PU.1 and GATA: components of a mast cell-specific interleukin 4 intronic enhancer.

Interleukin 4 (IL-4), a critical immunoregulatory cytokine, is produced by a subset of T lymphocytes and cells of the mast cell/basophil lineage. There are cell-specific differences in the regulatory elements that control IL-4 transcription in these two cell types. A 683-bp Bgl II fragment, located within the second intron of the murine IL-4 gene, was previously shown to exhibit mast cell-specific enhancer activity. To define critical cis-acting elements that regulate this enhancer, a series of deletions from the 5' and 3' ends of the Bgl II fragment were generated. Their effect on enhancer activity was assessed in IL-4-producing mast cell lines in transient transfection assays. Two functionally independent subregions, E1 and E2, were defined in this analysis. Both are required for full enhancer activity. Sequences identical to previously defined DNA-binding sites for SP1 and GATA are present within E1, and an ets binding site is located within E2. Although mutation of the SP1 sites had no effect on enhancer function, alteration of either the GATA or ets site reduced enhancer activity by 50-60%. Proteins that associate with the IL-4 intronic GATA and ets sites were detected in mast cell nuclear extracts by mobility-shift assays. Specific antibodies identified these factors as GATA-1 and GATA-2 and the ets family member PU.1. GATA-1, GATA-2, and PU.1 exhibit cell-specific expression, suggesting that these proteins play a critical role in the lineage-restricted activity of the IL-4 intronic enhancer in mast cells.