Exchange protein activated by cyclic AMP (Epac)-mediated induction of suppressor of cytokine signaling 3 (SOCS-3) in vascular endothelial cells.
Here, we demonstrate that elevation of intracellular cyclic AMP (cAMP) in vascular endothelial cells (ECs) by either a direct activator of adenylyl cyclase or endogenous cAMP-mobilizing G protein-coupled receptors inhibited the tyrosine phosphorylation of STAT proteins by an interleukin 6 (IL-6) receptor trans-signaling complex (soluble IL-6Ralpha/IL-6). This was associated with the induction of suppressor of cytokine signaling 3 (SOCS-3), a bona fide inhibitor in vivo of gp130, the signal-transducing component of the IL-6 receptor complex. Attenuation of SOCS-3 induction in either ECs or SOCS-3-null murine embryonic fibroblasts abolished the inhibitory effect of cAMP, whereas inhibition of SHP-2, another negative regulator of gp130, was without effect. Interestingly, the inhibition of STAT phosphorylation and SOCS-3 induction did not require cAMP-dependent protein kinase activity but could be recapitulated upon selective activation of the alternative cAMP sensor Epac, a guanine nucleotide exchange factor for Rap1. Consistent with this hypothesis, small interfering RNA-mediated knockdown of Epac1 was sufficient to attenuate both cAMP-mediated SOCS-3 induction and inhibition of STAT phosphorylation, suggesting that Epac activation is both necessary and sufficient to observe these effects. Together, these data argue for the existence of a novel cAMP/Epac/Rap1/SOCS-3 pathway for limiting IL-6 receptor signaling in ECs and illuminate a new mechanism by which cAMP may mediate its potent anti-inflammatory effects.
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.
Woolson
Hayley D
HD
Milne
Gillian R
GR
Rutherford
Claire
C
Palmer
Timothy M
TM
D016475:3T3 Cells; D000818:Animals; D002478:Cells, Cultured; D018932:Chemokine CCL2 / Q000378:metabolism; D000242:Cyclic AMP / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D006801:Humans; D015850:Interleukin-6 / Q000378:metabolism; D053613:Janus Kinase 1; D051379:Mice; D010766:Phosphorylation / Q000187:drug effects; D017027:Protein Tyrosine Phosphatases / Q000037:antagonists & inhibitors; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D019947:Receptors, Interleukin-6 / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
D018932:Chemokine CCL2; D020662:Guanine Nucleotide Exchange Factors; D015850:Interleukin-6; C116122:RAPGEF3 protein, human; D012333:RNA, Messenger; D019947:Receptors, Interleukin-6; C106644:SOCS3 protein, human; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D000242:Cyclic AMP; D011505:Protein-Tyrosine Kinases; C507904:JAK1 protein, human; C507905:Jak1 protein, mouse; D053613:Janus Kinase 1; D017868:Cyclic AMP-Dependent Protein Kinases; D017027:Protein Tyrosine Phosphatases