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. 2010 Sep 24;33(3):313-25.
doi: 10.1016/j.immuni.2010.09.001.

Positive and negative transcriptional regulation of the Foxp3 gene is mediated by access and binding of the Smad3 protein to enhancer I

Lili Xu  1 , Atsushi Kitani, Christina Stuelten, George McGrady, Ivan Fuss, Warren Strober
Affiliations

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. .

Abstract

The molecular mechanisms underlying retinoic acid (RA) augmentation of T cell receptor (TCR) and transforming growth factor-β (TGF-β)-induced Foxp3 transcription and inhibition of the latter by cytokines such as IL-27 were here shown to be related processes involving modifications of baseline (TGF-β-induced) phosphorylated Smad3 (pSmad3) binding to a conserved enhancer region (enhancer I). RA augmentation involved the binding of retinoic acid receptor (RAR) and retinoid X receptor (RXR) to a dominant site in enhancer I and a subordinate site in the promoter. This led to increased histone acetylation in the region of the Smad3 binding site and increased binding of pSmad3. Cytokine (IL-27) inhibition involved binding of pStat3 to a gene silencer in a second conserved enhancer region (enhancer II) downstream from enhancer I; this led to loss of pSmad3 binding to enhancer I. Thus, control of accessibility and binding of pSmad3 provides a common framework for positive and negative regulation of TGF-β-induced Foxp3 transcription.

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Figures

Figure 1
Figure 1. AP-1 site located in a Foxp3 enhancer region plays positive role on TCR/TGF-β induced Foxp3 gene expression
(A) Murine CD4+ T cells from Foxp3-GFP mice were stimulated with plate bound anti-CD3 (10µg/ml), soluble anti-CD28 (2µg/ml) and TGF-β (5ng/ml) with or without JNK inhibitor (10µM) for 5 days then collected for flow cytometry analysis. (B) Schematic diagram of Foxp3 gene (upper) and AP-1: NFAT and Smad3 sites in Foxp3 enhancer I region (lower). (C) Two different murine T cell lines LBRM (left) and EL4 (right) were transfected with Foxp3 promoter and enhancer I reporter construct (promoter+enhancer I) or the reporter construct with promoter AP-1 site deletion (promoter+enhancer I promoter AP-1 del) or the reporter construct with enhancer I AP-1 site deletion (promoter+enhancer I enhancer AP-1 del). Four hours later cells were split and stimulated with plate bound anti-CD3 (10µg/ml), soluble anti-CD28 (2µg/ml) with or without TGF-β (2ng/ml). Luciferase activity was measured 24 hours later and values were shown as the ratio of firefly luciferase activity/Renilla luciferase activity from the same well. Data represent four independent experiments. **p<0.01, compared to intact construct under same stimulation conditions.
Figure 2
Figure 2. TGF-βRI kinase activity is essential for TCR-/TGF-β-induced Foxp3 expression in murine T cells
(A) Purified CD4+ cells from Foxp3-GFP mice (upper panels) or B6 mice (lower panels) were stimulated with plate-bound anti-CD3 (10µg/ml), soluble anti-CD28 (2µg/ml) and TGF-β (5ng/ml) with or without ALK5 inhibitor for 4 days then subjected for flow cytometry analysis. (B) LBRM or EL4 cells were transfected with Foxp3 promoter and enhancer reporter construct then stimulated with plate bound anti-CD3 (10µg/ml), soluble anti-CD28 (2µg/ml) and TGF-β(2ng/ml) with or without ALK5 inhibitor for 20 hrs. Luciferase activity was measured 24 hours later and values were shown as the ratio of firefly luciferase activity/Renilla luciferase activity from the same well. Data are representative of three independent experiments. **p<0.01, compared to the luciferase activity without ALK5 inhibitor.
Figure 3
Figure 3. Identification of a Foxp3 silencer containing a Stat3 binding site
(A) Purified CD4+ cells from Stat3fl/fl and Stat3fl/fl; MMTV-Cre mice(left panels); Socs3fl/fl and Socs3fl/fl; MMTV-Cre mice(right panels) were stimulated with plate bound anti-CD3 (10µg/ml), soluble anti-CD28 (2µg/ml) and TGF-β(5ng/ml) with or without IL-27 (20ng/ml) for 4 days then collected for Foxp3 staining and subjected to flow cytometry analysis. (B) Alignment of human and mouse Foxp3 enhancer II region containing stat3 binding site(up) and the structure of Foxp3 promoter and enhancer I and enhancer II (contains stat3 binding site) reporter construct. (C) Murine T cell line LBRM were transfected with Foxp3 promoter and enhancer I reporter construct or Foxp3 promoter and Enhancer I and enhancer II reporter construct or Foxp3 promoter and Enhancer I and enhancer II reporter construct with stat3 binding site deletion then stimulated with plate bound anti-CD3 (10µg/ml), soluble anti-CD28 (2µg/ml) and TGF-β (2ng/ml). Luciferase activity was measured 24 hours later and values were shown as the ratio of firefly luciferase activity/Renilla luciferase activity from the same well. Data are representative of four independent experiments. *p<0.05, **p<0.01, compared to intact construct under same stimulation conditions.
Figure 4
Figure 4. The positive effect of retinoic acid on Foxp3 expression completely depends on intact TGF-βRI kinase activity and Smad3
(A) Purified CD4+ cells from Foxp3-GFP mice were stimulated with plate bound anti-CD3 (10µg/ml), soluble anti-CD28 (2µg/ml) and TGF-β (5ng/ml) with or without retinoic acid (100nM) and JNK kinase inhibitor (10µM), cyclosporine A (20nM), IL-27 (20ng/ml) or ALK5 inhibitor (5µM) for 4 days then collected for flow cytometry analysis. (B) Purified CD4+ cells from B6-WT littermate mice and B6-Smad3 knockout were stimulated with plate-bound anti-CD3 (10µg/ml), soluble anti-CD28 (1µg/ml), TGF-β(5ng/ml), RA (100nM) with or without ALK5 inhibitor (2.5µM) for 4 days. Cells were collected and stained with APC anti-Foxp3 (eBioscience) then subjected to flow cytometric analysis.
Figure 5
Figure 5. The enhancement of RA on TCR/TGF-β induced Foxp3 transcription is not due to increased Smad3 phosphorylation
(A) Purified CD4+ cells from Foxp3-GFP mice was stimulated with plate bound anti-CD3 (10µg/ml), soluble anti-CD28 (2µg/ml) and TGF-β at different concentrations as indicated with or without retinoic acid (200nM) for 4 days then collected for flow cytometry analysis. (B) Purified CD4+ cells from B6 mice were stimulated with TGF-β at different concentrations as indicated with or without retinoic acid (500nM) for 2 hours. Cells were collected and cell lysates were prepared and subjected to Western-Blot (left). Intensity of bands was measured using NIH Image software and showed as the ratio between p-Smad3 and Smad3 from the same sample (right). Data are representative of two independent experiments.
Figure 6
Figure 6. Retinoic acid directly regulates Foxp3 promoter and enhancer activity
(A) Location of two RAR-RXR binding sites in Foxp3 promoter and enhancer I regions. (B) LBRM (left) or EL4 (right) cells were transfected with a Foxp3 promoter and enhancer I reporter construct and stimulated with plate bound anti-CD3 (10µg/ml), soluble anti-CD28 (2µg/ml) plus TGF-β (2ng/ml) and retinoic acid at a series of concentration as indicated. Luciferase activity was measured 24 hours later and values were shown as the ratio of firefly luciferase activity/renilla luciferase activity from the same well. Data are representative of two independent experiments. **p<0.01, compared to the luciferase activity without RA. (C) EL4 cells were transfected with Foxp3 promoter and enhancer I reporter construct with deletion of the RAR-RXR binding site in either the promoter region or enhancer region (as indicated in A) or both and then stimulated with plate-bound anti-CD3 (10µg/ml), soluble anti-CD28 (2µg/ml) and TGF-β (2ng/ml) with or without retinoic acid (500nM) as indicated. (ProRAR-RXR del: promoter RAR-RXR deletion; EnhRAR-RXR del: enhancer I RAR-RXR deletion; Pro+Enh RAR-RXR del: promoter+enhancer I RAR-RXR deletion). Luciferase activity was measured 24 hours later and values were shown as the ratio of firefly luciferase activity/Renilla luciferase activity from the same well. Data are representative of three independent experiments. **p<0.01, compared to intact construct under same stimulation conditions.
Figure 7
Figure 7. RA increases histone acetylation at the Enhancer region containing NF-AT/Smad3 binding sites and facilitates increased Smad3 binding to Enhancer
(A) Purified CD4+ cells from B6 mice were stimulated with plate bound anti-CD3 (10µg/ml), soluble anti-CD28 (2µg/ml) and TGF-β (5ng/ml) with or without retinoic acid (200nM) for 48 hours. CHIP assay was performed using anti-acetyi histone H4 antibody or rabbit IgG. Precipitated chromatins were subjected to real time PCR using primers targeting enhancerI region (upper) or promoter region (lower). Values were shown as the percentage of corresponding input. Data are representative of three independent experiments. (B) Purified CD4+ cells from B6 mice were treated as in (A) with or without IL-27 (20ng/ml) for 2 hours. CHIP assay was performed using anti-Smad3 antibody or rabbit IgG. Precipitated chromatins were subjected to real time PCR using primers targeting enhancer I region. Values were shown as the percentage of corresponding input. Data are representative of two independent experiments. (C) Purified CD4+ cells from B6 mice were stimulated with plate bound anti-CD3 (10µg/ml), soluble anti-CD28 (2µg/ml) and TGF-β (5ng/ml) with or without JNK kinase inhibitor (10µM) for 2 hours. CHIP assay was performed using anti-Smad3 antibody or rabbit IgG as described in (B).
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