Host cell signaling in response to RSV infection

Abstract

RSV infection is the most important cause of hospitalization of infants, and is also the major cause for admissions in adults with chronic cardiac disease and pulmonary diseases. So far, there is no effective treatment or vaccine against RSV infection. Intensive studies have been performed to understand mechanisms and consequences of RSV-induced host cell signaling. My dissertation project provides three major contributions to this field.\r\nFirstly, I found that retinoic acid-inducible gene I (RIG-I) and Toll like receptor 3 (TLR3) play distinct roles in mediating RSV-induced innate immune responses. Short interfering RNA (siRNA)-mediated RIG-I \"knockdown\" significantly inhibited the translocation of nuclear factor-kappa B (NF-kappa B) and interferon response factor 3 (IRF3) to the nucleus at the early phase of viral infection. In contrast, siRNA-mediated TLR3 knockdown did not affect RSV-induced NF-kappa B binding to DNA but block the activating phosphorylation of NF-kappa B /RelA at serine residue 276.\r\nSecondly, I first demonstrated that RIG-I was involved in the activation of NIK/IKK alpha complex, two key noncanonical kinases that induce the protelytic processing of an I kappa B alpha-like inhibitor p100 to p52. I also proved that a fraction of RelA was associated with cytoplasmic p100. In addition, the RSV-induced proteolysis of p100 not only produces p52, but also releases RelA and increases its nuclear translocation. This finding suggested that part of the RelA activation in response to RSV infection was induced by the NIK/IKK alpha complex. Because inhibition of NIK/IKK alpha does not affect RSV replication but reduces inflammatory chemokine production, this protein complex could be a good target for drug treatment of RSV infection.\r\nThirdly, our previous study has reported the existence of IKK gamma delta, a splicing variant of IKK gamma, which excludes exon 5. I compared the function of IKK gamma and IKK gamma delta in response to ssRNA viruses. I found that in contrast to IKK gamma, which is essential for both NF-kappa B and IRF3 activation, IKK gamma delta failed to activate IRF3 in response to either Sendai virus or respiratory syncytial virus (RSV). However, IKK gamma delta mediated NF- kappa B activation was intact. I demonstrated that the missing region of IKK gamma delta made it unable to recruit TANK, a key factor that recruits atypical IKKs to activate the IRF3 pathway. \r\n