| Budget Amount *help |
¥4,160,000 (Direct Cost: ¥3,200,000、Indirect Cost: ¥960,000)
Fiscal Year 2011: ¥780,000 (Direct Cost: ¥600,000、Indirect Cost: ¥180,000)
Fiscal Year 2010: ¥1,430,000 (Direct Cost: ¥1,100,000、Indirect Cost: ¥330,000)
Fiscal Year 2009: ¥1,950,000 (Direct Cost: ¥1,500,000、Indirect Cost: ¥450,000)
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| Research Abstract |
In the course of evolution, influenza A viruses also have developed different mechanisms to counteract the IFN-induced antiviral activities. There is accumulating evidence that IFN-α/βand IFN-. are ineffectual against influenza A virus. Therefore, we hypothesized that influenza A virus may have evolved molecular mechanisms to evade the IFN-α/βand IFN-γ-dependent anti-viral pathways. To test this, we investigated IFN-induced MHC class II expression in A549 cells infected with influenza A virus. These cells are highly sensitive to IFN-induced MHC class II expression through Jak/Stat and CIITA pathways. The data show that influenza A virus inhibits IFN-induced upregulation of MHC class II.
Further, influenza A virus interferes with the host response by blocking the IFN-α/βand IFN-γsignal cascade through inhibition of phosphorylation of Stat1 on tyrosine 701, which is required for its translocation to the nucleus and DNA binding, and serine phosphorylation, which is required for the full tr
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anscriptional activation of the protein. Nuclear translocation of Stat1. upon IFN-. stimulation was significantly inhibited in influenza A virus-infected cells and this was associated with a decrease in tyrosine 701 and serine 727 phosphorylation of Stat1α.
The influenza virus-encoded NS1 has been shown to inhibit the host-cell antiviral responses. In order to investigate the effect of NS1 protein on tyrosine phosphorylation of Stat1, the cells transfected with NS1 expression vector or empty vector were treated with type I or type II IFN, and total cellular lysates were prepared for analyzing Stat1 phosphorylation by Western blotting. No significant inhibition of IFN-γ-induced tyrosine phosphorylation of Stat1 was observed in the cells transfected with NS1 expression vector. The inhibition of IFN-α-induced phosphorylation of Stat1 by influenza A virus infection is not due to NS1 protein.
The activation of Stat1 is ultimately dependent on the upstream signaling events of the IFN-γsignal transduction system, which includes IFNGR1, IFN-. receptor subunit 2(IFNGR2), Jak1, and Jak2. IFNGR1, IFNGR2, Jak1, Jak2, and Stat1 mRNAs were constitutively expressed in uninfected and influenza A virus-infected cells regardless of IFN-γtreatment, suggesting that influenza A virus infection did not affect transcription of the genes for these molecules. We found that Stat1α, IFNGR2, and Jak2 were equivalently expressed in uninfected and influenza A virus-infected cells, whereas there was a dramatic decrease of Jak1 and IFNGR1 proteins in infected cells. Together, these data suggest that Jak1 and IFNGR1 are decreased by a posttranscriptional mechanism. Less
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