Central role of double-stranded RNA-activated protein kinase in microbial induction of nitric oxide synthase

NO synthase 2 (NOS2) is induced in airway epithelium by influenza virus inf ection. NOS2 induction late in the course of viral infection may occur in r esponse to IFN-gamma, but early in infection gene expression may be induced by the viral replicative intermediate dsRNA through the dsRNA-activated pr otein kinase (PKR), Since PKR activates signaling pathways important in NOS 2 gene induction, we determined whether PKR is a component in the signal tr ansduction pathway leading to NOS2 gene expression after viral infection of airway epithelium. We show that NOS2 gene expression in human airway epith elial cells occurs in response to influenza A virus or synthetic dsRNA, Fur thermore, dsRNA leads to rapid activation of PKR, followed by activation of signaling components including NF-kappa B and IFN regulatory factor 1, NOS 2 expression is markedly diminished and IFN regulatory factor 1 and NF-kapp a B activation are substantially impaired in PKR null cells. Strikingly, NO S2 induction in response to LPS is abolished in PKR null cells, confirming a central role for PKR in the general signaling pathway to NOS2.