Diacylglycerol Kinase ζ Limits the Generation of Natural Regulatory T Cells

Natural regulatory T (nT(reg)) cells are important for maintaining tolerance to self-and foreign antigens, and they are thought to develop from thymocytes that receive strong T cell receptor (TCR)-mediated signals in the thymus. TCR engagement leads to the activation of phospholipase C-gamma 1, which generates the lipid second messenger diacylglycerol (DAG) from phosphatidylinositol 4,5-bisphosphate. We used mice that lack the zeta isoform of DAG kinase (DGK zeta), which metabolizes DAG to terminate its signaling, to enhance TCR-mediated signaling and identify critical signaling events in nT(reg) cell development. Loss of DGK zeta resulted in increased numbers of thymic CD25(+)Foxp3(-)CD4(+)nT(reg) cell precursors and Foxp3(+)CD4(+)nT(reg) cells in a cell-autonomous manner. DGK zeta-deficient T cells exhibited increased nuclear translocation of the nuclear factor kappa B subunit c-Rel, as well as enhanced extracellular signal-regulated kinase (ERK) phosphorylation in response to TCR stimulation, suggesting that these downstream pathways may contribute to nT(reg) cell development. Indeed, reducing c-Rel abundance or blocking ERK phosphorylation abrogated the increased generation of nT(reg) cells by DGK zeta-deficient thymocytes. The extent of ERK phosphorylation correlated with TCR-mediated acquisition of Foxp3 in immature thymocytes in vitro. Furthermore, the development of nT(reg) cells was augmented in mice in which ERK activation was selectively enhanced in T cells. Together, these data suggest that DGK zeta regulates the development of nT(reg) cells by limiting the extent of activation of the ERK and c-Rel signaling pathways.