Metadherin in Metastasis and Chemoresistance of Breast Cancer

摘要：大多数乳腺癌患者死于肿瘤复发，肿瘤扩散到远处的重要器官，并对目前可用的治疗方案产生抵抗。最近的研究发现Metadherin （MTDH）是一种候选转移基因，在促进乳腺癌转移和化疗耐药中起双重作用。我们提出的研究基于以下初步观察：1)MTDH位于8q22的中心，这是一个在预后不良的乳腺癌患者中经常扩增的基因组区域；2)超过40%的乳腺癌肿瘤标本中检测到MTDH过表达，与乳腺癌患者生存差、转移风险高密切相关；3)在实验转移模型中，MTDH过表达促进肿瘤向肺和其他器官转移。相反，通过RNA干扰抑制MTDH表达可减少肺转移；4) MTDH在体外促进乳腺肿瘤细胞对血管内皮细胞的粘附，提高动物转移试验中的转移播种效率；5) MTDH增强乳腺癌细胞对广谱化疗药物和其他生理应激的耐药能力。当癌细胞与内皮细胞共培养时，mtdh介导的化疗耐药最为明显。基于这些初步观察，我们假设MTDH的促转移和化疗耐药功能是通过其与内皮细胞表达的未知相互作用蛋白的相互作用介导的。这种相互作用激活下游信号事件，改变肿瘤和内皮细胞的基因表达。阻断MTDH与其相互作用蛋白之间的相互作用将抑制肿瘤转移并使肿瘤细胞对化疗敏感。我们的长期研究目标是阐明MTDH介导的乳腺癌转移和化疗耐药的分子机制，并探索抑制MTDH功能的治疗应用。为此，我们将使用遗传和生化方法来鉴定和表征介导肿瘤-内皮相互作用的mtdh相互作用蛋白，并探索抑制这种相互作用的潜在益处（Aim1）。我们将明确MTDH诱导化疗耐药的分子机制，并利用实验肿瘤发生和转移模型（Aim2）确定MTDH靶向的治疗潜力。此外，我们将产生MTDH转基因和敲除小鼠，并在遗传上容易发生乳腺肿瘤的转基因动物中测试MTDH表达改变对肿瘤发生和转移的影响。MTDH的转基因和敲除动物也将使我们能够直接解决MTDH在发育和乳腺功能中的生理作用（Aim3）。本研究将确定介导MTDH转移和化疗耐药功能的分子网络的关键组分，为预防或减少乳腺癌化疗耐药转移提供新的策略。Metadherin在乳腺癌转移和化疗耐药中的作用。公共卫生相关性：超过90%的乳腺癌相关死亡是由于不能手术的远端重要器官复发肿瘤抵抗常规化疗。我们提出的研究将为Metadherin在转移和化疗耐药中的分子机制提供新的见解。此外，我们的研究将促进基于Metadherin分子靶向的抗转移治疗药物的发展。

DESCRIPTION (provided by applicant): Metadherin in Metastasis and Chemoresistance of Breast Cancer Summary: Most breast cancer patients succumb to recurrent tumors that spread to distant vital organs and resist currently available therapeutic regiments. Recent studies have identified Metadherin (MTDH) as a candidate metastasis gene that plays a dual role in promoting breast cancer metastasis and chemoresistance. Our proposed study is based on the following preliminary observations: 1) MTDH is located at the epicenter of 8q22, a genomic region that is frequently amplified in poor-prognosis breast cancer patients; 2) MTDH overexpression is detected in over 40% of breast tumor speciemens, and is strongly correlated with poor survival and higher risk of metastasis for breast cancer patients; 3) MTDH overexpression promotes metastastasis to lung and other organs in an experimental metastasis model. Conversely, inhibition of MTDH expression by RNA interference reduces lung metastasis; 4) MTDH promotes adhesion of breast tumor cells to vascular endothelial cells in vitro and increases metastatic seeding efficiency in animal metastasis assays; 5) MTDH enhances chemoresistance of breast cancer cells to a broad spectrum chemotherapeutic agents as well as other physiological stresses. MTDH-mediated chemoresistance is most pronouced when cancer cells are co-cultured with endothelial cells. Based on these preliminary observations, we postulate that the pro-metastasis and chemoresistance functions of MTDH are mediated through its interaction with unknown interacting protein(s) expressed by endothelial cells. Such interaction activates downstream signaling events and alters gene expression in both tumor and endothelial cells. Blocking the interaction between MTDH and its interacting proteins will inhibit metastasis and sensitize tumor cells to chemotherapies. The long-term goals of our research are to elucidate the molecular mechanisms of breast cancer metastasis and chemoresistance mediated by MTDH and explore the therapeutic applications of inhibiting MTDH function. To this end, we will use genetic and biochemical approaches to identify and characterize MTDH-interacting proteins that mediate tumor-endothelium interaction and explore the potential benefit of inhibiting such interaction (Aim1). We will define the molecular mechanism of MTDH induced chemoresistance and determine the therapeutic potential of MTDH targeting using experimental tumorigenesis and metastasis models (Aim2). Furthermore, we will generate transgenic and knockout mice for MTDH and test the effect of altered MTDH expression on tumorigenesis and metastasis in transgenic animals that are genetically prone to developing mammary tumors. Transgenic and knockout animals of MTDH will also allow us to directly address the physiological role of MTDH in development and mammary gland function (Aim3). The proposed study will identify key components of the molecular network that mediate the metastasis and chemoresistance functions of MTDH and provide new strategies to prevent or reduce chemoresistant metastasis of breast cancer. Metadherin in Metastasis and Chemoresistance of Breast Cancer. PUBLIC HEALTH RELEVANCE: Over 90% of breast cancer related deaths are due to inoperable relapsed tumors in distant vital organs that resist conventional chemotherapies. Our proposed studies will provide novel insights into the molecular mechanism of Metadherin in metastasis and chemoresistance. Furthermore, our research will facilitate the development of anti-metastasis therapeutics based on molecular targeting of Metadherin.