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Effects of dimethylnitrosamine on RNA synthesis and metabolism in mouse liver
Abstract:
Following i.p. injection of dimethylnitrosamine into male C57BL mice, synthesis of liver nuclear heterogeneous RNA was inhibited significantly, reaching approximately 20% of control within 2 hr of a dose of 40 mg/kg. Synthesis of nucleolar RNA was also inhibited, although to a smaller extent, reaching about 70% of control after the same treatment. These effects were observed both during RNA synthesis in vivo and during in vitro transcription with isolated nuclei and nucleoli. Examination of RNA polymerases I and II, isolated and partially purified by diethylaminoethyl Sephadex column chromatography, did not indicate any change either in their activities in the transcription of exogenous DNA or in their in vivo binding to chromatin. On the other hand, the activity of purified chromatin as a template for transcription by added, partially purified RNA polymerase II was significantly reduced, suggesting that carcinogen-induced damage to chromatin was the cause of the observed inhibition of heterogeneous RNA synthesis. When purified DNA was used in place of chromatin as a template for transcription by partially purified RNA polymerase II, no inhibition was observed. Dimethylnitrosamine treatment had a pronounced effect on the kinetics of appearance of the cytoplasmic RNA species. Four hr after a 40-mg/kg dose of dimethylnitrosamine, the rate of appearance in the cytoplasm of polyadenylate-containing RNA was inhibited by 50%, while that of 4S, 18S, and 28S ribosomal RNA was inhibited by over 80%.
Insights
Dimethylnitrosamine carcinogen exposure significantly inhibits liver nuclear heterogeneous RNA synthesis in mice by damaging chromatin. This carcinogen also impairs the cytoplasmic appearance of various RNA species.
Area of Science:
- Biochemistry
- Molecular Biology
- Toxicology
Background:
- Dimethylnitrosamine is a potent carcinogen.
- RNA synthesis is crucial for cellular function and gene expression.
- Understanding the molecular mechanisms of carcinogen-induced toxicity is vital.
Purpose of the Study:
- To investigate the effects of dimethylnitrosamine on liver RNA synthesis in mice.
- To elucidate the molecular targets responsible for dimethylnitrosamine-induced inhibition of RNA synthesis.
Main Methods:
- In vivo and in vitro transcription assays using isolated nuclei and nucleoli.
- Isolation and partial purification of RNA polymerases I and II.
- Chromatin and DNA template activity assays.
- Analysis of cytoplasmic RNA appearance kinetics.
Main Results:
- Dimethylnitrosamine significantly inhibited heterogeneous nuclear RNA synthesis (to 20% of control) and nucleolar RNA synthesis (to 70% of control).
- RNA polymerase I and II activities and chromatin binding remained unchanged.
- Chromatin template activity was significantly reduced, while DNA template activity was unaffected.
- Dimethylnitrosamine impaired the cytoplasmic appearance of polyadenylate-containing RNA (by 50%) and ribosomal RNA (by over 80%).
Conclusions:
- Carcinogen-induced damage to chromatin, not RNA polymerases, is the primary cause of inhibited heterogeneous RNA synthesis.
- Dimethylnitrosamine disrupts RNA processing and transport, affecting cytoplasmic RNA levels.