一半的家族性乳腺癌患者有肿瘤抑制基因BRCA1突变，并患乳腺癌或卵巢癌。临床上多见散发型乳腺癌是高级别肿瘤其BRCA1蛋白表达水平下调。已知BRCA1蛋白功能有参与DNA修复、细胞周期阻滞，转录、凋亡和染色体重建。细胞失去这些蛋白可能与肿瘤发生、肿瘤对放疗和化疗的应答相关。我们前期观察到细胞受到照射后BRCA1通过出核报告子（CRM1）依赖机制从细胞核入细胞浆，细胞对放射或化疗药物治疗敏感性增加；而抑制BRCA1出核（neucleiexport NE）与细胞对药物毒性耐受性升高有关，而且我们研究发现BRCA1出核可能是依赖正常p53功能,但这个潜靶点细胞内机制不明，因此我们将利用肿瘤细胞研究BRCA1蛋白NE分子机制、及其与肿瘤细胞对药物毒性敏感性增加的关系；用人类肿瘤组织样本,进一步探索BRCA1NE可能是非突变型乳腺癌患者治疗靶点和预测子；通过分析BRCA1的亚细胞分布来预测治疗应答。

The tumor suppressor gene BRCA1 is mutated in up to 50% of cases of familial early-onset breast cancer and in most families with hereditary breast and ovarian cancers.A role for BRCA1 in sporadic breast cancer is indicated by decreased levels of its expression in high-grade tumors.BRCA1 protein functions in DNArepair,cell cycle checkpoint,transcription,and apoptosis.Dysfunction of these properties BRCA1 may be invoked in cancer development and in tumor response to radiation or chemotherapy.This nuclear shuttling protein, the role of BRCA1 localization in the control of its functions remains to be elucidated. Given the central role of BRCA1 in DNA damage repair, we hypothesized that depletion of nuclear BRCA1 would compromise its nuclear function in DNA repair and thereby result in enhanced cytotoxic response to DNA damage.If after exposure to ionizing radiation (IR) BRCA1 protein is exported from the nucleus into the cytoplasm through the nuclear export receptor (CRM1)-dependent mechanism. Interestingly, inhibition of BRCA1 nuclear export (NE) correlated with increased cellular resistance to IR induced toxicity. We need to prove that BRCA1 NE was dependent on normal function of p53, plays an important role in both breast cancer tumorigenesis and tumor response to therapy.Using established breast cancer cell lines,this proposal focuses on defining the role of DNA damage-induced BRCA1NE on cellular sensitivity to various cytotoxic agents,the mechanismsand the effect of p53 status in this response.Using pre-and post-treatment breast cancer specimens,we will show sequestering BRCA1 in the cytosol enhanced the cytotoxic response to ionizing radiation or cisplatin in human breast and colon cancer cells. Based on our observation that a dependence of the DNA damage-induced cell killing on the translocation and accumulation of BRCA1 in the cytosol. we will explore a novel role of cytoplasmic translocation of BRCA1, not only in controlling its DNA repair functions, but also in the regulation of cell death processes following DNA damage.We will propose that the status of BRCA1 nuclear/cytoplasmic shuttling might provide a molecular marker to predict tumor response and a potential novel target to sensitize cancer cells to DNA damage-based therapy.