Presence of new alternative exons in human and mouse Fli-1 genes

Ets factors and a newly identified polymorphism regulate Fli1 promoter activity in lymphocytes

Fli1 is an Ets family member that is essential for embryonic development. Increasing evidence suggests modulating Fli1 gene expression impacts lymphocyte development/function and is an important mediator in the autoimmune disease lupus. Fli1 is over-expressed in splenic lymphocytes in lupus prone mouse strains and in PBMCs of lupus patients. Presently, it is unknown how Fli1 gene expression is controlled in lymphocytes or how it becomes over-expressed in lupus. Therefore, we examined Fli1 regulation in a murine B cell line and T cell line and identified several cis-regulatory elements within a 230 bp region that contribute to Fli1 promoter activity. Ets factors Elf1, Tel and Fli1 bind in vitro to this region and increase endogenous Fli1 expression when over-expressed in a T cell line. In addition, we determined that a microsatellite located adjacent to the region containing these cis-regulatory elements is polymorphic in three lupus prone mouse strains and that the length of the microsatellite is inversely correlated with promoter activity in a T cell line. These results suggest that several Ets factors, including Fli1 itself, are involved in the transcriptional regulation of Fli1 in lymphocytes. Furthermore, the presence of a polymorphic microsatellite in the Fli1 promoter may contribute to increased Fli1 expression in T cells during lupus disease progression.

Regulation of Fli1 gene expression and lupus

Ets transcription factors function throughout development in such varied processes as cellular proliferation, apoptosis, differentiation and migration. Many have been implicated to play important roles in hematopoiesis, vasculogenesis/angiogenesis and myogenesis. Fli1 is an Ets family member that is essential for development and increasing evidence suggests modulating Fli1 gene expression impacts lymphocyte function and is important in the autoimmune disease lupus. Presently, it is unknown how Fli1 gene expression is controlled in lymphocytes. Identifying upstream regulators of Fli1 in lymphocytes will be critical for understanding lymphocyte development and the consequences of dysregulation and may be of value in developing future treatments for lupus.

Ets-1 regulates fli-1 expression in endothelial cells. Identification of ETS binding sites in the fli-1 gene promoter

To understand the role of the Ets-1 transcription factor during angiogenesis, we have overexpressed it in endothelial cells and analyzed the levels of expression of several candidate target genes involved in angiogenesis. The transcripts levels of the ETS transcription factor fli-1 are specifically up-regulated in endothelial cells, which overexpress Ets-1, but not in fibroblasts. Analysis of the promoter of the mouse fli-1 gene reveals that the 1-kb region that comprises the transcription starts and part of exon 1 is responsible for the response of the promoter to Ets-1. The -270/-41 fragment contains two known Spi-1-responding Ets binding sites (EBS), which are also necessary for the activation by Ets-1. In contrast to Spi-1, a third EBS is necessary for the full response of this promoter fragment to Ets-1. The rest of the promoter activity has been located in the -986/-505 region, where three active EBSs have been identified. Furthermore, endogenous Fli-1 was found to be bound to its own gene promoter and to be able to promote the transactivation of its gene. These results suggest that Ets-1 activates an auto-regulatory loop of expression of fli-1 in endothelial cells, a mechanism that could have significant implications for the endothelial cell fate.

IL-6 induces expression of the Fli-1 proto-oncogene via STAT3

Induction of gene expression by IL-6 has become an area of intense interest due to the role this cytokine plays in mediating aspects of inflammation, cellular differentiation, and proliferation. The ETS family of transcription factors represents a group of positive and negative regulators of transcription, that are differentially expressed in a cell and tissue specific manner. The ETS protein Fli-1 is known to induce differentiation in the erythroblastic leukemia cell line K562 along megakaryocytic developmental pathways. Here we show that IL-6 treatment of K562 induces the expression of Fli-1 via the STAT3 transcription factor. Upregulation of Fli-1 expression can be abrogated by the addition of AG490, a chemical inhibitor of JAK kinases, and by transfecting the cells with a dominant negative STAT3 expression construct.