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

Abstract

Hypoxia, through the hypoxia-inducible transcription factors HIF-1α and HIF-2α (HIFs), induces angiogenesis by up-regulating a common set of angiogenic cytokines. Unlike HIF-1α, which regulates a unique set of genes, most genes regulated by HIF-2α overlap with those induced by HIF-1α. Thus, the unique contribution of HIF-2α remains largely obscure. By using adenoviral mutant HIF-1α and adenoviral mutant HIF-2α constructs, where the HIFs are transcriptionally active under normoxic conditions, we show that HIF-2α but not HIF-1α regulates adenosine A2A receptor in primary cultures of human lung endothelial cells. Further, siRNA knockdown of HIF-2α completely inhibits hypoxic induction of A2A receptor. Promoter studies show a 2.5-fold induction of luciferase activity with HIF-2α 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-2α binding to this region is specific. In addition, we demonstrate that A2A receptor has angiogenic potential, as assessed by increases in cell proliferation, cell migration, and tube formation. Additional data show increased expression of A2A receptor in human lung tumor cancer samples relative to adjacent normal lung tissue. These data also demonstrate that A2A receptor is regulated by hypoxia and HIF-2α in human lung endothelial cells but not in mouse-derived endothelial cells.