CHROMATIN REMODELING OF THE INTERLEUKIN-2 GENE - DISTINCT ALTERATIONSIN THE PROXIMAL VERSUS DISTAL ENHANCER REGIONS

Known transcription factor-DNA interactions in the minimal enhancer of the murine interleukin-2 gene (IL-2) do not easily explain the T cell specificity of IL-2 regulation. To seek additional determinants of ce ll type specificity, in vivo methodologies were employed to examine ch romatin structure 5' and 3' of the 300 bp IL-2 proximal promoter/enhan cer region. Restriction enzyme accessibility revealed that until stimu lation the IL-2 proximal promoter/enhancer exists in a closed conforma tion in resting T and non-T cells alike, Within this promoter region, DMS and DNase I genomic footprinting also showed no tissue-specific di fferences prior to stimulation, However, DNase I footprinting of the d istal -600 to -300 bp region revealed multiple tissue-specific and sti mulation-independent DNase I hypersensitive sites. Gel shift assays de tected T cell-specific complexes binding within this region, which inc lude TCF/LEF or HMG family and probable Oct family components, Upon st imulation, new DNase I hypersensitive sites appeared in both the proxi mal and distal enhancer regions, implying that there may be a function al interaction between these two domains. These studies indicate that a region outside the established IL-2 minimal enhancer may serve as a stable nucleation site for tissue-specific factors and as a potential initiation site for activation-dependent chromatin remodeling.