Cell culture and transfection
HEK293T cells were maintained at 37°C in Dulbecco's modified Eagle's medium (DMEM) supplemented with 10% fetal bovine serum (Sigma), 100 IU/ml penicillin and 100 μg/ml streptomycin. Transient transfection of HEK293T cells was carried out using calcium phosphate method or Fugene6 transfection reagent (Roche). Y79 retinoblastoma cells were maintained in Iscove's modified Dulbecco's medium with 4 mM L-glutamine adjusted to contain 1.5 g/L sodium bicarbonate, 20% FBS. Transient transfection was carried out using TransIt LT1 (Mirus).