title: Adenylyl cyclase type 6 overexpression selectively enhances beta-adrenergic and prostacyclin receptor-mediated inhibition of cardiac fibroblast function because of colocalization in lipid rafts.
abstract: Cardiac fibroblasts produce and degrade extracellular matrix and are critical in regulating cardiac remodeling and hypertrophy. Fibroblasts are activated by factors such as transforming growth factor beta and inhibited by agents that elevate 3',5'-cyclic adenosine monophosphate (cAMP) levels. cAMP signal generation and response is known to be compartmentalized in many cell types in part through the colocalization of receptors and specific adenylyl cyclase isoforms in lipid rafts and caveolae. The present study sought to define the localization of key G protein-coupled receptors with adenylyl cyclase type 6 (AC6) in lipid rafts of rat cardiac fibroblasts and to determine if this colocalization was functionally relevant. We found that cardiac fibroblasts produce cAMP in response to agonists for beta-adrenergic (isoproterenol), prostaglandin EP2 (butaprost), adenosine (adenosine-5'-N-ethylcarboxamide, NECA), and prostacyclin (beraprost) receptors. Overexpression of AC6 increased cAMP production stimulated by isoproterenol and beraprost but not by butaprost or NECA. A key function of fibroblasts is the production of collagen. Isoproterenol- and beraprostmediated inhibition of collagen synthesis was also enhanced by AC6 overexpression, while inhibition by butaprost and NECA were unaltered. Lipid raft fractions from cardiac fibroblasts contain the preponderance of beta-adrenergic receptors and AC6 but exclude EP2 receptors. While we could not determine the localization of native prostacyclin receptors, we were able to determine that epitope-tagged prostanoid IP receptors (IPR) expressed in COS7 cells did localize, in part, in lipid raft fractions. These findings indicate that IP receptors are expressed in lipid rafts and can activate raft-localized AC isoforms. AC6 is completely compartmentized in lipid raft domains where it is activated solely by coresident G protein-coupled receptors to regulate cardiac fibroblast function.
authors.affiliation: Department of Pharmacology, University of Tennessee Health Science Center, 874 Union Ave., Crowe 115, Memphis, TN 38163, USA.
authors.forename: Xiaoqiu
authors.initials: X
authors.lastname: Liu
authors.forename: Muthusamy
authors.initials: M
authors.lastname: Thangavel
authors.forename: Shu Qiang
authors.initials: SQ
authors.lastname: Sun
authors.forename: Joseph
authors.initials: J
authors.lastname: Kaminsky
authors.forename: Penden
authors.initials: P
authors.lastname: Mahautmr
authors.forename: Jeremiah
authors.initials: J
authors.lastname: Stitham
authors.forename: John
authors.initials: J
authors.lastname: Hwa
authors.forename: Rennolds S
authors.initials: RS
authors.lastname: Ostrom
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D003094:Collagen / Q000096:biosynthesis; D000242:Cyclic AMP / Q000378:metabolism*; D005347:Fibroblasts / Q000378:metabolism; D015870:Gene Expression; D008297:Male; D021962:Membrane Microdomains / Q000378:metabolism; D051379:Mice; D032383:Myocytes, Cardiac / Q000378:metabolism; D021381:Protein Transport; D051381:Rats; D017207:Rats, Sprague-Dawley; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000378:metabolism*; D044006:Receptors, Epoprostenol; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism; D011982:Receptors, Prostaglandin / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: C491909:Ptgir protein, rat; D011943:Receptors, Adrenergic, beta; D044006:Receptors, Epoprostenol; D043562:Receptors, G-Protein-Coupled; D011982:Receptors, Prostaglandin; D003094:Collagen; D000242:Cyclic AMP; D000262:Adenylyl Cyclases; C121100:adenylyl cyclase 6