Relationships and host range of human, canine, simian and porcine isolates of simian virus 5 (parainfluenza virus 5) Sequence comparison of the V/P and F genes of 13 human, canine, porcine and simian isolates of simian virus 5 (SV5) revealed a surprising lack of sequence variation at both the nucleotide and amino acid levels (0-3 %), even though the viruses were isolated over 30 years and originated from countries around the world. Furthermore, there were no clear distinguishing amino acid or nucleotide differences among the isolates that correlated completely with the species from which they were isolated. In addition, there was no evidence that the ability of the viruses to block interferon signalling by targeting STAT1 for degradation was confined to the species from which they were isolated. All isolates had an extended cytoplasmic tail in the F protein, compared with the original W3A and WR monkey isolates. Sequence analysis of viruses that were derived from human bone-marrow cells isolated in London in the 1980s revealed that, whilst they were related more closely to one another than to the other isolates, they all had identifying differences, suggesting that they were independent isolates. These results therefore support previous data suggesting that SV5 can infect humans persistently, although the relationship of SV5 to any human disease remains highly contentious. Given that SV5 has been isolated on multiple occasions from different species, it is proposed that the term simian virus 5 is inappropriate and suggested that the virus should be renamed parainfluenza virus 5. INTRODUCTIONSimian virus type 5 (SV5) is in the genus Rubulavirus of the subfamily Paramyxovirinae of the family Paramyxoviridae. SV5 was first isolated from rhesus and cynomolgus monkey kidney-cell cultures and two of the original monkey isolates are referred to as WR and W3A (Hull et al., 1956;Choppin, 1964). It was thus thought initially that monkeys were the natural host for SV5, but epidemiological studies in the 1960s showed that wild monkeys do not have antibodies against the virus. However, these animals seroconvert in captivity and, on this basis, it was suggested that infection of monkeys occurs either in transit or shortly after contact with humans (Tribe, 1966;Atoynatan & Hsiung, 1969;Hsiung, 1972). Indeed, Tribe (1966) suggested that monkeys that were brought into captivity should be immunized immediately against SV5 to prevent them being infected with the virus. There is also experimental evidence supporting the contention that SV5 naturally infects humans (Hsiung, 1972; Goswami et al., 1984). For example, SV5 has been isolated on numerous occasions from a variety of human tissues, including bone-marrow cells (Goswami et al., 1984). Despite this, infection of humans with SV5 has remained a subject of some debate and controversy, fuelled by the fact that SV5 can contaminate primary monkey kidney-cell cultures (and other cell lines), which are commonly used to isolate viruses from clinical samples (Chanock et al., 1961;Hsiung...
Thogoto virus (THOV) is a tick-transmitted orthomyxovirus with a genome of six negative-stranded RNA segments. The sixth segment encodes two different transcripts: a spliced transcript that is translated into the matrix protein (M) and an unspliced transcript. Here, we report that the unspliced transcript encodes an elongated form of M named ML. A THOV isolate deficient in ML expression was an efficient interferon inducer, whereas ML-expressing wild-type strains were poor interferon inducers. These results were confirmed with recombinant THOVs rescued from cDNAs. Expression of ML efficiently suppressed activation of the beta interferon promoter by double-stranded RNA. These results indicate that ML is an accessory protein that functions as a potent interferon antagonist by blocking transcriptional activation of alpha/beta interferons.
The V protein of the paramyxovirus Nipah virus (NiV) has been shown to antagonize the interferon (IFN) response in human cells via sequestration of STAT1 and STAT2. This study describes a mutant of the NiV V protein, referred to as V(AAHL), that is unable to antagonize IFN signalling and demonstrates that a single amino acid substitution is responsible for its inactivity. The molecular basis for this was identified as a failure to interact with STAT1 and STAT2. It was also shown that NiV V, but not V(AAHL), was functional as an IFN antagonist in human, monkey, rabbit, dog, horse, pig and bat cells, which suggests that the ability of NiV to block IFN signalling is not a major constraint that prevents this virus from crossing species barriers.
Whilst screening various cell lines for their ability to respond to interferon (IFN), we noted that in comparison to other tissue culture cells AGS tumour cells, which are widely used in biomedical research, had very low levels of STAT1. Subsequent analysis showed that the reason for this is that AGS cells are persistently infected with parainfluenza virus type 5 (PIV5; formally known as SV5), a virus that blocks the interferon (IFN) response by targeting STAT1 for proteasome-mediated degradation. Virus protein expression in AGS is altered in comparison to the normal pattern of virus protein synthesis observed in acutely infected cells, suggesting that the AGS virus is defective. We discuss the relevance of these results in terms of the need to screen cell lines for persistent virus infections that can alter cellular functions.
Mapuera virus (MPRV) is a paramyxovirus that was originally isolated from bats, but its host range remains unknown. It was classified as a member of the genus Rubulavirus on the basis of structural and genetic features. Like other rubulaviruses it encodes a V protein (MPRV/V) that functions as an interferon (IFN) antagonist. Here we show that MPRV/V differs from the IFN antagonists of other rubulaviruses in that it does not induce the proteasomal degradation of STAT proteins, key factors in the IFN signalling cascade. Rather, MPRV/V prevents the nuclear translocation of STATs in response to IFN stimulation and inhibits the formation of the transcription factor complex ISGF3. We also show that MPRV/V blocks IFN signalling in cells from diverse mammalian species and discuss the IFN response as a barrier to cross-species infections.
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