Expression of cyclin D1 and p53 and its correlation with proliferative activity in the spectrum of esophageal carcinomas induced after duodenal content reflux and 2,6-dimethylnitrosomorpholine administration in rats

Alterations in expression of the p53 and cyclin D1 genes have been implicated in the development of esophageal carcinomas in both humans and animal models. We hypothesize that altered expression of cyclin D1 and p53 may be involved in the sequential development of esophageal carcinomas with glandular differentiation induced by the carcinogen, 2,6-dimethylnitrosomorpholine (DMNM) in rats with duodenal content reflux esophagitis. In the present study Sprague-Dawley rats were given DMNM 15 days after performing an esophago-jejunostomy in order to induce chronic duodenal content reflux esophagitis. Expression and localization of p53, cyclin D1 and Ki-67 were examined by immunohistochemical analyses. Twenty of 24 animals developed different types of esophageal carcinomas, including pure squamous carcinoma, adenosquamous carcinoma and pure adenocarcinoma. Undifferentiated basaloid areas were frequently observed in these tumors. Cyclin D1 overexpression was observed in hyperplastic lesions and increased through dysplasia and in undifferentiated areas of infiltrating carcinoma. Cyclin D1 expression coincided with increased Ki-67 expression and decreased along with cell differentiation. The p53 immunohistochemical pattern was parallel to that of cyclin D1, although the percentage of positive cells was usually smaller in all lesions and increased p53 expression started at the dysplastic stage. These findings suggest that overexpression of cyclin D1 may be an early event in DMNM-induced rat esophageal tumorigenesis, causing increased proliferation of esophageal stem cells. Abnormal p53 expression may then be required to promote the development of neoplastic transformation from dysplastic epithelium through invasive phenotype, being more evident in cancer cells with squamous differentiation.