? ? The American Association for Cancer Research reports that cancer has surpassed heart disease as the primary killer of Americans under 85 according to a 2004 survey. Understanding the mechanisms of cancer development is the first step towards cancer prevention. Scientists have observed that during early tumorigenesis, in addition to the oncogenic events, cell death including apoptosis is also significant. Why cell death accompanies cell proliferation during cancer development and how to use this cell death feature for cancer prevention are research topics which have not been explored. Our previous cancer prevention studies using the skin carcinogenesis model revealed that introducing a tumor promoter induced both cell proliferation and apoptosis. Enhancing oxidative stress by lowering the expression of the manganese superoxide dismutase (MnSOD) gene promoted both proliferation and apoptosis, leading to similar tumor incidence and multiplicity. Selective inhibition of cell proliferation but not apoptosis led to greater suppression of tumor incidence. In addition, in the mouse skin epidermal JB6 cell model, after treatment with a tumor promoter, the most important tumor suppressor, p53, was found to translocate into mitochondria and target MnSOD, leading to propagation of oxidative stress; inhibiting this wave of oxidative stress led to blocking p53 nuclear translocation. There are several questions which need to be clarified, including, what is the signal which triggers p53 mitochondrial translocation? How does mitochondrial p53 affect mitochondrial function? How does p53 interact with MnSOD? Will mutant p53 interact with MnSOD? Since generation of reactive oxygen species (ROS) is a common feature of the agents that can induce p53 mitochondrial migration, we hypothesize that oxidative stress may serve as the signal to initiate p53 translocation during tumorigenesis. In the limited number of studies on the role of mitochondrial p53, mitochondrial permeability transition and membrane potential seem to be the two major targets. Based on these facts, we propose to use our skin epidermal JB6 cell model, and select three agents that can induce ROS generation and have a direct effect on mitochondrial membrane potential to study how they can intervene in p53 mitochondrial translocation induced by a tumor promoter. These agents include cyclosporine A; carbonyl cyanide p-[trifluoromethoxy] phenylhydrazone (FCCP), these two have opposite effects on mitochondrial membrane potential; and one set of mitochondrial substrates (pyruvate/malate), as metabolism is a major function of mitochondria. In addition, mitochondrial functions including respiration, complex activity, and intrinsic cell death pathway will be assessed. Finally, we will study how mitochondrial p53 interacts with MnSOD using affinity pull-down assays and will investigate whether mutations in p53 affect this interaction. Overall, these studies will help to understand the apoptotic mechanisms during tumorigenesis, leading to a better design of apoptosis-aimed cancer prevention. ? ? ? ?
| Wittwer, Jennifer A; Robbins, Delira; Wang, Fei et al. (2011) Enhancing mitochondrial respiration suppresses tumor promoter TPA-induced PKM2 expression and cell transformation in skin epidermal JB6 cells. Cancer Prev Res (Phila) 4:1476-84 |
| Wang, Fei; Liu, Jianfeng; Robbins, Delira et al. (2011) Mutant p53 exhibits trivial effects on mitochondrial functions which can be reactivated by ellipticine in lymphoma cells. Apoptosis 16:301-10 |
| Wang, Fei; Fu, Xueqi; Chen, Xia et al. (2010) Mitochondrial uncoupling inhibits p53 mitochondrial translocation in TPA-challenged skin epidermal JB6 cells. PLoS One 5:e13459 |
| Liu, Jianfeng; St Clair, Daret K; Gu, Xin et al. (2008) Blocking mitochondrial permeability transition prevents p53 mitochondrial translocation during skin tumor promotion. FEBS Lett 582:1319-24 |
