Fig. 5. STAT1 transactivates a p21 promoter-luciferase reporter construct in MCF-7 cells but not in MDA-MB-231 cells. MCF-7 and MDA-MB-231 cells were transfected with constructs containing a luciferase gene downstream of various p21 promoter constructs. The cells were treated with 10 ng/ml IFN- for 24 h, and then luciferase was measured. Error bars, the mean of triplicate samples ± SE. The asterisk represents a statistically significant difference between control and IFN- (P < 0.05). Data shown are representative of three separate experiments.