Fig. 5.

Histone gene knockdown is not sufficient to resensitise breast cancer cells to epirubicin. a A total of 7 × 10⁴ ZR75-1 epirubicin-resistant (EpiR) cells and MDA-MB-231 EpiR cells were transfected with 30 nM of each siRNA (Dharmacon; GE Healthcare, Lafayette, CO, USA) targeting HIST1H2AC and HIST1H2BK (individual knockdowns not shown for simplicity). Negative controls included media only, Lipofectamine only or mock transfection with non-targeting siRNA. Percentage gene expression knock-down is shown in Additional file 1: Table S3. b IC₅₀ values were generated using non-linear regression analysis, and average values of two independent experiments are graphed. Error bars represent standard deviation. c Fold changes in gene expression of each histone variant relative to the housekeeping gene, RPL37A. d-e Histone knockdown effects on cell cycle and apoptosis for MDA-MB-231 and ZR-75-1. Tables show average percentages of cells in G1, S and G2 stages of cell cycle, and precent live versus dead cells in each experimental and control condition. Numbers in parenthesis indicate standard deviation between two experiments