB2.

Evolution of the genome of Human enterovirus B: incongruence between phylogenies of the VP1 and 3CD regions indicates frequent recombination within the species

Enteroviruses show a high degree of sequence variation both between and within serotypes due to the lack of proofreading of the viral RNA-dependent RNA polymerase. In addition, recombination is known to occur not only within but also between different serotypes. We have previously shown that capsid coding sequences of coxsackievirus B4 (CVB4) cluster in several coexisting genotypes (intergenotypic nucleotide difference of 12 % or more) whereas a single lineage of echovirus 30 (EV30) has been prevailing and evolving throughout the last two decades. In the major capsid gene, VP1, clustering of both nucleotide and amino acid sequences correlates with serotype. We have now determined a 501 nucleotide sequence in the non-structural 3CD region of CVB4 and EV30 field strains. Phylogenetic analysis revealed that sequences of Human enterovirus B (HEV-B) were segregated in the 3CD region into three distinct clusters without the VP1-associated serotype/genotype correlation. One of the clusters comprised the E2 strain of CVB4, the EV30 prototype and five other CVB4 field strains whereas the other two clusters, in addition to CVB4 and EV30 strains, also included other HEV-B serotypes. We believe that intertypic recombination is the most likely explanation for the observed incongruence. Similarity analysis based on complete genomes of the CVB4 and EV30 prototypes and the CVB4 E2 strain revealed that a putative recombination spot was mapped within the 2B gene. The incongruence observed in the two genomic domains (P1 and P3) suggests a certain degree of independent evolution, which may be explained by interserotypic recombination within an enterovirus species. It is thus difficult to exclude recombination in the history of any given strain.

Molecular analysis of the echovirus 18 prototype: evidence of interserotypic recombination with echovirus 9

Echovirus 18 (EV18) is one of the echovirus serotypes associated with human diseases and in particular aseptic meningitis. To facilitate studies of the molecular epidemiology of EV18 and the evolution of enteroviruses in general, the complete nucleotide (nt) sequence was determined for the echovirus 18 prototype strain (Metcalf, EV18M). Excluding the poly A sequence, the genome consists of 7410 nt divided into a 740 nt 5' untranslated region (5' UTR), a 6567 nt long open reading frame coding for a 2189 amino acid (aa) polyprotein and a 103 nt 3' UTR. Molecular analysis of the EV18M genome showed a typical enterovirus-like organization. Phylogenetic analysis of the structural and non-structural genes revealed a pattern of different relationships to other echo- and coxsackieviruses. Similarity analysis demonstrated that the Hill strain of echovirus 9 is most likely the result of a previous recombination event between ancestors of the echovirus 9 strain Barty (5' half of the genome) and EV18M (3' half). Using a maximum likelihood approach, the recombination point was mapped to the 2C gene.

Genetic characterization of the coxsackievirus B2 3' untranslated region

The secondary structure of the 3' untranslated region (3'UTR) of picornaviruses is thought to be important for the initiation of negative-strand RNA synthesis. In this study, genetic and biological analyses of the 3' terminus of coxsackievirus B2 (CVB2), which differs from other enteroviruses due to the presence of five additional nucleotides prior to the poly(A) tail, is reported. The importance of this extension was investigated using a 3'UTR mutant lacking the five nucleotides prior to the poly(A) tail and containing two point mutations. The predicted secondary structure within the 3'UTR of this mutant was less energetically favourable compared with that of the wild-type (wt) genotype. This mutant clone was transfected into green monkey kidney cells in four parallel experiments and propagated for multiple passages, enabling the virus to establish a stable revertant genotype. Genetic analysis of the virus progeny from these different passages revealed two major types of revertant. Both types showed wt-like growth properties and more stable and wt-like predicted secondary structures than the parent mutant clone. The first type of revertant neutralized the introduced point mutation with a compensatory second-site mutation, whereas the second type of revertant partly compensated for the deletion of the five proximal nucleotides by the insertion of nucleotides that matched the wt sequence. Therefore, the extended 3' end of CVB2 may be considered to be a stabilizing sequence for RNA secondary structure and an important feature for the virus.

A point mutation in VP1 of coxsackievirus B4 alters antigenicity

While coxsackievirus infections have been linked to several autoimmune diseases, very little is known about the immunogenicity of the coxsackieviruses. Using two genetically related variants of coxsackievirus B4, CB4-P and CB4-V, the relationship between virulence and antigenicity was examined. The virulent variant, CB4-V, was shown to be more antigenic than the avirulent CB4-P variant. The increased antigenicity of CB4-V was due to a single amino acid substitution in the VP1 capsid protein (a threonine residue at amino acid position 129), a site that had been previously identified as a major determinant of viral virulence. Thr-129 of VP1 is predicted to lie within a conformational B cell epitope. In addition, a nearby linear B cell epitope spanning residues 68 to 82 of VP1 was identified as a potential serotype-specific, neutralization antigenic site. The linear and conformational B cell epitopes of coxsackievirus B4 may be analogous to antigenic sites 1 and 1B of poliovirus. To address whether the increased antigenicity of CB4-V influenced the severity of disease, mouse strains that differ in their outcome to viral infection were analyzed. Mice that developed the most severe disease and succumbed to infection were more immunoresponsive than mice that survived infection with CB4-V. The data suggest that immune-mediated mechanisms play a role in the severity of CB4-V induced disease.

The complete consensus sequence of coxsackievirus B6 and generation of infectious clones by long RT-PCR

The full length sequence for the human pathogen coxsackievirus B6 (CVB6, Schmitt strain) has been determined. We used long RT-PCR to generate full length DNA amplicon of CVB6, and then directly sequenced the amplicons. One-step cloning of the full length amplicon enabled us to obtain an infectious clone of CVB6. RNA generated from CVB6 amplicon DNA or CVB6 clones, by transcription with T7 RNA polymerase, was demonstrated to be infectious upon transfection into HeLa cells in vitro. The CVB6 genome is characteristic of enteroviruses, with a 5'-non-translated region (743 nucleotides) followed by an open reading frame (encoding a 2184 amino acid polyprotein) and a 3'-non-translated region (100 nucleotides) and polyadenylated tail. The predicted amino acid sequence of CVB6 clustered with the other CVB serotypes and swine vesicular disease virus (SVDV).