Figure 8.
JNK but not XBP-1 contributes to proteasome inhibitor-induced autophagy. A: Wild-type and IRE1α/β-deficient MEFs were stimulated with bortezomib at the designated concentrations for 24 hours. Cells were harvested, and immunoblot assay was conducted for total JNK and phosphorylated JNK. B and C: Wild-type (a–e) and XBP-1-deficient (f–j) MEFs were treated with bortezomib (20 nmol/L, b, c, g, and h) or A23187 (2.5 μmol/L, d, e, i, and j) in the presence (c, e, h, and j) or absence (b, d, g, and i) of JNK inhibitor, SP600126 (25 μmol/L) for 16 hours. The punctation pattern of GFP-LC3B was assessed (B) and quantified (C). * and #P < 0.01 by one-way analysis of variance (SP600125 versus vehicle control for bortezomib or A23187-treated groups. *XBP-1+/+ cells; #XBP-1−/− cells). D: Bax-deficient HCT 116 cells that stably expressing GFP-LC3B were treated with vehicle control, bortezomib (20 nmol/L), or A23187 (2.5 μmol/L) with or without SP600126 (25 μmol/L) for 16 hours. The punctation pattern of GFP-LC3B was assessed and quantified. *P < 0.01 by one-way analysis of variance (SP600125 versus vehicle control for bortezomib or A23187-treated groups). E: Wild-type and XBP-1-deficient MEFs were treated with MG132 at the designated concentrations or with the ER stress inducers A23187 (A, 2.5 μmol/L), thapsigargin (TG, 0.5 μmol/L), or tunicamycin (TM, 5 μg/ml) for 24 hours. Immunoblot assay was then conducted.