Probing the constitutive activity among dopamine D1 and D5 receptors and their mutants

Bianca Plouffe*, Jean Philippe D'Aoust, Vincent Laquerre, Binhui Liang, Mario Tiberi

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingChapter

11 Citations (Scopus)

Abstract

Dopamine D1 and D5 receptors are prototypical cell-surface seven-transmembrane (TM) G protein-coupled receptors (GPCRs) mediating elevation of intracellular cAMP levels. The high level of constitutive activity of D5 receptor mediating intracellular cAMP production is one of the functional hallmarks distinguishing the closely related D1-like dopaminergic subtypes (D1 and D5). D1-like subtypes share over 80% identity within their TM regions. Thus, D1 and D5 receptors can serve as unparalleled and useful molecular tools to gain structural and mechanistic insights into subtype-specific determinants regulating GPCR constitutive activation and inverse agonism. A method has been developed that relies on the use of transfected human embryonic kidney 293 cells with wild-type (WT), epitope-tagged, chimeric, truncated, and mutant forms of mammalian D1 and D5 receptors using a modified DNA and calcium phosphate precipitation procedure. Receptor expression levels are quantified by a radioligand binding using [ 3 H]-SCH23390, a D1-like selective drug. Regulation of ligand-independent and dependent activity of WT and mutated D1 and D5 receptors is determined by whole cell cAMP assays using metabolic [ 3 H]-adenine labeling and sequential purification radiolabeled nucleotides over Dowex and alumina resin columns. Results on the regulation of D1 and D5 constitutive activity are presented here. Our studies indicate that dopamine-mediated D5 receptor stimulation in a dose-dependent manner is not always detectable, suggesting that D5 receptors can exist in a "locked" constitutively activated state. This "locked" constitutively active state of D5 receptor is not linked to aberrant high receptor expression levels or cell behavior, as D1 receptor function remains essentially unchanged in these cells. In fact, we show that phorbol ester treatment of cells harboring "locked" constitutively active D5 receptors abrogates constitutive activation of D5R to allow its stimulation by dopamine in a dose-dependent manner.

Original languageEnglish
Title of host publicationMethods in Enzymology
PublisherAcademic Press Inc.,U.S.
Pages295-328
Number of pages34
EditionC
DOIs
Publication statusPublished - 01 Jan 2010
Externally publishedYes

Publication series

NameMethods in Enzymology
NumberC
Volume484
ISSN (Print)0076-6879

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology

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