The ion channel activity of the influenza virus M(2) protein affects transport through the Golgi apparatus

High level expression of the M(2) ion channel protein of influenza virus inhibits the rate of intracellular transport of the influenza virus hemagglutinin (HA) and that of other integral membrane glycoproteins. HA coexpressed with M(2) is Properly folded, is not associated with GRP78-BiP, and trimerizes with the same kinetics as when HA is expressed alone. Analysis of the rate of transport of HA from the ER to the cis and medial Golgi compartments and the TGN indicated that transport through the Golgi apparatus is delayed. Uncleaved HA(0) was not expressed at the cell surface, and accumulation of HA at the plasma membrane was reduced to 75-80% of control cells. The delay in intracellular transport of HA on coexpression of M(2) was not observed in the presence of the M(2)-specific ion channel blocker, amantadine, indicating that the Golgi transport delay is due to the M(2) protein ion channel activity equilibrating pH between the Golgi lumen and the cytoplasm, and not due to saturation of the intracellular transport machinery. The Na+/H+ ionophore, monensin, which also equilibrates PH between the Golgi lumen and the cytoplasm, caused a similar inhibition of intracellular transport as M(2) protein expression did for HA and other integral membrane glycoproteins. EM data showed a dilation of Golgi cisternae in cells expressing the M(2) ion channel protein. Taken together, the data suggest a similarity of effects of M(2) ion channel activity and monensin on intracellular transport through the Golgi apparatus.