Ionizing radiation is a well known risk factor of thyroid cancer development, but the mechanism of radiation induced carcinogenesis is not clear. The RET/PTC oncogene, an activated form of the RET proto-oncogene, is frequently observed in papillary thyroid carcinoma (PTC); RET/PTC1, -2 and -3 are known to be the three major forms. High frequencies of RET/PTC rearrangements have been observed in radiation-associated PTC, such as those appearing post-Chernobyl or post-radiotherapy, but the rearrangement types dier between these two populations. We investigated whether a speci®c type of RET/PTC rearrangement was induced by X-rays in vivo and in vitro. In human normal thyroid tissues transplanted in scid mice, the RET/PTC1 rearrangement was predominantly detected throughout the observation period (up to 60 days) after X-ray exposure of 50 Gy. On the other hand, RET/PTC3 was detected only 7 days after X-irradiation, and no transcript of RET/PTC2 was detected. These results are supported by the results of an in vitro study. The RET/PTC1 rearrangement was preferentially induced in a dose-dependent manner by X-rays within a high dose range (10, 50 and 100 Gy) in four cell lines. On the other hand, RET/PTC3 was induced at a much lower frequency, and no induction of RET/PTC2 was observed. These results suggest that the preferential induction of the RET/PTC1 rearrangement may play an important role in the early steps of thyroid carcinogenesis induced by acute X-irradiation. Oncogene (2000) 19, 438 ± 443.

The validity of molecular studies using DNA and RNA extracted from decades-old formalin-fixed and paraffin-embedded tissue blocks has been demonstrated. The quality and usability of DNA and RNA from archival tissues are modified by various factors, such as the fixative, the fixation time, and the postmortem time. However, in contrast to DNA, there are no comprehensive studies quantitatively addressing the feasibility of RNA from old (more than 10 years) archival samples. This study examined the integrity of RNA extracted from 738 autopsy liver and 63 autopsy thyroid cancer tissue blocks procured during a span of nearly four decades, beginning in 1952 and ending in 1989, from the atomic bomb survivors. The integrity of RNA was assessed by amplification of c-BCR messenger RNA (mRNA) between two sequential exons with an intervening intron by reverse-transcription polymerase chain reaction (RT-PCR). The integrity of RNA was influenced by the age of the samples and the postmortem time, but not by the formalin-fixation period. It was possible to amplify more than 60% of the samples. Using these RNAs, the HCV genome in liver cancers and the H4-RET gene in thyroid cancers were detectable. This study illustrates the possibility of molecular studies using RNA from routinely prepared paraffin blocks stored for long periods and provides the statistics and critical factors to consider in assessing the feasibility of such contemplated studies.

Ionizing radiation is a well-known risk factor of cancer development, but the mechanism of radiation induced carcinogenesis is not clear. Chromosomal rearrangements induced by radiation most likely are one of the principal genetic alterations resulting in malignant transformation. The chimeric BCR-ABL associated with chronic myelogenous leukemia (CML) and H4-RET oncogenes associated with thyroid papillary carcinoma are the result of a translocation and inversion, respectively. In vitro studies showed these genes were induced by high-doses of X-irradiation in cell lines. Studies also show that therapeutic external X-ray doses as high as 60 Gy for treatment of various childhood cancers including Hodgkin's disease signi®cantly increase the risk of thyroid cancer. Therefore, we examined the induction and persistence of these chimeric genes in human thyroid tissues transplanted in scid mice after 50 Gy exposure as a function of time for 2 months to elucidate the early events of thyroid carcinogenesis. The H4-RET genes were detected on day 2 and throughout the 2 month period. On the other hand, BCR-ABL genes were detected on day 2 and were undetectable subsequently. These results suggest that ionizing radiation causes various oncogene activations, but cells with only speci®c gene alteration uniquely associated with thyroid carcinogenesis are selectively retained demonstrating one of the early events in the beginnings of radiation carcinogenesis in human thyroid tissues.

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To identify the genetic events that must be involved in thyroid tumor progression, we initially investigated p53 gene alterations in 10 papillary adenocarcinomas, 4 follicular adenocarcinomas, and 8 undifferentiated carcinomas. Base substitutional mutations in exons 5 to 8 and loss of heterozygosity (LOH) of the p53 gene were not detected in papillary or follicular adenocarcinomas. However, 7 of 8 undifferentiated carcinomas were carrying base substitutional mutations, and LOH was detected in 3 of 5 informative cases. Furthermore, to verify that the p53 gene alterations are truly involved in tumor progression, DNA from individual foci of the four undifferentiated carcinomas coexisting with a differentiated focus and from one follicular adenocarcinoma with an undifferentiated focus was analyzed by direct sequencing and polymerase‐chain‐reaction‐restriction‐fragment‐length polymorphism (PCR‐RFLP). Base substitutional mutations in the p53 gene from exons 5 to 8 were identified exclusively in the undifferentiated foci, but not in the differentiated foci. LOH was observed in 3 of 4 informative undifferentiated foci. In one of these positive cases, LOH was observed in both papillary adenocarcinoma and undifferentiated carcinoma. However, a p53 gene mutation at codon 248 was detected in the undifferentiated carcinoma but not in the papillary adenocarcinoma. The results imply that LOH occurs first in papillary adenocarcinoma followed by a p53 mutation during the transition from papillary adenocarcinoma to undifferentiated carcinoma. Maintenance of LOH during tumor progression excludes the possibility that these different histological foci are derived from different origins and represents molecular evidence that undifferentiated carcinoma is very likely derived from preexisting papillary adenocarcinoma. Furthermore, these results strongly suggest that the mutated p53 gene plays a crucial role in de‐differentiation during the progression of thyroid tumors.

Multilocus sequence analysis based on hypervariable housekeeping proteins was utilized to differentiate closely related species in the family Enterobacteriaceae. Of 150 housekeeping proteins, the top 10 hypervariable proteins were selected and concatenated to obtain distance data. Distances between concatenated proteins within the family were 0.9-41.2%, whereas the 16S rRNA and atpD-gyrB-infB-rpoB concatenated sequence (4MLSA) distances were 0.8-6.0% and 0.9-22.1%, respectively. These data indicate that phylogenetic analysis by concatenation of hypervariable proteins is a powerful tool for discriminating species in the family Enterobacteriaceae. To confirm the discriminatory power of the 10 chosen concatenated hypervariable proteins (C10HKP), phylogenetic trees based on C10HKP, 4MLSA, and the 16S rRNA gene were constructed. Comparison of average bootstrap values among C10HKP, 4MLSA and 16S rRNA genes indicated that the C10HKP tree was the most reliable. Location via the C10HKP tree was consistent with existing assignments for almost all species in the family Enterobacteriaceae. However, the C10HKP tree suggested that several species (including Enterobacter massiliensis, Escherichia vulneris, Escherichia hermannii, and Salmonella subterranea) should be reassigned to different clusters than those defined in previous analyses. Furthermore, E. hermannii and S. subterranea appeared to fall onto a branch independent from those occupied by the other Enterobacteriaceae. Therefore, we propose Atlantibacter gen. nov., such that E. hermannii and S. subterranea would be transferred to genus Atlantibacter as Atlantibacter hermannii, comb. nov. and Atlantibacter subterranea. comb. nov., respectively.

To determine if the risk of hepatocellular carcinoma (HCC) is reduced by consumption of soya foods, we conducted a case-control study within a cohort of Japanese A-bomb survivors. We compared the prediagnosis consumption of isoflavone-rich miso soup and tofu to HCC risk, adjusting for hepatitis B (HBV) and C (HCV) viral infections, the major HCC risk factors in this population. The study included 176 pathologist-confirmed cases of HCC diagnosed in 1964-1988 and 560 controls who died of diseases other than liver cancer. We examined dietary information collected at least 2 years before diagnosis or death and tissue-based measures of viral hepatitis. Using logistic regression, crude ORs were 0.5 (95% CI 0.29-0.95) and 0.5 (95% CI 0.20-0.99) for high vs. low miso soup and tofu intake, respectively. Adjusting for year of birth, sex, HBV, HCV and other factors, the OR for miso soup was unchanged at 0.5 (95% CI 0.14-1.55), and miso results were similar when ORs were recalculated separately for earlier and later birth cohorts to assess consistency of results. The adjusted OR for tofu was 0.9 (95% CI 0.20-3.51). We also found a statistically significant (p < 0.0001) interaction between sex and HCV, with risk of HCC being substantially higher for women. We conclude that consumption of miso soup and other soya foods may reduce HCC risk. ' 2005 Wiley-Liss, Inc.

A novel polymerase chain reaction method was developed to preferentially amplify a segment of DNA containing a base substitution mutation. This technique uses a pair of dideoxynucleotide-labeled oligonucleotides (18 mers) of normal sequences as blockers located between the two primers. By virtue of a subtle difference in the melting temperature between the blocker-normal DNA and blocker-mutant DNA hybrids, the method allows preferential amplification of the mutant DNA. We used the human N-ras gene as a model. Two different types of N-ras mutations could be effectively amplified when they were present with an excess amount of normal DNA at a ratio of 1:10(3). Furthermore, the sensitivity was increased 10-fold by using single strand conformation polymorphism analysis for the amplified products, and mutant DNA was detected in the presence of a 10(4) times excess amount of normal DNA.