Positive and Negative Transcriptional Regulation of the Foxp3 Gene is Mediated by Access and Binding of the Smad3 Protein to Enhancer I

Lili Xu. et. al. Immunity. 33:313–325 (2010)

Speaker: Bernard Kiro (祁晨恩)                                   Time: 14:00~15:00, Feb 23, 2011

Commentator: Huan-Yao Lei Ph.D.(黎煥耀博士)       Place: Room 601

Abstract:

Naïve CD4⁺ T cells can differentiate to four different subtypes of effector T cells after activation. It is now well established that naïve CD4⁺ T cells can differentiate to CD4⁺CD25⁺Foxp3⁺ regulatory T cells (Tregs) upon stimulation with T cell receptor- transforming growth factor beta (TCR-TGF-b) signal. Previous studies reveal that TCR-TGF-b stimulation plus retinoic acid (RA), a metabolite of vitamin A, can enhance the expression of Foxp3 in T cell compared to TCR-TGF-b alone by inhibiting the expression of pro-inflammatory cytokine receptor, such as Interleukin (IL)-27, which can inhibit Foxp3 expression. Smad3, a downstream signal transduction molecule of TGF-b receptor, recently has been shown to play an important role in the TGF-b induction of Foxp3 expression. But the underlying mechanism behind TCR-TGF-b-RA regulation of Foxp3 expression is still unclear. To address this question, luciferase reporter constructs compose of Foxp3 promoter and its enhancer (I and II) with or without deletion of AP-1, STAT3 or retinoid X receptor (RXR)/ retinoic acid receptors (RAR) binding site were transfected into EL4-LAF and LBRM T cell lines and primary T cells to evaluate luciferase expression under the stimulation of TCR-TGF-b with or without RA. Primary T cell from STAT3-deficient or Foxp3-GFP mice were also tested for their ability to express Foxp3 by TCR-TGF-b with or without RA. The result showed that deletion of STAT3 binding site in enhancer II or STAT3-deficiency abrogates IL-27 inhibition of Foxp3 expression, and deletion of Smad3 and AP-1 site impairs induction of Foxp3 by TCR-TGF-b signal. In conclusion, RA, STAT3 and AP-1 controls the access and binding of Smad3 to enhancer I to positive or negative regulate Foxp3 transcription.

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