Tumor Suppression by Telomere Dysfunction Induced Senescence

描述（由申请人提供）：大多数癌症是由进化过程引起的，因为体细胞染色体中的突变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，后生动物发展了许多天生的肿瘤抑制机制，其中之一是被称为细胞衰老的终末生长停滞。近年来，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恶性病变前细胞中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，从而阻止人类肿瘤的进展，人们仍然知之甚少。对人类细胞培养的研究表明，细胞衰老是由一系列压力触发的，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，当端粒由于持续的细胞增殖和其他压力而变得非常短时，它们被认为是双链DNA断裂，并启动信号级联，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，而不是恶性癌症的对应物，显示功能失调的端粒和其他细胞衰老标志物。因此，我们的数据表明，TDIS是一种关键的、普遍的肿瘤抑制机制，它限制了人类恶性肿瘤的生长。此外，我们发现致癌信号，通常与癌症生长的开始有关，显著加速了人类癌前细胞的端粒侵蚀和功能障碍。因此，一旦细胞生长控制机制受到损害，端粒可能充当过度增殖应激的哨兵，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及其恶性对应物的TDIS标记物，2)生成一个小鼠肿瘤模型系统，可以分析TDIS是否抑制肿瘤细胞异种移植物中转化的人类细胞的恶性进展。此外，我们将确定在导致异常细胞增殖的条件下端粒功能障碍的原因。我们将使用检测方法来测量端粒缩短、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。本实验将揭示TDIS在预防人类肿瘤进展中的作用，确定新的肿瘤分期诊断标志物，并为恶性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.