Abstract LB-145: Absence of pro-apoptotic protein Bax extended the life span of ku70−/− mice with accelerated aging phenotype

Abstract

Abstract Bax is a proapoptotic Bcl-2 family protein. Previously, we found that Ku70 functions as a Bax inhibitor in the cell. Ku70 is 70 kDa protein expressed in the cytosol and nucleus, and Ku70 is required for the nonhomologous end-joining (NHEJ) pathway of DNA double strand break (DSB) repair in the nucleus. In the cytosol, Ku70 binds to Bax, and this interaction inhibits the cytotoxic activity of Bax. Ku70 null mice show a premature aging phenotype due to the absence of NHEJ-dependent DSB repair. We hypothesized that increased sensitivity to Bax-mediated cell death may contribute to the disease phenotype of Ku70 null mice. To determine our hypothesis, ku70−/−bax+/− and ku70−/−bax−/− mice were generated (all mice were on C57BL background). Interestingly, both ku70−/−bax+/− and ku70−/−bax−/− had a longer life spans than ku70−/− mice. The 50% mortality of ku70−/−, ku70−/−bax+/−, ku70−/−bax−/− was 21 weeks (n=36), 36 weeks (n=20), and 37 weeks (n=7) respectively. Some of these mutant mice developed T-lymphoma (ku70−/− (17%<), ku70−/−bax+/− (33%), and ku70−/−bax−/− (20%)). Ku70−/− MEFs (mouse embryonic fibroblasts) showed increased apoptosis sensitivity and accelerated cellular senescence during passage in comparison with wild type MEFs, as previously reported. ku70−/−bax+/− and ku70−/−bax−/− showed significantly higher survival in the apoptosis sensitivity test than ku70−/− MEFs. Cellular senescence of MEFs was analyzed including expressions of senescence associated β-galactosidase and phospho-γ H2AX. Bax deficiency did not show significant effects on the onset of cellular senescence of ku70−/− MEFs. The lung alveoli of ku70−/− mice were structurally normal (single alveolar cell layer); however, the lungs of ku70−/−bax+/− and ku70−/−bax−/− mice had abnormal multiple alveolar cell layers. The mechanism of this abnormal alveolar development is under investigation. We analyzed histology of several organs, blood cell count, and locomotion activities of these mutant mice. These data suggest that Bax-deficiency improved the overall health condition of Ku70 null mice. Previous studies demonstrated that p53 deletion was not able to extend the life span of Ku70 or Ku80 null mice due to increased cancer development (Li et al. 2009). In addition, p21 deletion was not able to extend the life span of Ku80 null mice even though p21 deletion significantly delayed cellular senescence of Ku80 null MEFs (Zhao et al, 2009). The present study suggests that increased Bax-mediated apoptosis rather than increased cellular senescence may be the major cause of the shortened life span of Ku70 null and NHEJ-defective mutant mice. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-145. doi:10.1158/1538-7445.AM2011-LB-145