Loss of heterozygosity at the N-ras locus in 7,12-dimethylbenz[a] anthracene-induced rat leukemia.
The 7,12-dimethylbenz[a]anthracene (DMBA)-induced rat leukemia model enables scientists to analyze cells altered by carcinogens at various stages of leukemogenesis. We have reported that a consistent type of point mutation. A-->T transversion at the second base in codon 61 of the N-ras gene, was present in this leukemia and that this mutation appeared in bone marrow cells as early as 48 h after a single dose of DMBA. In addition, two leukemia cell lines with the N-ras mutation had no wild-type N-ras allele. Therefore, we examined whether these alterations were essential to the DMBA-induced leukemias. In the study reported here, we confirmed the occurrence of this N-ras mutation in 18 (86%) of 21 primary leukemias and loss of the N-ras wild-type allele in 12 (67%) of 18 leukemias with the mutated N-ras. By using microsatellite markers on chromosome 2, loss of heterozygosity (LOH) at the N-ras locus was observed in eight leukemias, all of which were shown to have lost the wild-type N-ras allele by mutant-allele-specific amplification. These results suggest that LOH related to loss of the wild-type N-ras allele reproducibly occurs in leukemias with the N-ras mutation. Considering the timing of the N-ras mutation and LOH, it is likely that the N-ras mutation is induced early, and cells that have lost the wild-type N-ras allele seem to develop into leukemia. We believe that this system provides a suitable model for studying a series of genetic alterations from the earliest stage of carcinogenesis that cannot be approached in human malignancies.
Osaka
M
M
Department of Pathology, Faculty of Medicine, Kyoto University, Japan.
Matsuo
S
S
Koh
T
T
Sugiyama
T
T
D015127:9,10-Dimethyl-1,2-benzanthracene; D000818:Animals; D004273:DNA, Neoplasm / Q000235:genetics; D005260:Female; D011905:Genes, ras; D006579:Heterozygote; D007942:Leukemia, Experimental / Q000235:genetics*; D008297:Male; D051381:Rats; D017384:Sequence Deletion; D014407:Tumor Cells, Cultured
D004273:DNA, Neoplasm; D015127:9,10-Dimethyl-1,2-benzanthracene