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Carcinogen specificity in the activation of transforming genes by direct-acting alkylating agents
Abstract:
DNAs from rat nasal and mouse skin carcinomas and fibrosarcomas induced by the alkylating agents methylmethane sulfonate (MMS), beta-propiolactone (BPL), and dimethylcarbamyl chloride (DMCC) were tested for their ability to transform NIH3T3 cells by DNA transfection. Each of eight MMS-induced rat nasal carcinomas and two of five BPL-induced mouse skin tumors were positive in the transfection assay while all of four fibrosarcomas and six carcinomas induced by DMCC were negative. Anchorage independent growth, tumorigenicity in nude mice, and secondary transfection confirmed the transformed phenotype of the positive transfectants. The transfectants from MMS-induced tumor DNAs did not contain restriction fragments homologous to rat H-, K- or N-ras oncogenes although exogenous (rat) tumor-derived DNA sequences were detected in transfectant genomes by Southern analysis. In contrast a BPL-induced mouse skin tumor showed evidence of containing activated H-ras. These results suggest specificity among causal chemical carcinogens for activation of transforming genes in experimental tumors.
Insights
DNA transfection assays revealed that chemical carcinogens methylmethane sulfonate (MMS) and beta-propiolactone (BPL) can activate transforming genes in experimental tumors, unlike dimethylcarbamyl chloride (DMCC). This suggests carcinogen specificity in oncogene activation.
Area of Science:
- Molecular biology
- Chemical carcinogenesis
- Oncology
Background:
- Alkylating agents like methylmethane sulfonate (MMS), beta-propiolactone (BPL), and dimethylcarbamyl chloride (DMCC) are known to induce experimental tumors.
- Understanding the molecular mechanisms of chemical carcinogenesis, specifically oncogene activation, is crucial for cancer research.
Purpose of the Study:
- To investigate the ability of DNA from chemically induced rat nasal and mouse skin tumors to transform NIH3T3 cells.
- To determine if specific chemical carcinogens exhibit specificity in activating cellular transforming genes.
Main Methods:
- DNA transfection assay using NIH3T3 cells to detect transforming activity in tumor DNA.
- Anchorage-independent growth, tumorigenicity in nude mice, and secondary transfection assays to confirm transformed phenotype.
- Southern blot analysis to detect oncogene homology (H-, K-, N-ras) and exogenous DNA sequences.
Main Results:
- DNA from MMS-induced rat nasal carcinomas and some BPL-induced mouse skin tumors transformed NIH3T3 cells.
- DMCC-induced tumors (carcinomas and fibrosarcomas) showed no transforming activity.
- Transfectants from MMS-induced tumors lacked ras oncogene activation but contained exogenous DNA; a BPL-induced tumor showed activated H-ras.
Conclusions:
- Chemical carcinogens demonstrate specificity in activating cellular transforming genes during experimental tumor formation.
- MMS and BPL can induce tumors through mechanisms involving activation of transforming genes, while DMCC may act via different pathways.