MDR HCT-116 cells exhibit an increase in calcium signaling-dependent UPR and autophagy. WT and MDR HCT-116 cells were treated with 50 µM cisplatin or vehicle for 12 h and subsequently (A) stained with Fura-2/AM to determine the cellular calcium release (×200 magnification) and (B) quantified using ImageJ (n=400 cells); one-way ANOVA was used for statistical analysis. (C) Western blotting analysis of ER stress- and UPR-related markers in WT and MDR cells with or without cisplatin exposure. (D) Fluorescence images of autophagic vesicles stained with Cyto-ID® Autophagy reagent (green) in WT and MDR cells (×1,000 magnification); nuclei were stained with Hoechst 33342 (blue). (E) Quantification of fluorescence intensity presented of cells presented in part (D); one-way ANOVA was used for statistical analysis. (F) Representative immunoblots of autophagy marker protein expressions in whole-cell protein lysates. **P<0.01; ***P<0.001; ****P<0.0001. ATG, autophagy-related gene; cis, cisplatin; eIF2α, eukaryotic initiation factor 2α; ER, endoplasmic reticulum; GRP78, glucose-regulated protein 78; IRE1α, inositol-requiring kinase 1α; MDR, multidrug resistant; ns, not significant; p-, phosphorylated; PERK, PKR-like endoplasmic reticulum kinase; UPR, unfolded protein response; veh, vehicle; WT, wild-type.