Signaling-Biased and Constitutively Active Dopamine D2 Receptor Variant

Area of Science:

• Neuroscience
• Molecular Biology
• Pharmacology

Background:

• A novel dopamine D2 receptor (D2) mutation, D2-I212F, was identified in a family with a hyperkinetic movement disorder.
• This mutation alters the receptor's interaction with G proteins and arrestins, affecting downstream signaling pathways.
• Understanding the precise molecular mechanisms of this mutation is crucial for comprehending the disorder's pathogenesis.

Purpose of the Study:

• To characterize the functional consequences of the D2-I212F mutation on D2 receptor signaling.
• To investigate the role of G protein-coupled receptor kinase 2 (GRK2) in mediating the mutant receptor's activity.
• To explore the implications of D2-I212F constitutive activity in a relevant physiological context.

Main Methods:

• HEK 293 cell assays to assess G protein (Gαi1, GαoA) and arrestin3 recruitment.
• Measurement of forskolin-stimulated cyclic AMP accumulation.
• Competition binding assays, mouse midbrain slice electrophysiology, and molecular dynamics simulations.

Main Results:

• D2-I212F exhibits enhanced basal activity and higher potency for Gαi1 activation compared to wild-type D2.
• GRK2 influences quinpirole's efficacy for arrestin recruitment to D2-I212F, indicating biased signaling.
• D2-I212F shows increased basal GαoA activation, enhanced inhibition of cAMP, and higher quinpirole affinity, confirming constitutive activity.

Conclusions:

• D2-I212F is a constitutively active and signaling-biased D2 receptor mutant.
• The mutation's pathogenic effects are linked to altered G protein and arrestin interactions.
• Brain region-specific outcomes may depend on the expression levels of G proteins and GRKs.