Tomonori Miyazawa

Homozygous deletions and point mutations of the Ikaros gene in γ-ray-induced mouse thymic lymphomas

Our previous genome-wide analysis of allelic loss for thymic lymphomas that were induced by γ-irradiation in F1 hybrid mice between BALB/c and MSM strains suggested the centromeric region on chromosome 11 as a site harboring a tumor suppressor gene. Interestingly, to this region the mouse Ikaros gene was mapped which was postulated to participate in oncogenic process from the study of Ikaros knockout mice. Here we show fine allelic loss mapping in the vicinity of Ikaros in 191 lymphomas, indicating that the critical region of allelic loss was centered at the Ikaros locus. PCR analysis revealed that nine lymphomas failed to give PCR-amplification for either of two exon primer pairs, indicative of homozygous deletion. Six and five mutations were detected in the N-terminal zinc finger domain and the activation domain of Ikaros, respectively, and six of the eleven were frameshift or nonsense mutations that resulted in truncation of Ikaros protein. The results strongly suggest a direct role for Ikaros in development of mouse thymic lymphomas. This provides the experimental basis for further analysis of Ikaros mutations in human cancer.

Genetic loci controlling susceptibility to γ-ray-induced thymic lymphoma

BALB/c is a susceptible strain for the development of γ-ray induced mouse thymic lymphoma whereas MSM shows resistance. Association analysis of 220 backcross mice between the two strains using 67 markers was carried out to identify loci involved in the control of susceptibility. The genotype of mice with lymphoma showed excess heterozygosity relative to MSM homozygosity at D2Mit15 and D4Mit12 and was skewed toward MSM-derived alleles at D5Mit5. The P values in Mantel-Cox test were 0.0048 (D2Mit15), 0.0034 (D4Mit12) and 0.0048 (D5Mit5), suggesting association at the three loci in the susceptibility. Cooperative effect on lymphomagenesis was also observed among the three loci. To obtain independent evidence for linkage at D4Mit12, we made partially congenic mice in which a D4Mit12 region in BALB/c was replaced by MSM-derived homolog. Examination for the lymphoma susceptibility in 78 progeny of the congenic mice confirmed the effect of the locus near D4Mit12 (P=0.0037). The result, together with the linkage analysis, shows that the locus near D4Mit12 is regarded as a confirmed linkage but the other two loci as marginally suggestive.

Allelic Losses in Mouse Skin Tumors Induced by γ‐Irradiation of p53 Heterozygotes

Skin tumors were induced by γ‐irradiation in F1 mice between C3H/He or BALB/c and MSM carrying a p53‐deficient allele. The incidence was 39.1% (34/87) in p53 (KO/+) mice of the C3H/MSM genetic background and 14.3% (19/133) in those of the BALB/MSM background. Interestingly, most of the tumors (82%) lost the wild‐type p53 allele and no skin tumor was found in p53 (+/+) F1 mice. This suggests a requirement of p53 loss for the skin cancer development. Genome scan localized a chromosomal locus showing frequent allelic losses near D12Mit2, which may harbor a tumor suppressor gene. In addition, 23 loci distributed on 13 chromosomes exhibited allelic losses at frequencies of more than 20%. The genome‐wide occurrence of allelic losses suggests that genomic instability of the skin tumors may be implicated in radiation‐induced carcinogenesis. The present study is the first to report a mouse model system useful for the analysis of radiation induction of skin cancer in man.

Complete Response of Isolated Para-aortic Lymph Node Recurrence from Rectosigmoid Cancer Treated by Chemoradiation Therapy with Capecitabine/Oxaliplatin plus Bevacizumab: A Case Report.

Para-aortic lymph node recurrence is a rare type of metastasis from colorectal cancer, and no treatment has yet been established. Here, we report on a case of isolated para-aortic lymph node metastasis from rectosigmoid cancer that showed complete response to chemoradiation therapy with capecitabine/oxaliplatin plus bevacizumab. A 58-year-old woman underwent high anterior resection for rectosigmoid cancer in 2009. Para-aortic lymph node recurrence occurred in 2011. She underwent radiation therapy (50 Gy) and 8 courses of capecitabine/oxaliplatin plus bevacizumab. Abdominal computed tomography and positron emission tomography with 18-fluorodeoxyglucose did not reveal any para-aortic lymph node recurrence after chemoradiation therapy. Hence, this case was interpreted as a complete response. No recurrence was noted 6 months after the complete response. Chemoradiation therapy with capecitabine/oxaliplatin plus bevacizumab is likely to be effective in treating patients with para-aortic lymph node recurrence.

Complete Response of Liver Metastasis of Gastric Cancer Treated by S-1 Chemoradiotherapy: A Case Report

This paper presents a case of suspected liver metastasis of gastric cancer and a virtual complete response to S-1 chemoradiotherapy. A 69-year-old man underwent distal gastrectomy for gastric cancer in 2008. Multiple liver metastases occurred in 2009. He underwent 15 courses of S-1 therapy and radiation therapy (37.5 Gy). Abdominal computed tomography showed virtual complete disappearance of liver metastasis after chemoradiotherapy. Hence, this case was interpreted as a complete response. No sign of recurrence was noted 18 months after complete response was confirmed. S-1 chemoradiotherapy is likely to be effective in treating patients with liver metastases of gastric cancer.

Genetic Mapping and Allelic Loss Analysis in Mouse Thymic Lymphomas of Helios and Aiolos Belonging to the Ikaros Gene Family

The Ikaros gene undergoes bi‐allelic changes at a high frequency in γ‐ray‐induced mouse thymic lymphomas, suggesting the relevance of Ikaros to the lymphoma development. Here we test whether Helios and Aiolos, two other members of the Ikaros gene family, are also involved in lymphomagenesis. Genetic mapping showed that Helios is located between D1Mit531 and D1Mit19 on chromosome 1 and Aiolos is between D11Mit222 and D11Mit332 on chromosome 11. Analysis using polymorphic markers around the two regions revealed that neither locus exhibited allelic loss in the 78 lymphomas that were induced in p53 wild‐type mice, whereas in 102 p53(KO/+) mouse‐derived lymphomas Helios and Aiolos loci showed allelic loss in 8% (8/102) and 33% (34/102), respectively. However, 33 of the 34 lymphomas showing allelic loss at Aiolos were/j53(KO/‐) and were accompanied by loss of the p53 wild‐type allele on the same chromosome. Homozygous deletion and mutation analyses failed to detect bi‐allelic alterations. These results do not suggest any obvious contribution of Helios or Aiolos to oncogenesis of the mouse thymic lymphomas.