Folding Efficiency Is Rate-limiting in Dopamine D4 Receptor Biogenesis

Kathleen Van Craenenbroeck,Stewart D Clark,Michael J Cox,James N Oak,Fang Liu,Hubert H.M Van Tol

doi:10.1074/jbc.m414043200

Kathleen Van Craenenbroeck, Stewart D Clark + Show 4 more

Open Access

https://doi.org/10.1074/jbc.m414043200

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Abstract

Dopamine receptors are G protein-coupled receptors that are critically involved in locomotion, reward, and cognitive processes. The D2 class of dopamine receptors (DRD2, -3, and -4) is the target for antipsychotic medication. DRD4 has been implicated in cognition, and genetic studies have found an association between a highly polymorphic repeat sequence in the human DRD4 coding region and attention deficit hyperactivity disorder. Using DRD4 as a model, we show that antipsychotics can function as potent pharmacological chaperones up-regulating receptor expression and can also rescue a non-functional DRD4 folding mutant. This chaperone-mediated up-regulation involves reduced degradation by the 26 S proteasome; likely via the stabilization of newly synthesized receptor in the endoplasmic reticulum. Dopamine itself can function as a chaperone when shuttled into the cell by means of the dopamine transporter. Furthermore, different repeat variants of DRD4 display differential sensitivity to this chaperone effect. These data suggest that folding efficiency may be rate-limiting for dopamine receptor biogenesis and that this efficiency differs between receptor variants. Consequently, the clinical profile of dopaminergic ligands, including antipsychotics, may include their ability to serve as pharmacological chaperones.

Highlights

Dopamine receptors are G protein-coupled receptors that are critically involved in locomotion, reward, and cognitive processes
Increased DRD4 Expression by Chemical Chaperones—It has become clear that several chemicals such as glycerol and dimethyl sulfoxide (Me2SO) can act as chemical chaperones that assist the folding of wild-type and mutant proteins, including receptors, allowing them to achieve a functional state [5, 6, 21]
Increased DRD4 Expression by Pharmacological Chaperones—In light of the data obtained with the chemical chaperones, we investigated whether DRD4 ligands are effective as pharmacological chaperones

Summary

Introduction

Dopamine receptors are G protein-coupled receptors that are critically involved in locomotion, reward, and cognitive processes. Increased DRD4 Expression by Chemical Chaperones—It has become clear that several chemicals such as glycerol and dimethyl sulfoxide (Me2SO) can act as chemical chaperones that assist the folding of wild-type and mutant proteins, including receptors, allowing them to achieve a functional state [5, 6, 21]. Treatment of DRD4 expressing cells with the agonist quinpirole (10 ␮M, 16 h) resulted in an increased expression of the receptor as measured by ligand binding (Bmax, 719 Ϯ 60 versus 1587 Ϯ 66 fmol of receptor/mg of membrane protein).

Results

Conclusion