Analysis of Immunodeficiencies with defective DNA damage response

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We sought to analyze molecular mechanism of immunodeficiency caused by defective DNA damage response working on cells from disorders including ataxia-telangiectasia (AT), Artemis deficiency, and Nijmegen breakage syndrome (NBS1 deficiency).We have so far revealed that S645 of Artemis is phosphorylated by ATM upon DNA damaging reagent. Through this study, we have shown 70-kDa molecule is associated with Artemis and controls stability of Artemis. The interaction requires phosphorylation of Artemis, but the site is not in the hitherto-known region. A new role of Artemis was also demonstrated. Endonuclease activity of Artemis was shown to be required for double strand DNA break when DNA replication is stalled in a ragging strand. This process was dependent on ATM. Further investigation is currently in progress.DNA damage response (DDR) is absolutely required for diversification of immune receptors; and disrupted DDR during the process leads to chromosomal aberration. We analyzed involvement of the DDR molecules in tumorigenesis, and found that DDR is activated in pre-malignant stage. The loss of DDR led to malignant transformation of the cells with mutation in p53 in some cases (Leukemia 2006).ATM and Ku70/80 were shown to be degraded upon oxidative stress leading to cellular apoptosis (Ann NY Acad Sci 2006, Int J Biochem Cell Biol. 2008)。 The cells escaped from apoptosis may lead to acquisition of chromosomal aberration.We diagnosed 14 patients with AT, 2 DNA ligase IV deficiency, 2 Mre11deficiency (ATLD) and one Cernunnos deficiency. Finally, we carried out the first nation-wide survey for AT. We observed phenotypic variety between sibling cases with AT. Hyper-IgM was noted in 10% of the patients indicating involvement of ATM in class switch recombination.