title: Receptor subtype-induced targeting and subtype-specific internalization of human alpha(2)-adrenoceptors in PC12 cells.
abstract: The three alpha(2)-adrenergic receptor subtypes have distinct tissue distributions, desensitization properties, and, in some cell types, subtype-specific subcellular localization and trafficking properties. The subtypes also differ in their neuronal physiology. Therefore, we have investigated the localization and targeting of human alpha(2)-adrenoceptors (alpha(2)-AR) in PC12 cells, which were transfected to express the alpha(2)-AR subtypes A, B, and C. Inspection of the receptors by indirect immunofluorescence and confocal microscopy showed that alpha(2A)-AR were mainly targeted to the tips of the neurites, alpha(2B)-AR were evenly distributed in the plasma membrane, and alpha(2C)-AR were mostly located in an intracellular perinuclear compartment. After agonist treatment, alpha(2A)- and alpha(2B)-AR were internalized into partly overlapping populations of intracellular vesicles. Receptor subtype-specific changes in PC12 cell morphology were also discovered: expression of alpha(2A)-AR, but not of alpha(2B)- or alpha(2C)-AR, induced differentiation-like changes in cells not treated with NGF. Also alpha(2B)-AR were targeted to the tips of neurites when they were coexpressed in the same cells with alpha(2A)-AR, indicating that the targeting of receptors to the tips of neurites is a consequence of a change in PC12 cell membrane protein trafficking that the alpha(2A)-subtype induces. The marked agonist-induced internalization of alpha(2A)-AR observed in both nondifferentiated and differentiated PC12 cells contrasts with earlier results from non-neuronal cells and points out the importance of the cellular environment for receptor endocytosis and trafficking. The targeting of alpha(2A)-AR to nerve terminals in PC12 cells is in line with the putative physiological role of this receptor subtype as a presynaptic autoreceptor.
authors.affiliation: Department of Pharmacology, University of Turku, FIN-20520 Turku, Finland.
authors.forename: T
authors.initials: T
authors.lastname: Olli-Lähdesmäki
authors.forename: J
authors.initials: J
authors.lastname: Kallio
authors.forename: M
authors.initials: M
authors.lastname: Scheinin
mesh_terms: D000317:Adrenergic alpha-Antagonists / Q000493:pharmacokinetics; D000818:Animals; D002454:Cell Differentiation; D002462:Cell Membrane / Q000502:physiology* / Q000648:ultrastructure; D018076:DNA, Complementary; D019084:Fluorescent Antibody Technique, Indirect; D006801:Humans; D019329:Idazoxan / Q000031:analogs & derivatives / Q000493:pharmacokinetics; D018613:Microscopy, Confocal; D016501:Neurites / Q000502:physiology* / Q000648:ultrastructure; D016716:PC12 Cells; D051381:Rats; D018341:Receptors, Adrenergic, alpha-2 / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D011994:Recombinant Proteins / Q000032:analysis / Q000096:biosynthesis; D014162:Transfection
chemical_list: C547768:ADRA2A protein, human; C547771:ADRA2B protein, human; C547774:ADRA2C protein, human; D000317:Adrenergic alpha-Antagonists; D018076:DNA, Complementary; D018341:Receptors, Adrenergic, alpha-2; D011994:Recombinant Proteins; C058525:2-methoxyidazoxan; D019329:Idazoxan