PTPROt transcription is regulated by BCL6. (A) BCL6 represses PTPROt promoter-driven transcription in a dose-dependent manner; 350 ng of PTPROt promoter luciferase reporter construct (pGL3-Luc-PTPROt −1108 + 381) was cotransfected with empty vector or increasing doses (5-100 ng) of a BCL6 expression vector (pMT2T-HA-BCL6) into HEK293T cells. Luciferase activities were evaluated as described (see “Luciferase assays”). (B) WT-BCL6 but not BCL6 mutants repress PTPROt promoter-driven transcription. pGL3-Luc-PTPROt-1103 + 381 was cotransfected with 100 ng of vectors encoding either HA-BCL6 or 1 of 2 BCL6 mutants lacking either the amino-terminal transcriptional repressor domain (BCL6-ZF) or the carboxy-terminal DNA binding zinc-finger domain (BCL6-ΔZF) and luciferase activities were determined thereafter. In both panels A and B, representative luciferase activities from 3 independent experiments were normalized to Renilla luciferase activity and represented as fold change ± SD.