c-Jun N-terminal kinase negatively regulates dsRNA and RSV induction of tumor necrosis factor- alpha transcription in human epithelial cells.

Secretion of inflammatory cytokines is the initial step of the immune response to viral infections. This innate immune response is mediated by the expression of a variety of cytokines, exemplified by tumor necrosis factor- alpha (TNF-alpha). The presence of dsRNA during viral infections is a key step in activation of several signaling pathways, including protein kinase R (PKR), toll-like receptor 3 (TLR3), mitogen-activated protein kinase (MAPK), activator protein-1 (AP-1), interferon regulatory factors (IRFs), and NF-kappaB pathways, which are all relevant in the expression of inflammatory cytokines. We previously reported that PKR and p38 MAPK were required for dsRNA and viral induction of inflammatory cytokines in epithelial cells. Here, we report that activation of c-Jun N-terminal kinase (JNK) during dsRNA treatment or respiratory syncytial viral (RSV) infection negatively regulates the induction of TNF-alpha in human epithelial cells. Inhibition of JNK by a pharmacologic inhibitor showed that expression of TNF-alpha increased following both dsRNA treatment and infection with RSV. Importantly, transfection of epithelial cells with a dominant-negative mutant of JNK significantly increased dsRNA induction of TNF-alpha. The mechanism by which JNK inhibition increases TNF-alpha induction appears to be through p38 MAPK activation. Our data show that JNK is a negative regulator of dsRNA and RSV induction of TNF-alpha expression and, thus, may act as a counterbalance to proinflammatory signals generated during viral infections.

Viral induction of inflammatory cytokines in human epithelial cells follows a p38 mitogen-activated protein kinase-dependent but NF-kappa B-independent pathway.

The initial step in an immune response toward a viral infection is the induction of inflammatory cytokines. This innate immune response is mediated by expression of a variety of cytokines exemplified by TNF-alpha and IL-1beta. A key signal for the recognition of intracellular viral infections is the presence of dsRNA. Viral infections and dsRNA treatment can activate several signaling pathways including the protein kinase R pathway, mitogen-activated protein kinase (MAPK) pathways, and NF-kappaB, which are important in the expression of inflammatory cytokines. We previously reported that activation of protein kinase R was required for dsRNA induction of TNF-alpha, but not for IL-1beta. In this study, we report that activation of the p38 MAPK pathway by respiratory viral infections is necessary for induction of inflammatory cytokines in human bronchial epithelial cells. Inhibition of p38 MAPK by two different pharmacological inhibitors showed that expression of both TNF-alpha and IL-1beta required activation of this signaling pathway. Interestingly, inhibition of NF-kappaB did not significantly reduce viral induction of either cytokine. Our data show that, during the initial infections of epithelial cells with respiratory viruses, activation of the p38 MAPK pathway is associated with induction of inflammation, and NF-kappaB activation may be less important than previously suggested.

Protein kinase R regulates double-stranded RNA induction of TNF-alpha but not IL-1 beta mRNA in human epithelial cells.

Epithelial cells represent the initial site of respiratory viral entry and the first line of defense against such infections. This early antiviral response is characterized by an increase in the production of proinflammatory cytokines such as TNF-alpha and IL-1 beta. dsRNA, which is a common factor present during the life cycle of both DNA and RNA viruses, is known to induce TNF-alpha and IL-1 beta in a variety of cells. In this work we provide data showing that dsRNA treatment induces TNF-alpha and IL-1 beta in human lung epithelial cells via two different mechanisms. Our data show that dsRNA activation of dsRNA-activated protein kinase (PKR) is associated with induction of TNF-alpha but not IL-1 beta expression. An inhibitor of PKR activation blocked the dsRNA-induced elevations in TNF-alpha but not IL-1 beta mRNA in epithelial cells. Data obtained from infection of epithelial cells with a vaccinia virus lacking the PKR inhibitory polypeptide, E3L, revealed that PKR activation was essential for TNF-alpha but not for IL-1 beta expression. In this report, we provide experimental support for the differential regulation of proinflammatory cytokine expression by dsRNA and viral infections in human airway epithelial cells.