Abstract
RAD51 recombinase is one of the DNA damage repair proteins associated with breast cancer risk. Apart from its function to maintain genomic integrity within the cell nucleus, RAD51 localized to the cytoplasm has also been implicated in breast malignancy. However, limited information exists on the roles of cytoplasmic vs. nuclear RAD51 in breast cancer progression and patient prognosis. In the present study, the association of cytoplasmic and nuclear RAD51 with clinical outcomes of patients with breast cancer was analyzed, revealing that elevated cytoplasmic RAD51 expression was associated with breast cancer progression, including increased cancer stage, grade, tumor size, lymph node metastasis and chemoresistance, along with reduced patient survival. By contrast, elevated nuclear RAD51 expression largely had the inverse effect. Results from in vitro investigations supported the cancer‑promoting effect of RAD51, showing that overexpression of RAD51 promoted breast cancer cell growth, chemoresistance and metastatic ability, while knockdown of RAD51 repressed these malignant behaviors. The current data suggest that differential expression of subcellular RAD51 had a distinct impact on breast cancer progression and patient survival. Specifically, cytoplasmic RAD51 in contrast to nuclear RAD51 was potentially an adverse marker in breast cancer.