Dephosphorylation studies of SKNSH-SY 5Y cell Tau proteins by endogenous phosphatase activity.

Recent data have shown that the microtubule-associated Tau proteins are phosphorylated but to a lesser extent than PHF-Tau proteins which are the major components of Alzheimer's disease paired helical filaments. These normal Tau proteins are highly sensitive to the endogenous phosphatase activity during post-mortem delay. In order to understand the basic equilibrium between phosphatase and kinase activities, phosphorylation and dephosphorylation mechanisms of Tau proteins were studied in neuroblastoma cells. The present results demonstrate that an endogenous phosphatase activity is present and directed on Tau proteins in the SKNSH-SY 5Y cell extracts. Interestingly, the okadaic acid-induced hyperphosphorylated Tau proteins are more resistant to the phosphatase activity than the control Tau proteins. Our data emphasize the value of this in vitro cellular model for the study of biological conditions that control Tau protein phosphorylation levels.