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beta -Arrestins regulate protease-activated receptor-1 desensitization but not internalization or Down-regulation
May M Paing1, Amy B Stutts, Trudy A Kohout
1Department of Pharmacology, School of Medicine, University of North Carolina at Chapel Hill, North Carolina 27599-7365, USA.
The Journal of Biological Chemistry
|November 6, 2001
Summary
Beta-arrestins differentially regulate G protein-coupled receptor (GPCR) desensitization, with beta-arrestin 1 being crucial for protease-activated receptor-1 (PAR1) desensitization. PAR1 internalization occurs via a novel phosphorylation-dependent, beta-arrestin-independent pathway.
Area of Science:
- Cell Biology
- Molecular Pharmacology
- Signal Transduction
Background:
- Beta-arrestins (betaarr1 and betaarr2) bind phosphorylated G protein-coupled receptors (GPCRs), mediating desensitization and internalization.
- Protease-activated receptor-1 (PAR1), a thrombin-activated GPCR, undergoes phosphorylation critical for its desensitization and internalization, but the role of beta-arrestins in PAR1 trafficking and signaling remains unclear.
Purpose of the Study:
- To investigate the role of beta-arrestin isoforms in the desensitization and internalization of protease-activated receptor-1 (PAR1).
- To elucidate the specific contribution of betaarr1 and betaarr2 to PAR1 signaling and trafficking pathways.
Main Methods:
- Utilized mouse embryonic fibroblasts (MEFs) genetically deficient in beta-arrestin isoforms (betaarr1, betaarr2, or both) to study PAR1 signaling and trafficking.
- Compared PAR1 desensitization and internalization in knockout MEFs versus wild-type cells.
- Examined the internalization of a PAR1 cytoplasmic tail mutant defective in phosphorylation.
Main Results:
- PAR1 desensitization was significantly impaired in MEFs lacking both betaarr1 and betaarr2, and notably, also in cells lacking only betaarr1.
- Despite the impairment in desensitization, PAR1 internalization and degradation occurred normally in betaarr1/betaarr2 double knockout cells via a dynamin- and clathrin-dependent pathway.
- A phosphorylation-defective PAR1 mutant failed to internalize in both wild-type and beta-arrestin knockout cells, indicating a distinct internalization mechanism.
Conclusions:
- Individual beta-arrestin isoforms differentially regulate GPCR desensitization, with betaarr1 playing a key role in PAR1 desensitization.
- PAR1 utilizes a novel phosphorylation-dependent internalization pathway that is independent of beta-arrestins, involving clathrin-coated pits.
- These findings reveal a distinct mechanism for GPCR internalization that diverges from beta-arrestin-mediated pathways.