p53 activates transcription from the human BCL6 p53RE. (A) U2OS cells were cotransfected with 1 μg of wild-type BCL6 reporter vector and either an empty vector (Ctr) or wild-type p53-expressing vector in increasing concentrations. Results display mean ± SD of 4 independent experiments, each in triplicate. □ indicates control. (B) U2OS cells were cotransfected with 1 μg of wild-type BCL6 reporter vector and either an empty vector (Ctr) or 500 ng of either wild-type p53 (wt p53) or mutated p53-R175H (mut p53) expressing vectors. Results display mean ± SD of 3 independent experiments, each in triplicate. □ indicates control. (C) U2OS cells were cotransfected with 1 μgof either wild-type BCL6 reporter vector (wt p53RE) or BCL6 reporter vector with a mutation in the first decamer of the p53RE (mut1 p53RE) or in both decamers (mut1 + 2 p53RE) and 500 ng of either wild-type p53-expressing vector or an empty vector. Results displayed are fold activations of luciferase of each of the reporter vectors measured after addition of wild-type p53 divided by that measured after addition of an empty vector. Results display mean ± SD of 4 independent experiments, each in triplicate.