||Alzheimer’s disease (AD), one of the most common dementia, is characterized by the formation two types of aggregation in the brain: senile plaques and neurofibrillary tangles (NFTs). NFTs are composed of hyperphosphorylated Tau. Tau protein mainly expressed in brain and was identified as one of the microtubule-associated proteins (MAPs). Hyperphophorylation on Tau affects its binding to tubulin and capacity to promote microtubule assembly. A number of proline-directed kinase capable of phosphorylating PHF-Tau have been identified, including Glycogen Synthase Kinase-3β (GSK-3β). Here we demonstrated that GSK3β can co-purify with PHFs and can co-localize with Tau in vitro in N18 cells. To examine the phosphorylation mechanism of Tau by GSK-3β, N-terminal, C-terminal, T231A, T231E, 154~441, S396A, S400A, S404A, S413A and S396A S400A mutants of Tau were used, respectively. We were able to demonstrate that phosphorylation on Thr231 and Ser404 in Tau may play important roles for GSK3β phosphorylation and its functional regulation. Most importantly, we have proved that T231P motif is necessary and critical for Tau phosphorylation by GSK3β.|
Moreover, we used T231E, S396E and S400E mutants of Tau to understand the functional regulation of Tau by GSK3β phosphorylation by tubulin assembly assay. Surprisingly, we observed all of these Tau mutants can promote tubulin assembly and form tubulin bundles in N18 cells.
It has been proved that Pin1 WW domain can bind to Cdc2-phosphorylated Thr-231-Pro motif of Tau and restore the ability of Tau to promote tubulin assembly. In this study, we also studied whether Pin1 can regulate GSK3β- phosphorylated Tau. The results show that Pin1 WW domain can bind to phosphorylated Thr-231 of Tau by GSK3β and restore the ability of Tau to promote tubulin assembly.