Microtubule polymerization

The influences of herbicides on cell division fall into two classes, ie, dismption of the mitotic sequence and inhibition of mitotic entry from interphase (G, S, G2). If ceU-cycle analyses indicate increases in abnormal mitotic figures, combined with decreases in one or more of the normal mitotic stages, the effect is upon mitosis. Mitotic effects usually involve the microtubules of the spindle apparatus in the form of spindle depolymerization, blocked tubulin synthesis, or inhibited microtubule polymerization (163). Alkaloids such as colchicine [64-86-8J,viahla.stiae [865-21-4] and vincristine [57-22-7] dismpt microtubule function (164). Colchicine prevents microtubule formation and promotes disassembly of those already present. Vinblastine and vincristine also bind to free tubulin molecules, precipitating crystalline tubulin in the cytoplasm. The capacities of these dmgs to interfere with mitotic spindles, blocking cell division, makes them useful in cancer treatment. 

A new antitumor drug, taxol, has been isolated from the bark of Taxus brevifolia, the Pacific yew tree. Like vinblastine and colchicine, taxol inhibits cell replication by acting on microtubules. Unlike these other antimitotic drugs, however, taxol stimulates microtubule polymerization and stabilizes microtubules. 

The remarkable success of taxol in treatment of breast and ovarian cancers stimulated research efforts to synthesize taxol directly and to identify new antimitotic agents that, like taxol, stimulate microtubule polymerization. 

In vitro culture isolated brain cells exposed for 20 h to graded concentrations of nickel chloride up to 116 mg Ni/L DOMESTIC DOG, Canis familiaris Diet Time- and dose-dependent effects on kinetics of brain microtubule polymerization effects reversed on removal of Ni2+ from culture media 4... 

Fig. 4. Transmission electron microscopy of MTP reaction mixtures, (a) An opened area is seen in a microtubule polymerized in the presence of an IC concentration (3 x 10 W) of deoxydesethyl VBL (5). (b) Single spirals are formed from MTP and 10 M 5. (c) Spiral aggregates are formed from MTP and 10 M VBL. (d) MTP incubated with an lCs concentration (2 X 10 Af) of epimethyldeoxydesethyl VBL (4) formed spiral aggregates both free in solution (single arrows) and associated with microtubules (double arrows), (e) Greater magnification of MTP incubated with an 1C , concentration (2 x 10 M) of methyldeoxyde-sethyl VBL (3) displays a free spiral (arrow) and spiralized material on the microtubules. Bar, 0.1 p.m.

Vinblastine, vincristine, and structurally related analogs inhibit microtubule polymerization by 50% at concentrations in the range 0.1-1 xM, and the process of tubulin addition to preformed microtubules, at steady state, is comparably sensitive to inhibition by these agents (5). As shown in Table I, the differences in values for inhibition of steady-state tubulin addition by vinblastine, vincristine, vindesine, and vinepidine were relatively small, but the pattern of activity in the tubulin addition system did not parallel that observed when the compounds were evaluated for effects on the proliferation of B16 melanoma cells in vitro. Vinepidine was more than twice as potent as vinblastine as an inhibitor of steady-state tubulin addition but nearly 10-fold less potent than vinblastine as an inhibitor of cell growth (i). 

The pathway of exchangeable-site GTP hydrolysis associated with bovine brain microtubule polymerization was... 

Although taxanes bind to p-tubulin promoting microtubule polymerization and stabilization of the spindle complex, they serve to cause a sustained mitotic block at the metaphase/anaphase boundary. This block will occur at a lower concentration than that which is required to increase the microtubule mass (10). However, it is not completely clear how this interaction with microtubules translates into cell death. Morphologic features and the characteristic DNA fragmentation patterns seen in the setting of apoptosis have been documented in tumor cells after therapy with taxanes (10). These observations are accompanied by the phosphorylation of Bcl-2, an anti-apoptotic protein, changing the cellular balance between Bax and Bcl-2 to a status that favors apoptosis (11). 

Hunter, A. W., and Wordeman, L. (2000). How motor proteins influence microtubule polymerization dynamics./ Cell Sci. 113, 4379-4389. 

Oteiza PI, Golub MS, Gershwin ME, et al. 1989. The influence of high dietary aluminum on brain microtubule polymerization in mice. Toxicol Lett 47 279-285. 

MT in the cell [5,10]. The interference with microtubule polymerization dynamics is regarded as the basis of drug activity rather than their effect on MT polymer mass. 

Antibodies to OP-tyrosine will be made. These antibodies will be used to diagnose OP exposure in a biosensor assay with saliva, sweat, or urine. New biomarkers of OP exposure will be identified using mass spectrometry and the new OP-tyrosine antibodies. The identification of new biomarkers for low-dose OP exposme is expected to lead to an understanding of how neurotoxicity is caused by OP doses that are too low to inhibit acetylcholinesterase. For example, it is possible that disruption of microtubule polymerization by OP-adduct formation may explain cognitive impairment from OP exposure. 

Biochemical Studies Diminutol not only inhibited the microtubule polymerization in both interphase and mitosis extract, but also caused microtubules to shorten in interphase and prevented proper spindle formation in mitosis in Xenopus XL177 cells at a concentration of 50 p,M. The effects on cells were reversible, and, after diminutol was washed out, normal microtubule arrays in... 

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