Receptor Number and Caveolar Co-localization Determine Receptor Coupling Efficiency to Adenylyl Cyclase

Rennolds S. Ostrom, Caroline Gregorian, Ryan M. Drenan, Yang Xiang, John W. Regan, Paul A. Insel

Research output: Contribution to journalArticle

204 Scopus citations

Abstract

Recent evidence suggests that many signaling molecules localize in microdomains of the plasma membrane, particularly caveolae. In this study, overexpression of adenylyl cyclase was used as a functional probe of G protein-coupled receptor (GPCR) compartmentation. We found that three endogenous receptors in neonatal rat cardiomyocytes couple with different levels of efficiency to the activation of adenylyl cyclase type 6 (AC6), which localizes to caveolin-rich membrane fractions. Overexpression of AC6 enhanced the maximal cAMP response to β1-adrenergic receptor (β 1AR)-selective activation 3.7-fold, to β 2AR-selective activation only 1.6-fold and to prostaglandin E 2 (PGE2) not at all. Therefore, the rank order of efficacy in coupling to AC6 is β1AR > β2AR > prostaglandin E2 receptor (EP2R). β2AR coupling efficiency was greater when we overexpressed the receptor or blocked its desensitization by expressing βARKct, an inhibitor of G protein-coupled receptor kinase activation, but was not significantly greater when cells were treated with pertussis toxin. Assessment of receptor and AC expression indicated co-localization of AC5/6, β1AR, and β 2AR, but not EP2R, in caveolin-rich membranes and caveolin-3 immunoprecipitates, likely explaining the observed activation of AC6 by β2AR subtypes but lack thereof by PGE2. When cardiomyocytes were stimulated with a βAR agonist, β2AR were no longer found in caveolin-3 immunoprecipitates; an effect that was blocked by expression of βARKct. Thus, agonist-induced translocation of β2AR out of caveolae causes a sequestration of receptor from effector and likely contributes to the lower efficacy of β2AR coupling to AC6 as compared with β1AR, which do not similarly translocate. Therefore, spatial co-localization is a key determinant of efficiency of coupling by particular extracellular signals to activation of GPCR-linked effectors.

Original languageEnglish (US)
Pages (from-to)42063-42069
Number of pages7
JournalJournal of Biological Chemistry
Volume276
Issue number45
DOIs
StatePublished - Nov 9 2001

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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