High Resistance of Human Parainfluenza Type 2 Virus Protein-Expressing Cells to the Antiviral and Anti-Cell Proliferative Activities of Alpha/Beta Interferons: Cysteine-Rich V-Specific Domain Is Required for High Resistance to the Interferons

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Abstract
Human parainfluenza type 2 virus (hPIV-2)-infected HeLa (HeLa-CA) cells and hPIV-2 V-expressing HeLa (HeLa-V) cells show high resistance to alpha/beta interferons (IFN-α/β) irrespective of whether vesicular stomatitis virus or Sindbis virus is used as a challenge virus. When Sindbis virus is used, these cells show high susceptibility to human IFN-γ. Furthermore, the multiplication of HeLa-V cells is not inhibited by IFN-α/β. HeLa cells expressing the N-terminally truncated V protein show resistance to IFN-α/β, showing that the IFN resistance determinant maps to the cysteine-rich V-specific domain. A complete defect of Stat2 is found in HeLa-CA and HeLa-V cells, whereas the levels of Stat1 expression are not significantly different among HeLa, HeLa-CA, HeLa-P, and HeLa-V cells, indicating that IFN-α/β resistance of HeLa-CA and HeLa-V cells is due to a defect of Stat2. HeLa-SV41V cells show high resistance to all IFNs, and no expression of Stat1 can be detected. Stat2 mRNA is fully detected in HeLa-V cells. Stat2 was scarcely pulse-labeled in the HeLa-V cells, indicating that synthesis of Stat2 is suppressed or Stat2 is very rapidly degraded in HeLa-V cells. The V protein suppresses the in vitro translation of Stat2 mRNA more extensively than that of Stat1 mRNA. An extremely small amount of Stat2 can be detected in HeLa-V cells treated with proteasome inhibitors. The half-life of Stat2 is approximately 3.5 and 2 h in uninfected and hPIV-2-infected HeLa cells, respectively. This study shows that synthesis of Stat2 may be suppressed and Stat2 degradation is also enhanced in hPIV-2-infected HeLa and HeLa-V cells.

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