Inhibition of ornithine decarboxylase by alpha-difluoromethylornithine induces apoptosis of HC11 mouse mammary epithelial cells

The effect of a-difluoromethylornithine (DFMO) on the apoptosis of HC11 mou se mammary epithelial cells was investigated. The involvement of reactive o xygen species (ROS) and Bcl-2 protein in the mechanism of apoptosis induced by ornithine decarboxylase (ODC) inhibition was also assessed. DFMO (0.1, 1 and 5 mM) induced apoptosis of HC11 cells in dose- and time-dependent man ner. Apoptosis manifests itself with morphological features like: cell shri nkage, condensation of chromatin, pyknosis and fragmentation of nucleus, fo llowed by secondary necrosis (putrosis). The decrease in the nuclear DNA co ntents appearing as the hypodiploidal peak sub-G, in the DNA histogram was not dependent on the presence of prolactin (5 mu g/ml) in DFMO-treated cult ures. Apoptosis induced by ODC inhibition was associated with a rapid incre ase in ROS concentration in HC11 cells observed within Ih after DFMO treatm ent. The down-regulation of Bcl-2 as a decrease in cell number expressing b cl-2 and a lowered Bcl-2 protein content in cells expressing this protoonco gene was also noted. The administration of putrescine (50 mu M) lowered the number of early-apoptotic, late-apoptotic and necrotic cells. Moreover, it increased the number of cells expressing bcl-2. In conclusion, the disturb ance of cellular polyamine homeostasis by inhibition of their synthesis enh ances mammary epithelial cell susceptibility to apoptosis. It may occur in the mammary gland at the end of lactation, when the depletion of circulatin g lactogenic hormones and activation of intra-mammary apoptogenic factors e xpression take place.