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.
Lung cancer increases with age, and loss of the tumor suppressor RhoB, which gradually decreases in the lung with aging, correlates with lung cancer progression. We propose to investigate the role of RhoB during pulmonary aging and lung tumorigenesis without or with mutant K-ras activation or cigarette smoke exposure in different mouse model systems, and explore the translational implication for healthy pulmonary aging and lung cancer prevention by restoring RhoB expression in aged mice.