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

抗原提呈树突状细胞(DC)是获得性免疫反应的关键调节细胞，在各种炎症性疾病中发挥重要作用。抗原捕获后，外周组织(如肠道和皮肤)中的DC被激活，并向淋巴器官迁移。我们遵循的概念是，转化生长因子-β受体和蛋氨酸酪氨酸激酶信号通路对DC归巢和外周组织迁出具有拮抗作用。转化生长因子-β信号通路通过抑制表皮树突状细胞(朗格汉斯细胞；LCS)的迁移来维持其稳定的表型。相反，通过使用条件Met基因敲除(Metfl/fl)小鼠模型，我们最近发现LCS和真皮DC中的Met信号是皮肤迁移所必需的。已知转化生长因子-β受体和甲硫氨酸在控制上皮细胞向间充质转化(EMT)过程中发挥重要作用，而Met是EMT的有效诱导者。这个项目的主要目标是调查Met-Signal在DC中执行EMT计划的概念，这对DC的发展和功能至关重要。我们的目的是确定Met调节DC迁移的分子机制和相关因素。全球基因和microRNA表达谱将识别树突状细胞中的Met靶基因，以进一步了解细胞类型特定的信号级联。此外，我们将使用Metfl/fl小鼠模型来确认Met信号的特异性。为了更好地了解这些影响是否源于因子的转录后修饰，如磷酸化，我们将在分子水平上专门研究GAB1-Shp2-ERK/MAPK信号级联反应，并采用条件GAB1基因敲除(Gab1fl/fl)小鼠模型。细胞运动特性的改变，包括局部粘连的解体，细胞骨架的重塑，以及足体的形成，都被认为是EMT计划的一部分。Met信号是否参与DC的足体形成或功能尚不清楚，这将通过Metfl/fl小鼠模型进行测试。作为补充，将使用激酶抑制剂和siRNA方法分析信号通路和因素在迁移、黏附和足体形成分析中的功能作用。最后，我们将讨论树突状细胞中Met信号在皮肤和肠道炎症性小鼠疾病模型中的生理作用。综上所述，这项研究将揭示在DC中通过Met信号执行EMT程序是否代表DC发展和功能中的关键机制。这可能为免疫调节疾病的治疗提供新的策略。

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.