| Autor: |
Rodriguez-Contreras D; Research Service, VA Portland Health Care System, and Department of Behavioral Neuroscience, Oregon Health & Science University, Portland, Oregon 97239, United States., Condon AF; Vollum Institute, Oregon Health & Science University, Portland, Oregon 97239, United States., Buck DC; Research Service, VA Portland Health Care System, Portland, Oregon 97239, United States., Asad N; New York University Abu Dhabi, Saadiyat Island, PO Box 129188, Abu Dhabi, United Arab Emirates., Dore TM; New York University Abu Dhabi, Saadiyat Island, PO Box 129188, Abu Dhabi, United Arab Emirates., Verbeek DS; Expertise Center Movement Disorders and Department of Genetics, University of Groningen, 9700 AB Groningen, The Netherlands., Tijssen MAJ; Expertise Center Movement Disorders and Department of Neurology, University of Groningen, 9700 AB Groningen, The Netherlands., Shinde U; Department of Chemical Physiology & Biochemistry, Oregon Health & Science University, Portland, Oregon 97239, United States., Williams JT; Vollum Institute, Oregon Health & Science University, Portland, Oregon 97239, United States., Neve KA; Research Service, VA Portland Health Care System, and Department of Behavioral Neuroscience, Oregon Health & Science University, Portland, Oregon 97239, United States. |
| Abstrakt: |
A dopamine D2 receptor mutation was recently identified in a family with a novel hyperkinetic movement disorder. Compared to the wild type D2 receptor, the novel allelic variant D2-I 212 F activates a Gα i1 β 1 γ 2 heterotrimer with higher potency and modestly enhanced basal activity in human embryonic kidney (HEK) 293 cells and has decreased capacity to recruit arrestin3. We now report that omitting overexpressed G protein-coupled receptor kinase-2 (GRK2) decreased the potency and efficacy of quinpirole for arrestin recruitment. The relative efficacy of quinpirole for arrestin recruitment to D2-I 212 F compared to D2-WT was considerably lower without overexpressed GRK2 than with added GRK2. D2-I 212 F exhibited higher basal activation of Gα oA than Gα i1 but little or no increase in the potency of quinpirole relative to D2-WT. Other signs of D2-I 212 F constitutive activity for G protein-mediated signaling, in addition to basal activation of Gα i/o , were enhanced basal inhibition of forskolin-stimulated cyclic AMP accumulation that was reversed by the inverse agonists sulpiride and spiperone and a ∼4-fold increase in the apparent affinity of D2-I 212 F for quinpirole, determined from competition binding assays. In mouse midbrain slices, inhibition of tonic current by the inverse agonist sulpiride in dopamine neurons expressing D2-I 212 F was consistent with our hypothesis of enhanced constitutive activity and sensitivity to dopamine relative to D2-WT. Molecular dynamics simulations with D2 receptor models suggested that an ionic lock between the cytoplasmic ends of the third and sixth α-helices that constrains many G protein-coupled receptors in an inactive conformation spontaneously breaks in D2-I 212 F. Overall, these results confirm that D2-I 212 F is a constitutively active and signaling-biased D2 receptor mutant and also suggest that the effect of the likely pathogenic variant in a given brain region will depend on the nature of G protein and GRK expression. |
