Aberrant expression of cyclin D1 in pulmonary proliferative lesions induced by high doses of urethane in transgenic mice carrying the human prototypec-H-ras gene

In our previous study, when rasH2 mice and non-transgenic (non-Tg) litterma tes were injected intraperitoneally with 1,000 mg/kg of urethane once or th ree times at two-day intervals, the incidence of lung proliferative lesions in rasH2 mice given triple doses of urethane was significantly increased, compared to that in rasH2 mice given a single dose of urethane, and the mut ation frequency of the transgene in lung tumors in rasH2 mice given triple doses was lower than that in rasH2 mice given a single dose of urethane. In the present study, differential immunohistochemical expressions of Cyclin D1 and PCNA, that lead to abnormal cell proliferation and tumor development due to uncontrolled G1-S transition in the cell cycle, as well as p53 tumo r suppressor gene in pulmonary proliferative lesions obtained from our prev ious study were investigated. Over-expression of Cyclin D1 in hyperplasias in rasH2 mice given triple doses was significantly increased, compared to t hat in the single-injection group, but no significant differences in Cyclin D1 between the single and triple injection groups were observed in hyperpl asias in non-Tg mice or lung tumors in either rasH2 or non-Tg mice. There w ere no differences in the PCNA labeling index of hyperplasias in rasH2 or n on-Tg mice between the triple-injection and single-injection groups, while the PCNA labeling index tended to be increased in the tumor, compared with that in hyperplasias. There was neither mutation of p53 nor an increase in immunoreactivity of wild type p53 in these proliferative lesions. These res ults suggest that cyclin D1 over-expression in alveolar/bronchiolar hyperpl asias in rasH2 mice in the triple-injection group is not only indicative of a high cell proliferation rate but also of an important role in the proces s of malignant transformation.