Mutations in the Fusion Protein Cleavage Site of Avian Paramyxovirus Serotype 2 Increase Cleavability and Syncytium Formation but Do Not Increase Viral Virulence in Chickens

Virginia-Maryland Regional College of Veterinary Medicine, University of Maryland, College Park, MD 20742, USA.
Journal of Virology (Impact Factor: 4.44). 03/2011; 85(11):5394-405. DOI: 10.1128/JVI.02696-10
Source: PubMed


Avian paramyxovirus serotype 2 (APMV-2) is one of the nine serotypes of APMV, which infect a wide variety of avian species around the world. In this study, we constructed a reverse genetics system for recovery of infectious recombinant APMV-2 strain Yucaipa (APMV-2/Yuc) from cloned cDNA. The rescued recombinant virus (rAPMV-2) resembled the biological virus in growth properties in vitro and in pathogenicity in vivo. The reverse genetics system was used to analyze the role of the cleavage site of the fusion (F) protein in viral replication and pathogenesis. The cleavage site of APMV-2/Yuc (KPASR↓F) contains only a single basic residue (position -1) that matches the preferred furin cleavage site [RX(K/R)R↓]. (Underlining indicates the basic amino acids at the F protein cleavage site, and the arrow indicates the site of cleavage.) Contrary to what would be expected for this cleavage sequence, APMV-2 does not require, and is not augmented by, exogenous protease supplementation for growth in cell culture. However, it does not form syncytia, and the virus is avirulent in chickens. A total of 12 APMV-2 mutants with F protein cleavage site sequences derived from APMV serotypes 1 to 9 were generated. These sites contain from 1 to 5 basic residues. Whereas a number of these cleavage sites are associated with protease dependence and lack of syncytium formation in their respective native viruses, when transferred into the APMV-2 backbone, all of them conferred protease independence, syncytium formation, and increased replication in cell culture. Examination of selected mutants during a pulse-chase experiment demonstrated an increase in F protein cleavage compared to that for wild-type APMV-2. Despite the gains in cleavability, replication, and syncytium formation, analysis of viral pathogenicity in 9-day-old embryonated chicken eggs, 1-day-old chicks, and 2-week-old chickens showed that the F protein cleavage site mutants did not exhibit increased pathogenicity and remained avirulent. These results imply that structural features in addition to the cleavage site play a major role in the cleavability of the F protein and the activity of the cleaved protein. Furthermore, cleavage of the F protein is not a determinant of APMV-2 pathogenicity in chickens.

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Available from: Sunil K Khattar, May 19, 2015

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Article: Mutations in the Fusion Protein Cleavage Site of Avian Paramyxovirus Serotype 2 Increase Cleavability and Syncytium Formation but Do Not Increase Viral Virulence in Chickens

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    • "(Panda et al., 2004a; Peeters et al., 1999; Romer–Oberdörfer et al., 2006). There had been reports to throw more light on this aspect, suggesting that there would be proteins other than F that contributes to pathogenicity of NDV (Kommers et al., 2003; De Leeuw et al., 2003; Wakamatsu et al., 2006a; Subbiah et al., 2011). "

    Advances in Animal and Veterinary Sciences 01/2014; 2(3s):40-48.
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    • "A recent study with an avirulent avian paramyxovirus serotype 2 (APMV-2) virus showed that this virus does not require exogenous protease supplementation for growth in cell culture. In addition, recombinant APMV-2 viruses in which the cleavage site was replaced by that of APMV serotypes 1 to 9 gained in cleavability, replication and syncytium formation in infected cells, but remained avirulent for chickens [66]. Also, a recombinant NDV LaSota virus (NDFLtag), containing a velogenic cleavage site motif, showed an increase in virulence after one passage in chicken brain as determined by an increase in ICPI from 1.3 to 1.7, while sequence analysis of the entire F gene did not show any mutations [67]. "
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