MAPKinase signaling and AP-1-regulated gene expression in cellular responses to DNA damage

Abstract

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 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.