Total p53

Cells were incubated in cell lysis buffer (no. 9803; Cell Signaling Technology, Danvers, MA) followed by centrifugation at 13,000 rpm for 10 minutes. Supernatants were collected, and protein concentrations were determined using the Bradford Assay (Bio-Rad, Hercules, CA). Protein lysates were electrophoresed on Tris-glycine SDS polyacrylamide gels and transferred onto Immobilon-P membrane. Incubation with antibodies was performed according to Cell Signaling Technology-recommended procedures and proteins were visualized using ECL (Pierce). p16^Ink4A, p19^ARF, p21, Total-p53, cdc2 were from Abcam. Phospho-p53(Ser15), Cyclin B1, Phospho-SAPK/JNK(Thr183/Tyr185), Total-SAPK/JNK and β-Actin were from Cell Signaling Technology.

K₂Cr₂O₇ (molecular weight, 294.18) was purchased from Duksan pure chemical Company Limited, (Ansan, South Korea). Penicillin-streptomycin solution, trypsin-EDTA solution, DMEM, and 1% antibiotic-antimycotic solution were obtained from Life Technologies GIBCO (Grand Island, NY, USA). Fetal bovine serum (FBS) and an in vitro toxicology assay kit were purchased from Sigma-Aldrich (St. Louis, MO). The antibodies used for immunoblotting were against phospho P53, phospho ERK1/2, total ERK1/2, total AKT1 (Cell Signaling Technology, Beverly, MA), phospho P38 (Santa Cruz Biotechnology Inc., Santa Cruz, CA), phospho AKT1, phospho JNK1/2, total P53, total JNK1/2, total P38, BAX, BCL2, CASP9, CASP3, PARP, beta-actin (Abcam, Cambridge, MA), and cytochrome c (ENZO Diagnostics Inc., Farmingdale, NY).