The Role of Thoc1 in Normal Development and Cancer

描述（由申请人提供）：本申请的长期目标是了解Thoc1基因的正常功能，并评估其作为癌症治疗和预后分子靶点的潜在适用性。Thoc1编码一种蛋白（pThoc1），该蛋白最近被鉴定为进化上保守的TREX复合体的一个组成部分。TREX是基因子集有效转录延伸所必需的，它将延伸与RNA加工和核输出过程物理耦合。Thoc1的酵母同源物对生存能力不是必需的，但该基因的缺失会导致细胞寿命缩短，生长速度降低，对DNA损伤的敏感性增加。同样，pThoc1缺失的人类癌细胞也表现出生长、生存能力降低和对基因毒性化疗药物的耐药性。相比之下，正常分化的细胞相对不受pThoc1缺失的影响。在多细胞生物体内，Thoc在正常发育和癌症中的生理需求尚未得到评估。我们假设，癌细胞的生长和生存是唯一依赖于Thoc表达的，特别是在存在DNA损伤的情况下。为验证这一假设而提出的一般实验方法是使用基因工程的Thoc等位基因和乳腺癌小鼠模型来测量pThoc缺失对正常发育和恶性转化的影响。提出了4个具体目的：1)检测pThoc1缺失是否在体外抑制恶性转化。2)确定pThoc1缺失是否影响正常乳腺发育。3)确定pThoc1缺失是否在体内抑制乳腺癌的发生。4)评估pThoc1水平是否影响乳腺癌对基因毒性治疗的反应。癌细胞积累遗传和表观遗传改变，赋予它们不必要的增殖潜力，但也使它们具有独特的脆弱性。因此，有可能确定癌细胞生存所需的基因，而不是正常细胞。这种合成的致死性基因相互作用确定了治疗的潜在分子靶标，有望对癌细胞产生更大的特异性。该研究的成功完成将为Thoc1是这样一个分子靶点提供原理证明。由于pThoc1是新发现的TREX复合体的一个组成部分，因此它具有一种新的作用机制。基于靶向pThoc1的治疗和诊断有望产生新的临床反应，为新的联合治疗提供机会，并获得潜在独立于当前使用标准的预后信息。这项拟议的研究与人类健康高度相关，因为显然需要针对癌细胞具有更大特异性的新的分子靶向疗法。提出的实验将确定pThoc1是否是开发新疗法和预后测试的有希望的靶标。

DESCRIPTION (provided by applicant): The long-term objectives of this application are to understand the normal function of the Thoc1 gene and to assess its potential suitability as a molecular target for cancer therapy and prognosis. Thoc1 encodes a protein (pThoc1) that has recently been identified as a component of the evolutionarily conserved TREX complex. TREX is required for the efficient transcriptional elongation of a subset of genes, and it physically couples elongation to the processes of RNA processing and nuclear export. The yeast orthologue of Thoc1 is not essential for viability, but loss of this gene causes reduced cellular lifespan, reduced growth rate, and increased sensitivity to DNA damage. Similarly, human cancer cells depleted of pThoc1 exhibit reduced growth, viability, and resistance to genotoxic chemotherapeutics. In contrast, normal differentiated cells are relatively unaffected by loss of pThoc1. The physiological requirements for Thoc in normal development and cancer have yet to be assessed in vivo in a multicellular organism. We hypothesize that cancer cells are uniquely dependent on Thoc expression for growth and viability, particularly in the presence of DNA damage. The general experimental approach proposed for testing the hypothesis is to measure the effects of pThoc loss on normal development and malignant transformation using genetically engineered Thoc alleles and autochthonous mouse models of breast cancer. 4 specific aims are proposed: 1) Test whether pThoc1 depletion inhibits malignant transformation in vitro. 2) Determine if pThoc1 depletion affects normal mammary gland development. 3) Ascertain whether pThoc1 depletion inhibits breast carcinogenesis in vivo. 4) Assess whether pThoc1 levels influence the response of breast cancer to genotoxic therapy. Cancer cells accumulate genetic and epigenetic alterations that endow them with unwanted proliferative potential, but also burden them with unique vulnerabilities. Thus, it is possible to identify genes that are required for the viability of cancer cells, but not normal cells. Such synthetic lethal genetic interactions identify potential molecular targets for therapy that promise to yield greater specificity for cancer cells. Successful completion of the proposed study will provide proof of principle that Thoc1 is such a molecular target. Since pThoc1 is a component of the newly discovered TREX complex, it functions with a novel mechanism of action. Therapies and diagnostics based on targeting pThoc1 are expected to yield novel clinical responses, opportunities for novel combination therapies, and prognostic information potentially independent of currently used criteria. The proposed research is highly relevant to human health because new molecularly targeted therapies with greater specificity for cancer cells are clearly needed. The experiments proposed will determine whether pThoc1 is a promising target for the development of new therapies and prognostic tests.