Related Experiment Videos
Sister chromatid exchanges induced by DNA demethylating agents persist through several cell cycles in mammalian cells
Abstract:
Eukaryotic DNA methylation has been extensively studied in recent years. The ability of many carcinogens to interfere with DNA methylation has not yet been directly related to their tumorigenic activity. Recent data obtained using L-ethionine and 5-azacytidine--both demethylating agents--showed a small but significant increase in the sister chromatid exchange (SCE) rate induced in mammalian cells (human lymphocytes and CHO cells). In this paper we show that the SCE increase induced by both these agents in Chinese hamster ovary (CHO) cells persists for as long as 10 cell cycles. On the other hand mitomycin-C and u.v. light-induced SCEs show a rapid decrease to the control value, as reported for all known SCE inducers. We suggest that DNA demethylation and SCEs are connected through a perturbation of the cell machinery at the level of the replication fork, producing an increase of the error-prone ligation. Since the methylation level is maintained (inherited), the SCE increase produced by these recombinational events will not be corrected through several cell cycles.
Insights
DNA demethylating agents L-ethionine and 5-azacytidine increase sister chromatid exchange (SCE) rates in mammalian cells. This increase persists for 10 cell cycles, unlike other inducers, suggesting a link between DNA demethylation and persistent SCE.
Area of Science:
- Molecular Biology
- Genetics
- Cell Biology
Background:
- Eukaryotic DNA methylation is crucial for cellular processes.
- Carcinogen interference with DNA methylation is linked to tumorigenesis.
- Demethylating agents L-ethionine and 5-azacytidine increase sister chromatid exchange (SCE) rates.
Purpose of the Study:
- To investigate the persistence of SCE induction by demethylating agents.
- To explore the relationship between DNA demethylation and SCE.
- To understand the mechanism underlying persistent SCE.
Main Methods:
- Treatment of Chinese hamster ovary (CHO) cells with L-ethionine and 5-azacytidine.
- Monitoring SCE rates over multiple cell cycles (up to 10).
- Comparison with SCE induction by mitomycin-C and UV light.
Main Results:
- L-ethionine and 5-azacytidine induced a persistent increase in SCE rates in CHO cells.
- This SCE increase lasted for at least 10 cell cycles.
- Mitomycin-C and UV light induced transient SCE increases, returning to control levels rapidly.
Conclusions:
- DNA demethylation may be linked to persistent SCE.
- A perturbed replication fork and error-prone ligation could explain the sustained SCE increase.
- Inherited methylation patterns may prevent correction of recombination events over several cell cycles.