Interactome mapping of Rin-like signaling in T cells

Our immune system offers us protection against thousands of pathogens every day. The so-called T cells play an important role in this process. The development of T cells takes place in the thymus and is crucial for the development of a diverse and functional adaptive immune system. In the thymus, the T cells are trained, can develop and be divided into further subgroups. One of these groups is formed by the cytotoxic T cells. They kill cells that have been infected by viruses. Another group is formed by the T helper cells (Th cells). Th cells are crucial for adaptive immunity because they control tailored immune responses to invading pathogens. When a Th cell leaves the thymus and enters the human lymphatic system, it is still nave and cannot yet coordinate a specific immune response. However, if it comes into contact with parts of the pathogen through other immune cells such as dendritic or B cells, it develops into further subgroups, including, for example, the follicular T helper cell (Tfh). This developmental process is also called Th cell differentiation. Tfh cells support the B cells in the production of high-affinity antibodies, whereby they lead to immune protection in the event of infection or after vaccination. We recently discovered that the protein Rin-like (Rinl) acts as a negative regulator of Tfh cell differentiation. In the absence of Rinl, the number of Tfh cells and germinal center B cells are increased. Moreover, signaling events within nave Th cells are affected. This suggests that Rinl controls Tfh cell differentiation via signaling pathways in Th cells. Based on these results, we aim to decipher the Rinl-dependent molecular mechanisms that control Tfh differentiation by identifying and characterizing interaction partners of Rinl. To achieve a holistic view on the Rinl protein network, we will apply proximity labeling in combination with mass spectrometry. Proximity labeling enables the identification of permanent and transient protein-protein interactions in cellulo or in vivo, while seizing their spatial-temporal dimension. This allows an unprecedented view of protein interaction networks and their cell- type-specific regulation during development and differentiation. We will establish in vivo proximity labeling, characterize the in vivo network of Rinl-protein interactions in Th cells in the steady state and during the acute immune response, and further characterize Rinl interactors and their role in Rinl-dependent signaling events. Studying the Rinl network and Rinl-interacting factors and their role in Rinl-dependent signaling events will unravel new regulatory mechanisms during early T cell activation, which affect Tfh cell differentiation and consequently immune responses. These findings will pave the way for new therapeutic approaches leading to the treatment of immune-mediated diseases, such as autoimmune diseases, T cell lymphomas or allergies.