Activated Ras/MEK inhibits the antiviral response of alpha interferon by reducing STAT2 levels.
The ability of interferon (IFN) to induce the expression of antiviral genes, and therefore suppress viral infection, is dependent on the activity of cellular suppressors. The Ras/MEK pathway is one of these cellular suppressors, since the activation of Ras/MEK permits viral replication in the presence of alpha IFN (IFN-alpha). Here, we have investigated the mechanism by which activated Ras/MEK inhibits the IFN-alpha response. We found that the induction of antiviral proteins in response to IFN-alpha was impaired in Ras-transformed NIH 3T3 (RasV12) cells. The inhibition of the Ras/MEK pathway restored the IFN-mediated induction of antiviral genes, indicating that activated Ras interrupts the IFN pathway upstream of antiviral gene transcription. Indeed, the IFN-induced phosphorylation of signal transducer and activator of transcription 1 (STAT1) and STAT2 was inhibited in RasV12 cells compared to that of vector control cells. In addition, we found that the total amount of STAT2 was reduced in RasV12 cells. To determine if the impaired IFN-alpha response can be rescued by restoring the overall level of STAT2, we overexpressed STAT2 in RasV12 cells. The IFN-alpha-induced phosphorylation of STAT1 and STAT2, as well as the expression of antiviral protein, were restored, and IFN-induced antiviral protection was partially restored. Moreover, we demonstrated that the downregulation of STAT2 levels by Ras/MEK was mediated at the transcriptional level. Thus, the activation of the Ras/MEK pathway reduces the amount of STAT2 available for propagating the IFN signal, resulting in the impairment of the IFN-alpha-induced antiviral response.
Christian
Sherri L
SL
Division of BioMedical Sciences, Faculty of Medicine, Memorial University of Newfoundland, 300 Prince Philip Dr., St. John's, Newfoundland A1B3V6, Canada.
Collier
Thaddeus W
TW
Zu
Dong
D
Licursi
Maria
M
Hough
Chris M
CM
Hirasawa
Kensuke
K
D000818:Animals; D015536:Down-Regulation; D005786:Gene Expression Regulation; D016898:Interferon-alpha / Q000276:immunology*; D020935:MAP Kinase Signaling System; D051379:Mice; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism*; D041681:NIH 3T3 Cells; D010766:Phosphorylation; D050794:STAT1 Transcription Factor / Q000378:metabolism; D050795:STAT2 Transcription Factor / Q000378:metabolism*; D014158:Transcription, Genetic; D054243:Vesicular Stomatitis / Q000276:immunology; D014721:Vesicular stomatitis Indiana virus / Q000276:immunology; D018631:ras Proteins / Q000378:metabolism*
D016898:Interferon-alpha; D050794:STAT1 Transcription Factor; D050795:STAT2 Transcription Factor; C494080:Stat1 protein, mouse; C494085:Stat2 protein, mouse; D020929:Mitogen-Activated Protein Kinase Kinases; D018631:ras Proteins