Ku70

We present evidence that inactivation of the Ku70 gene leads to a propensity for malignant transformation both in vitro and in vivo. In vitro, Ku70 −/− mouse fibroblasts displayed an increased rate of sister chromatid exchange and a high frequency of spontaneous neoplastic transformation. In vivo, Ku70 −/− mice, known to be defective in B but not T lymphocyte maturation, developed thymic and disseminated T cell lymphomas at a mean age of 6 months with CD4 + CD8 + tumor cells. These findings directly demonstrate that Ku70 deficiency facilitates neoplastic growth and suggest a novel role of the Ku70 locus in tumor suppression.