Western blotting was performed as described previously.21 22 (link) Image acquisition and quantitation of band intensity were performed using a Chemdoc Imager (Bio-Rad, Hercules, California, USA). For immunoprecipitation assays, cells were lysed in buffer (50 mM Tris·HCl, pH 8.0, 150 P and 0.5% Nonidet P-40) and centrifuged at 16,000×g for 30 min to remove cellular debris. Cleared lysates were subjected to immunoprecipitation with appropriate antibodies. For immunocytochemistry, cells were fixed in 4% paraformaldehyde at room temperature for 15 min, permeabilized in 5% Triton X-100 for 5 min, and stained using appropriate primary antibodies. The secondary antibodies used for these experiments were anti-mouse or anti-rabbit IgG conjugated to Alexa Fluor 488 or Alexa Fluor 594, and nuclei were stained with 4’,6-diamidino-2-phenylindole (Life Technologies).