Constitutive phosphorylation by protein kinase C regulates D1 dopamine receptor signaling

Area of Science:

• Molecular Pharmacology
• Neuroscience
• Cell Signaling

Background:

• The D(1) dopamine receptor (D(1) DAR) undergoes phosphorylation by various protein kinases, but specific sites and functional impacts remain unclear.
• Understanding D(1) DAR post-translational modifications is crucial for deciphering dopamine signaling pathways.

Purpose of the Study:

• To investigate the role of protein kinase C (PKC) in the phosphorylation of the D(1) DAR.
• To identify the functional consequences of PKC-mediated D(1) DAR phosphorylation on receptor activity and signaling.

Main Methods:

• Site-directed mutagenesis was employed to identify specific serine residues mediating PKC phosphorylation on the D(1) DAR.
• Experiments involved phorbol ester treatment, Gq-mediated pathway activation, and PKC inhibitors to study phosphorylation.
• Functional assays assessed D(1) DAR expression, desensitization, G protein coupling, and cAMP accumulation in wild-type and mutant receptors.

Main Results:

• Protein Kinase C (PKC) phosphorylates the D(1) DAR constitutively, independent of agonist stimulation.
• Five serine residues were identified as key sites for PKC phosphorylation.
• PKC phosphorylation enhanced G protein coupling and cAMP accumulation, while not affecting D(1) DAR expression or desensitization.

Conclusions:

• Constitutive PKC phosphorylation of the D(1) DAR dampens dopamine-mediated receptor activation.
• This dampening effect on dopamine signaling is context-specific, depending on cellular PKC isozyme expression.
• PKC-mediated phosphorylation represents a novel regulatory mechanism for D(1) DAR signaling.