The Protein Phosphatase PP2A/Bα Binds to the Microtubule-associated Proteins Tau and MAP2 at a Motif Also Recognized by the Kinase Fyn

Jean-Marie Sontag,Viyada Nunbhakdi-Craig,Charles L White,Shelley Halpain,Estelle Sontag

doi:10.1074/jbc.m111.338681

Abstract

The predominant brain microtubule-associated proteins MAP2 and tau play a critical role in microtubule cytoskeletal organization and function. We have previously reported that PP2A/Bα, a major protein phosphatase 2A (PP2A) holoenzyme, binds to and dephosphorylates tau, and regulates microtubule stability. Here, we provide evidence that MAP2 co-purifies with and is dephosphorylated by endogenous PP2A/Bα in bovine gray matter. It co-localizes with PP2A/Bα in immature and mature human neuronal cell bodies. PP2A co-immunoprecipitates with and directly interacts with MAP2. Using in vitro binding assays, we show that PP2A/Bα binds to MAP2c isoforms through a region encompassing the microtubule-binding domain and upstream proline-rich region. Tau and MAP2 compete for binding to and dephosphorylation by PP2A/Bα. Remarkably, the protein-tyrosine kinase Fyn, which binds to the proline-rich RTPPKSP motif conserved in both MAP2 and tau, inhibits the interaction of PP2A/Bα with either tau or MAP2c. The corresponding synthetic RTPPKSP peptide, but not the phosphorylated RpTPPKSP version, competes with Tau and MAP2c for binding to PP2A/Bα. Significantly, down-regulation of PP2A/Bα and deregulation of Fyn-Tau protein interactions have been linked to enhanced tau phosphorylation in Alzheimer disease. Together, our results suggest that PP2A/Bα is part of segregated MAP2 and tau signaling scaffolds that can coordinate the action of key kinases and phosphatases involved in modulating neuronal plasticity. Deregulation of these compartmentalized multifunctional protein complexes is likely to contribute to tau deregulation, microtubule disruption, and altered signaling in tauopathies.

Highlights

The microtubule-associated proteins tau and MAP2 are dephosphorylated by phosphatase 2A (PP2A), a major brain Ser/Thr phosphatase
B␣-containing PP2A Holoenzymes Co-purify with HMWMAP2 from Bovine Gray Matter—To investigate whether PP2A could co-purify with endogenous MAP2, MAPs were first prepared from adult bovine cortical GM
This approach was based on the observations that HMW-MAP2 is primarily distributed in neuronal cell bodies and dendrites, and that somatodendritic regions are concentrated in GM [34]

Summary

Background

The microtubule-associated proteins tau and MAP2 are dephosphorylated by PP2A, a major brain Ser/Thr phosphatase. Our results suggest that PP2A/B␣ is part of segregated MAP2 and tau signaling scaffolds that can coordinate the action of key kinases and phosphatases involved in modulating neuronal plasticity Deregulation of these compartmentalized multifunctional protein complexes is likely to contribute to tau deregulation, microtubule disruption, and altered signaling in tauopathies. A conserved proline-rich Fyn-binding motif in MAP2 and tau plays a critical role in regulating the interaction of PP2A/B␣ with both MAPs. Our data underscore the importance of both MAP2 and tau as multivalent, compartmentalized anchoring proteins for major signaling enzymes like PP2A/B␣ and Fyn. We propose that deregulation of these protein-protein interactions has the potential to contribute to alterations in normal enzyme-substrate relationships and signaling pathways in AD

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION