Cells in the human body have to deal with DNA damage daily, either caused by external or internal sources. The DDR is particularly strong in stem cells. Since these cells have a long life span and... Show moreCells in the human body have to deal with DNA damage daily, either caused by external or internal sources. The DDR is particularly strong in stem cells. Since these cells have a long life span and are essential for tissue homeostasis, tolerance to damaged DNA would lead to accumulation of mutations and malignant transformation. In addition, accumulation of damaged DNA would lead to loss of the stem cell pool and contribute to aging. In this thesis I investigated the role of the DNA damage response in the context of stem cells as well as cancer cells, from the response to different DNA damaging agents, to the importance of the interaction with the extracellular matrix in combination with the presence of oncogenes. In order to acquire a complete picture of the DNA damage response in mES cells, and therefore elucidate novel pathways involved in this particular response, we combined OMICS techniques such as Functional Genomics, Transcriptomics and Phosphoprotoemics, that once overlapped, allowed us to find novel pathways that where not previously described to be involved in the DNA damage response. Show less
The work presented in this thesis has focused on the role of Mitogen Activated Protein Kinases (MAPKs) and their major downstream targets, the AP-1 transcription factors, in particular the AP-1... Show moreThe work presented in this thesis has focused on the role of Mitogen Activated Protein Kinases (MAPKs) and their major downstream targets, the AP-1 transcription factors, in particular the AP-1 components ATF3, Fra1, c-Jun, ATF-2 and c-Fos. Chapter II provides information on the signaling pathways involved in the activation of ATF-2 and ATF3 in the response of primary human fibroblasts to ionizing radiation. In chapter III c-Jun and ATF3, the MAPK JNK and the MAPK-phosphatase MKP-1 are identified as important sensors of UV-induced-DNA damage in transcribed genes. Chapter IV shows that ATF3 acts as an antiapoptotic JNK target in T98G glioblastoma cells, whereas Fra1 seems to act as a proapoptotic effector of both JNK and ERK. In addition, it is shown that ATF3 and Fra1 have opposite effects on cisplatin-induced S phase arrest. Chapter V shows that Fra1 also can exhibit a pro-apoptotic function in UV-irradiated fibroblasts. Furthermore, this chapter reports an as yet unknown function of JNK: repression of the transactivating activity of c-Jun/Fos(- like) dimers, mediated via hyper-phosphorylation of the c-Jun transactivation domain. The data further emphasizes that c-Jun/Fos(-like) and c-Jun/ATF dimers and their respective target genes can exhibit opposite functions in DNA damage responses. Show less
