Interleukin-2 (IL-2) Regulates the Accessibility of the IL-2-Responsive Enhancer in the IL-2 Receptor α Gene to Transcription Factors

Interleukin-2 (IL-2) responsiveness of T lymphocytes is controlled through transcription of the IL-2 receptor (IL-2R) α subunit by antigen and by IL-2 itself. IL-2 induces IL-2Rα transcription via an IL-2-responsive enhancer (IL-2rE), whose activity depends on the cooperative binding of IL-2-induced STAT5 to two sites and of constitutively active Elf-1 to a third one. Here we describe the changes in IL-2rE chromatin that occur in normal T lymphocytes upon activation of IL-2Rα expression. In cells induced to transiently express IL-2Rα with concanavalin A (which mimics antigen), none of the IL-2rE sites is occupied despite the presence of Elf-1 and STAT1, which bind to the IL-2rE in vitro. The two STAT binding sites are occupied rapidly upon IL-2 stimulation, concomitantly with STAT5 activation. Occupation of the Elf-1 binding site is delayed, although Elf-1 concentration and binding activity are not modified by IL-2. Digestion of T-cell chromatin with DNase I and micrococcal nuclease shows that IL-2 induces the appearance of nuclease-hypersensitive sites flanking the IL-2rE. Thus IL-2, in addition to activating STAT5, appears to regulate IL-2Rα transcription by making IL-2Rα chromatin accessible to transcription factors.