Fig. 5.

Reactivation of UPR after restoration of ER homeostasis. (A) T-REx293 cells were treated with 10 nM Dox and DTT (1 mM) for indicated time. After 4 h of DTT treatment, DTT-containing medium was exchanged for regular medium for 12 h. Cells were then reexposed to ER stress by treatment with DTT (1 mM) ). (B) Xbp-1 mRNA splicing was determined by RT-PCR. Total and phosphorylated IRE1 were detected by Western blotting as in Figure 4. The normalized ratio of the signals from the two blots is displayed. (C) Three-state model for activation of mammalian IRE1.