For Western blotting, cell lysates were prepared in RIPA buffer [50 mM Tris-HCl, pH 7.4, 150 mM NaCl, 2 mM EDTA, 1% Nonidet P-40 (vol/vol), 0.1% SDS (w/vol)] containing Protease Inhibitor Cocktail (Roche) and quantified by Bradford assay (Bio-Rad). Equivalent amounts of each sample were resolved by SDS-PAGE, transferred to a PVDF membrane, and Western blotted with anti-HA 12CA5 monoclonal antibodies (Invitrogen; 1:5,000) and HRP-conjugated goat anti-mouse secondary antibodies (Southern Biotechnology; 1:5,000).