The PRH/Hex repressor protein causes nuclear retention of Groucho/TLE co-repressors

The Proline-Rich Homeodomain protein (PRH/Hex) is a transcription factor that functions as an important regulator of vertebrate development and many other processes in the adult including haematopoiesis. The Groucho/TLE family of co-repressor proteins also regulate development and modulate the activity of many DNA-binding transcription factors during a range of diverse cellular processes including haematopoiesis. We have shown previously that PRH is a repressor of transcription in haematopoietic cells and that an Eh-1 motif present within the N-terminal transcription repression domain of PRH mediates binding to Groucho/TLE proteins and enables co-repression. Here we demonstrate that PRH regulates the nuclear retention of TLE proteins during cellular fractionation. We show that transcriptional repression and the nuclear retention of TLE proteins requires PRH to bind to both TLE and DNA. In addition, we characterise a trans-dominant negative PRH protein that inhibits wild type PRH activity by sequestering TLE proteins to specific sub-nuclear domains. These results demonstrate that transcriptional repression by PRH is dependent on TLE availability and suggest that sub-nuclear localisation of TLE plays an important role in transcriptional repression by PRH.