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Role of Paxillin in Lung Cancer

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Lung cancer is a devastating illness with a poor overall survival. In order to dramatically impact on this disease, new targets and mechanisms have to be identified. One hallmark of lung cancer is enhanced cell motility, migration, invasion and early metastasis to lymph nodes and other organs. The cytoskeleton, especially actin-based, is intrinsically involved in these biological functions of lung cancer. We have previously shown that the focal adhesion is dramatically affected by transformation by various oncogenes, especially in lung cancer. In particular, the 68 kDa focal adhesion protein paxillin is dramatically altered (over-expressed and activated through phosphorylation) in non-small cell lung cancer (NSCLC). In preliminary data, we show for the first time that there are somatic mutations of the paxillin gene in NSCLC. In large cell carcinoma, for example, mutational frequency is up to 18%. There are differences in the mutational frequencies for the various histologies of lung cancer. The mutations were localized in between the LD domains (important for binding other molecules such as FAK) and in the LIM domains (zinc finger domains important in actin binding). Also, there were differences in paxillin gene mutations in lung cancer samples from African Americans, Caucasians, and Taiwanese. The most frequent mutation of paxillin, A127T, lead to enhanced lung cancer cell survival, tumor growth in vivo as well as enhanced angiogenesis. Using two-dimensional PAGE, the mutant A127T also led to differential protein expression in H522 NSCLC cells as compared to wild-type paxillin. We have also identified a subset of NSCLC that have amplification of the paxillin gene. Paxillin also was phosphorylated in response to activation of the receptor tyrosine kinase c-Met in lung cancer. Interestingly, in some cell lines with A127T mutation, there was a mutation of c-Met (R988C, juxtamembrane domain). Based on our most recent findings, we would propose the following aims: 1. Determine the expression, amplification, and mutations of paxillin in NSCLC and correlate with demographic and clinical factors, pertinent biological markers (such as c-Met) and patient survival; 2. Determine the biological functions of paxillin and mutated paxillin in NSCLC. Also, determine the potential for therapeutic inhibition in lung cancer; 3. Determine the combined role of paxillin and c-Met in NSCLC biological functions, angiogenesis and metastasis. In performing these studies, we will have arrived at novel mechanisms for transformation, metastasis and ultimately therapy against lung cancer. PUBLIC HEALTH RELEVANCE: Lung cancer is a devastating illness with frequent metastases and poor response to therapy. We have determined that the cytoskeletal protein paxillin plays an important role in lung cancer, especially as related to cell motility/migration with ultimate metastasis. We have also identified that paxillin gene can be selectively mutated and/or amplified in lung cancer and thereby make them more aggressive. Our goal is to study the role of paxillin in lung cancer and ultimately arrive at novel therapy against this difficult disease.
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