title: Sindbis virus induced phosphorylation of IRF3 in human embryonic kidney cells is not dependent on mTOR.
abstract: The mammalian target of rapamycin (mTOR) plays critical roles in immunity. We previously showed that infection of human embryonic kidney (HEK) cells with Sindbis virus (SIN), an enveloped RNA alphavirus, profoundly suppresses Akt/mTOR signaling, and host translation late during infection. To understand how SIN mediated suppression of mTOR affects innate response, we analyzed phosphorylation of interferon regulatory factor 3 (IRF3) and expression of two antiviral genes. Here we show strong phosphorylation of IRF3, and an increase in mRNA levels for antiviral genes interferon stimulated gene (ISG)56 and interferon gamma inducible protein (IP)-10 when intracellular viral RNA levels are high during late infection. The mTOR inhibitors rapamycin and torin1 do not block, but mildly upregulate these responses. Even after prolonged treatment with Ly294002, the PI3K inhibitor only partially blocks SIN induced phosphorylation of IRF3. While Ly294002 treatment downregulated the SIN induced expression of ISG56 mRNA levels, it had no effect on SIN induced upregulation of IP-10 expression. These results point to SIN replication-mediated activation of IRF3, independent of mTOR function, when host protein synthesis is severely suppressed by virus infection.
authors.affiliation: Department of Microbiology and Immunology, Meharry Medical College, School of Medicine, Nashville, Tennessee, USA.
authors.forename: Nisha R
authors.initials: NR
authors.lastname: Dhanushkodi
authors.forename: Vidyarani
authors.initials: V
authors.lastname: Mohankumar
authors.forename: Ramaswamy
authors.initials: R
authors.lastname: Raju
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D018354:Alphavirus Infections / Q000378:metabolism*; D015153:Blotting, Western; D002460:Cell Line; D057809:HEK293 Cells; D006801:Humans; D007202:Indicators and Reagents; D050838:Interferon Regulatory Factor-3 / Q000378:metabolism*; D007668:Kidney / Q000166:cytology / Q000196:embryology / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000096:biosynthesis; D010766:Phosphorylation; D010957:Plasmids / Q000235:genetics; D012367:RNA, Viral / Q000096:biosynthesis; D016601:RNA-Binding Proteins; D060888:Real-Time Polymerase Chain Reaction; D018121:Receptors, Cytokine / Q000235:genetics; D012845:Sindbis Virus; D058570:TOR Serine-Threonine Kinases / Q000502:physiology*; D014157:Transcription Factors / Q000235:genetics; D010948:Viral Plaque Assay; D014779:Virus Replication
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D007202:Indicators and Reagents; D050838:Interferon Regulatory Factor-3; D019869:Phosphatidylinositol 3-Kinases; D012367:RNA, Viral; D016601:RNA-Binding Proteins; D018121:Receptors, Cytokine; D058570:TOR Serine-Threonine Kinases; D014157:Transcription Factors; C484290:IFIT1 protein, human; C104577:IP10-Mig receptor; C494232:IRF3 protein, human