The epithelial-mesenchymal transition (EMT) is characterized by the loss of cell-cell adhesion and cell polarity in epithelial cells and the acquisition of motile and invasive properties. While essential for development, the EMT is one mechanism by which tumors can acquire the capability to undergo tissue invasion and metastasis. It is therefore important to identify novel therapies that can inhibit the EMT, but few assays for EMT inhibitors in high throughput screens (HTS) have developed. A change in fibroblast growth factor receptor 2 (FGFR2) splicing occurs during the EMT and using an innovative luciferase-based splicing reporter assay we previously carried out a genome-wide high throughput cDNA expression screen for regulators of this splicing switch. This screen identified the epithelial cell type specific splicing regulators ESRP1 and ESRP2 demonstrating the feasibility of cell-based splicing assays in high throughput, array-based screens. An extensive set of ESRP-regulated exons switch splicing during the EMT, indicating that global changes in alternative splicing occur during this process. A change in this splicing network is a thus a dynamic feature of the EMT and changes in splicing of ESRP-regulated targets can be used as a biomarker for the EMT. In this application we will develop more robust next generation splicing reporter assays using ESRP- regulated exons that undergo profound """"""""switch-like"""""""" changes in splicing and configure them for HTS assays using the Molecular Libraries Production Centers Network (MLPCN).
In Aim 1, we will adapt existing minigene reporters containing ESRP regulated exons and flanking intronic regulatory sequences for HTS in the context of our established luciferase-based reporter minigenes. The reporters will include exons whose inclusion is activated as well as those that undergo skipping during the EMT. Additional reporters will also be developed for use in counter-screens to prioritize HTS hits.
In Aim 2, these screens will be configured for screening in 384 well format and pilot screens will be carried out using several small compound libraries as well as several previously described compounds that have been shown to function as general modulators of splicing. These compounds will be screened in mesenchymal cells for splicing changes indicative of the reverse process of mesenchymal to epithelial transition (MET) and in epithelial cells for inhibition or reversal of an inducible EMT. Successful completion of this pilot phase of this funding mechanism (PAR-10-182) in year one will enable us to submit these assays for the larger scale screening phase using the MLPCN library of compounds. Such screens hold great promise to yield novel small molecule regulators of splicing, including a subset that broadly promote epithelial-specific splicing pathways to inhibit or reverse the EMT and block cancer metastasis. Such compounds will potentially include those that affect signaling pathways or other upstream events that might potently activate broad transcriptional and post-transcriptional gene expression programs that inhibit the EMT.
The epithelial to mesenchymal transition (EMT) is the process by which cancer cells can escape from the primary site and metastasize to distant sites and is therefore a target for novel cancer therapies. We have identified regulators of alternative splicing that control an epithelial splicing network that is lost during the EMT, suggesting that a mesenchymal splicing program can promote the EMT and that these splicing changes serve as biomarkers for this process. The current application will use innovative splicing assays to carry out screens for novel compounds that inhibit this splicing transition and thereby identify lead compounds for drugs to prevent tumor metastasis.
