Evidence that avian reovirus sigmaA protein is an inhibitor of the double-stranded RNA-dependent protein kinase.
The results of a previous study demonstrated that avian reovirus is highly resistant to the antiviral effects of interferon and suggested that the double-stranded RNA (dsRNA)-binding sigmaA protein might play an important role in that resistance. To gather more evidence on the interferon-inhibitory activity of sigmaA protein, its gene was cloned into the prokaryotic maltose-binding protein (MBP) gene fusion vector pMalC and into the recombinant vaccinia virus WRS2. The two recombinant sigmaA proteins displayed a dsRNA-binding affinity similar to that of sigmaA protein synthesized in avian reovirus-infected cells. Interestingly, MBP-sigmaA, but not MBP, was able to relieve the translation-inhibitory activity of dsRNA in reticulocyte lysates by blocking the activation of endogenous dsRNA-dependent enzymes. In addition, transient expression of sigmaA protein in HeLa cells rescued gene expression of a vaccinia virus mutant lacking the E3L gene, and insertion of the sigmaA-encoding gene into vaccinia virus conferred protection for the virus against interferon in chicken cells. Further studies demonstrated that expression of recombinant sigmaA in mammalian cells interfered with dsRNA-dependent protein kinase (PKR) function. From these results we conclude that sigmaA is capable of reversing the interferon-induced antiviral state by down-regulating PKR activity in a manner similar to other virus-encoded dsRNA-binding proteins.
González-López
Claudia
C
Departamento de Bioquímica y Biología Molecular, Facultad de Farmacia, Universidad de Santiago de Compostela, 15782 Santiago de Compostela, Spain.
Martínez-Costas
José
J
Departamento de Bioquímica y Biología Molecular, Facultad de Farmacia, Universidad de Santiago de Compostela, 15782 Santiago de Compostela, Spain.
Esteban
Mariano
M
Centro Nacional de Biotecnología, CSIC, Campus Universidad Autónoma, 28049 Madrid, Spain.
Benavente
Javier
J
Departamento de Bioquímica y Biología Molecular, Facultad de Farmacia, Universidad de Santiago de Compostela, 15782 Santiago de Compostela, Spain.
D000818:Animals; D000914:Antibodies, Viral; D002642:Chick Embryo; D015870:Gene Expression; D006367:HeLa Cells; D006801:Humans; D066298:In Vitro Techniques; D007372:Interferons / Q000378:metabolism / Q000494:pharmacology; D030101:Orthoreovirus, Avian / Q000235:genetics / Q000276:immunology / Q000472:pathogenicity / Q000502:physiology*; D014176:Protein Biosynthesis; D012330:RNA, Double-Stranded / Q000235:genetics / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012156:Reticulocytes / Q000378:metabolism; D014616:Vaccinia virus / Q000187:drug effects / Q000235:genetics / Q000276:immunology; D014758:Viral Core Proteins / Q000235:genetics / Q000502:physiology*; D014779:Virus Replication / Q000187:drug effects; D019892:eIF-2 Kinase / Q000037:antagonists & inhibitors* / Q000378:metabolism
D000914:Antibodies, Viral; D012330:RNA, Double-Stranded; D016601:RNA-Binding Proteins; D011993:Recombinant Fusion Proteins; D014758:Viral Core Proteins; C403292:sigmaA protein, avian reovirus; D007372:Interferons; D019892:eIF-2 Kinase