RGS2 and RGS4 proteins: New modulators of the κ-opioid receptor signaling

Area of Science:

• Molecular Pharmacology
• Cell Signaling
• G protein-coupled receptors

Background:

• Regulators of G protein Signaling (RGS) proteins, particularly RGS4, are known to interact with μ- and δ-opioid receptors.
• The role of RGS proteins in the signaling of the κ-opioid receptor (κ-OR) remains largely undefined.

Purpose of the Study:

• To investigate the interaction between κ-OR and members of the RGS B/R4 subfamily, specifically RGS2 and RGS4.
• To determine the functional consequences of RGS2 and RGS4 interaction with κ-OR on G protein coupling and downstream signaling.

Main Methods:

• Generation of glutathione S-transferase (GST) fusion peptides of the κ-OR carboxyl-terminus (κ-CT).
• Pull-down assays to assess direct interaction between RGS proteins and κ-CT domains.
• Co-precipitation studies in living cells to confirm constitutive and agonist-induced association.
• Functional assays measuring adenylyl cyclase inhibition and ERK1,2 phosphorylation in cells expressing RGS2 and/or RGS4 with κ-OR.

Main Results:

• RGS2 and RGS4 directly bind to distinct domains within the κ-CT.
• RGS2 and RGS4 associate with κ-OR both constitutively and upon activation.
• RGS2 and RGS4 influence the selectivity of G protein coupling for κ-OR.
• Expression of RGS2 and/or RGS4 attenuates κ-agonist-mediated adenylyl cyclase inhibition and ERK1,2 phosphorylation.

Conclusions:

• RGS2 and RGS4 are novel interacting partners of the κ-opioid receptor.
• These RGS proteins play a critical role in negatively regulating κ-OR signaling pathways.
• The findings elucidate a new mechanism for controlling κ-OR G protein coupling selectivity and signal transduction.