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Cancer predisposition and hematopoietic failure in Rad50(S/S) mice
Carla F Bender1, Michael L Sikes, Ruth Sullivan
1Laboratory of Genetics, University of Wisconsin Medical School, Madison, Wisconsin 53706 USA.
Abstract:
Mre11, Rad50, and Nbs1 function in a protein complex that is central to the metabolism of chromosome breaks. Null mutants of each are inviable. We demonstrate here that hypomorphic Rad50 mutant mice (Rad50(S/S) mice) exhibited growth defects and cancer predisposition. Rad50(S/S) mice died with complete bone marrow depletion as a result of progressive hematopoietic stem cell failure. Similar attrition occurred in spermatogenic cells. In both contexts, attrition was substantially mitigated by p53 deficiency, whereas the tumor latency of p53(-/-) and p53(+/-) animals was reduced by Rad50(S/S). Indices of genotoxic stress and chromosomal rearrangements were evident in Rad50(S/S) cultured cells, as well as in Rad50(S/S) and p53(-/-) Rad50(S/S) lymphomas, suggesting that the Rad50(S/S) phenotype was attributable to chromosomal instability. These outcomes were not associated with overt defects in the Mre11 complex's previously established double strand break repair and cell cycle checkpoint regulation functions. The data indicate that even subtle perturbation of Mre11 complex functions results in severe genotoxic stress, and that the complex is critically important for homeostasis of proliferative tissues.
Insights
Subtle defects in the Mre11-Rad50-Nbs1 complex cause severe genotoxic stress and tissue failure. This highlights the complex
Area of Science:
- Molecular Biology
- Genetics
- Cell Biology
Background:
- The Mre11-Rad50-Nbs1 (MRN) complex is crucial for DNA repair and maintaining genomic stability.
- Null mutations in MRN complex genes lead to inviability, indicating essential roles.
Purpose of the Study:
- To investigate the in vivo consequences of hypomorphic mutations in the MRN complex, specifically Rad50.
- To determine the impact of impaired Rad50 function on organismal health, cancer predisposition, and tissue homeostasis.
Main Methods:
- Generation and analysis of hypomorphic Rad50 mutant mice (Rad50(S/S)).
- Assessment of hematopoietic stem cell and spermatogenic cell attrition in Rad50(S/S) mice, with and without p53 deficiency.
- Evaluation of tumor latency and genomic instability markers in mutant mice.
Main Results:
- Rad50(S/S) mice displayed growth defects, cancer predisposition, and bone marrow/spermatogenic cell failure.
- p53 deficiency mitigated cell attrition but accelerated tumor development in Rad50(S/S) mice.
- Genotoxic stress and chromosomal instability were observed, despite intact canonical DNA repair and checkpoint functions.
Conclusions:
- Even minor disruptions in MRN complex function induce significant genotoxic stress and compromise proliferative tissue homeostasis.
- The MRN complex plays a critical role in maintaining genomic integrity and preventing tumorigenesis beyond its established DNA repair roles.