Lipopolysaccharide rapidly modifies adenosine receptor transcripts in murine and human macrophages: role of NF-κB in A2A adenosine receptor induction

The A2A adenosine receptor (A2AAR) mediates anti-inflammatory actions of adenosine in a variety of cell types. LPS (lipopolysaccharide) was reported to induce a small (100-fold increase in A2AAR mRNA. LPS-induced increases in mRNA for A2AAR and TNFα (tumour necrosis factor α) are reduced by 90% in IPMΦ pretreated with the NF-κB (nuclear factor κB) inhibitor, BAY 11-7082 {(E)3-[(4-methylphenyl)sulphonyl]-2-propenenitrile; 10 μM}. In Wehi-3 cells exposed to LPS, A2AAR and A2BAR transcripts are elevated by 290- and 10-fold respectively, the A1AR transcript is unchanged and the A3AR transcript is decreased by 67%. The induction of A2AAR mRNA by LPS is detectable after 1 h, reaches a peak at 6 h at 600 times control and remains elevated beyond 24 h. The ED50 (effective dose) of LPS is 2.3 ng/ml. A2AAR receptor number, measured by 125I-ZM241385 binding to whole cells, is undetectable in naïve cells and increases linearly at a rate of 23 receptors·cell−1·min−1 to a Bmax of 348 fmol/mg (28000 receptors/cell) in 20 h. The increase in receptor number is correlated with an increase in the potency of an A2A agonist (4-{3-[6-amino-9-(5-ethylcarbamoyl-3,4-dihydroxy-tetrahydro-furan-2-yl)-9H-purin-2-yl]-prop-2-ynyl}-cyclohexanecarboxylic acid methyl ester; referred to as ATL146e) to stimulate cAMP in these cells. After LPS pretreatment, the potency of the A2A agonist, ATL146e, to reduce TNFα release from IPMΦ was increased by 200-fold. The results support the hypothesis that regulation of adenosine receptor expression, especially up-regulation of the A2AAR, is part of a delayed feedback mechanism initiated through NF-κB to terminate the activation of human and mouse macrophages.