You are here:
CHARACTERIZATION OF A LOSS OF HETEROZYGOSITY CANCER HAZARD IDENTIFICATION ASSAY.
Citation:
Chen, T., K H. Brock, D Collard, AND M M. Moore. CHARACTERIZATION OF A LOSS OF HETEROZYGOSITY CANCER HAZARD IDENTIFICATION ASSAY. Presented at Environmental Mutagen Society Meeting, New Orleans, LA, April 9-14, 2000.
Description:
Tumor development generally requires the loss of heterozygosity (LOH) at one or more loci. Thus, the ability to determine whether a chemical is capable of causing LOH is an important part of cancer hazard identification. The mouse lymphoma assay detects a broad spectrum of genetic damage, including gene and chromosomal mutations. Nethyl-N-nitrosourea (ENU) is considered to be a super point mutagen. To elucidate the possible mechanisms of Tk mutation induction by point mutagens, Tk+/- L5178Y cells were treated with different doses of ENU. Measurement of mutant clone size showed that 36% of the ENU-induced mutants and 66% of the spontaneous mutants were small clones. DNA isolated from 556 Tk-/- mutants from the 100 ug ENU/ml treatment group and the control was analyzed for allele loss at the Tk1 locus using allele-specific PCR. The percentage of large colony mutants that had lost one Tk allele was distinctly different in the ENU-induced and spontaneous mutants. Twenty three percent of ENU-induced large colony mutants lost their Tk1b allele, whereas 73% of large colonies from the control culture lost the allele (p < 0.001). However, the percentages of allele loss in ENU induced and spontaneous small colony mutants were similar (98% in ENU and 91 in the control). With regard to the total mutants, our data indicate that ENU, a potent point mutagen, induces equal proportions of point mutations (50% of the total mutants) and LOH mutations at the Tk locus of mouse lymphoma cells. Because ENU induces predominately point mutations, the allele loss caused by ENU is likely not due to deletion. Perhaps the mutants result from somatic recombination and/or chromosome loss with duplication of the remaining chromosome.