Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P10636 (tau protein)
 5,110 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Expression of tau protein in non-neuronal cells can result in a redistribution of the microtubule cytoskeleton into thick bundles of tau-containing microtubules (Lewis et al.: Nature 342:498-505, 1989; Kanai et al.: J Cell Biol 109:1173-1184, 1989). We reconstituted microtubule bundles using purified tubulin and tau in order to study the assembly of these structures. Taxol-stabilized tubulin polymers were incubated with various concentrations of recombinant human tau and examined by electron microscopy. With increasing concentrations of tau 3 (tau isoform containing three microtubule binding domains) or tau 4 (isoform containing four microtubule binding domains) the microtubules changed orientation from a random distribution to loosely and tightly packed parallel arrays and then to thick cables. In contrast, tau 4L, the tau isoform containing four microtubule binding domains plus a 58-amino acid insert near the N-terminus, showed minimal bundling activity. tau 4-induced bundling could be inhibited by the addition of 0.5 M NaCl or 0.4 mM estramustine phosphate, conditions which are known to inhibit tau binding to microtubules. A tau construct that contained only the microtubule binding domains plus 19 amino acids to the C-terminus was fully capable of bundling microtubules. Phosphorylation of tau 3 with cAMP-dependent protein kinase had no effect on its ability to induce microtubule bundling. These results indicate that tau protein is directly capable of bundling microtubules in vitro, and suggests that different tau isoforms differ in their ability to bundle microtubule filaments.
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PMID:Tau protein induces bundling of microtubules in vitro: comparison of different tau isoforms and a tau protein fragment. 136 May 42

The primary sequence of the microtubule-associated protein tau contains multiple repeats of the sequence -X-Ser/Thr-Pro-X-, the consensus sequence for the proline-directed protein kinase (p34cdc2/p58cyclin A). When phosphorylated by proline-directed protein kinase in vitro, tau was found to incorporate up to 4.4 mol of phosphate/mol of protein. Isoelectric focusing of the tryptic phosphopeptides demonstrated the presence of five distinct peptides with pI values of approximately 6.9, 6.5, 5.6-5.9, 4.7, and 3.6. Mapping of the tryptic phosphopeptides by high performance liquid chromatography techniques demonstrated three distinct peaks. Data from gas phase sequencing, amino acid analysis, and phosphoamino acid analysis suggest that proline-directed protein kinase phosphorylates tau at four sites. Each site demonstrates the presence of a proline residue on the carboxyl-terminal side of the phosphorylated residue. Two phosphorylation sites are located adjacent to the three-repeat microtubule-binding domain that has been found to be required for the in vivo co-localization of tau protein to microtubules. Two other putative phosphorylation sites are located within the identified epitope of the monoclonal antibody Tau-1. Phosphorylation of these sites altered the immunoreactivity of tau to Tau-1 antibody. Since the neuronal microtubule-associated protein tau is multiply phosphorylated in Alzheimer's disease, and Tau-1 immunoreactivity is similarly reduced in neurofibrillary tangles and enhanced after dephosphorylation, phosphorylation at one or more of these sites may correlate with abnormally phosphorylated sites in tau protein in Alzheimer's disease.
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PMID:Proline-directed phosphorylation of human Tau protein. 142 6

We performed phosphate analysis of tau proteins isolated from normal human brain, tau proteins associated with paired helical filaments (PHF-tau), and Alzheimer tau not associated with PHF. These tau fractions were of high purity. Normal and Alzheimer tau were purified by heat treatment, acid extraction and calmodulin-affinity chromatography with or without HPLC. Fractions containing primarily PHF-tau polypeptides of 60, 64 and 68 kDa and their degraded fragments were purified either on a sucrose density gradient as filaments (PHF) or by heat treatment and acid extraction as amorphous proteins (PHF-tau). PHF and PHF-tau were found to contain 6-8 mol phosphate/mol protein while normal and Alzheimer tau proteins contained 1.9 and 2.6 mol phosphate/mol protein, respectively. Upon 2-h incubation with alkaline phosphatase, PHF lost two of the phosphate groups without apparent changes in the stability and morphology of PHF. The released phosphate originated from the N-terminal half of PHF-tau as determined by immunoblotting with antibodies to epitopes blocked by phosphorylation. Tau-1 and E-2, and by a prominent shift in the electrophoretic mobility of some fragments of PHF-tau. The shift in mobility was not observed with the C-terminal fragments of 25-26 kDa, which retained the epitope to Tau 46. The results suggest that the phosphorylation sites not affected by phosphatase may be located in the 25-26 kDa C-terminal region of PHF-tau and may play a role in structural stability of PHF.
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PMID:Phosphate analysis and dephosphorylation of modified tau associated with paired helical filaments. 147 94

The antineoplastic drug estramustine is an adduct of estradiol and nor-nitrogen mustard. It has been shown that this drug interferes with microtubule assembly, an effect mediated by estramustine interaction with microtubule-associated proteins (MAPs). In the present report we demonstrate that estramustine and the phosphorylated derivative of the drug, estramustine-phosphate, inhibit the secretion of interleukin-3 by WEHI-3B cells. These studies also show that the estramustine derivative specifically interacts with a MAPs component found in these cells, which exhibited characteristics ressembling those of tau protein isoforms. Western blots using a unique monoclonal antibody MTB6.22 that recognizes microtubule-binding domains on MAPs, indicated that this WEHI protein factor contained the antigenic determinant that are functionally significant for microtubule assembly. ELISA assays using this antibody, also showed a decrease in the levels of the immunoreactive protein in WEHI cells after treatment with EMP. Interestingly, it has been recently described that the action of estramustine-phosphate is mediated by a direct interaction with MAP-binding sites on the microtubule surface, which are recognized by the site-specific monoclonal antibody. These findings together with immuno-precipitation experiments using anti-interleukin-3 antibodies and the inhibitory effect of the estramustine derivative on WEHI secretion process suggest that this anti-mitotic agent may block IL-3 secretion by a mechanism involving its interaction with a 'tau-like' MAPs component present in these cells.
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PMID:The antineoplastic agent estramustine and the derivative estramustine-phosphate inhibit secretion of interleukin-3 in leukemic cells. Possible roles of MAPs. 148 50

We have analyzed the in vitro phosphorylation of tau protein by Ca2+/calmodulin-dependent protein kinase, casein kinase II, and proline-directed serine/threonine protein kinase. These kinases phosphorylate tau protein in sites localized in different regions of the molecule, as determined by peptide mapping analyses. Focusing on the phosphorylation of tau by protein kinase C, it was calculated as an incorporation of 4 mol of phosphate/mol of tau. Limited proteolysis assays suggest that the phosphorylation sites could be located within the tubulin-binding domain. Direct phosphorylation of synthetic peptides corresponding to the cysteine-containing tubulin-binding region present in both fetal and adult tau isoforms demonstrates that serine 313 is modified by protein kinase C. Phosphorylation of the synthetic peptide by protein kinase C diminishes its binding to tubulin, as compared with the unphosphorylated peptide.
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PMID:Microtubule-associated protein tau is phosphorylated by protein kinase C on its tubulin binding domain. 163 8

The most characteristic cellular change in Alzheimer's disease is the accumulation of aberrant filaments, the paired helical filaments (PHF), in the affected neurons. There is growing evidence from a number of laboratories that dementia correlates better with the accumulation of PHF than of the extracellular amyloid, the second major lesion of Alzheimer's disease. PHF are both morphologically and biochemically unlike any of the normal neurofibrils. The major polypeptides in isolated PHF are microtubule-associated protein tau. Tau in PHF is phosphorylated differently from tau in microtubules. This abnormal phosphorylation of tau in PHF occurs at several sites. The accumulation of abnormally phosphorylated tau in the affected neurons in Alzheimer's disease brain precedes both the formation and the ubiquitination of the neurofibrillary tangles. In Alzheimer's disease brain, tubulin is assembly competent, but the in vitro assembly of microtubules is not observed. In vitro, the phosphate groups in PHF are less accessible than those of tau to alkaline phosphatase. The in vitro dephosphorylated PHF polypeptides stimulate microtubule assembly from bovine tubulin. It is hypothesized that a defect in the protein phosphorylation/dephosphorylation system is one of the earliest events in the cytoskeletal pathology in Alzheimer's disease. Production of nonfunctional tau by its phosphorylation and its polymerization into PHF most probably contributes to a microtubule assembly defect, and consequently, to a compromise in both axoplasmic flow and neuronal function. Index Entries: Alzheimer's disease; mechanisms of neuronal degeneration; neurofibrillary changes; paired helical filaments: biochemistry; microtubule-associated protein tau; abnormal phosphorylation; ubiquitination; microtubule assembly; axoplasmic flow; protein phosphorylation/dephosphorylation.
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PMID:Ubiquitination and abnormal phosphorylation of paired helical filaments in Alzheimer's disease. 172 45

Six hours after heat shocking 2- to 3-month-old male and female Sprague-Dawley rats at 42 degrees C for 15 min, we analyzed tau protein immunoreactivity in SDS extracts of cerebrums and peripheral nerves by using immunoblot analysis and immunohistochemistry with the anti-tau monoclonal antibody Tau-1, which recognizes a phosphate-dependent non-phosphorylated epitope, and with 125I-labeled protein A. In the cerebral extracts, we found altered phosphorylation of tau in heat-shocked females, characterized by a marked reduction in the amount of nonphosphorylated tau, a doubling of the ratio of total (phosphorylated plus nonphosphorylated) tau to nonphosphorylated tau, and the appearance of the slowest moving phosphorylated tau polypeptide (68 kDa). Similar, but milder, changes were observed in male rats. These changes progressively increased in females from 3 to 6 h after heat shocking. In contrast, both phosphorylated tau and nonphosphorylated tau were reduced in peripheral nerves after heat shocking. In immunoblots of SDS extracts from Alzheimer disease-affected brain, the two slowest moving phosphorylated tau polypeptides (62 kDa and 66 kDa, respectively) were detected by Tau-1 after dephosphorylation and by Tau-2 (an anti-tau-monoclonal antibody that recognizes a phosphate-independent epitope) without prior dephosphorylation only in regions that contained tau immunoreactivity in histologic preparations. In addition, quantitative immunoblot analysis of cortex and the underlying white matter with Tau-1 and 125I-labeled protein A showed that the amount of phosphorylated tau progressively increased in the Alzheimer disease-affected cerebral cortex, while concurrently a proportionally lesser amount of tau entered the white matter axons. The similar findings for the rat heat-shock model and Alzheimer disease suggest that life stressors may play a role in the etiopathogenesis of Alzheimer disease.
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PMID:Altered phosphorylation of tau protein in heat-shocked rats and patients with Alzheimer disease. 190 45

In aged human brain and particularly in Alzheimer's disease brain, paired helical filaments (PHFs) accumulate in the neuronal cell. Recently, it has been found that the highly phosphorylated tau protein, one of the microtubule-associated proteins (MAPs), is a component of PHF. The authors attempted to clarify the mechanism underlying the accumulation of PHF from the following two aspects; 1) What is the mechanism of phosphorylation of tau protein? 2) Is the highly phosphorylated tau protein capable of forming PHFs? From rat or bovine microtubule proteins we partially purified and characterized a novel protein kinase that specifically phosphorylated tau and MAP2 among many proteins in the brain extract, and which formed a PHF epitope on the phosphorylated human tau. This enzyme was one of the protein serine/threonine kinases and was independent of known second messengers. The phosphorylation of tau by this enzyme was stimulated by tubulin under the condition of microtubule formation, suggesting that the phosphorylation of tau could occur concomitantly with microtubule formation in the brain. Since this kinase was usually bound to tau but not directly to tubulin, the enzyme was associated with microtubules through tau. From these properties related to tau, this kinase is designated as tau protein kinase. The tau that been phosphorylated with this kinase using [gamma-32P]ATP as a phosphate donor, was digested by endoprotinase Lys-C to produce three labeled fragments, K1, K2 and K3. These three fragments were sequenced and the phosphorylation sites on tau by this kinase were identified. The K2 fragment overlapped with the tau-1 site known to be one of the phosphorylation site in PHF. This result strengthens the possibility that tau protein phosphorylated by tau protein kinase is incorporated into PHF. Tubulin binding sites on tau were located between K1 and K3 fragments, while K2 fragment was located in the neighboring to N-terminus of K1. No phosphorylated sites were found on the tubulin-binding domain of tau, leading us to the idea that the interaction of tau with tubulin could induce conformational changes on tau making it accessible to effects of the kinase. We detected -SP- as a sequence common to three major phosphorylation sites on K1, K2 and K3 fragments. Neurofilament-specific kinase and growth-associated histone H1 kinase are known to recognize the consensus sequence including -SP-. These enzymes exhibit certain properties similar to tau protein kinase and seem to play a crucial role in the regulation of neurite outgrowth or cell growth, through the phosphorylation of a specific substrate, neurofilaments or histone H1, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:[Phosphorylation of tau protein]. 212 Apr 90

A Mn2+/phospholipid-dependent protein phosphatase has been identified and characterized from brain membranes. The phosphatase contains three subunits with molecular weights of 64,000, 54,000, and 35,000 in a 1:1:1 molar ratio. On gel filtration, the enzyme has an apparent molecular weight of approximately 180,000. The phosphatase was active on many substrates, including p-nitrophenyl phosphate, phosphotyrosine, phosphothreonine, phosphorylase a, myelin basic protein, histones, type 1 phosphatase inhibitor-2, microtubule tau protein, and synapsin I. To dephosphorylate phosphoproteins, the phosphatase was dependent on such acidic phospholipids as phosphatidylinositol and phosphatidylserine but not on neutral phospholipids such as phosphatidylcholine and phosphatidylethanolamine. The phospholipid-mediated activation of the phosphatase was time and dose dependent and could be reversed by Triton X-100 or gel filtration. Kinetic study further indicates that phospholipid was able to increase the Vmax of the phosphatase but had no effect on the Km value for substrates, suggesting a direct interaction of phospholipids with the phosphatase. Conversely, in order to dephosphorylate phosphoamino acids such as phosphotyrosine and phosphothreonine, this phosphatase was entirely dependent on Mn2+. Phospholipids had no effect on the dephosphorylation of phosphoamino acids, whereas Mn2+ had no effect on the dephosphorylation of phosphoproteins. It is concluded that this Mn2+/phospholipid-dependent membrane phosphatase has two distinct activation mechanisms. The enzyme requires Mn2+ to dephosphorylate micromolecules, whereas acidic phospholipids are needed to dephosphorylate macromolecules. This suggests that Mn2+ and phospholipids may play a role in regulating the substrate specificity of this multisubstrate membrane phosphatase.
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PMID:Purification and characterization of a Mn2+/phospholipid-dependent protein phosphatase from pig brain membranes. 255 48

Somatostatin and neuropeptide Y are two neuropeptides that are of particular interest in Alzheimer's disease because they are reported to be depleted in cerebral cortex. In the present study we examined somatostatin, neuropeptide Y, and nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase neurons in nine cortical regions in both normal and Alzheimer's disease brains. These three neurochemical markers show a high degree of co-localization (greater than 90%) in nonpyramidal neurons that are primarily distributed in cortical layers II-III, V-VI, and, most prominently, in infracortical white matter. The highest cell density was in temporal and parietal association cortex. The major morphological abnormality in Alzheimer's disease brains was a marked pruning and distortion of fiber plexuses with an apparent reduction in fiber density. In contrast, perikaryal density was preserved except for a reduction in parietal association cortex. Approximately 10 to 15% of senile plaques in the inferior temporal gyrus contained abnormal neurites. Additional abnormal collections of neurites without plaque cores were frequently found in layers II-III and V-VI. Neuropeptide Y and somatostatin were co-localized in abnormal neurites, suggesting an origin from local intrinsic neurons in which the two peptides are co-localized. Double immunofluorescence staining for both tau protein, a major antigenic component of paired helical filaments, and either somatostatin or neuropeptide Y showed that these neurons do not contain tau-immunoreactive neurofibrillary tangles. The morphological correlate of reduced somatostatin and neuropeptide Y content in Alzheimer's disease brain therefore appears to be a distortion and reduction in fiber plexuses. In addition, it is apparent that these neurons can develop widespread morphological abnormalities in the absence of neurofibrillary tangle formation.
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PMID:Cortical somatostatin, neuropeptide Y, and NADPH diaphorase neurons: normal anatomy and alterations in Alzheimer's disease. 289 22


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