Ets motifs are necessary for endothelial cell-specific expression of a 723-bp Tie-2 promoter/enhancer in Hprt targeted transgenic mice

Objective - Tie- 2 is an endothelial cell - specific receptor tyrosine kinase that is involved in the remodeling of blood vessels and angiogenesis. Our goal was to characterize Tie- 2 promoter function as a means of providing insight into the mechanisms of endothelial cell - specific gene regulation. Methods and Results - When targeted to the Hprt locus of mice, a small Tie- 2 promoter fragment ( containing a 300- bp intronic enhancer coupled upstream to a 423- bp core promoter) ( T- short) directed widespread endothelial cell expression in vivo. The T- short promoter contains 2 clusters of Ets sites, one in the first exon, the other in the intronic enhancer. In cultured endothelial cells, a combined mutation of the Ets motifs resulted in a significant reduction in promoter activity. Consistent with these results, the same Ets mutations resulted in a loss of detectable expression of the T- short promoter in all vascular beds with the notable exception of the brain. Conclusions - These results suggest that the T- short promoter contains information for widespread expression in the vascular tree, Ets sites are necessary for in vivo promoter activity, and the shorter Tie- 2 fragment may be useful as a tool to direct heterologous gene expression within the intact endothelium.