Differential expression of adenosine receptors in human endothelial cells -: Role of A2B receptors in angiogenic factor regulation

Adenosine has been reported to stimulate or inhibit the release of angiogenic factors depending on the cell type examined. To test the hypothesis that differential expression of adenosine receptor subtypes contributes to endothelial cell heterogeneity, we studied microvascular (HMEC-1) and umbilical vein (HUVEC) human endothelial cells. Based on mRNA level and stimulation of adenylate cyclase, we found that HUVECs preferentially express A(2A) adenosine receptors and HMEC-1 preferentially express AN receptors. Neither cells expressed A(1) or A(3) receptors. The nonselective adenosine agonist 5'-N-ethylcarboxamidoadenosine (NECA) increased expression of interleukin-8 (IL-8), basic fibroblast growth factor (bFGF), and vascular endothelial growth factor (VEGF) in HMEC-1, but had no effect in HUVECs. In contrast, the selective A(2A), agonist 2-p-(2-carboxyethyl)phenylethylamino-NECA (CGS 21680) had no effect on expression of these angiogenic factors. Cotransfection of each type of adenosine receptors with a luciferase reporter in HMEC-1 showed that A,[, receptors, but not A,, A2A, or A3, activated IL-8 and VEGF promoters. These effects were mimicked by constitutively active alphaG(q), alphaG(12), and alphaG(13) but not alphaG(13) or alphaG(13). Furthermore, stimulation of phospholipase C indicated coupling of A,B receptors to G, proteins in HMEC-1. Thus, differential expression of adenosine receptor subtypes contributes to functional heterogeneity of human endothelial cells. A(2B), receptors, predominantly expressed in human microvascular cells, modulate expression of angiogenic factors via coupling to G, and possibly via G(12/13).