Otsura Niwa

Transient infiltration of neutrophils into the thymus in association with apoptosis induced by whole-body X-irradiation.

Generally, the process of apoptosis does not cause leakage of noxious cytosolic contents and is therefore non‐inflammatory. However, as previously shown, macrophages ingesting apoptotic CTLL‐2 cells produced pro‐inflammatory cytokines, particularly interleukin‐8 (IL‐8) and macrophage inflammatory protein‐2 (MIP‐2), a murine IL‐8 homolog. This predicted that rapid and massive apoptosis may induce neutrophil accumulation in vivo. In this study, we tested this prediction by inducing apoptosis by whole‐body X‐irradiation in mice. After exposure to 4 Gy X‐ray irradiation, mice exhibited considerable apoptosis of thymic cells, which was associated with transient infiltration of neutrophils as well as MIP‐2 mRNA expression. In contrast, in p53‐deficient mice in which irradiation‐induced apoptosis was suppressed, as has been reported, infiltration of neutrophils into the thymus was less than that found in p53+/+ mice. Taken together, these results suggest that massive and rapid apoptosis can result in infiltration of neutrophils. J. Leukoc. Biol. 67: 780–784; 2000.

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

Introduction Ataxia-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.

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.

Lack of Evidence for the Involvement of Type-C and Type-B Retroviruses in Radiation Leukemogenesis of NFS Mice

Southern blot analysis revealed no difference between the DNA from radiation-induced thymic lymphomas and DNA from normal NFS mice. The probes used in the Southern blot analyses used a murine leukemia virus (MuLV) env DNA probe (pXenv), which specifically hybridizes with xenotropic and recombinant viral env genes, and mouse mammary tumor virus (MMTV) DNA probes (MMTV gag-pol, MMTV env, and MMTV LTR). This suggests that radiation leukemogenesis was not associated with gross alteration of the organization of these retroviral genomes. In DNA from radiation-induced thymic lymphoma, there was no indication of gross rearrangement in the common integration site of MuLV, pim-1, or in the common integration sites of MMTV, int-1 and int-2. Dot blot analysis of RNA from radiation-induced thymic lymphomas and normal thymuses demonstrated that there was no substantial difference between them in the expression of retroviral sequences, pim-1, pvt-1, int-1, or int-2, although transcripts that could be hybridized to the retroviral sequences were slightly elevated in some radiation-induced thymic lymphomas. These results show that radiation leukemogenesis does not appear to involve the activation of endogenous type-C and type-B retroviruses.