Concentration-dependent effects of sodium butyrate in Chinese hamster cells: cell-cycle progression, inner-histone acetylation, histone H1 dephosphorylation, and induction of an H1-like protein

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Abstract
A unified quantitative study of the effects of butyrate concentration upon cell-cycle progression, modification of all inner histones, dephosphorylation of histone H1 and enhancement of an H1-like protein (BEP) in Chinese hamster ovary CHO cells is presented. Flow cytometric analysis shows that exposure to butyrate enriches CHO cultures in G1 cells and, at sufficient butyrate concentration, leads to G1 arrest. Additionally, butyrate alters the rate of cell-cycle progression through G2/M and through S. Two-dimensional polyacrylamide electrophoresis and radiolabeling in butyrate-treated cultures indicate the presence of at least 1 site of internal acetylation in histone H2A, 4 sites of internal acetylation in histone H2B, 5 sites of internal acetylation in histone H3 and 4 sites of internal acetylation in histone H4. Histone H2A is also appreciably phosphorylated, so that it is acetylated and phosphorylated at a total of up to 3 sites. The distribution of modified species for all the inner (core) histones was quantified from 2-dimensional gels by using 3 different methods of analysis: direct densitometry of excised portions of the gel, scintillation spectrometry of 3H-labeled histones and microdensitometry of photographic negatives. At 15 mM butyrate, 26% of H2B is acetylated at 3-4 sites, 37% of H3 is acetylated at 3-5 sites and 50% of H4 is acetylated at 3-4 sites. Histone H1 is dephosphorylated as a function of butyrate concentration, and the dephosphorylation can be correlated with an increased proportion of G1 cells in culture. There is also a significant increase in the cellular content of 2 other proteins when cells are exposed to butyrate. The increase in 1 of these, BEP, was quantified as a function of butyrate concentration after 24 h of exposure to butyrate. BEP appears to be related to histone H10 and to an induced protein IP25. The other protein (UP), which has a MW of .apprx. 15,000, was not identified. Butyrate induces a 2-fold increase in the cellular content of UP and a change in the distribution of UP molecular species.