The role of the tumor suppressor RhoB in pulmonary aging and lung tumorigenesis

 描述(申请人提供)：肺癌是全球癌症相关死亡的主要原因，通常发生在吸烟者中。大多数肺癌是在65岁以上的人被诊断出来的。尽管衰老促进癌症的过程远不清楚，但有证据表明，突变的积累和老年组织中炎症的增加推动了癌症的发展，而PI3K/AKT/mTOR通路等信号通路的激活促进了癌症的发展。我们以前的研究表明，Akt的激活是由烟草成分诱导的，在肺癌的形成、维持和化疗耐药中起着重要的作用。利用微阵列图谱，我们显示了肿瘤抑制基因RhoB在支气管上皮细胞从永生化到完全转化的过程中下调。RhoB是通过Akt介导的对FOXO3a的致癌抑制而被抑制的，FOXO3a是一种位于长寿和肿瘤抑制之间的转录因子。在前馈方式中，RhoB还抑制人支气管上皮细胞中Akt的活性。RhoB缺失在肺癌中是一种常见的事件，它可能在肺癌发生过程中导致Akt的激活。此外，随着小鼠年龄的增长，RhoB启动子在肺组织中逐渐沉默，并在人类肺癌中受到表观遗传抑制。RhoB基因的逐渐缺失可能会增加呼吸道上皮细胞基因组的不稳定性，加速肺部衰老，并使受损细胞更容易发生癌症进展，尤其是当暴露在香烟烟雾中时。我们假设RhoB肺的缺失促进了肺老化和肺肿瘤的发生。我们的初步数据表明，在A/J小鼠衰老过程中，RhoB蛋白在肺中减少，并因暴露于可激活Akt的烟草致癌物NNK而进一步减少。这些结果通过测试以下特定目标，为研究RhoB在肺衰老/癌症界面上的作用提供了强有力的理论基础。特异性Aim1将研究RhoB在小鼠肺老化和肿瘤发生中的作用。通过比较年龄匹配、野生型和RhoB基因敲除的LSL K-ras G12D C57BL/6小鼠之间肺组织DNA损伤和基因组不稳定性、支气管肺泡灌洗液细胞成分和炎性细胞因子谱以及肿瘤多样性和大小的年龄相关性变化，我们将能够直接评估RhoB基因缺失在肺老化和肺肿瘤发生过程中的生物学后果。具体目标2将确定老年小鼠中RhoB的重建是否能防止肺癌的发生。通过在肿瘤形成前在老年LSL K-ras G12D C57BL/6或香烟烟雾暴露的A/J肺癌小鼠模型中基因恢复RhoB的表达，我们将能够测试RhoB的重建是否可以预防或减轻老年小鼠的肺肿瘤发生。这些创新的研究将为肺老化和肺癌的发展提供机械性的见解。此外，它们在保护肺功能和通过重新激活RhoB来预防老年人群肺癌方面具有潜在的临床意义。

 DESCRIPTION (provided by applicant): Lung cancer is the leading cause of cancer-related death worldwide, and commonly occurs in smokers. Most lung cancers are diagnosed when people are older than 65 years of age. Although the process by which aging promotes cancer is far from clear, evidence suggests that the accumulation of mutations and increased inflammation in aged tissues drive cancer development, which is promoted by activation of signaling pathways such as the PI3K/AKT/mTOR pathway. Our previous studies demonstrated that Akt activation is induced by tobacco components and is important for lung cancer formation, maintenance, and chemoresistance. Using microarray profiling, we showed that the tumor suppressor RhoB is down regulated in bronchial epithelial cells as they progress from immortalization to full transformation. RhoB is suppressed by Akt-mediated oncogenic inhibition of FoxO3A, a transcription factor at the interface between longevity and tumor suppression. In a feedforward manner, RhoB also suppresses Akt activity in human bronchial epithelial cells. RhoB loss is a frequent event in lung cancer, which could contribute to Akt activation during carcinogenesis. In addition, the RhoB promoter is gradually silenced in lung tissue as mice age, and is epigenetically suppressed in human lung cancer. The gradual loss of RhoB might increase genome instability of airway epithelial cells, accelerate pulmonary aging, and make damaged cells more vulnerable to cancer progression, especially when exposed to cigarette smoke. We hypothesize that loss of RhoB lung promotes contributes to pulmonary aging and lung tumorigenesis. Our preliminary data demonstrates that RhoB protein is decreased in the lungs of A/J mice during aging and is further decreased by exposure to the tobacco carcinogen NNK that activates Akt. These results provide strong rationale to study the role of RhoB at the lung aging/cancer interface by testing the following specific aims. Specific Aim1 will investigate the role of RhoB on mouse lung aging and tumorigenesis. By comparing age-dependent changes of DNA damage and genomic instability in lung tissue, bronchoalveolar lavage cell composition and inflammatory cytokine profile, as well as tumor multiplicity and size between the age-matched, wildtype and RhoB knockout LSL K-ras G12D C57BL/6 mice without or with mutant K-ras activation, we will be able to directly assess the biological consequences of RhoB loss during pulmonary aging and lung tumorigenesis. Specific Aim 2 will determine if reconstitution of RhoB in aged mice prevents lung tumorigenesis. By genetically restoring RhoB expression in aged LSL K-ras G12D C57BL/6 or cigarette smoke-exposed A/J lung tumor mouse models before tumor formation, we will be able to test whether reconstitution of RhoB could prevent or attenuate lung tumorigenesis in aged mice. These innovative studies will provide mechanistic insight into pulmonary aging and the development of lung cancer. Moreover, they have potential clinical implications for preservation of lung function and prevention of lung cancer in elderly populations through reactivation of RhoB.