Expression of angiopoietin-2 in endothelial cells is controlled by positive and negative regulatory promoter elements

Objective - Angiopoietin-2 (Ang-2) is a non - signal transducing ligand of the endothelial receptor tyrosine kinase Tie-2. Ang-2 is produced by endothelial cells and acts as an autocrine regulator mediating vascular destabilization by inhibiting Angiopoietin-1- mediated Tie-2 activation. To examine the transcriptional regulation of Ang-2, we studied the Ang-2 promoter in endothelial cells and nonendothelial cells. Methods and Results - The human Ang- 2 promoter contains a 585- bp region around the transcriptional start site ( - 109 to + 476) that is sufficient to control endothelial cell - specific and cytokine-dependent Ang- 2 expression. Strong repressor elements of Ang- 2 - promoter activity are located in the 5'-region of the promoter and in the first intron. The Ets family transcription factors Ets-1 and Elf-1 act as strong enhancers of endothelial cell Ang- 2 - promoter activity. Ets-binding sites - 4 and - 7 act as positive regulators, whereas Ets-binding site - 3 acts as negative regulator. Demethylation experiments revealed that the Ang- 2 gene ( in contrast to the Tie-2 gene) is not controlled by imprinting. Conclusions - The data determine unique positive and negative regulatory mechanisms of endothelial cell Ang- 2 expression and provide further evidence for the critical role of Ang- 2 as a key autocrine regulator of vascular stability and responsiveness.