A, B Mild induction of ER stress by chemical means protected cells against ferroptosis. MDA-MB-231 cells were pretreated with Brefeldin A (BFA, A) or tunicamycin (B) for 3 h, followed by 10 uM erastin for 24 h before measuring the viability with CellTiter-Glo®. The data were represented as mean ± SD (n = 3; ** p < 0.01; ****p < 0.0001; two-way ANOVA). C The changes in the levels of ZIP7 and HERPUD1 mRNA upon ZIP7 knockdown was validated by qRT-PCR. MDAMB231 cells were transfected with ZIP7 siRNA, and RNA samples were collected for qRT-PCR after 48 h of transfection. The data were represented as mean ± SD (n = 3; ***p < 0.001; ****p < 0.0001; one-way ANOVA). D Induction of HERPUD1 and xCT protein upon ZIP7 knockdown. Cell lysates were collected after 72 h transfection of non-targeting control (NC) or ZIP7 siRNA. For tunicamycin control, cells were treated with 0.2 μg/ml of tunicamycin for 20 h. E, F HERPUD1 induction conferred ZIP7-mediated ferroptosis resistance. MDAMB231 (E) or HT-1080 (F) cells were transfected with either siNC, or siZIP7_2, siHERPUD1, or both siRNAs for 48 h, and treated with the indicated concentration of erastin for an additional 24 h. The cell viability was measured by CellTiter-Glo®. The data were represented as mean ± SD (n = 3; ****p < 0.0001; two-way ANOVA). G Working model for ZIP7 knockdown mediated ferroptosis resistance. ZIP7 exports zinc ion into the cytosol from ER to maintain zinc homeostasis. In the absence of ZIP7, zinc accumulates in the ER, triggering ER stress response and the induction of HERPUD1 mRNA and protein expression to protect cells against ferroptosis.