JNK1/2 is necessary for KPR-induced HO-1 expression. (A) HPAEpiCs were pretreated with various concentrations of SP600125 for 1 h and then incubated with DMSO or KPR (10 μM) for 16 h. The protein expression of HO-1 was determined by Western blot using GAPDH as a loading control. (B) Cells were pretreated with/without SP600125 (10 μM) for 1 h, and then incubated with DMSO or KPR (10 μM) for 6 h or 8 h. The HO-1 mRNA expression and promoter activity were analyzed by real-time PCR (6 h) and promoter activity assay (8 h), respectively. (C) Cells were transfected with scrambled (scrb), JNK1, or JNK2 siRNA, and then incubated with KPR (10 μM) for 16 h. The protein levels of HO-1, JNK1/2, and GAPDH were determined by Western blot. (D) Cells were transfected with PKCα, JNK1, or JNK2 siRNA, and then incubated with KPR (10 μM) for the indicated time intervals. The levels of phospho-JNK1/2, total JNK1/2, and total PKCα were determined by Western blot. Data are expressed as mean ± SEM (n = 5), analyzed with one way ANOVA and Dunnett’s post hoc test. # p < 0.01, as compared with the cells exposed to vehicle alone; or significantly different as indicated.