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The behaviour of nuclear proteins during nitrosamine-induced carcinogenesis
Abstract:
Dimethylnitrosamine given after partial hepatectomy reduces the synthesis of DNA, histone, and, to a lesser extent, of nonhistone proteins, the inhibition being general rather than for specific nuclear proteins. The extent of inhibition of macromolecular synthesis is greatest when the carcinogen is given a few hours after the operation. As a higher incidence of hepatocellular carcinoma is induced when dimethylnitrosamine is injected later, during the wave of DNA replication, it appears that inhibition of nuclear protein synthesis is not a relevant factor in carcinogenesis, unless it relates to loss of a specific non-histone protein present in small amounts. Analysis of sequentially extracted groups of non-histone proteins by 2D electrophoresis did not reveal any changes produced by treatment with dimethylnitrosamine. Animals fed a diet containing diethylnitrosamine showed an increased incorporation of amino acid into histone. Electrophoretic analysis of non-histone proteins revealed two reproducible effects of feeding the carcinogenic diet: relative to the bulk of nuclear non-histone protein, there was a reduction in the amount of a slightly basic 65000 mol. wt. polypeptide, and an increase in the level of a high molecular weight protein that was almost undetectable in material from normal rats. As these changes were not induced by partial hepatectomy of normal animals, it is possible that they are related to malignancy rather than to the associated increase in cell replication.
Insights
Dimethylnitrosamine inhibits macromolecular synthesis after partial hepatectomy, with effects varying based on timing. Changes in nuclear proteins may relate to malignancy, not just cell replication.
Area of Science:
- Hepatocarcinogenesis research
- Molecular biology of cancer
Background:
- Partial hepatectomy triggers significant cell proliferation.
- Carcinogens like dimethylnitrosamine (DMN) and diethylnitrosamine (DEN) are known to induce liver cancer.
Purpose of the Study:
- To investigate the impact of DMN on macromolecular synthesis following partial hepatectomy.
- To explore the relationship between DMN-induced changes in nuclear proteins and hepatocellular carcinoma development.
- To analyze alterations in non-histone proteins induced by DEN exposure.
Main Methods:
- Partial hepatectomy followed by DMN administration at different time points.
- Analysis of DNA, histone, and non-histone protein synthesis.
- Two-dimensional electrophoresis for non-histone protein analysis.
- Feeding rats a diet containing DEN.
Main Results:
- DMN administration post-hepatectomy inhibited DNA, histone, and non-histone protein synthesis, most significantly when given shortly after surgery.
- Inhibition of general nuclear protein synthesis by DMN did not correlate with increased tumor incidence.
- DEN feeding increased amino acid incorporation into histone.
- DEN exposure altered non-histone proteins, decreasing a 65,000 mol. wt. polypeptide and increasing a high molecular weight protein.
Conclusions:
- Inhibition of general nuclear protein synthesis is unlikely to be the primary mechanism in DMN-induced carcinogenesis.
- Specific alterations in non-histone proteins induced by DEN may be linked to malignancy rather than compensatory cell proliferation.