Genetic pathways of replicative senescence and its function in tumorigenesis

描述（由申请人提供）：为了维持组织稳态和正常功能，受损细胞需要被替换或修复。在哺乳动物中，这一过程需要大量的细胞增殖。这种大规模增殖的后果是突变的积累，其中一些可能针对致癌基因。为了抑制癌前细胞的增殖和存活，必须有有效的肿瘤抑制机制，衰老就是其中之一。衰老限制了细胞的增殖能力，从而阻碍了肿瘤发生所必需的多种突变的积累。此外，异常的致癌激活、DNA损伤或氧化应激也可以激活衰老，提供了一种失效保护机制，防止有肿瘤转化风险的细胞增殖。克服衰老是癌细胞获得的基本特性。尽管它很重要，但人们对衰老的分子调控知之甚少，许多关键的调控因子仍未被确定。我们的长期目标是了解衰老的分子调控及其在肿瘤发生中的作用。我们最近发现Smurf2是一种新的衰老调节剂。它的表达在人成纤维细胞中响应端粒缩短而上调，这种表达升高足以诱导衰老。我们的初步研究发现，下调Smurf2可以延缓人类成纤维细胞的衰老，而缺乏Smurf2的小鼠胚胎成纤维细胞在培养中是不朽的。我们假设Smurf2通过其调节p16和p21衰老途径的能力来调节衰老，因此Smurf2可能在肿瘤发生中发挥重要作用。在本提案中，我们将描述Smurf2在衰老调控和肿瘤发生中的功能，有三个具体目的。在Aim 1中，我们将描述Smurf2在调节p16衰老途径中的功能。在Aim 2中，我们将研究Smurf2调控p21衰老途径的机制。在Aim 3中，我们将研究Smurf2的功能及其在肿瘤发生中的衰老调控。这些研究将为Smurf2在肿瘤发生中的作用提供直接证据。此外，这些研究将在衰老途径中发现新的遗传成分，并为衰老如何被调节提供新的见解，这是实现衰老在癌症治疗中的巨大希望的重要一步。

DESCRIPTION (provided by applicant): To maintain tissue homeostasis and normal functions, damaged cells need to be replaced or repaired. In mammals, such process requires extensive cell proliferation. A consequence of this massive proliferation is the accumulation of mutations, some of which may target cancer causing genes. To constrain the proliferation and survival of precancerous cells, potent tumor suppression mechanisms must be functional, one of which is senescence. Senescence limits proliferative capacity of cells, thus impeding the accumulation of multiple mutations that are necessary for tumorigenesis. Furthermore, aberrant oncogenic activation, DNA damage or oxidative stress can also activate senescence, providing a failsafe mechanism that prevents the proliferation of cells at risk for neoplastic transformation. Overcoming senescence is an essential property acquired by cancer cells. Despite its importance, the molecular regulation of senescence is poorly understood, and many of the critical regulators remain unidentified. Our long-term goal is to understand the molecular regulation of senescence and its function in tumorigenesis. We recently have identified Smurf2 as a novel regulator of senescence. Its expression is up-regulated in response to telomere shortening in human fibroblasts, and such elevated expression is sufficient to induce senescence. Our preliminary studies have found that down-regulation of Smurf2 postpones senescence in human fibroblasts, whereas mouse embryonic fibroblasts deficient in Smurf2 are immortal in culture. We hypothesize that Smurf2 regulates senescence through its ability to modulate the p16 and p21 senescence pathways, and that consequently Smurf2 might play an important role in tumorigenesis. In this proposal, we will characterize the function of Smurf2 in senescence regulation and tumorigenesis with three specific aims. In Aim 1, we will characterize the function of Smurf2 in regulation of the p16 senescence pathway. In Aim 2, we will study the mechanism by which Smurf2 regulates the p21 senescence pathway. In Aim 3, we will investigate the function of Smurf2 and its regulation of senescence in tumorigenesis. These studies will provide direct evidence for a function of Smurf2 in tumorigenesis. Furthermore, these studies will identify new genetic components in the senescence pathways, and provide new insight into how senescence is regulated, an important step towards the fulfillment of the great promise of senescence in cancer treatment.