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Snail-Dependent Malignant Conversion of Airway Epithelium

Institution: University of California, Los Angeles
Investigator(s): Tonya Walser, Ph.D.
Award Cycle: 2011 (Cycle 20) Grant #: 20KT-0055 Award: $266,934
Subject Area: Cancer
Award Type: New Investigator Awards

Initial Award Abstract
Tobacco smoke-induced lung inflammation is a risk factor for lung cancer development. Several potent inflammation-associated proteins operate by increasing levels of a protein called Snail. Snail functions by decreasing levels of E-cadherin, a protein critical for maintenance of contacts between cells lining the lungs. Without E-cadherin, cells lining the airways break apart and move around freely in a process known as epithelial-to-mesenchymal transition (EMT). EMT is often activated during cancer invasion and metastasis. To date, however, the roles of inflammation, Snail, and EMT in early lung cancer development have not been defined. Using cells derived from normal lung tissues to model the onset of lung cancer, our preliminary results indicate that high levels of Snail cause a specialized cell type found in the lung, lung stem cells, to multiply and behave more aggressively than normal. Although stem cells are helpful in many settings, in the context of cancer, they almost always have negative implications. Our laboratory-based studies are the first to describe a connection between Snail, EMT, stem cells, and the initiation of lung cancer. In fact, we recently made the important discovery that Snail transforms otherwise normal lung cells into cancer cells that grown in mice. We are also the first to report high levels of Snail in human lungs during the earliest stages of lung cancer development.

In Aim 1 of the proposed studies, we will use cells derived from two types of normal lung tissues (modeling two types of early lung cancer) that we have engineered to produce high levels of Snail, and we will separate the resulting cells into subsets based on their stem cell-like characteristics. We will expand our preliminary results by evaluating each subset of stem cells in an assay that will tell us if one subset behaves more like cancer cells than the others. We will also determine if the most aggressive stem cell subset has the capacity to initiate tumor growth in mice.

In Aim 2, we will determine the contribution of two genes, c-MYC and GAS1, to the aggressive behavior of the stem cell subset with high levels of Snail. Our preliminary results indicate that when Snail levels are high, c-MYC levels are also high; c-MYC has been linked to cancer-like behavior. Similarly, our preliminary results indicate that when Snail levels are high, GAS1 levels are low; GAS1 has been linked to anti-cancer-like behavior. Therefore, we will genetically manipulate the cells with high levels of Snail so that they no longer produce c-MYC and so that they again produce high levels of GAS1. We will then determine if alterations in c-MYC or GAS1 block the ability of Snail to transform the normal stem cell subset into cancer cells. Ultimately, if Snail-initiated lung cancer requires c-MYC and GAS1, these genes and pathways regulating their production would represent novel targets for prevention and therapy.

In Aim 3, we will examine clinical samples containing areas of normal, premalignant, and malignant lung tissue to identify the same Snail over-expressing cells we found to be overly aggressive in our laboratory-based studies. Using a specialized microscope, we will isolate the cells with high levels of Snail from each of the three regions, and we will analyze the genetics of each group to identify Snail-related changes the cells undergo as the disease progresses. From this dataset, we will be able to determine the relevance of our findings in Aim 2 to human disease. The results will also help us to identify molecules that are the most clinically relevant to the transformation of normal lung tissue into cancerous lung tissue so we can make them the focus of our future investigations.

In summary, understanding the interactions of proteins and cell types responsible for the initiation of lung cancer will provide new opportunities for disease prevention and early detection. Our novel findings thus far combined with funding for the more detailed proposed studies will allow us to make a significant contribution to knowledge about the signaling events driving lung cancer initiation and progression and to the research mission of the TRDRP.