Early tyrosine phosphorylation events following adenosine A receptor in human neutrophils: identification of regulated pathways.

Activation of the adenosine receptor (AR) elevates intracellular levels of cAMP and acts as a physiologic inhibitor of inflammatory neutrophil functions. In this study, we looked into the impact of AR engagement on early phosphorylation events. Neutrophils were stimulated with well-characterized proinflammatory agonists in the absence or presence of an AR agonist {3-[4-[2-[ [6-amino-9-[(2R,3R,4S,5S)-5-(ethylcarbamoyl)-3,4-dihydroxy-oxolan-2-yl]purin-2-yl]amino] ethyl] phenyl] propanoic acid (CGS 21680)}, PGE, or a mixture of the compounds RO 20-1724 and forskolin. As assessed by immunoblotting, several proteins were tyrosine phosphorylated; CGS 21680 markedly decreased tyrosine phosphorylation levels of 4 regions (37-45, 50-55, 60, and 70 kDa). Key signaling protein kinases-p38 MAPK, Erk-1/2, PI3K/Akt, Hck, and Syk-showed decreased phosphorylation, whereas Lyn, SHIP-1, or phosphatase and tensin homolog (PTEN) was spared. PGE or the intracellular cAMP-elevating combination of RO 20-1724 and forskolin mostly mimicked the effect of CGS 21680. Together, results unveil intracellular signaling pathways targeted by the AR, some of which might be key in modulating neutrophil functions.