Cell lines and animals
SK-N-SH cells, obtained from Shanghai Cell Bank of Chinese Academy of Medical Sciences, were maintained in DMEM (Gibco) with 10% fetal calf serum (Gibco), and cultivated at 37°C in a 5% CO2humidified incubator. 6 week female BALB/c mice, each weighing 18 to 20 g (SCXK Hebei 2008-1-003), were purchased from the Experimental Animal Center of Hebei Province (SPF grade, SYXK Hebei 2008-0026) and housed in a specific pathogen-free facility. Spirit, diet and defecation of mice were regularly observed and recorded. All experiments were conducted in accordance with the principles and procedures outlined in the Guideline of Institutional Experimental Animal Review Committee.