INFLUENCE OF HDAC INHIBITOR SODIUM BUTYRATE ON THE EXPRESSION OF DNA REPAIR GENES Rad51 AND XRCC5 IN mEras-Waf1+/+ AND mEras-Waf1–/–.

Mouse embryonal fibroblasts with knockout of CDKN1A gene encoding p21/Waf1 protein transformed by oncogenes E1A and cHa-ras (mEras-Waf1–/– cell line) have been used to assess the level of DNA repair genes expression — Rad51 and XRCC5 after treatment with HDAC inhibitor sodium butyrate as compared with their control counterparts (mEras-Waf1+/+ cells). mEras-Waf1–/– cells are characterized by the elevated amount of single-stranded DNA breaks and g-H2A.X histone foci associated with these breaks. According to immunofluorescence and immunobloting data, Rad51 and Ku80 proteins are highly expressed in the nuclei of both studied cell lines. The level of Ku80 is higher in cells with CDKN1A gene knockout. When cells were treated with DNA-damaging agent adriamycin, there was an additional accumulation of Rad51 foci in the nuclei. However, sodium butyrate reduced considerably the content of Rad51 and Ku80 proteins both in mEras-Waf1+/+ and mEras-Waf1–/– cells as well as in the cells treated by adriamycin. RT-PCR and immunobloting data show that inhibitory effect of sodium butyrate takes place at the level of Rad51 and XRCC5 gene transcription and the content of Rad51 and Ku80 proteins. The observed suppressive effect of HDACI on DNA repair components explains in part the mechanisms of antiproliferative function of HDAC inhibitors. Surprisingly, sodium butyrate was shown to activate the pluripotent genes transcription in mEras-Waf1+/+ and mEras-Waf1–/– cells, as exemplified by upregulation of Oct-4, Sox-2, Klf4, implying that these pluripotent genes are under negative control at the level of chromatin structure.