Most cancer deaths are due to the systemic dissemination of cancer cells and the formation of secondary tumors (metastasis) in distant organs. Obviously, the migratory and invasive capabilities of cancer cells are critical parameters in the metastatic cascade. 90% of all cancers originate from epithelial tissues and, to leave the primary tumor and to invade into the surrounding tissue, tumor cells dissolve their cell-cell contacts and adjust their cell-matrix adhesion sites to a more transient, migratory and invasive mode. Such temporary and reversible phenomenon is known as epithelial-to-mesenchymal transition (EMT), a multistage process that involves distinct genetic and epigenetic alterations and leads to metastasizing, tumor-seeding cells with stem cell-like capabilities, potentially cancer stem cells.

In the past years, the work of many laboratories, including our own, has demonstrated that the dramatic changes in gene expression that occur during EMT and cancer metastasis are regulated by a large number of transcription factors and miRNAs. Most of these transcription factors, such as Klf4, Sox4, Lhx2, Dlx2, FoxC2, FoxF2, Tcf/b-catenin and several others, and miRNAs, such as members of the miR-200 family, function as master switches during embryonic organogenesis or in the maintenance of embryonic or somatic stem cells. Moreover, a number of epigenetic modifications play a role in EMT and malignant tumor progression. These results indicate that complex transcriptional and post-transcriptional regulatory circuits control the multiple stages of EMT and malignant tumor progression. However, the regulation of the activities of these transcription factors and miRNAs and the identification and functional contribution of their direct target genes has only begun to be explored.

We here propose to dissect at a comprehensive level the functional contribution of EMT transcription factors and miRNAs to EMT and malignant tumor progression. In an ongoing genome-wide functional screen, we have identified a number of transcription factors that are critical for the EMT process to occur. Moreover, we have identified a list of miRNAs that change in their expression during EMT. First, we will employ gain and loss of function approaches in cellular experimental systems in vitro to delineate the regulatory functions of selected transcription factors and miRNAs during EMT. Employing chromatin-immunoprecipitation in combination with next generation sequencing we will identify the direct targets of selected transcription factors. Moreover, high-throughput sequencing of RNAs isolated by crosslinking immunoprecipitation (HITS-CLIP) will be used to identify the genes that are regulated in their expression by miRNAs during EMT. These experiments are aimed at the identification and functional validation of the transcriptional regulatory circuits underlying EMT. Finally, we will use mouse models of cancer to determine in proof-of-concept experiments the contribution of selected EMT transcription factors, miRNAs and their target genes to malignant tumor progression and eventually their potential suitability as therapeutic targets. Finally, we will assess the significance of our findings in cancer patients and evaluate whether the gene signatures identified here may provide prognostic tools for the prediction of clinical outcome. From these experiments we not only anticipate novel insights into the molecular regulation of malignant tumor progression but also envision developing new strategies towards innovative cancer diagnosis, prognosis and therapy.