Human syndromes with genomic instability and multiprotein machines that repair DNA double-strand breaks*

C. De la Torre1, J. Pincheira2 and J.F. López-Sáez3

1Biological Research Centre, CSIC, Madrid, Spain, 2Human Genetics Program, ICBM, School of Medicine, University of Chile, Santiago, Chile and 3Department of Biology, Autonomous University of Madrid, Madrid, Spain
*This review is dedicated to Liles (Dr. Matilde H. Navarrete), a great woman and scientist that shared with us her enthusiasm with cell beauty and left us on May, 2002 after a long and brave fight against uncontrolled proliferation

Offprint requests to: Prof. Dr. C. De la Torre, CIB-CSIC, Velázquez, 144, E-28006 Madrid, Spain. Fax: +34-91-562 75 18. e-mail: delatorrec@cib.csic.es

 

Summary. The present report deals with the functional relationships among protein complexes which, when mutated, are responsible for four human syndromes displaying cancer proneness, and whose cells are deficient in DNA double-strand break (DSB) repair. In some of them, the cells are also unable to activate the proper checkpoint, while in the others an unduly override of the checkpoint-induced arrest occurs. As a consequence, all these patients display genome instability. In ataxia-telangiectasia, the mutated protein (ATM) is a kinase, which acts as a transducer of DNA damage signalling. The defective protein in the ataxia-telangiectasia-like disorder is a DNase (the Mre11 nuclease) that in vivo produces single-strand tails at both sides of DSBs. Mre11 is always present with the Rad50 ATPase in a protein machine: the nuclease complex. In mammals, this complex also contains nibrin, the protein mutated in the Nijmegen syndrome. Nibrin confers new abilities to the nuclease complex, and can also bind to BRCA1 (one of the two proteins mutated in familial breast cancer). BRCA1 has a central motif that binds with high affinity to cruciform DNA, a structure present in places where the DNA loops are anchored to the chromosomal axis or scaffold. The BRCA1·cruciform DNA complex should be released to allow the nuclease complex to work in DNA recombinational repair of DSBs. BRCA1 also acts as a scaffold for the assembly of ATPases such as Rad51, responsible for the somatic homologous recombination. Loss of the BRCA1 gene prevents cell survival after exposure to cross-linkers. The BRCA1-RING domain is an E3-ubiquitin ligase. It can mono-ubiquitinate the FANCD2 protein, mutated in one of the Fanconi anemia complementation groups, to regulate it. Finally, during DNA replication, the nuclease complex and its activating ATM kinase are integrated in the BRCA1-associated surveillance complex (BASC) that contains, among others, enzymes required for mismatch excision repair. In short, the proteins missing in these syndromes have in common their BRCA1-mediated assembly into multimeric machines responsible for the surveillance of DNA replication, DSB recombinational repair, and the removal of DNA cross-links. Histol. Histopathol. 18, 225-244 (2003)

Key words: Ionizing radiation, Double-strand breaks, Multimeric repair machines, Ataxia telangiectasia, Ataxia telangiectasia-like disorder, Nijmegen breakage syndrome, Fanconi anemia, Familial breast and ovary cancer, BRCA1-associated surveillance complex

DOI: 10.14670/HH-18.225