Genomweite funktionelle Analyse von p53-Bindungsstellen via ChIPseq

The transcription factor p53 is one of the most important human tumor suppressors and regulates expression of genes especially in the fields of apoptosis, DNA-repair and cell cycle arrest. Therefore it is regularly described as ”guardian of the genome“. Its central role in suppression of tumor development becomes apparent considering the fact that it is mutated in about half of all human tumors. Very often those mutations lie in the region of the central DNA binding domain. First of all activation of p53 by cellular stress, e.g. hypoxia, DNA-damage or activation of oncogenes, leads (depending on the extent and duration of damage or stimulus) to either cell cycle arrest and DNA-repair or the destruction of the cell by apoptosis. How p53 makes this decision in detail and activates different sets of target genes, is unclear though. The data of this thesis prove that DNA binding cooperativity plays a vital role in these processes. In this thesis genomwide DNA-binding of p53 was examined via the ChIPseq method. For the first time p53-wildtype and p53-mutants with variable DNA-binding cooperativity were compared concerning the properties of their binding sites and target gene selection. For the functional analysis a particular focus was on apoptotic genes and genes from the fields of cell cycle arrest and DNA-repair. The data in this thesis prove that a rather high DNA-binding cooperativity is necessary for binding and activation of apoptotic target genes, whereas cell cycle arrest- and DNA-repair genes are often bound and activated even by less cooperative p53. One p53-mutant with excessively impaired DNA-binding cooperativity did not show significant binding and activation of gene expression. In times of ”targeted therapy“ a protein that is impaired in its function in about half of all cancer patients is a promising candidate for future cancer therapies. Considering the frequency of mutations in the DNA-binding domain of p53, restoration of p53- cooperativity is a promising target. This thesis can therefore make a contribution to understanding the importance and consequences of DNA-binding cooperativity and to their therapeutical application.