The GATA-1 and Spi-1 transcriptional factors bind to a GATA/EBS dual element in the Fli-1 exon 1

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Abstract
Fli-1 is a proto-oncogene which is rearranged in tumors induced by three different retroviruses, Cas-Br-E, F-MuLV, and 10A1. This gene is a member of the Ets gene family, a class of transcription factors that recognize and bind to a DNA motif known as the Ets binding site (EBS). Our laboratory has previously cloned and characterized the promoter region of both human and mouse Fli-1 genes. We had then identified several regulatory elements conserved between the two species. Two of them, an exon 1 GATA/EBS dual element and an EBS element located in the 5′ end of intron 1, were analysed in the present study. EMSA analysis performed with nuclear extracts from different cell lines showed that the EBS element in intron 1 (EBSi) was bound by one potential Ets-related ubiquitous factor. The GATA/EBS element was bound by several factors that seemed Ets-related, one of which was found to be specifically expressed in hematopoietic cells. the GATA/EBS dual element was thus chosen for further analysis. A human Fli-1-derived genomic fragment containing the GATA/EBS led to enhanced transcription when positioned upstream of the SV40 promoter in the erythroleukemic HEL cell line. In addition, an increasing number of GATA/EBS oligonucleotides upstream of this same promoter resulted in a copy number-dependent increase in luciferase activity which was greatly reduced when the EBS consensus sequence was mutated. One of the factors binding to the GATA/EBS region was identified to be Spi-1 by supershift analysis and was also shown to bind to the EBS element of the human Ets-2 gene. Supershift analysis also demonstrated the binding of the GATA-1 factor to the GATA/EBS dual element. Our results suggest that Spi-1 and GATA-1 might play a key role in the regulation of Fli-1.