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Brief Definitive Reports |
Chain/CD25 Promoter Is a Target for Nuclear Factor of Activated T Cells


Institute of Virology and Immunobiology, University of Würzburg, D-97080 Würzburg, Germany
| Abstract |
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chain/CD25 is strongly induced at the transcriptional level after T cell activation. We show here that nuclear factor of activated T cell (NF-AT) factors are involved in the control of CD25 promoter induction in T cells. NF-ATp and NF-ATc bind to two sites around positions –585 and –650 located upstream of the proximal CD25 promoter. Immediately 3' from these NF-AT motifs, nonconsensus sites are located for the binding of AP-1–like factors. Mutations of sites that suppress NF-AT binding impair the induction and strong NF-ATp–mediated transactivation of the CD25 promoter in T cells. In T lymphocytes from NF-ATp–deficient mice, the expression of CD25 is severely impaired, leading to a delayed IL-2 receptor expression after T cell receptor (TCR)/CD3 stimulation. Our data indicate an important role for NF-AT in the faithful expression of high affinity IL-2 receptors and a close link between the TCR-mediated induction of IL-2 and IL-2 receptor
chain promoters, both of which are regulated by NF-AT factors.
Key Words: interleukin 2 receptor nuclear factor of activated T cells transcription factors T cells NF-AT factors
The high affinity IL-2 receptor consists of three individual polypeptides, the
Nuclear factor of activated T cell (NF-AT) factors comprise a family of transcription factors that contribute to the induced expression of numerous lymphokine and receptor genes in T cells. Similar to NF-
The following oligonucleotides were used for the mutagenesis of NF-AT sites:
(i) (–667) GCTAGACTTAAAATCTATCATTGCAGCTGTAAACAC (–632)
CGATCTGAATTTTAGATAGTAACGTCGACATTTGTG; and
(ii) (–596) CCCACACCCATGATACTATGAATCGTGCATCAGAG (–562)
GGGTGAGGGTACTATGATACTTAGCACGTAGTCTC
The underlined nucleotides indicate the mutations.
Immunofluorescence and Flow Cytometry.
DNase I Footprint Protection Assays and EMSAs.
Electromobility shift assays (EMSAs) were performed as previously described (11), using 2 µg nuclear proteins and 0.5 µg poly [d(I-C)]. In supershift EMSAs, 0.5 µg of either an NF-ATp–specific Ab (Cat. no. 06-348; UBI) or an NF-ATc–specific mAb (7A6) (12) were added to the incubations. When the DNA binding of GST–NF-ATp was tested, 0.5–1.5 µg of bacterial proteins prepared by affinity column chromatography (11) were incubated along with 0.5 µg poly [d(I-C)]. The following oligonucleotides were used as probes:
(iii) (–596)gatcCCCACACCCATGGAACTATGAATCGTG (–571)
GGGTGTGGGTACCTTGATACTTAGCACctag;
(iv) (–663)gatcGACTTAAAATCTTCCATTGCAGCTGTA (–635)
CTGAATTTTAGAAGGTAACGTCGACATctag; and
(v) (–667)GCTAGACTTAAAATCTTCCATTGCAGCTGTAAACAC (–632)
CGATCTGAATTTTAGAAGGTAACGTCGACATTTGTG
The small letters indicate linker nucleotides.
, β, and
chains. Although the β and
chains are shared by other lymphokine receptors, the
chain (CD25) is restricted to the IL-2 receptor, and is expressed by a variety of lymphoid cells (for review see reference 1). The induction of CD25 in T cells is controlled at the transcriptional level through two DNA sequence elements, a proximal promoter/enhancer spanning the nucleotides between positions –54 and –584 in the mouse and –64 and –276 in humans, and a distal enhancer spanning
80 nucleotides around position –1350 in the mouse and –3750 (or –4150, according to another nomenclature) in the human CD25 gene (2–6). The activity of the promoter is rapidly induced by TCR-mediated signals or IL-1, and is controlled by an array of transcription factors, in particular by nuclear factor (NF)-
B, Elf-1, SRF, and HMG I(Y). The induction of the distal enhancer is controlled by IL-2, which induces signal transducer and activator of transcription (Stat)5, a member of the family of Stat transcription factors. Stat5 binds in concert with Elf-1, HMG I(Y), and GATA factors to multiple sites of the distal enhancer and contributes to its IL-2–mediated full expression in activated peripheral T lymphocytes (4–6).
B factors, the nuclear translocation and activity of NF-AT factors is stimulated by TCR-mediated signals (for review see reference 7). The DNA-binding domains of NF-AT and NF-
B/Rel factors share a common architecture (8) and, therefore, recognize overlapping DNA sequence motifs. These common properties between NF-AT and NF-
B (a major regulator of the CD25 promoter), and reports on the inhibition of CD25 expression by cyclosporin A (9) (an inhibitor of phosphatase calcineurin and, therefore, of nuclear translocation of NF-AT; reference 7), prompted us to investigate whether NF-AT factors participate in CD25 promoter control. We show here that NF-ATp and NF-ATc bind to two sites located immediately upstream of the proximal CD25 promoter. Mutations within the NF-AT sites that suppress NF-AT binding impair CD25 promoter induction. Accordingly, the induction of CD25 is markedly delayed in T cells from NF-ATp–deficient mice. These findings implicate an important role for NF-AT factors in the inducible expression of high affinity IL-2 receptors after T cell activation.
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Materials and Methods
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Abstract
Materials and Methods
Results and Discussion
References
Cell Culture, Construction, and Transfection of CD25 Promoter Luciferase Plasmids.
Murine El4 T thymoma cells and human Jurkat T leukemia cells were grown in RPMI medium containing 5% FCS. 2 x 107 cells were transfected using the DEAE dextran protocol with 2.5 µg DNA of the CD25 promoter-luciferase reporter constructs alone or 0.5–2.5 µg DNA of reporter constructs (as indicated in the figure legends) along with 2 µg of a pLGP3-based vector expressing full-length murine NF-ATp (NF-AT1-C; reference 10) or an RSV-LTR vector expressing human NF-ATc. Human 293 embryonic kidney cells were cultured in DMEM and transfected using a calcium phosphate transfection protocol. The luciferase reporter gene construct contains the wild-type murine CD25 promoter spanning the nucleotides up to position –2556 (4). Mutations in one or both of the NF-ATp binding sites around positions –585 and –650 were introduced into the promoter fragment from +1 to –800 using the QuikChangeTM site-directed mutagenesis kit (Stratagene Corp., La Jolla, CA) according to the manufacturer's instructions.
For Ab stainings, 2–8 x 105 cells were incubated on ice with mAbs at saturating concentrations. Fluorescein- and PE-labeled mAbs (Pharmingen, San Diego, CA) were used for two- and three-color immunofluorescence. For three-color flow cytometry, cells were stained first with biotinylated mAbs (PharMingen) for 15 min and were subsequently incubated with streptavidin-Red670 (GIBCO BRL, Eggenstein, Germany) and FITC- and PE-labeled mAbs for 15 min. Results obtained after analysis on a FACScan® flow cytometer (Becton Dickinson, Mountain View, CA) using Lysys II software (Becton Dickinson) are shown as log dot-plots or histograms.
In DNase I footprint protection assays, end-labeled DNA probes were prepared using [
-32P]ATP and polynucleotide kinase. 104 cpm (
0.2 ng) of the following DNA fragments from the murine CD25 promoter (4) were used: (a) the HindIII–SacII fragment spanning the nucleotides from position +94 to –268; and (b) the SacII–BglII fragment spanning the nucleotides from –268 to –801. Fragment (a) was recut with EspI, and fragment (b) with DraI generating DNA fragments of
150–300 bp. These were incubated for 60 min with a bacterially expressed glutathione S-transferase (GST)–NF-ATp protein (11) containing the DNA-binding domain of murine NF-ATp. The samples were processed and fractionated on 6% polyacrylamide, 42% urea-sequencing gels.
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Results and Discussion
Top
Abstract
Materials and Methods
Results and Discussion
References
To determine whether the CD25 promoter is a target for NF-AT, we cotransfected a CD25 promoter–driven luciferase reporter gene with NF-ATp– and NF-ATc–specific expression vectors into El4 T and 293 cells. Treatment of 293 cells with TPA plus ionomycin (T+I) led to a <2-fold, and treatment of El4 cells with T+Con A led to an 8–9-fold, induction of activity of CD25 promoter spanning the nucleotides up to position –2556 (4), and to a 12-fold induction of a shorter CD25 promoter reaching up to –800. Cotransfection of an NF-ATp expression vector into El4 cells resulted in a strong, 40-fold induction of activity of the longer CD25 promoter and in an up to 60-fold induction of the shorter CD25 promoter fragment after T+Con A treatment of cells (Fig. 1). Cotransfection with the NF-ATc vector gave rise to only a slight increase in promoter activity. In 293 cells, the overexpression of both NF-AT factors resulted in a six- to ninefold increase in CD25 promoter activity (Fig. 1).
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To demonstrate a functional role for the two NF-ATp sites, we introduced mutations into the NF-AT motifs of each site, or into both sites, in the context of the 800-bp wild-type CD25 promoter fragment. These mutations led to a loss of NF-AT binding in EMSAs using nuclear proteins from induced Jurkat cells (see Fig. 2 D, lanes 18–20) or GST–NF-ATp (data not shown). When the mutated CD25 promoter/luciferase constructs were transfected into El4 T cells alone or with an NF-ATp expression vector their induction was severely impaired compared with the wild-type promoter. The T+Con A–mediated 16-fold induction of the 800-bp CD25 promoter fragment was almost abolished (Fig. 3 A) and its >25-fold transactivation by NF-ATp was reduced to a 2–3-fold increase for the mutated promoter (Fig. 3 B).
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-CD3 Abs for 2–24 h in vitro, a marked increase of CD25 surface expression was detected after 6–12 h, which became even more pronounced after 24 h. Due to the strong stimulation of the CD25 promoter by secreted IL-2 (2), >50% of T cells express large amounts of CD25 48 h after stimulation (Fig. 4). On NF-ATp–/– LN T cells, CD25 expression was found to be distinctly delayed, becoming clearly detectable only 24 h after induction in spite of high, unimpaired IL-2 production of NF-ATp–/– T cells (13). In addition, fewer cells expressed high levels of CD25 after induction for 48 h (Fig. 4).
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Finally, it should be pointed out that several properties of NF-ATp–/– mice, such as the impaired clonal deletion of T cells and expansion of lymphoid organs (13, 15, 16), are shared by the mice deficient for IL-2 and IL-2 receptors (17–19). We assume that the impaired CD25 expression might contribute to the development of this phenotype in NF-ATp–/– mice, which is reminiscent of other mice with defects in the IL-2 signaling system.
| Acknowledgments |
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This work was supported by grants from the Wilhelm-Sander-Stiftung (to E. Serfling) and the Deutsche Forschungsgemeinschaft, SFBs 165 and 465 (to A. Schimpl and E. Serfling).
Submitted: 27 January 1998
Revised: 29 July 1998
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