(A) Expression of the gene encoding PIAS1 is ER stress-inducible. Quantitative real-time PCR analysis of expression of the PIAS1 mRNA in MEF cells in response to thapsigargin (0,2µM) or dithiothreitol (5µg/ml) for 2 and 4 hours, respectively. Expression values were normalized to β-actin mRNA levels. Fold changes of mRNA are shown by comparing the mRNA expression values of treated cells to that of the control cells. Each bar denotes the mean ± STDEV (n=3 experiments). (B) Sumoylation represses the transcriptional activity of ATF6 on the UPRE-containing reporter. The plasmid vector control, the vector expressing the activated human ATF6 or its mutant isoforms K1R, K2R, or K1,2R, the luciferase reporter vector under the control of UPRE, and the internal control vector expressing β-galactosidase (LacZ) under the control of CMV (cytomegalovirus) promoter (pCMV-lacZ) were co-transfected into COS1 cells. The luciferase activities were measured at 36 hours post transfection, and the values were shown after the normalization to the internal control LacZ levels.