Dopamine D1 and adenosine A1 receptors form functionally interacting heteromeric complexes

Area of Science:

• Neuroscience
• Molecular Pharmacology
• Cell Biology

Background:

• Antagonistic interactions between adenosine A(1) receptors (A(1)R) and dopamine D(1) receptors (D(1)R) have been observed in the brain.
• The molecular mechanisms underlying these receptor interactions require further elucidation.

Purpose of the Study:

• To investigate the molecular basis of the antagonistic interactions between A(1)R and D(1)R.
• To determine if A(1)R and D(1)R form heteromers and how this affects receptor signaling and desensitization.

Main Methods:

• Cotransfection of mouse fibroblast cells with human A(1)R and D(1)R or D(2)R cDNAs.
• Coimmunoprecipitation assays to detect receptor heteromerization.
• Confocal laser microscopy for colocalization studies.
• Agonist pretreatment to assess effects on heteromerization, coclustering, and cAMP accumulation.

Main Results:

• A(1)R and D(1)R, but not A(1)R and D(2)R, were found to coimmunoprecipitate, indicating selective heteromerization.
• A high degree of A(1)R and D(1)R colocalization was observed in both cotransfected cells and cortical neurons.
• A(1)R agonist pretreatment induced A(1)R/D(1)R coclustering, which was blocked by combined A(1)R and D(1)R agonist pretreatment.
• Combined D(1)R and A(1)R agonist pretreatment significantly reduced D(1)R agonist-induced cAMP accumulation.

Conclusions:

• A(1)R/D(1)R heteromerization is a likely molecular basis for the antagonistic modulation of D(1)R signaling by A(1)R in the brain.
• A(1)R/D(1)R heteromers play a role in desensitization mechanisms and receptor trafficking, as evidenced by the blockade of agonist-induced coclustering and cAMP accumulation.