Figure 4. Zhangfei regulates p53-mediated cell growth and UPR. (A) Zhangfei-induced transcription from a promoter with p53 response elements is mediated by p53. D-17 cells were transfected with 0.5 µg of p53 response element containing promoter (pCAT3B-p53), 1 µg of plasmid expressing Zhangfei (pcZF) and 100 pM of si-RNA against p53 (si-p53) or non-targeting siRNA control (si-cont), 48 h after transfection, cells were analyzed for CAT activity or p53, Zhangfei and GAPDH proteins (inset). (B) Zhangfei-mediated suppression of cell growth is mediated through p53. D-17 cells were transfected with 100 pM of si-RNA against p53 (siRNA-p53) or non-targeting siRNA control (siRNA-cont). Eight hours after transfection, cells were either mock-infected or infected with Adeno-ZF, and growth characteristics were measured using WST-1 assay at 0 h, 24 h, 48 h, and 72 h after infection. (C) Zhangfei-mediated suppression of UPR genes is mediated by p53. D-17 cells were transfected 100 pM of siRNA-p53 or non-targeting siRNA-control. Forty-eight hours after transfection, cells were treated with thapsigargin for 4 h and harvested. Differences in levels of transcripts (Xbp1s, CHOP, and GRP78) were determined by qRT-PCR. The results were expressed as fold changes relative to mock-infected cells. The means and standard deviations of experiments (n = 3) are shown. P < 0.05 were considered to be significant.