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Cytochrome P450 CYP1B1 determines susceptibility to 7, 12-dimethylbenz[a]anthracene-induced lymphomas
J T Buters1, S Sakai, T Richter
1National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
Summary
Cytochrome P450 1B1 (CYP1B1) is essential for the carcinogenicity of DMBA, a potent carcinogen. CYP1B1-null mice show resistance to DMBA-induced lymphomas and tumors, highlighting its role in extrahepatic carcinogenesis.
Area of Science:
- Biochemistry
- Toxicology
- Genetics
Background:
- Cytochrome P450 (P450) enzymes play critical roles in xenobiotic metabolism and carcinogenesis.
- CYP1B1 is implicated in the metabolism of various environmental pollutants and carcinogens.
- The specific role of CYP1B1 in chemical carcinogenesis, particularly at extrahepatic sites, requires further elucidation.
Purpose of the Study:
- To investigate the role of CYP1B1 in the carcinogenicity of 7,12-dimethylbenz[a]anthracene (DMBA).
- To determine if CYP1B1 is essential for mouse development and its inducibility by aryl hydrocarbon receptor agonists.
- To compare the metabolic activity and toxicity of DMBA in wild-type versus CYP1B1-null cells and mice.
Main Methods:
- Generation of CYP1B1-null mice via targeted gene disruption.
- Assessment of CYP1B1 expression in embryonic fibroblasts (EF) and tissues using aryl hydrocarbon receptor agonist.
- In vitro metabolism and toxicity studies of DMBA in wild-type and CYP1B1-null EF.
- In vivo carcinogenicity studies in wild-type and CYP1B1-null mice administered DMBA.
Main Results:
- CYP1B1-null mice exhibit normal development and no observable phenotype.
- CYP1B1 is not detectable in CYP1B1-null mice, while wild-type cells express it basally and inducibly.
- CYP1B1-null EF are resistant to DMBA-mediated toxicity and show no significant DMBA metabolism.
- Wild-type mice administered DMBA have a significantly higher incidence of lymphomas and skin tumors compared to CYP1B1-null mice.
- CYP1B1, not CYP1A1, mediates DMBA carcinogenicity, particularly at extrahepatic sites.
Conclusions:
- CYP1B1 is not essential for mouse development but is crucial for DMBA-induced carcinogenesis.
- Extrahepatic CYP1B1 plays a critical role in mediating the carcinogenic effects of DMBA.
- CYP1A1, despite high in vitro metabolic activity, is insufficient for DMBA carcinogenesis.
- These findings underscore the importance of extrahepatic P450s in susceptibility to chemical carcinogens and human cancer risk.