An intron transcriptional enhancer element regulates IL-4 gene locus accessibility in mast cells

The cell type-specific expression of a gene is dependent on developmentally regulated modifications in chromatin structure that allow accessibility of basal and inducible transcription factors. In this study, we demonstrate t hat a cis-acting element in the second intron of the murine IL-4 gene has a dual function in regulating transcription in mast cells as well as chromat in accessibility of the IL-4 gene locus through its influence on the methyl ation state of the gene. Previous studies have shown that mast cell-restric ted transcription factors GATA-1/2 and PU.1 associate with the intron eleme nt and regulate its activity. In this study, we use DNase I footprinting an d mutational analyses to identify two additional sites that contribute to t he element's ability to enhance transcription. One of these sites associate s preferentially with STAT5a and STAT5b. We also demonstrate that deletion of the element or mutation of the GATA binding site in the context of a sta bly integrated IL-4 genomic construct prevents maintenance of a demethylate d locus in IL-4-producing mast cells, These data indicate that, analogous t o Ig and TCR intron regulatory elements, the intron enhancer has an essenti al role in maintaining developmentally regulated demethylation at the IL-4 gene locus, In addition, they indicate that members of the GATA family of t ranscription factors likely play an important role in these processes.