RI-BPI specifically inhibits the transcriptional and biologic function of BCL6. (A) BCL6 immunoprecipitation (IP) in OCI-Ly1 cell lysates after exposure to RI-BPI^biotin or CP^biotin (control) peptides. Anti-IgG was used as control for the IP. Detection of complexes was done using avidin-HRP conjugates. (B) Reporter assays performed in 293T cells transfected with BTB-fusion constructs as indicated. Cells were exposed to control peptide (□) or RI-BPI 5 μM (), 10 μM (), or 20 μM (■). Fold repression is expressed versus the effect of each dose on a GAL4-DBD vector control for each experiment, relative to a TK-Renilla internal control. (C) Chromatin IP from OCI-Ly1 cells treated with CP 20 μM (□) or RI-BPI 20 μM (■) using antibodies against SMRT, BCL6, and actin (as a negative control) and amplifying the promoter region surrounding the BCL6 binding site on the TP53 gene by quantitative PCR. Results are expressed as percentage relative to the input. (D) Real-time detection of mRNA of the endogenous BCL6 target genes ATR (□) and TP53 (), and the control gene CD20 (■), performed in the BCL6-dependent cell lines OCI-Ly7, OCI-Ly10, and OCI-Ly1 and in the BCL6-independent cell line OCI-Ly4, after treatment with RI-BPI 20 μM and CP 20 μM. Results are expressed as fold change in mRNA abundance mediated by RI-BPI over CP.