Inhibition of NF-κB-mediated gene transcription by the human A2B adenosine receptor in Chinese hamster ovary cells

NF-kappaB is a transcription factor that plays a vital role in regulating inducible gene expression in immune and inflammatory responses. In view of the well documented effects of adenosine on immune and inflammatory responses, we have explored whether adenosine A(1), A(2B) and A(3) receptors regulate NF-kappaB activity in transfected Chinese hamster ovary (CHO) cells using a luciferase reporter gene construct. No increases in NF-kappaB activity were observed in CHO-A(1), -A(2B) and -A(3) cells stimulated with the non-selective adenosine receptor agonist 5 ' -N-ethyl-carboxamidoadenosine. Elevating intracellular cyclic AMP (cAMP) levels using forskolin (direct activator of adenylyl cyclase) and rolipram (type IV, cAMP-specific phosphodiesterase inhibitor), inhibited NF-kappaB activity in CHO cells. Adenosine A(2B) receptor stimulation also inhibited NF-kappaB activity, whereas adenosine A(1) and A(3) receptor activation had no effect. These data reflect the known coupling of adenosine A(2B) receptors to increases in cAMP. In conclusion, adenosine A(1), A(2B) and A(3) receptors do not directly activate NF-kappaB in CHO cells. However, adenosine A(2B) receptor activation significantly inhibited NF-kappaB activity. Inhibition of NF-kappaB activity by the adenosine A(2B) receptor may contribute to the anti-inflammatory effects of adenosine.