Herpes simplex virus 1 serine/threonine kinase US3 hyperphosphorylates IRF3 and inhibits beta interferon production.
Viral infection initiates a series of signaling cascades that lead to the transcription of interferons (IFNs), finally inducing interferon-stimulated genes (ISGs) to eliminate viruses. Viruses have evolved a variety of strategies to modulate host IFN-mediated immune responses. Herpes simplex virus 1 (HSV-1) US3, a Ser/Thr kinase conserved in alphaherpesviruses, was previously reported to counteract host innate immunity; however, the molecular mechanism is elusive. In this study, we report that US3 blocks IFN-β production by hyperphosphorylating IFN regulatory factor 3 (IRF3). Ectopic expression of US3 protein significantly inhibited Sendai virus (SeV)-mediated activation of IFN-β and IFN-stimulated response element (ISRE) promoters and the transcription of IFN-β, ISG54, and ISG56. US3 was also shown to block SeV-induced dimerization and nuclear translocation of IRF3. The kinase activity was indispensable for its inhibitory function, as kinase-dead (KD) US3 mutants K220M and D305A could not inhibit IFN-β production. Furthermore, US3 interacted with and hyperphosphorylated IRF3 at Ser175 to prevent IRF3 activation. Finally, the US3 KD mutant viruses were constructed and denoted K220M or D305A HSV-1, respectively. Cells and mice infected with both mutant viruses produced remarkably larger amounts of IFN-β than those infected with wild-type HSV-1. For the first time, these findings provide convincing evidence that US3 hyperphosphorylates IRF3, blocks the production of IFN-β, and subverts host innate immunity.
Soochow University, Institutes of Biology and Medical Sciences, Suzhou, China.
Shuai
S
Wang
Kezhen
K
Wang
Rongtuan
R
Lin
Chunfu
C
Zheng
D020816:Amino Acid Motifs; D000818:Animals; D015536:Down-Regulation; D005260:Female; D006561:Herpes Simplex / Q000235:genetics* / Q000378:metabolism* / Q000821:virology; D018259:Herpesvirus 1, Human / Q000201:enzymology* / Q000235:genetics; D006801:Humans; D050838:Interferon Regulatory Factor-3 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016899:Interferon-beta / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism*
D050838:Interferon Regulatory Factor-3; D014764:Viral Proteins; D016899:Interferon-beta; D017346:Protein Serine-Threonine Kinases; C095207:US3 protein, Human herpesvirus 1