p38 Mitogen-Activated Protein Kinase-Dependent Hyperinduction of Tumor Necrosis Factor Alpha Expression in Response to Avian Influenza Virus H5N1

Abstract

Avian influenza A virus subtype H5N1 can infect humans to cause a severe viral pneumonia with mortality rates of more than 30%. The biological basis for this unusual disease severity is not fully understood. We previously demonstrated that in contrast to human influenza A virus subtypes including H1N1 or H3N2, the H5N1 virus associated with the "bird flu" outbreak in Hong Kong in 1997 (H5N1/97) hyperinduces proinflammatory cytokines, including tumor necrosis factor alpha (TNF-␣), in primary human macrophages in vitro. To delineate the molecular mechanisms involved, we analyzed the role of transcription factor NF-B and cellular kinases in TNF-␣ dysregulation. H5N1 and H1N1 viruses did not differ in the activation of NF-B or degradation of IB-␣ in human macrophages. However, we demonstrated that unlike H1N1 virus, H5N1/97 strongly activates mitogen-activated protein kinase (MAPK), including p38 MAPK and extracellular signalregulated kinases 1 and 2. Specific inhibitors of p38 MAPK significantly reduced the H5N1/97-induced TNF-␣ expression in macrophages. Taken together, our findings suggest that H5N1/97-mediated hyperinduction of cytokines involves the p38 MAPK signaling pathway. These results may provide insights into the pathogenesis of H5N1 disease and rationales for the development of novel therapeutic strategies.

Induction of Proinflammatory Cytokines in Primary Human Macrophages by Influenza A Virus (H5N1) Is Selectively Regulated by IFN Regulatory Factor 3 and p38 MAPK

“…Previous reports have shown that p38 kinase regulates influenza virus-induced RANTES expression in bronchial epithelial cells (39) and is involved in TNF-␣ production during H5N1 infection (18). Therefore, we explored the effect of IRF3 knockdown and p38 kinase inhibitor treatment both singly and in combination on H5N1-induced cytokine and chemokine expression.…”

“…p38 kinase is essential for virus-induced cytokine production by bronchial epithelial cells including IL-6, IL-8, and GM-CSF (15)(16)(17). We have shown that p38 kinase is involved in the hyperinduction of TNF-␣ expression in H5N1-infected macrophages (18), although the mechanisms underlying this hyperinduction of cytokine by H5N1 influenza virus have not been elucidated. Recent studies have reported hyperactivation of phospho-p38 kinase with increased cytokine concentrations in plasma samples of patients infected with severe seasonal influenza A virus (19).…”

Essential Impact of NF-κB Signaling on the H5N1 Influenza A Virus-Induced Transcriptome

“…Recently, Lee et al (6) showed in a macrophage model that p38 MAPK signaling is of major importance for the hypercytokinemia in H5N1 influenza virus-infected individuals (6). The p38 MAPK signaling pathway triggers a broad spectrum of transcription factors, among them activating transcription factor 2.…”

“…Fifteen micrograms of the empty retroviral pCFG5-IEGZ HA vector or pCFG5-IEGZ IKK2KD expressing dominant negative IKK2 (29) was transfected into 3 ϫ 10 6 Phoenix packaging cells with polyethyleneimine as described previously for HEK293 (33) and selected with 250 g/ml Zeocin (Invitrogen) for 2 wk to gain stable producer cells. Three ϫ 10 6 stable producer cells were seeded on 100-mm dishes 48 h before transduction.…”

“…Infections with HPAIV are characterized by a hyperreaction of the host immune response accompanied by massive production of cytokines and chemokines (4,5). This overproduction of cytokines and chemokines, known as cytokine storm is a cell intrinsic phenomenon (6). Growing evidence supports the contribution of endothelial cells in this process.…”