Histone H3 phosphorylation and acetylation

Ser-10 phosphorylation of H3 precedes acetylation at Lys-14 and at Lys-9 [87-89] (Fig. 7). In studies with EGF-stimulated mouse fibroblasts, preventing the 

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Chetmg P, Tanner KG, Cheung WL, Sassone-Corsi P, Denu JM, Allis CD (2000) Synergistic coupling of histone H3 phosphorylation and acetylation in response to epidermal growth factor stimulation. Mol Cell 5(6) 905-915... 

Salvador, L.M., Park, Y., Cottom, J., Maizels, E.T., Jones, J.C., Schillace, R.V., Carr, D.W., Cheung, P., Allis, C.D., Jameson, J.L., Hunzicker-Dunn, M. 2001. Follicle-stimulating hormone stimulates protein kinase A-mediated histone H3 phosphorylation and acetylation leading to select gene activation in ovarian granulosa cells. J. Biol. Chem. 276, 40146-40155. 

Figure 4. Histone modification cross-talk between phosphorylation of histone H3 (SIO) and acetylation of histone H3 (K14) or methylation of histone H3 (K9). Histone H3 phoshorylation at SIO can enhance acetylation of histone H3 at K14 (Cheung et at, 2000), (Lo et at, 2000). (b) Histone H3 phoshorylation at SIO abolish acetylation of histone H3 at K9 (Edmondson et at, 2002). (c) Histone H3 phoshorylation at SIO inhibits methylation of histone H3 at K9 (Rea et at, 2000). (d) methylation of histone H3 at K9 interferes with phosphorylation of histone H3 at SIO. Phosphorylation is represented by the blue flag, acetylation is represented by the black flag, and methylation represented by the green flag...

The core unit of the chromatin, the nucleosome, consists of histones arranged as an octamer consisting of a (H3/ H4)2-tetramer complexed with two histone H2A/H2B dimers. Accessibility to DNA-binding proteins (for replication, repair, or transcription) is achieved by posttranslational modifications of the amino-termini of the histones, the histone tails phosphorylation, acetylation, methylation, ubiquitination, and sumoyla-tion. Especially acetylation of histone tails has been linked to transcriptional activation, leading to weakened interaction of the core complexes with DNA and subsequently to decondensation of chromatin. In contrast, deacetylation leads to transcriptional repression. As mentioned above, transcriptional coactivators either possess HAT activity or recruit HATs. HDACs in turn act as corepressors. 

We have discussed phosphorylation of histone H3, which has been studied in many organisms. Phosphorylation of histone H3 (SIO) has two opposite main functions. One is necessary to initiate chromosome condensation during mitosis and meiosis, while the other is transcriptional activation. Current evidence shows that a combination of phosphorylation of H3 (SIO) and methylation of H3 (K9) or acetylation H3 (K9, K14) play important roles in these phenomena including cell cycle related chromosome dynamics and transcriptional activation. These results suggest that a combination of different histone modifications excute different biological outcomes. 

Lo WS, Trievel RC, Rojas JR, Duggan L, Hsu JY, Allis CD, Marmorstein R, Berger SL (2000) Phosphorylation of serine 10 in histone H3 is functionally linked in vitro and in vivo to Gcn5-mediated acetylation at lysine 14. Mol Cell 5(6) 917—926... 

The phenylselenocysteine has also been used successfully to chemically append analogues of methyl- or acetyl-lysine, important histone modifications that can contribute to chromatin structure and accessibility of transcriptional machinery in eukaryotes. By introducing phenylselenocysteine into the Xenopus histone H3, both acetyl-lysine and mono-, di-, and trimethyl-lysine analogues were appended to the purified unnatural amino acid-containing FI 3 protein (Figure 10). " Additionally, the H3 protein with a modification mimicking acetylation of lysine 9 can be deactylated by a histone deacetylation complex and is also a substrate for phosphorylation by Aurora B kinase. Such purified and chemically labeled histones are likely functional in nucleosomes, and preparation of specifically modified histones for comprehensive analysis of chromatin structure and accessibility is particularly suited to this chemical labeling technique. 

The four core histones, H2A, H2B, H3, H4 and their variants, and the linker histone HI subtypes are susceptible to a wide range of post-synthetic modifications, including acetylation, phosphorylation, methylation, ubiquitination, and ADP-ribosylation (Figs. 1 and 2). In this chapter, the four latter modifications and their functions in chromatin structure and function are presented. 

Cell cycle studies of histone phosphorylation using synchronized Chinese hamster ovary cells and HeLa S-3 cells demonstrated that HI and H3 are phosphorylated at different times during the cell cycle, while H2A and H4 are phosphorylated at uniform rates throughout the cell cycle [4—6]. Kinetic studies of the phosphorylation of H2A and H4 in trout testis indicate that these histones are phosphorylated shortly after synthesis [7]. Phosphorylation of H4 did not occur appreciably until after a series of acetylation and deacetylation events, while H2A was phosphorylated shortly after synthesis followed by dephosphorylation. 

Fig. 7. Interplay between different modifications on histones H3 and H4. The modifications include methylation (M), acetylation (Ac), and phosphorylation (P). Positive and negative affects are shown.

Fig. 1. Histone modifications on the nucleosome core particle. The nucleosome core particle showing 6 of the 8 core histone N-terminal tail domains and 2 C-terminal tails. Sites of post-translational modification are indicated by coloured symbols that are defined in the key (lower left) acK = acetyl lysine, meR = methyl arginine, mcK = methyl lysine, PS = phosphoryl serine, and uK = ubiquitinated lysine. Residue numbers are shown for each modification. Note that H3 lysine 9 can be either acetylated or methylated. The C-terminal tail domains of one H2A molecule and one H2B molecule are shown (dashed lines) with sites of ubiquitination at H2A lysine 119 (most common in mammals) and H2B lysine 123 (most common in yeast). Modifications are shown on only one of the two copies of histones H3 and H4 and only one tail is shown for H2A and H2B. Sites marked by green arrows are susceptible to cutting by trypsin in intact nucleosomes. Note that the cartoon is a compendium of data from various organisms, some of which may lack particular modifications e.g., there is no H3meK9 in S. cerevisiae. (From Ref [7].)...

In recent years attention has been focused on the N-terminal "tails" of histones H3 and H4 (Fig. 27-4) in which lysine side chains undergo reversible acetylation and which may also be phosphorylated and... 

Histones are basic proteins that are made up by a globular domain and an N-terminal tail that protrudes from the nucleosome. Nucleosomes form the basic unit of chromatin and are made up by a complex of DNA wrapped around an octamer of histones formed by pairs of the histones H2A, H2B, H3, and H4 (45,46) (Fig. 1). Post-translational modification of the core histone tails by methylation, acetylation, phosphorylation, ubiquitina-tion, or sumoylation can alter the structure of the nucleosomes and thus alter gene expression. These post-translational modifications determine the structure and pattern of chromatin condensation and determine the histone code that drives gene transcriptional regulation (47,48). Below are briefly described the factors determining the histone acetylation and methylation. 

As discussed, histones are an integral part of nucleo-somes, the basic repeating structural unit of chromatin. The amino termini of histone proteins can be modified post-translationally by processes that include acetylation, methylation, phosphorylation, and ubiquination. Acetylation of the lysines on the amino termini of histones H3 and H4 by histone acetyltransferases decreases histone-DNA interaction and improves the accessibility of DNA to transcriptional activation. On the contrary, histone deacetylation by histone deacetylases promotes the formation of compact nucleo-somes, leading to repression of transcription. Histone deacetylation is in fact a key component to the assembly of heterochromatin, the transcriptionally inactive chromatin. Methylation of the ninth amino acid residue, lysine, on histone H3 generates a binding site for heterochromatin protein (HP 1) and thus is another key event in heterochromatin formation. Phosphorylation of the tenth amino acid, serine, on histone H3 is important for chromosome condensation and mitosis. 

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