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Heterodimers of α1B- and α1D-Adrenergic Receptors Form a Single Functional Entity

Heterologous expression of α 1D -adrenergic receptors (α 1D -ARs) in most cell types results in intracellular retention and little or no functionality. We showed previously that heterodimerization with α 1B -ARs promotes surface localization of α 1D -ARs. Here, we report that the α 1B -/α 1D -...

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Bibliographic Details
Published in:Molecular pharmacology 2006-01, Vol.69 (1), p.45
Main Authors: Chris Hague, Sarah E. Lee, Zhongjian Chen, Steven C. Prinster, Randy A. Hall, Kenneth P. Minneman
Format: Article
Language:English
Online Access:Get full text
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Summary:Heterologous expression of α 1D -adrenergic receptors (α 1D -ARs) in most cell types results in intracellular retention and little or no functionality. We showed previously that heterodimerization with α 1B -ARs promotes surface localization of α 1D -ARs. Here, we report that the α 1B -/α 1D -AR interaction has significant effects on the pharmacology and signaling of the receptors, in addition to the effects on trafficking described previously. Upon coexpression of α 1B -ARs and epitope-tagged α 1D -ARs in both human embryonic kidney 293 and DDT 1 MF-2 cells, α 1D -AR binding sites were not detectable with the α 1D -AR selective antagonist 8-[2-(4-(2-methoxyphenyl)piperazin-1-yl)ethyl]-8-azaspiro[4,5]decane-7,9-dione (BMY 7378), despite the ability to detect α 1D -AR protein using confocal microscopy, immunoprecipitation, and a luminometer cell-surface assay. However, the α 1B -AR-selective mutant F18A conotoxin showed a striking biphasic inhibition in α 1B /α 1D -AR-expressing cells, revealing that α 1D -ARs were expressed but did not bind BMY 7378 with high affinity. Studies of norepinephrine-stimulated inositol phosphate formation showed that maximal responses were greatest in α 1B /α 1D -AR-coexpressing cells. Stable coexpression of an uncoupled mutant α 1B -AR (Δ12) with α 1D -ARs resulted in increased responses to norepinephrine. However, Schild plots for inhibition of norepinephrine-stimulated inositol phosphate formation showed a single low-affinity site for BMY 7378. Thus, our findings suggest that α 1B /α 1D -AR heterodimers form a single functional entity with enhanced functional activity relative to either subtype alone and a novel pharmacological profile. These data may help to explain why α 1D -ARs are often pharmacologically undetectable in native tissues when they are coexpressed with α 1B -ARs.
ISSN:0026-895X
1521-0111
DOI:10.1124/mol.105.014985