Phosphorylation Sites on Tau Identified by Nanoelectrospray Mass Spectrometry

Differences In Vitro Between the Mitogen-Activated Protein Kinases ERK2, c-Jun N-Terminal Kinase and P38, and Glycogen Synthase Kinase-3β

Authors

  • C. Hugh Reynolds,

  • Joanna C. Betts,

  • Walter P. Blackstock,

  • Angel R. Nebreda,

  • Brian H. Anderton


  • Abbreviations used: AD, Alzheimer's disease; ERK2, extracellular signal-regulated kinase 2; GSK3, glycogen synthase kinase 3; IMAC, immobilised metal affinity chromatography; JNK, c-Jun N-terminal kinase; MAP, mitogen-activated protein; MARK, microtubule affinity-regulating kinase; nanoES-MS, nanoelectrospray mass spectrometry; PHF, paired helical filament; SAPK, stress-activated protein kinase.

Address correspondence and reprint requests to Dr. C. H. Reynolds at Department of Neuroscience, Institute of Psychiatry, De Crespigny Park, Denmark Hill, London SE5 8AF, U.K. E-mail: h.reynolds@iop.kcl.ac.uk

Abstract

Abstract: The stress-activated kinases c-Jun N-terminal kinase (JNK) and p38 are members of the mitogen-activated protein (MAP) kinase family and take part in signalling cascades initiated by various forms of stress. Their targets include the microtubule-associated protein tau, which becomes hyperphosphorylated in Alzheimer's disease. It is necessary, as a forerunner for in vivo studies, to identify the protein kinases and phosphatases that are responsible for phosphate turnover at individual sites. Using nanoelectrospray mass spectrometry, we have undertaken an extensive comparison of phosphorylation in vitro by several candidate tau kinases, namely, JNK, p38, ERK2, and glycogen synthase kinase 3β (GSK3β). Between 10 and 15 sites were identified for each kinase. The three MAP kinases phosphorylated Ser202 and Thr205 but not detectably Ser199, whereas conversely GSK3β phosphorylated Ser199 but not detectably Ser202 or Thr205. Phosphorylated Ser404 was found with all of these kinases except JNK. The MAP kinases may not be strictly proline specific: p38 phosphorylated the nonproline sites Ser185, Thr245, Ser305, and Ser356, whereas ERK2 was the most strict. All of the sites detected except Thr245 and Ser305 are known or suspected phosphorylation sites in paired helical filament-tau extracted from Alzheimer brains. Thus, the three MAP kinases and GSK3β are importantly all strong candidates as tau kinases that may be involved in the pathogenic hyperphosphorylation of tau in Alzheimer's disease.

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