SMAD2 Is Essential for TGFβ-mediated Th17 Cell Generation*

Abstract

Transforming growth factor ␤ (TGF␤) is an immune modulatory cytokine that is critical for the development and homeostasis of the immune system (1). The absence of TGF␤ activity in mice leads to deregulated, hyperactive T cell activations resulting in early onset fatal multiorgan autoimmunity. Recent studies have highlighted the dominant function of TGF␤ in the differentiation of T cell subsets. TGF␤ can initiate transcription of Foxp3 in naive conventional CD4 ϩ T (Tconv) 2 cells to generate induced regulatory T (iTreg) cells. Moreover, in conjunction with the pro-inflammatory cytokine IL-6, TGF␤ promotes differentiation of Tconv cells to Th17 cells (2-4) that contribute to the pathogenesis of autoimmune disorders. However, Th17 cells are also necessary for combating infectious diseases such as oral candidiasis and enteritis, caused by Candida albicans and Citrobacter rodentium, respectively (5). Hence, for CD4 ϩ T cells, TGF␤ controls the balance between inflammation and quiescence.Although extensive progress has been made in understanding the effect of TGF␤ on T cell differentiation and function, detailed characterization of the biochemical basis of TGF␤ signaling in T cells has lagged significantly. In common with other cell types, TGF␤ binds to TGF␤ receptor II on T cells, which leads to the recruitment of TGF␤ receptor I to the complex and activation of cytoplasmic transcription factors SMAD2 and SMAD3. In most cells, activated SMAD2 and SMAD3 translocate to the nucleus in a complex with SMAD4 to regulate target gene transcription (6). Some genes in the TGF␤ pathway are redundantly regulated by SMAD2 and SMAD3, but unique target genes of specific SMADs also exist, suggesting that each possesses distinct functions. Hence, differential activation of SMADs may biochemically account for context-dependent pleiotropic effects of TGF␤.Using mice deficient in individual SMADs, it has been shown that Smad3 and Smad4 are necessary for efficient TGF␤-mediated generation of FOXP3 ϩ T cells but not for the differentiation of naive CD4 ϩ T cells to the Th17 lineage (7-9). However, results from a recent study led to the contrasting conclusion that receptor SMADs are not necessary for TGF␤ signaling in T cells (10). Here, analysis of T cellspecific Smad2-deficient mice indicates that in contrast to SMAD3 and SMAD4, SMAD2 plays a non-redundant role in the generation of Th17 cells in vitro and in vivo. The diminution in IL-17 production by CD4 ϩ T cells correlates with accelerated loss of Il6ra expression and a corresponding decrease in STAT3 activation in Smad2-deficient T cells, suggesting that SMAD2 specifically modulates the cross-talk between TGF␤ and IL-6 in Th17 cell differentiation. EXPERIMENTAL PROCEDURES Mice-Smad2fl/fl mice (11) generated in the Robertson laboratory were provided by Dr. Richard Flavell. These mice were backcrossed six times to the C57BL/6 background before analysis. Smad2 conditional KO (CKO) mice were generated using hCD2 Cre Tgϩ mice (C57BL/6 background). Rag1 Ϫ/Ϫ and C57BL/6 mice were purchased...

Effects of exposure to extremely low-frequency electromagnetic fields on the differentiation of Th17 T cells and regulatory T cells

“…Yang et al 2007). SMAD2/3 are phosphorylated in response to TGF-β1 binding to its receptor, and is critical for the development of suppressive Treg cells and essential for Th17 cell production (Malhotra et al 2010). …”

Genetic controls of Th17 cell differentiation and plasticity

“…T cells deficient in Smad2 had substantial reduced Th17 differentiation in vitro. Also Malhotra et al and Martinez et al reported that Smad2 is required for Th17 response in vivo in host defense to pathogen infection and in autoimmune disease (Malhotra et al, 2010;Martinez et al, 2010). Takimoto et al analyzed T cells deficient in both Smad2 and Smad3 and found that they even had a greater defect in Th17 cell differentiation than Smad2 -/-T cells (Takimoto et al, 2010).…”

“…It is not clear whether different pathways or components downstream of TGFβ signaling is involved in Th17 and TGFβ-induced Treg (iTreg) generation; Smad2, 3 and 4 was recently reported each to be partially required for iTreg generation while it was dispensable for generation of Th17 cells (Yang et al, 2008a;Martinez et al, 2009Martinez et al, , 2010Malhotra et al, 2010;Takimoto et al, 2010).…”

“…Furthermore, Martinez et al reported that in T cells deficient in Smad3, Th17 cell differentiation was enhanced in vitro and in vivo . Subsequently, Smad2 was reported by several groups to positively regulate Th17 cell differentiation (Malhotra et al, 2010;Martinez et al, 2010;Takimoto et al, 2010). T cells deficient in Smad2 had substantial reduced Th17 differentiation in vitro.…”

Cytokines in Systemic Sclerosis: Focus on IL-17

“…Both transcription factors ROR t and ROR have a synergistic effect in promoting Th17-cell differentiation and have similar and redundant functions. Furthermore, Smad2 was reported by several groups to positively regulate Th17 cell differentiation and Th17 immune response in vivo during pathogen infection or in autoimmune disease (Malhotra et al 2010) (Martinez et al 2010) (Takimoto et al 2010). Smad2 might be a co-factor for ROR t to mediate the expression of Th17-specific genes (Martinez et al 2010).…”