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Activation of c-Ha-ras-1 proto-oncogene by in vitro modification with a chemical carcinogen, benzo(a)pyrene
Abstract:
Chemical carcinogenesis generally proceeds via the formation of strongly electrophilic reactants, termed ultimate carcinogens. The observation that many ultimate carcinogens are potent mutagens and the results of studies on the covalent binding of carcinogens to cellular macromolecules suggest that tumour initiation results from mutations arising from the binding of ultimate carcinogens to DNA. Recently, gene transfer experiments have shown that some tumours contain activated oncogenes which are members of the ras gene family (reviewed in refs 6. 7) and which differ by single base pair substitutions from their non-transforming counterparts, the proto-oncogenes (see, for example, refs 8-11). Here we have used clones of the c-Ha-ras-1 proto-oncogene to show that reaction in vitro with an ultimate carcinogen generates a transforming oncogene when the modified DNA is introduced into NIH 3T3 cells. As DNA is the only cellular macromolecule present in the reactions, our experiments also show that reaction of an ultimate carcinogen with DNA alone can lead to the induction of mutations in mammalian cells.
Insights
Chemicals that cause cancer form ultimate carcinogens, which can mutate DNA. This study shows that reacting DNA with these carcinogens creates cancer-causing oncogenes, demonstrating DNA mutation
Area of Science:
- Molecular Biology
- Genetics
- Cancer Research
Background:
- Chemical carcinogenesis involves ultimate carcinogens, which are electrophilic reactants.
- Ultimate carcinogens are potent mutagens, and their binding to DNA is linked to tumor initiation.
- Activated oncogenes, such as the ras gene family, are found in tumors and differ from proto-oncogenes by single base pair substitutions.
Purpose of the Study:
- To investigate if the reaction of an ultimate carcinogen with DNA alone can generate a transforming oncogene.
- To demonstrate that DNA is the target macromolecule for mutations induced by ultimate carcinogens.
Main Methods:
- Cloning of the c-Ha-ras-1 proto-oncogene.
- In vitro reaction of the proto-oncogene with an ultimate carcinogen.
- Introduction of the modified DNA into NIH 3T3 cells via gene transfer.
Main Results:
- The reaction of the c-Ha-ras-1 proto-oncogene with an ultimate carcinogen in vitro generated a transforming oncogene.
- The modified DNA, when introduced into NIH 3T3 cells, induced transformation.
- These results indicate that DNA alone, when reacted with an ultimate carcinogen, can lead to mutations.
Conclusions:
- The reaction of ultimate carcinogens with DNA can directly induce mutations leading to oncogene activation.
- This study provides evidence that DNA is the sole cellular macromolecule necessary for initiating mutations by ultimate carcinogens.
- The findings support the hypothesis that DNA damage by ultimate carcinogens is a critical step in chemical carcinogenesis.