Cholesterol-dependent separation of the beta2-adrenergic receptor from its partners determines signaling efficacy: insight into nanoscale organization of signal transduction

J Biol Chem. 2008 Sep 5;283(36):24659-72. doi: 10.1074/jbc.M800778200. Epub 2008 Jun 19.

Abstract

Determining the role of lipid raft nanodomains in G protein-coupled receptor signaling remains fraught by the lack of assays directly monitoring rafts in native membranes. We thus combined extensive biochemical and pharmacological approaches to a nanoscale strategy based on bioluminescence resonance energy transfer (BRET) to assess the spatial and functional influence of cholesterol-rich liquid-ordered lipid nanodomains on beta2 adrenergic receptor (beta2AR) signaling. The data revealed that whereas beta2AR did not partition within liquid-ordered lipid phase, a pool of G protein and adenylyl cyclase (AC) were sequestered in these domains. Destabilization of the liquid-ordered phase by cholesterol depletion led to a lateral redistribution of Galphas and AC that favored interactions between the receptor and its signaling partners as assessed by BRET. This resulted in an increased basal and agonist-promoted beta2AR-stimulated cAMP production that was partially dampened as a result of constitutive protein kinase A-dependent phosphorylation and desensitization of the receptor. This restraining influence of nanodomains on beta2AR signaling was further substantiated by showing that liquid-ordered lipid phase stabilization using caveolin overexpression or increasing membrane cholesterol amount led to an inhibition of beta2AR-associated signaling. Given the emerging concept that clustering of receptors and effectors into signaling platforms contributes to the efficacy and selectivity of signal transduction, our results support a model whereby cholesterol-promoted liquid-ordered lipid phase-embedding Gs and AC allows their lateral separation from the receptor, thus restraining the basal activity and controlling responsiveness of beta2AR signaling machinery within larger signaling platforms.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenylyl Cyclases / metabolism
  • Adrenergic Agonists / pharmacology
  • Caveolins / biosynthesis
  • Cell Line
  • Cholesterol / metabolism*
  • Cyclic AMP-Dependent Protein Kinases / metabolism
  • GTP-Binding Protein alpha Subunits / metabolism
  • Humans
  • Membrane Microdomains / metabolism*
  • Models, Biological*
  • Phosphorylation / drug effects
  • Receptors, Adrenergic, beta-2 / metabolism*
  • Signal Transduction / drug effects
  • Signal Transduction / physiology*

Substances

  • Adrenergic Agonists
  • Caveolins
  • GTP-Binding Protein alpha Subunits
  • Receptors, Adrenergic, beta-2
  • Cholesterol
  • Cyclic AMP-Dependent Protein Kinases
  • Adenylyl Cyclases