Western blotting

Cells were lysed in RIPA buffer with 1 : 100 protein inhibitor for 30 min on ice. The supernatants were collected as total protein after centrifugation at 15 000 g for 30 min. Equal amounts of protein were separated by sodium dodecyl sulfate polyacrylamide electrophoresis followed by western blotting. The protein bands were visualized by enhanced chemiluminescence (Millipore, Billerica, MA, USA) according to the manufacturer's instructions, and data were quantified using densitometry analysis. Experiments were repeated three times, and the bands were scanned and quantified.