Peroxisome proliferator-activated receptors (PPAR) are members of the nuclear hormone receptor superfamily which act as ligand-activated transcription factors. Three isoforms have been identified, PPAR alpha, gamma, and delta, all of which bind to specific DNA sequences as heterodimers with the retinoic acid X-receptors. PPARgamma has been shown to be activated by the synthetic antidiabetic thiazolidinediones (TZD) such as ciglitazone and troglitazone as well as by prostaglandin D and J derivatives which may function as endogenous activators. While an important role for PPARgamma has been defined in adipocyte differentiation, this molecule is expressed in a variety of cell types including non-small cell lung cancer cells (NSCLC). Data from our laboratory and other investigators have shown that activators of PPARgamma inhibit transformed growth of NSCLC. However, these agents engage additional pathways, and conflicting data has been obtained in other types of cancer, indicating both a pro- and anti-tumorigenic role for PPARs. PPARdelta has been shown to be activated by prostacyclin and its stable analog iloprost. The role of PPARdelta in the development cancer is also not clear, with studies demonstrating both a tumorigenic and anti-tumorigenic role. Preliminary studies from our laboratory have shown that overexpression of PPARgamma in multiple NSCLC lines selectively inhibited anchorage-independent growth in soft agar in vitro, and the development of lung tumors in xenograft models. Analysis of gene expression using microarrays suggests that these inhibitory effects may be mediated through altered expression of integrins and enzymes that modulate extracellular matrix, implicating alterations in cell migration and invasion. Overexpression of PPARdelta in NSCLC inhibits PPARgamma activity and leads to increased soft agar colony formation. For both isoforms of PPAR the molecular mechanisms whereby PPARs regulate lung tumorigenesis are poorly understood. The goal of this proposal is to employ molecular and pharmacological approaches to test the hypothesis that activation of specific PPAR isoforms has opposing effects on the development of lung cancer, and to identify potential mechanisms which may account for these effects.
Four specific aims are proposed.
Specific aim 1 will examine the effects of overexpressing PPARgamma and delta on the transformed growth of NSCLC lines, and compare the response with effects of putative specific pharmacological agents.
Specific Aim 2 will define the molecular changes induced by overexpression of PPARs on cell morphology, migration and differentiation, using 2-dimensional and three dimensional tissue culture.
Specific Aim 3 will develop transgenic mice specifically overexpressing PPARs, and assess their role in carcinogenesis models.
Specific Aim 4 will examine PPAR expression using a tissue microarray derived from human lung cancer samples. These studies will help to define the role of PPARs in lung tumorigenesis, and help to define new targets for therapeutic intervention.
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