The tumor tissues were briefly homogenized in 200 µl of solution A (10 mM HEPES [pH 7.9], 1.5 mM MgCl2, 10 mM KCl, 0.5 mM dithiothreitol, 0.2 mM phenylmethylsulfonylfluoride), vortexed vigorously, incubated on ice for 10 min, and then centrifuged at 15000 rpm for 15 min.