RSV-induces RelA release from cytoplasmic 100 kDa NF-kappa B2 complexes via a novel retinoic acid inducible gene-I-NF-kappa B inducing kinase (NIK) signaling pathway

Liu P, Li K, Garofalo RP, Brasier AR
Source: J Biol Chem
Publication Date: (2008)
Issue: epub: online
Research Area:
Cancer Research/Cell Biology
Cells used in publication:
Embryonic fibroblast, mouse (MEF) immort
Species: mouse
Tissue Origin: embryo
Nucleofector® I/II/2b
Respiratory Syncytial Virus (RSV) is a primary cause of severe lower respiratory tract infection in children worldwide. RSV infects airway epithelial cells, where it activates inflammatory genes via the NF-B pathway. NF-B is controlled by two pathways, a canonical pathway that releases sequestered RelA complexes from the IBa inhibitor, and a second, the noncanonical pathway, that releases RelB from the 100 kDa NF-B2 complex. Recently we found that the retinoic acid inducible gene I (RIG-I) is a major intracellular RSV sensor upstream of the canonical pathway. In this study, we surprisingly found that RIG-I silencing also inhibited p100 processing to 52 kDa NF-B2 ("p52"), suggesting that RIG-I was functionally upstream of the noncanonical regulatory kinase complex composed of NIK.IKKa subunits. Co-immunoprecipitation experiments not only demonstrated that NIK associated with RIG-I and its downstream adaptor, mitochondrial antiviral signaling (MAVS), but also showed the association between IKKa and MAVS. To further understand the role of NIK.IKKa pathway, we compared RSV-induced NF-B activation using wild type, IKK-/-, NIK-/- and IKKa-/- deficient MEF cells. Interestingly, we found that in canonical pathway-defective IKK-/- cells, RSV induced RelA by liberation from p100 complexes. RSV was still able to activate IP10, Rantes and Gross gene expression in IKK-/- cells, and this induction was inhibited by siRNA mediated RelA knockdown but not RelB silencing. These data suggest that part of the RelA activation in response to RSV infection was induced by a "cross-talk" pathway involving the noncanonical NIK.IKKa complex downstream of RIG-I.MAVS. This pathway may be a potential target for RSV treatment.