Wild-Type p53 Regulates Apoptosis of Human Breast Cancer Cells.

Background: The tumor suppressor wild-type p53 is known for its role in inducing apoptosis in tumor cells. This study investigated the relationship between wild-type p53 and protein phosphatase 1 (PP1) and caspase in promoting apoptosis of breast cancer cells.

Methods: Human breast cancer cell lines MCF-7 and MDA-MB-231 obtained from the American Type Culture Collection were used in this study. Small interference RNAs (Si-RNA) and plasmids were used to regulate wild-type p53 expression in these two tumor cell lines through liposome-mediated transfection. GSK-2830371 (PP1 inhibitor) and zVAD (Caspase inhibitor) were employed to further verify the PP1 activating function of wild-type p53 in Caspase-dependent MCF-7 and MDA-MB-231 apoptosis. PP1 activity was quantitatively detected by phosphorus colorimetric assay. Co-immunoprecipitation (Co-IP), flow cytometry assay, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay, Western blot, the real-time reverse transcriptase-polymerase chain reaction (RT-qPCR), and immunofluorescence staining were used to analyze cell apoptosis degree and marker protein expression.

Results: The expression level of PP1 in the breast cancer cells was successfully regulated by cell transfection. The phosphatase activity was increased, and obvious apoptotic cytological characteristics were observed in p53-overexpressed breast cancer cells. p53 knockdown/overexpression increased/decreased the level of B cell lymphoma 2 (Bcl-2), and decreased/increased levels of Caspase-3, cleaved Caspase-3, cleaved Caspase-8, Cytochrome C (Cyt-C), Truncated BID (tBid), Bcl-2-associated X (Bax), and cell apoptosis (p < 0.01). The promotion of proteins and apoptosis induced by p53 overexpression was reversed by GSK-2830371 or zVAD.

Conclusion: Wild-type p53 might promote Caspase-dependent apoptosis of human breast cancer cells through PP1 activation.