Establishment of Ire1-expressing cell lines and RNAi Ire1- / MEFs were obtained from R. Kaufman (University of Michigan Medical Center, Ann Arbor, MI), and XBP1 / MEFs were obtained from L. Glimcher (Harvard School of Public Health, Boston, MA). All cells were maintained at 37°C and 5% CO 2 in DME supplemented with 10% fetal calf serum, Gln, and antibiotics. We generated Ire1- / MEFs containing induction of ERdj4 by DTT, RIDD remained intact when cells were treated with both 1NM-PP1 and DTT (Fig. 4 F) .