title: Inhibition of beta-adrenergic receptor trafficking in adult cardiocytes by MAP4 decoration of microtubules.
abstract: Decreased beta-adrenergic receptor (beta-AR) number occurs both in animal models of cardiac hypertrophy and failure and in patients. beta-AR recycling is an important mechanism for the beta-AR resensitization that maintains a normal complement of cell surface beta-ARs. We have shown that 1) in severe pressure overload cardiac hypertrophy, there is extensive microtubule-associated protein 4 (MAP4) decoration of a dense microtubule network; and 2) MAP4 microtubule decoration inhibits muscarinic acetylcholine receptor recycling in neuroblastoma cells. We asked here whether MAP4 microtubule decoration inhibits beta-AR recycling in adult cardiocytes. [(3)H]CGP-12177 was used as a beta-AR ligand, and feline cardiocytes were isolated and infected with adenovirus containing MAP4 (AdMAP4) or beta-galactosidase (Adbeta-gal) cDNA. MAP4 decorated the microtubules extensively only in AdMAP4 cardiocytes. beta-AR agonist exposure reduced cell surface beta-AR number comparably in AdMAP4 and Adbeta-gal cardiocytes; however, after agonist withdrawal, the cell surface beta-AR number recovered to 78.4 +/- 2.9% of the pretreatment value in Adbeta-gal cardiocytes but only to 56.8 +/- 1.4% in AdMAP4 cardiocytes (P < 0.01). This result was confirmed in cardiocytes isolated from transgenic mice having cardiac-restricted MAP4 overexpression. In functional terms of cAMP generation, beta-AR agonist responsiveness of AdMAP4 cells was 47% less than that of Adbeta-gal cells. We conclude that MAP4 microtubule decoration interferes with beta-AR recycling and that this may be one mechanism for beta-AR downregulation in heart failure.
authors.affiliation: Gazes Cardiac Research Institute, Cardiology Division, Medical University of South Carolina, and Department of Veterans Affairs Medical Center, Charleston, South Carolina 29403, USA.
authors.forename: Guangmao
authors.initials: G
authors.lastname: Cheng
authors.forename: Fei
authors.initials: F
authors.lastname: Qiao
authors.forename: Thomas N
authors.initials: TN
authors.lastname: Gallien
authors.forename: Dhandapani
authors.initials: D
authors.lastname: Kuppuswamy
authors.forename: George
authors.initials: G
authors.lastname: Cooper
mesh_terms: D000256:Adenoviridae / Q000235:genetics; D000318:Adrenergic beta-Agonists / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D002415:Cats; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D015536:Down-Regulation / Q000502:physiology; D005260:Female; D015870:Gene Expression; D018014:Gene Transfer Techniques; D006352:Heart Ventricles / Q000166:cytology / Q000378:metabolism; D006801:Humans; D008297:Male; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000235:genetics* / Q000378:metabolism*; D008870:Microtubules / Q000378:metabolism*; D009206:Myocardium / Q000166:cytology / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000166:cytology / Q000378:metabolism*; D011412:Propanolamines / Q000378:metabolism / Q000494:pharmacology; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D014316:Tritium
chemical_list: D000318:Adrenergic beta-Agonists; D008869:Microtubule-Associated Proteins; D011412:Propanolamines; D011943:Receptors, Adrenergic, beta; D014316:Tritium; D000242:Cyclic AMP; C033394:CGP 12177