Loss of E-cadherin function is a critical event that is associated with epithelial-to-mesenchymal transition, invasiveness and the metastatic phenotype in human colorectal cancer and other carcinomas. Inappropriate activation of the canonical Wnt pathway is another critical event in the transition from normal epithelium to the neoplastic phenotype in colorectal cancer. Although it is well accepted that perturbation of these pathways represent important hallmarks of neoplastic tranformation, their mechanisms of transduction and regulation under normal and pathological conditions are poorly understood. We have developed highly reliable and sensitive assays for re-expression of E-cadherin in the SW620 colorectal cancer cell line that normally expresses very low levels of E-cadherin. Similarly, we have also developed a robust biochemical assay that recapitulates activation of the canonical Wnt pathway by the Wnt coreceptor, LRP6. Both of these assays have been adapted for a 384-well format. We now propose to interrogate regulation of E-cadherin expression and canonical Wnt signaling using a chemical genetics-based approach in a high-throughput screen to identify compounds that induce expression of E-cadherin in SW620 cells and that perturb degradation of beta-catenin and Axin, two key regulators of signaling through the canonical Wnt pathway. Our initial screen of 6,400 small molecules has already identified several lead compounds in both of these assays and we propose screen a total of 160,000 compounds. We propose to validate lead compounds from this initial screen in a variety of in vitro and in vivo assays. Our preliminary studies indicate that the small molecule trichostatin A, a histone deacetylase inhibitor, acts to induce E-cadherin expression in SW620 cells. We will explore its role in E-cadherin expression as well as its potential for regulating Wnt signaling. Finally, we will identify the mechanisms of action and potential targets of validated compounds by testing their effects on candidate cellular pathways as well as in biochemically reconstituted reactions.
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