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Antimicrotubule agents induce polyploidization of human leukaemic cell lines with megakaryocytic features
B van der Loo1, Y Hong, V Hancock
1Department of Medicine, King's College School of Medicine and Dentistry, London, UK.
Abstract:
In most eukaryotic cells the regular alternation of chromosome reduplication and cell division is controlled by interdependent relationships which prevent progression to the next cell-cycle phase unless the preceding phase has been completed. Megakaryocytes become polyploid by allowing many rounds of DNA replication without completion of intervening mitoses. To assess the role of cell-cycle dependencies in megakaryocytopoiesis we examined human cell lines which express megakaryocytic features for their ability to continue DNA synthesis and undergo polyploidization in the presence of mitotic poisons. Treatment of HEL cells with colcemid blocked cell division but not cellular DNA synthesis. DNA content distributions of cells treated with colcemid for 48 h showed a marked increase in the proportion of polyploid cells (57.6% +/- 9.9%, n = 16), an increase in cellular size and nuclear lobation. Identical effects were observed in HEL cells treated with colchicine, nocodazole or taxol but not with the inactive compound lumicolchicine. Induction of polyploidization by antimicrotubule agents was also observed in the megakaryoblastic cell lines MEG-01, DAMI and UT-7 but not in the T-cell line MOLT-4 or the promyelocytic cell line HL-60. These results suggest that dependency of DNA replication on completion of the previous mitosis is suppressed in the megakaryocytic lineage.
Insights
Megakaryocytes, crucial for platelet production, can replicate DNA without dividing. This study shows megakaryocytic cell lines bypass cell-cycle checkpoints, enabling polyploidization even when cell division is blocked.
Area of Science:
- Cell Biology
- Hematopoiesis
- Molecular Biology
Background:
- Eukaryotic cell cycles normally alternate DNA replication and division, with checkpoints preventing progression until prior phases are complete.
- Megakaryocytes achieve polyploidy through multiple DNA replications without intervening cell divisions, a process distinct from typical cell cycles.
Purpose of the Study:
- To investigate the role of cell-cycle dependencies in megakaryocytopoiesis (megakaryocyte development).
- To determine if megakaryocytic cell lines can undergo DNA synthesis and polyploidization despite blocked cell division.
Main Methods:
- Examined human cell lines with megakaryocytic features (HEL, MEG-01, DAMI, UT-7) and control cell lines (MOLT-4, HL-60).
- Treated cells with mitotic poisons (colcemid, colchicine, nocodazole, taxol) that disrupt microtubule function and block cell division.
- Assessed DNA synthesis, cellular size, nuclear lobation, and DNA content distribution to quantify polyploidization.
Main Results:
- Colcemid treatment blocked cell division but not DNA synthesis in HEL cells, leading to increased polyploid cells (57.6% +/- 9.9%).
- Antimicrotubule agents induced polyploidization in megakaryoblastic cell lines (MEG-01, DAMI, UT-7) but not in control cell lines.
- Cellular size and nuclear lobation also increased in response to mitotic poisons.
Conclusions:
- The dependency of DNA replication on the completion of mitosis is suppressed in the megakaryocytic lineage.
- Megakaryocytic cell lines exhibit a unique ability to bypass cell-cycle checkpoints, facilitating polyploidization.