Molecular and cellular events of dopamine D1 receptor-mediated tau phosphorylation in SK-N-MC cells

Microtubules are involved in the formation of axons and dendrites, maintenance of neuronal morphology, and cellular trafficking. Recent studies suggest that drugs affecting dopamine activity in the brain can induce cytoskeletal modifications. For instance, we have demonstrated in acute rat brain slices a molecular chain of events connecting dopamine D1 receptor to aberrant phosphorylation of the microtubule-associated protein tau. However, the molecular and cellular effects of tau phosphorylated by means of the activation of dopamine receptors were unexplored. Here we used SK-N-MC cells, which express endogenously functional D1 receptors, to demonstrate that levels of phosphorylated tau at serines 199-202 or 214 are increased by a calcium-dependent pathway subsequent to D1 receptor stimulation. Using selective pharmacological tools, we showed that enhanced intracellular calcium lead to cyclin-dependent kinase 5 (cdk5) activation, by calpain proteolysis of p35 to p25, as well as glycogen synthase kinase 3β (GSK3β) activation, by its phosphorylation at tyrosine 216. Interestingly, while the activation of protein kinase A (PKA) led directly to the phosphorylation of tau at serine 214, tau phosphorylation at serines 199-202 was independent of PKA. In addition, inhibition of cdk5 or GSK3β prevented the decrease in cell viability induced by D1 receptor stimulation whereas PKA inhibition had no influence. Our data demonstrate that activation of cdk5 and GSK3β following D1 receptor stimulation could have profound influence on both the neuronal cytoskeletal constituent tau and cell survival in SK-N-MC cells.