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

 描述（由申请人提供）：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还远未明确，但有证据表明，衰老组织中突变的积累和炎症的增加推动了癌症的发展，这是通过激活信号通路如PI 3 K/AKT/mTOR通路来促进的。我们以前的研究表明，Akt激活是由烟草成分诱导的，并且对于肺癌的形成、维持和化学抗性是重要的。使用微阵列分析，我们发现，肿瘤抑制因子RhoB在支气管上皮细胞中下调，因为它们从永生化到完全转化。RhoB受到Akt介导的FoxO 3A致癌抑制的抑制，FoxO 3A是长寿和肿瘤抑制之间界面的转录因子。RhoB还以前馈方式抑制人支气管上皮细胞中的Akt活性。RhoB丢失是肺癌中的常见事件，其可能有助于癌发生过程中Akt的激活。此外，RhoB启动子随着小鼠年龄的增长在肺组织中逐渐沉默，并且在人类肺癌中受到表观遗传学抑制。RhoB的逐渐丢失可能会增加气道上皮细胞的基因组不稳定性，加速肺衰老，并使受损细胞更容易受到癌症进展的影响，特别是当暴露于香烟烟雾时。我们假设RhoB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，RhoB蛋白在A/J小鼠的肺部在衰老过程中减少，并通过暴露于激活Akt的烟草致癌物NNK进一步减少。这些结果提供了强有力的理由来研究RhoB在肺老化/癌症界面的作用，通过测试以下具体目标。特异性Aim 1将研究RhoB对小鼠肺衰老和肿瘤发生的作用。通过比较肺组织中DNA损伤和基因组不稳定性的年龄依赖性变化、支气管肺泡灌洗细胞组成和炎性细胞因子谱，以及年龄匹配的、野生型和RhoB敲除LSL K-ras G12 D C57 BL/6小鼠（无或有突变K-ras活化）之间的肿瘤多样性和大小，我们将能够直接评估在肺老化和肺肿瘤发生期间RhoB损失的生物学后果。特定目标2将确定老年小鼠中RhoB的重建是否可以预防肺肿瘤的发生。通过在肿瘤形成之前在老年LSL K-ras G12 D C57 BL/6或香烟烟雾暴露的A/J肺肿瘤小鼠模型中遗传恢复RhoB表达，我们将能够测试RhoB的重建是否可以预防或减弱老年小鼠中的肺肿瘤发生。这些创新的研究将为肺老化和肺癌的发展提供机制性的见解。此外，它们具有通过RhoB的再激活来保护肺功能和预防老年人群中的肺癌的潜在临床意义。

 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.