Novel Roles of GATA1 in Regulation of Angiogenic Factor AGGF1 and Endothelial Cell Function

AGGF1 is an angiogenic factor, and its deregulation is associated with a vascular malformation consistent with Klippel-Trenaunay syndrome (KTS). This study defines the molecular mechanism for transcriptional regulation of AGGF1 expression. Transcription of AGGF1 starts at two nearby sites, -367 and -364 bp upstream of the translation start site. Analyses of 5'- and 3'-serial promoter deletions defined the core promoter/regulatory elements, including two repressor sites (from -1971 to -3990 and from -7521 to -8391, respectively) and two activator sites (a GATA1 consensus binding site from -295 to -300 and a second activator site from -129 to -159). Both the GATA1 site and the second activator site are essential for AGGF1 expression. A similar expression profile was found for GATA1 and AGGF1 in cells (including various endothelial cells) and tissues. Electrophoretic mobility shift assay and chromatin immunoprecipitation assays demonstrated that GATA1 was able to bind to the AGGF1 DNA in vitro and in vivo. Overexpression of GATA1 increased expression of AGGF1. We identified one rare polymorphism -294C>T in a sporadic KTS patient, which is located in the GATA1 site, disrupts binding of GATA1 to DNA, and abolishes the GATA1 stimulatory effect on transcription of AGGF1. Knockdown of GATA1 expression by siRNA reduced expression of AGGF1, and resulted in endothelial cell apoptosis and inhibition of endothelial capillary vessel formation and cell migration, which was rescued by purified recombinant human AGGF1 protein. These results demonstrate that GATA1 regulates expression of AGGF1 and reveal a novel role for GATA1 in endothelial cell biology and angiogenesis.