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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The tau protein is a neuronal microtubule-associated protein. Apart of its physiological function-the binding to and stabilization of microtubules-tau is found in Alzheimer's disease brain as insoluble fibers, the so-called "paired helical filaments" (PHFs). Investigating the fundamentals of tau polymerization is indispensable for identifying inhibitory conditions or compounds preventing PHF formation, which may slow down or even stop the degeneration of neurons in Alzheimer's disease. In this chapter, we describe the methods necessary for studying the characteristics of tau polymerization to PHFs. These include: a purification protocol for recombinantly expressed tau; a general method for the polyanion induced polymerization of tau to PHFs; the quantitation of PHFs by a fluorescence-based assay; the imaging and verification of PHFs by negative stain transmission electron microscopy.
Methods Mol Biol 2005
PMID:Purification of recombinant tau protein and preparation of Alzheimer-paired helical filaments in vitro. 1598 May 94

Mammalian septins constitute a family of at least 12 GTP-binding proteins that can form hetero-oligomers and that are sometimes found in association with actin or microtubule filaments. However, their functions are not understood. Using RNA interference, we found that suppression of septin expression in HeLa cells caused a pronounced increase in microtubule stability. Mass spectroscopic analysis of proteins coprecipitating with Sept6 identified the microtubule-associated protein MAP4 as a septin binding partner. A small, proline-rich region in the C-terminal half of MAP4 bound directly to a Sept 2:6:7 heterotrimer, and to the Sept2 monomer. The trimer blocked the ability of this MAP4 fragment to bind and bundle microtubules in vitro. In intact cells, MAP4 was required for the stabilization of microtubules induced by septin depletion. Moreover, septin depletion increased the number of cells with abnormal nuclei, and this effect was blocked by gene silencing of MAP4. These data identify a novel molecular function for septins in mammalian cells: the modulation of microtubule dynamics through interaction with MAP4.
Mol Biol Cell 2005 Oct
PMID:Mammalian septins regulate microtubule stability through interaction with the microtubule-binding protein MAP4. 1609 51

We have previously demonstrated that EPAC1 interacts with light chain (LC) 2 of microtubule-associated protein (MAP) 1A. In the present study, we investigated whether the structurally related LC1 of MAP1B also interacts with EPAC1. We demonstrate that LC1 copurifies with EPAC1 from extracts of PC-12 cells, using cyclic AMP-agarose. Using recombinant LC1 and LC2 in pull-down and solid phase binding assays, we demonstrate direct interaction with a glutathione S-transferase-fusion of the cyclic AMP-binding (CAMP) domain of EPAC1. We also tested whether LC1 directed intracellular targeting of EPAC1 through its interaction with the CAMP domain. EPAC1 was found be in the soluble and particulate, nuclear/perinuclear fractions of cells. We found that the catalytic (CAT) domain of EPAC1, and not the CAMP domain, was responsible for recruitment to the nuclear/perinuclear fraction of cells. The targeting sequence responsible was located between amino acids 764 and 838 of EPAC1. Overexpresssion of an isolated CAT domain in COS1 cells was found to displace endogenous EPAC1 from the nuclear/perinuclear fraction, thereby inhibiting EPAC-activated Rap1 in this compartment. In contrast, LC1 was not able to compete for the binding of EPAC1 to this fraction. LC1, however, was able to enhance interaction of EPAC1 with cyclic AMP and heightened the ability of EPAC to activate Rap1. Antibody disruption of EPAC1/LC1 interaction in PC-12 cells ablated the ability of cyclic AMP to activate Rap1. LC1 is therefore not involved in intracellular targeting of EPAC1, but it is rather a molecular chaperone of EPAC activity toward Rap1.
Mol Pharmacol 2006 Jan
PMID:Microtubule-associated protein 1B-light chain 1 enhances activation of Rap1 by exchange protein activated by cyclic AMP but not intracellular targeting. 1624 78

TPX2, a microtubule-associated protein, is required downstream of Ran-GTP to induce spindle assembly. TPX2 activity appears to be tightly regulated during the cell cycle, and we report here one molecular mechanism for this regulation. We found that TPX2 protein levels are cell cycle regulated, peaking in mitosis and declining sharply during mitotic exit. TPX2 is degraded in mitotic extracts, as well as in HeLa cells exiting from mitosis. This instability depends, both in vitro and in vivo, on the anaphase-promoting complex/cyclosome (APC/C), a ubiquitin ligase that controls mitotic progression. In a reconstituted system, TPX2 is efficiently ubiquitinated by APC/C that has been activated by Cdh1. Two discrete elements in TPX2 are required for recognition by APC/C(Cdh1): a KEN box and a novel element in amino acids 1 to 86. Interestingly, the latter element, which has no known APC/C recognition motifs, is required for the ubiquitination of TPX2 by APC/C(Cdh1) in vitro and for its degradation in vivo. We conclude that APC/C(Cdh1) controls the stability of TPX2, thereby ensuring accurate regulation of the spindle assembly in the cell cycle.
Mol Cell Biol 2005 Dec
PMID:Anaphase-promoting complex/cyclosome controls the stability of TPX2 during mitotic exit. 1628 63

Multiple mitotic kinesins and microtubule-associated proteins (MAPs) act in concert to direct cytokinesis (Glotzer, M. 2005. Science. 307:1735-1739). In anaphase cells, many of these proteins associate with an antiparallel array of microtubules termed the central spindle. The MAP and microtubule-bundling protein PRC1 (protein-regulating cytokinesis 1) is one of the key molecules required for the integrity of this structure (Jiang, W., G. Jimenez, N.J. Wells, T.J. Hope, G.M. Wahl, T. Hunter, and R. Fukunaga. 1998. Mol. Cell. 2:877-885; Mollinari, C., J.P. Kleman, W. Jiang, G. Schoehn, T. Hunter, and R.L. Margolis. 2002. J. Cell Biol. 157:1175-1186). In this study, we identify an interaction between endogenous PRC1 and the previously uncharacterized kinesin KIF14 as well as other mitotic kinesins (MKlp1/CHO1, MKlp2, and KIF4) with known functions in cytokinesis (Hill, E., M. Clarke, and F.A. Barr. 2000. EMBO J. 19:5711-5719; Matuliene, J., and R. Kuriyama. 2002. Mol. Biol. Cell. 13:1832-1845; Kurasawa, Y., W.C. Earnshaw, Y. Mochizuki, N. Dohmae, and K. Todokoro. 2004. EMBO J. 23:3237-3248). We find that KIF14 targets to the central spindle via its interaction with PRC1 and has an essential function in cytokinesis. In KIF14-depleted cells, citron kinase but not other components of the central spindle and cleavage furrow fail to localize. Furthermore, the localization of KIF14 and citron kinase to the central spindle and midbody is codependent, and they form a complex depending on the activation state of citron kinase. Contrary to a previous study (Di Cunto, F., S. Imarisio, E. Hirsch, V. Broccoli, A. Bulfone, A. Migheli, C. Atzori, E. Turco, R. Triolo, G.P. Dotto, et al. 2000. Neuron. 28:115-127), we find a general requirement for citron kinase in human cell division. Together, these findings identify a novel pathway required for efficient cytokinesis.
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PMID:KIF14 and citron kinase act together to promote efficient cytokinesis. 1643 29

Mutations in gigaxonin were identified in giant axonal neuropathy (GAN), an autosomal recessive disorder. To understand how disruption of gigaxonin's function leads to neurodegeneration, we ablated the gene expression in mice using traditional gene targeting approach. Progressive neurological phenotypes and pathological lesions that developed in the GAN null mice recapitulate characteristic human GAN features. The disruption of gigaxonin results in an impaired ubiquitin-proteasome system leading to a substantial accumulation of a novel microtubule-associated protein, MAP8, in the null mutants. Accumulated MAP8 alters the microtubule network, traps dynein motor protein in insoluble structures and leads to neuronal death in cultured wild-type neurons, which replicates the process occurring in GAN null mutants. Defective axonal transport is evidenced by the in vitro assays and is supported by vesicular accumulation in the GAN null neurons. We propose that the axonal transport impairment may be a deleterious consequence of accumulated, toxic MAP8 protein.
Hum Mol Genet 2006 May 01
PMID:Gene targeting of GAN in mouse causes a toxic accumulation of microtubule-associated protein 8 and impaired retrograde axonal transport. 1656 60

Type I lissencephaly results from mutations in the doublecortin (DCX) and LIS1 genes. We generated Dcx knockout mice to further understand the pathophysiological mechanisms associated with this cortical malformation. Dcx is expressed in migrating interneurons in developing human and mouse brains. Video microscopy analyses of such tangentially migrating neuron populations derived from the medial ganglionic eminence show defects in migratory dynamics. Specifically, the formation and division of growth cones, leading to the production of new branches, are more frequent in knockout cells, although branches are less stable. Dcx-deficient cells thus migrate in a disorganized manner, extending and retracting short branches and making less long-distant movements of the nucleus. Despite these differences, migratory speeds and distances remain similar to wild-type cells. These novel data thus highlight a role for Dcx, a microtubule-associated protein enriched at the leading edge in the branching and nucleokinesis of migrating interneurons.
Hum Mol Genet 2006 May 01
PMID:Branching and nucleokinesis defects in migrating interneurons derived from doublecortin knockout mice. 1657 5

We report here an efficient functional genomic analysis by combining information on the gene expression profiling, cellular localization, and loss-of-function studies. Through this analysis, we identified Cep55 as a regulator required for the completion of cytokinesis. We found that Cep55 localizes to the mitotic spindle during prometaphase and metaphase and to the spindle midzone and the midbody during anaphase and cytokinesis. At the terminal stage of cytokinesis, Cep55 is required for the midbody structure and for the completion of cytokinesis. In Cep55-knockdown cells, the Flemming body is absent, and the structural and regulatory components of the midbody are either absent or mislocalized. Cep55 also facilitates the membrane fusion at the terminal stage of cytokinesis by controlling the localization of endobrevin, a v-SNARE required for cell abscission. Biochemically, Cep55 is a microtubule-associated protein that efficiently bundles microtubules. Cep55 directly binds to MKLP1 in vitro and associates with the MKLP1-MgcRacGAP centralspindlin complex in vivo. Cep55 is under the control of centralspindlin, as knockdown of centralspindlin abolished the localization of Cep55 to the spindle midzone. Our study defines a cellular mechanism that links centralspindlin to Cep55, which, in turn, controls the midbody structure and membrane fusion at the terminal stage of cytokinesis.
Mol Biol Cell 2006 Sep
PMID:Cep55, a microtubule-bundling protein, associates with centralspindlin to control the midbody integrity and cell abscission during cytokinesis. 1679 Apr 97

Cytoskeletal components play an important role in maintaining cellular architecture and internal organization, with clear involvement of defining cell shape, in cell division and other cellular processes, such as neurite extension and maintenance. Alterations of cytoskeleton in human neuroblastoma SK-N-SH cells after exposure to different concentrations of tri-ocresyl phosphate (TOCP) for 12 hr were investigated. TOCP decreased the cell viability in a dose-dependent manner; the viability of SK-N-SH was reduced to approximately 50% of baseline after a 12-hour exposure to TOCP at high concentration (5 mM). Biochemical characterization by western blotting revealed that 1 and 5 mM concentrations of TOCP significantly inhibited the expression of neurofilament high molecular weight protein (NF-H), and that 5 mM TOCP inhibited expression of microtubule-associated protein 2c and tau protein, but not beta-actin. Indirect immunofluorescence analysis revealed that higher concentrations of TOCP decreased the length of neuritis and changed the structure of microfilaments, which are associated with NF-H. In addition, activities of neuropathy target esterase and acetylcholinesterase were significantly reduced after exposure to 5 mM TOCP for 12 hr. Together, these results suggested that the loss of cytoskeletal components is the early event during the process of TOCP toxicity towards human neuroblastoma SK-N-SH cells.
Mol Cell Biochem 2006 Oct
PMID:Effect of tri-o-cresyl phosphate on cytoskeleton in human neuroblastoma SK-N-SH cell. 1690 9

The tau gene encodes a microtubule-associated protein that is critical for neuronal survival and function. Splicing defects in the human tau gene lead to frontotemporal dementia with Parkinsonism linked to chromosome 17 (FTDP-17), an autosomal dominant neurodegenerative disorder. Genetic mutations associated with FTDP-17 often affect tau exon 10 alternative splicing. To investigate mechanisms regulating tau exon 10 alternative splicing, we have developed a green fluorescent protein reporter for tau exon 10 skipping and an expression cloning strategy to identify splicing regulators. A role for SRp54 (also named SFRS11) as a tau exon 10 splicing repressor has been uncovered using this strategy. The overexpression of SRp54 suppresses tau exon 10 inclusion. RNA interference-mediated knock-down of SRp54 increases exon 10 inclusion. SRp54 interacts with a purine-rich element in exon 10 and antagonizes Tra2beta, an SR-domain-containing protein that enhances exon 10 inclusion. Deletion of this exonic element eliminates the activity of SRp54 in suppressing exon 10 inclusion. Our data support a role of SRp54 in regulating tau exon 10 splicing. These experiments also establish a generally useful approach for identifying trans-acting regulators of alternative splicing by expression cloning.
Mol Cell Biol 2006 Sep
PMID:SRp54 (SFRS11), a regulator for tau exon 10 alternative splicing identified by an expression cloning strategy. 1694 17


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