Computer-assisted image analysis of caveolin-1 involvement in the internalization process of adenosine A2A-dopamine D2 receptor heterodimers.

A functional aspect of horizontal molecular networks has been investigated experimentally, namely the heteromerization between adenosine A2A and dopamine D2 receptors and the possible role of caveolin-1 in the cotrafficking of these molecular complexes. This study has been carried out by means of computer-assisted image analysis procedure of laser images of membrane immunoreactivity of caveolin-1, A2A, D1, and D2 receptors obtained in two clones of Chinese hamster ovary cells—one transfected with A2A and dopamine D1 receptors and the other one with A2A and D2 receptors. Cells were treated for 3 h with 10 µM D1 receptor agonist SKF 38393, 50 µM D2-D3 receptor agonist quinpirole, and 200 nM A2A receptor agonist CGS 21680. In A2A-D1-cotransfected cells, caveolin-1 was found to colocalize with both A2A and D1 receptors and treatment with SKF 38393 induced internalization of caveolin-1 and D1 receptors, with a preferential internalization of D1 receptors colocalized with caveolin-1. In A2A-D2-cotransfected cells, caveolin-1 was found to colocalize with both A2A and D2 receptors and either CGS 21680 or quinpirole treatment induced internalization of caveolin-1 and A2A and D2 receptors, with a preferential internalization of A2A and D2 receptors colocalized with caveolin-1. The results suggest that A2A and D2 receptors and caveolin-1 likely interact forming a macrocomplex that internalizes upon agonist treatment. These observations are discussed in the frame of receptor oligomerization and of the possible functional role of caveolin-1 in the process of co-internalization and, hence, in controlling the permanence of receptors at the plasma membrane level (prerequisite for receptor mosaic organization and plastic adjustments) and in the control of receptor desensitization.