Identification of a distant T-bet enhancer responsive to IL-12/Stat4 and IFNgamma/Stat1 signals

T-bet plays a critical role in controlling IFNgamma expression, Th1 polarization, and CD8 cytolytic development. Its regulation has been demonstrated to be mostly IFNgamma/Stat1 dependent while IL-12/Stat4 independent. Here we show that IL-12/Stat4 binds to a distant highly conserved STAT-responsive T-bet enhancer, and induces IFNgamma/Stat1-independent T-bet expression in CD8 T cells. Luciferase reporter assay showed that both Stat4 and Stat1 activate reporter gene expression from constructs containing a wild-type but not mutated T-bet enhancer. Studies in virus-infected mice demonstrated that the IL-12/Stat4/T-bet cascade operates in vivo and regulates IFNgamma in CD8 T cells. Together, we provide a novel mechanism for T-bet regulation, and suggest that IL-12/Stat4/T-bet play an important role in CD8 effector responses.     

T helper 1-inducing property of IL-27/WSX-1 signaling is required for the induction of experimental colitis

BACKGROUND: WSX-1, a component of the interleukin (IL)-27 receptor, is a novel class I cytokine receptor with homology to the IL-12 receptor beta2 chain. Initially, WSX-1 signaling was reported to play an important role in the promotion of T helper-1 responses, but recent reports have revealed an anti-inflammatory property in WSX-1 signaling. In the present study, we investigated the role of IL-27/WSX-1 signaling in a murine colitis model, dextran sulfate sodium (DSS) colitis, by using WSX-1 knockout (KO) mice. METHODS: First, we observed whether WSX-1 KO mice developed colitis spontaneously. Second, we induced DSS colitis in WSX-1 KO and wild-type (WT) mice. RESULTS: WSX-1 KO mice were observed not to develop colitis spontaneously. The severity of DSS colitis was decreased in WSX-1 KO mice in comparison with WT mice in association with a reduced production of interferon-gamma, IL-6, and tumor necrosis factor-alpha by lamina propria mononuclear cells from WSX-1 KO mice and the absence of T-bet expression in the colon from WSX-1 KO mice. CONCLUSIONS: This study revealed the inflammatory property of IL-27/WSX-1 signaling in intestinal inflammation. As a result, IL-27/WSX-1 signal pathway may thus be a promising candidate for the therapeutic intervention of human inflammatory bowel diseases such as Crohn's disease and ulcerative colitis.     

The molecular basis of IL-21-mediated proliferation

Interleukin-21 (IL-21) is a type I cytokine that modulates functions of T, B, natural killer (NK), and myeloid cells. The IL-21 receptor (IL-21R) is closely related to the IL-2 receptor beta chain and is capable of transducing signals through its dimerization with the common cytokine receptor gamma chain (gamma(c)), the protein whose expression is defective in humans with X-linked severe combined immunodeficiency. To clarify the molecular basis of IL-21 actions, we investigated the role of tyrosine residues in the IL-21R cytoplasmic domain. Simultaneous mutation of all 6 tyrosines greatly diminished IL-21-mediated proliferation, whereas retention of tyrosine 510 (Y510) allowed full proliferation. Y510 efficiently mediated IL-21-induced phosphorylation of Stat1 and Stat3, but not of Stat5, and CD8(+) T cells from Stat1/Stat3 double knock-out mice exhibited decreased proliferation in response to IL-21 + IL-15. In addition, IL-21 weakly induced phosphorylation of Shc and Akt, and consistent with this, specific inhibitors of the MAPK and PI3K pathways inhibited IL-21-mediated proliferation. Collectively, these data indicate the involvement of the Jak-STAT, MAPK, and PI3K pathways in IL-21 signaling.