Carcinogenesis Advance Access published online on May 8, 2009
Carcinogenesis, doi:10.1093/carcin/bgp117
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DNA double-strand break repair activities in mammary epithelial cells - influence of endogenous p53 variants
1 Department of Obstetrics and Gynaecology of the University of Ulm, Prittwitzstrasse 43, D-89075 Ulm, Germany
Corresponding author: Prof. Dr. Lisa Wiesmüller, Universitätsfrauenklinik, Prittwitzstrasse 43, D-89075 Ulm, Germany, phone: +49-731-50058800, FAX: +49-731-50058810, e-mail: lisa.wiesmueller{at}uni-ulm.de
Intriguingly, all ten breast cancer susceptibility genes known today are directly or indirectly related to DNA double-strand break (DSB) repair suggesting a critical role of DSB repair dysfunction in the etiology of this tumor entity. We and others had previously provided evidence indicating that the breast cancer susceptibility gene product p53 controls DSB repair. Experiments with ectopically expressed proteins showed that oncogenic mutants of p53 deregulate homologous recombination (HR) and possibly also non-homologous end joining (NHEJ). Here, we systematically analyzed the role of different p53 variants endogenously expressed in a series of mammary epithelial cell lines. We provide evidence that endogenous wild-type p53 represses HR, particularly between short homologies which strengthens the idea of a quality control mechanism underlying HR regulation. To a lesser extent, p53 also down-regulates microhomology-mediated NHEJ and single-strand annealing (SSA). Our data also suggest that repression of NHEJ regulation may require the extreme C-terminus, whereas the oligomerization and core domains are involved in HR regulation. We show that depending on the individual mutation, p53 mutants retain more or less partial DSB repair down-regulatory activities, when compared to loss of p53. All in all, relative effects on distinct DSB repair pathways and discrimination between HR substrates with perfectly versus imperfectly homologous sequences represent good markers for a p53 defect due to a specific mutation. Thus, advanced DSB repair analysis may serve as a novel assay for the functional classification of p53 mutations.
Key Words: breast cancer • DNA double-strand break repair • homologous recombination • p53 • truncating mutation
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Received February 27, 2009; revised April 19, 2009; accepted May 1, 2009.