Adenosine augments IL-10 production by macrophages through an A2B receptor-mediated posttranscriptional mechanism.
Adenosine receptor ligands have anti-inflammatory effects and modulate immune responses by up-regulating IL-10 production by immunostimulated macrophages. The adenosine receptor family comprises G protein-coupled heptahelical transmembrane receptors classified into four types: A1, A2A, A2B, and A3. Our understanding of the signaling mechanisms leading to enhanced IL-10 production following adenosine receptor occupancy on macrophages is limited. In this study, we demonstrate that adenosine receptor occupancy increases IL-10 production by LPS-stimulated macrophages without affecting IL-10 promoter activity and IL-10 mRNA levels, indicating a posttranscriptional mechanism. Transfection experiments with reporter constructs containing sequences corresponding to the AU-rich 3'-untranslated region (UTR) of IL-10 mRNA confirmed that adenosine receptor activation acts by relieving the translational repressive effect of the IL-10 3'-UTR. By contrast, adenosine receptor activation failed to liberate the translational arrest conferred by the 3'-UTR of TNF-alpha mRNA. The IL-10 3'-UTR formed specific complexes with proteins present in cytoplasmic extracts of RAW 264.7 cells. Adenosine enhanced binding of proteins to a region of the IL-10 3'-UTR containing the GUAUUUAUU nonamer. The stimulatory effect of adenosine on IL-10 production was mediated through the A(2B) receptor, because the order of potency of selective agonists was 5'-N-ethylcarboxamidoadenosine (NECA) > N6-(3-iodobenzyl)-adenosine-5'-N-methyluronamide (IB-MECA) > 2-chloro-N6-cyclopentyladenosine (CCPA) = 2-p-(2-carboxyethyl)phenethylamino-5'-N-ethyl-carboxamidoadenosine (CGS-21680). Also, the selective A2B antagonist, alloxazine, prevented the effect of adenosine. Collectively, these studies identify a novel pathway in which activation of a G protein-coupled receptor augments translation of an anti-inflammatory gene.
Németh
Zoltán H
ZH
Department of Surgery, University of Medicine and Dentistry of New Jersey (UMDNJ)- New Jersey Medical School, Newark, NJ 07103, USA.
Lutz
Carol S
CS
Csóka
Balázs
B
Deitch
Edwin A
EA
Leibovich
S Joseph
SJ
Gause
William C
WC
Tone
Masahide
M
Pacher
Pál
P
Vizi
E Sylvester
ES
Haskó
György
G
D020413:3' Untranslated Regions; D000241:Adenosine / Q000502:physiology*; D058908:Adenosine A2 Receptor Agonists; D000818:Animals; D002460:Cell Line; D005786:Gene Expression Regulation / Q000276:immunology*; D016753:Interleukin-10 / Q000096:biosynthesis*; D008024:Ligands; D008070:Lipopolysaccharides / Q000494:pharmacology; D008264:Macrophages / Q000378:metabolism*; D051379:Mice; D011401:Promoter Regions, Genetic; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000032:analysis; D043704:Receptor, Adenosine A2B / Q000502:physiology*
D020413:3' Untranslated Regions; D058908:Adenosine A2 Receptor Agonists; D008024:Ligands; D008070:Lipopolysaccharides; D012333:RNA, Messenger; D043704:Receptor, Adenosine A2B; D016753:Interleukin-10; D000241:Adenosine