title: Role of Epac1 in mediating anti-proliferative effects of prostanoid EP(2) receptors and cAMP in human lung fibroblasts.
abstract: In lung fibroblasts, proliferation is inhibited by activation of EP(2) prostanoid receptors which are known to couple to adenylyl cyclase. Beside the classic target of cAMP, protein kinase A (PKA), alternative cAMP effectors have been identified, among them Epac (exchange protein activated by cAMP). The present study aimed to illuminate transduction pathways mediating the anti-proliferative effects of EP(2) receptors in lung fibroblasts. Proliferative activity of human lung fibroblasts was determined by measuring [(3)H]-thymidine incorporation. The selective EP(2) receptor agonist butaprost inhibited [(3)H]-thymidine incorporation by 75%, an effect mimicked by forskolin, the phosphodiesterase inhibitor IBMX, the stable cAMP analogues dibutyryl-cAMP and bromo-cAMP, as well as by the Epac selective cAMP analogues 8-pCPT-2'-O-Me-cAMP and Sp-8-pCPT-2'-O-Me-cAMPS, whereas the PKA selective agonist 6-Bnz-cAMP was inactive. The PKA inhibitor Rp-8-Br-cAMPS inhibited butaprost-induced phosphorylation of CREB (cAMP response element-binding protein), but did not affect butaprost-induced inhibition of [(3)H]-thymidine incorporation. Partial knockdown of Epac1 by specific siRNA transfection resulted in a marked attenuation of the inhibitory potency of butaprost, whereas transfection of Epac2 siRNA or non-silencing siRNA did not affect the effectiveness of butaprost to inhibit [(3)H]-thymidine incorporation. In conclusion, Epac1 rather than the classic cAMP effector PKA is a crucial element in the signal transduction pathway mediating anti-proliferative effects of EP(2) receptor activation.
authors.affiliation: Institute of Pharmacology and Toxicology, University of Bonn, Reuterstrasse 2b, 53113, Bonn, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Haag
authors.forename: M
authors.initials: M
authors.lastname: Warnken
authors.forename: U R
authors.initials: UR
authors.lastname: Juergens
authors.forename: K
authors.initials: K
authors.lastname: Racké
mesh_terms: D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000527:Alprostadil / Q000031:analogs & derivatives / Q000494:pharmacology; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D003094:Collagen / Q000378:metabolism; D000242:Cyclic AMP / Q000502:physiology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D004789:Enzyme Activation; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D055785:Gene Knockdown Techniques; D020662:Guanine Nucleotide Exchange Factors / Q000819:agonists / Q000378:metabolism / Q000502:physiology*; D006801:Humans; D008168:Lung / Q000166:cytology*; D010766:Phosphorylation; D034741:RNA, Small Interfering / Q000235:genetics; D018078:Receptors, Prostaglandin E / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D013873:Thionucleotides / Q000494:pharmacology
chemical_list: C105593:8-bromoadenosine-3',5'-cyclic monophosphorothioate; D020662:Guanine Nucleotide Exchange Factors; C116122:RAPGEF3 protein, human; D034741:RNA, Small Interfering; D018078:Receptors, Prostaglandin E; D013873:Thionucleotides; D015124:8-Bromo Cyclic Adenosine Monophosphate; D003094:Collagen; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D000527:Alprostadil; C048491:butaprost