RESUMO
Influenza A viruses cause lung disease via an incompletely understood mechanism that involves the accumulation of liquid within the lungs. The accumulation of lung liquid is normally prevented by epithelial Na(+) absorption, a transport process regulated via several pathways including phosphoinositide-3-kinase (PI3K). Since the influenza A virus encodes a non-structural protein (NS1) that can activate this kinase, we now explore the effects of NS1 upon the biophysical properties of human airway epithelial cells. Transient expression of NS1 depolarized electrically isolated cells maintained in glucocorticoid-free medium by activating a cation conductance identical to the glucocorticoid-induced conductance seen in single cells. This response involved PI3K-independent and PI3K-dependent mechanisms. Infecting glucocorticoid-deprived cells with influenza A virus disrupted the normal electrical coupling between neighbouring cells, but also activated a conductance identical to that induced by NS1. This response to virus infection was only partially dependent upon NS1-mediated activation of PI3K. The presence of NS1 allows influenza A to modify the biophysical properties of infected cells by activating a Na(+)-permeable conductance. Whilst the activation of Na(+)-permeable channels may be expected to increase the rate of Na(+) absorption and thus reduce the volume of liquid in the lung, liquid does normally accumulate in influenza A-infected lungs. The overall effect of influenza A on lung liquid volume may therefore reflect a balance between the activation and inhibition of Na(+)-permeable channels.
Assuntos
Vírus da Influenza A/patogenicidade , Canais Iônicos/metabolismo , Sistema Respiratório/metabolismo , Sistema Respiratório/virologia , Fenômenos Biofísicos , Linhagem Celular , Dexametasona/farmacologia , Células Epiteliais/efeitos dos fármacos , Células Epiteliais/metabolismo , Células Epiteliais/virologia , Humanos , Vírus da Influenza A/genética , Influenza Humana/metabolismo , Influenza Humana/virologia , Transporte de Íons/efeitos dos fármacos , Fosfatidilinositol 3-Quinases/metabolismo , Sistema Respiratório/citologia , Sódio/metabolismo , Transfecção , Proteínas não Estruturais Virais/genética , Proteínas não Estruturais Virais/toxicidadeRESUMO
Recent work has demonstrated that the PI3K (phosphoinositide 3-kinase) signalling pathway is important for efficient influenza A virus replication. Activation of PI3K in virus-infected cells is mediated by the viral NS1 protein, which binds directly to the p85beta regulatory subunit of PI3K and causes the PI3K-dependent phosphorylation of Akt (protein kinase B). Given that recombinant influenza A viruses unable to activate PI3K signalling are attenuated in tissue culture, the PI3K pathway could be a novel target for the development of future anti-influenza drugs.
