14-3-3 Binds to and Mediates Phosphorylation of Microtubule-associated Tau Protein by Ser9-phosphorylated Glycogen Synthase Kinase 3β in the Brain

Zongfei Yuan,Alka Agarwal-Mawal,Hemant K Paudel

doi:10.1074/jbc.m308298200

Zongfei Yuan, Alka Agarwal-Mawal + Show 1 more

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https://doi.org/10.1074/jbc.m308298200

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Abstract

In mammalian brain, tau, glycogen synthase kinase 3beta (GSK3beta), and 14-3-3, a phosphoserine-binding protein, are parts of a multiprotein tau phosphorylation complex. Within the complex, 14-3-3 simultaneously binds to tau and GSK3beta (Agarwal-Mawal, A., Qureshi, H. Y., Cafferty, P. W., Yuan, Z., Han, D., Lin, R., and Paudel, H. K. (2003) J. Biol. Chem. 278, 12722-12728). The molecular mechanism by which 14-3-3 connects GSK3beta to tau within the complex is not clear. In this study, we find that GSK3beta within the tau phosphorylation complex is phosphorylated on Ser(9). From extracts of rat brain and rat primary cultured neurons, Ser(9)-phosphorylated GSK3beta precipitates with glutathione-agarose beads coated with glutathione S-transferase-14-3-3. Similarly, from rat brain extract, Ser(9)-phosphorylated GSK3beta co-immunoprecipitates with tau. In vitro, 14-3-3 binds to GSK3beta only when the kinase is phosphorylated on Ser(9). In transfected HEK-293 cells, 14-3-3 binds to Ser(9)-phosphorylated GSK3beta and does not bind to GSK3beta (S9A). Tau, on the other hand, binds to both GSK3beta (WT) and GSK3beta (S9A). Moreover, 14-3-3 enhances the binding of tau with Ser(9)-phosphorylated GSK3beta by approximately 3-fold but not with GSK3beta (S9A). Similarly, 14-3-3 stimulates phosphorylation of tau by Ser(9)-phosphorylated GSK3beta but not by GSK3beta (S9A). In transfected HEK-293 cells, Ser(9) phosphorylation suppresses GSK3beta-catalyzed tau phosphorylation in the absence of 14-3-3. In the presence of 14-3-3, however, Ser(9)-phosphorylated GSK3beta remains active and phosphorylates tau. Our data indicate that within the tau phosphorylation complex, 14-3-3 connects Ser(9)-phosphorylated GSK3beta to tau and Ser(9)-phosphorylated GSK3beta phosphorylates tau.

Highlights

In mammalian brain, tau, glycogen synthase kinase 3␤ (GSK3␤), and 14-3-3, a phosphoserine-binding protein, are parts of a multiprotein tau phosphorylation complex
We find that GSK3␤ within the tau phosphorylation complex is phosphorylated on Ser9
Since GSK3␤ is phosphorylated on Ser9 in vivo (19 –21), we have investigated the interaction of 14-3-3 and GSK3␤ within the tau phosphorylation complex

Summary

Introduction

Tau, glycogen synthase kinase 3␤ (GSK3␤), and 14-3-3, a phosphoserine-binding protein, are parts of a multiprotein tau phosphorylation complex. Insulin-activated AKT phosphorylates GSK3␤ on Ser9 [21, 23], this phosphorylation stimulates GSK3␤-catalyzed tau phosphorylation and dissociation of tau from microtubules (24 – 26). These observations suggest that in neurons, Ser9-phosphorylated GSK3␤ may phosphorylate tau. Ser phosphorylation is implicated in down-regulating GSK3␤ activity These observations raise the question of how Ser9phosphorylated GSK3␤ could phosphorylate tau in the brain

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