The Other Side of Opioid Receptor Signalling: Regulation by Protein-Protein Interaction

Opiate drugs mediate their analgesic, euphoriant, and rewarding effects by activating opioid receptors. Pharmacological and molecular studies have demonstrated the existence of three opioid receptor subtypes, mu, delta, and kappa-that couple predominantly to Gi/Go types of G proteins to regulate the activity of a diverse array of effector systems. Ample experimental evidence has demonstrated that these receptors can physically interact with a variety of accessory proteins, confirming that signal transduction of the opioid receptors is not restricted to heterotrimeric G protein activation. Such interactions can alter the effectiveness of agonist-driven cell signalling, determine the signals generated and alter the trafficking, targeting, fine tuning and cellular localization of these receptors by providing a scaffold that links the receptors to the cytoskeletal network. The current review will summarize opioid receptor interacting partners and their role as currently understood. Increasing knowledge of the mechanisms by which these interactions are regulated is expected to address problems related to phenomena such as pain perception, tolerance and dependence that occur upon chronic opiate administration and define whether disruption of such interactions may contribute to the development of novel therapeutic strategies.