Effects of the ß-agonist, isoprenaline, on the down-regulation, functional responsiveness and trafficking of ß2-adrenergic receptors with N-terminal polymorphisms.
Cell Biol Int
; 36(12): 1171-83, 2012.
Article
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| MEDLINE
| ID: mdl-22938397
ABSTRACT
The ß2-AR (ß2-adrenergic receptor) is an important target for respiratory and CVD (cardiovascular disease) medications. Clinical studies suggest that N-terminal polymorphisms of ß2-AR may act as disease modifiers. We hypothesized that polymorphisms at amino acids 16 and 27 result in differential trafficking and down-regulation of ß2-AR variants following ß-agonist exposure. The functional consequences of the four possible combinations of these polymorphisms in the human ß2-AR (designated ß2-AR-RE, ß2-AR-GE, ß2-AR-RQ and ß2-AR-GQ) were studied using site-directed mutagenesis and recombinant expression in HEK-293 cells (human embryonic kidney cells). Ligand-binding assays demonstrated that after 24 h exposure to 1 µM isoprenaline, isoforms with Arg16 (ß2-AR-RE and ß2-AR-RQ) underwent increased down-regulation compared with isoforms with Gly16 (ß2-AR-GE and ß2-AR-GQ). Consistent with these differences in down-regulation between isoforms, prolonged isoprenaline treatment resulted in diminished cAMP response to subsequent isoprenaline challenge in ß2-AR-RE relative to ß2-AR-GE. Confocal microscopy revealed that the receptor isoforms had similar co-localization with the early endosomal marker EEA1 following isoprenaline treatment, suggesting that they had similar patterns of internalization. None of the isoforms exhibited significant co-localization with the recycling endosome marker Rab11 in response to isoprenaline treatment. Furthermore, we found that prolonged isoprenaline treatment led to a higher degree of co-localization of ß2-AR-RE with the lysosomal marker LAMP1 (lysosome-associated membrane protein 1) compared with that of ß2-AR-GE. Taken together, these results indicate that a mechanism responsible for differential responses of these receptor isoforms to the ß-agonist involves differences in the efficiency with which agonist-activated receptors are trafficked to the lysosomes for degradation, or differences in degradation in the lysosomes.
Texto completo:
1
Colección:
01-internacional
Base de datos:
MEDLINE
Asunto principal:
Polimorfismo Genético
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Regulación hacia Abajo
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Receptores Adrenérgicos beta 2
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Agonistas Adrenérgicos beta
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Transporte de Proteínas
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Isoproterenol
Límite:
Humans
Idioma:
En
Revista:
Cell Biol Int
Año:
2012
Tipo del documento:
Article
País de afiliación:
Estados Unidos