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Alkylating antitumor agents reduce histone acetyl-transferase activity
Abstract:
N-Mustard depresses the acetylation of histones in Ehrlich ascites and Walker carcinoma cells. It is demonstrated that this effect is not caused by an accelerated deacetylation but is due to an inhibition of the acetyl-transferase reaction. Employing 4-sulphonatoethylthio-cyclophosphamide it is demonstrated that the alkylating agent affects predominantly the acetylation of a chromatin fraction which is soluble in 0.1M NaCl after digestion with micrococcal nuclease. After removal of the alkylating agent, the recovery of histone acetylation is relatively slow and--in contrast to the repair of DNA cross-links--characterized by a 4-hr lag period. The reduction of histone acetylation by N-mustard is much less expressed in cells which are resistant to the drug than in the sensitive parental lines. This is in contrast to DNA-interstrand cross-links in Walker cells where both N-mustard sensitive and resistant cells inhibit the same cross-link frequency and identical repair rates. Based on these data it is concluded that the inhibition of histone acetylation may be an important part of the mechanism by which alkylating agents inhibit tumor growth.
Insights
N-Mustard inhibits histone acetylation by blocking the acetyl-transferase reaction, not by increasing deacetylation. This effect is less pronounced in drug-resistant cells, suggesting a role in tumor growth inhibition.
Area of Science:
- Biochemistry
- Molecular Biology
- Cancer Research
Background:
- Histone acetylation regulates gene expression and is crucial for cellular processes.
- Alkylating agents like N-Mustard are used in cancer chemotherapy.
- The precise mechanisms by which N-Mustard affects cellular processes, including histone modification, are not fully understood.
Purpose of the Study:
- To investigate the effect of N-Mustard on histone acetylation in cancer cells.
- To determine whether N-Mustard inhibits histone acetylation through altered deacetylation or impaired acetyl-transferase activity.
- To explore the relationship between histone acetylation inhibition and drug resistance.
Main Methods:
- Treatment of Ehrlich ascites and Walker carcinoma cells with N-Mustard and 4-sulphonatoethylthio-cyclophosphamide.
- Assay of histone acetylation and deacetylation rates.
- Analysis of chromatin fractions.
- Comparison of drug-sensitive and drug-resistant cell lines.
Main Results:
- N-Mustard inhibits the acetyl-transferase reaction, leading to reduced histone acetylation.
- The drug primarily affects the acetylation of a specific chromatin fraction.
- Recovery of histone acetylation after drug removal shows a significant lag period.
- N-Mustard-induced reduction in histone acetylation is less pronounced in resistant cell lines compared to sensitive lines.
- This contrasts with DNA cross-linking, which shows similar inhibition and repair in both sensitive and resistant cells.
Conclusions:
- N-Mustard's inhibition of histone acetylation is primarily due to reduced acetyl-transferase activity.
- The differential effect on histone acetylation in resistant vs. sensitive cells suggests its importance in drug efficacy.
- Inhibition of histone acetylation may be a key mechanism underlying the anti-tumor effects of alkylating agents.