Dopamine D1 receptor activation induces tau phosphorylation via cdk5 and GSK3 signaling pathways

Increasing evidence is demonstrating that drugs affecting dopamine levels in the brain induce cytoskeletal modifications. These evolving changes may impact neuronal synaptic plasticity as cytoskeletal constituents are involved in the maintenance of dendritic processes, and any alterations in their stability could influence major cellular compartments of neurons, such as dendrites, spines and synapses. Here, we describe a molecular chain of events that links dopamine D1 receptor activation to hyperphosphorylation of the microtubule-associated protein tau, which is normally involved in microtubules stabilization. We show, in SK-N-MC cells and rat striatal sections, that phosphorylation of tau at serines 199-202 and 214 appears to be mediated through activation of calcium-dependent intracellular mechanism, subsequent to D1 receptor-induced cAMP-dependent protein kinase A (PKA). We demonstrate, using pharmacological tools, that PKA activation causes increase of calcium levels, leading to cyclin-dependent kinase 5 activation by calpain proteolysis of p35 to p25 and glycogen synthase kinase 3beta activation by its phosphorylation at tyrosine 216. The D2 receptor agonism or lowering cAMP levels has no effect in our experimental settings. Moreover, we do not observe any association between phosphorylated tau and cellular damage. These data unravel novel mechanisms of tau hyperphosphorylation during G-protein-coupled receptor activation and are the first to show that stimulation of D1 receptors could have a profound influence on the neuronal cytoskeletal constituent tau.