Specific rearrangement of the microtubular network during the cell cycle phases and correlation with micronucleation and death induced by anticancer drugs in NIH/3T3 subcultures.

The changes of the microtubular network induced by microtubule destabilizing (Vinblastine, VBL) and stabilizing (Taxol, TAX) agents were studied in NIH/3T3 fibroblastic cells in conventional culture conditions (NIHb) and in a subpopulation (NIHs), obtained after serum deprivation and expressing different morphofunctional features and higher cytokinetic activity. In this cell model, we analyzed VBL and TAX effects on cell cycle and microtubular network, in relation to cell death. In NIHb cells, VBL induced higher microtubule depolymerization, prevalence of tubulin paracrystals and micronucleation, while, in NIHs cells, lower depolymerization and appearance of tubulin spiral-like structures, with lower micronucleation, increase of apoptosis and disappearance of high polyploid cells. DNA static cytofluorometry of cells showing paracrystals or spirals permitted correlation of the appearance of these tubulin aggregation forms with the cell cycle phases. In NIHb cultures, the DNA content curves, in cells with paracrystals or spirals, showed a similar trend, with a higher frequency of the two anomalies in the G2/M phase. In NIHs cultures, paracrystals and spirals are found in G2/M cells, while G1 cells showed prevailingly paracrystals. TAX induced the appearance of microtubule bundles in the two cultures. The prevalence of circular bundles was found in NIHb cells, while a higher number of linear bundles was shown in NIHs cells. In NIHb cells, circular bundles were related to higher apoptosis and micronucleation. DNA cytofluorometry, in cells with linear or circular bundles, showed that the latter was present with high frequency in NIHb cells in all the cell cycle phases; in NIHs cells, they appeared, with lower frequency, prevailing in the S-G2/M phase. Furthermore, in NIHs cells, the appearance of linear bundles in G1 cells was related to a lower micronucleation. These finding showed that microtubule reorganization in different cell cycle phases could play a role in the progression of nuclear fragmentation/micronucleation relating to cell death.