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. 2015 Apr 6;125(5):1955–1967. doi: 10.1172/JCI78863

Figure 7. The abundance of SEC63 and XBP1s determines IRE1α activity.

Figure 7

(A) Maximal IRE1α activation in DKO cells in the basal state (no tunicamycin) evidenced by complete p-IRE1α and complete splicing of XBP1. WT and DKO cells without and with treatment with tunicamycin were subjected to immunoblotting analysis with indicated antibodies. Bottom panel, Xbp1 mRNA splicing measured by RT-PCR. Note that Xbp1 KO cells produce mutant Xbp1 mRNA lacking exon 2 sequences that undergo splicing but do not encode functional protein due to translational frame-shifting. (B) XBP1 and SEC63 suppress IRE1α phosphorylation in unstressed DKO cells. XBP1 also suppresses IRE1α activation in tunicamycin-stressed DKO cells. DKO cells were reconstituted with XBP1, XBP1s, or SEC63 by retroviral transduction. IRE1α activation was measured by immunoblotting analysis. Bottom panels, IRE1α-mediated splicing of the endogenous mutant Xbp1* and the transgenic human XBP1 mRNAs were measured by RT-PCR. *Splicing assay with mouse Xbp1 primers.