Phosphorylation of tau by glycogen synthase kinase 3β affects the ability of tau to promote microtubule self-assembly

Abstract

To study the effects of phosphorylation by glycogen synthase kinase-3beta (GSK-3beta) on the ability of the microtubule-associated protein tau to promote microtubule self-assembly, tau isoform 1 (foetal tau) and three mutant forms of this tau isoform were investigated. The three mutant forms of tau had the following serine residues, known to be phosphorylated by GSK-3, replaced with alanine residues so as to preclude their phosphorylation: (1) Ser-199 and Ser-202 (Ser-199/202-->Ala), (2) Ser-235 (Ser-235-->Ala) and (3) Ser-396 and Ser-404 (Ser-396/404-->Ala). Wild-type tau and the mutant forms of tau were phosphorylated with GSK-3beta, and their ability to promote microtubule self-assembly was compared with the corresponding non-phosphorylated tau species. In the non-phosphorylated form, wild-type tau and all of the mutants affected the mean microtubule length and number concentrations of assembled microtubules in a manner consistant with enhanced microtubule nucleation. Phosphorylation of these tau species with GSK-3beta consistently reduced the ability of a given tau species to promote microtubule self-assembly, although the affinity of the tau for the microtubules was not greatly affected by phosphorylation since the tau species remained largely associated with the microtubules. This suggests that the regulation of microtubule assembly can be controlled by phosphorylation of tau at sites accessible to GSK-3beta by a mechanism that does not necessarily involve the dissociation of tau from the microtubules.

Transient phosphorylation of tumor associated microtubule associated protein (TMAP)/cytoskeleton associated protein 2 (CKAP2) at Thr-596 during early phases of mitosis

“…Properties of microtubuleassociated proteins (MAPs) are often regulated by phosphorylation. For instance, phosphorylation of MAP2C, MAP1B, and Tau by GSK-3 results in a decrease in their ability to bind and stabilize microtubules (Lovestone et al, 1996;Wagner et al, 1996;Utton et al, 1997). Similarly, Cdk1-mediated phosphorylation of another MAP, XMAP215 at the onset of mitosis has been reported to reduce its microtubule-stabilizing activity (Vasquez et al, 1999).…”

Tau-induced neurodegeneration: mechanisms and targets

“…In vitro, GSK-3 phosphorylates tau on ~40 Ser/Thr residues, and 348 CK1 is the only other kinase comparable to GSK-3 in that it phosphorylates tau residues in similar numbers [31] . GSK-3 phosphorylation reduces the capability of tau to promote microtubule assembly in vitro and in cells [33,34] . GSK-3 together with the activity of other kinases such as CK1, Cdk5, and MARK, has the ability to signifi cantly affect tau phosphorylation and modulate its neuronal function [35][36][37][38] .…”

Glycogen Synthase Kinase 3β Phosphorylates Tau at Both Primed and Unprimed Sites

“…Protein kinase A (21), microtubule affinity regulating kinases (22), cyclin-dependent protein kinase 5 (cdk5) 1 /p35[p25] (23,24), and glycogen synthase kinase 3␤ (GSK3␤) (25)(26)(27)(28)(29) have been shown to phosphorylate tau in situ. Although all these kinases can phosphorylate tau in situ, there is emerging evidence that GSK3␤ may play a major role in regulating tau phosphorylation both in physiological and pathological conditions.…”