Cells were lysed with RIPA buffer (50 mM Tris/CL, pH 7.2, 1% deoxycholate, 0.15% sodium dodecylsulfate, 150 mM sodium chloride, 50 mM sodium fluoride, 10 mM EDTA, 1% NP-40, 1 mM PMSF, protease inhibitors). Aliquots with equal total concentrations of cleared lysates (20,0006g; 10 min; 4uC) were mixed with 2x-urea buffer (200 mM Tris, pH 6.8; 8 M urea; 5% sodium dodecyl sulfate (SDS); 0.1 mM EDTA; 0.03% bromphenol blue; 1.5% dithiothreitol) and denatured for 25 min at 50uC. Samples were then fractionated on 10% SDS-polyacrylamide gels, blotted to polyvinylidene difluoride (PVDF) membranes (Millipore) and subjected to enhanced chemiluminescence detection (Pierce) using specific antisera directed against phosphorylated or non-phosphorylated cdc2-cyclin B kinase (Cell Signaling Technology), GAPDH (Abcam), the cytosolic tail of the MeV F protein [81] , or influenza A/WSN virus M2 (Thermo Scientific). Immunostained PVDF membranes were developed using a ChemiDoc XRS digital imaging system (Bio-Rad) and horseradish peroxidase conjugated anti-species IgG (mouse or rabbit) antibodies. For densitometry, signals were quantified using the Quanti-tyOne software package (Bio-Rad).