Abstract 812: GATA3 Expression is Essential for Tie2 Expression and Angiopoietin-1/Tie2-mediated signaling in Endothelium
The endothelium displays remarkable heterogeneity in health and disease. Endothelial phenotypes are modulated in space and time by mechanisms that involve the highly coordinated combinatorial action of transcriptional modules. Recent studies have provided increasing evidence that GATA factors function as dynamic responsive genes, coupling changes within the extra-cellular environment to changes in downstream target gene expression. Here we show, that among the GATA transcription family, GATA2, 3, and 6 are expressed in endothelial cells. However, there are significant differences in the expression of GATA factors in different vascular beds. GATA3 is high selectively expressed in endothelial cells from larger vessels in mice and cultured human umbilical vein endothelial cells (HUVEC), coronary artery, pulmonary artery, and afferent large lymphatic endothelial cells, but not dermal microvascular and micro lymphatic endothelial cells. To determine the functional relevance of the GATA3 in endothelial cells, we carried out DNA microarrays of HUVEC treated with two independent siRNAs to GATA3. GATA3 knockdown revealed a group of genes that are associated with angiogenesis including the angiopoietin (Ang)-1/Tie2 axis. Knockdown of GATA3 in HUVEC leads to marked reduction in Tie2 protein expression, which causes profound defects in Ang-1-mediated AKT signaling, cell migration and tube formation. In contrast, GATA3 knockdown failed to alter VEGF-mediated signaling, or angiogenesis activities. In electrophoretic gel mobility shift assays and chromatin immunoprecipitation analysis, GATA3 binds to regulatory regions within the 5′ UTR of the Tie2 gene. In co-transfection assays, GATA3 transactivates the Tie2 promoter and cooperates with the Ets transcription factors, NERF2 or ELF1. In the presence of inflammatory stimuli, GATA3 expression is markedly downregulated, which leads to a profound reduction in Tie2 promoter and the protein expression in HUVEC. Taken together, the present study suggests that the expression of GATA3 is indispensable for Tie2 expression and Ang-1-mediated signaling in endothelial cells.