Bmi-1 is a polycomb group protein necessary for cellular proliferation and maintenance of stem cell phenotype. The current study was undertaken to determine the radioprotective effects of Bmi-1 in human epithelial cells. Primary normal human keratinocytes (NHK) from oral mucosa or epidermis were infected with retroviral vectors expressing Bmi-1. NHK infected with empty virus (NHK/B0) rapidly underwent premature senescence upon exposure to 5 or 10 Gy of ionizing radiation (IR). However, the cells transduced with Bmi-1 (NHK/Bmi-1) maintained cell proliferation and clonogenicity after IR. To determine the mechanism underlying the radioresistance conferred by Bmi-1, we compared the DNA damage response (DDR), production of reactive oxygen species (ROS), and DNA repair activities in both cell types. NHK/B0 and NHK/Bmi-1 cells demonstrated rapid induction of DDR after 5 Gy irradiation. ROS production was increased by irradiation, but Bmi-1 transduction suppressed the ROS production. Irradiation strongly induced the genes encoding the enzymes involved in ROS production, mainly of NADPH oxidase subunits, but Bmi-1 completely abolished the expression of these genes. Chromatin immunoprecipitation (ChIP) revealed binding of Bmi-1 to the promoter regions of these genes in vivo, suggesting transcriptional repression by Bmi-1. In vitro DNA end joining and in vivo double strand break (DSB) repair activities were enhanced in NHK/Bmi-1 cells compared with NHK/B0. These data indicate that Bmi-1 enhances the radioresistance of NHK in part by mitigating the genotoxicity of radiation. This study was supported in part by the grants, UCLA/CBPR (U19) from NIAID and R01DE18295/K02DE18959 from NIDCR/NIH.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1410.