HEK293T cells purchased from ATCC (ATCC No. CRL-11268 TM , USA) were cultured in Dulbecco's Modified Eagle Medium (Invitrogen, USA) containing 10% fetal bovine serum. Plasmids were transfected into HEK 293T cells using Lipofectamine 2000 Reagent (Invitrogen, USA), and this process was carried out according to the manual guidelines. After 48 hours, culture media was removed and rinsed once with PBS (pH 7.4), and then dissolved (0.2 ml/hole). After the collection, the sample was heated for 5 min at 100uC, and then stored at 220uC.