Abstract

Balancing the rates of cell proliferation and cell death is important in maintaining normal tissue homeostasis. The relationship among apoptosis, cell proliferation and factors influencing apoptosis according to the histologic types in chemically induced mammary tumorigenesis appears important in understanding the pathogenesis of breast carcinoma. In this study, we investigated alterations in the kinetics of cell proliferation and apoptosis during rat mammary tumorigenesis induced by 7, 12-dimethylbenzanthracene (DMBA) and we related these changes to the expressions of bcl-2, p53, and TGF-beta. Seven-week-old female Sprague-Dawley rats were divided into an experimental group (20 mg/ml DMBA by oral intubation) and a control group. The results were as follows. 1. In the experimental group, breast tumors occurred in twenty two of fifty nine rats(37.3%, 22/59), and the total number of tumors was 100 (4.5 2.0/rat). The histological classification was infiltrating ductal carcinomas (n=5), ductal carcinomas with focal invasion (n=10), intraductal carcinomas (n=36), adenomas accompanied with intraductal proliferation (n=35), intraductal proliferation (n=9), and adenomas (n=5); 2. The differentiation of terminal end bud into alveolar bud (AB) in the experimental group was significantly lower than that of the control group (p<0.05); 3. BrdU labeled tumor cells were mainly located at the peripheral portion of tumor cell nests. BrdU labeling indices were highest in ductal carcinomas, less pronounced in intraductal proliferation, and lowest in adenomas, whereas apoptosis levels were highest in adenomas, less pronounced in intraductal proliferation, and lowest in ductal carcinomas (p<0.05); 4. p53 protein was not expressed in any breast tumors. Although the expression of bcl-2 protein was highest in infiltrating and focal infiltrative ductal carcinomas (58.3%), compared with adenomas, intraductal proliferation, and intraductal carcinomas (p<0.05), the extent of its expression was less than 1% of all tumor cells; 5. TGF-beta was mainly expressed in the central portion of tumor cell nests rather than in peripheral portion, and TGF-beta immunoreactive tumor cells displayed good differentiation and did not reveal BrdU immunoreactivity. TGF-beta labeling index of infiltrating and focal infiltrative ductal carcinomas was significantly higher than that of intraductal carcinomas, intraductal proliferation, and adenomas (p<0.05). Based on these results, it is thought that high cell proliferation and the suppression of apoptosis are closely associated with DMBA-induced rat mammary carcinogenesis. However, the suppression of apoptosis is not related to p53 mutation, bcl-2, and TGF-beta. TGF-beta seems to be reversely related to tumor cell proliferation but closely associated with the progression of the tumor, especially an invasion of breast carcinomas.

• Keywords: Breast carcinoma;Cell proliferation;Apoptosis;DMBA;TGF-