RNA Polymerase I regulation by chromatin remodelling

Cell proliferation and growth is correlated with effective protein synthesis and ribosome biogenesis. The transcription of the 47S pre-ribosomal RNA by RNA Polymerase I (RNA Pol I) machinery is the rate-limiting step of ribosome biogenesis and can accounts for more than 50% of total cellular transcription. RNA Polymerase I transcription is a highly energy-consuming process which requires regulation at various stages. In the work presented in this thesis, we have investigated the regulation of RNA Pol I transcription, and investigated the stress response triggered by impaired RNA Pol I transcription. We showed in study I that the ATP dependent chromatin remodelling complex B-WICH is required to maintain an open chromatin landscape at the ribosomal DNA (rDNA) gene promoter in order to allow for transcription initiation by RNA Pol I. In absence of B-WICH, the NuRD complex reconfigures the chromatin landscape to an inaccessible state. We showed in study II that impairment of RNA Pol I transcription by deleting WSTF, a core subunit of B-WICH resulted in cell cycle arrest and apoptosis. More severe inhibition of RNA Pol I transcription through chemical compounds resulted in activation of cellular stress response cascades including but not limited to cell cycle arrest, unfolded protein response and oxidative stress response. We showed in study III that RNA Pol I transcription was increased during epithelial-mesenchymal transition (EMT) in the context of development and disease. The association of the EMT-driving transcription factor SNAIL1 with the rDNA gene promoter was shown to be essential in EMT triggered RNA Pol I transcription. The work presented in this thesis demonstrates the importance of RNA Pol I transcription regulation in maintaining cellular homeostasis