Hypersensitivity ofKu80-deficient cell lines and mice to DNA damage: The effects of ionizing radiation on growth, survival, and development

Abstract

We recently have shown that mice deficient for the 86-kDa component (Ku80) of the DNA-dependent protein kinase exhibit growth retardation and a profound deficiency in V(D)J (variable, diversity, and joining) recombination. These defects may be related to abnormalities in DNA metabolism that arise from the inability of Ku80 mutant cells to process DNA double-strand breaks. To further characterize the role of Ku80 in DNA double-strand break repair, we have generated embryonic stem cells and pre-B cells and examined their response to ionizing radiation. Ku80 ؊/؊ embryonic stem cells are more sensitive than controls to ␥-irradiation, and pre-B cells derived from Ku80 mutant mice display enhanced spontaneous and ␥-ray-induced apoptosis. We then determined the effects of ionizing radiation on the survival, growth, and lymphocyte development in Ku80-deficient mice. Ku80 ؊/؊ mice display a hypersensitivity to ␥-irradiation, characterized by loss of hair pigmentation, severe injury to the gastrointestinal tract, and enhanced mortality. Exposure of newborn Ku80 ؊/؊ mice to sublethal doses of ionizing radiation enhances their growth retardation and results in the induction of T cell-specific differentiation. However, unlike severe combined immunodeficient mice, radiation-induced T cell development in Ku80 ؊/؊ mice is not accompanied by extensive thymocyte proliferation. The response of Ku80-deficient cell lines and mice to DNA-damaging agents provides important insights into the role of Ku80 in growth regulation, lymphocyte development, and DNA repair.

Transfer of Ku86 RNA antisense decreases the radioresistance of human fibroblasts

“…Indeed, no human syndrome and no mutant cells lines deficient for Ku protein have been reported, in contrast to the situation in rodents, in which several syndromes have been reported as well as several cell lines mutated for Ku86 or Ku70. 34 The extreme radiosensitivity and DSB repair deficiency found in these mutated rodent cell lines, as well as in the Ku86 49 or Ku70 50 knockout mice, 49 justify the hypothesis that a comparable mechanism could be involved in human cells. In addition, a recent study suggests that in human cells Ku might also represent the major DNA-binding component of DNAPKcs, because human peripheral B lymphocytes expressing a truncated form of Ku86 (Ku69) were unable to recruit the DNA-PKcs and were deficient in the enzymatic activity of the DNA-complex.…”

Chemosensitivity of B cell chronic lymphocytic leukemia and correlated expression of proteins regulating apoptosis, cell cycle and DNA repair

“…[32][33][34] Direct evidence that Ku80 is involved in inhibition of apoptosis comes from the observation that pre-B cells of Ku80(−/−) mutant mice show increased spontaneous and gamma-rayinduced apoptosis. 35 Furthermore, Ku70/80 was found to be expressed independently of the cell cycle in viable but not in apoptotic HL-60 cells. 36 Also, Bcl-2 was found to sustain the levels of DNA-PK by inhibiting the proteolytic cleavage of this enzymatic complex.…”

Radiation-hypersensitive cancer patients do not manifest protein expression abnormalities in components of the nonhomologous end-joining (NHEJ) pathway

“…It generally facilitates end-joining by aligning DNA ends, and it specifically recruits both XRCC4-ligase IV and DNA-PK CS to DNA ends (Nick_McElhinny et al, 2000). Ku80-deficient ES cells and pre-B-cell lines are hypersensitive to IR (Nussenzweig et al, 1997) and consistent with the radiation-hypersensitive phenotype of the cell lines, Ku80 mutant mice also display extreme radiosensitivity (Nussenzweig et al, 1997). Mice lacking Ku70 are immunodeficient and growth retarded, and Ku70-deficient ES cells have increased radiosensitivity, defective DNA end binding activity and an inability to support V(D)J recombination (Gu et al, 1997a, b).…”