Inactivation of plasmid reporter gene expression by one benzo(a) pyrene diol-epoxide DNA adduct in adult rat hepatocytes

Polycyclic aromatic hydrocarbons such as benzo(a)pyrene diol-epoxide (BPDE-I) cause hepatocellular carcinoma. To identify short-term carcinogen effects, we studied hepatocytes transfected with nonreplicating plasmids, adducted covalently with BPDE-I, varying in promoter structure and encoded reporte...

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Bibliographic Details
Published in:Cancer research (Chicago, Ill.) Ill.), 1993-05, Vol.53 (10), p.2279-2286
Main Authors: KOCH, K. S, FLETCHER, R. G, GROND, M. P, INYANG, A. I, LU, X. P, BRENNER, D. A, LEFFERT, H. L
Format: Article
Language:English
Subjects:
7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide - pharmacology
Animals
Benzopyrenes - metabolism
Benzopyrenes - pharmacology
Biological and medical sciences
Carcinogenesis, carcinogens and anticarcinogens
Chemical agents
DNA - genetics
DNA - metabolism
DNA - pharmacology
DNA Adducts
DNA, Superhelical - genetics
DNA, Superhelical - metabolism
Gene Expression Regulation - drug effects
Liver - cytology
Liver - drug effects
Liver - physiology
Medical sciences
Plasmids - genetics
Plasmids - physiology
Rats
RNA, Messenger - genetics
Transcription, Genetic
Transfection
Tumors
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Summary:Polycyclic aromatic hydrocarbons such as benzo(a)pyrene diol-epoxide (BPDE-I) cause hepatocellular carcinoma. To identify short-term carcinogen effects, we studied hepatocytes transfected with nonreplicating plasmids, adducted covalently with BPDE-I, varying in promoter structure and encoded reporter gene (beta-galactosidase or luciferase). BPDE inactivated gene expression as a first-order function of BPDE concentration in adduction reactions. No evidence of cytotoxicity, diminished coprecipitation and availability, enhanced nicking of supercoiled forms and reduced cellular uptake, or instability of adducted plasmids was observed. At low BPDE:plasmid ratios, inactivation occurred with 1 adduct/plasmid within a target 23-27% of plasmid bases. Using nuclear extracts and BPDE-adducted G-free cassette-encoding plasmids, the fraction of full-length RNA polymerase II-initiated transcripts also declined as a first-order function of BPDE concentration when approximately 3 adducts were distributed among 48% of plasmid bases. These observations suggest that carcinogens such as BPDE block mRNA transcription along DNA templates by forming limited numbers of persistent adducts at coding or noncoding sites.
ISSN:0008-5472
1538-7445