Site-specific Dephosphorylation of Tau Protein at Ser/Thr in Response to Microtubule Depolymerization in Cultured Human Neurons Involves Protein Phosphatase 2A

doi:10.1074/jbc.271.10.5589

Site-specific Dephosphorylation of Tau Protein at Ser/Thr in Response to Microtubule Depolymerization in Cultured Human Neurons Involves Protein Phosphatase 2A (*)

From the (1)David Mahoney Institute of Neurological Sciences and the
(2)Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-4283

^§ To whom correspondence should be addressed:
Dept. of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, HUP, Maloney Bldg., Rm. A009, 36th and Spruce Sts., Philadelphia, PA 19104-4283
. Tel.: 215-662-6427; Fax: 215-349-5909.

Abstract

Tau proteins isolated from paired helical filaments, the major building blocks of Alzheimer's disease neurofibrillary tangle, are abnormally phosphorylated and unable to bind microtubules. To examine the dynamics of tau phosphorylation and to identify specific tau phosphorylation sites involved in the stabilization of microtubules, we treated cultured postmitotic neuron-like cells (NT2N) derived from a human teratocarcinoma cell line (NTera2/D1) with drugs that depolymerize microtubules (i.e. colchicine or nocodazole). This led to the recovery of dephosphorylated tau from the NT2N cells as monitored by a relative increase in the electrophoretic mobility of tau and an increase in the turnover of [P]PO-labeled tau. However, not all phosphorylation sites on tau are affected by colchicine or nocodazole. Ser/Thr appears to be completely and specifically dephosphorylated by protein phosphatase 2A since this dephosphorylation was blocked by inhibitors of protein phosphatase 2A but not by inhibitors of protein phosphatase 2B. These findings, together with the recent observation that protein phosphatase 2A is normally bound to microtubules in intact cells, suggest that the polymerization state of microtubules could modulate the phosphorylation state of tau at specific sites in the normal and Alzheimer's disease brain.

Footnotes

↵* This work was supported by grants from the National Institutes of Health. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¹ The abbreviations used are:

PHF

paired helical filament

MT

microtubule

PP1

PP2A, PP2B, protein phosphatase 1, 2A, and 2B, respectively

CNS

central nervous system

mAb

monoclonal antibody

MES

4-morpholineethanesulfonic acid

PAGE

polyacrylamide gel electrophoresis

MAP

microtubule-associated protein

TPCK

L-1-tosylamido-2-phenylethyl chloromethyl ketone

TLCK

1-chloro3-tosylamido-7-amino-2-heptanone.
↵²S. E. Merrick and V. M.-Y. Lee, unpublished data.
- Received March 9, 1995.
- Revision received December 12, 1995.