Tumor Suppression by Telomere Dysfunction Induced Senescence

描述(申请人提供)：大多数癌症是由进化过程产生的，因为突变积累在体细胞的染色体上，使它们能够逃避控制细胞生长的增殖抑制。为了对抗失控的细胞增殖，后生动物发展了许多天生的肿瘤抑制机制，其中之一是称为细胞衰老的终末生长停滞。近年来，随着我们和其他人发现了新的衰老标志物，这种应激反应在阻止癌前病变中的细胞方面的生物学作用和重要性已经得到证明。然而，为什么细胞在体内发生衰老，从而阻止人类肿瘤的发展，仍然知之甚少。在人类细胞培养中的研究表明，细胞衰老是由许多压力引发的，包括端粒功能障碍，端粒是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压力，它们被认为是双链DNA断裂，并启动了一系列信号级联，导致端粒功能障碍诱导的细胞衰老(TDIs)。在这项提议中，我们证明了在三个人类癌症前驱病变中的大多数细胞，但在它们的恶性肿瘤对应病变中，显示出功能失调的端粒和其他细胞衰老的标志。因此，我们的数据表明，TDIS是一种关键的和普遍的肿瘤抑制机制，它限制了癌前人类肿瘤的生长。此外，我们还发现，通常与癌症生长有关的致癌信号会极大地加速癌前人类细胞的端粒侵蚀和功能障碍。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，就会迅速诱导细胞衰老。为了验证这些预测，我们将1)通过荧光显微镜分析一些常见的癌症前驱病变以及它们的恶性对应部位的TDIs标记，2)建立一个小鼠肿瘤模型系统，该系统可以分析TDIs是否抑制肿瘤细胞异种移植中转化的人类细胞的恶性进展。此外，我们还将在导致细胞异常增殖的条件下确定端粒功能障碍的原因。我们将使用分析方法来测量端粒缩短、功能障碍和结构，使用正向和反向基因干预来操纵端粒功能障碍，并确定触发TDIS的关键端粒维持因素。这些拟议的实验将揭示TDIs在防止人类肿瘤进展方面的影响，识别肿瘤分期的新诊断标记物，并为癌症前人类细胞端粒功能障碍的原因提供详细的见解。这一知识对于开发防止人类癌症恶性进展的新疗法至关重要。

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.