Phosphorylation of tau by glycogen synthase kinase 3β in intact mammalian cells influences the stability of microtubules

Tau is a neuronal microtubule-associated protein found predominantly in axons. Hyperphosphorylation of tau reduces the stability of microtubules, which may be a pathogenic mechanism in Alzheimer's disease. To understand the different effects between tau and glycogen synthase kinase 3 beta (GSK-3 beta) phosphorylated tau on the organization and stability of microtubules, we performed transfection studies on 3T3 cells using EGFP-tau (Enhanced Green Fluorescence Protein-au) and GSK-3 beta to quantify the stability of microtubules. Laser confocal microscope observation revealed that thick and thin microtubule bundles could be induced by-tau and GSK-3 beta phosphorylated tau. The bundles appeared either to be relatively straight or to form a ring around the circumference of the cell. Both the thick and thin microtubule bundles were resistant to colchicine-induced dissociation, with thick bundles more resistant than thin bundles. The bundles induced by GSK-3 beta phosphorylated tau were sensitive to colchicine, and could be reversed by the addition of LiCl, an inhibitor of GSK-3 beta. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.