Fig. 4

Combinatorial treatments increase CRC cell apoptosis, but not through DNA damage or ER stress enhancement. a Apoptosis-associated DNA fragmentation of HCT116, DLD-1, and HT-29 cells after sequential treatments with 1 μM 5-aza-dC and 5–50 μM etoposide (n = 3). Figure 1a shows the treatment scheme. Data are presented as means ± SD. *P < 0.05 compared with DNA demethylating agent treatment group and topoisomerase inhibitor treatment group. Representative histograms are presented in Additional file 3: Figure S2. b Representative Annexin V-FITC/PI-double staining histograms of HCT116 cells after sequential treatments with 1 μM 5-aza-dC and 10 μM etoposide. Figure 1a shows the treatment scheme. More results are presented in Additional file 4: Figure S3. c Representative immunoblot of γH2A.X (Ser139) expression from HCT116 cells sequentially treated with 1 μM 5-aza-dC and 25 μM etoposide/irinotecan (n = 3). H2A.X served as a loading control. d Representative immunoblot of CHOP expression from HCT116 cells sequentially treated with 1 μM 5-aza-dC and 25 μM etoposide/irinotecan (n = 4). Actin served as a loading control. Figure 1a shows the treatment scheme. Jurkat cells treated with 25 μM etoposide served as a positive control. C - control, eto - etoposide