Receptor internalization

Fig. 17. The receptor-internalization process via a coated pit in which receptors are internalized and processed in a multistep pathway before being recycled...

The majority of functional assays involve primary signaling. In the case of GPCRs, this involves activation of G-proteins. However, receptors have other behaviors— some of which can be monitored to detect ligand activity. For example, upon stimulation many receptors are desensitized through phosphorylation and subsequently taken into the cell and either recycled back to the cell surface or digested. This process can be monitored by observing ligand-mediated receptor internalization. For... 

Adie, E. J., et al. (2002). A pH-sensitive fluor CypHer 5, used to monitor agonist-induced G-proein coupled receptor internalization in live cells. Bio techniques 33 1152-1157. 

Desensitization describes the rapid signal attenuation in response to stimulation of cells by receptor agonists. Changes in the coupling efficiency of receptors to signal transduction pathways and receptor internalization can account for desensitization and the development of pharmacodynamic tolerance. 

Cheng ZJ, Zhao J, Sun Y, Hu W, Wu YL, Cen B, Wu GX, Pei G (2000) Beta-arrestin differentially regulates the chemokine receptor CXCR4-mediated signaling and receptor internalization, and this implicates multiple interaction sites between beta-arrestin and CXCR4. J Biol Chem 275 2479-2485... 

Orsini MJ, Benovic JL (1998) Characterization of dominant negative arrestins that inhibit beta2-adreneigic receptor internalization by distinct mechanisms. J Biol Chem 273(51) 34616-34622 Paredes MF, Li G, Berger O, Baraban SC, Pleasure SJ (2006) Stromal-derived factor-1 (CXCL12) regulates laminar position of Cajal-Retzius cells in normal and dysplastic brains. J Neurosci 26 9404-9412... 

An assay that produces multiple biological readouts. Most commonly used in relation to the mathematical analysis of an image acquired using an automated microscope whereby analysis algorithms quantify cellular parameters (e.g., number, motility, neurite outgrowth, size, shape) and subcellular events (e.g., receptor internalization, protein translocation, protein expression nuclei shape). 

Orsini MJ, Parent JL, Mundell SJ, Marchese A, Benovic JL. Trafficking of the HIV coreceptor CXCR4 role of arrestins and identification of residues in the C-terminal tail that mediate receptor internalization. J Biol Chem 1999 274(43) 31076-31086. 

Buprenorphine does not cause dependence in humans [96]. Unbke morphine, buprenorphine desensitizes the /< receptor coupling to adenylyl cyclase [80]. The desensitization occurs in the absence of any receptor internalization or downregu-lation [80]. The desensitization of the /x receptor may be the underlying basis for why buprenorphine does not cause a heightened adenylyl cyclase activity in // receptor-responsive cells. Buprenorphine s unique cellular regulation of the // receptor may explain its ability to be a non-addictive analgesic as well as its usefulness in treating opiate dependence. 

Cvejic et al. [133] and Trapaidze et al. [134] have reported that the C-terminus of the 8 receptor is essential for the internalization and downregulation of the receptors. Truncation of the 8 receptor attenuates receptor internalization. Residue Thr353 seems to be selectively involved in the internalization of the receptor, since mutation of this amino acid blocks the internalization process. Recent studies by Chu et al. [135] not only confirm the role of the C-terminus in internalizing the 8 receptor but have shown that clathrin-coated pits are involved in the internalization since a K44I mutant of dynamin I blocks the rapid internalization of the 8 receptor. These studies have identified a structural basis for the differential regulation of the three opiate receptors. 

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