Yumiko Nitta

Unstable Expression of E‐Cadherin Adhesion Molecules in Metastatic Ovarian Tumor Cells

E‐Cadherin is a member of the cadherin family, which plays a key role in intercellular adhesion in various tumors as well as in normal tissues. Here, we examined the expression of this adhesion molecule in a murine ovarian tumor line OV2944, whose sublines show different degrees of spontaneous metastasis from subcutaneous sites; sublines LM‐1 and LM‐3 exhibit a low metastatic activity but a variant subline HM‐1 has a high metastatic activity. When the expression of E‐cadherin in these cells was examined by immunoblot analysis, the highly metastatic HM‐1 cells was found to express an extremely small amount of this molecule, as compared with a high level of E‐cadherin expression in the weakly metastatic LM‐1 and LM‐3 cells. Northern blot analysis showed that the amount of tanscripts from the E‐cadherin gene is proportional to the amount of proteins detected in these cells. Immunofluorescence staining revealed that cells of the highly metastatic line were heterogeneous, that is, their cultures contained both E‐cadherin‐positive and negative cells. In contrast, cells of the weakly metastatic lines homogeneously expressed E‐cadherin. When the highly metastatic line was subcloned, all the subclones consisted of E‐cadherin‐positive and negative cells. These results suggest that the expression of E‐cadherin gene is not stably controlled in the highly metastatic line.

Induction of Transplantable Tumors by Repeated Subcutaneous Injections of Natural and Synthetic Vitamin E in Mice and Rats

Natural vitamin E and synthetic vitamin E (dl/‐α‐tocopheryl acetate) were tested for their tnmorigenicity in rodents. Transplantable tumors, at the site of injection, were induced by repeated injections of these compounds in two strains of mice, NFS/N and C57BL/6N × C3H/He Fl, and in a strain of rats, Fischer 344. Natural vitamin E was tumorigenic in both strains of female mice only when injected with soya oil. In contrast, dl‐α‐tocopheryl acetate alone was capable of inducing tumors in Fischer 344 rats. Only one out of 5 male NFS/N mice given dl‐α‐tocopheryl acetate developed a tumor. Therefore, Fischer 344 rats were more susceptible to tumor formation by dl‐α‐tocopheryl acetate than NFS/N mice. dl‐α‐Tocopheryl acetate with soya oil or with palm oil also resulted in the formation of transplantable tumors in NFS/N mice and Fischer 344 rats. There was no difference in the tumor incidence between mice treated with dl‐α‐a‐tocopheryl acetate alone and dl‐α‐tocopheryl acetate plus soya oil or palm oil. However, in rats, the incidence was lower for a group treated with dl‐α‐tocopheryl acetate plus palm oil than for those with dl‐αa‐tocopheryl acetate alone and with dl‐α‐tocopheryl acetate plus soya oil.

Gamma-ray dose response of ESR signals in tooth enamel of cows and mice in comparison with human teeth

The ESR dose responses of the tooth enamel samples prepared from teeth of cow and mice were examined in comparison with that of human. The samples were prepared with combined procedures of mechanical and chemical treatments of teeth. The ESR dose response was extracted from the total ESR spectra of tooth enamel samples by a specially developed matrix method. The dosimetric signal was found to be increased linearly with gamma dose for all studied tooth enamel samples. The radiation sensitivity of cow tooth enamel was found to be close to that of human teeth while that of mouse teeth was about 25% lower. The present results indicate that, having high radiation sensitivity, cow and mouse teeth can be used for retrospective radiation dosimetry in low-dose level.

Effects of radioactive iodine (131I) on the thyroid of newborn, pubertal and adult rats

Abstract Age is a potent modifier of thyroid cancer. The short latency for the development of thyroid cancer in the post-Chernobyl cases proposes that we need to be sure of the thyroid susceptibility to internal exposure, especially at young ages. We started a large-scale carcinogenesis project 6 years ago with the purpose to evaluate the carcinogenic potential of 131I when irradiated at young ages. First, we established a method to estimate the absorbed doses in the thyroid of different age groups. Irradiation at 1 week of age caused heavier exposure than at 4 and 9 weeks of age by eight times, while damages of the thyroid tissue were more obvious in the 4-week-old groups than in the 1-week-old groups. Second, we tested the responsiveness of thyroid epithelium to radiation. Apoptosis was not detected in the 1-week-old-thyroid epithelium, however, it did appear in the 4-week-old thyroid epithelium. While the proliferating cell nuclear antigen (PCNA)-labeling index was vice versa. Third, the carcinogenesis of 131I has been tested. Papillary carcinomas have developed in rats internally irradiated with 131I at the age of 1 week. A very low dose rate of irradiation by 131I could induce thyroid carcinomas with a short latency.