The subtleties of µ-opioid receptor phosphorylation

Abstract

The link between µ-opioid receptor phosphorylation and function is of critical importance to our understanding of the mechanisms underlying tolerance to opioid drugs. Increasingly sophisticated techniques are needed to assess the phosphorylation status of GPCRs, such as the use of phosphosite-specific antibodies that can monitor the kinetics of phosphorylation and dephosphorylation of individual residues in a receptor. Here the use of phosphosite-specific antibodies, raised against phosphorylated residues in the COOH-terminus of the µ-opioid receptor is discussed, along with some of the important findings that this approach has so far revealed. These include the finding that the µ-opioid receptor is constitutively phosphorylated, and that upon agonist removal it undergoes dephosphorylation equally well whether it is at the cell surface or internalized in endosomes. Thus already these phosphosite-specific antibodies are providing important new information about µ-opioid receptor function and the actions of opioid drugs.

Linked article: This article is a commentary on Doll et al., pp. 298-307 of this issue. To view this paper visit http://dx.doi.org/10.1111/j.1476-5381.2011.01382.x.

Figure 1

Diagrammatic representation of the rat µ-opioid receptor with the amino acid sequence of the intracellular COOH-terminus shown. The three amino acids against which phosphosite-specific antibodies were raised are shown in red and numbered. Other serine and threonine residues in the COOH-terminus are shown as bold and in black.