Activation of the A(3) adenosine receptor inhibits fMLP-induced Rac activation in mouse bone marrow neutrophils.
Adenosine is released from injured or hypoxic tissues where it exerts numerous anti-inflammatory effects including suppression of neutrophil functions. Although most previous work has implicated the A(2A)AR, we have recently shown that selective activation of the abundantly expressed A(3)AR inhibits neutrophil superoxide production and chemotaxis providing a potential mechanistic explanation for the efficacy of A(3)AR agonists in experimental animal models of inflammation. In this study, we hypothesized that the A(3)AR suppresses neutrophil functions by inhibiting the monomeric GTPase Rac, a central regulator of chemokine-directed neutrophil migration and superoxide production. We found that pre-treating neutrophils with the highly selective A(3)AR agonist CP-532,903 reduced fMLP-induced Rac activation using an ELISA-based assay that detects all three Rac isoforms. CP-532,903 also inhibited fMLP-induced F-actin formation, a downstream effector function of Rac relevant to neutrophil migration, but not activation of ERK1/2 or p38. Pre-treating neutrophils with CP-532,903 did not stimulate cAMP production or alter fMLP-induced calcium transients, implicating that A(3)AR stimulation does not inhibit Rac activation or neutrophil activities by suppressing Ca(2+) signaling, elevating the intracellular concentration of cAMP, or by cross-desensitizing fMLP receptors. Our results suggest that activation of the A(3)AR signals to suppress neutrophil functions by interfering with the monomeric GTPase Rac, thus contributing to the ant-inflammatory actions of adenosine.
Department of Pharmacology and Toxicology and the Cardiovascular Center, Medical College of Wisconsin, Milwaukee, 53226, United States.
Dharini
D
van der Hoeven
Elizabeth T
ET
Gizewski
John A
JA
Auchampach
D000241:Adenosine / Q000494:pharmacology; D000818:Animals; D000893:Anti-Inflammatory Agents / Q000494:pharmacology*; D001854:Bone Marrow Cells; D051379:Mice; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D009504:Neutrophils / Q000378:metabolism*; D043684:Receptor, Adenosine A3 / Q000378:metabolism / Q000502:physiology*; D020744:rac GTP-Binding Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism
D000893:Anti-Inflammatory Agents; D043684:Receptor, Adenosine A3; D009240:N-Formylmethionine Leucyl-Phenylalanine; D020744:rac GTP-Binding Proteins; D000241:Adenosine