Abstract
At least six histone H1 variants exist in somatic mammalian cells that bind to the linker DNA and stabilize the nucleosome particle contributing to higher order chromatin compaction. In addition, H1 seems to be actively involved in the regulation of gene expression. However, it is not well known whether the different variants have distinct roles or if they regulate specific promoters. We have explored this by inducible shRNA-mediated knock-down of each of the H1 variants in a human breast cancer cell line. Rapid inhibition of each H1 variant was not compensated for by changes of expression of other variants. Microarray experiments have shown a different subset of genes to be altered in each H1 knock-down. Interestingly, H1.2 depletion caused specific effects such as a cell cycle G1-phase arrest, the repressed expression of a number of cell cycle genes, and decreased global nucleosome spacing. On its side, H1.4 depletion caused cell death in T47D cells, providing the first evidence of the essential role of an H1 variant for survival in a human cell type. Thus, specific phenotypes are observed in breast cancer cells depleted of individual histone H1 variants, supporting the theory that distinct roles exist for the linker histone variants.
Highlights
Eukaryotic DNA is packaged into chromatin through its association with histone proteins
The linker histone H1 sits at the base of the nucleosome near the DNA entry and exit sites and is involved in the folding and stabilization of the 30 nm chromatin fiber [1,2]
Histone H1 participates in nucleosome spacing and formation of the higher-order chromatin structure
Summary
Eukaryotic DNA is packaged into chromatin through its association with histone proteins. The linker histone H1 sits at the base of the nucleosome near the DNA entry and exit sites and is involved in the folding and stabilization of the 30 nm chromatin fiber [1,2]. Histone H1 is a lysine-rich protein with a short basic N-terminal tail, a highly conserved central globular domain and a long positively-charged Cterminal tail. These tails are post-translationally modified, mostly by phosphorylation, and by acetylation and methylation [4,5]. CDK-dependent phosphorylation of H1 occurs progressively throughout the cell cycle, with a maximum during mitosis [6]
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