Doo-Pyo Hong

Atm heterozygous deficiency enhances development of mammary carcinomas in p53 heterozygous knockout mice

IntroductionAtaxia-telangiectasia is an autosomal-recessive disease that affects neuro-immunological functions, associated with increased susceptibility to malignancy, chromosomal instability and hypersensitivity to ionizing radiation. Although ataxia-telangiectasia mutated (ATM) heterozygous deficiency has been proposed to increase susceptibility to breast cancer, some studies have not found excess risk. In experimental animals, increased susceptibility to breast cancer is not observed in the Atm heterozygous deficient mice (Atm+/-) carrying a knockout null allele. In order to determine the effect of Atm heterozygous deficiency on mammary tumourigenesis, we generated a series of Atm+/- mice on the p53+/- background with a certain predisposition to spontaneous development of mammary carcinomas, and we examined the development of the tumours after X-irradiation.MethodsBALB/cHeA-p53+/- mice were crossed with MSM/Ms-Atm+/- mice, and females of the F1 progeny ([BALB/cHeA × MSM/Ms]F1) with four genotypes were used in the experiments. The mice were exposed to X-rays (5 Gy; 0.5 Gy/min) at age 5 weeks.ResultsWe tested the effect of haploinsufficiency of the Atm gene on mammary tumourigenesis after X-irradiation in the p53+/- mice of the BALB/cHeA × MSM/Ms background. The singly heterozygous p53+/- mice subjected to X-irradiation developed mammary carcinomas at around 25 weeks of age, and the final incidence of mammary carcinomas at 39 weeks was 31% (19 out of 61). The introduction of the heterozygous Atm knockout alleles into the background of the p53+/- genotype significantly increased the incidence of mammary carcinoma to 58% (32 out of 55) and increased the average number of mammary carcinomas per mouse. However, introduction of Atm alleles did not change the latency of development of mammary carcinoma.ConclusionOur results indicate a strong enhancement in mammary carcinogenesis by Atm heterozygous deficiency in p53+/- mice. Thus, doubly heterozygous mice represent a useful model system with which to analyze the interaction of heterozygous genotypes for p53, Atm and other genes, and their effects on mammary carcinogenesis.

Analysis of highly frequent allelic loss region on distal chromosome 12 in murine radiation-induced lymphomas.

Recent genetic studies of tumorigenesis have strongly suggested an existence of tumor suppressor gene(s) on murine chromosome 12 and human chromosome 14q32. We previously described that putative tumor suppressor gene(s) might reside between D12Mit53 and D12Mit233. We analyzed three genes, Tcl1, Yy1 and Tnfalphaip2, which had been mapped around the region, as the candidates in radiation lymphomagenesis of (BALB/c x MSM/Ms)F1 hybrid mice. The locus order and distances of the three genes and microsatellite loci were estimated as follows: [centromere] - Tcl1-(> or =0.085 cM)-D12Mit50-(0.085 cM)D12Mit132-(1.96 cM)D12Mit122-(0.085 cM)D12Mit53-(1.37 cM)-[D12Mit233,D12Mit279,Yy1]-(0.085 cM)-D12Mit181-(> or =0.17 cM)-Tnfalphaip2 - [telomere]. Allele losses at Tcl1, Yy1 genes and D12Mit233 were observed in 94(45%), 143(68%) and 147(70%) of 210 lymphomas, respectively. In semi-quantitative analysis of Yy1 mRNA levels by RT-PCR, kinetics of the yield of the Yy1-cDNA-specific PCR products showed almost the same profiles among thymic lymphomas with allelic loss at Yy1, lymphomas with both alleles retained and normal thymus. These results suggest that Tcl1, Yy1 and Tnfalphaip2 genes are not predominantly involved in radiation lymphomagenesis of mice. In further analysis of the common allelic loss region, we found new loci, Y152pR1 and Y184pR2, from YACs which located in the hot region between D12Mit53 and D12Mit233, and the highest frequency of allelic loss (71%) was observed at the Y184pR2 locus. The LOH patterns of individual lymphomas suggest that putative tumor suppressor gene(s) lies between Y152pR1 and Y184pR2.