Adenosine A2A receptor is a unique angiogenic target of HIF-2α in pulmonary endothelial cells

Hypoxia, through the hypoxia-inducible transcription factors HIF-1 alpha and HIF-2 alpha(HIFs), induces angiogenesis by up-regulating a common set of angiogenic cytokines. Unlike HIF-1 alpha, which regulates a unique set of genes, most genes regulated by HIF-2 alpha overlap with those induced by HIF-1 alpha. Thus, the unique contribution of HIF-2 alpha remains largely obscure. By using adenoviral mutant HIF-1 alpha and adenoviral mutant HIF-2 alpha constructs, where the HIFs are transcriptionally active under normoxic conditions, we show that HIF-2 alpha but not HIF-1 alpha regulates adenosine A(2A) receptor in primary cultures of human lung endothelial cells. Further, siRNA knockdown of HIF-2 alpha completely inhibits hypoxic induction of A(2A) receptor. Promoter studies show a 2.5-fold induction of luciferase activity with HIF-2 alpha cotransfection. Analysis of the A(2A) receptor gene promoter revealed a hypoxia-responsive element in the region between -704 and -595 upstream of the transcription start site. By using a ChIP assay, we demonstrate that HIF-2 alpha binding to this region is specific. In addition, we demonstrate that A(2A) receptor has angiogenic potential, as assessed by increases in cell proliferation, cell migration, and tube formation. Additional data show increased expression of A(2A) receptor in human lung tumor cancer samples relative to adjacent normal lung tissue. These data also demonstrate that A(2A) receptor is regulated by hypoxia and HIF-2 alpha in human lung endothelial cells but not in mouse-derived endothelial cells.