Abstract
The known diverse effects of adenosine on mitogenesis may be related to changes in mitogen-activated protein kinases. In this study we therefore compared the phosphorylation of extracellular-regulated kinase 1/2 (ERK1/2) via the four known human adenosine receptors A1, A2A, A2B, and A3, stably transfected into Chinese hamster ovary (CHO) cells. The adenosine analog 5′-N-ethylcarboxamidoadenosine (NECA), known to act on all subtypes, had no effect on untransfected CHO cells, but did cause a substantial time- and dose-dependent phosphorylation in CHO cells transfected with each of the receptors. The maximal phosphorylation was highest in A1 and A3receptor-transfected cells, intermediate in A2A and low in A2B receptor-expressing CHO cells. For all receptors the half-maximal ERK1/2 phosphorylation was observed at 19–115 nM NECA. NECA acting on adenosine A2B receptors was much more potent in stimulating ERK1/2 phosphorylation (EC50 = 19 nM) than cAMP formation (EC50 = 1.4 μM). Stimulation with the endogenous ligand adenosine resulted in the same pattern of ERK1/2 phosphorylation as NECA. Concentrations of adenosine that occur physiologically caused an increased phosphorylation after 5 min in CHO cells transfected with any one of the four adenosine receptors. Adenosine at levels reached during ischemia (3 μM) induced a more pronounced, but still transient, activation of ERK1/2. In conclusion, this study shows that all the human adenosine receptors transfected into CHO cells are able to activate ERK1/2 at physiologically relevant concentrations of the endogenous agonist.
Footnotes
- Received December 14, 1999.
- Accepted May 22, 2000.
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Send reprint requests to: Gunnar Schulte, Karolinska Institutet, Department of Physiology and Pharmacology, Section of Molecular Neuropharmacology, S-171 77 Stockholm, Sweden. E-mail: gunnar.schulte{at}fyfa.ki.se
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This study was supported by the Swedish Medical Research Council (2553), by the European Commission (EURCAR), and by Karolinska Institutet. Some of these results have been presented in abstract form at the 1999 International Society for Neurochemistry/European Society for Neurochemistry meeting in Berlin, Germany.
- The American Society for Pharmacology and Experimental Therapeutics
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