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Background  Genetic BRCA2 insufficiency is associated with breast cancer development; however, in sporadic breast cancer cases, high BRCA2 expression is paradoxically correlated with poor prognosis. Because DSS1, a mammalian component of the transcription/RNA export complex, is known to stabilize BRCA2, we investigated how the expression of DSS1 is associated with clinical parameters in breast cancers.    Methods   DSS1  mRNA and p53 protein were examined by RT-PCR and immunohistochemical staining of breast cancer specimens to classify  DSS1  high  and  DSS1  low  or p53 high  and p53 low  groups. Patient survival was compared using Kaplan-Meier method.  DSS1  high  or  DSS1  low  breast cancer cells were prepared by retroviral cDNA transfection or  DSS1  siRNA on proliferation, cell cycle progression, and survival by flow cytometric analyses with or without anti-cancer drugs.    Results  In comparison to patients with low levels of DSS1, high-DSS1 patients showed a poorer prognosis, with respect to relapse-free survival period. The effect of DSS1 was examined in breast cancer cells  in vitro . DSS1 high-expression reduces the susceptibility of MCF7 cells to DNA-damaging drugs, as observed in cell cycle and apoptosis analyses.  DSS1  knockdown, however, increased the susceptibility to the DNA-damaging drugs camptothecin and etoposide and caused early apoptosis in p53 wild type MCF7 and p53-insufficient MDA-MB-231 cells.  DSS1  knockdown suppresses the proliferation of drug-resistant MDA-MB-231 breast cancer cells, particularly effectively in combination with DNA-damaging agents.    Conclusion  Breast cancers with high DSS1 expression have worse prognosis and shorter relapse-free survival times. DSS1 is necessary to rescue cells from DNA damage, but high DSS1 expression increases drug resistance. We suggest that DSS1 expression could be a useful marker for drug resistance in breast cancers, and DSS1 knockdown can induce tumor apoptosis when used in combination with DNA-damaging drugs.

Breast cancers with high DSS1 expression that potentially maintains BRCA2 stability have poor prognosis in the relapse-free survival