title: Coronavirus gene 7 counteracts host defenses and modulates virus virulence.
abstract: Transmissible gastroenteritis virus (TGEV) genome contains three accessory genes: 3a, 3b and 7. Gene 7 is only present in members of coronavirus genus a1, and encodes a hydrophobic protein of 78 aa. To study gene 7 function, a recombinant TGEV virus lacking gene 7 was engineered (rTGEV-Δ7). Both the mutant and the parental (rTGEV-wt) viruses showed the same growth and viral RNA accumulation kinetics in tissue cultures. Nevertheless, cells infected with rTGEV-Δ7 virus showed an increased cytopathic effect caused by an enhanced apoptosis mediated by caspase activation. Macromolecular synthesis analysis showed that rTGEV-Δ7 virus infection led to host translational shut-off and increased cellular RNA degradation compared with rTGEV-wt infection. An increase of eukaryotic translation initiation factor 2 (eIF2α) phosphorylation and an enhanced nuclease, most likely RNase L, activity were observed in rTGEV-Δ7 virus infected cells. These results suggested that the removal of gene 7 promoted an intensified dsRNA-activated host antiviral response. In protein 7 a conserved sequence motif that potentially mediates binding to protein phosphatase 1 catalytic subunit (PP1c), a key regulator of the cell antiviral defenses, was identified. We postulated that TGEV protein 7 may counteract host antiviral response by its association with PP1c. In fact, pull-down assays demonstrated the interaction between TGEV protein 7, but not a protein 7 mutant lacking PP1c binding motif, with PP1. Moreover, the interaction between protein 7 and PP1 was required, during the infection, for eIF2α dephosphorylation and inhibition of cell RNA degradation. Inoculation of newborn piglets with rTGEV-Δ7 and rTGEV-wt viruses showed that rTGEV-Δ7 virus presented accelerated growth kinetics and pathology compared with the parental virus. Overall, the results indicated that gene 7 counteracted host cell defenses, and modified TGEV persistence increasing TGEV survival. Therefore, the acquisition of gene 7 by the TGEV genome most likely has provided a selective advantage to the virus.
authors.affiliation: Centro Nacional de Biotecnología, CNB, CSIC, Department of Molecular and Cell Biology, Darwin 3, Campus Universidad Autónoma de Madrid, Cantoblanco, Madrid, Spain.
authors.forename: Jazmina L G
authors.initials: JL
authors.lastname: Cruz
authors.forename: Isabel
authors.initials: I
authors.lastname: Sola
authors.forename: Martina
authors.initials: M
authors.lastname: Becares
authors.forename: Berta
authors.initials: B
authors.lastname: Alberca
authors.forename: Joan
authors.initials: J
authors.lastname: Plana
authors.forename: Luis
authors.initials: L
authors.lastname: Enjuanes
authors.forename: Sonia
authors.initials: S
authors.lastname: Zuñiga
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002460:Cell Line; D005761:Gastroenteritis, Transmissible, of Swine / Q000401:mortality / Q000821:virology; D005814:Genes, Viral / Q000276:immunology*; D054884:Host-Pathogen Interactions / Q000276:immunology*; D007113:Immunity, Innate; D013552:Swine; D005760:Transmissible gastroenteritis virus / Q000235:genetics / Q000276:immunology* / Q000472:pathogenicity; D014764:Viral Proteins / Q000235:genetics / Q000502:physiology; D014774:Virulence; D014779:Virus Replication
chemical_list: D014764:Viral Proteins