PT - JOURNAL ARTICLE AU - Mohammed M.A. Safhi AU - Claire Rutherford AU - Catherine Ledent AU - William A. Sands AU - Tim M. Palmer TI - PRIMING OF SIGNAL TRANSDUCER AND ACTIVATOR OF TRANSCRIPTION PROTEINS FOR CYTOKINE-TRIGGERED POLYUBIQUITYLATION AND DEGRADATION BY THE A<sub>2A</sub> ADENOSINE RECEPTOR AID - 10.1124/mol.109.062455 DP - 2010 Jan 01 TA - Molecular Pharmacology PG - mol.109.062455 4099 - http://molpharm.aspetjournals.org/content/early/2010/02/25/mol.109.062455.short 4100 - http://molpharm.aspetjournals.org/content/early/2010/02/25/mol.109.062455.full AB - Here we demonstrate that overexpression of the human A2A adenosine receptor (A2AAR) in vascular endothelial cells confers an ability of interferon-α and a soluble IL-6 receptorα/IL-6 (sIL-6Rα/IL-6) trans-signaling complex to trigger the down-regulation of signal transducer and activator of transcription (STAT) proteins. Interestingly, STAT down-regulation could be reversed by co-incubation with A2AAR-selective inverse agonist ZM241385 but not adenosine deaminase, suggesting that constitutive activation of the receptor was responsible for the effect. Moreover, STAT down-regulation was selectively abolished by proteasome inhibitor MG132 while lysosome inhibitor chloroquine was without effect. Down-regulation required Janus kinase (JAK) activity and a Tyr705→Phe-mutated STAT3 was resistant to the phenomenon, suggesting that JAK-mediated phosphorylation of this residue is required. Consistent with this hypothesis, treatment of A2AAR-overexpressing cells with sIL-6Rα/IL-6 triggered the accumulation of polyubiquitylated wild-type but not Tyr705→Phe-mutated STAT3. Support for a functional role of this process was provided by the observation that A2AAR overexpression attenuated the JAK/STAT-dependent up-regulation of vascular endothelial growth factor receptor-2 by sIL-6Rα/IL-6. Consistent with a role for endogenous A2AARs in regulating STAT protein levels, prolonged exposure of endogenous A2AARs in endothelial cells with ZM241385 in vitro triggered the up-regulation of STAT3, while deletion of the A2AAR in vivo potentiated STAT1 expression and phosphorylation. Together, these experiments support a model whereby the A2AAR can prime JAK-phosphorylated STATs for polyubiquitylation and proteasomal degradation, and represents a new mechanism by which an anti-inflammatory seven transmembrane receptor can negatively regulate JAK/STAT signaling.The American Society for Pharmacology and Experimental Therapeutics