Abstract
We compared the phosphorylation and internalization properties of constitutively active alpha-1b adrenergic receptor (AR) mutants carrying mutations in two distant receptor domains, i.e., at A293 in the distal part of the third intracellular loop and at D142 of the DRY motif lying at the end of the third transmembrane domain. For the A293E and A293I mutants the levels of agonist-independent phosphorylation were 150% and 50% higher than those of the wild-type alpha-1b AR, respectively. On the other hand, for the constitutively active D142A and D142T mutants, the basal levels of phosphorylation were similar to those of the wild-typealpha-1b AR and did not appear to be further stimulated by epinephrine. Overexpression of the guanyl nucleotide binding regulatory protein-coupled receptor kinase GRK2 further increases the basal phosphorylation of the A293E mutant, but not that of D142A mutant. Both the wild-type alpha-1b AR and the A293E mutant could undergo β-arrestin-mediated internalization. The epinephrine-induced internalization of the constitutively active A293E mutant was significantly higher than that of the wild-typealpha-1b AR. In contrast, the D142A mutant was impaired in its ability to interact with β-arrestin and to undergo agonist-induced internalization. Interestingly, a double mutant A293E/D142A retained very high constitutive activity and regulatory properties of both the A293E and D142A receptors. These findings demonstrate that two constitutively activating mutations occurring in distant receptor domains of the alpha-1b AR have divergent effects on the regulatory properties of the receptor.
Footnotes
- Received May 29, 1998.
- Accepted October 30, 1998.
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Send reprint requests to: Dr. Susanna Cotecchia, Institut de Pharmacologie et de Toxicologie. 27, Rue du Bugnon, Faculté de Médecine, 1005 Lausanne, Switzerland. E-mail:susanna.cotecchia{at}ipharm.unil.ch
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This work was supported by Fonds National Suisse de la Recherche Scientifique Grant 31–51043.97 and by European Community Grant BMH4-CT97–2152.
- The American Society for Pharmacology and Experimental Therapeutics
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