Anticancer Plant Secondary Metabolites Induce Linker Histone Depletion from Chromatin

Many plant secondary metabolites (PSMs) were shown to intercalate into DNA helix or interact with DNA grooves. This may influence histone-DNA interactions changeing chromatin structure and genome functioning.

Nucleosome stability and linker histone H1.2, H1.4 and H1.5 localizations were studied in HeLa cells after the treatment with 15 PSMs, which are DNA-binders and possess anticancer activity according to published data. Chromatin remodeler CBL0137 was used as a control. Effects of PSMs were studied using fluorescent microscopy, flowcytometry, quantitative reverse transcriptase-polymerase chain reaction (RT-qPCR), western-blotting.

We showed that 1-hour treatment with CBL0137 strongly inhibited DNA synthesis and caused intensive linker histone depletion consistent with nucleosome destabilization. None of PSMs caused nucleosome destabilization, while most of them demonstrated significant influence on linker histone localizations. In particular, cell treatment with 11 PSMs at non-toxic concentrations induced significant translocation of the histone H1.5 to nucleoli and most of PSMs caused depletion of the histones H1.2 and H1.4 from chromatin fraction. Curcumin, resveratrol, berberine, naringenin, and quercetin caused significant redistribution of all three variants of the studied linker histones showing some overlap of PSM effects on linker histone DNA-binding. We demonstrated that PSMs, which induced the most significant redistribution of the histone H1.5 (berberine, curcumin and naringenin), influence the proportion of cells synthesizing DNA, expressing or non-expressing cyclin B and influence cell cycle distribution. Berberine induction of H1.5 translocations to nucleoli was shown to occur independently on the phases of cell cycle (metaphase was not analyzed).

For the first time we revealed PSM influence on linker histone location in cell nuclei that opens a new direction of PSM research as anticancer agents.