Novel interaction of the dopamine D2 receptor and the Ca2+ binding protein S100B:: Role in D2 receptor function

S100B is a calcium-binding protein with both extracellular and intracellular regulatory activities in the mammalian brain. We have identified a novel interaction between S100B and the dopamine D-2 receptor. Our results also suggest that the binding of S100B to the dopamine D-2 receptor enhances receptor signaling. This conclusion is based on the following observations: 1) S100B and the third cytoplasmic loop of the dopamine D-2 receptor interact in a bacterial two-hybrid system and in a poly-histidine pull-down assay; 2) immunoprecipitation of the D-2 receptor also precipitates FLAG-S100B from human embryonic kidney 293 cell homogenates and endogenous S100B from rat neostriatal homogenates; 3) S100B immunoreactivity was detected in cultured neostriatal neurons expressing the D-2 receptor; 4) a putative S100B binding motif is located at residues 233 to 240 of the D-2 receptor, toward the amino terminus of the third cytoplasmic loop. D-3-IC3, which does not bind S100B, does not contain this motif; and 5) coexpression of S100B in D-2 receptor-expressing 293 cells selectively increased D-2 receptor stimulation of extracellular signal-regulated kinases and inhibition of adenylate cyclase.