Cytoskeleton functions

Malorni, W., Straface, E., Di Genova, G., Fattorossi, A., Rivabene, R., Camponeschi, B., Masella, R., and Viora, M., 1997, Oxidized low-density hpoproteins affect natural killer cell activity by impairing cytoskeleton function and altering the cytokine network, Exp. Cell Res. 236 436-445. 

One theory of the pathogenesis of Alzheimer s disease proposes that increased production or decreased secretion of the Ap peptides leads to accumulation of these peptides. A second theory proposes that an abnormal x-protein causes the formation of intracellular neurofibrillary tangles. x-Proteins are important in the maintenance of cytoskeleton function and axonal transport of proteins. Another theory is that Ap accumulation is a precipitating factor that is followed by the development of the x-enriched tangles in the dying neurons. 

Yarar, D., Waterman-Stoier, C M. and Schmid, S.L. (2005) A dynamic actin cytoskeleton functions at multiple stages of clathrin-mediated endocytosis. Mol. Biol. Cell 16,964-975. 

Juliano, R. L. 2002. Signal transduction by cell adhesion receptors and the cytoskeleton functions of integrins, cadherins, selectins, and immunoglobulin-superfamily members. Ann. Rev. Pharmacol. Toxicol. 42 283-323. 

SegaU, J.E. and Gerisch, G. (1989). Genetic approaches to cytoskeleton function and the control of cell motflity. Curr. Opin. Cell Biol. 1, 44-50. 

Fig. 1. The GP Ib-IX-V complex. The complex consists of seven transmembrane polypeptides denoted GP Iba (mol wt 145,000), GP IbP (mol wt 24,000), GPIX (mol wt 17,000) and GP V (mol wt 82,000), in a stoichiometry of 2 2 2 1. The hatched region represents the plasma membrane. The area above the hatched region represents the extracellular space that below represents the cytoplasm. The complex is a major attachment site between the plasma membrane and the cytoskeleton. Two molecules associated with the cytoplasmic domain are depicted a 14-3-3 dimer, which may mediate intracellular signaling, and actin-binding protein, which connects the complex to the cortical cytoskeleton and fixes its position and influences its function.

The cytoskeleton also contains different accessory proteins, which, in accordance with their affinities and functions, are designated as microtubule-associated proteins (MAPs), actin-binding proteins (ABPs), intermediate-filament-associated proteins (IFAPs), and myosin-binding proteins. This chapter is focused on those parts of the cytoskeleton that are composed of microfilaments and microtubules and their associated proteins. The subject of intermediate filaments is dealt with in detail in Volume 2. 

More than 50 proteins have been discovered in the cytosol of nonmuscle cells that bind to actin and affect the assembly and disassembly of actin filaments or the cross-linking of actin filaments with each other, with other filamentous components of the cytoskeleton, or with the plasma membrane. Collectively, these are known as actin-binding proteins (ABPs). Their mechanisms of actions are complex and are subject to regulation by specific binding affinities to actin and other molecules, cooperation or competition with other ABPs, local changes in the concentrations of ions in the cytosol, and physical forces (Way and Weeds, 1990). Classifications of ABPs have been proposed that are based on their site of binding to actin and on their molecular structure and function (Pollard and Cooper, 1986 Herrmann, 1989 Pollard et al., 1994). These include the following ... 

Thus far, microtubules and actin filaments and their associated proteins have been discussed to advantage as independent cytoskeletal components. In actual fact, all of the components of the cytoskeleton (including intermediate filaments) are precisely integrated with one another (Langford, 1995), as well as with various cytoplasmic organelles, the nuclear membrane, the plasma membrane, and the extracellular matrix. In its totality the cytoskeleton subserves many coordinated and regulated functions in the cell ... 

The membrane cytoskeleton (inclusive of the submembranous actin-spec-trin network) may function in the establishment and maintenance of restricted domains of specific proteins on the plasma membrane of polarized epithelial cells (Rodriguez-Boulan and Nelson, 1989 Mays et al., 1994). 

Mays, R.W., Beck, K.A.. Nelson, W.J. (1994). Organization and function of the cytoskeleton in polarized epithelial cells a component of the protein sorting machinery. Curr. Opin. Cell Biol. 6, 16-24. 

Tiwari, S.C., Wick, S.M., Williamson, R.E., Gunning, B.E. (1984). Cytoskeleton and integration of cellular function in cells of higher plants. J. Cell Biol. 99,63S-69S. 

In order to anticipate possible modes of regulation of cytoskeleton dynamics in vivo, it is necessary (a) to identify the kinetic intermediates involved in the polymerization process and to characterize their structural and functional properties and (b) to define the essential elementary steps in the hydrolysis process. 

Nonmuscle cells perform mechanical work, including self-propulsion, morphogenesis, cleavage, endocytosis, exocytosis, intracellular transport, and changing cell shape. These cellular functions are carried out by an extensive intracellular network of filamentous structures constimting the cytoskeleton. The cell cytoplasm is not a sac of fluid, as once thought. Essentially all eukaryotic cells contain three types of filamentous struc-mres actin filaments (7-9.5 nm in diameter also known as microfilaments), microtubules (25 nm), and intermediate filaments (10-12 nm). Each type of filament can be distinguished biochemically and by the electron microscope. 

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