Respiratory Syncytial Virus (RSV) Nonstructural Protein 1 (NS1) Regulates Host Defense by Modulating LGP2

Abstract

RSV NS1 attenuates type-I IFN production by modulating RLRs (Rig-I like receptors), which comprise RIG-I (retinoic acid inducible gene), MAVS (mitochondrial antiviral signaling) and LGP2 (laboratory of genetics and physiology 2), however the precise mechanism of NS1 inhibition of the host's innate antiviral immune response is unclear. We have shown that NS1 localizes to the mitochondria following RSV infection, binds to MAVS and thereby inhibits MAVS-RIG-I interaction required for IFN production. Here we have found that NS1 also increases LGP2 expression and that LGP2 is required for NS1-mediated attenuation of IFN-β. Human alveolar epithelial A549 cells were infected with wt RSV or RSV with an NS1 deletion (ΔNS1) or transfected with plasmid encoding NS1. Interaction between MAVS and RIG-I and expression of LGP2 in the presence or absence of NS1 was determined by immunoprecipitation and western blot in both infection and transfection models. The role of LGP2 in the NS1-mediated immune response was investigated using siLGP2, qRT-PCR and immunoblot analysis in A549 cells and in a stable HEK-293 cell line for regulating expression of NS1. Results show that NS1 elevates the expression of LGP2 by immunoblot analyses. In a stable cell line, NS1 is shown to upregulate LGP2 expression by 16h post induction in a dose-dependent manner. Furthermore, downregulating LGP2 by the expression of siLGP2 prevents the NS1-induced attenuation of IFN-β. Together these results show that RSV-NS1 upregulates LGP2, which in turn downregulates IFN-β production, suggesting NS1 modulation of LGP2 provides an additional pathway for RSV regulation of host defense.