Supersensitivity and Desensitization
Kenneth J. Broadley in Autonomic Pharmacology, 2017
Also present in crude preparations of β-ARK was a factor termed β-arrestin. This is analogous to arrestin, the 48 kDa protein that inactivates rhodopsin kinase in the rhodopsin photoreceptor system. β-ARK is comparable with rhodopsin kinase, the retinal enzyme that phosphorylates and inactivates only the light-bleached form of rhodopsin. Thus, arrestin inhibits transducin, the retinal G protein, from interacting with the phosphorylated rhodopsin. β-Arrestin interacts with the β-ARK phosphorylated receptor leading to enhanced uncoupling from the Gs regulatory protein. Therefore both β-ARK and β-arrestin are required for this agonist-specific phosphorylation and uncoupling process, leading to homologous desensitization. Human β-ARK has now been cloned and sequenced. It also interacts with the βγ-subunits of the G protein by the C-terminal portion of β-ARK. The β-ARK-βγ complex is thereby anchored in the cell membrane and allows for more efficient receptor phosphorylation and desensitization. This would occur when the receptors are activated to release the βτ-subunit and would thus facilitate termination of receptor activation through the phosphorylation process.
Chemokine Receptor Expression and Regulatory Mechanisms
Thomas R. O’Brien in Chemokine Receptors and AIDS, 2019
Desensitization is defined as diminished responsiveness of a signaling system to subsequent stimuli following initial stimulation (48). The mechanism of G-protein-coupled receptor desensitization has been studied in great detail for the visual and adrenergic systems (48, 49). From these studies, two types of desensitization, termed “homologous” and “heterologous,” have been described. Homologous desensitization occurs in receptors in the agonist-occupied state and involves phosphorylation by G-protein-coupled receptor kinases. Several of the G-protein-coupled receptor kinases were identified in leukocytes (50). Homologously phosphorylated receptors associate with members of the arrestin family of proteins which results in a decreased affinity of the receptor for G-proteins and in receptor internalization.
Experimental perturbations to investigate cardiovascular physiology
Neil Herring, David J. Paterson in Levick's Introduction to Cardiovascular Physiology, 2018
When studying receptor agonists, ideally a full dose- response curve should be carried out, but this is often limited by the viability of experimental preparations over time. If a single dose or a few doses only are to be used, it is important to do preliminary experiments to establish that these are appropriate and not subthreshold or supramaximal. Also, when designing experimental protocols with agonists, it should be remembered that continual stimulation can lead to desensitization and eventually internalization of the receptors. An example of this is with the β adrenergic receptor, which after continued stimulation, becomes phos- phorylated by a beta-adrenergic receptor kinase 1 (beta- ARK-1) or G-protein coupled receptor kinase 2. Binding of beta-arrestin-1 then leads to desensitization of the receptor and its internalization via endocytosis. The activity of beta- arrestin-1 and beta-ARK-1 are influenced by the levels of cyclic adenosine monophosphate, the second messenger of the β adrenergic receptor itself.
β-arrestin 2 quenches TLR signaling to facilitate the immune evasion of EPEC
Published in Gut Microbes, 2020
Zijuan Chen, Ruixue Zhou, Yihua Zhang, Doudou Hao, Yu Wang, Shichao Huang, Ningning Liu, Chunmei Xia, Nissan Yissachar, Feng Huang, Yiwei Chu, Dapeng Yan
β-arrestin 2 is distributed in most mammalian tissues and cells and was originally identified as a negative regulator in the desensitization and internalization of heterotrimeric guanine nucleotide-binding protein-coupled receptor (GPCR). After phosphorylation of GPCRs by GPCR kinases (GRKs), β-arrestins translocate from the cytoplasm to the cell membrane and directly interact with the phosphorylated GPCRs, resulting in the dissociation of receptors from heterotrimeric G proteins, which quenches GPCR signaling.19,20 Besides, β-arrestin 2 acts as a scaffold protein by associating with various signaling molecules to change its binding partners’ distribution and modulate their activity, such as Src family kinases, E3 ligase, and MAP kinases.21,22 For example, when stimulated with Ang II, a β-arrestin 2 activator, JNK3 was exported from the nucleus and co-localized with β-arrestin 2 in the endosome, where ASK1 phosphorylated JNK3 in a β-arrestin 2-dependent manner.23 Furthermore, accumulating studies have indicated that β-arrestin 2 plays an important role in regulating immune signaling. For example, β-arrestin 2 interacts with TRAF6 to negatively regulate TLR signaling in innate immunity,24 inhibits insulin resistance by regulating Src and Akt signaling, and interacts with KIR2DL1 in NK cells to facilitate inhibitory signaling.25 These results suggest that β-arrestin 2 functions in various signaling pathways by interacting with different molecules. However, whether β-arrestin 2 plays roles in host and microbe interaction is unclear.
Opioid MOP receptor agonists in late-stage development for the treatment of postoperative pain
Published in Expert Opinion on Pharmacotherapy, 2022
Qiu Qiu, Joshua CJ Chew, Michael G Irwin
Tolerance is the reduced effect of a drug after repeated administration, or the requirement for dose escalation to achieve the same effect. Tolerance is well described with the chronic use of opioids but can also occur in the acute setting. The occurrence of acute tolerance is clinically, a function of dose, time, and fractional receptor occupancy [36]. After activation, the MOP receptor is phosphorylated by kinases including GPCR kinase. The phosphorylated receptor subsequently binds to β-arrestin. β-arrestin mediates the formation of endocytic complexes and receptor internalization [15]. Reduction in available receptors in the cell membrane results in pharmacological tolerance. A reduction in the recruitment of β-arrestin may lead to decreased tolerance and this is a therapeutic target for new drugs [37]. Moreover, the NOP receptor may also play a role in tolerance, with studies reporting attenuated tolerance with NOP receptor agonism and antagonism [38, 39].
In vitro prediction of in vivo pseudo-allergenic response via MRGPRX2
Published in Journal of Immunotoxicology, 2021
Linu M. John, Charlotte M. Dalsgaard, Claus B. Jeppesen, Kilian W. Conde-Frieboes, Katrine Baumann, Niels P. H. Knudsen, Per S. Skov, Birgitte S. Wulff
The commercially-available PathHunter eXpress MRGPRX2 CHO-K1 β-Arrestin GPCR assay (DiscoverX, Fremont, CA) was used to evaluate the potency of test compounds. This assay measured the activation MRGPRX2 by detecting β-arrestin recruitment using a homogeneous, gain-of-signal assay based on Enzyme Fragment Complementation (EFC) technology. The assay employs a β-galactosidase (β-gal) enzyme split into two fragments, the Enzyme Donor (ED) and Enzyme Acceptor (EA). Independently these fragments have no β-gal activity; however, when brought together in in solution, they form an active β-gal enzyme. Since β-arrestin recruitment occurs independent of G-protein coupling, the assay provided a direct measure of receptor activation. As such, MRGPRX2 is tagged with the small fragment of β-gal (a low-affinity version of ED) and co-expressed in cells stably expressing β-arrestin tagged with EA. Activation of MRGPRX2 stimulated binding of β-arrestin to the tagged GPCR, forcing complementation of ED and EA, resulting in the formation of an active β-gal enzyme. The resulting active enzyme hydrolyzed substrate present in the PathHunter detection reagent to generate light.
Related Knowledge Centers
- G Protein
- Photoreceptor Cell
- Protein
- Rhodopsin
- Signal Transduction
- Phosphorylation
- G Protein-Coupled Receptor
- Serine/Threonine-Specific Protein Kinase
- G Protein-Coupled Receptor Kinase
- Arrestin Beta 2