1. ¹Center for Neurovirology and Cancer Biology, College of Science and Technology, Temple University, 1900 North 12th Street, Biology Life Science Building, Philadelphia, PA 19122, USA
2. ²Center for Biotechnology, College of Science and Technology, Temple University, 1900 North 12th Street, Biology Life Science Building, Philadelphia, PA 19122, USA
3. ³Department of Pathology and Laboratory Medicine, College of Medicine, Drexel University, 1800 Lombard Street, Philadelphia, PA 19146, USA

Correspondence: K Reiss, Center for Neurovirology and Cancer Biology, Temple University, Biology Life Sciences Bldg. Room 230, 1900 North 12th Street Philadelphia, PA 19122, USA. E-mail: [email protected]

Received 18 September 2004; Revised 21 December 2004; Accepted 22 December 2004; Published online 14 March 2005.

Abstract

During metastases, cancer cells are temporarily exposed to the condition in which interactions with extracellular environment can be restricted (anchorage-independence). We demonstrate that the sensitivity of prostate cancer cell lines, DU145 and PC-3, to genotoxic treatment (cisplatin and -irradiation) increased several folds when cells were forced to grow in anchorage-independence. This enhanced drug sensitivity was associated with a severe impairment of homologous recombination-directed DNA repair (HRR). The mechanism involves Rad51, which is the major enzymatic component of HRR. The protein level of Rad51 and its recruitment to DNA double-strand breaks (DSBs) were both attenuated. Rad51 deficiency in anchorage-independence was not associated with Rad51 promoter activity, and was not compensated by a constitutive overexpression of Rad51 cDNA. Instead, Rad51 protein level and its ability to colocalize with DSBs were restored in the presence of proteosome inhibitors, or when cells from the suspension cultures were allowed reattachment. Presented results indicate that anchorage-independence sensitizes prostate cancer cells to genotoxic agents; however, it also attenuates faithful component of DNA repair by targeting stability of Rad51. This temporal attenuation of HRR may contribute to the accumulation mutations after DNA damage, and possibly the selection of new adaptations in cells, which survived genotoxic treatment.