Removal of the carboxy terminus of the A2A-adenosine receptor blunts constitutive activity: differential effect on cAMP accumulation and MAP kinase stimulation

Naunyn Schmiedebergs Arch Pharmacol. 2002 Oct;366(4):287-98. doi: 10.1007/s00210-002-0617-z. Epub 2002 Aug 28.


The A(2A)-adenosine receptor has an extended carboxy terminus (approximately 120 amino acids), the role of which is poorly defined. In human endothelial cells and in HEK293 cells, the A(2A)-receptor controls at least two independent signalling pathways, i.e. increased cyclic adenosine 3',5'-monophosphate (cAMP) formation via its cognate G protein G(s) and increased phosphorylation of mitogen-activated protein kinase (MAP kinase) by recruiting p21(ras). In order to address the role of the carboxy terminus in signal transfer, we generated HEK293 cells that stably expressed the full-length (wt) receptor and truncated versions [A(2A)-R(1-360) and A(2A)-R(1-311)] at comparable levels (approximately 0.5 pmol/mg) in the plasma membrane. The effects of truncation were divergent with respect to the two effectors regulated by the receptor. In intact cells carrying A(2A)-R(wt) and A(2A)-R(1-360), cAMP accumulation was more potently activated by an A(2A)-agonist than in cells expressing A(2A)-R(1-311). Similarly, A(2A)-R(wt) and A(2A)-R(1-360)--but not A(2A)-R(1-311)--caused constitutive (=agonist-independent) elevation of cAMP which was reversed by the addition of A(2A)-antagonists. In membranes prepared from these cells, however, the three receptors displayed no constitutive activity in stimulating adenylyl cyclase and they did not differ in apparent agonist affinity. Truncation of the A(2A)-receptor did also not decrease the potency of an A(2A)-agonist to stimulate MAP kinase in intact cells. We conclude that the carboxy terminus defines both (a) the level of constitutive activity, i.e. the equilibrium R<--> R*, in intact cells only, indicating a role for a component that is lost upon cell lysis, and (b) the efficiency of signal transfer in alternative pathways.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Line
  • Cyclic AMP / metabolism*
  • Dose-Response Relationship, Drug
  • Humans
  • Mitogen-Activated Protein Kinases / biosynthesis*
  • Purinergic P1 Receptor Antagonists
  • Receptor, Adenosine A2A
  • Receptors, Purinergic P1 / genetics*
  • Receptors, Purinergic P1 / metabolism*
  • Receptors, Purinergic P1 / physiology
  • Signal Transduction / drug effects
  • Signal Transduction / physiology
  • Transfection / methods


  • Purinergic P1 Receptor Antagonists
  • Receptor, Adenosine A2A
  • Receptors, Purinergic P1
  • Cyclic AMP
  • Mitogen-Activated Protein Kinases