ER stress up-regulates TRAIL-R2 through a PERK-dependent, CHOP and Ire1-independent mechanism. MDA-MB231 cells were transfected with scrambled (c) or CHOP (a), IRE1α (b) or PERK (c, d) siRNAs for 48 h to silence protein expression. Transfected cells were then treated with tunicamycin for 15 h prior to the analysis of protein knockdown and TRAIL-R2 expression by western blotting (a, b, c) or cell surface levels of TRAIL-R2 by flow cytometry (d). Results are representative of at least three independent experiments