Interferon-induced ISG15 conjugation inhibits influenza A virus gene expression and replication in human cells.
The ubiquitin-like ISG15 protein, as well as its conjugating enzymes, is induced by type I interferons (IFNs). Experiments using ISG15 knockout (ISG15(-/-)) mice established that ISG15 and/or its conjugation inhibits the replication of influenza A virus. However, in contrast to the virus inhibition results for mice, the rates of virus replication in ISG15(+/+) and ISG15(-/-) mouse embryo fibroblasts in tissue culture were similar. Here we focus on human tissue culture cells and on the effect of ISG15 and/or its conjugation on influenza A virus gene expression and replication in such cells. We demonstrate that IFN-induced antiviral activity against influenza A virus in human cells is significantly alleviated by inhibiting ISG15 conjugation using small interfering RNAs directed against ISG15-conjugating enzymes. IFN-induced antiviral activity against influenza A virus protein synthesis was reduced 5- to 20-fold by suppressing ISG15 conjugation. The amounts of the viral proteins that were restored by these siRNA treatments were approximately 40 to 50% of the amounts produced in cells that were not pretreated with IFN. Further, we show that ISG15 conjugation inhibits influenza A virus replication 10- to 20-fold at early times after infection in human cells. These results show that ISG15 conjugation plays a substantial role in the antiviral state induced by IFN in human cells. In contrast, we show that in mouse embryo fibroblasts ISG15 conjugation not only does not affect influenza A virus replication but also does not contribute to the IFN-induced antiviral activity against influenza A virus gene expression.
Institute for Cellular and Molecular Biology, University of Texas at Austin, Austin, TX 78712, USA.
Tien-Ying
TY
Hsiang
Chen
C
Zhao
Robert M
RM
Krug
D000818:Animals; D000998:Antiviral Agents / Q000494:pharmacology; D002460:Cell Line; D016207:Cytokines / Q000378:metabolism*; D015967:Gene Expression Regulation, Viral; D006801:Humans; D009980:Influenza A virus / Q000235:genetics* / Q000502:physiology; D007251:Influenza, Human / Q000378:metabolism / Q000821:virology; D016899:Interferon-beta / Q000378:metabolism* / Q000494:pharmacology; D051379:Mice; D011485:Protein Binding; D034741:RNA, Small Interfering / Q000494:pharmacology; D044763:Ubiquitin-Conjugating Enzymes / Q000378:metabolism; D014452:Ubiquitins / Q000378:metabolism*; D014764:Viral Proteins / Q000096:biosynthesis; D014779:Virus Replication
D000998:Antiviral Agents; D016207:Cytokines; D034741:RNA, Small Interfering; D014452:Ubiquitins; D014764:Viral Proteins; C074034:ISG15 protein, human; D016899:Interferon-beta; C471622:UBE2L6 protein, human; D044763:Ubiquitin-Conjugating Enzymes