title: A four amino acid deletion polymorphism in the third intracellular loop of the human alpha 2C-adrenergic receptor confers impaired coupling to multiple effectors.
abstract: The alpha(2)-adrenergic receptors (alpha(2)ARs) play a critical role in modulating neurotransmitter release in the central and peripheral sympathetic nervous systems. A polymorphism of the alpha(2)AR subtype localized to human chromosome 4 (the pharmacologic alpha(2C)AR subtype) within an intracellular domain has been identified in normal individuals. The polymorphism (denoted Del322-325) is because of an in-frame 12-nucleic acid deletion encoding a receptor lacking Gly-Ala-Gly-Pro in the third intracellular loop. To delineate the functional consequences of this structural alteration, Chinese hamster ovary cells were permanently transfected with constructs encoding wild-type human alpha(2C)AR and the polymorphic receptor. The Del322-325 variant had decreased high affinity agonist binding (K(H) = 7.3 +/- 0.95 versus 3.7 +/- 0.43 nm; %R(H) = 31 +/- 4 versus 49 +/- 4) compared with wild-type indicating impaired formation of the agonist-receptor-G protein complex. The polymorphic receptor displayed markedly depressed epinephrine-promoted coupling to G(i), inhibiting adenylyl cyclase by 10 +/- 4.3% compared with 73 +/- 2.4% for wild-type alpha(2C)AR. This also was so for the endogenous ligand norepinephrine and full and partial synthetic agonists. Depressed agonist-promoted coupling to the stimulation of MAP kinase ( approximately 71% impaired) and inositol phosphate production ( approximately 60% impaired) was also found with the polymorphic receptor. The Del322-325 receptor was approximately 10 times more frequent in African-Americans compared with Caucasians (allele frequencies 0.381 versus 0.040). Given this significant loss of function phenotype in several signal transduction cascades and the skewed ethnic prevalence, Del322-325 represents a pharmacoethnogenetic locus and may also be the basis for interindividual variation in cardiovascular or central nervous system pathophysiology.
authors.affiliation: Departments of Medicine and Molecular Genetics, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267, USA.
authors.forename: K M
authors.initials: KM
authors.lastname: Small
authors.forename: S L
authors.initials: SL
authors.lastname: Forbes
authors.forename: F F
authors.initials: FF
authors.lastname: Rahman
authors.forename: K M
authors.initials: KM
authors.lastname: Bridges
authors.forename: S B
authors.initials: SB
authors.lastname: Liggett
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000378:metabolism*; D000595:Amino Acid Sequence; D000596:Amino Acids / Q000235:genetics*; D000818:Animals; D001483:Base Sequence; D006224:Cricetinae; D017931:DNA Primers; D006801:Humans; D008969:Molecular Sequence Data; D011110:Polymorphism, Genetic; D011485:Protein Binding; D018341:Receptors, Adrenergic, alpha-2 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017384:Sequence Deletion; D015398:Signal Transduction
chemical_list: C547774:ADRA2C protein, human; D000316:Adrenergic alpha-Agonists; D000596:Amino Acids; D017931:DNA Primers; D018341:Receptors, Adrenergic, alpha-2