STAT3-mediated suppression of the pre-induction silencer Ets-2 in activated T helper cells.

BACKGROUND: Interleukin-2 (IL-2) is the first cytokine produced by naive T helper (Th) cells after antigen recognition and is essential for initiating Th cell proliferation and differentiation. We previously identified the transcription factor Ets-2 as a pre-induction silencer of IL-2, showing that its downregulation upon Th cell activation permits IL-2 transcription. However, the upstream mechanisms regulating Ets-2 expression remain undefined. Given the central role of STAT family transcription factors in Th cell gene regulation, we investigated whether STAT signaling controls Ets-2 transcription. METHODS AND RESULTS: Bioinformatic analysis identified STAT binding motifs within the Ets-2 promoter. Using the Jurkat T cell line as a model, we examined changes in STAT3, Ets-2, and IL-2 expression following cell activation. STAT3 function was assessed through overexpression and knockdown experiments, with Ets-2 mRNA and protein levels measured by real-time PCR and western blotting. Chromatin immunoprecipitation was used to determine direct binding of STAT3 to the Ets-2 promoter. Our results showed that cell activation led to increased STAT3 mRNA and protein expression, accompanied by reduced Ets-2 expression and enhanced IL-2 production. STAT3 overexpression significantly decreased Ets-2 mRNA and protein levels, whereas STAT3 knockdown resulted in increased Ets-2 expression. Chromatin immunoprecipitation demonstrated direct binding of phosphorylated STAT3 (Tyr705) to the Ets-2 promoter. CONCLUSIONS: STAT3 acts as a negative regulator of Ets-2 transcription in Th cells through direct binding in its phosphorylated form to the Ets-2 promoter, establishing a causal suppressive pathway linking STAT3 activation to IL-2 de-repression.