Role of the WNK1 pathway and osmoregulation in T cell migration and activation

The immune system of mammals is critical for protection from infections caused by bacteria, viruses and other microorganisms. An essential part of the immune system is a white blood cell termed a T cell. T cells move around the body, travelling between different tissues via the blood system, searching for signs of infection. If they find such infections, they stop, become activated, divide rapidly and turn into specialised cells that actively fight the infection. Some T cells become killers, destroying infected cells, others become helpers that actively support the production of antibodies that are essential to clear infections. Thus, the migration and activation of T cells is a vital part of the immune response to infectious disease. We have discovered an enzyme in T cells called WNK1 which is essential for the migration and activation of T cells. Surprisingly, we have found that WNK1 controls the movement of water into the cells, which is important for the migration and activation of the T cells. We will now study how WNK1 controls this water movement and why water movement is required for T cells to migrate and become activated. We will do this by analysing the biochemical processes inside the T cells that are controlled by WNK1. Furthermore, we will discover how WNK1 contributes to immune responses, especially to infections by respiratory viruses such as influenza.

CD4+ T cells are an essential part of the adaptive immune system, providing help to B cells, CD8+ T cells and innate immune cells, and migration and antigen-induced activation are critical for their function. We have previously discovered a novel pathway regulated by the WNK1 kinase which is required for CD4+ T cell migration in response to the chemokine CCL21 binding to the CCR7 receptor. WNK1 has been studied most extensively in the kidney where it acts as an osmoregulator transducing signals via the OXSR1 and STK39 kinases and the SLC12A-family of ion co-transporters resulting in movement of Na+, K+ and Cl- ions from urine into the blood. We have shown that signalling from CCR7 activates WNK1 and that this kinase regulates CD4+ T cell migration. Furthermore, we have recently found that WNK1 is also activated by signals from the T cell antigen receptor (TCR), and that WNK1-deficient CD4+ T cells have a profound defect in antigen-induced proliferation and cannot support a T-dependent antibody response. Surprisingly, we have discovered that the requirement for WNK1 in T cell migration and activation depends on WNK1-regulated water movement into the cell. In this proposed research program, using mouse genetics, cell biology, imaging and biochemistry we will investigate the role of each protein in the WNK1 pathway that is expressed in CD4+ T cells (WNK1, OXSR1, STK39, SLC12A2, SLC12A4, SLC12A6 and SLC12A7), assessing their roles in CCR7-driven migration and TCR-induced activation. We will determine how the regulation of water movement by this pathway impacts on these cellular processes. Finally, we will assess the importance of each protein in this pathway in CD4+ T-dependent immune responses. Overall, these studies will provide an in-depth analysis of a novel signalling pathway that plays a critical role in CD4+ T cell function and, more broadly, reveal how cell volume changes driven by water movement regulate cell migration and activation.