Identification of an Activated c-Ki-ras Oncogene in Rat Liver Tumors Induced by Aflatoxin B1

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 83; no. 24; pp. 9418 - 9422
• Main Authors: McMahon, Gerald, Hanson, Linda, Lee, Jung-Ja, Wogan, Gerald N.
• Format: Journal Article
• Language: English
• Published: Washington, DC National Academy of Sciences of the United States of America 01.12.1986; National Acad Sciences
• Subjects: 3T3 cells; Aflatoxin B1; Aflatoxins - pharmacology; Animals; Biological and medical sciences; Cell Line; Cell physiology; Cell transformation and carcinogenesis. Action of oncogenes and antioncogenes; Cell Transformation, Neoplastic; DNA; DNA, Neoplasm - genetics; Fundamental and applied biological sciences. Psychology; Gels; Gene Expression Regulation - drug effects; GTP-Binding Proteins - genetics; Liver; Liver Neoplasms - genetics; Mice; Molecular and cellular biology; NIH 3T3 cells; Oncogenes; Proto-Oncogene Proteins - genetics; Proto-Oncogenes; ras genes; Rats; Transfection; Tumor cell line; Tumors; Rat; Induction; Liver; Rodentia; Mycotoxin; Activation; Identification; Cell transformation; Carcinogenesis; Vertebrata; Mammalia; Animal; C-Onc gene; Malignant transformation; Tumor; Mechanism of action; Aflatoxin
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.83.24.9418

Weanling male Fischer rats were administered 40 intraperitoneal injections of aflatoxin B1 (25 μ g per animal per day) over a 2-month period. This chronic dosing regimen resulted in the sequential formation of hyperplastic foci, preneoplastic nodules, and hepatocellular carcinomas in all of the animals treated. The presence of transforming DNA sequences was detected by formation of anchorage-independent foci after transfection of tumor-derived DNA in NIH 3T3 mouse fibroblasts. Transfection of genomic DNA isolated from individual tumors from eight animals resulted in specific transforming activities ranging from 0.05 to 0.2 foci per μ g of DNA. Primary transfectant DNAs were analyzed by Southern blot hybridization with DNA probes homologous to c-Ha-ras, c-Ki-ras, and N-ras oncogenes. A highly amplified c-Ki-ras oncogene of rat origin was detected in transformants derived from tumors in two of the eight animals tested. There was no evidence to suggest the presence of c-Ha-ras or N-ras sequences in any of the transformants. Analysis of primary liver tumor DNA showed no Ki-ras DNA amplification when compared to control liver DNA samples. Increased levels of c-Ki-ras p21 proteins were detected in 3T3 transformants containing activated rat c-Ki-ras genes. The presence of c-Ki-ras sequences of rat origin capable of inducing transformed foci can be taken as evidence that the c-Ki-ras gene has been activated in the primary liver tumors.