Differential Taxol-dependent arrest of transformed and nontransformed cells in the G1 phase of the cell cycle, and specific-related mortality of transformed cells.

Abstract

Abstract. Taxol (paclitaxel) induces a microtubule hyperassembled state, and effectively blocks cells in mitosis. Here we report that Taxol also induces a stable late-G1 block in nontransformed and WI-38 mammalian fibroblast cells, but not in T antigen-transformed cells of the same parental lineage. G1 arrest is characterized by partially dephosphorylated pRb, and inactive cdk2 kinase. Nontransformed cells recover normally from Taxol arrest. In contrast, T antigen transformed cells continue inappropriately past both G1 and G2-M in the presence of Taxol, and undergo a rapid death upon release. These results demonstrate a microtubule sensitive step in G1 regulation of nontransformed fibroblast cells. Also, Taxol selectively induces death of transformed cells, possibly because they slip the Taxol-dependent G1 arrest, as well as G2/M arrest, which are both specific to nontransformed cells. M ICROTUBULES play distinct roles at different stages of the cell cycle. During interphase, they establish cell polarity, are involved in the organization of the cytoplasm, and play a vital role in vesicle transport. During mitosis, microtubules form into a mitotic spindle that is centrally important both in chromosome congression to the metaphase plate and in chromatid separation during anaphase.In mitosis, the role of microtubules in regulating mitotic exit extends beyond their mechanical function in chromosome movement. Microtubules also have an intrinsic regulatory function in mitotic exit, perhaps serving as the site of degradation of cyclin B and for inactivation of p34 cdc2 kinase (Kubiak et al., 1993;Andreassen and Margolis, 1994). We have recently found that there is a strong correlation between the assembly state of microtubules and the metabolic ability of the cell to inactivate p34 cdc2 and induce mitotic exit (Andreassen and Margolis, 1994). Nocodazole inhibits microtubule assembly in a concentration-dependent manner (Hoebeke et al., 1976;Jordan et al., 1992), and concentrations of nocodazole that block microtubule assembly also inhibit the activation of the mitotic exit machinery. In contrast to nocodazole, Taxol (paclitaxel) induces hyperassembly of microtubules (Schiff et al., 1979;Jordan et al., 1993). BHK cells blocked with Taxol in mitosis undergo inappropriate mitotic exit, either through the checkpoint override activity of the protein kinase inhibi-

Multiple centrosomes arise from tetraploidy checkpoint failure and mitotic centrosome clusters in p53 and RB pocket protein-compromised cells

“…To analyze cell-cycle profiles, cells were prepared for flow cytometry by using propidium iodide as a marker for DNA content, as described (35). Data were collected by using a FACScan flow cytometer, and results were analyzed by using CELLQUEST software (both from Becton Dickinson).…”

Paclitaxel-induced cell death

“…20 All of these features of paclitaxel suggest that it may differentially kill cancer cells but spare normal cells.…”

Inactivation of wild-type p53 by a dominant negative mutant renders MCF-7 cells resistant to tubulin-binding agent cytotoxicity

“…It is generally accepted that TBA inhibit cell proliferation by inducing a sustained mitotic arrest at the metaphase/anaphase transition, which is associated with the formation of an incomplete metaphase plate of chromosomes and an abnormal assembly of spindle microtubules (Jordan et al, 1996;Rudner and Murray, 1996). However other mechanisms for taxane-induced cytotoxicity have been reported, including a late G 1 block in non-transformed cells (Trielli et al, 1996) and inhibition of centrosomal duplication in late G 2 (Paoletti et al, 1997).…”