ROG negatively regulates T-cell activation but is dispensable for Th-cell differentiation.

Stimulation of T cells through T-cell receptors leads to the induction of many effector genes, including cyclins, cytokines, and adhesion molecules, that mediate the activation and proliferation of T cells. As uncontrolled T-cell activation can result in harmful T-cell-mediated autoimmunity, the activation of T cells must be tightly regulated. NF-AT and NF-κB are two important transactivators of the effector genes during T-cell activation (10, 13, 28). Surprisingly, combined deficiency of two NF-AT members, NF-ATc2 and NF-ATc3, results in T-cell hyperproliferation, overproduction of type 2 Th cytokines, and the development of a lymphoproliferative disease (27). These unexpected observations argue strongly that NF-AT also negatively regulates T-cell activation. We have previously shown that ROG, a transcriptional repressor, is induced rapidly upon T-cell activation by NF-AT, in particular NF-ATc2, and that the induction of ROG is impaired in T cells lacking NF-ATc2 (18). More importantly, restoration of ROG attenuates T-cell hyperproliferation and delays the onset of lymphoproliferative disease in NF-ATc2/NF-ATc3 doubly deficient (NF-AT DKO) mice. Thus, deficiency of ROG may partly explain the paradoxical phenotype of NF-ATc2/NF-ATc3 deficiency. ROG is therefore a part of an NF-AT-initiated negative feedback mechanism regulating the activation of T cells. In addition to its potential role in regulating T-cell activation, ROG may play a regulatory role in the differentiation and function of Th cells. Th cells can be divided into two functional subsets based on their secreted cytokines (5, 19). Type 1 Th (Th1) cells produce gamma interferon (IFN-γ), and type 1 Th immune responses are responsible for eradicating intracellular microorganisms. Type 2 Th (Th2) cells produce interleukin-4 (IL-4), IL-5, and IL-13 and are important for immunity against parasitic infection. Several transcription factors have been shown to play crucial roles in regulating the differentiation and function of Th cells. The Th1-cell-specific transcription factor, T-bet, is essential for the differentiation of Th1 cells and for mounting effective type 1 adaptive immune responses (31, 32). The counterpart of T-bet in Th2 cells is GATA-3. GATA-3 is preferentially expressed in Th2 cells and is induced by the IL-4/Stat6 signaling pathway (23, 34, 35). Deficiency of GATA-3 results in a profound defect in the differentiation and function of Th2 cells in vivo and in vitro (24). Several groups, including ours, have shown that overexpression of ROG in vitro interferes with the function of GATA-3 and suppresses the expression of Th2 cytokines (6, 17, 22). In addition, the level of ROG is significantly higher in CD8+ Tc than in CD4+ Th cells (22), prompting the investigators to postulate that the higher level of ROG might render CD8+ Tc cells poor IL-4 producers. Despite these reports, the function of ROG has yet to be confirmed by loss-of-function approaches. Furthermore, how ROG suppresses the activation of T cells is still poorly understood. To address these questions, we have generated ROG-deficient (ROGKO) mice. Our studies indicate that ROG can indeed function as a negative regulator of T-cell activation. The effect of ROG is at least partly mediated by inhibiting the binding of NF-κB to the IL-2 promoter, thereby suppressing anti-CD3-induced proliferation. However, ROGKO Th cells can differentiate into Th1 and Th2 cells normally, and ROGKO mice are capable of mounting appropriate Th immune responses in vivo. Thus, our results depict a novel one-way cross-regulation between NF-AT and NF-κB in T cells and show that ROG is dispensable for the differentiation and function of Th cells.