Human breast cancer MCF-7, T47D, and MDA-MB-435 and colorectal cancer HCT116 cells were treated with tamoxifen. Cellular senescence was measured by SA-尾-gal staining and based on the protein expression of p53 and p21Cip1/WAF1. The production of reactive oxygen species (ROS) was determined by staining with CM-H2DCFDA and dihydroethidium (DHE). CK2 activity was assessed with a specific peptide substrate.
Tamoxifen promoted senescence phenotype and ROS generation in MCF-7 and HCT116 cells. The ROS scavenger, N-acetyl-l-cysteine (NAC), and the NADPH oxidase inhibitor, apocynin, almost completely abolished this event. Tamoxifen inhibited the catalytic activity of CK2. Overexpression of CK2伪 antagonized senescence mediated by tamoxifen, indicating that tamoxifen induced senescence via a CK2-dependent pathway. A well-known CK2 inhibitor, 5,6-dichloro-1-尾-d-ribofuranosylbenzimidazole (DRB), also stimulated ROS production and senescence in MCF-7 cells. Finally, experiments using T47D (wild-type p53) and MDA-MB-435 (mutant p53) cell lines suggested that tamoxifen induces p53-independent ROS production as well as p53-dependent senescence in breast cancer cells.
These results demonstrate that tamoxifen promotes senescence through a ROS-p53-p21Cip1/WAF1 dependent pathway by inhibiting CK2 activity in breast cancer and colon cancer cells.