Inhibition of ENaC activity by the Influenza Virus M2 proton channel

The mechanisms by which replicating influenza viruses decrease the activity of ENaC have not been elucidated. Herein we show that the influenza transmembrane protein (M2), a hydrogen channel, decreases levels and activity of ENaC in Xenopus oocytes, H441, and A549 cells transfected with a M2‐GFP cDNA. The regions of M2 protein responsible for this effect were localized to two separate portions of C‐terminus, between amino acids 52‐62 and 78‐82. This effect did not require M2 activation by low pH, and was prevented by MG‐132, a proteasome inhibitor. Furthermore, M2 has no effect when co‐expressed with ENaC bearing the Liddle mutations. Surface biotinylation of oocytes indicates that ENaC levels in cell membranes are reduced in the presence of M2. Pre‐treatment of both Xenopus oocytes and cells with GSH‐ester prevented the deleterious effects of M2 on ENaC. Together, these data suggest that M2 protein increases free radical production which results in ENaC endocytosis and proteasomal degradation by promoting increased ENaC ubiquitination. These results are the first indication that M2 regulates host ion channel function and suggest a mechanism for the influenza‐induced rhinorrhea and life‐threatening alveolar edema in humans. This Research was supported by NIH HL311979 grant to Sadis Matalon and NIH AI071393 grant to James Noah.