Heterodimerization of Mu Opioid Receptor Protomer with Dopamine D2 Receptor Modulates Agonist-Induced Internalization of Mu Opioid Receptor.

Vasudevan Vasudevan,Fuxe Fuxe,Borroto-Escuela Borroto-Escuela,Huysentruyt Huysentruyt,Saini Saini,Stove Stove

doi:10.3390/biom9080368

Abstract

The interplay between the dopamine (DA) and opioid systems in the brain is known to modulate the additive effects of substances of abuse. On one hand, opioids serve mankind by their analgesic properties, which are mediated via the mu opioid receptor (MOR), a Class A G protein-coupled receptor (GPCR), but on the other hand, they pose a potential threat by causing undesired side effects such as tolerance and dependence, for which the exact molecular mechanism is still unknown. Using human embryonic kidney 293T (HEK 293T) and HeLa cells transfected with MOR and the dopamine D2 receptor (D2R), we demonstrate that these receptors heterodimerize, using an array of biochemical and biophysical techniques such as coimmunoprecipitation (co-IP), bioluminescence resonance energy transfer (BRET1), Fӧrster resonance energy transfer (FRET), and functional complementation of a split luciferase. Furthermore, live cell imaging revealed that D2LR, when coexpressed with MOR, slowed down internalization of MOR, following activation with the MOR agonist [D-Ala2, N-MePhe4, Gly-ol]-enkephalin (DAMGO).

Highlights

For hundreds of years, opioids have been used in the management of pain, mediating their analgesic effect primarily via binding to the mu opioid receptor (MOR) [1,2,3]
Coimmunoprecipitation Indicates that MOR and D2 R Heterodimerize in Transfected HEK 293T Cells
Co-IP results indicate that MOR can heterodimerize with D2S R as well, proving that the interaction sites for the dimer do not lie in the stretch of 29 amino acids of ICL3, unlike reported for D1 R-D2 R heterodimers [38] (Figure S1)

Summary

Introduction

Opioids have been used in the management of pain, mediating their analgesic effect primarily via binding to the mu opioid receptor (MOR) [1,2,3]. MOR, a member of the Class A G protein-coupled receptor (GPCR) subfamily, is activated by both endogenous opioid peptides as well as exogenous opioids [5]. The latter constitute the potent analgesics, which carry the risk of being used as substances of abuse [6,7]. The mechanism of tolerance, defined as the decline in effect of a drug due to its chronic exposure, is not known exactly, it has been linked to receptor desensitization and recruitment of β-arrestin in vivo [8,9,10,11,12]. There are numerous studies that demonstrated that in highly tolerant animals, there was no change in expression

Methods

Results

Discussion

Conclusion