A pool of β-tubulin is hyperphosphorylated at serine residues in Alzheimer disease brain (original) (raw)
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FEBS Letters, 1994
Microtubule-associated protein tau is abnormally hyperphosphorylated and forms the major protein subunit of paired helical filaments (PHF) in Alzheimer disease brains. The abnormally phosphorylated sites Ser-199, Ser-202, Ser-396 and Ser-404 but not Ser-46 and Ser-235 of Alzheimer tau were found to be dephosphorylated by protein phosphatase-1 and this dephosphorylation was activated by Mn*'. In contrast, protein phosphatase-2C did not dephosphorylate any of these sites. Both protein phosphatase-1 and -2C had high activities towards ["P]tau phosphorylated by CAMPdependent protein kinase. These results suggest that both protein phosphatase-1 and -2C might be associated with normal phosphorylation state of tau, but only the former and not the latter phosphatase is involved in its abnormal phosphorylation in Alzheimer disease.
Proceedings of The National Academy of Sciences, 1986
A monoclonal antibody to the microtubuleassociated protein X (tau) labeled some neurofibrillary tangles and plaque neurites, the two major locations of paired-helical filaments (PHF), in Alzheimer disease brain. The antibody also labeled isolated PHF that had been repeatedly washed with NaDodSO4. Dephosphorylation of the tissue sections with alkaline phosphatase prior to immunolabeling dramatically increased the number of tangles and plaques recognized by the antibody. The plaque core amyloid was not stained in either dephosphorylated or nondephosphorylated tissue sections. On immunoblots PHF polypeptides were labeled readily only when dephosphorylated. In contrast, a commercially available monoclonal antibody to a phosphorylated epitope of neurordaments that labeled the tangles and the plaque neurites in tissue did not label any PHF polypeptides on immunoblots. The PHF polypeptides, labeled with the monoclonal antibody to 7, electrophoresed with those polypeptides recognized by antibodies to isolated P1F. The antibody to 7-labeled microtubules from normal human brains assembled in vitro but identically treated Alzheimer brain preparations had to be dephosphorylated to be completely recognized by this antibody. These findings suggest that 7 in Alzheimer brain is an abnormally phosphorylated protein component of PH1.
Journal of Neurochemistry, 1992
Abstract: The microtubule-associated protein τ which stimulates the assembly of α-β tubulin heterodimers into microtubules, is abnormally phosphorylated in Alzheimer's disease (AD) brain and is the major component of paired helical filaments. In the present study, the levels of τ and abnormally phosphorylated τ were determined in brain homogenates of AD and age-matched control cases. A radioimmuno-slot-blot assay was developed, using a primary monoclonal antibody, Tau-1, and a secondary antibody, antimouse 125I-immunoglobulin G. To assay the abnormally phosphorylated τ, the blots were treated with alkaline phosphatase before immunolabeling. The levels of total τ were about eightfold higher in AD (7.3 ± 2.7 ng/μg of protein) than in control cases (0.9 ± 0.2 ng/μg), and this increase was in the form of the abnormally phosphorylated protein. These studies indicate that the abnormal phosphorylation—not a decrease in the level of τ—is a likely cause of neurofibrillary degeneration in AD.
The FASEB Journal, 2008
In Alzheimer disease (AD)-affected neurons, the Tau protein is found in an aggregated and hyperphosphorylated state. A common hypothesis is that Tau hyperphosphorylation causes its dissociation from the microtubular surface, with consequently a breakdown of the microtubules (MTs) and aggregation of the unbound Tau. We evaluated the effect of Tau phosphorylation on both tubulin assembly and MT binding. We show that the cyclin-dependent kinase 2/cyclin A3 kinase complex can generate the AT8 and AT180 AD-specific phospho-epitopes and use NMR spectroscopy to validate qualitatively and quantitatively the phospho content of our samples. The simultaneous presence of both epitopes disables the tubulin assembly capacity of Tau in conditions whereby Tau is the driving force for the assembly process but does not, however, inhibit MT assembly when the latter is driven by an increased tubulin concentration. When compared to the isolated MT binding repeats (K d 3.0؍ M), the phospho-Tau retains a substantial affinity for preformed MTs (K d 11؍ nM), suggesting that the phosphorylated proline-rich region still participates in the binding event. Our results hence indicate that the sole phosphorylation at the AT8/AT180 epitopes, although leading to a functional defect for Tau, is not sufficient for its dissociation from the MT surface and subsequent aggregation as observed in AD.
FEBS Letters, 1996
The microtubule-associated protein tau in human brain consists of six molecular isoforms derived from a single gene by alternative mRNA-splicing and further modified by posttranslational processing. In the present study, the distribution of tau isoforms in grey and white matter of human temporal cortex was investigated by two-dimensional gelelectrophoresis. More than 80 isoforms were detected. The pattern of isoforms obtained after treatment with alkaline phosphatase was still more complex than those of recombinant tau, indicating that posttranslational modifications other than phosphorylation contribute to the molecular heterogeneity of tau. The tau isoform D according to Goedert [I] containing four tubulin-binding regions shown to promote tubulin polymerisation most efficiently was present in higher amounts in white as compared to grey matter. The pattern of isoform distribution was not significantly altered in Alzheimer's disease. It is concluded that molecular isoforms that differ in their tubulin-binding characteristics are differentially distributed in subceliular neuronal compartments and/or neuronal types.
Current Medicinal Chemistry, 2008
Alzheimer disease (AD) is the most common cause of dementia in adults. The current therapy for AD has only moderate efficacy in controlling symptoms, and it does not cure the disease. Recent studies have suggested that abnormal hyperphosphorylation of tau in the brain plays a vital role in the molecular pathogenesis of AD and in neurodegeneration. This article reviews the current advances in understanding of tau protein, regulation of tau phosphorylation, and the role of its abnormal hyperphosphorylation in neurofibrillary degeneration. Furthermore, several therapeutic strategies for treating AD on the basis of the important role of tau hyperphosphorylation in the pathogenesis of the disease are described. These strategies include (1) inhibition of glycogen synthase kinase-3β (GSK-3β), cyclin-dependent kinase 5 (cdk5), and other tau kinases; (2) restoration of PP2A activity; and (3) targeting tau O-GlcNAcylation. Development of drugs on the basis of these strategies is likely to lead to disease-modifying therapies for AD.
Disruption of microtubule network by Alzheimer abnormally hyperphosphorylated tau
Acta Neuropathologica, 2007
Hyperphosphorylated tau has long been proposed as the key molecule disrupting normal neuronal microtubule dynamics and leading to neuroWbrillary degeneration in Alzheimer disease. Here we provide a direct evidence of hyperphosphorylated tau-induced disruption of microtubule network. Using Nocodozole-treated and detergent-extracted cells, we created a neuronal environment in mouse embryonic Wbroblasts, 3T3 cells, by replacing their cytoplasm with adult rat brain cytosol. By recreating neuronal microtubule network in these cells, we were able to follow the eVects of hyperphosphorylated tau on microtubule dynamics in real time. Whereas recombinant human brain tau promoted assembly and bundling of microtubules, abnormally hyperphosphorylated tau isolated from Alzheimer disease brain cytosol (AD P-tau) inhibited the assembly and disrupted preformed microtubule network by sequestering normal brain tau and MAP2. This breakdown of the microtubule network was reversed by treatment of the extracted cells with protein phosphatase-2A. This study, for the Wrst time, provides direct mechanistic insights into the molecular basis of both axonal and dendritic neurodegeneration seen in Alzheimer disease.
Phosphorylated tau can promote tubulin assembly
Proceedings of the National Academy of Sciences, 1999
Phosphorylation can affect the function of microtubule-associated protein tau. Here, the human brain tau with 441 amino acids was phosphorylated by cyclic-AMPdependent protein kinase (PKA) or glycogen synthase kinase-3. PKA-phosphorylated tau (2.7 mol phosphates͞mol) does not promote tubulin assembly as judged by spectrophotometric and atomic force microscopy measurements, unless trimethylamine N-oxide (TMAO), a natural occurring osmolyte, is included in these assays. TMAO is also found to promote tubulin assembly of glycogen synthase kinase-3-phosphorylated tau (1.6 mol phosphates͞mol). TMAO does not act by causing a chemical dephosphorylation of phosphorylated tau, but it acts to overcome the functional deficit caused by phosphorylation. PKA-phosphorylated tau binds to tubulin in the presence of TMAO and lowers the critical concentration of tubulin needed for assembly. From these data, we conclude that PKA-phosphorylated tau retains the ability to bind tubulin and promote tubulin assembly. TMAO is required, however, to sensitize the reaction. Possible uses of TMAO in relation to studies of tubulin assembly in vitro, in intact cells, and in relation to Alzheimer's disease are presented in this report.
Kinases and phosphatases and tau sites involved in Alzheimer neurofibrillary degeneration
European Journal of Neuroscience, 2007
Microtubule associated protein (MAP) tau is abnormally hyperphosphorylated in Alzheimer's disease (AD) and related tauopathies; in this form it is the major protein subunit of paired helical filaments (PHF) ⁄ neurofibrillary tangles. However, the nature of protein kinases and phosphatases and tau sites involved in this lesion has been elusive. We investigated self-assembly and microtubule assembly promoting activities of hyperphosphorylated tau isolated from Alzheimer disease brain cytosol, the AD abnormally hyperphosphorylated tau (AD P-tau) before and after dephosphorylation by phosphoseryl ⁄ phosphothreonyl protein phosphatase-2A (PP-2A), and then rephosphorylation by cyclic AMP-dependent protein kinase (PKA), calcium, calmodulin-dependent protein kinase II (CaMKII), glycogen synthase kinase-3b (GSK-3b) and cyclin-dependent protein kinase 5 (cdk5) in different kinase combinations. We found that (i) dephosphorylation of AD P-tau by PP-2A inhibits its polymerization into PHF ⁄ straight filaments (SF) and restores its binding and ability to promote assembly of tubulin into microtubules; (ii) rephosphorylation of PP-2A-dephosphorylated AD P-tau by sequential phosphorylation by PKA, CaMKII and GSK-3b or cdk5, and as well as by cdk5 and GSK-3b, promotes its self-assembly into tangles of PHF similar to those seen in Alzheimer brain, and (iii) phosphorylation of tau sites required for this pathology are Thr231 and Ser262, along with several sites flanking the microtubule binding repeat region. Phosphorylation of recombinant human brain tau 441 yielded similar results as the PP-2A dephosphorylated AD P-tau, except that mostly SF were formed. The conditions for the abnormal hyperphosphorylation of tau that promoted its self-assembly also induced the microtubule assembly inhibitory activity. These findings suggest that activation of PP-2A or inhibition of either both GSK-3b and cdk5 or one of these two kinases plus PKA or CaMKII might be required to inhibit Alzheimer neurofibrillary degeneration.
Neurochemistry International, 1995
The abnormally phosphorylated forms of tau factor are major constituents of neurofibrillary tangles in Alzheimer's disease brain. In order to investigate protein phosphatases which are related to dephosphorylation of abnormal phosphorylation sites, we examined the dephosphorylation of tau factor phosphorylated by three proline-directed type protein kinases. Tau factor phosphorylated by cdc2 kinase and tau protein kinase II was dephosphorylated by the holoenzyme of protein phosphatase 2A and calcineurin, while either the catalytic subunit of protein phosphatase 2A or protein phosphatase 2C could not catalyze the dephosphorylation. From the kinetic analysis, we concluded that tau factors phosphorylated by the protein kinases serve as good substrates for protein phosphatase 2A and calcineurin. On the other hand, tau factor phosphorylated by glycogen synthase kinase 3c~ was dephosphorylated by the catalytic subunit of protein phosphatases 2A as well as the holoenzyme of protein phosphatase 2A and calcineurin. It has been reported that serines 199, 202 and 396 according to the numbering of the longest human tau isoform are among the major abnormal phosphorylation sites of tau factor. We synthesized two phosphopeptides which contained phosphoserines 199 and 202 or phosphoserine 396 and prepared the polyclonal antibodies specific for the phosphopeptides. Using these antibodies, we confirmed that the holoenzyme of protein phosphatase 2A and calcineurin could dephosphorylate phosphoserines 199, 202 and 396 in tau factor. The catalytic subunit of protein phosphatase 2A could dephosphorylate phosphoserine 396 but not phosphoserines 199 and 202. Neurofibrillary tangles in Alzheimer's disease brain were immunostained with both antibodies but the normal neurons in the normal aged brains were not. These results suggest that protein phosphatase 2A and calcineurin can be involved in the dephosphorylation of abnormal phosphorylation sites in tau factor and that the dephosphorylation of phosphoserine 396 is differently regulated from phosphoserines 199 and 202. Tau factor is a low molecular weight microtubuleassociated protein and regulates the formation of *Author to whom all correspondence should be addressed. Abbreviations: Anti-PP-1 antibody, antibody to phosphopeptide-l; anti-PP-2 antibody, antibody to phosphopeptide-2; CaM kinase II, Ca2+/calmodulin-dependent protein kinase II ; cyclic AMP-kinase, cyclic AMP-dependent protein kinase; GSK3~, glycogen synthase kinase 3~; MAP kinase, mitogen-activated protein kinase; MAPs, microtubule-associated proteins; MES, 2-(Nmorpholino)-ethane sulfonic acid; PVDF membrane, polyvinylidene difluoride membrane ; SDS PAGE, sodium dodecyl sulfate-polyacrylamide gel electrophoresis ; TPK I, tau protein kinase I ; TPKII, tau protein kinase I1. cytoskeletal architecture (Cleveland et al., 1977b; Weingarten et al., 1975). Reversible phosphorylation and dephosphorylation reactions apparently regulate functions of tau factor. It has been found that phosphorylated tau factor accumulates in neurofibrillary tangles in the brain of Alzheimer's disease (Ihara et al., 1986 ; Iqbal et al., 1986 ; Kosik et al., 1986 ; Wood et al., 1986). However, these abnormal phosphorylation sites of tau factor in the disease have not completely been elucidated yet. In order to understand the pathophysiology of Alzheimer's disease, it is important to identify protein kinases and protein phosphatases which are related to the phosphorylation and dephosphorylation of abnormal 205