FoxO-Dependent Regulation of Diacylglycerol Kinase α Gene Expression

Diacylglycerol kinase a (DGK alpha) regulates diacylglycerol levels, catalyzing its conversion into phosphatidic acid. The alpha isoform is central to immune response regulation; it downmodulates Ras-dependent pathways and is necessary for establishment of the unresponsive state termed anergy. DGK alpha functions are regulated in part at the transcriptional level although the mechanisms involved remain poorly understood. Here, we analyzed the 5' end structure of the mouse DGK alpha gene and detected three binding sites for forkhead box O (FoxO) transcription factors, whose function was confirmed using luciferase reporter constructs. FoxO1 and FoxO3 bound to the 5' regulatory region of DGK alpha in quiescent T cells, as well as after interleukin-2 (IL-2) withdrawal in activated T cells. FoxO binding to this region was lost after complete T cell activation or IL-2 addition, events that correlated with FoxO phosphorylation and a sustained decrease in DGK alpha gene expression. These data strongly support a role for FoxO proteins in promoting high DGK alpha levels and indicate a mechanism by which DGK alpha function is downregulated during productive T cell responses. Our study establishes a basis for a causal relationship between DGK alpha downregulation, IL-2, and anergy avoidance.