SITE-SPECIFIC DEPHOSPHORYLATION OF TAU-PROTEIN AT SER(202) THR(205) IN RESPONSE TO MICROTUBULE DEPOLYMERIZATION IN CULTURED HUMAN NEURONS INVOLVES PROTEIN PHOSPHATASE 2A/

Tau proteins isolated from paired helical filaments, the major buildin g blocks of Alzheimer's disease neurofibrillary tangle, are abnormally phosphorylated and unable to bind microtubules. To examine the dynami cs of tau phosphorylation and to identify specific tau phosphorylation sites involved in the stabilization of microtubules, we treated cultu red postmitotic neuron-like cells (NT2N) derived from a human teratoca rcinoma cell line (NTera2/D1) with drugs that depolymerize microtubule s (i.e. colchicine or nocodazole). This led to the recovery of dephosp horylated tau from the NT2N cells as monitored by a relative increase in the electrophoretic mobility of tau and an increase in the turnover of [P-32]PO4-labeled tau. However, not all phosphorylation sites on t an are affected by colchicine or nocodazole. Ser(202)/Thr(205) appears to be completely and specifically dephosphorylated by protein phospha tase 2A since this dephosphorylation was blocked by inhibitors of prot ein phosphatase 2A but not by inhibitors of protein phosphatase 2B. Th ese findings, together with the recent observation that protein phosph atase 2A is normally bound to microtubules in intact cells, suggest th at the polymerization state of microtubules could modulate the phospho rylation state of tau at specific sites in the normal and Alzheimer's disease brain.