Fig. 4.

Sensitivity of MCF-7 cells to tamoxifen is regulated by p53 and survivin. a Nogo-B receptor (NgBR) knockdown increases p53 protein level and decreases survivin in MCF-7-TamR cells. Protein levels were determined by western blot analysis. b Quantitative analyses of proteins presented in Fig. 3a were carried out using ImageJ and were normalized to the housekeeping gene β-actin. Data are presented as fold changes in the siNgBR group compared to the non-silencing (NS) group. c Knockdown of p53 increases survivin level in MCF-7 cells. MCF-7 cells were transfected with siRNA specifically targeting p53 as described in “Methods”. The protein levels of p53, NgBR, survivin and β-actin were determined using western blot analysis. d Quantitative analyses of proteins presented in Fig. 3c were carried out using ImageJ and were normalized to β-actin. Data are presented as fold changes in the sip53 group compared to the NS group. e Knockdown of p53 increases the clonogenenicity of MCF-7 cells. Clonogenic survival assay was used for measuring clonogenicity of MCF-7 cells treated with 4-OHT (1 μM). f Quantification of colony number in colony formation assays is presented in Fig. 3e. g Survivin knockdown increases apoptosis of MCF-7-TamR cells induced by 4-OHT (5 μM). h Percentages of apoptotic cells in Fig. 3g are shown in the bar graph. i Knockdown of p53 decreases the sensitivity of NgBR-deficient MCF-7 cells to tamoxifen. NgBR knockdown restored the sensitivity to tamoxifen, which is attenuated by silencing p53. j Quantification of colony number in colony formation assays described in Fig. 3i. The data are from three separate repeat experiments, and are presented as the mean ± SD (*p < 0.05, n = 3)