PERSISTENT ACTIVATION OF RELA BY RESPIRATORY SYNCYTIAL VIRUS INVOLVESPROTEIN-KINASE-C, UNDERPHOSPHORYLATED I-KAPPA-B-BETA, AND SEQUESTRATION OF PROTEIN PHOSPHATASE 2A BY THE VIRAL PHOSPHOPROTEIN

Respiratory syncytial virus (RSV) activated the RelA (p65) subunit of nuclear factor kappa B (NF-kappa B) over many hours postinfection. The initial activation coincided with phosphorylation and degradation of I kappa B alpha, the cytoplasmic inhibitor of RelA, During persistent activation of NF-kappa B at later times in infection, syntheses of inh ibitors I kappa B beta as well as I kappa B beta were restored. Howeve r, the resynthesized I kappa B beta was in an underphosphorylated stat e, which apparently prevented inhibition of NF-kappa B. Use of specifi c inhibitors suggested that the pathway leading to the persistent-but not the initial-activation of NF-kappa B involved signaling through pr otein kinase C (PKC) and reactive oxygen intermediates of nonmitochond rial origin, whereas phospholipase C or D played little or no role. Th us, RSV infection led to the activation of NF-kappa B by a biphasic me chanism: a transient or early activation involving phosphorylation of the inhibitor I kappa B polypeptides, and a persistent or long-term ac tivation requiring PKC and the generation of hypophosphorylated I kapp a B beta. At least a part of the activation was through a novel mechan ism in which the viral phosphoprotein P associated with but was not de phosphorylated by protein phosphatase 2A and thus sequestered and inhi bited the latter. We postulate that this led to a net increase in the phosphorylation state of signaling proteins that are responsible for R elA activation.