HDAC inhibitor sodium butyrate sensitizes E1A+Ras-transformed cells to DNA damaging agents by facilitating formation and persistence of γH2AX foci

Abstract

HDAC inhibitors (HDACi) suppress the growth of tumor cells due to induction of cell cycle arrest, senescence or apoptosis. Recent data demonstrate that HDACi can interfere with DNA Damage Response (DDR) thereby sensitizing the cells to DNA damaging agents. Here, we show that HDACi sodium butyrate (NaBut) potentiates the formation of γH2AX foci predominantly in S-phase E1A+Ras cells. Accumulation of γH2AX foci sensitizes the cells toward such DNA damaging agents as irradiation (IR) and adriamycin. In fact, NaBut potentiates the persistence of γH2AX foci induced by genotoxic agents. The synergizing effects depend on DNA damaging factors and on the order of NaBut treatment. Indeed, NaBut treatment for 24 h leads to an accumulation of G₁-phase cells and a lack of S-phase cells, therefore, adriamycin, a powerful S-phase-specific inhibitor, when added to NaBut-treated cells, is unable to substantially add γH2AX foci. In contrast, IR produces both single- and double-strand DNA breaks at any stage of the cell cycle and was shown to increase γH2AX foci in NaBut-treated cells. Further, a lifetime of IR-induced γH2AX foci depends on the subsequent presence of HDACi. Correspondingly, NaBut withdrawal leads to the extinction of IR-induced γH2AX foci. This necessitates HDACi to hold the IR-induced γH2AX foci unrepaired. However, the IR-induced γH2AX foci persist after long-term NaBut treatment (72 h) even after washing the drug. Thus, although signaling pathways regulating H2AX phosphorylation in NaBut-treated cells remain to be investigated, the obtained results show that NaBut potentiates effects of DNA damaging agents by facilitating formation and persistence of γH2AX foci.

Keywords: :

• DNA damage
• cell cycle arrest
• histone-deacetylase inhibitors
• senescence
• γH2AX foci

Disclosure of Potential Conflicts of Interest

No potential conflicts of interest were disclosed.

Acknowledgments

Authors thank Lyudmila Supanko for technical help in the process of performing the work and Xenia Strunnikova for critical reading the manuscript. The work was supported by Russian Foundation for Basic Research (RFBR): No. 09-04-00466 (VAP) and No. 10-04-01152 (TVP), Russian Academy of Sciences Program “Molecular and Cell Biology” (VAP), and grant from the St.Petersburg State University (VAP), Contract No. 1.37.122.2011, grant the committee on Science and Higher Education of the Government of St. Petersburg (MAV).

Note

Supplemental material can be found at: www.landesbioscience.com/journals/cbt/article/18365/.