DZNep represses Bcl-2 expression and modulates apoptosis sensitivity in response to Nutlin-3a

ABSTRACT

MDM2 antagonists stabilize and activate wild-type p53, and histone methyltransferase (HMT) inhibitors reduce methylation on histone lysines and arginines. Both MDM2 antagonists and HMT inhibitors are being developed as cancer therapeutics. Wild-type p53 expressing HCT116 colon cancer cells were resistant to apoptosis in response to the MDM2 antagonist Nutlin-3a. However, co-treatment with the HMT inhibitor DZNep sensitized the cells to Nutlin-3a-induced apoptosis. This sensitization resulted from reduced activity of the Bcl-2 gene promoter and a reduction in Bcl-2 mRNA and protein. Surprisingly, DZNep reduced Bcl-2 expression in other colon cancer cell lines (RKO, SW48, and LoVo) but failed to sensitize them to Nutlin-3a. We found these cell lines express elevated levels of Bcl-2 or other Bcl-2-family proteins, including Bcl-xL, Mcl-1, and Bcl-w. Knockdown of Mcl-1 and/or treatment with specific or pan Bcl-2-family inhibitors (BH3 mimetics) sensitized RKO, SW48, and LoVo cells to apoptosis by Nutlin-3a. The results demonstrate 1) DZNep represses the Bcl-2 gene promoter and affects apoptosis sensitivity by reducing Bcl-2 protein expression, and 2) elevated expression of pro-survival Bcl-2 family members protects colon cancer cells from Nutlin-3a-induced apoptosis. Targeting Bcl-2 proteins via DZNep or BH3 mimetics could increase the therapeutic potential of MDM2-antagonists like Nutlin-3a in colon cancer.

KEYWORDS:

• Nutlin-3a
• DZNep
• Bcl-2

Author Contributions

Y.Z. conducted the experiments for Figs. 2–8 and prepared the figures.

R.E.P. conducted the experiments in Figs. 1 and 8E.

L.D. contributed to design of the experiments, interpretation of the data, and writing the manuscript.

C.G.M. devised the study, contributed to the design of experiments and data interpretation, and wrote the initial draft.

All authors proofread the manuscript and contributed to the final submitted manuscript.

Disclosure of potential conflicts of interest

No potential conflicts of interest were disclosed.

Acknowledgments

This work was supported by National Cancer Institute grant 1 R21 CA185036-01A1 (to C.G.M) and by a grant from the Swim Across America Foundation (to C.G.M).

Additional information

Funding

NIH/NCI (R21 CA185036-01A1)