Premium
P3‐208: Phosphorylation‐dependent association of tau with the neuronal membrane
Author(s) -
Pooler Amy M.,
Hanger Diane P.
Publication year - 2009
Publication title -
alzheimer's and dementia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.713
H-Index - 118
eISSN - 1552-5279
pISSN - 1552-5260
DOI - 10.1016/j.jalz.2009.04.981
Subject(s) - cytosol , phosphorylation , kinase , tau protein , cell fractionation , chemistry , intracellular , microbiology and biotechnology , cyclin dependent kinase 5 , membrane , biochemistry , biology , protein kinase c , enzyme , alzheimer's disease , medicine , mitogen activated protein kinase kinase , disease
Background: Tau is an abundant cytosolic protein which, in Alzheimer’s disease, becomes hyperphosphorylated and aggregates to form paired helical filaments (PHF) and intracellular tangles. In neurons, tau is able to regulate microtubule stability by associating with the microtubules in a phosphorylation-dependent manner. However, in addition to being cytosolic, it was recently demonstrated in PC12 cells that approximately 20% of tau is associated with the plasma membrane. Membrane-associated tau is predominantly dephosphorylated, at least at the PHF-1 epitope. Objective: To determine whether tau is associated with the neuronal membrane, and to investigate the mechanisms regulating this association. Methods: In 7 DIV cultured rat cortical neurons, we performed cellular fractionation by ultracentrifugation. We analyzed levels of tau in both the cytosolic and the membrane fractions using western blotting. Results: Fractionation of cortical neurons revealed significant amounts of tau in the membrane fraction. This tau was only weakly PHF-1-positive, but was strongly detected by tau-1, an antibody against tau dephosphorylated at Ser199/202. In order to investigate whether phosphorylation regulates tau trafficking, we treated neurons with inhibitors of tau kinases and performed cellular fractionation. Inhibition of either glycogen synthase kinase-3 (GSK-3) by lithium or casein kinase 1 (CK1) by IC261 resulted in increased levels of dephosphorylated tau associated with membranes, but not in the cytosol. Kinase inhibition was accompanied by a significant increase in the total amount of tau in the membrane relative to the cytosolic fraction. IC261 significantly increased membrane-associated tau levels within 30 minutes of treatment. The effect of IC261 on membrane-association of tau was reversible: four hours posttreatment, tau localization in treated cells was similar to that of control cells. Finally, the effect of IC261 was prevented by pre-treatment with okadaic acid to inhibit phosphatase activity. Conclusions: We conclude that dephosphorylation of tau, especially at CK1 and GSK-3 sites, enhances trafficking of tau from the cytosolic compartment to the neuronal membrane.