Impact of adenomatous polyposis coli (APC) tumor supressor gene in human colon cancer cell lines on cell cycle arrest by apigenin

This research assessed the importance of the adenomatous polyposis coli (APC) tumor suppressor mutation in the ability of apigenin to induce cell cycle arrest using HT29-APC cells, which contain inducible wild-type APC under the metallothionein promoter. HT29-GAL cells, containing beta-galactosidase (GAL), were included as control. Treatment with apigenin (0, 20, 40, 60, and 80 mu M) for 48 h resulted in reduction in the cell number (P<0.05) concurrent with flow cytometry results showing a dose-dependent accumulation of cells in the G2/M phase in both HT29-APC and HT29-GAL cells without ZnCl2 treatment. Flow cytometric analysis showed an increase (P<0.05) in the percentage of cells in G2/M when HT29-APC cells were treated with 80 pM apigenin for 120 h. This increase was not present in HT29-APC cells when treated with both 80 mu M apigenin and 100 pM ZnCl2 for 120 h. Western blot analysis verified the induction of APC protein expression in ZnCl2-treated HT29-APC cells but not in ZnCl2-treated HT29-GAL cells. Apigenin plus ZnCl2 treatment increased the expression of APC protein in HT29-APC cells by 50 fold above expression observed with ZnCl2 alone. Upon induction of the APC gene with ZnCl2 in HT29-APC cells, the percentage of apoptotic cells increased significantly (P<0.05) after 120-h treatment. Additionally, apigenin treatment (80 mu M) further increased the percentage of apopototic HT29-APC following ZnCl2 treatment to induce wild-type APC expression. These results suggest that APC dysfunction may be critical for apigenin to induce cell cycle arrest in human colon cancer cell lines and furthermore, apigenin enhances APC expression and apoptosis in cells with wild-type APC. (C) 2007 Wiley-Liss, Inc.