Induction of apoptosis in breast cancer cells by TPA

Bcl-2, Fax and p53 gene products have been linked to programmed cell death pathways. p21(WAF1) has been shown to mediate p53-induced cell cycle arrest and to inhibit cyclin-dependent kinase activity. We have analysed the expr ession of these genes and apoptosis induced by 12-O-tetradecanoyl-phorbol-1 3-acetate (TPA) in several human breast cancer cell line. We found up-regul ation of p2l(WAF1) and Bax expressions, however, the expressions of p53 and Bcl-2 genes remained unchanged in TPA-treated cells. Furthermore, DNA ladd er formation and PARP cleavage were observed after treatment for 24 h, indi cating apoptotic cell death. Flow cytometry with 7-amino actinomycin D stai ning showed that the number of apoptotic cells increased with longer treatm ent of TPA. From these results, we conclude that TPA is not only a tumor pr omoter, but also induces apoptosis in breast cancer cells. TPA-induced apop tosis appears to be mediated through a p53-independent pathway, and the up- regulation of p21(WAF1) and Bar may be the molecular mechanisms by which TP A induces apoptosis.