The cAMP-responsive Rap1 guanine nucleotide exchange factor, Epac, induces smooth muscle relaxation by down-regulation of RhoA activity. J Biol Chem 2011 May 13;286(19):16681-92
Date
04/02/2011Pubmed ID
21454546Pubmed Central ID
PMC3089510DOI
10.1074/jbc.M110.205062Scopus ID
2-s2.0-79955764385 (requires institutional sign-in at Scopus site) 94 CitationsAbstract
Agonist activation of the small GTPase, RhoA, and its effector Rho kinase leads to down-regulation of smooth muscle (SM) myosin light chain phosphatase activity, an increase in myosin light chain (RLC(20)) phosphorylation and force. Cyclic nucleotides can reverse this process. We report a new mechanism of cAMP-mediated relaxation through Epac, a GTP exchange factor for the small GTPase Rap1 resulting in an increase in Rap1 activity and suppression of RhoA activity. An Epac-selective cAMP analog, 8-pCPT-2'-O-Me-cAMP ("007"), significantly reduced agonist-induced contractile force, RLC(20), and myosin light chain phosphatase phosphorylation in both intact and permeabilized vascular, gut, and airway SMs independently of PKA and PKG. The vasodilator PGI(2) analog, cicaprost, increased Rap1 activity and decreased RhoA activity in intact SMs. Forskolin, phosphodiesterase inhibitor isobutylmethylxanthine, and isoproterenol also significantly increased Rap1-GTP in rat aortic SM cells. The PKA inhibitor H89 was without effect on the 007-induced increase in Rap1-GTP. Lysophosphatidic acid-induced RhoA activity was reduced by treatment with 007 in WT but not Rap1B null fibroblasts, consistent with Epac signaling through Rap1B to down-regulate RhoA activity. Isoproterenol-induced increase in Rap1 activity was inhibited by silencing Epac1 in rat aortic SM cells. Evidence is presented that cooperative cAMP activation of PKA and Epac contribute to relaxation of SM. Our findings demonstrate a cAMP-mediated signaling mechanism whereby activation of Epac results in a PKA-independent, Rap1-dependent Ca(2+) desensitization of force in SM through down-regulation of RhoA activity. Cyclic AMP inhibition of RhoA is mediated through activation of both Epac and PKA.
Author List
Zieba BJ, Artamonov MV, Jin L, Momotani K, Ho R, Franke AS, Neppl RL, Stevenson AS, Khromov AS, Chrzanowska-Wodnicka M, Somlyo AVAuthor
Magdalena Chrzanowska PhD Professor in the Pharmacology and Toxicology department at Medical College of WisconsinMESH terms used to index this publication - Major topics in bold
1-Methyl-3-isobutylxanthineAnimals
Aorta
Bronchi
Calcium
Down-Regulation
Fibroblasts
Guanine Nucleotide Exchange Factors
Humans
Isoproterenol
Lysophospholipids
Mice
Muscle, Smooth
Myosin-Light-Chain Phosphatase
Phosphorylation
Rats
rap1 GTP-Binding Proteins
rhoA GTP-Binding Protein
