Naturally occurring substitutions in the P/V gene convert the noncytopathic paramyxovirus simian virus 5 into a virus that induces alpha/beta interferon synthesis and cell death.
The V protein of the paramyxovirus simian virus 5 (SV5) is responsible for targeted degradation of STAT1 and the block in alpha/beta interferon (IFN-alpha/beta) signaling that occurs after SV5 infection of human cells. We have analyzed the growth properties of a recombinant SV5 that was engineered to be defective in targeting STAT1 degradation. A recombinant SV5 (rSV5-P/V-CPI-) was engineered to contain six naturally occurring P/V protein mutations, three of which have been shown in previous transfection experiments to disrupt the V-mediated block in IFN-alpha/beta signaling. In contrast to wild-type (WT) SV5, human cells infected with rSV5-P/V-CPI- had STAT1 levels similar to those in mock-infected cells. Cells infected with rSV5-P/V-CPI- were found to express higher-than-WT levels of viral proteins and mRNA, suggesting that the P/V mutations had disrupted the regulation of viral RNA synthesis. Despite the inability to target STAT1 for degradation, single-step growth assays showed that the rSV5-P/V-CPI- mutant virus grew better than WT SV5 in all cell lines tested. Unexpectedly, cells infected with rSV5-P/V-CPI- but not WT SV5 showed an activation of a reporter gene that was under control of the IFN-beta promoter. The secretion of IFN from cells infected with rSV5-P/V-CPI- but not WT SV5 was confirmed by a bioassay for IFN. The rSV5-P/V-CPI- mutant grew to higher titers than did WT rSV5 at early times in multistep growth assays. However, rSV5-P/V-CPI- growth quickly reached a final plateau while WT rSV5 continued to grow and produced a final titer higher than that of rSV5-P/V-CPI- by late times postinfection. In contrast to WT rSV5, infection of a variety of cell lines with rSV5-P/V-CPI- induced cell death pathways with characteristics of apoptosis. Our results confirm a role for the SV5 V protein in blocking IFN signaling but also suggest new roles for the P/V gene products in controlling viral gene expression, the induction of IFN-alpha/beta synthesis, and virus-induced apoptosis.
Wansley
Elizabeth K
EK
Department of Microbiology and Immunology, Wake Forest University School of Medicine, Winston-Salem, NC 27157-1064, USA.
Parks
Griffith D
GD
D019943:Amino Acid Substitution; D000818:Animals; D017209:Apoptosis; D002417:Cattle; D002460:Cell Line; D002522:Chlorocebus aethiops; D003588:Cytopathogenic Effect, Viral; D004268:DNA-Binding Proteins / Q000378:metabolism; D005814:Genes, Viral; D049452:Green Fluorescent Proteins; D006801:Humans; D016898:Interferon-alpha / Q000096:biosynthesis* / Q000235:genetics; D016899:Interferon-beta / Q000096:biosynthesis* / Q000235:genetics; D008164:Luminescent Proteins / Q000235:genetics; D016296:Mutagenesis; D010252:Paramyxoviridae / Q000235:genetics / Q000254:growth & development / Q000472:pathogenicity*; D010750:Phosphoproteins / Q000235:genetics / Q000502:physiology*; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000096:biosynthesis; D012367:RNA, Viral / Q000096:biosynthesis; D016601:RNA-Binding Proteins; D050794:STAT1 Transcription Factor; D015534:Trans-Activators / Q000378:metabolism; D014764:Viral Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D015678:Viral Structural Proteins / Q000235:genetics / Q000502:physiology*
D004268:DNA-Binding Proteins; D016898:Interferon-alpha; D008164:Luminescent Proteins; C097018:P protein, Simian parainfluenza virus 5; D010750:Phosphoproteins; D012333:RNA, Messenger; D012367:RNA, Viral; D016601:RNA-Binding Proteins; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D015534:Trans-Activators; C097019:V protein, Simian parainfluenza virus 5; D014764:Viral Proteins; D015678:Viral Structural Proteins; D049452:Green Fluorescent Proteins; D016899:Interferon-beta