Tau in Alzheimer disease brain is highly phosphorylated and aggregated into paired helical filaments comprising characteristic neurofibrillary tangles. Here we have analyzed insoluble Tau (PHF-tau) extracted from Alzheimer brain by mass spectrometry and identified 11 novel phosphorylation sites, 10 of which were assigned unambiguously to specific amino acid residues. This brings the number of directly identified sites in PHFtau to 39, with an additional six sites indicated by reactivity with phosphospecific antibodies to Tau. We also identified five new phosphorylation sites in soluble Tau from control adult human brain, bringing the total number of reported sites to nine. To assess which kinases might be responsible for Tau phosphorylation, we used mass spectrometry to determine which sites were phosphorylated in vitro by several kinases. Casein kinase 1␦ and glycogen synthase kinase-3␤ were each found to phosphorylate numerous sites, and each kinase phosphorylated at least 15 sites that are also phosphorylated in PHF-tau from Alzheimer brain. A combination of casein kinase 1␦ and glycogen synthase kinase-3␤ activities could account for over three-quarters of the serine/threonine phosphorylation sites identified in PHF-tau, indicating that casein kinase 1␦ may have a role, together with glycogen synthase kinase-

No abstract

Defective axonal transport has been proposed as an underlying mechanism that may give rise to neurodegeneration. We investigated the effect of phosphorylation on the axonal transport of tau, a neuronal protein that stabilizes microtubules and is hyperphosphorylated and mislocalized in Alzheimer's disease. We report here that specific inhibition of glycogen synthase kinase-3 (GSK-3) reduces tau phosphorylation and significantly decreases the overall rate of axonal transport of tau in rat cortical neurons. Tau mutants, with serine/threonine targets of GSK-3 mutated to glutamate to mimic a permanent state of phosphorylation, were transported at a significantly increased rate compared to wild-type tau. Conversely, tau mutants, in which alanine replaced serine/threonine to mimic permanent dephosphorylation, were transported at a decreased rate compared to wild-type tau. We also found that tau interacts with the light chain of kinesin-1 and that this is dependent on the phosphorylation state of tau. Tau phosphorylation by GSK-3 increased binding, and dephosphorylated tau exhibited a reduced association with kinesin-1. We conclude that GSK-3 phosphorylation of tau modulates its axonal transport by regulating binding to kinesin-1. Hyperphosphorylated tau in Alzheimer's disease appearing first in distal portions of axons may result from aberrant axonal transport of phosphorylated tau reported here.

Recent reports have demonstrated that interactions between the microtubule-associated protein tau and the nonreceptor tyrosine kinase Fyn play a critical role in mediating synaptic toxicity and neuronal loss in response to b-amyloid (Ab) in models of Alzheimer's disease. Disruption of interactions between Fyn and tau may thus have the potential to protect neurons from Ab-induced neurotoxicity. Here, we investigated tau and Fyn interactions and the potential implications for positioning of these proteins in membrane microdomains. Tau is known to bind to Fyn via its Src-homology (SH)3 domain, an association regulated by phosphorylation of PXXP motifs in tau. Here, we show that Pro216 within the PXXP(213-216) motif in tau plays an important role in mediating the interaction of tau with Fyn-SH3. We also show that tau interacts with the SH2 domain of Fyn, and that this association, unlike that of Fyn-SH3, is influenced by Fyn-mediated tyrosine phosphorylation of tau. In particular, phosphorylation of tau at Tyr18, a reported target of Fyn, is important for mediating Fyn-SH2-tau interactions. Finally, we show that tyrosine phosphorylation influences the localization of tau to detergent-resistant membrane microdomains in primary cortical neurons, and that this trafficking is Fyn-dependent. These findings may have implications for the development of novel therapeutic strategies aimed at disrupting the tau ⁄ Fyn-mediated synaptic dysfunction that occurs in response to elevated Ab levels in neurodegenerative disease. Structured digital abstractl Fyn physically interacts with tau by pull down (View interaction) l Fyn physically interacts with tau by pull down (View interaction)