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Regulation of DNA synthesis by the higher-order chromatin structure
D Kunnev1, A Gospodinov, G Russev
1Institute of Molecular Biology, Bulgarian Academy of Sciences, Sofia.
Abstract:
Mouse erythroleukemia cells were treated with the topoisomerase II poison VP-16, the intrastrand crosslinking agent cis-DDP, and the ribonucleotide reductase inhibitor hydroxyurea. In all cases, the rate of DNA synthesis decreased as a result of the treatment. To study the mechanism of inhibition of DNA chain elongation, we determined DNA synthesis in a cell-free replication system containing isolated nuclei and cytoplasmic extracts. The rate of DNA synthesis in the reactions containing nuclei isolated from untreated cells and extracts from cells treated with the three drugs were slightly reduced and did not show significant differences between the drugs. In the systems containing nuclei from cells treated with cis-DDP, DNA synthesis was again slightly inhibited; synthesis in nuclei treated with hydroxyurea was enhanced, and synthesis in the systems containing nuclei from cells treated with VP-16 was significantly reduced. DNA synthesis was reduced to the same extent in a system containing nuclei isolated from untreated cells that had been briefly sonicated to introduce a limited number of double-strand breaks in the DNA. As VP-16 and sonication mediate changes in chromatin topology, these results suggest that, along with the trans-acting signal transduction pathways, there is a topologic mechanism for regulation of DNA synthesis in the S phase of the cell cycle.
Insights
DNA synthesis inhibition was studied using VP-16, cis-DDP, and hydroxyurea. VP-16 significantly reduced DNA synthesis, suggesting a topological mechanism regulating DNA replication during the S phase of the cell cycle.
Area of Science:
- Cell Biology
- Molecular Biology
- Genetics
Background:
- DNA synthesis is a critical process during the S phase of the cell cycle.
- Various agents can inhibit DNA synthesis, impacting cell proliferation.
- Understanding the mechanisms of DNA synthesis inhibition is crucial for cancer therapy and cell cycle regulation studies.
Purpose of the Study:
- To investigate the mechanism by which VP-16, cis-DDP, and hydroxyurea inhibit DNA chain elongation.
- To differentiate between drug effects on cytoplasmic factors versus nuclear DNA replication machinery.
- To explore the role of chromatin topology in regulating DNA synthesis.
Main Methods:
- Treatment of mouse erythroleukemia cells with VP-16, cis-DDP, and hydroxyurea.
- Analysis of DNA synthesis rates in cell-free replication systems using isolated nuclei and cytoplasmic extracts.
- Induction of double-strand DNA breaks via sonication in isolated nuclei.
Main Results:
- All three drugs decreased the overall rate of DNA synthesis in intact cells.
- Cytoplasmic extracts from treated cells showed minimal inhibition of DNA synthesis in untreated nuclei.
- Nuclei from VP-16 treated cells exhibited significantly reduced DNA synthesis, similar to nuclei with induced double-strand breaks.
- Nuclei from hydroxyurea treated cells showed enhanced DNA synthesis, while cis-DDP showed slight inhibition.
Conclusions:
- VP-16's inhibition of DNA synthesis is linked to alterations in chromatin topology, affecting nuclear DNA replication.
- A topological mechanism, in addition to trans-acting signal transduction, likely regulates DNA synthesis during the S phase.
- The study highlights distinct mechanisms of DNA synthesis inhibition by different classes of drugs.