In situ dephosphorylation of tau by protein phosphatase 2A and 2B in fetal rat primary cultured neurons.

Using antibodies recognizing the phosphorylation state of specific sites, phosphorylation states of tau were monitored in fetal rat primary cultured neurons. When cultured neurons were treated with okadaic acid (OA) or calyculin A (CalA) at concentrations sufficient to inhibit protein phosphatase 2A (PP2A), phosphorylation of Ser-199/Ser-202 (numbered according to the human tau 441) and Ser-235 increased. On the other hand, treatment with Ca2+ ionophore, A23187, induced dephosphorylation of Ser-199/Ser-202, Thr-205, Ser-396 and Ser-404, and this dephosphorylation was repressed by inhibitors of protein phosphatase 2B (PP2B), cyclosporin A and FK506. These results indicate that PP2A and PP2B are differentially involved in dephosphorylation of tau in neurons.