Pathways of homologous recombinantion and DNA interstrand cross-link repair : roles of mammalian RAD54 and SNMI

The aim of this thesis is to investigate mammalian DNA interstrand cross-link (ICL) repair. ICLs are formed by a number of agents used in tumor therapy, like mitomycin C and cisplatin. They constitute one of the most toxic damages to DNA, as they inhibit DNA strand separation. However, little is known about the mechanisms of !CL repair. A number of DNA repair pathways exist, each involved in the repair of specific types of DNA damage that continuously threaten cellular function. An intriguing aspect of ICL repair is the involvement of several of these repair pathways, mainly nucleotide excision repair, homologous recombination, and postreplication/translesion repair. An overview of the involvement of these different repair pathways in ICL repair is given in Chapter 4. This chapter also depicts putative models describing the co-operation of these pathways in repairing ICLs. Next to genes involved in several repair pathways, other genes have been isolated that are exclusively involved in ICL repair, such as yeast SNMJ. snml mutant yeast cells are sensitive to a number of ICL agents, but they are hardly or not sensitive to other DNAdamaging agents. As described in Chapter 5, we have investigated the human and mouse homologs of Snml. We isolated mouse SNMJ and made embryonic stem cells and mice deficient for SNMJ. Both cells and mice are viable and sensitive to mitomycin C. These results indicate that mammalian Snm 1 is involved in the cellular response to at least some types of!CLs. We also showed that Snml is probably not involved in the homologous recombination pathway of ICL repair, as two parameters for homologous recombination, the formation of mitomycin C-induced Rad51 foci and sister chromatid exchanges, are not affected in SNMJ-deficient mouse cells.