NS1 protein of 2009 pandemic influenza A virus inhibits porcine NLRP3 inflammasome-mediated interleukin-1 beta production by suppressing ASC ubiquitination.

5 years ago

NS1 protein of 2009 pandemic influenza A virus inhibits porcine NLRP3 inflammasome-mediated interleukin-1 beta production by suppressing ASC ubiquitination.

Qiang Liu, Shelby L Landreth, GuanQun Liu, Yan Zhou, Sathya N Thulasi Raman, Hong-Su Park

The inflammasome represents a molecular platform for the innate immune regulation and controls the pro-inflammatory cytokine production. NLRP3 inflammasome is comprised of NLRP3, ASC and pro-caspase-1. When NLRP3 inflammasome is activated, it causes ASC speck formation and caspase-1 activation, resulting in the maturation of IL-1β. NLRP3 inflammasome is regulated at multiple levels, with one level being post-translational modification. Interestingly, ubiquitination of ASC has been reported to be indispensable for the activation of NLRP3 inflammasome. Influenza A virus (IAV) infection induces NLRP3 inflammasome-dependent IL-1β secretion, which contributes to the host antiviral defense. However, IAVs have evolved multiple antagonizing mechanisms, one of which is executed by viral NS1 protein to suppress the NLRP3 inflammasome. In this study we compared IL-1β production in porcine alveolar macrophages in response to IAV infection and found that the 2009 pandemic H1N1 induced less IL-1β than swine influenza viruses (SIVs). Further study revealed the NS1 C-terminus of pandemic H1N1 but not that of SIV, was able to significantly inhibit the NLRP3 inflammasome-mediated IL-1β production. This inhibitory function was attributed to the impaired ASC speck formation and suppression of ASC ubiquitination. Moreover, we identified two target lysine residues, K110 and K140 which are essential for both porcine ASC ubiquitination, as well as NLRP3 inflammasome-mediated IL-1β production. These results revealed a novel mechanism by which NS1 protein of the 2009 pandemic H1N1 suppresses the NLRP3 inflammasome activation.IMPORTANCE Influenza A virus (IAV) infection activates NLRP3 inflammasome, resulting in the production of IL-1β which contributes to the host innate immune response. ASC, an adaptor protein of NLRP3, forms specks that are critical for the inflammasome activation. Here, we report that NS1 C-terminus of the 2009 pandemic H1N1 has functions to suppress porcine IL-1β production by inhibiting the ASC speck formation and ASC ubiquitination. Furthermore, the ubiquitination sites on porcine ASC were identified. The information gained here may contribute to an in-depth understanding of porcine inflammasome activation and regulation in response to different IAVs, helping to further enhance our knowledge on innate immune responses to influenza virus infection in pigs.

Publisher URL: http://doi.org/10.1128/JVI.00022-18

DOI: 10.1128/JVI.00022-18