BCL6 represses PTPROt via direct interactions with the PTPROt promoter region. (A) BCL6 binds to the PTPROt promoter in vivo. Chromatin immunoprecipitation was performed in 2 DLBCL cell lines (DHL4 and DHL6) using BCL6 antibody or normal IgG as control. The target amplicons in the PTPROt promoter include the 3 predicted BCL6 binding sites (BS1-3, ■) and 2 distant upstream or downstream control regions (C1 and C2, □). The BCL6 versus IgG ratio was calculated for each region and normalized to control region 1. (B) BCL6-mediated repression of PTPROt promoter requires intact BCL6 binding sites. PTPROt-promoter-driven luciferase constructs with or without the individual or combined mutations in the predicted BCL6 binding sites were cotransfected with pMT2T-HA-BCL6 into HEK293T cells. Luciferase activities were determined thereafter.