The Role of Met Tyrosine Kinase Signaling in Dendritic Cells for Regulation of Cell Motility, Migration, and Immune Response

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Antigen-presenting dendritic cells (DCs) are key regulators of adaptive immune responses and play a crucial role in various inflammatory diseases. Following antigen capture, DCs residing in peripheral tissues, such as intestine and skin, are activated and migrate towards lymphoid organs. We follow the concept that TGF-beta receptor and the Met tyrosine kinase signaling pathways have an antagonistic activity on DC homing in and emigration from peripheral tissues. TGF-beta-signaling is essential to maintain the stationary phenotype of epidermal DCs (Langerhans cells; LCs) by inhibiting their migration. In contrast, by employing a conditional Met-knockout (Metfl/fl) mouse model we recently identified Met-signaling in LCs and dermal DCs as essential for emigration from skin. Signaling by TGF-beta receptors and Met are known to play important roles in controlling epithelial-to-mesenchymal transition (EMT) where Met is a potent inducer of EMT. The main objective in this project is to survey the concept that Met-signaling executes an EMT program in DCs, which is crucial for their development and function. We aim at identifying molecular mechanisms and factors involved in migration regulation of DCs by Met. Global gene and microRNA expression profiling will identify Met target genes in DCs to provide further insight into the cell type specific signal cascade. Furthermore, we will use the Metfl/fl mouse model to confirm Met-signaling specificity. To better understand whether or not these effects are due to post-transcriptional modifications of factors, such as phosphorylation, we will specifically address the Gab1-Shp2-ERK/MAPK signaling cascade on the molecular level and by employing a conditional Gab1-knockout (Gab1fl/fl) mouse model. Changes in motile properties of cells including disassembly of focal adhesions, cytoskeleton remodeling, and the formation of podosomes are recognized as part of the EMT program. Whether Met-signaling is involved in podosome formation or function in DCs is yet unknown and this will be tested using the Metfl/fl mouse model. Complementary, the functional role of signaling pathways and factors on migration, adhesion, and podosome formation assays will be analyzed using kinase inhibitors and siRNA approaches. Finally, we will address the physiological role of Met-signaling in DCs in inflammatory mouse disease models in skin and intestine. Taken together, this research shall reveal whether execution of an EMT program by Met-signaling in DCs represents a crucial mechanism in DC development and function. This may provide novel strategies for treatment of immune-regulated diseases.