Chemopreventive effects of green tea polyphenols correlate with reversible induction of p57 expression
Anticancer Res 2001 Nov-Dec;21(6A):3743-8
Hsu S; Lewis JB; Borke JL; Singh B; Dickinson DP; Caughman GB; Athar M; Drake L; Aiken AC; Huynh CT; Das BR; Osaki T; Schuster GS
Department of Oral Biology and Maxillofacial Pathology, School of Dentistry, Medical College of Georgia, Augusta 30912-1126, USA. email@example.com .
Green tea polyphenols are known to induce apoptosis in certain types of tumor cells. However, the mechanism(s) that enables normal cells to evade the apoptotic effect is still not understood. In this study, Western blot analysis combined with cycloheximide treatment was used to examine the effects of green tea polyphenols on the expression levels of p57, a cyclin-dependent kinase and apoptosis inhibitor, in normal human keratinocytes and in the oral carcinoma cell lines SCC25 and OSC2. The results showed that the most potent green tea polyphenol, (-)-epigallocatechin-3-gallate (EGCG), induced p57 in normal keratinocytes in a dosage- and time-dependent manner, while the levels of p57 protein in oral carcinoma cells were unaltered. The differential response in p57 induction was consistent with the apoptosis status detected by annexin V assay. The data suggest that the chemopreventive effects of green tea polyphenols may involve p57-mediated cell cycle regulation in normal epithelial cells.