The β2-adrenergic receptor is a prototypical member of a diverse family of G-protein coupled receptors (GPCRs), the largest family of receptors for hormones and drugs. The β2-adrenergic receptor is an important target for medications in asthma and cardiovascular disease. The intracellular location of the β2-adrenergic receptor in tissues is likely to have a significant impact on how the tissues respond to β-agonist medications. For that reason, it is important to understand mechanisms underlying signaling and regulation of the receptor in response to agonists. Thus, method for visualizing β2-adrenergic receptor would be of utility. In the study, described in Chapter II, I characterized a panel of six β2-adrenergic receptor antibodies for their ability to recognize human and rat β2-adrenergic receptor in HEK 293 cells in indirect immunofluorescence assays. We identified one antibody capable of recognizing human but not rat β2-adrenergic receptor, one antibody capable of recognizing rat but not human receptor, and one antibody recognizing both rat and human β2-adrenergic receptors. The antibodies were used to localize β2-adrenergic receptors in primary cultures of rat airway epithelial and smooth muscle cells. In HEK 293 cells, the receptors were localized to the cell surface. In contrast, about half of the receptors were found in intracellular compartment in primary cultures. We anticipate that the antibodies we identified will serve as a valuable tool for studies of expression and trafficking of the β 2-adrenergic receptor in tissues.
N-terminal polymorphisms of the β2-adrenergic receptor consist of substitution of glycine for arginine at amino acid position 16 and substitution of glutamic acid for glutamine at position 27. Studies have shown that N-terminal polymorphisms of the β2-adrenergic receptor may influence therapeutic responses to β-agonists. In my second project, described in Chapter III, I used a recombinant expression system to study the effect of β-agonist on the expression, trafficking and signaling of the β2-adrenergic receptor with N-terminal polymorphisms. In ligand binding assays, I found that β2-adrenergic receptor isoforms were differentially down-regulated as a result of prolonged β-agonist treatment. Importantly, these differences in down-regulation are translated into changes in functional cyclic AMP response. To explore the mechanism of differential down-regulation, a detailed temporal and spatial analysis of trafficking of the YFP-tagged polymorphic receptors was performed. The results of our experiments are consistent with the notion that enhanced down-regulation of isoforms with Arg16 could be due to enhanced traffic of isoforms with Arg16 in lysosomal compartment for degradation. This may provide the basis for differential response to β-agonist therapy in patients.
|Advisor:||Cornett, Lawrence E.|
|School:||University of Arkansas for Medical Sciences|
|School Location:||United States -- Arkansas|
|Source:||DAI-B 70/04, Dissertation Abstracts International|
|Subjects:||Molecular biology, Cellular biology, Physiology|
|Keywords:||Asthma, Beta-agonists, Beta2-adrenergic receptor, Down-regulation, GPCR, Trafficking|
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