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

HDAC Inhibitor Sodium Butyrate Attenuates the DNA Repair in Transformed but Not in Normal Fibroblasts

Many cancer therapy strategies cause DNA damage leading to the death of tumor cells. The DNA damage response (DDR) modulators are considered as promising candidates for use in combination therapy to enhance the efficacy of DNA-damage-mediated cancer treatment. The inhibitors of histone deacetylases (HDACis) exhibit selective antiproliferative effects against transformed and tumor cells and could enhance tumor cell sensitivity to genotoxic agents, which is partly attributed to their ability to interfere with DDR. Using the comet assay and host-cell reactivation of transcription, as well as γH2AX staining, we have shown that sodium butyrate inhibited DNA double-strand break (DSB) repair of both endo- and exogenous DNA in transformed but not in normal cells. According to our data, the dysregulation of the key repair proteins, especially the phosphorylated Mre11 pool decrease, is the cause of DNA repair impairment in transformed cells. The inability of HDACis to obstruct DSB repair in normal cells shown in this work demonstrates the advantages of HDACis in combination therapy with genotoxic agents to selectively enhance their cytotoxic activity in cancer cells.

p21Waf1 deficiency does not decrease DNA repair in E1A+cHa-Ras transformed cells by HDI sodium butyrate

This study aimed to explore a role of p21Waf1 in γH2AX foci formation and DNA repair as assessed by a Host-Cell Reactivation Assay in wild-type (p21Waf+/+) and p21Waf1-deficient E1A+Ras-transformed cells. p21Waf1+/+ cells have low γH2AX background compared to p21Waf1-/- cells. The treatment with histone deacetylase inhibitor (HDI) sodium butyrate (NaBut) causes to accumulation of γH2AX in p21Waf+/+ cells with little effect in p21Waf-/- cells. Moreover, NaBut inhibits DNA repair in wt cells but not in p21Waf1-/- cells. This could be explained by the weakening of GADD45 and PCNA proteins binding in NaBut-treated p21Waf1-expressing cells but not in p21Waf1-/- cells. We suggest that in wt-ERas cells NaBut activates both p21Waf1 expression and a release of p21Waf1 from the complexes with E1A that leads to suppression of DNA repair and promotes γH2AX persistency. The absence of p21Waf1 is by itself considered by the cell as stressful factor with formation of γH2AX. But the lack of p21Waf1 interferes with an inhibitory effect of NaBut to inhibit DNA repair and thereby to stop concomitant accumulation of harmful mutations. We conclude that p21Waf1 is directly involved in control of genome integrity and DNA repair acting through modulation of the components of the DNA repair machinery.