title: Selective inhibition of cytokine-activated extracellular signal-regulated kinase by cyclic AMP via Epac1-dependent induction of suppressor of cytokine signalling-3.
abstract: Here we demonstrate that elevation of cyclic AMP (cAMP) levels in human umbilical vein endothelial cells (HUVECs) specifically attenuates ERK1,2 activation in response to either leptin or a soluble interleukin IL-6 receptor-alpha/IL-6 (sIL-6R alpha/IL-6) trans-signalling complex but not protein kinase C activator phorbol 12-myristate 13-acetate. The inhibitory effects of cAMP on sIL-6R alpha/IL-6-stimulated phosphorylation of ERK1,2 and STAT3 were abolished by either short interfering (si) RNA-mediated knockdown or genetic ablation of suppressor of cytokine signalling-3 (SOCS-3). The inhibitory effect of cAMP could not be reversed by inhibition of cAMP-dependent protein kinase (PKA) but was blocked by depletion of the alternative intracellular cAMP sensor exchange protein activated by cAMP 1 (Epac1), which is also required to observe SOCS-3 accumulation in response to cAMP. Interestingly, the ability of cAMP elevation to inhibit IL-6 signalling was blocked by ERK inhibition. Consistent with this observation, cAMP elevation in HUVECs produced a transient yet robust activation of ERK, and subsequent phosphorylation of transcription factor C/EBP beta, both of which were resistant to PKA inhibition. However, siRNA depletion and immunoblotting experiments revealed that neither Epac1 nor Epac2 contributed to the PKA-independent activation of ERK1,2 observed following cAMP elevation. Together, these observations suggest that while SOCS-3 induction and subsequent inhibition of cytokine-mediated phosphorylation of ERK1,2 and STAT3 in response to cAMP require Epac1 and a transient PKA-independent activation of the ERK pathway, these two events are controlled by distinct mechanisms. In addition, it reveals a novel Epac-dependent mechanism by which cAMP can specifically inhibit ERK in response to cytokine receptor activation.
authors.affiliation: Biochemistry and Cell Biology, Faculty of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, Scotland, UK.
authors.forename: Hayley D
authors.initials: HD
authors.lastname: Woolson
authors.forename: Victoria S
authors.initials: VS
authors.lastname: Thomson
authors.forename: Claire
authors.initials: C
authors.lastname: Rutherford
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Yarwood
authors.forename: Timothy M
authors.initials: TM
authors.lastname: Palmer
mesh_terms: D022782:CCAAT-Enhancer-Binding Protein-beta / Q000378:metabolism; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D016207:Cytokines / Q000494:pharmacology*; D042783:Endothelial Cells / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D055785:Gene Knockdown Techniques; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D006801:Humans; D015850:Interleukin-6 / Q000494:pharmacology; D053698:Interleukin-6 Receptor alpha Subunit / Q000378:metabolism; D020738:Leptin / Q000494:pharmacology; D010766:Phosphorylation; D034741:RNA, Small Interfering / Q000378:metabolism; D050796:STAT3 Transcription Factor / Q000378:metabolism; D015398:Signal Transduction; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
chemical_list: D022782:CCAAT-Enhancer-Binding Protein-beta; D016207:Cytokines; D020662:Guanine Nucleotide Exchange Factors; D015850:Interleukin-6; D053698:Interleukin-6 Receptor alpha Subunit; D020738:Leptin; C116122:RAPGEF3 protein, human; D034741:RNA, Small Interfering; C106644:SOCS3 protein, human; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D048049:Extracellular Signal-Regulated MAP Kinases