DNA damage response in CD133+stem/progenitor cells from umbilical cord blood: Low level of endogenous foci and high recruitment of 53BP1

Purpose : Human hematopoietic stem cells (HSC) are thought to be a major target of radiation-induced leukemogenesis and also provide a relevant cellular model for assessing cancer risk. Cluster of designation 133+ (CD133+) is a marker found in human progenitor and hematopoietic stem cells. Our study examined the repair of radiation-induced DNA double-strand breaks (DSB) in CD133+ umbilical cord blood cells (UCBC). Materials and methods : After gamma-irradiation, endogenous and induced DSB were evaluated in CD133+ UCBC, CD133 - UCBC and peripheral blood lymphocytes (PBL) in terms of phosphorylated histone 2A family member X (gamma H2AX) and tumor suppressor p53 binding protein 1 (53BP1) foci. Results : We found that repair signaling in CD133 + UCBC is different from CD133 + UCBC and PBL. These differences include lower endogenous DSB levels and higher 53BP1 recruitment. Conclusions : Our data, together with a recent report on radiation-induced g H2AX and 53BP1 foci in CD34 + cells, indicate enhanced DNA repair capacity in HSC as compared to mature lymphocytes.