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G(1) and G(2) cell-cycle arrest following microtubule depolymerization in human breast cancer cells
April L Blajeski1, Vy A Phan, Timothy J Kottke
1Department of Molecular Pharmacology and Experimental Therapeutics, Tumor Biology Program, Mayo Graduate School, Mayo Clinic, 200 First Street SW, Rochester, MN 55905, USA.
Abstract:
Microtubule-depolymerizing agents are widely used to synchronize cells, screen for mitotic checkpoint defects, and treat cancer. The present study evaluated the effects of these agents on normal and malignant human breast cell lines. After treatment with 1 microM nocodazole, seven of ten breast cancer lines (type A cells) arrested in mitosis, whereas the other three (type B cells) did not. Similar effects were observed with 100 nM vincristine or colchicine. Among five normal mammary epithelial isolates, four exhibited type A behavior and one exhibited type B behavior. Further experiments revealed that the type B cells exhibited a biphasic dose-response curve, with mitotic arrest at low drug concentrations (100 nM nocodazole or 6 nM vincristine) that failed to depolymerize microtubules and a p53-independent p21(waf1/cip1)-associated G(1) and G(2) arrest at higher concentrations (1 microM nocodazole or 100 nM vincristine) that depolymerized microtubules. Collectively, these observations provide evidence for coupling of premitotic cell-cycle progression to microtubule integrity in some breast cancer cell lines (representing a possible "microtubule integrity checkpoint") and suggest a potential explanation for the recently reported failure of some cancer cell lines to undergo nocodazole-induced mitotic arrest despite intact mitotic checkpoint proteins.
Insights
Some breast cancer cells resist mitotic arrest from microtubule-depolymerizing drugs, revealing a potential "microtubule integrity checkpoint." This response differs from normal cells and suggests new therapeutic strategies for cancer treatment.
Area of Science:
- Cell Biology
- Cancer Research
- Pharmacology
Background:
- Microtubule-depolymerizing agents are crucial tools in cell biology and cancer therapy.
- Understanding differential cellular responses to these agents is vital for optimizing their use.
Purpose of the Study:
- To investigate the varied responses of normal and malignant human breast cells to microtubule-depolymerizing agents.
- To elucidate the mechanisms underlying resistance to mitotic arrest in certain cancer cell lines.
Main Methods:
- Treatment of human breast cell lines (normal and malignant) with nocodazole, vincristine, and colchicine at varying concentrations.
- Analysis of cell cycle progression, mitotic arrest, and microtubule depolymerization.
- Investigation of p53 and p21(waf1/cip1) involvement in cellular responses.
Main Results:
- Seven of ten breast cancer lines and four of five normal mammary epithelial isolates exhibited mitotic arrest (Type A).
- Three breast cancer lines and one normal isolate showed resistance to mitotic arrest (Type B).
- Type B cells displayed a biphasic dose-response, with G1/G2 arrest at higher drug concentrations and failed mitotic arrest at lower concentrations.
Conclusions:
- Evidence suggests a "microtubule integrity checkpoint" coupling cell cycle progression to microtubule stability in some breast cancer cells.
- Differential responses to microtubule agents may explain treatment failures and offer insights into cancer cell vulnerabilities.