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Evidence for suppressed activity of the transcription factor NFAT1 at its proximal binding element P0 in the IL-4 promoter associated with enhanced IL-4 gene transcription in T cells of atopic patients.
Allergen-specific T cells in atopic patients are polarized IL-4-producing Th2 cells, promoting IgE synthesis by B cells. The molecular basis for increased IL-4 gene expression in atopy is not fully understood. IL-4 gene regulation in general involves the nuclear factor of activated T cells (NFAT) family of transcription factors, of which NFAT1 and NFAT2 are most prominent in peripheral T cells. Recently, a unique inhibitory role of NFAT1 in IL-4 gene control was shown in the mouse. In a series of electrophoretic mobility shift assays with protein extracts of highly polarized Th2 clones from atopics and Th1 clones from controls we compared DNA-binding activities at the two NFAT-binding elements P0 and P1 of the crucial proximal human IL-4 promoter. At the most proximal P0 site, NFAT-containing complexes devoid of NFAT2 were readily inducible in the Th1 clones, but hardly or not in the Th2 clones. In contrast, both in Th1 and Th2 clones NFAT-containing complexes were strongly inducible at the P1 site, consisting of NFAT2 and a P0-compatible NFAT activity, without apparent differences between Th1 and Th2 clones. Like in Th2 clones, suppressed NFAT-P0 complex formation was observed also at the polyclonal level in peripheral blood mononuclear cells (PBMC) of three of five severe atopic dermatitis patients with strongly elevated serum IgE levels, but not in control PBMC. These findings suggest that high-level IL-4 production in atopic Th2 cells is associated with selective reduction of suppressive NFAT1 activity at the IL-4 P0 element and that some patients with this multifactorial disease may have a putative systemic disorder at this level.
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