Additional file 4: of PERK induces resistance to cell death elicited by endoplasmic reticulum stress and chemotherapy

Effects of chemotherapeutic drugs in human chemosensitive breast cancer cells with acquired resistance to ER stress. a. Release of the necrosis marker HMGB1 to culture media of human chemosensitive breast cancer MCF7 cells and the ER stress-resistant clone MCF7/Tun, grown in fresh medium (Ctrl) or in media containing: thapsigargin (Tg), tunicamycin (Tun), brefeldin A (Bfa), doxorubicin (Dox), cisplatin (Pt), as indicated in Methods. Data are mean ± SD (n = 3). *p < 0.001 vs MCF7 Ctrl cells; °p < 0.001 for MCF7/Tun treated cells vs MCF7 treated cells. b. Viability of cells measured by Neutral red staining. Data are mean ± SD (n = 3). *p < 0.05 vs MCF7 Ctrl cells; °p < 0.02 for MCF7/Tun treated cells vs MCF7 treated cells. c. Whole cell lysates were analyzed for the expression of MRP1. β-tubulin expression was used as control of equal protein loading. The figure is representative of 3 experiments with similar results. d. MRP1 mRNA levels were measured by qRT-PCR. Data are mean ± SD (n = 3). *p < 0.01 vs MCF7 cells. e. MRP1 protein on cell surface was measured by flow cytometry. Left panel: data are presented as mean fluorescence intensity (MFI) ± SD (n = 3). *p < 0.02 vs MCF7 cells. Right panel: representative flow cytometry histograms. Grey peak: non immune isotypic antibody. f. Intracellular doxorubicin content, an index of MRP1 activity, measured by fluorimetry. Data are mean ± SD (n = 3). *p < 0.005 vs MCF7 cells. (TIF 1434 kb)