title: Relationship between internalization and mRNA decay in down-regulation of recombinant type 1 angiotensin II receptor (AT1) expression in smooth muscle cells.
abstract: In vascular smooth muscle cells, the hormone angiotensin II is thought to cause internalization of the seven-transmembrane domain type 1 angiotensin II receptor (AT1-R) but it also suppresses expression of the receptor mRNA. As for similarly regulated members of this gene superfamily, the relative roles of these processes in receptor down-regulation are not well understood. In this study a recombinant AT1-R mRNA was synthesized in A7r5 vascular smooth muscle cells from a tetracycline-suppressible promoter using a retroviral vector system. Angiotensin II induces a profound internalization of the cell surface AT1-R protein but has no effect on steady-state AT1-R mRNA levels. Shortly after either bolus or prolonged dosing with angiotensin II, cell surface AT1-R expression recovers, indicating the existence of a significant restorative externalization pathway. The extent of this recovery is attenuated markedly when transcription of the recombinant AT1-R gene is suppressed by cotreatment of the cells with anhydrotetracycline. Although agonist-stimulated internalization appears to contribute directly to a loss of AT1-R protein, these observations provide direct evidence that a reduction in AT1-R mRNA content plays a significant role in sustained AT1-R down-regulation.
authors.affiliation: Department of Pharmacology, Graduate Division of Biological and Biomedical Sciences, Emory University School of Medicine, Atlanta, Georgia, USA.
authors.forename: B
authors.initials: B
authors.lastname: Adams
authors.forename: T S
authors.initials: TS
authors.lastname: Obertone
authors.forename: X
authors.initials: X
authors.lastname: Wang
authors.forename: T J
authors.initials: TJ
authors.lastname: Murphy
mesh_terms: D000804:Angiotensin II / Q000378:metabolism; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D015536:Down-Regulation; D004622:Embryo, Mammalian / Q000166:cytology; D005822:Genetic Vectors / Q000235:genetics; D007150:Immunohistochemistry; D007700:Kinetics; D009131:Muscle, Smooth, Vascular / Q000378:metabolism* / Q000502:physiology; D010587:Phagocytosis; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D044140:Receptor, Angiotensin, Type 1; D044139:Receptor, Angiotensin, Type 2; D011945:Receptors, Angiotensin / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D012190:Retroviridae / Q000235:genetics; D013752:Tetracycline / Q000494:pharmacology
chemical_list: D012333:RNA, Messenger; D044140:Receptor, Angiotensin, Type 1; D044139:Receptor, Angiotensin, Type 2; D011945:Receptors, Angiotensin; D011994:Recombinant Proteins; D000804:Angiotensin II; D013752:Tetracycline