Genistein inactivates bcl-2, delays the G2/M phase of the cell cycle, and induces apoptosis of human breast adenocarcinoma MCF-7 cells

The aim of this study was to identify the molecular mechanism of action of the isoflavone, genistein. Genistein at 0.15 mM caused IMCF-7 apoptotic cell death, which was accompanied by cell cycle delay in the G2/M phase. Twenty-four hours post-treatment, 47.3% of the IMCF-7 cells accumulated at G2/M, compared with 19.9% in the untreated controls. At 0.15 mM, genistein caused an increase in the steady-state levels of the wild-type tumour suppressor p53, which was attributed to stabilising the tumour suppressor protein, since p53 mRNA levels did not increase. Prior to the upregulation of p53, which became evident within 6h of genistein treatment, there was increased bcl-2 phosphorylation at 30 min post-treatment. Although early changes (30-120 min) in the phosphotyrosine peptide patterns were not detected, after 24 h, genistein inhibited phosphorylation of several peptides. These results suggest that genistein's dual roles of protein tyrosine kinase inhibitor and topoisomerase II inhibitor are essential for the initiation of apoptosis. (C) 1998 Elsevier Science Ltd. All rights reserved.