Signaling pathways leading to phosphorylation of Akt and GSK-3ß by activation of cloned human and rat cerebral D2and D3 receptors.

ABSTRACT

Although dopamine (DA) regulates the serine/threonine kinase Akt and its downstream substrate glycogen synthase kinase-3ß (GSK-3ß), the direct influence of dopaminergic receptors remains poorly characterized. Short-term incubation of Chinese hamster ovary (CHO)-expressed human (h)D(2L) and hD3) receptors with DA (maximal effect, 5-10 min) phosphorylated Akt (Thr308 and Ser473) and GSK-3ß (Ser9), actions blocked by the selective D2 and D3 antagonists, 3-[4-(4-chlorophenyl)-4-hydroxypiperidin-l-yl]methyl-1H-indole (L741,626) and (3aR,9bS)-N[4-(8-cyano-1,3a,4,9b-tetrahydro-3H-benzopyrano[3,4-c]pyrrole-2-yl)-butyl] (4-phenyl)benzamide (S33084), respectively. Similar findings were acquired with the specific D2/D3 receptor agonist quinelorane, which also enhanced (10 min after administration) levels of p-Akt and p-GSK-3ß in rat nucleus accumbens, an action blocked by the D2/D3 receptor antagonist raclopride. Akt and GSK-3ß phosphorylation mediated via CHO-expressed hD(2L) and hD3 receptors was prevented by pertussis toxin and by inhibitors of insulin-like growth factor-1 receptors as well as phosphatidylinositol 3-kinase and Src. Likewise, chelation of intracellular Ca²+ and interference with an "atypical" phorbol ester-insensitive protein kinase C (PKC) abolished recruitment of Akt and GSK-3ß. Inactivation of PKCµ blocked Akt and GSK-3ß phosphorylation at hD(2L) receptors. However, blockade of conventional PKC isoforms attenuated the actions of DA at hD3 receptors only. Furthermore, phospholipase C (PLC), calmodulin, and Akt inhibitors abolished DA-induced GSK-3ß phosphorylation by hD3 receptors, whereas phosphorylation by hD(2L) receptors partially involved calmodulin, Akt, and extracellular signal-regulated kinase (ERK) 1/2. In conclusion, at both hD(2L) and hD3 receptors, DA elicited a G(i/o)- and Ca²+/calmodulin-dependent phosphorylation of Akt and GSK-3ß via transactivation of insulin-like growth factor 1 receptor. However, significant differences were seen regarding the involvement of PLC, calmodulin, and ERK1/2.