Porcine Epidemic Diarrhea Virus 3C-Like Protease-Mediated Nucleocapsid Processing: Possible Link to Viral Cell Culture Adaptability.
Porcine epidemic diarrhea virus (PEDV) causes severe diarrhea and high mortality rates in newborn piglets, leading to massive losses to the swine industry worldwide during recent epidemics. Intense research efforts are now focusing on defining viral characteristics that confer a growth advantage, pathogenicity, or cell adaptability in order to better understand the PEDV life cycle and identify suitable targets for antiviral or vaccine development. Here, we report a unique phenomenon of PEDV nucleocapsid (N) cleavage by the PEDV-encoded 3C-like protease (3Cpro) during infection. The identification of the 3Cpro cleavage site at the C terminus of N supported previous observations that PEDV 3Cpro showed a substrate requirement slightly different from that of severe acute respiratory syndrome coronavirus (SARS-CoV) 3Cpro and revealed a greater flexibility in its substrate recognition site. This cleavage motif is present in the majority of cell culture-adapted PEDV strains but is missing in emerging field isolates. Remarkably, reverse-genetics-derived cell culture-adapted PEDVAVCT12harboring uncleavable N displayed growth retardation in Vero E6-APN cells compared to the wild-type virus. These observations altogether shed new light on the investigation and characterization of the PEDV nucleocapsid protein and its possible link to cell culture adaptation.


OBJECTIVE
Recurrent PEDV outbreaks have resulted in enormous economic losses to swine industries worldwide. To gain the upper hand in combating this disease, it is necessary to understand how this virus replicates and evades host immunity. Characterization of viral proteins provides important clues to mechanisms by which viruses survive and spread. Here, we characterized an intriguing phenomenon in which the nucleocapsids of some PEDV strains are proteolytically processed by the virally encoded main protease. Growth retardation in recombinant PEDV carrying uncleavable N suggests a replication advantage provided by the cleavage event, at least in the cell culture system. These findings may direct us to a more complete understanding of PEDV replication and pathogenicity.
Virology and Cell Technology Laboratory, National Center for Genetic Engineering and Biotechnology (BIOTEC), National Science and Technology Development Agency, Pathumthani, Thailand.
Peera
P
Jaru-Ampornpan
Virology and Cell Technology Laboratory, National Center for Genetic Engineering and Biotechnology (BIOTEC), National Science and Technology Development Agency, Pathumthani, Thailand.|Norwich Medical School, University of East Anglia, Norfolk, United Kingdom.
Juggragarn
J
Jengarn
Virology and Cell Technology Laboratory, National Center for Genetic Engineering and Biotechnology (BIOTEC), National Science and Technology Development Agency, Pathumthani, Thailand.
Asawin
A
Wanitchang
Virology and Cell Technology Laboratory, National Center for Genetic Engineering and Biotechnology (BIOTEC), National Science and Technology Development Agency, Pathumthani, Thailand anan.jon@biotec.or.th.
Anan
A
Jongkaewwattana
D000595:Amino Acid Sequence; D000818:Animals; D018929:Cell Culture Techniques; D002522:Chlorocebus aethiops; D018352:Coronavirus Infections / Q000821:virology; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D016679:Genome, Viral; D019251:Nucleocapsid / Q000737:chemistry / Q000378:metabolism*; D053485:Porcine epidemic diarrhea virus / Q000502:physiology*; D059748:Proteolysis; D013552:Swine; D013553:Swine Diseases / Q000821:virology; D014709:Vero Cells; D014764:Viral Proteins / Q000378:metabolism*
D014764:Viral Proteins; D003546:Cysteine Endopeptidases
3C-like protease; cell adaptation; nucleocapsid; porcine epidemic diarrhea virus