Stimulation of p70S6 kinase phosphorylation by the A(2A) adenosine receptor in primary human endothelial cells and in CHO cells heterologously expressing the receptor

The A(2A) adenosine receptor is prototypically coupled to stimulation of ad enylyl cyclase by means of G(s). However, in human endothelial cells, adeno sine stimulates proliferation and mitogen-activated protein kinase (MBP kin ase) by means of the A(2A) receptor in a manner that is independent of cAMP . Here, we have investigated the regulation of p70S6-kinase, which relays s ignals from membrane-bound growth factor receptors to stimulation of transl ational efficiency in the G1 phase of the cell cycle. Our experiments show that adenosine analogues promote phosphorylation of p70S6 kinase in endothe lial cells. The pharmacologic profile indicates that this effect is mediate d by means of the A(2A) receptor. We have confirmed this pharmacologic clas sification by using a transfected Chinese hamster ovary-(CHO) A(2A) cell li ne (which stably expresses the human A(2A) adenosine receptor); all finding s that were obtained in endothelial cells were faithfully reproduced in CHO -A(2A). The signalling cascade that links the receptor to p70S6 kinase is i ndependent of cAMP and MAP kinase activation but sensitive to rapamycin. Fu rthermore, the A(2A)-receptor-dependent activation of p70S6 kinase stimulat ion relies on a phosphatidylinositol-3 kinase isoform, because it is inhibi ted by wortmannin and the synthetic inhibitor LY294002. Conversely, MAP kin ase stimulation by the A(2A) receptor was not affected by wortmannin. Taken together, our experiments show that the A(2A) adenosine receptor regulates cAMP levels, MAP kinase, and p70S6 kinase in human endothelial cells by me ans of three independent pathways. Drug Dev. Res. 45:140-150, 1998. (C) 199 8 Wiley-Liss, Inc.