Treatment of senescent cells with trichostatin A (TSA) increases H4-K16Ac and decreases DNA compaction in a rapid and reversible manner. A) Deconvoluted mass spectra of intact core histones in senescent cells treated with dimethyl sulfoxide (DMSO) or TSA for 24 hours. For each acetylation state of H4, unmodified, mono- and di-methylated K20 forms are visible. B) Relative abundance of H4 acetylation states measured at the protein level on deconvoluted mass spectra (Figure 9A). Error bars show SD of two biological replicates. C) Immunoblotting analyses of H4-K12Ac, H4-K16Ac and H3 (loading control). D) DNA 4',6'-diamidino-2-phenylindole (DAPI) staining of representative nuclei and corresponding DAPI coefficient of variation (CV) values. E) Boxplots of DAPI CV (n > 110, from one experiment). *DNA compaction statistically different from solvent DMSO control (P < 10-5, Welch t-test). F) DNA DAPI staining of representative nuclei from senescent cells that had been treated with TSA for 24 hours and then washed to remove TSA and further incubated with fresh medium for 1 or 6 hours. DMSO: WI-38hTERT/GFP-RAF-ER + 20 nM 4-HT (3 days) + 0.1% dimethyl sulfoxide (DMSO) 24 hours; TSA: WI-38hTERT/GFP-RAF-ER + 20 nM 4-HT (3 days) + 410 nM TSA 24 hours.