H3-specific nucleohistone kinase of bovine thymus chromatin. Purification, characterization, and specificity for threonine residue 3

Association of histone modification with the development of schizophrenia

Schizophrenia, influenced by genetic and environmental factors, may involve epigenetic alterations, notably histone modifications, in its pathogenesis. This review summarizes various histone modifications including acetylation, methylation, phosphorylation, ubiquitination, serotonylation, lactylation, palmitoylation, and dopaminylation, and their implications in schizophrenia. Current research predominantly focuses on histone acetylation and methylation, though other modifications also play significant roles. These modifications are crucial in regulating transcription through chromatin remodeling, which is vital for understanding schizophrenia's development. For instance, histone acetylation enhances transcriptional efficiency by loosening chromatin, while increased histone methyltransferase activity on H3K9 and altered histone phosphorylation, which reduces DNA affinity and destabilizes chromatin structure, are significant markers of schizophrenia.

β-N-Acetylglucosamine (O-GlcNAc) is a novel regulator of mitosis-specific phosphorylations on histone H3

O-Linked β-N-acetylglucosamine, or O-GlcNAc, is a dynamic post-translational modification that cycles on and off serine and threonine residues of nucleocytoplasmic proteins. The O-GlcNAc modification shares a complex relationship with phosphorylation, as both modifications are capable of mutually inhibiting the occupation of each other on the same or nearby amino acid residue. In addition to diabetes, cancer, and neurodegenerative diseases, O-GlcNAc appears to play a significant role in cell growth and cell cycle progression, although the precise mechanisms are still not well understood. A recent study also found that all four core nucleosomal histones (H2A, H2B, H3, and H4) are modified with O-GlcNAc, although no specific sites on H3 were reported. Here, we describe that histone H3, a protein highly phosphorylated during mitosis, is modified with O-GlcNAc. Several biochemical assays were used to validate that H3 is modified with O-GlcNAc. Mass spectrometry analysis identified threonine 32 as a novel O-GlcNAc site. O-GlcNAc was detected at higher levels on H3 during interphase than mitosis, which inversely correlated with phosphorylation. Furthermore, increased O-GlcNAcylation was observed to reduce mitosis-specific phosphorylation at serine 10, serine 28, and threonine 32. Finally, inhibiting OGA, the enzyme responsible for removing O-GlcNAc, hindered the transition from G2 to M phase of the cell cycle, displaying a phenotype similar to preventing mitosis-specific phosphorylation on H3. Taken together, these data indicate that O-GlcNAcylation regulates mitosis-specific phosphorylations on H3, providing a mechanistic switch that orchestrates the G2-M transition of the cell cycle.

H3 phosphorylation: dual role in mitosis and interphase

Chromatin condensation and subsequent decondensation are processes required for proper execution of various cellular events. During mitosis, chromatin compaction is at its highest, whereas relaxation of chromatin is necessary for DNA replication, repair, recombination, and gene transcription. Since histone proteins are directly complexed with DNA in the form of a nucleosome, great emphasis is put on deciphering histone post-translational modifications that control the chromatin condensation state. Histone H3 phosphorylation is a mark present in mitosis, where chromatin condensation is necessary, and in transcriptional activation of genes, when chromatin needs to be decondensed. There are four characterized phospho residues within the H3 N-terminal tail during mitosis: Thr3, Ser10, Thr11, and Ser28. Interestingly, H3 phosphorylated at Ser10, Thr11, and Ser28 has been observed on genomic regions of transcriptionally active genes. Therefore, H3 phosphorylation is involved in processes requiring opposing chromatin states. The level of H3 phosphorylation is mediated by opposing actions of specific kinases and phosphatases during mitosis and gene transcription. The cellular contexts under which specific residues on H3 are phosphorylated in mitosis and interphase are known to some extent. However, the functional consequences of H3 phosphorylation are still unclear.

cAMP signaling regulates histone H3 phosphorylation and mitotic entry through a disruption of G2 progression

cAMP signaling is known to have significant effects on cell growth, either inhibitory or stimulatory depending on the cell type. Study of cAMP-induced growth inhibition in mammalian somatic cells has focused mainly on the combined role of protein kinase A (PKA) and mitogen-activated protein (MAP) kinases in regulation of progression through the G1 phase of the cell cycle. Here we show that cAMP signaling regulates histone H3 phosphorylation in a cell cycle-dependent fashion, increasing it in quiescent cells but dramatically reducing it in cycling cells. The latter is due to a rapid and dramatic loss of mitotic histone H3 phosphorylation caused by a disruption in G2 progression, as evidenced by the inhibition of mitotic entry and decreased activity of the CyclinB/Cdk1 kinase. The inhibition of G2 progression induced through cAMP signaling is dependent on expression of the catalytic subunit of PKA and is highly sensitive to intracellular cAMP concentration. The mechanism by which G2 progression is inhibited is independent of both DNA damage and MAP kinase signaling. Our results suggest that cAMP signaling activates a G2 checkpoint by a unique mechanism and provide new insight into normal cellular regulation of G2 progression.

cAMP signaling induces rapid loss of histone H3 phosphorylation in mammary adenocarcinoma-derived cell lines

The phosphorylation of histone H3 is known to play a role in regulation of transcription as well as preparation of chromosomes for mitosis. Various signaling cascades induce H3 phosphorylation, particularly at genes activated by these pathways. In this study, we show that signaling can also have the opposite effect. Activators of cAMP signaling induce a rapid and potent loss of H3 phosphorylation. This effect is not mediated through a cAMP metabolite since a membrane-permeable form of AMP had no effect on H3 phosphorylation and a phosphodiesterase-resistant cAMP analog efficiently reduced it. cAMP is also the likely regulator of H3 phosphorylation under physiological conditions since only supra-pharmacological doses of cGMP induce the loss of H3 phosphorylation. The loss of phosphorylation is specific for histone H3 since we do not observe drastic losses in total phosphorylation of other histones. In addition, other H3 modifications are unaffected with the exception of lysine 9 methylation, which is elevated. Analysis of cell growth and cell cycle shows that cAMP signaling inhibits cell growth and arrests cells at both G1 and G2/M. Similar effects of cAMP signaling on H3 phosphorylation are observed in a variety of mammary adenocarcinoma-derived cell lines. In syngeneic human breast-derived cell lines, one diploid and non-transformed, the other derived from a ductal carcinoma, the loss of H3 phosphorylation is significantly more sensitive to cAMP concentration in the transformed cell line.

Inducible covalent posttranslational modification of histone H3

The physiological state of a eukaryotic cell is determined by endogenous and exogenous signals, and often the endpoint of the pathways that transmit these signals is DNA. DNA is organized into chromatin, a nucleoprotein complex, which not only facilitates the packaging of DNA within the nucleus but also serves as an important factor in the regulation of gene function. The nucleosome is the basic unit of chromatin and generally consists of approximately two turns of DNA wrapped around an octamer of core histone proteins. Each histone also contains an accessible N-terminal tail that extends outside the chromatin complex and is subject to posttranslational modifications that are crucial in the regulation of gene expression. Two distinct categories of histone posttranslational modification have been observed: (i) inducible or stimulation-dependent and (ii) mitosis-dependent. Stimulation by mitogens or stress leads to rapid transient posttranslational modifications of histones, in particular histone H3, which are mechanistically and temporarily distinct from modifications associated with mitosis. This Review focuses mainly on the inducible phosphorylation of histone H3 brought about by different stimuli, such as epidermal growth factor, 12-O-tetradecanoylphorbol-13-acetate, arsenite, or ultraviolet radiation. We examine the most recent, and at times controversial, research data concerning the identity of the histone H3 kinases responsible for this phosphorylation. In addition, the interdependence of phosphorylation and acetylation will be discussed in light of data showing patterns of inducible modification at specific genes.

The kinase haspin is required for mitotic histone H3 Thr 3 phosphorylation and normal metaphase chromosome alignment

Post-translational modifications of conserved N-terminal tail residues in histones regulate many aspects of chromosome activity. Thr 3 of histone H3 is highly conserved, but the significance of its phosphorylation is unclear, and the identity of the corresponding kinase unknown. Immunostaining with phospho-specific antibodies in mammalian cells reveals mitotic phosphorylation of H3 Thr 3 in prophase and its dephosphorylation during anaphase. Furthermore we find that haspin, a member of a distinctive group of protein kinases present in diverse eukaryotes, phosphorylates H3 at Thr 3 in vitro. Importantly, depletion of haspin by RNA interference reveals that this kinase is required for H3 Thr 3 phosphorylation in mitotic cells. In addition to its chromosomal association, haspin is found at the centrosomes and spindle during mitosis. Haspin RNA interference causes misalignment of metaphase chromosomes, and overexpression delays progression through early mitosis. This work reveals a new kinase involved in composing the histone code and adds haspin to the select group of kinases that integrate regulation of chromosome and spindle function during mitosis and meiosis.

Mitotic phosphorylation of histone H3 at threonine 3

Nuclear envelope-peripheral heterochromatin fractions contain multiple histone kinase activities. In vitro assays and amino-terminal sequencing show that one of these activities co-isolates with heterochromatin protein 1 (HP1) and phosphorylates histone H3 at threonine 3. Antibodies recognizing this post-translational modification reveal that in vivo phosphorylation at threonine 3 commences at early prophase in the vicinity of the nuclear envelope, spreads to pericentromeric chromatin during prometaphase and is fully reversed by late anaphase. This spatio-temporal pattern is distinct from H3 phosphorylation at serine 10, which also occurs during cell division, suggesting segregation of differentially phosphorylated chromatin to different regions of mitotic chromosomes.

Histone kinase activity of buffalo sperm chromatin

Phosphorylation of buffalo sperm chromatin proteins under optimum conditions (8 mM Mg2+, pH 8.0, and at 30 degrees C) using [gamma-32P]ATP and endogenous protein kinase activity was linear for 15 min incubation time and up to 330 micrograms protein. The 32P transferred from [gamma-32P]ATP was located in protein as a phosphoester bond. Fractionation with 1.2 M NaCl-4 M urea-0.2 M 2-mercaptoethanol-1 mM PMSF followed by acid treatment solubilized 87% of the total chromatin proteins termed "sperm histones." The remaining 21% nonhistone protein was tightly bound to DNA. Follow-up of the label showed 91% of the 32P in sperm histone and 9% with DNA-associated proteins. Histone kinase activity was solubilized with 0.35 M NaCl, which extracted 70% of the initial enzyme activity associated with chromatin. Of the different histones tested as substrates, histone kinase phosphorylated only histone H3 and, therefore, is highly specific for arginine rich histone. It also phosphorylates the acidic protein, casein. Cyclic AMP at concentrations up to 50 microM had no effect on the phosphorylation of histone H3. Phosphoamino acid analysis using histone H3 as the substrate showed serine to be the acceptor amino acid for phosphoester link.

Stimulation of a Ca(2+)-calmodulin-activated histone 3 arginine kinase in quiescent rat heart endothelial cells compared to actively dividing cells

A Ca(2+)-calmodulin-activated histone 3 kinase was partially purified from nuclear extracts of dividing and quiescent rat heart endothelial cells. The histone 3 phosphorylating activity was 20-100-fold higher in quiescent than in dividing cells. Base hydrolysis followed by amino acid analysis revealed that histone 3 was phosphorylated on arginine. Further investigations were conducted to determine whether phosphorylation of histone 3 also occurred in vivo. Cells were incubated for 3 h in a phosphate-free medium supplemented with [32P]phosphoric acid. It was observed that the nuclear content of arginine-phosphorylated histone 3 was considerably higher in quiescent than in dividing rat heart endothelial cells. The histone 3 arginine kinase is a component of a complex containing a Ca(2+)-dependent calmodulin-binding protein of apparent molecular mass of 85 kDa. Using polyclonal antibodies to an 85-kDa protein, also the major Ca(2+)-dependent calmodulin-binding component of the histone 3 arginine kinase from calf thymus, an immunoreactive protein of identical apparent molecular mass was found to be present in equal amounts both in dividing and quiescent cells. We propose that the 85-kDa protein is either the histone 3 arginine kinase or one of its subunits and that phosphorylation of histone 3 is involved with cell cycle exit in eukaryotes.

Mitosis-specific histone H3 phosphorylation in vitro in nucleosome structures

A mechanism of mitosis-specific enhancement of histone H3 phosphorylation was analyzed in vitro in terms of nucleosome structure. The incorporation of [32P]phosphate into DNA-bound H3 was approximately 5-7 times higher than in DNA-free H3 using the catalytic subunit of cAMP-dependent protein kinase. The two major N-terminal serine sites, including the mitosis-specific site (Ser10) and Ser28, were extensively phosphorylated in the DNA-bound forms. These phosphorylation patterns were identical to those of nucleosomal H3. In contrast, the H3 in DNA-free octamers was very slightly phosphorylated. The major site of H3 phosphorylation in DNA-free H3 was Thr118 in the C-terminus. Results indicate that DNA-binding is essential for the high level of mitosis-specific H3 phosphorylation, and that the nucleosome structure promotes H3 N-terminal phosphorylation in vitro. It also suggests the possibility that H1 prevents H3 phosphorylation during interphase of the cell cycle.

Histones and their modifications

Histones constitute the protein core around which DNA is coiled to form the basic structural unit of the chromosome known as the nucleosome. Because of the large amount of new histone needed during chromosome replication, the synthesis of histone and DNA is regulated in a complex manner. During RNA transcription and DNA replication, the basic nucleosomal structure as well as interactions between nucleosomes must be greatly altered to allow access to the appropriate enzymes and factors. The presence of extensive and varied post-translational modifications to the otherwise highly conserved histone primary sequences provides obvious opportunities for such structural alterations, but despite concentrated and sustained effort, causal connections between histone modifications and nucleosomal functions are not yet elucidated.

The induction of chromosome condensation in tsBN2, a temperature-sensitive mutant of BHK21, inhibited by the calmodulin antagonist, W-7

The induction of premature chromosome condensation (PCC) in tsBN2 cells, a temperature-sensitive (ts) mutant of BHK21/13 which shows PCC at the non-permissive temperature, was almost completely inhibited by 40 microM W-7, an antagonist of calmodulin. The mitotic phosphorylation of histone H1 and H3 was also inhibited by W-7. W-5, a chlorine-deficient analogue of W-7 and which interacts weakly with calmodulin, did not inhibit the induction of PCC, even at a dose of 80 microM. The content of calmodulin in tsBN2 cells was increased by a temperature shift to 40.5 degrees C. All these results suggested that calmodulin is required for the chromosome condensation.

A new cAMP independent protein kinase tightly bound to DNA, in rat liver nuclei

A protein kinase has been characterized among the proteins tightly bound to DNA. It is not extracted with 1 M NaCl and is released by extensive DNase I digestion. This enzyme is able to phosphorylate nucleosomal histones, essentially H2B and H3, and several non-histone proteins associated with DNA, on serine residue(s). It does not phosphorylate protamine, casein, phosvitin and the chromosomal non-histone proteins extracted with 1 M NaCl and is cAMP independent. This protein kinase can be distinguished from the previously described enzymes.

Effects of thyrotropin on thyroid chromatin. Enhanced sensitivity to micrococcal nuclease and increased nuclear protein phosphorylation

Thyroid slices were incubated with or without TSH for 2 or 5 h. Nuclei were then prepared, subjected to mild digestion with micrococcal nuclease, and centrifuged at 1200 X g. The amount of DNA in 1200 X g supernatants was increased by TSH at 5 h, but not at 2 h. In parallel studies, thyroid slices were incubated with 32Pi and labeling of acid-soluble nuclear proteins was examined. TSH-dependent increases in labeling of histones H1 and H3, and of the high mobility group protein HMG 14, were observed at 2 h; however, there were no apparent changes in TSH-dependent labeling between 2 and 5 h, in nuclease-sensitive or in bulk chromatin. These results suggest that the observed TSH-dependent changes in the micrococcal nuclease-sensitivity of thyroid nuclear chromatin were not induced directly by changes in the phosphorylation of the histones or HMG 14.