Carcinogenesis Advance Access originally published online on January 23, 2004
Carcinogenesis 2004 25(8):1305-1313; doi:10.1093/carcin/bgh092
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Carcinogenesis vol.25 no.8 © Oxford University Press 2004; all rights reserved.
ARTICLE |
Recombination at chromosomal sequences involved in leukaemogenic rearrangements is differentially regulated by p53
1 Universitätsfrauenklinik, Prittwitzstrasse 43, D-89075 Ulm, 2 Heinrich-Pette-Institut für Experimentelle Virologie und Immunologie an der Universität Hamburg, Martinistrasse 52, D-20251 Hamburg and 3 Institut für Pharmazeutische Biologie, Johann Wolfgang Goethe Universität, Biozentrum, N230, R303, Marie-Curie-Strasse 9, D-60439 Frankfurt/Main, Germany
4 To whom correspondence should be addressed Email: lisa.wiesmueller{at}medizin.uni-ulm.de
Chromosomal translocations and retroviral integration events at breakpoint cluster regions (bcrs) have been associated with leukaemias. To directly compare the effect of different cis-regulatory sequences on recombination, we adapted our SV40 based model system to the analysis of correspondingly selected bcrs from the TAL1, LMO2, retinoic acid receptor 
(RAR) and MLL genes. We show that a 399 bp fragment from the MLL bcr is sufficient to cause a 3–4-fold stimulation of spontaneously occurring DNA exchange and to respond to etoposide by up to 10-fold further elevated frequencies, i.e. to mimic the fragility of the 8.3 kb bcr during chemotherapy. To analyse the regulatory role of p53 in recombination involving leukaemia-related sequences, we stably expressed wtp53 and a transactivation negative mutant. Consistent with the proposed role of p53 as a suppressor of error-prone recombination, both p53 proteins down-regulated recombination with most of the sequences tested, even with the MLL bcr after etoposide treatment. Surprisingly, however, p53 stimulated recombination, in constructs carrying the RAR bcr fragment. This is the first study, which provides evidence for a stimulatory role of p53 in homologous recombination. Our data further indicate that inhibition of topoisomerase I can mimic the effects of p53 on stimulating recombination on the RAR bcr. Thus, these data also firstly describe a biological role of the biochemical interactions between p53 and topoisomerase I that may have implications for a gain-of-function phenotype of certain p53 mutants in genetic destabilization.
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