Histones ADP ribosylation

Histone ADP-ribosylation was first reported in 1968 [290]. Poly(ADP-ribosylation) has been implicated in several nuclear processes, including DNA replication, repair and recombination [291-294]. Histone HI and the four core histones are modified by adenosine diphospho (ADP) ribosylation which involves the transfer of the ADP-ribose moiety of NAD to the histone acceptor (Figs. 1 and 2). HI is the principle poly(ADP-ribosylated) histone, while core histones are ADP-ribosylated to a minor extent [295-297]. HI is modified at Glu residues 2, 14 (or 15), and 116 (or 117) and at Lys located at the C-terminus [25,298,299]. Poly(ADP-ribosylated) HI is associated with dynamically acetylated core histones [295]. There is conflicting results as to whether poly(ADP-ribosylation) of HI promotes chromatin decondensation [300-304]. 

The enzyme catalyzing the addition of ADP-ribose units onto the histones and itself is poly(ADP-ribose) polymerase or synthetase. Poly(ADP-ribose) polymerase is a nuclear, DNA-dependent enzyme that is stimulated by DNA breaks [302]. This property of the enzyme would target its action to sites that have DNA strand breaks (regions of the genome involved in replication, repair, recombination). The enzyme is associated with chromatin areas and perichromatin regions in interphase Chinese hamster ovary cells [312]. Degradation of the ADP-ribose polymer is catalyzed by the nuclear enzyme poly(ADP-ribose) glycohydrolase and ADP-ribosyl protein lyase. 

Realini and Althaus [313] have put forth the hypothesis that poly(ADP-ribosylation) may have a function in histone shuttling. They propose that poly(ADP-ribose) polymerase directed to sites of DNA strand breaks would auto-modify itself generating multiple ADP-ribose polymers. The polymers would lead to the dissociation of the histones from DNA onto the polymers. The DNA would now be free for processing (e.g., by enzymes involved in excision repair). The action of poly(ADP-ribose) glycohydrolase would degrade the 

ADP-ribose polymers, leading to the release of the histones which would rebind the DNA. 

Relationships between histone methylation and DNA methylation and histone acetyation and DNA methylation have been reported [191,314,315], A similar relationship may exist between poly(ADP ribosylated) HI and DNA methylation. Inhibition of poly(ADP-ribose) polymerase with 3-aminobenzamide increases the susceptibility of L929 mouse fibroblast nuclei to be methylated by endogenous DNA methyltransferases [316,317], Further, there is evidence that poly(ADP ribosylation) protects CpG islands located at the 5 end of housekeeping genes from methylation [318], Future studies will likely reveal an interesting dynamic relationship between histone methylation, histone acetylation, and histone poly(ADP-ribosylation). 

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In attempts to reconstitute nucleosomes on SV40 circular DNA, Cap-lan et al. (37) observed that if the histones were ADP-rihosylated prior to reconstitution assembly of nucleosomes was inhibited by as much as 80%. If nucleosomes were first allowed to assemble, then modified by ADP-ribosylation, no eflPect on stability was observed. These data led the authors to speculate that ADP-ribosylation of histones prior to nucleosome assembly might be of physiological importance. Perella and Lea (168, 169) have shown that in rat liver nuclei, polyamines cause an increase in histone Hi ADP-ribosylation and histone HI dimer synthesis, which is accompanied by a decrease in core histone ADP-ribosylation. Data such as these have led to speculation that Hi dimer formation may function in the condensation or stabilization of chromatin fibers (35, 119). The data of Lorimer et al. (124) indicate that dimer synthesis is inversely related to the nuclear activity of the poly(ADP-ribose) glycohydrolase. Thus, these authors (124) inferred that the Hl-Hl-polymer complex formation is of a transient nature. As pointed out by Purnell et al. (171), if this crosslink were to function in the stabilization of chromatin, the modified histone Hi would have... 

ADP-ribosylated proteins of plasmacytoma mRNP were examined by lithium dodecyl sulfate polyacrylamide slab gels and autoradiography. At least 5 main labeled bands of 116 kDa, 45 kDa, 38 kDa and 30 kDa were observed. The labeling increases with the increase of NAD concentration in the incubation medium parallel to a decrease of electrophoretic mobility of some bands. This may be attributed to a more potent ADP-ribosylation of these proteins as it has been observed with histones ADP-ribosylated by a... 

Covalent links of histones HI, H2A, H2B, and H3 with poly(ADP-ribose) have been reported (for references, see Hayaishi and Ueda, 1977). Furthermore, a histone HI dimer linked by poly(ADP-ribose) has been reported. The increase in ADP-ribosylation is concomitant with cellular replication and ADP-ribosylation has been proposed as a trigger for in vivo replication in eukaryotic cells. 

Adamietz P, Rudolph A (1984) ADP-ribosylation of nuclear proteins in vivo. Identification of histone H2B as a major acceptor for mono- and poly(ADP-ribose) in dimethyl sulfate-treated hepatoma AH 7974 cells. J Biol Chem 259 6841-6846... 

Krupitza G, Cerutti P (1989) Poly(ADP-ribosylation) of histones in intact human keratinocytes. Biochemistry 28 4054 060... 

Kun E, Kirsten E, Ordahl CP (2002) Coenzymatic activity of randomly broken or intact double-stranded DNAs in auto and histone HI trans-poly(ADP-ribosylation), catalyzed by poly(ADP-ribose) polymerase (PARP I). J Biol Chem 277 39066-39069 Kun E, Kirsten E, Mendeleyev J, Ordahl CP (2004) Regulation of the enzymatic catalysis of poly(ADP-ribose) polymerase by dsDNA, polyamines, Mg2-F, Ca2-F, histones HI and H3, and ATP. Biochemistry 43 210-216... 

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. 

Fig. 1. Core histone modifications. Human histone N-terminal and in some cases C-terminal amino acid sequences are shown. The modifications include methylation (M), acetylation (Ac), phosphorylation (P), ubiquitination (U), and ADP ribosylation (step ladder). The sites of trypsin digestion of histones in nucleosomes are indicated (T).

Fig. 2. Histone HI modifications. Sites of phosphorylation (P) and ADP ribosylation (step ladder) on mouse Hl -3 are shown.

As described above, histones are much more than passive structural players within chromatin. Dynamic post-translational modifications of these proteins confer specialized chemical proprieties to chromatin of both informational and structural nature with important functional implications. The highly conserved sites for acetylation, methylation, phosphorylation, ADP-ribosylation, and ubiquitination events on histone tails appear to orchestrate functional activities that range from transcriptional activation and repression to DNA repair and recombination. 

Fig. 6. Post-translational modifications of core and linker histones. The sites of acetylation, phosphorylation, poly-ADP ribosylation, methylation, and ubiquitination are incficated by numbers that correspond to the amino acid position from the N-termini of the molecules. The nomenclature of histone HI variants is as in Fig. 3. The length of C- and N-terminal tails is in relative scale between core histones to illustrate primary structural differences between these proteins.

From a different perspective, circumstantial evidence suggests that ADPr may have a functional role in the activation of transcription. PARP copurifies with TFnC [230] and upregulates AP-2 (Activator Protein 2) controlled transcription. However, these results need to be interpreted cautiously, as a molecular mechanism for ADP-ribosylation of targeted histones has yet to be identified. 

ADP-ribosylation has also been implicated as a proteolytic antagonist during embryonic development [231]. Following fertilization in sea urchin, sperm-specific histones are degraded by the sperm-histone-selective (SpH) protease and subsequently replaced by cleavage stage histone variants. During this process, the maternal replacement histones are protected from proteolysis by ADP-ribosylation. 

Yet another hypothesis considers the somatic variant Hle of histone HI, in its poly(ADP-ribosyl)ated isoform, as a nuclear traw -acting factor involved in maintaining the methylation pattern on DNA [161]. 

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