Influenza virus M2 protein inhibits epithelial sodium channels by increasing reactive oxygen species

Area of Science:

• Cell Biology
• Virology
• Respiratory Physiology

Background:

• Influenza viruses disrupt epithelial sodium channel (ENaC) function, but the underlying mechanisms remain unclear.
• ENaCs are crucial for regulating airway surface liquid and lung fluid balance.

Purpose of the Study:

• To elucidate the mechanism by which influenza M2 protein down-regulates ENaC expression and function.
• To investigate the role of oxidative stress and cellular degradation pathways in M2-mediated ENaC dysfunction.

Main Methods:

• Expression of M2 protein in Xenopus oocytes and human airway cell lines (H441, A549).
• Measurement of ENaC membrane levels and amiloride-sensitive currents.
• Assessment of reactive oxygen species (ROS) production and effects of antioxidants and kinase inhibitors.
• Investigation using proteasome/lysosome inhibitors (MG-132) and analysis of Liddle ENaCs.

Main Results:

• Influenza M2 protein expression decreased ENaC membrane levels and amiloride-sensitive currents in both oocytes and airway cells.
• A specific M2 C-terminal region was critical for this down-regulation.
• M2-induced ENaC reduction was linked to increased reactive oxygen species (ROS) and was prevented by antioxidants and PKC inhibitors.
• Inhibition of proteasome and lysosome pathways blocked M2's effect, suggesting enhanced degradation.

Conclusions:

• Influenza M2 protein triggers oxidative stress, activating protein kinase C (PKC) pathways.
• This leads to enhanced endocytosis and proteasomal degradation of ENaCs, reducing their function.
• This mechanism contributes to influenza-associated airway and lung fluid dysregulation, potentially causing edema.