Attenuated DNA Damage Repair by Trichostatin A through BRCA1 Suppression

Abstract

Recent studies have demonstrated that some histone deacetylase (HDAC) inhibitors enhance cellular radiation sensitivity. However, the underlying mechanism for such a radiosensitizing effect remains unexplored. Here we show evidence that treatment with the HDAC inhibitor trichostatin A (TSA) impairs radiation-induced repair of DNA damage. The effect of TSA on the kinetics of DNA damage repair was measured by performing the comet assay and gamma-H2AX focus analysis in radioresistant human squamous carcinoma cells (SQ-20B). TSA exposure increased the amount of radiation-induced DNA damage and slowed the repair kinetics. Gene expression profiling also revealed that a majority of the genes that control cell cycle, DNA replication and damage repair processes were down-regulated after TSA exposure, including BRCA1. The involvement of BRCA1 was further demonstrated by expressing ectopic wild-type BRCA1 in a BRCA1 null cell line (HCC-1937). TSA treatment enhanced radiation sensitivity of HCC-1937/wtBRCA1 clonal cells, which restored cellular radiosensitivity (D(0) = 1.63 Gy), to the control level (D(0) = 1.03 Gy). However, TSA had no effect on the level of radiosensitivity of BRCA1 null cells. Our data demonstrate for the first time that TSA treatment modulates the radiation-induced DNA damage repair process, in part by suppressing BRCA1 gene expression, suggesting that BRCA1 is one of molecular targets of TSA.

Novel HSP90 inhibitors, NVP-AUY922 and NVP-BEP800, radiosensitise tumour cells through cell-cycle impairment, increased DNA damage and repair protraction

“…The authors suggest that 17DMAG inhibits the repair of DNA DSBs induced by radiation (Dote et al, 2006), Similarly, an inhibition of homologous DNA recombination repair, that is, degradation of BRCA2 and alteration of Rad51 by 17-AAG, causes the radiosensitisation of prostate carcinoma DU145 and lung squamous carcinoma SQ-5 cell lines (Noguchi et al, 2006). Similar effects on histone gH2AX, for example, prolonged persistence of DNA damage measured by this sensitive marker, have been shown in several studies using HDAC inhibitors that indirectly block Hsp90 by acetylation (Zhang et al, 2007;Zuco et al, 2010). As suggested by a reviewer, we analysed the expression of several DNA repair proteins, including Ku70, Ku80, Rad50, Rad51, DNA-PKcs and BRCA2.…”

Selective inhibition of histone deacetylase 6 (HDAC6) induces DNA damage and sensitizes transformed cells to anticancer agents

“…Enhanced DNA damage observed in culture with combined inhibitors has been attributed to induction of histone hyperacetylation by the HDAC inhibitor, resulting in a more open chromatin structure, making DNA more susceptible to damage by various toxic agents (35). Pan-HDAC inhibitors such as SAHA can suppress DNA repair proteins in transformed cells, resulting in failure to repair DNA damage (36)(37)(38). HDAC6 inhibition does not cause accumulation of acetylated histones.…”

Histone deacetylase inhibitors and genomic instability

“…This study showed that Ku70 acetylation does not affect the formation of a complex with its natural partner, Ku80; but, when the authors mimicked acetylation by replacing key lysines with glutamines, the ability of Ku70 to bind DNA extremities was suppressed [65]. involved in both DSB sensing and repair) [66]. In this study, TSA did not sensitize BRCA1-null cells to irradiation, whereas a cell line complemented with a BRCA1 wild-type allele showed a TSA-dependent enhanced susceptibility to IR, suggesting that down-regulation of BRCA1 is a key event in HDACI-induced radiosensitization [66].…”

“…involved in both DSB sensing and repair) [66]. In this study, TSA did not sensitize BRCA1-null cells to irradiation, whereas a cell line complemented with a BRCA1 wild-type allele showed a TSA-dependent enhanced susceptibility to IR, suggesting that down-regulation of BRCA1 is a key event in HDACI-induced radiosensitization [66]. However, the picture is likely to be much more complex since this study did not detect a change in gene expression for the key strand transfer protein RAD51, whereas another group found that it was downregulated to one third of its normal levels following treatment with PCI-24781, another broadspectrum HDACI [67].…”