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Beta-arrestin-dependent formation of beta2 adrenergic receptor-Src protein kinase complexes
L M Luttrell1, S S Ferguson, Y Daaka
1Howard Hughes Medical Institute and Department of Medicine, Duke University Medical Center, Durham, NC 27710, USA.
Abstract:
The Ras-dependent activation of mitogen-activated protein (MAP) kinase pathways by many receptors coupled to heterotrimeric guanine nucleotide binding proteins (G proteins) requires the activation of Src family tyrosine kinases. Stimulation of beta2 adrenergic receptors resulted in the assembly of a protein complex containing activated c-Src and the receptor. Src recruitment was mediated by beta-arrestin, which functions as an adapter protein, binding both c-Src and the agonist-occupied receptor. beta-Arrestin 1 mutants, impaired either in c-Src binding or in the ability to target receptors to clathrin-coated pits, acted as dominant negative inhibitors of beta2 adrenergic receptor-mediated activation of the MAP kinases Erk1 and Erk2. These data suggest that beta-arrestin binding, which terminates receptor-G protein coupling, also initiates a second wave of signal transduction in which the "desensitized" receptor functions as a critical structural component of a mitogenic signaling complex.
Insights
Beta-arrestin acts as an adapter protein, recruiting Src tyrosine kinases to activated beta2 adrenergic receptors. This interaction is crucial for initiating mitogen-activated protein (MAP) kinase signaling pathways.
Area of Science:
- Cellular signaling
- Molecular biology
- Biochemistry
Background:
- Mitogen-activated protein (MAP) kinase pathways are activated by receptors coupled to G proteins.
- Activation of these pathways often requires Src family tyrosine kinases.
- Beta2 adrenergic receptors are G protein-coupled receptors involved in various cellular responses.
Purpose of the Study:
- To investigate the role of beta-arrestin in the activation of MAP kinase pathways by beta2 adrenergic receptors.
- To elucidate the mechanism by which Src family kinases are recruited to these receptors.
- To understand the function of the "desensitized" receptor in signal transduction.
Main Methods:
- Stimulation of beta2 adrenergic receptors in cells.
- Analysis of protein complex assembly using techniques like co-immunoprecipitation.
- Utilizing dominant-negative mutants of beta-arrestin to inhibit specific interactions.
- Measuring the activation of MAP kinases Erk1 and Erk2.
Main Results:
- Stimulation of beta2 adrenergic receptors led to the formation of a protein complex including activated c-Src and the receptor.
- Beta-arrestin was identified as an adapter protein mediating the recruitment of c-Src to the agonist-occupied receptor.
- Mutants of beta-arrestin that impaired c-Src binding or receptor targeting inhibited beta2 adrenergic receptor-mediated MAP kinase activation.
- These findings indicate that beta-arrestin binding initiates a second signaling wave.
Conclusions:
- Beta-arrestin binding to G protein-coupled receptors, while terminating G protein coupling, initiates a distinct mitogenic signaling pathway.
- The "desensitized" receptor, bound by beta-arrestin, serves as a scaffold for the assembly of a mitogenic signaling complex involving Src tyrosine kinases.
- This study reveals a novel role for beta-arrestin in coupling receptor desensitization to the activation of Ras-MAP kinase pathways via Src family kinases.