The effects of taxol on the organization of the cytoskeleton in cultured ovarian granulosa cells.

Exposure of ovarian granulosa cells to taxol, a potent microtubule assembly promoting and stabilization agent, results in a time and dose-dependent alteration in the organization of cytoplasmic filaments (microtubules, microfilaments, intermediate filaments) and organelles. Transmission electron microscopy and fluorescence microscopy are used in conjunction with various antimitotic drugs to evaluate the action of taxol on suspension and monolayer cultures. Taxol treatment (1.0 microM) of freshly isolated suspended cells for 4 h leads to the formation of multiple bundles of microtubules emanating from a single centrosomal organizing center. Within 4 h after addition to monolayer cultures, 1.0 microM taxol induces a lateral aggregation of microtubules which, by 12 to 24 h of treatment, results in the appearance of dense bundles of tightly-packed microtubules located near the centrosome, close to the outer nuclear envelope, and at peripheral cytoplasmic sites. By electron microscopy, both lateral and end-on associations between bundled microtubules and the nuclear envelope are apparent. During the course of taxol-induced bundling, intermediate filaments are altered from a normally dispersed fibrous network into perinuclear aggregates. Microtubule bundling is also associated with a rearrangement of actin filaments from stress fibers into a marginal distribution, and actin appears to be excluded from sites of bundle formation. When granulosa cells are treated with equivalent concentrations of the microtubule-disrupting drugs, colchicine or nocodazole, either before or during taxol treatment, bundle formation is prevented suggesting that an intact microtubule network is required for taxol-induced bundling. Colchicine, but not nocodazole, is able to reverse the effects of taxol on bundle formation. The data suggest that the cellular distribution of cytoplasmic organelles, intermediate filaments, and microfilaments are regulated by the cytoplasmic microtubule complex.