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Interaction between ionizing radiation and supercoiled DNA within human tumor cells
A T Vaughan1, A M Milner, D G Gordon
1Department of Immunology, University of Birmingham, United Kingdom.
Abstract:
We have analyzed DNA supercoiling within histone-free nuclei (nucleoids) using four human squamous cell carcinoma cell lines that express varying degrees of radiosensitivity. The entire DNA, arranged as negative supercoiled loops attached to the nuclear matrix, was extracted from single cells, stained with ethidium bromide, and passed through a flow cytometer recording both light scatter and red (DNA) fluorescence. Supercoiled loops of DNA from all cells were unwound with a low concentration of ethidium bromide, as seen by increased light scatter. Nucleoids from radiosensitive but not radioresistant cells resisted the transition from zero to positive supercoiling at higher concentrations of ethidium bromide. The profile of red DNA fluorescence from ethidium bromide-stained nucleoids showed that the radiosensitive cells expressed a greater variation in the total amount of ethidium bromide bound. After 12 Gy of gamma-radiation, radiosensitive cell lines produced nucleoids that contained a greater proportion of relaxed supercoiled DNA, making them larger than those from radioresistant cell lines. We suggest these observations are secondary effects resulting from an altered affinity between supercoiled looped DNA and the nuclear matrix. Combined with radiation damage, these structural alterations may lead to a more complex type of damage to repair within the radiosensitive cell lines.
Insights
Radiosensitive cancer cells exhibit altered DNA supercoiling and nuclear matrix interactions, leading to increased DNA damage complexity after radiation exposure. These structural differences impact DNA repair efficiency.
Area of Science:
- Cell Biology
- Molecular Biology
- Radiation Oncology
Background:
- DNA supercoiling is crucial for genome organization and function.
- Nuclear matrix interactions influence DNA structure and accessibility.
- Understanding radiosensitivity is key for cancer treatment optimization.
Purpose of the Study:
- To investigate DNA supercoiling differences in radiosensitive versus radioresistant cancer cells.
- To explore the relationship between DNA supercoiling, nuclear matrix, and radiosensitivity.
- To assess the impact of gamma radiation on DNA structure in these cell lines.
Main Methods:
- Analysis of DNA supercoiling in histone-free nuclei (nucleoids) from human squamous cell carcinoma lines.
- Flow cytometry with ethidium bromide staining to measure DNA fluorescence and light scatter.
- Assessment of nucleoid structural changes after gamma irradiation.
Main Results:
- Radiosensitive cells showed resistance to supercoiling transitions and greater variation in ethidium bromide binding.
- Gamma radiation induced more relaxed supercoiled DNA in radiosensitive cells.
- Nucleoids from radiosensitive cells were larger post-irradiation, suggesting altered DNA-nuclear matrix interactions.
Conclusions:
- Observed structural alterations in radiosensitive cells are likely due to modified DNA-nuclear matrix affinity.
- These alterations, combined with radiation damage, may result in more complex DNA repair challenges.
- Findings suggest a link between DNA supercoiling dynamics, nuclear architecture, and cellular radiosensitivity.