Tumor Suppression by Telomere Dysfunction Induced Senescence

描述（由申请人提供）：大多数癌症是通过进化过程产生的，因为突变在体细胞染色体中积累，使它们能够逃脱控制细胞生长的增殖限制。为了对抗不受控制的细胞增殖，后生动物开发了许多先天肿瘤抑制机制，其中之一是称为细胞衰老的终末生长停滞。近年来，随着我们和其他人鉴定出新的衰老标记物，这种应激反应在癌前病变中阻止细胞的生物学作用和重要性已经得到证实。然而，为什么细胞在体内经历衰老，从而防止人类肿瘤进展，仍然知之甚少。 对人类细胞培养的研究表明，细胞衰老是由许多压力引发的，包括端粒功能障碍，线性染色体的物理末端。我们的研究表明，当端粒变得非常短时，由于持续的细胞增殖和其他应激，它们被认为是双链DNA断裂并启动信号级联反应，导致端粒功能障碍诱导的细胞衰老（TDIS）。在这个提议中，我们证明了三种人类癌症前体病变中的大多数细胞，而不是恶性肿瘤中的大多数细胞，显示出功能失调的端粒和其他细胞衰老的标志物。因此，我们的数据表明，TDIS是一个关键的和普遍的肿瘤抑制机制，限制恶性前人类肿瘤的生长。此外，我们发现，致癌信号，通常与癌症生长的启动，显着加速端粒侵蚀和功能障碍的癌前人类细胞。因此，端粒可能作为过度增殖应激的哨兵，一旦细胞生长控制机制受损，过度增殖应激迅速诱导细胞衰老。 为了测试这些预测，我们将1）通过荧光显微镜分析许多常见的癌症前体病变以及它们的恶性对应物的TDIS标志物，和2）产生小鼠肿瘤模型系统，其可以分析TDIS是否抑制肿瘤细胞异种移植物中转化的人细胞的恶性进展。此外，我们将3）确定在导致异常细胞增殖的条件下端粒功能障碍的原因。我们将使用分析来测量端粒缩短，功能障碍和结构，采用正向和反向遗传干预来操纵端粒功能障碍，并确定触发TDIS的关键端粒维持因子。 拟议的实验将揭示TDIS在预防人类肿瘤进展方面的影响，确定肿瘤阶段的新诊断标志物，并提供对癌前人类细胞中端粒功能障碍原因的详细见解。这些知识对于开发预防人类癌症恶性进展的新疗法至关重要。 公共卫生相关性：拟议的研究将揭示早期人类肿瘤生长停滞的原因，并将揭示端粒功能障碍作为一种新的和潜在的普遍存在的肿瘤阶段生物标志物。这些知识不仅对癌症治疗的风险评估和决策至关重要，而且可能有助于开发阻止恶性和转移性癌症进展的新型抗癌药物和疗法。

DESCRIPTION (provided by applicant): Most cancers arise by an evolutionary process as mutations accumulate in chromosomes of somatic cells allowing them to escape the proliferative restrains that control cell growth. To counteract uncontrolled cellular proliferation, metazoans developed a number of innate tumor suppressing mechanisms, one of them being a terminal growth arrest called cellular senescence. In recent years, as we and others identified novel senescence markers, the biological role and importance of this stress response in arresting cells in pre- malignant lesions has been demonstrated. Why cells undergo senescence in vivo and thereby prevent tumor progression in humans however, remains poorly understood. Studies in human cell cultures revealed that cellular senescence is triggered by a number of stresses including dysfunction of telomeres, the physical ends of linear chromosomes. Our studies revealed that when telomeres become critically short, due to continuous cell proliferation and other stresses, they become recognized as double strand DNA breaks and initiate a signaling cascade that results in telomere dysfunction induced cellular senescence (TDIS). In this proposal we demonstrate that the majority of cells in three human cancer precursor lesions, but not in their malignant cancer counterparts, display dysfunctional telomeres and other markers of cellular senescence. Our data therefore indicate that TDIS is a critical and universal tumor suppressing mechanism that limits the growth of pre-malignant human neoplasias. In addition, we discovered that oncogenic signals, often associated with initiation of cancer growth, dramatically accelerate telomere erosion and dysfunction in pre-malignant human cells. It is therefore possible that telomeres act as sentinels of hyperproliferative stresses that rapidly induce cellular senescence once cellular growth control mechanisms become compromised. To test these predictions we will 1) analyze a number of common cancer precursor lesions as well as their malignant counterparts for markers of TDIS by fluorescence microscopy and 2) generate a mouse tumor model system that can analyze whether TDIS suppresses malignant progression of transformed human cells in tumor cell xenografts. In addition we will 3) determine the causes for telomere dysfunction under conditions that cause aberrant cell proliferation. We will use assays to measure telomere-shortening, -dysfunction and - structure, employ forward- and reverse- genetic interventions to manipulate telomere dysfunction, and identify telomere maintenance factors critical for triggering TDIS. The proposed experiments will reveal the impact of TDIS in preventing human tumor progression, identify novel diagnostic markers for tumor stage, and provide detailed insights into the causes of telomere dysfunction in pre-malignant human cells. This knowledge is critical for developing novel therapies that prevent the malignant progression of human cancer. PUBLIC HEALTH RELEVANCE: The proposed studies will uncover the causes for growth arrest of early stage human tumors and will reveal telomere dysfunction as a novel and potentially ubiquitous biomarker for tumor stage. Not only is this knowledge critical for risk assessment and decisions on cancer treatment, but it will likely facilitate the development of novel anti-cancer drugs and therapies that stop progression of malignant- and metastatic- cancers.