Dulbecco's modified Eagle's medium/F12 medium, fetal bovine serum, 0.25% trypsin-EDTA, recombinant human epidermal growth factor, and an insulin-transferrin-selenium supplement were purchased from Invitrogen/Gibco (Carlsbad, CA, USA). Six-, 24-, and 96-well culture plates and cell culture flasks were purchased from Corning (Corning, NY, USA). The ROS detection reagent 2′,7′-dichlorodihydrofluorescein diacetate (H2DCFDA) was purchased from Abcam (Cambridge, UK). A Cell Counting Kit-8 was purchased from Dojindo Laboratories (Kumamoto, Japan), and an Annexin V-fluorescein isothiocyanate (FITC)/propidium iodide (PI) Apoptosis Detection Kit I was purchased from BD Biosciences (San Diego, CA, USA). A Pierce LDH Cytotoxicity Assay Kit was purchased from Thermo Fisher Scientific (Rockford, IL, USA). The following antibodies were purchased from Cell Signaling Technology (Danvers, MA, USA): anti-microtubule associated protein 1 light chain 3 beta (LC3B) (#3868), anti-sequestosome 1 (SQSTM1) (#88588), anti-beclin 1 (BECN1) (#3495), anti-autophagy-related gene 5 (ATG5) (#12994), anti-β-actin (#3700), anti-mTOR (#2983), anti-phospho-mTOR (#5536), anti-Caspase3 (#14220), horseradish peroxidase (HRP)-conjugated anti-rabbit immunoglobulin G (IgG) (#7076), HRP-conjugated antimouse IgG (#7072), Alexa Fluor 488-labeled donkey antirabbit IgG (#4412), and Alexa Fluor 555-labeled donkey antimouse IgG (#4409). An antibody specific for DDIT4 (#10638) was purchased from Proteintech Group (Rosemont, IL, USA). The anti-DDIT4 (#10638; Proteintech Group) and anti-SQSTM1 (#88588; Cell Signaling Technology) were used for immunofluorescence. All reagent-grade chemicals were purchased from Sigma-Aldrich (St. Louis, MO, USA) unless otherwise indicated.