Neonatal diethylstilbestrol treatment alters the estrogen-regulated expression of both cell proliferation and apoptosis-related proto-oncogenes (c-jun, c-fos, c-myc, bax, bcl-2, and bcl-x) in the hamster uterus.

In the Syrian hamster, neonatal diethylstilbestrol (DES) treatment and then postpubertal estrogen stimulation induces hyperplasia plus apoptosis (preneoplastic responses) and ultimately neoplasia in the endometrial epithelial cell compartment. As part of a project to investigate the molecular and cellular mechanisms responsible for this phenomenon, expression of several proto-oncogenes (c-jun, c-fos, c-myc, bax, bcl-2 and bcl-x) was compared in estrogen-stimulated uteri from control versus neonatally DES-treated hamsters. According to Northern blot analysis of total uterine RNA, levels of the 3.2-kb c-jun and 2.4-kb c-myc transcripts were not altered by neonatal DES treatment. However, the 1.0 kb bax and 2.7 kb bcl-x transcript levels were significantly increased in the neonatally DES-exposed uteri. According to immunohistochemical analysis of paraformaldehyde-fixed and paraffin-embedded tissue sections, levels of c-Jun, c-Fos, c-Myc, Bax, and Bcl-x proteins were enhanced dramatically in both the luminal and glandular epithelial cells of neonatally DES-exposed uteri. In contrast, the immunostaining signal for Bcl-2 protein was decreased consistently in the epithelial cells of neonatally DES-exposed uteri. In conclusion, neonatal DES treatment induced persistent and epithelial cell-specific imbalances in the estrogen-regulated uterine expression of c-jun, c-fos, c-myc, bax, bcl-2, and bcl-x proto-oncogenes. These imbalances likely play a role in the molecular mechanism by which neonatal DES treatment induces altered estrogen responsiveness including hyperplasia, apoptosis, and ultimately neoplasia in the epithelial compartment of the hamster uterus.