Specific inhibition of nuclear factor-kappaB-dependent inflammatory responses by cell type-specific mechanisms upon A2A adenosine receptor gene transfer.
Adenosine is a potent inhibitor of inflammatory processes, and the A(2A) adenosine receptor (A(2A)AR) plays a key nonredundant role as a suppresser of inflammatory responses in vivo. In this study, we demonstrate that increasing A(2A)AR gene expression suppressed multiple inflammatory responses in both human umbilical vein endothelial cells (HUVECs) and rat C6 glioma cells in vitro. In particular, the induction of the adhesion molecule E-selectin by either tumor necrosis factor alpha (TNFalpha) or Escherichia coli lipopolysaccharide (LPS) was reduced by more than 70% in HUVECs, whereas inducible nitric-oxide synthase (iNOS) induction was abolished in C6 cells after exposure to interferon-gamma in combination with LPS and TNFalpha, suggesting that the receptor inhibited a common step in the induction of each of these pro-inflammatory genes. Consistent with this hypothesis, A(2A)AR expression inhibited the activation of NF-kappaB, a key transcription factor whose proper function was essential for optimal iNOS and E-selectin induction. However, although NF-kappaB binding to target DNA was severely compromised in both cell types, the mechanisms by which this occurred were distinct. In C6 cells, A(2A)AR expression blocked IkappaBalpha degradation by inhibiting stimulus-induced phosphorylation, whereas in HUVECs, A(2A)AR expression inhibited NF-kappaB translocation to the nucleus independently of any effect on IkappaBalpha degradation. Together, these observations suggest that A(2A)AR-mediated inhibition NF-kappaB activation is a critical aspect of its anti-inflammatory signaling properties and that the molecular basis of this inhibition varies in a cell type-specific manner.
Sands
William A
WA
Molecular Pharmacology Group, Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow, G12 8QQ, United Kingdom.
Martin
Anthony F
AF
Strong
Elaine W
EW
Palmer
Timothy M
TM
D002448:Cell Adhesion / Q000502:physiology; D019040:E-Selectin / Q000378:metabolism; D004730:Endothelium, Vascular / Q000378:metabolism*; D018014:Gene Transfer Techniques; D005910:Glioma; D006801:Humans; D020672:I-kappa B Proteins / Q000378:metabolism; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D009000:Monocytes / Q000166:cytology; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000037:antagonists & inhibitors / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000096:biosynthesis*; D052247:Nitric Oxide Synthase Type II; D043705:Receptor, Adenosine A2A / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D019040:E-Selectin; D020672:I-kappa B Proteins; D016328:NF-kappa B; C000606204:NFKBIA protein, human; C000606206:Nfkbia protein, rat; D043705:Receptor, Adenosine A2A; D014409:Tumor Necrosis Factor-alpha; D000072000:NF-KappaB Inhibitor alpha; C496319:NOS2 protein, human; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; D048031:JNK Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases