A3 adenosine receptor activation triggers phosphorylation of protein kinase B and protects rat basophilic leukemia 2H3 mast cells from apoptosis

Adenosine accumulates to high levels in inflamed or ischemic tissues and activates A(3) adenosine receptors (ARs) on mast cells to trigger degranulation. Here we show that stimulation of rat basophilic leukemia (RBL)-2H3 mast-like cells with the A(3) AR agonists N-6-(3-iodo) benzyl-5'-N-methylcarboxamidodoadenosine (IB-MECA; 10 nM) or inosine (10 muM) stimulates phosphorylation of protein kinase B (Akt). IB-MECA (1 muM) also causes a >50% reduction in apoptosis caused by exposure of RBL-2H3 cells to UV light. Akt phosphorylation is not stimulated by 100 nM N-6-cyclopentyladenosine (A(1)-selective) or CGS21680 (A(2A)-selective) and is absent in cells pretreated with wortmannin or pertussis toxin. The K-I values of the AR antagonists BW-1433 and 8-sulfophenyltheophylline (8-SPT) were determined in radioligand binding assays for all four subtypes of rat ARs: BW-1433 (A(1), 5.8 +/- 1.0 nM; A(2A), 240 +/- 37; A(2B),30 +/- 10; A(3), 12,300 +/- 3,700); 8-SPT (A(1), 3.2 +/- 1.2 muM; A(2A),57 +/- 4; A(2B), 2.2 +/- 0.8; A(3), >100). BW-1433 and the A(3)-slective antagonist MRS1523 (5 muM), but not 8-SPT (100 muM), block IB-MECA-induced protection from apoptosis, confirming the A(3) AR as the mediator of the antiapoptotic response. The data suggest that adenosine and inosine activate Gi-coupled A(3) ARs to protect mast cells from apoptosis by a pathway involving the beta gamma subunits of Gi, phosphatidylinositol 3-kinase beta, and Akt. We speculate that activation of A(3) ARs on mast cells or other cells that express A(3) ARs (e.g., eosinophils) may facilitate their survival and accumulation in inflamed tissues.