Adenosine A 2A 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 A_2A receptor in primary cultures of human lung endothelial cells. Further, siRNA knockdown of HIF-2α completely inhibits hypoxic induction of A_2A 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 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-2α in human lung endothelial cells but not in mouse-derived endothelial cells.