Date of Award
Bachelor of Science (B.S.) in Biochemistry and University Honors
Dopamine -- Receptors -- Physiological effect, Central Nervous System -- Effect of dopamine on, G proteins -- Receptors
G protein-dependent and independent signaling pathways perform crucial roles in dopamine-related physiological and pathological processes. A pivotal role of dopamine in the CNS is the control of locomotion; disruption to dopaminergic systems, such as reduced striatal D2 receptor availability, contributes to the development of movement disorders. Affected members of a family with dystonia, a movement disorder, are heterozygous for a SNP in exon 4 of D2DR (c.634A>T p.I212F), a missense variant located within the third intracellular loop; specifically, the variation is in the middle of a short stretch of residues that have been found to be critical for binding of arrestin and several other dopamine receptor-interacting proteins. The comparative actions between D2-WT and D2-I212F were analyzed in their effects on both the G protein-mediated pathway and the arrestin3 pathway. It was shown that the D2-I212F variant was only 34% as effective as D2-WT at recruiting arrestin3, a deficiency that is likely to have important behavioral consequences. Additionally, quinpirole stimulation of D2-I212F produced dose-dependent inhibition of cAMP accumulation; it was observed that lower concentrations of quinpirole were able to fully activate the rare variant. To further investigate whether this missense variant causes movement disorders, a condition that mimics the heterozygosity (D2-WT/D2-I212F), for the SNP affected patients have, was utilized and tested. Co-transfection of D2-WT and D2-I212F trended toward a shift in the EC50, where D2-WT/D2-I212F were different from D2-WT expressed alone, but the difference was not statistically different. This variant is likely to have decreased arrestin-mediated signaling and enhanced G protein-mediated signaling, so behaviors and cellular functions mediated by those two pathways will be altered according to patients with this variant.
Kunz, Alex R., "BRET Assays to Determine Altered Function of a D2DR Variant in G protein-Independent and -Dependent Pathways" (2019). University Honors Theses. Paper 785.