1. ¹Division of Cancer Biology, Department of Medicine, Evanston Northwestern Healthcare Research Institute, Northwestern University Feinberg School of Medicine, Evanston, IL, USA
2. ²Department of Radiation Oncology, New England Medical Center, Tufts University School of Medicine, Boston, MA, USA

Correspondence: Dr Q Gao, Division of Cancer Biology, Department of Medicine, Evanston Northwestern Healthcare Research Institute, Northwestern University Feinberg School of Medicine, 1001 University Place, Evanston, IL 60201, USA. E-mail: Q-GAO@Northwestern.edu

Received 13 June 2005; Revised 26 August 2005; Accepted 29 August 2005; Published online 3 October 2005.

Abstract

DSS1 is an evolutionarily conserved acidic protein that binds to BRCA2. However, study of the function of DSS1 in mammalian cells has been hampered because endogenous DSS1 has not been detectable by Western blotting. Here, we developed a modified Western blotting protocol that detects endogenous DSS1 protein, and used it to study the function of DSS1 and its interaction with BRCA2 in mammalian cells. We found that essentially all BRCA2 in human cell lines is associated with DSS1. Importantly, we found that RNAi knockdown of DSS1 in human cell lines led to dramatic loss of BRCA2 protein, mainly due to its increased degradation. Furthermore, the stability of BRCA2 mutant devoid of the DSS1-binding domain is unaffected by the depletion of DSS1. Most notably, like BRCA2 depletion, DSS1 depletion also led to hypersensitivity to DNA damage. These results demonstrated that the stability of BRCA2 protein in mammalian cells depends on the presence of DSS1. Deletion or mutation of DSS1 or suppression of its expression by other mechanisms are therefore potential causative mechanisms for human breast and ovarian cancer. Such mechanisms may be relevant to sporadic as well as familiar breast cancer where BRCA1 and BRCA2 mutations are not present.