Publikationsserver der RWTH Aachen University
Die Regulation der c-MYC-abhängigen Genexpression durch SIRT1 und ASH2
Abstract
dc:descriptionThe c-MYC oncoprotein acts as a transcription factor and regulates different aspects of cell behaviour including proliferation, transformation and apoptosis. Deregulated expression of c-MYC is a common feature of many human malignancies and contributes to the transformation of normal to malignant cells. In spite of the well-characterised biological relevance of c-MYC, little information is available how c-MYC affects gene regulation at the molecular level. Transcriptional regulation of target genes is at least in part achieved by recruiting cofactors and complexes to target promoters. These factors act by modifying c-MYC and histones on c-MYC bound promoters, resulting in altered c-MYC stability and transcriptional activity as well as in changes in chromatin structure. The histone acetyltransferases (HATs) CBP and p300 act as such cofactors, acetylating c-MYC and thereby increasing its stability and its capacity to activate transcription. Another c-MYC interacting protein is the Trithorax protein ASH2, an oncoprotein and core member of several histone methyltransferase (HMT) complexes, which methylate histone H3 at lysine 4 (H3-K4) resulting in activation of gene expression. The aim of this work was to investigate, if the HAT-dependent acetylation of c-MYC is antagonized by histone decetylases (HDACs) and to analyse the functional consequences. Furthermore, the role of ASH2 in cell behaviour and its functional interaction with c-MYC should be investigated and overlapping c-MYC and ASH2 target genes should be identified. In this study it could be shown that c-MYC and the Sirtuin family member SIRT1, an NAD+-dependent deacetylase, interact and that c-MYC serves as a direct substrate of SIRT1. Furthermore it could be demonstrated in coexpression experiments and inhibitor studies that SIRT1 is responsible for c-MYC deacetylation in cells. Since CBP and p300 stimulate c-MYC-dependent activation, the influence of SIRT1 on this stimulation was examined. SIRT1 represses the HAT-mediated transcriptional stimulation, which is not due to a general inhibitory effect of SIRT1 on p300, suggesting that the repression is the result of the SIRT1-dependent deacetylation of c-MYC. Furthermore, the deacetylation of c-MYC enhances its ubiquitination, presumably by generating unmodified lysine residues, which afterwards can be targeted by E3 ubiquitin ligases. Analysis of ASH2 in tumour lines demonstrates that ASH2 is essential for proliferation. Preliminary findings indicate that c-MYC and ASH2 cooperate in regulating proliferation. Knockdown experiments revealed that the amount of ASH2 protein correlates with the level of global H3-K4 trimetylation in cells, a modification tightly associated with active transcription. Since c-MYC recruits HMT activity and binds to ASH2, the specificity of the c-MYC-bound HMT and its dependency on ASH2 was analysed. It could be shown that the HMT recruited by c-MYC trimethylates H3-K4 and that this is dependent on ASH2. Assuming that c-MYC and ASH2 cooperate in the regulation of gene expression, which is supported by the observation that the transformation of primary rat cells by c-MYC is dependent on ASH2, a gene expression analysis was performed in c-MYC and ASH2 transformed cells, to detect overlapping subsets of genes, that are differentially regulated in both settings. Comprehensive comparison of these regulated genes to known c-MYC target genes revealed 41 potential candidates that are regulated by c-MYC and ASH2. Together, the present study describes c-MYC as a substrat for SIRT1 dependent deacetylation, whereby SIRT1 is repressing c-MYC transactivation and enhances its ubiquitination. Furthermore this work suggests a cooperation of c-MYC and ASH2 in target gene activation and transformation.
Degree
thesis:*- Grantor dc:publisher
- Publikationsserver der RWTH Aachen University
- Year dc:date
- 2008
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- Kapelle, Karsten
- Contributors dc:contributor
-
- Lüscher, Bernhard
Subjects
dc:subject × 8Rights
dc:rights- Statement dc:rights
-
- info:eu-repo/semantics/openAccess
- Language dc:language
- ger