Paralemmin interacts with D3 dopamine receptors: implications for membrane localization and cAMP signaling.

Paralemmin is a novel lipid-anchored protein, which is highly expressed in neuronal plasma membranes. In this study, we demonstrate that paralemmin specifically interacts with the third intracellular loop of the D3 dopamine receptor. Utilizing co-immunoprecipitation and glutathione-S-transferase (GST) pulldown strategies, we demonstrate that paralemmin interacts exclusively with D3, but not D2 or D4 dopamine receptors or beta-adrenergic receptors. Immunocytochemistry demonstrated co-localization of paralemmin and D3 receptor in vivo in hippocampus and cerebellum and in vitro in glial and neuronal cultures. Deletion mutational analysis indicates that amino acids 154-230 of paralemmin strongly interacted with amino acids 211-227 and 281-330 of the third intracellular loop of D3 receptor. The consequences of these interactions were investigated by co-expression in HEK293 cells. Cell surface biotinylation experiments demonstrate that paralemmin decreased D3 receptor concentration at the plasma membrane. Consistent with this observation, paralemmin expression decreased dopamine-stimulated adenylate cyclase activity. However, paralemmin also decreased basal, isoproterenol and forskolin-stimulated adenylate cyclase activity, suggesting a more general cellular function for paralemmin. Taken together, paralemmin has been implicated as a potent modulator of cellular cAMP signaling within the brain.