Functional beta-adrenergic receptor signalling on nuclear membranes in adult rat and mouse ventricular cardiomyocytes.
OBJECTIVE
We sought to determine if different beta-adrenergic receptor (betaAR) subtypes, and their associated signalling machinery, are functionally localized to nuclear membranes.


METHODS
Employing enriched nuclear preparations, we assayed the specific presence of betaAR by measuring 125I-cyanopindolol (CYP) binding, Western blotting, confocal microscopy and functional assays.


RESULTS
Western blots of rat heart nuclear fractions and confocal immunofluorescent analysis of adult rat and mouse ventricular cardiomyocytes displayed the presence of beta 1AR and beta 3AR but, surprisingly, not the beta 2AR on nuclear membranes. Nuclear localization of downstream signalling partners Gs, Gi and adenylyl cyclases II and V/VI was also demonstrated. The functional relevance of nuclear betaAR was shown by receptor-mediated stimulation of adenylyl cyclase activity by isoproterenol but not the beta 3AR-selective agonist CL 316243 in enriched nuclear preparations. We also examined the effect of subtype-selective ligands on the initiation of RNA synthesis in isolated nuclei. Both isoproterenol and another beta 3AR-selective agonist, BRL 37344, increased RNA synthesis which was inhibited by pertussis toxin (PTX). Neither a beta 1AR-selective agonist, xamoterol, nor a beta 2AR-selective agonist, procaterol, was able to stimulate transcription. However, both CGP 20712A and ICI 118,551 blocked isoproterenol-mediated effects to varying extents. PTX treatment also revealed that nuclear betaAR may be coupled to other signalling pathways in addition to Gi, as stimulation under these conditions reduced initiation of transcription below basal levels.


CONCLUSIONS
These results highlight differential subcellular localization for betaAR subtypes and indicate that betaAR may have specific roles in regulating nuclear function in cardiomyocytes.
Boivin
Benoit
B
Centre de recherche, Institut de Cardiologie de Montréal, Canada.
Lavoie
Catherine
C
Vaniotis
George
G
Baragli
Alessandra
A
Villeneuve
Louis-Robert
LR
Ethier
Nathalie
N
Trieu
Phan
P
Allen
Bruce G
BG
Hébert
Terence E
TE
D000262:Adenylyl Cyclases / Q000378:metabolism; D058667:Adrenergic beta-3 Receptor Agonists; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D015153:Blotting, Western / Q000379:methods; D004149:Dioxoles / Q000494:pharmacology; D004983:Ethanolamines / Q000494:pharmacology; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000378:metabolism; D006352:Heart Ventricles; D007093:Imidazoles / Q000494:pharmacology; D020120:Iodocyanopindolol / Q000378:metabolism; D007545:Isoproterenol / Q000494:pharmacology; D051379:Mice; D018613:Microscopy, Confocal / Q000379:methods; D032383:Myocytes, Cardiac / Q000378:metabolism*; D009685:Nuclear Envelope / Q000737:chemistry / Q000378:metabolism*; D037342:Pertussis Toxin / Q000494:pharmacology; D011412:Propanolamines / Q000494:pharmacology; D051381:Rats; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D018342:Receptors, Adrenergic, beta-1 / Q000032:analysis / Q000378:metabolism; D018343:Receptors, Adrenergic, beta-2 / Q000032:analysis / Q000378:metabolism; D022702:Receptors, Adrenergic, beta-3 / Q000032:analysis / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*
D058667:Adrenergic beta-3 Receptor Agonists; D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D004149:Dioxoles; D004983:Ethanolamines; D007093:Imidazoles; D011412:Propanolamines; D011943:Receptors, Adrenergic, beta; D018342:Receptors, Adrenergic, beta-1; D018343:Receptors, Adrenergic, beta-2; D022702:Receptors, Adrenergic, beta-3; C076126:disodium (R,R)-5-(2-((2-(3-chlorophenyl)-2-hydroxyethyl)-amino)propyl)-1,3-benzodioxole-2,3-dicarboxylate; C026777:ICI 118551; C057368:BRL 37344; D020120:Iodocyanopindolol; C049763:CGP 20712A; D037342:Pertussis Toxin; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D019205:GTP-Binding Protein alpha Subunits, Gs; D000262:Adenylyl Cyclases; D007545:Isoproterenol