ABSTRACT
Chk2 is an effector kinase important for the activation of cell cycle checkpoints, p53, and apoptosis in response to DNA damage. Mus81 is required for the restart of stalled replication forks and for genomic integrity. Mus81(Δex3-4/Δex3-4) mice have increased cancer susceptibility that is exacerbated by p53 inactivation. In this study, we demonstrate that Chk2 inactivation impairs the development of Mus81(Δex3-4/Δex3-4) lymphoid cells in a cell-autonomous manner. Importantly, in contrast to its predicted tumor suppressor function, loss of Chk2 promotes mitotic catastrophe and cell death, and it results in suppressed oncogenic transformation and tumor development in Mus81(Δex3-4/Δex3-4) background. Thus, our data indicate that an important role for Chk2 is maintaining lymphocyte development and that dual inactivation of Chk2 and Mus81 remarkably inhibits cancer.
Subject(s)
Cell Differentiation , DNA-Binding Proteins/metabolism , Endonucleases/metabolism , Genomic Instability , Lymphocytes/cytology , Neoplasms/metabolism , Neoplasms/pathology , Protein Serine-Threonine Kinases/metabolism , Animals , Cell Lineage , Cells, Cultured , Checkpoint Kinase 2 , DNA-Binding Proteins/genetics , Endonucleases/genetics , Enzyme Activation , Gene Expression Regulation, Developmental , Lymphocytes/immunology , Mice , Mice, Knockout , Mitosis , Neoplasms/genetics , Protein Serine-Threonine Kinases/deficiency , Thymus Gland/cytology , Thymus Gland/immunology , Tumor Suppressor Protein p53/metabolismABSTRACT
Mus81 plays an integral role in the maintenance of genome stability and DNA repair in mammalian cells. Deficiency of Mus81 in human and mouse cells results in hypersensitivity to interstrand cross-linking (ICL) agents and elevated levels of genomic instability. Furthermore, Mus81-mutant mice are susceptible to spontaneous lymphomas. The role of cellular checkpoints in mediating the phenotypes observed in Mus81-deficient cells and mice is currently unknown. In this study, we have observed increased activation of p53 in Mus81(-/-) cells in response to ICL-induced DNA damage. In addition, p53 inactivation completely rescued the ICL hypersensitivity of Mus81(-/-) cells, signifying p53 is essential for the elimination of ICL-damaged cells in the absence of Mus81. Confirming that p53 acts as a critical checkpoint for the Mus81 repair pathway, a synergistic increase of spontaneous and ICL-induced genomic instability was observed in Mus81(-/-)p53(-/-) cells. To clarify the genetic interactions of Mus81 and p53 in tumor suppression, we monitored Mus81(-/-)p53(-/-) and control mice for the development of spontaneous tumors. Significantly, we show that loss of even a single allele of Mus81 drastically modifies the tumor spectrum of p53-mutant mice and increases their predisposition to developing sarcomas. Our results reveal a key role for p53 in mediating the response to spontaneous and ICL-induced DNA damage that occurs in the absence of Mus81. Furthermore, our data show that loss of Mus81, in addition to p53, is a key step in sarcoma development.
Subject(s)
DNA Damage/physiology , DNA-Binding Proteins/genetics , Endonucleases/genetics , Lymphoma/genetics , Sarcoma, Experimental/genetics , Tumor Suppressor Protein p53/genetics , Animals , B-Lymphocytes/cytology , B-Lymphocytes/immunology , Cell Differentiation/genetics , Cell Differentiation/immunology , Cell Growth Processes/genetics , Cell Growth Processes/immunology , DNA/drug effects , DNA/genetics , DNA-Binding Proteins/deficiency , Endonucleases/deficiency , Female , G2 Phase/physiology , Gene Silencing , Genes, p53 , Genomic Instability , Lymphoma/immunology , Lymphoma/metabolism , Lymphoma/pathology , Male , Mice , Mice, Inbred C57BL , Mice, Knockout , Mitomycin/pharmacology , Sarcoma, Experimental/immunology , Sarcoma, Experimental/metabolism , Sarcoma, Experimental/pathology , T-Lymphocytes/cytology , T-Lymphocytes/immunology , Tumor Suppressor Protein p53/biosynthesis , Tumor Suppressor Protein p53/deficiencyABSTRACT
Mus81-Eme1 endonuclease has been implicated in the rescue of stalled replication forks and the resolution of meiotic recombination intermediates in yeast. We used gene targeting to study the physiological requirements of Mus81 in mammals. Mus81-/- mice are viable and fertile, which indicates that mammalian Mus81 is not essential for recombination processes associated with meiosis. Mus81-deficient mice and cells were hypersensitive to the DNA cross-linking agent mitomycin C but not to gamma-irradiation. Remarkably, both homozygous Mus81-/- and heterozygous Mus81+/- mice exhibited a similar susceptibility to spontaneous chromosomal damage and a profound and equivalent predisposition to lymphomas and other cancers. These studies demonstrate a critical role for the proper biallelic expression of the mammalian Mus81 in the maintenance of genomic integrity and tumor suppression.
