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Changes in chromatin structure in NIH 3T3 cells induced by valproic acid and trichostatin


Valproic acid (VPA) and trichostatin A (TSA) are known histone deacetylase inhibitors (HDACIs) with epigenetic activity that affect chromatinsupra-organization, nuclear architecture, and cellular proliferation, particularly in tumor cells. In this study, chromatin remodeling witheffects extending to heterochromatic areas was investigated by image analysis in non-transformed NIH 3T3 cells treated for different periodswith different doses of VPA and TSA under conditions that indicated no loss of cell viability. Image analysis revealed chromatindecondensation that affected not only euchromatin but also heterochromatin, concomitant with a decreased activity of histone deacetylasesand a general increase in histone H3 acetylation. Heterochromatin protein 1-a (HP1-a), identified immunocytochemically, was depleted fromthe pericentromeric heterochromatin following exposure to both HDACIs. Drastic changes affecting cell proliferation and micronucleation but not alteration in CCND2 expression and in ratios of Bcl-2/Bax expression and cell death occurred following a 48-h exposure of the NIH 3T3cells particularly in response to higher doses of VPA. Our results demonstrated that even low doses of VPA (0.05 mM) and TSA (10 ng/mL)treatments for 1 h can affect chromatin structure, including that of the heterochromatin areas, in non-transformed cells. HP1-a depletion,probably related to histone demethylation at H3K9me3, in addition to the effect of VPA and TSA on histone H3 acetylation, is induced on NIH3T3 cells. Despite these facts, alterations in cell proliferation and micronucleation, possibly depending on mitotic spindle defects, require alonger exposure to higher doses of VPA and TSA. J. Cell. Biochem. 115: 1937-1947, 2014. (AU)

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