GATA-DEPENDENT EXPRESSION OF THE INTERLEUKIN-1 RECEPTOR-RELATED T1 GENE IN MAST-CELLS

The murine delayed-early serum-responsive gene T1 encodes glycoprotein s of the interleukin-1 receptor family. Transcriptional initiation in fibroblasts is regulated by c-Fos and gives rise to a rare 5-kb mRNA a nd an abundant 2.7-kb mRNA. These transcripts are translated into a re ceptor-like membrane anchored protein and a secreted protein consistin g only of the ectodomain. In mast cells, T1 gene transcription is init iated 10.5 kb further upstream than in fibroblasts and gives rise pred ominantly to the 5-kb transcript under normal growth conditions. Here we demonstrate that calcium ionophore stimulation of mast cells result ed in an upregulation of T1 gene expression and a switch from the long to the short T1 transcript. This was paralleled by the disappearance of the receptor-type T1 protein on the mast cell surface and the secre tion of large amounts of the truncated T1 protein. c-Pos and a T1 enha ncer, which have previously been identified to be essential for T1 exp ression in fibroblasts, were not required for calcium ionophore-mediat ed T1 gene upregulation. Overexpression of the transcription factor GA TA-1 in mast cells caused elevated T1 synthesis. Three GATA elements w ere identified in the minimal GATA-responsive mast cell promoter. Muta tional analysis revealed that all three GATA elements are involved in T1 gene expression. Point mutations within the middle GATA element eli minated promoter activity completely, while mutations of the distal an d proximal GATA binding sites reduced promoter strength by factors of 2 and 5, respectively. Exogenous expression of GATA-1 was not sufficie nt to activate the mast cell-specific promoter in NIH 3T3 fibroblasts.