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

The A (2A) adenosine receptor (A (2A) AR) mediates anti-inflammatory actions of adenosine in a variety of cell types. LPS (lipopolysaccharide) was reported to induce a small (100-fold increase in A (2A) AR mRNA. LPS-induced increases in mRNA for A (2A) AR and TNFalpha (tumour necrosis factor alpha) are reduced by 90% in IPMPhi pretreated with the NF-kappaB (nuclear factor kappaB) inhibitor, BAY 11-7082 (E) 3- (4-methylphenyl) sulphonyl-2-propenenitrile; 10 microM. In Wehi-3 cells exposed to LPS, A (2A) AR and A (2B) AR transcripts are elevated by 290- and 10-fold respectively, the A (1) AR transcript is unchanged and the A (3) AR transcript is decreased by 67%. The induction of A (2A) AR 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. A (2A) AR receptor number, measured by 125I-ZM241385 binding to whole cells, is undetectable in naïve cells and increases linearly at a rate of 23 receptors x cell (-1) x min (-1) to a B (max) 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 A (2A) 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 A (2A) agonist, ATL146e, to reduce TNFalpha release from IPMPhi was increased by 200-fold. The results support the hypothesis that regulation of adenosine receptor expression, especially up-regulation of the A (2A) AR, is part of a delayed feedback mechanism initiated through NF-kappaB to terminate the activation of human and mouse macrophages.