DN XBP1 expression is toxic and has profound effects on ER stress gene transcription. A, MTT assay of INS-1E cells after 24 h of infection with increasing doses of adenoviruses encoding LacZ, DN ATF6, and DN XBP1. ** and ***, p < 0.01 and p < 0.001, respectively, for pairwise comparison of DN ATF6 with DN XBP1 (n = 3). B–F, Q-PCR of BiP, Atf4, Chop, endogenous Atf6, and endogenous Xbp1 mRNA in INS-1E cells after infection with 20 units/cell of the adenoviruses for 16 h followed by 20 μm CPA or vehicle for 6 h (n = 3). *, **, and ***, p < 0.05, p < 0.01, and p < 0.001 relative to LacZ plus vehicle control. #, ##, and ###, p < 0.05, p < 0.01, and p < 0.001 relative to LacZ plus CPA. Error bars, S.E.