MK2/3 in immune regulation by dendritic cells

Dendritic cells (DC) orchestrate the function of the immune system. They act on the notion of danger by assuming a strongly immune stimulatory phenotype for approximately one day. This is followed by the activation of negative immune regulatory feedback loops signalling the termination of an immune response. We used expression profiling and RNA interference to spot molecules in human DCs participating to immune suppression. We identified the MAPKAP kinase 2 (MK2) as a potent mediator of in switching DCs from the immune stimulatory into the immune suppressive mode. The underlying hypothesis of this project is based on notion that DCs dynamically adapt to immunological challenges in their environment. DC maturation following the encounter of a danger signal is well studied and understood. In contrast, only scarce information about the molecules involved in the switch from the immune stimulatory to an immune suppressive DC mode is available. Our first objective, therefore, is to deepen the understanding of these negative immune regulatory feedback loops in DCs. We will use DCs from MK2-/- knockout mice - as well as MK3-/- and double knockout mice as in the murine system MK3 has the capacity to complement for deficient MK2 function - for presentation of ovalbumin derived peptide epitopes to TCR transgenic OT-I and OT-II mice. In addition, we will explore the possibility of using tyrosine kinase (TK) inhibitors specific for MK2/3, as well as inhibitors of other molecules, such as p38, which is also a component of the MK2 dependent signalling pathway. DCs have the potential for utilisation as therapeutic immune modulators in cancer, autoimmunity, allergy, or transplantation. Hence, our second objective is to study the potential of DCs from MK2-/- and/or MK3-/- mice as compared to wild type DCs as tools for in vivo immune modulation. Mice bearing an experimental tumour will be treated with tumour antigen charged DCs in which MK2/3 expression is disrupted by knockout or over-expression, RNAi, or TK inhibitors. Studying autoimmunity will be done using the same DCs charged with synthetic peptides derived from proteins of the melanin synthesis for targeting melanocytes using coat de-colouration of black mice as an indicator for autoimmunity. A tolerance induction model will be based on the acceptance of a transplant of allogeneic haematopoietic stem cells. The data generated in this project will improve the understanding of immune regulation by providing evidence for distinct differentiation dependent DC functions. Furthermore, blocking of MK2 may be a critical feature of a next generation of DC immune therapeutics for the treatment of cancer, autoimmunity, allergies, as well as tolerance induction for improving allogeneic transplant acceptance.

In the course of this project, the signaling molecule MK2 has been identified as a major regulator of inflammatory immune responses. The aim of our study was to investigate the function of MK2 in dendritic cells, which form a crucial link between the innate and the adaptive immune system. Dendritic cells communicate with other cells of the immune system about distinguishing healthy from infectious processes. They are therefore responsible for the triggering or suppression of a specific immune response a responsibility requiring tight regulation. MK2 has been identified as a key molecule involved in this stringent control of dendritic cell- mediated immune responses. MK2 acts as a hub within one of the most important signaling routes in immune cells, linking intra- and extracellular signaling mechanisms. Whereas the molecule itself gets activated inside a cell, it mediates the release of other signaling molecules into the extracellular space, where they contribute to the propagation of inflammation. We were able to demonstrate that MK2 in dendritic cells attenuates a specific arm of cellular immunity, with severe consequences especially in the setting of autoimmune diseases. This immune suppressive role of MK2 became clear upon repeated initiation of an immune response, underlining its contribution to multi-layered regulatory mechanisms. By down- modulating such immune responses MK2 prevents damage to the organism caused by excessive inflammatory processes. In addition, it became evident that MK2 is also involved in the recognition of tumors by the immune system. In a model of malignant melanoma we could show that MK2 in dendritic cells promotes the ability of a tumor to evade immune recognition and thereby facilitates tumor growth. Similar observations were made in a glioblastoma model and underlined how MK2 contributes to the suppression of an immune response launched against a growing tumor. Ultimately, our findings are of high relevance with regard to the clinical development of MK2 inhibitors as therapeutics for the treatment of autoimmune disease as well as tumor patients.