The ion channel activity of the influenza virus M2 protein affects transport through the Golgi apparatus.

Abstract

High level expression of the M2 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 M2 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 HA0 was not expressed at the cell surface, and accumulation HA at the plasma membrane was reduced to 75-80% of control cells. The delay in intracellular transport of HA on coexpression of M2 was not observed in the presence of the M2-specific ion channel blocker, amantadine, indicating that the Golgi transport delay is due to the M2 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 M2 protein expression did for HA and other integral membrane glycoproteins. EM data showed a dilation of Golgi cisternae in cells expressing the M2 ion channel protein. Taken together, the data suggest a similarity of effects of M2 ion channel activity and monensin on intracellular transport through the Golgi apparatus.

Novel Cis-acting Element GASE Regulates Transcriptional Induction by the Golgi Stress Response

“…Upon monensin treatment, swollen vesicles emerged near the nucleus (Panels D and G), and YFP-Golgi marker was located in the membrane of these vesicles (Panels E, F, H and I), which is consistent with previous studies (Dinter and Berger, 1998;Tartakoff, 1983). This suggests that most of these swollen vesicles were derived from the Golgi apparatus, and that monensin is effective in HeLa cells, in accord with the findings of Lamb and colleagues that monensin treatment inhibits post-Golgi transport of viral HA protein in HeLa cells (Sakaguchi et al, 1996). After 12 h of monensin treatment, the cytosol of HeLa cells was filled with numerous swollen vesicles (Panel J) in which YFP-Golgi was localized (Panels K and L).…”

Viroporins: structure, function and potential as antiviral targets

“…2B expression also alters cellular trafficking, evidenced by effects on the passage of vesicular stomatitis virus G glycoprotein to the cell surface (Doedens & Kirkegaard, 1995). Expression of both IAV M2 (Ciampor et al, 1992a(Ciampor et al, , b, 1995Sakaguchi et al, 1996;Takeuchi & Lamb, 1994;Takeuchi et al, 1994) and HCV p7 (Griffin et al, 2004;Wozniak et al, 2010) has been shown to induce a monensin-like de-acidification of the trans-Golgi/endosomal system, which serves to protect acid-labile proteins/particles during egress. This effect is highly likely to dysregulate cellular trafficking and the resultant surface expression of various proteins.…”

Toxicity of Influenza A Virus Matrix Protein 2 for Mammalian Cells is Associated with its Intrinsic Proton-Channeling Activity

“…6,19 M2 proton channel activity is known to be cytotoxic in heterologous expression systems, such as E. coli, 20,21 with especially severe effects seen in insect cells and S. cerevisiae, with no overt toxicity observed in vertebrate cells. 21,22 …”