Regulation of the histone acetyltransferase p300 by TRIM25

点击翻译按钮获取中文摘要

Due to its acetyltransferase-activity, its E3 ligase activity and by acting as a scaffold for protein-protein interactions, p300 is essential for a multitude of cellular processes and its misregulation is involved in several diseases. Yet, despite its importance, our knowledge about its regulation is still very limited. While we were investigating the regulation of p53 by TRIM25 (Zhang et al., 2015), we observed that in the presence of TRIM25 p300 abundance and p300-dependent p53 activity were strongly decreased. TRIM25 is a member of the TRIM-protein family, a protein family that is characterized by the presence of a tripartite motif at the N-terminus of TRIM proteins consisting of a RING-domain, one or two B-boxes and a coiled-coil region. Despite having a RING-domain and E3 ligase activity e.g. towards 14-3-3 sigma, TRIM25 was unable to target p300 for degradation by 26S proteasomes. Instead, we could inhibit p300 degradation by inhibitors of lysosomes. How TRIM25 targets p300 to lysosomal degradation is not known. We hypothesize that TRIM25 somehow mediates that p300 aggregates in cellular aggresomes that are then fitted into the autophagy pathway. In this context, TRIM25 could participate in the aggregation of p300 in aggresomes or in the delivery of p300 to autophagosomes. By using inhibitors of various degradation pathways and dominant negative mutants, by downregulating proteins that may be involved in p300 degradation with RNAi, by investigating whether and which post-translational modifications are involved, by investigating protein-protein-interactions and by microscopic studies, we will challenge our hypothesis and determine whether (i) p300 is degraded by the authophagy pathway (ii) whether degradation of p300 involves the formation of aggresomes and (iii) how TRTIM25 mediates the degradation of p300. Since p300 is a central node of transcriptional control, we further hypothesize that via the regulation of p300, TRIM25 has an as yet undervalued impact on gene transcription. We propose to investigate the transcriptome of cells and tissues with and without TRIM25 in a genome wide manner. Downregulation of p300 by RNAi in some of the cells will allow us to distinguish between p300-dependent and p300-independent processes. In summary, the proposed experiments will strongly increase our knowledge about the regulation of p300 and the activity of TRIM25, In addition, they may allow additional and novel insights into the function of TRIM proteins as autophagy-re/adaptors, a function that only recently has been elucidated.