To address this possibility, we performed a LUC reporter assay. A pGL3-LUC vector subcloned with the promoter region from –1500 bp to the Prdm1 transcription start site [29] was co-transfected with a pMIG-Egr-2 vector to 293T cells. As shown in Figure 3A, Egr-2 significantly enhanced the activity of the Prdm1 promoter. Next, a ChIP assay was performed with antibodies against Egr-2 to investigate whether Egr-2 directly binds to the promoter region of Blimp-1 in CD4+ T cells. Among four Selleck Decitabine promoter regions examined (−3000 bp, −2000 bp, −1000 bp, and +1000 bp from its transcription

site) of Blimp-1, only one region (−1000 bp) showed significant enrichment compared with control, indicating that Egr-2 specially binds to the Blimp-1 promoter, but not to Lag3 and Il10 promoters (Fig. 3B and Supporting Information Fig. 2A). Cretney et al. reported that Blimp-1 binds to intron 1 of the Il10 locus and, together Nutlin-3 mouse with IFN regulatory factor-4, directly regulates IL-10 expression in CD4+CD25+ Treg cells by the remodeling of active chromatin at the Il10 locus [28]. Our observation suggested that IL-10 regulation with Blimp-1 was controlled by Egr-2. STAT1 and STAT3 have been shown to be crucial for IL-10 production from IL-27-stimulated

naïve CD4+ T cells [17]. We investigated the effect of STAT1 and STAT3 deficiencies on IL-27-induced Egr-2 expression. As shown in Figure 4A and B, Egr-2 induction by IL-27 in CD4+ T cells was impaired by a STAT3 deficiency, but not by a STAT1 deficiency. When we analyzed the induction of Il10 transcription and IL-10 protein expression by IL-27 in STAT1- and STAT3-deficient

CD4+ T cells, IL-10 protein induction by IL-27 was abolished both in STAT1 KO and in STAT3 CKO CD4+ T cells, although IL-10 mRNA expression levels were slightly up-regulated by IL-27 in STAT1 KO CD4+ T cells (Fig. 4C and D). These results suggest that IL-27-induced Egr-2 expression in CD4+ T cells is mostly dependent on STAT3, although both STAT1 and STAT3 are important for IL-10 production by IL-27. Next, we investigated the effect of other STAT1 or STAT3 activating cytokines for Egr-2 induction. IL-6 and IFN-γ were selected as the representatives of cytokines activating STAT3- and STAT1-mediated pathways, respectively. As shown in Figure 4E, IL-6 induced Egr-2 expression as effectively as IL-27 Sorafenib manufacturer in CD4+ T cells, but IFN-γ did not. Interestingly, both IL-10 and Blimp-1 mRNA expressions were also elevated by IL-6, but expression levels seemed to be lower than those by IL-27 (Fig. 4F). IL-6 is a type I cytokine that shares structural homology and a receptor subunit, gp130, with IL-27 and has already been shown to induce IL-10 in CD4+ T cells [17]. These results suggest that Egr-2 is important for IL-10 production mediated both by IL-27 and by IL-6 through the STAT3-dependent pathway. To examine the role of Egr-2 in inflammatory cytokine production, we investigated the production of IFN-γ and IL-17 in response to IL-27 stimulation.