MAP kinase-mediated phosphorylation of distinct pools of histone H3 at S10 or S28 via mitogen- and stress-activated kinase 1/2

Growth factor-induced activation of MSK2 leads to phosphorylation of H3K9me2S10 and corresponding changes in gene expression

Extracellular signals are transmitted through kinase cascades to modulate gene expression, but it remains unclear how epigenetic changes regulate this response. Here, we provide evidence that growth factor-stimulated changes in the transcript levels of many responsive genes are accompanied by increases in histone phosphorylation levels, specifically at histone H3 serine-10 when the adjacent lysine-9 is dimethylated (H3K9me2S10). Imaging and proteomic approaches show that epidermal growth factor (EGF) stimulation results in H3K9me2S10 phosphorylation, which occurs in genomic regions enriched for regulatory enhancers of EGF-responsive genes. We also demonstrate that the EGF-induced increase in H3K9me2S10ph is dependent on the nuclear kinase MSK2, and this subset of EGF-induced genes is dependent on MSK2 for transcription. Together, our work indicates that growth factor-induced changes in chromatin state can mediate the activation of downstream genes.

Mitogen- and stress-activated protein kinase (MSK1/2) regulated gene expression in normal and disease states

The mitogen- and stress-activated protein kinases (MSK) are epigenetic modifiers that regulate gene expression in normal and disease cell states. MSK1 and 2 are involved in a chain of signal transduction events bringing signals from the external environment of a cell to specific sites in the genome. MSK1/2 phosphorylate histone H3 at multiple sites, resulting in chromatin remodeling at regulatory elements of target genes and the induction of gene expression. Several transcription factors (RELA of NF-κB and CREB) are also phosphorylated by MSK1/2 and contribute to induction of gene expression. In response to signal transduction pathways, MSK1/2 can stimulate genes involved in cell proliferation, inflammation, innate immunity, neuronal function, and neoplastic transformation. Abrogation of the MSK-involved signaling pathway is among the mechanisms by which pathogenic bacteria subdue the host's innate immunity. Depending on the signal transduction pathways in play and the MSK-targeted genes, MSK may promote or hinder metastasis. Thus, depending on the type of cancer and genes involved, MSK overexpression may be a good or poor prognostic factor. In this review, we focus on mechanisms by which MSK1/2 regulate gene expression, and recent studies on their roles in normal and diseased cells.

Mutation of histone H3 serine 28 to alanine influences H3K27me3-mediated gene silencing in Arabidopsis thaliana

Histone modifications are essential for chromatin activity and play an important role in many biological processes. Trimethylation of histone H3K27 (H3K27me3) is a repressive modification established by Polycomb Repressive Complex 2 (PRC2). Although the presence of the histone H3 serine 28 phosphorylation (H3S28ph) modification at adjacent amino acid residues has both positive and negative effects on Polycomb silencing in mammals, little is known about the effect of H3S28ph on H3K27me3-mediated gene silencing in plants. In this study, we show that mutating H3S28A in Arabidopsis (Arabidopsis thaliana) causes a dominant-negative effect that leads to an early-flowering phenotype by promoting the expression of flowering-promoting genes independently of abnormal cell division. While H3S28ph levels decreased due to the H3S28A mutation, H3K27me3 levels at the same loci did not increase. Moreover, we observed decreased H3K27me3 levels at some known PRC2 target genes in H3.3S28A transgenic lines, rather than the expected enhanced H3K27me3-mediated silencing. In line with the reduced H3K27me3 levels, the expression of the PRC2 catalytic subunits CURLY LEAF and SWINGER decreased. Taken together, these data demonstrate that H3.3S28 is required for PRC2-dependent H3K27me3-mediated silencing in Arabidopsis, suggesting that H3S28 has a noncanonical function in H3K27me3-mediated gene silencing.

Modulation of the p38 MAPK Pathway by Anisomycin Promotes Ferroptosis of Hepatocellular Carcinoma through Phosphorylation of H3S10

Hepatocellular carcinoma (HCC) is a prevalent malignant tumor worldwide. Ferroptosis is emerging as an effective target for tumor treatment as it has been shown to potentiate cell death in some malignancies. However, it remains unclear whether histone phosphorylation events, an epigenetic mechanism that regulates transcriptional expression, are involved in ferroptosis. Our study found that supplementation with anisomycin, an agonist of p38 mitogen-activated protein kinase (MAPK), induced ferroptosis in HCC cells, and the phosphorylation of histone H3 on serine 10 (p-H3S10) was participated in anisomycin-induced ferroptosis. To investigate the anticancer effects of anisomycin-activated p38 MAPK in HCC, we analyzed cell viability, colony formation, cell death, and cell migration in Hep3B and HCCLM3 cells. The results showed that anisomycin could significantly suppress HCC cell colony formation and migration and induce HCC cell death. The hallmarks of ferroptosis, such as abnormal accumulation of iron and elevated levels of lipid peroxidation and malondialdehyde, were detected to confirm the ability of anisomycin to promote ferroptosis. Furthermore, coincubation with SB203580, an inhibitor of activated p38 MAPK, partially rescued anisomycin-induced ferroptosis. And the levels of p-p38 MAPK and p-H3S10 were successively increased by anisomycin treatment. The relationship between p-H3S10 and ferroptosis was revealed by ChIP sequencing. The reverse transcription PCR and immunofluorescence results showed that NCOA4 was upregulated both in mRNA and protein levels after anisomycin treatment. And by C11-BODIPY staining, we found that anisomycin-induced lipid reactive oxygen species was reduced after NCOA4 knockdown. In conclusion, the anisomycin-activated p38 MAPK promoted ferroptosis of HCC cells through H3S10 phosphorylation.

MSK-Mediated Phosphorylation of Histone H3 Ser28 Couples MAPK Signalling with Early Gene Induction and Cardiac Hypertrophy

Heart failure is a leading cause of death that develops subsequent to deleterious hypertrophic cardiac remodelling. MAPK pathways play a key role in coordinating the induction of gene expression during hypertrophy. Induction of the immediate early gene (IEG) response including activator protein 1 (AP-1) complex factors is a necessary and early event in this process. How MAPK and IEG expression are coupled during cardiac hypertrophy is not resolved. Here, in vitro, in rodent models and in human samples, we demonstrate that MAPK-stimulated IEG induction depends on the mitogen and stress-activated protein kinase (MSK) and its phosphorylation of histone H3 at serine 28 (pH3S28). pH3S28 in IEG promoters in turn recruits Brg1, a BAF60 ATP-dependent chromatin remodelling complex component, initiating gene expression. Without MSK activity and IEG induction, the hypertrophic response is suppressed. These studies provide new mechanistic insights into the role of MAPK pathways in signalling to the epigenome and regulation of gene expression during cardiac hypertrophy.

Programmable human histone phosphorylation and gene activation using a CRISPR/Cas9-based chromatin kinase

Histone phosphorylation is a ubiquitous post-translational modification that allows eukaryotic cells to rapidly respond to environmental stimuli. Despite correlative evidence linking histone phosphorylation to changes in gene expression, establishing the causal role of this key epigenomic modification at diverse loci within native chromatin has been hampered by a lack of technologies enabling robust, locus-specific deposition of endogenous histone phosphorylation. To address this technological gap, here we build a programmable chromatin kinase, called dCas9-dMSK1, by directly fusing nuclease-null CRISPR/Cas9 to a hyperactive, truncated variant of the human MSK1 histone kinase. Targeting dCas9-dMSK1 to human promoters results in increased target histone phosphorylation and gene activation and demonstrates that hyperphosphorylation of histone H3 serine 28 (H3S28ph) in particular plays a causal role in the transactivation of human promoters. In addition, we uncover mediators of resistance to the BRAF V600E inhibitor PLX-4720 in human melanoma cells using genome-scale screening with dCas9-dMSK1. Collectively, our findings enable a facile way to reshape human chromatin using CRISPR/Cas9-based epigenome editing and further define the causal link between histone phosphorylation and human gene activation.

Histone phosphorylation is a ubiquitous post-translational modification. Here the authors present a programmable chromatin kinase, dCas9-dMSK1, that enables controlled histone phosphorylation and specific gene activation.

Oxycodone self-administration activates the mitogen-activated protein kinase/ mitogen- and stress-activated protein kinase (MAPK-MSK) signaling pathway in the rat dorsal striatum

To identify signaling pathways activated by oxycodone self-administration (SA), Sprague–Dawley rats self-administered oxycodone for 20 days using short—(ShA, 3 h) and long-access (LgA, 9 h) paradigms. Animals were euthanized 2 h after SA cessation and dorsal striata were used in post-mortem molecular analyses. LgA rats escalated their oxycodone intake and separated into lower (LgA-L) or higher (LgA-H) oxycodone takers. LgA-H rats showed increased striatal protein phosphorylation of ERK1/2 and MSK1/2. Histone H3, phosphorylated at serine 10 and acetylated at lysine 14 (H3S10pK14Ac), a MSK1/2 target, showed increased abundance only in LgA-H rats. RT-qPCR analyses revealed increased AMPA receptor subunits, GluA2 and GluA3 mRNAs, in the LgA-H rats. GluA3, but not GluA2, mRNA expression correlated positively with changes in pMSK1/2 and H3S10pK14Ac. These findings suggest that escalated oxycodone SA results in MSK1/2-dependent histone phosphorylation and increases in striatal gene expression. These observations offer potential avenues for interventions against oxycodone addiction.

AURKB promotes gastric cancer progression via activation of CCND1 expression

Aurora kinase B (AURKB) triggers the phosphorylation of serine 10 on histone H3 (H3S10ph), which is important for chromosome condensation and cytokinesis during mitosis in mammals. However, how exactly AURKB controls cell cycle and contributes to tumorigenesis as an oncoprotein under pathological conditions remains largely unknown. Here, we report that AURKB promotes gastric cancer cell proliferation in vitro and in vivo. Silencing AURKB expression inhibits gastric cell proliferation and arrests the cell cycle in G₂/M phase. We demonstrate that cyclin D1 (CCND1) is a direct downstream target of AURKB that plays a key role in gastric cancer cell proliferation. AURKB is able to activate the expression of CCND1 through mediating H3S10ph in the promoter of the CCND1 gene. Furthermore, we show that AZD1152, a specific inhibitor of AURKB, can suppress the expression of CCND1 in the gastric cancer cells and inhibit cell proliferation in vitro and in vivo. Importantly, we found that high AURKB and CCND1 expression levels are correlated with shorter overall survival of gastric cancer patients. This study demonstrates that AURKB promotes gastric tumorigenesis potentially through epigenetically activating CCND1 expression, suggesting AURKB as a promising therapeutic target in gastric cancer.

Global virus outbreaks: Interferons as 1st responders

Outbreaks of severe virus infections with the potential to cause global pandemics are increasing. In many instances these outbreaks have been newly emerging (SARS coronavirus), re-emerging (Ebola virus, Zika virus) or zoonotic (avian influenza H5N1) virus infections. In the absence of a targeted vaccine or a pathogen-specific antiviral, broad-spectrum antivirals would function to limit virus spread. Given the direct antiviral effects of type I interferons (IFNs) in inhibiting the replication of both DNA and RNA viruses at different stages of their replicative cycles, and the effects of type I IFNs on activating immune cell populations to clear virus infections, IFNs-α/β present as ideal candidate broad-spectrum antivirals.

Mitogen and stress- activated protein kinase regulated gene expression in cancer cells

The mitogen- and stress-activated protein kinases activated by the extracellular-signal-regulated kinase 1/2 and/or stress-activated protein kinase 2/p38 mitogen-activated protein kinase pathways are recruited to the regulatory region of a subset of genes termed immediate-early genes, often leading to their induction. These genes, many of which code for transcription factors, have been directly linked to the phenotypic events in carcinogenesis. In this paper, we focus on the mitogen- and stress-activated protein kinases; their discovery, activation, H3 phosphorylation and recent discoveries in their roles in cancer.

Mitogen- and stress-activated protein kinase 1 is required for gonadotropin-releasing hormone-mediated activation of gonadotropin α-subunit expression

Pituitary gonadotropin hormones are regulated by gonadotropin-releasing hormone (GnRH) via MAPK signaling pathways that stimulate gene transcription of the common α-subunit (Cga) and the hormone-specific β-subunits of gonadotropin. We have reported previously that GnRH-induced activities at these genes include various histone modifications, but we did not examine histone phosphorylation. This modification adds a negative charge to residues of the histone tails that interact with the negatively charged DNA, is associated with closed chromatin during mitosis, but is increased at certain genes for transcriptional activation. Thus, the functions of this modification are unclear. We initially hypothesized that GnRH might induce phosphorylation of Ser-10 in histone 3 (H3S10p) as part of its regulation of gonadotropin gene expression, possibly involving cross-talk with H3K9 acetylation. We found that GnRH increases the levels of both modifications around the Cga gene transcriptional start site and that JNK inhibition dramatically reduces H3S10p levels. However, this modification had only a minor effect on Cga expression and no effect on H3K9ac. GnRH also increased H3S28p and H3K27ac levels and also those of activated mitogen- and stress-activated protein kinase 1 (MSK1). MSK1 inhibition dramatically reduced H3S28p levels in untreated and GnRH-treated cells and also affected H3K27ac levels. Although not affecting basal Cga expression, MSK1/2 inhibition repressed GnRH activation of Cga expression. Moreover, ChIP analysis revealed that GnRH-activated MSK1 targets the first nucleosome just downstream from the TSS. Given that the elongating RNA polymerase II (RNAPII) stalls at this well positioned nucleosome, GnRH-induced H3S28p, possibly in association with H3K27ac, would facilitate the progression of RNAPII.

How does chromatin package DNA within nucleus and regulate gene expression?

The human body is made up of 60 trillion cells, each cell containing 2 millions of genomic DNA in its nucleus. How is this genomic deoxyribonucleic acid [DNA] organised into nuclei? Around 1880, W. Flemming discovered a nuclear substance that was clearly visible on staining under primitive light microscopes and named it 'chromatin'; this is now thought to be the basic unit of genomic DNA organization. Since long before DNA was known to carry genetic information, chromatin has fascinated biologists. DNA has a negatively charged phosphate backbone that produces electrostatic repulsion between adjacent DNA regions, making it difficult for DNA to fold upon itself. In this article, we will try to shed light on how does chromatin package DNA within nucleus and regulate gene expression?

Mitogen-induced distinct epialleles are phosphorylated at either H3S10 or H3S28, depending on H3K27 acetylation

Stimulation of the MAPK pathway results in mitogen- and stress-activated protein kinase 1/2 (MSK1/2)-catalyzed phosphorylation of histone H3 at serine 10 or 28 and expression of immediate-early (IE) genes. In 10T1/2 mouse fibroblasts, phosphorylation of H3S10 and H3S28 occurs on different H3 molecules and in different nuclear regions. Similarly, we show that mitogen-induced H3S10 and H3S28 phosphorylation occurs in separate pools in human primary fibroblasts. High-resolution imaging studies on both cell types reveal that H3S10 and H3S28 phosphorylation events can be induced in a single cell but on different alleles, giving rise to H3S10ph and H3S28ph epialleles. Coimmunoprecipitation and inhibition studies demonstrate that CBP/p300-mediated H3K27 acetylation is required for MSK1/2 to phosphorylate S28. Although the K9ac and S10ph marks coexist on H3, S10 phosphorylation is not dependent on K9 acetylation by PCAF. We propose that random targeting of H3S10 or H3S28 results from the stochastic acetylation of H3 by CBP/p300 or PCAF, a process comparable to transcriptional bursting causing temporary allelic imbalance. In 10T1/2 cells expressing Jun, at least two of three alleles per cell were induced, a sign of high expression level. The redundant roles of H3S10ph and H3S28ph might enable rapid and efficient IE gene induction.

The Chromatin Modifier MSK1/2 Suppresses Endocrine Cell Fates during Mouse Pancreatic Development

Type I diabetes is caused by loss of insulin-secreting beta cells. To identify novel, pharmacologically-targetable histone-modifying proteins that enhance beta cell production from pancreatic progenitors, we performed a screen for histone modifications induced by signal transduction pathways at key pancreatic genes. The screen led us to investigate the temporal dynamics of ser-28 phosphorylated histone H3 (H3S28ph) and its upstream kinases, MSK1 and MSK2 (MSK1/2). H3S28ph and MSK1/2 were enriched at the key endocrine and acinar promoters in E12.5 multipotent pancreatic progenitors. Pharmacological inhibition of MSK1/2 in embryonic pancreatic explants promoted the specification of endocrine fates, including the beta-cell lineage, while depleting acinar fates. Germline knockout of both Msk isoforms caused enhancement of alpha cells and a reduction in acinar differentiation, while monoallelic loss of Msk1 promoted beta cell mass. Our screen of chromatin state dynamics can be applied to other developmental contexts to reveal new pathways and approaches to modulate cell fates.

Protein kinase Msk1 physically and functionally interacts with the KMT2A/MLL1 methyltransferase complex and contributes to the regulation of multiple target genes

BACKGROUND

The KMT2A/MLL1 lysine methyltransferase complex is an epigenetic regulator of selected developmental genes, in part through the SET domain-catalysed methylation of H3K4. It is essential for normal embryonic development and haematopoiesis and frequently mutated in cancer. The catalytic properties and targeting of KMT2A/MLL1 depend on the proteins with which it complexes and the post-translational protein modifications which some of these proteins put in place, though detailed mechanisms remain unclear.

RESULTS

KMT2A/MLL1 (both native and FLAG-tagged) and Msk1 (RPS6KA5) co-immunoprecipitated in various cell types. KMT2A/MLL1 and Msk1 knockdown demonstrated that the great majority of genes whose activity changed on KTM2A/MLL1 knockdown, responded comparably to Msk1 knockdown, as did levels of H3K4 methylation and H3S10 phosphorylation at KTM2A target genes HoxA4, HoxA5. Knockdown experiments also showed that KMT2A/MLL1 is required for the genomic targeting of Msk1, but not vice versa.

CONCLUSION

The KMT2A/MLL1 complex is associated with, and functionally dependent upon, the kinase Msk1, part of the MAP kinase signalling pathway. We propose that Msk1-catalysed phosphorylation at H3 serines 10 and 28, supports H3K4 methylation by the KMT2A/MLL1 complex both by making H3 a more attractive substrate for its SET domain, and improving target gene accessibility by prevention of HP1- and Polycomb-mediated chromatin condensation.

MSK1 triggers the expression of the INK4AB/ARF locus in oncogene-induced senescence

The tumor suppressor proteins p15(INK4B), p16(INK4A), and p14(ARF), encoded by the INK4AB/ARF locus, are crucial regulators of cellular senescence. The locus is epigenetically silenced by the repressive Polycomb complexes in growing cells but is activated in response to oncogenic stress. Here we show that the mitogen- and stress-activated kinase (MSK1) is up-regulated after RAF1 oncogenic stress and that the phosphorylated (activated) form of MSK1 is significantly increased in the nucleus and recruited to the INK4AB/ARF locus. We show that MSK1 mediates histone H3S28 phosphorylation at the INK4AB/ARF locus and contributes to the rapid transcriptional activation of p15(INK4B) and p16(INK4A) in human cells despite the presence of the repressive H3K27me3 mark. Furthermore, we show that upon MSK1 depletion in oncogenic RAF1-expressing cells, H3S28ph presence at the INK4 locus and p15(INK4B) and p16(INK4A) expression are reduced. Finally, we show that H3S28-MSK-dependent phosphorylation functions in response to RAF1 signaling and that ERK and p38α contribute to MSK1 activation in oncogene-induced senescence.

Regulation of chromatin structure via histone post-translational modification and the link to carcinogenesis

The loss of genome integrity contributes to the development of tumors. Although genome instability is associated with virtually all tumor types including both solid and liquid tumors, the aberrant molecular origins that drive this instability are poorly understood. It is now becoming clear that epigenetics and specific histone post-translational modifications (PTMs) have essential roles in maintaining genome stability under normal conditions. A strong relationship exists between aberrant histone PTMs, genome instability, and tumorigenesis. Changes in the genomic location of specific histone PTMs or alterations in the steady-state levels of the PTM are the consequence of imbalances in the enzymes and their activities catalyzing the addition of PTMs ("writers") or removal of PTMs ("erasers"). This review focuses on the misregulation of three specific types of histone PTMs: histone H3 phosphorylation at serines 10 and 28, H4 mono-methylation at lysine 20, and H2B ubiquitination at lysine 120. We discuss the normal regulation of these PTMs by the respective "writers" and "erasers" and the impact of their misregulation on genome stability.

Sensing core histone phosphorylation - a matter of perfect timing

Systematic analysis of histone modifications has revealed a plethora of posttranslational modifications that mediate changes in chromatin structure and gene expression. Histone phosphorylation is a transient histone modification that becomes induced by extracellular signals, DNA damage or entry into mitosis. Importantly, phosphorylation of histone proteins does lead not only to the binding of specific reader proteins but also to changes in the affinity for readers or writers of other histone modifications. This induces a cross-talk between different chromatin modifications that allows the spatio-temporal control of chromatin-associated events. In this review we will summarize the progress in our current knowledge of factors sensing reversible histone phosphorylation in different biological scenarios. This article is part of a Special Issue entitled: Molecular mechanisms of histone modification function.

•

Signal induced histone phosphorylation is associated with local chromatin opening and transcriptional activation.

•

Histone phosphorylation is also linked with chromatin condensation during mitosis.

•

Histone phosphorylation marks are important for regulation of the DNA damage response.

•

Specific reader proteins recognize histone phosphorylation marks alone or in combination with other histone modifications.

•

Histone phosphorylation affects the affinity of readers or writers of other histone modifications.

Sensing cellular states--signaling to chromatin pathways targeting Polycomb and Trithorax group function

Cells respond to extra- and intra-cellular signals by dynamically changing their gene expression patterns. After termination of the original signal, new expression patterns are maintained by epigenetic DNA and histone modifications. This represents a powerful mechanism that enables long-term phenotypic adaptation to transient signals. Adaptation of epigenetic landscapes is important for mediating cellular differentiation during development and allows adjustment to altered environmental conditions throughout life. Work over the last decade has begun to elucidate the way that extra- and intra-cellular signals lead to changes in gene expression patterns by directly modulating the function of chromatin-associated proteins. Here, we review key signaling-to-chromatin pathways that are specifically thought to target Polycomb and Trithorax group complexes, a classic example of epigenetically acting gene silencers and activators important in development, stem cell differentiation and cancer. We discuss the influence that signals triggered by kinase cascades, metabolic fluctuations and cell-cycle dynamics have on the function of these protein complexes. Further investigation into these pathways will be important for understanding the mechanisms that maintain epigenetic stability and those that promote epigenetic plasticity.

TNF and MAP kinase signalling pathways

The binding of tumour necrosis factor α (TNFα) to cell surface receptors engages multiple signal transduction pathways, including three groups of mitogen-activated protein (MAP) kinases: extracellular-signal-regulated kinases (ERKs); the cJun NH2-terminal kinases (JNKs); and the p38 MAP kinases. These MAP kinase signalling pathways induce a secondary response by increasing the expression of several inflammatory cytokines (including TNFα) that contribute to the biological activity of TNFα. MAP kinases therefore function both upstream and down-stream of signalling by TNFα receptors. Here we review mechanisms that mediate these actions of MAP kinases during the response to TNFα.

Role of ERK signaling in activity-dependent modifications of histone proteins

It is well-established that neuronal intracellular signaling governed by the extracellular signal-regulated kinase (ERK/MAPK) plays a crucial role in long-term adaptive changes that occur during cognitive processes. ERK is a downstream component of a conserved signaling module that is activated by the serine/threonine kinase, Raf, which activates the MAPK/ERK kinase (MEK)1/2 protein kinases, which, in turn, activate ERK1/2. This signaling pathway has been reported to be activated in numerous physiological conditions due to a variety of stimuli, ranging from the activation of ionotropic glutamatergic receptors to metabotropic dopaminergic receptors and neurotrophin receptors. Interestingly, activated ERK can have early and late downstream effects at both the nuclear and synaptic levels. Locally, ERK signaling results in transient changes in the efficacy of synaptic transmission by modifying both pre- and post-synaptic targets. Once translocated into the nucleus, ERK signaling may control transcription by targeting several different regulators of gene expression such as transcription factors and histone proteins. ERK function is considered fundamental in processes such as long-term memory storage and drug addiction, by means of its role in activity-dependent epigenetic modifications that occur in the brain. In this review, we summarize the current understanding of ERK action in the neuroepigenetic processes underlying physiological responses, cognitive processes and drug addiction.

Nuclear CaMKII enhances histone H3 phosphorylation and remodels chromatin during cardiac hypertrophy

Calcium/calmodulin-dependent protein kinase II (CaMKII) plays a central role in pathological cardiac hypertrophy, but the mechanisms by which it modulates gene activity in the nucleus to mediate hypertrophic signaling remain unclear. Here, we report that nuclear CaMKII activates cardiac transcription by directly binding to chromatin and regulating the phosphorylation of histone H3 at serine-10. These specific activities are demonstrated both in vitro and in primary neonatal rat cardiomyocytes. Activation of CaMKII signaling by hypertrophic agonists increases H3 phosphorylation in primary cardiac cells and is accompanied by concomitant cellular hypertrophy. Conversely, specific silencing of nuclear CaMKII using RNA interference reduces both H3 phosphorylation and cellular hypertrophy. The hyper-phosphorylation of H3 associated with increased chromatin binding of CaMKII occurs at specific gene loci reactivated during cardiac hypertrophy. Importantly, H3 Ser-10 phosphorylation and CaMKII recruitment are associated with increased chromatin accessibility and are required for chromatin-mediated transcription of the Mef2 transcription factor. Unlike phosphorylation of H3 by other kinases, which regulates cellular proliferation and immediate early gene activation, CaMKII-mediated signaling to H3 is associated with hypertrophic growth. These observations reveal a previously unrecognized function of CaMKII as a kinase signaling to histone H3 and remodeling chromatin. They suggest a new epigenetic mechanism controlling cardiac hypertrophy.

Domain requirements of the JIL-1 tandem kinase for histone H3 serine 10 phosphorylation and chromatin remodeling in vivo

The JIL-1 kinase localizes to Drosophila polytene chromosome interbands and phosphorylates histone H3 at interphase, counteracting histone H3 lysine 9 dimethylation and gene silencing. JIL-1 can be divided into four main domains, including an NH2-terminal domain, two separate kinase domains, and a COOH-terminal domain. In this study, we characterize the domain requirements of the JIL-1 kinase for histone H3 serine 10 (H3S10) phosphorylation and chromatin remodeling in vivo. We show that a JIL-1 construct without the NH2-terminal domain is without H3S10 phosphorylation activity despite the fact that it localizes properly to polytene interband regions and that it contains both kinase domains. JIL-1 is a double kinase, and we demonstrate that both kinase domains of JIL-1 are required to be catalytically active for H3S10 phosphorylation to occur. Furthermore, we provide evidence that JIL-1 is phosphorylated at serine 424 and that this phosphorylation is necessary for JIL-1 H3S10 phosphorylation activity. Thus, these data are compatible with a model where the NH2-terminal domain of JIL-1 is required for chromatin complex interactions that position the kinase domain(s) for catalytic activity in the context of the state of higher order nucleosome packaging and chromatin structure and where catalytic H3S10 phosphorylation activity mediated by the first kinase domain is dependent on autophosphorylation of serine 424 by the second kinase domain. Furthermore, using a lacO repeat tethering system to target mutated JIL-1 constructs with or without catalytic activity, we show that the epigenetic H3S10 phosphorylation mark itself functions as a causative regulator of chromatin structure independently of any structural contributions from the JIL-1 protein.

Exposure to estrogen and ionizing radiation causes epigenetic dysregulation, activation of mitogen-activated protein kinase pathways, and genome instability in the mammary gland of ACI rats

The impact of environmental mutagens and carcinogens on the mammary gland has recently received a lot of attention. Among the most generally accepted carcinogenic agents identified as factors that may increase breast cancer incidence are ionizing radiation and elevated estrogen levels. However, the molecular mechanisms of mammary gland aberrations associated with radiation and estrogen exposure still need to be further elucidated, especially the interplay between elevated hormone levels and radiation. Therefore, in the present study, we investigated molecular changes induced in rat mammary gland tissue by estrogen, ionizing radiation, and the combined action of these two carcinogens using a well-established ACI rat model. We found that continuous exposure of intact female ACI rats to elevated levels of estrogen or to both estrogen and radiation resulted in significant hyperproliferative changes in rat mammary glands. In contrast, radiation exposure alone did not induce hyperplasia. Interestingly, despite the obvious disparity in mammary gland morphology, we did not detect significant differences in the levels of genomic methylation among animals exposed to estrogen, radiation, or both agents together. Specifically, we observed a significant global genomic hypomethylation at 6 weeks of exposure. However, by 12 and 18 weeks, the levels of global DNA methylation returned to those of age-matched controls. We also found that combined exposure to radiation and estrogen significantly altered the levels of histone H3 and H4 methylation and acetylation. Most importantly, we for the first time demonstrated that estrogen and radiation exposure caused a significant induction of p42/44 MAPK and p38 pathways that was paralleled by elevated levels of H3S10 phosphorylation, a well-established biomarker of genome and chromosome instability. The precise role of MAPK pathways and their inter-relationship with H3S10 phosphorylation and genome instability in mammary gland tissues needs to be explored further.

Transcription factors Runx1 to 3 are expressed in the lacrimal gland epithelium and are involved in regulation of gland morphogenesis and regeneration

PURPOSE

Lacrimal gland (LG) morphogenesis and repair are regulated by a complex interplay of intrinsic factors (e.g., transcription factors) and extrinsic signals (e.g., soluble growth/signaling factors). Many of these interconnections remain poorly characterized. Runt-related (Runx) factors belong to a small family of heterodimeric transcription factors known to regulate lineage-specific proliferation and differentiation of stem cells. The purpose of this study was to define the expression pattern and the role of Runx proteins in LG development and regeneration.

METHODS

Expression of epithelial-restricted transcription factors in murine LG was examined using immunostaining, qRT-PCR, and RT(2)Profiler PCR microarrays. The role of Runx transcription factors in LG morphogenesis was studied using siRNA and ex vivo LG cultures. Expression of Runx transcription factors during LG regeneration was assessed using in vivo model of LG regeneration.

RESULTS

We found that Runx factors are expressed in the epithelial compartment of the LG; in particular, Runx1 was restricted to the epithelium with highest level of expression in ductal and centroacinar cells. Downregulation of Runx1 to 3 expression using Runx-specific siRNAs abolished LG growth and branching and our data suggest that Runx1, 2, and 3 are partially redundant in LG development. In siRNA-treated LG, reduction of branching correlated with reduction of epithelial proliferation, as well as expression of cyclin D1 and the putative epithelial progenitor cell marker cytokeratin-5. Runx1, Runx3, and cytokeratin-5 expression increased significantly in regenerating LG and there was modest increase in Runx2 expression during LG differentiation.

CONCLUSIONS

Runx1 and 2 are new markers of the LG epithelial lineage and Runx factors are important for normal LG morphogenesis and regeneration.

Elucidating combinatorial histone modifications and crosstalks by coupling histone-modifying enzyme with biotin ligase activity

Histone post-translational modifications (PTMs) often form complex patterns of combinations and cooperate to specify downstream biological processes. In order to systemically analyse combinatorial PTMs and crosstalks among histone PTMs, we have developed a novel nucleosome purification method called Biotinylation-assisted Isolation of CO-modified Nucleosomes (BICON). This technique is based on physical coupling of the enzymatic activity of a histone-modifying enzyme with in vivo biotinylation by the biotin ligase BirA, and using streptavidin to purify the co-modified nucleosomes. Analysing the nucleosomes isolated by BICON allows the identification of PTM combinations that are enriched on the modified nucleosomes and function together within the nucleosome context. We used this new approach to study MSK1-mediated H3 phosphorylation and found that MSK1 not only directly phosphorylated H3, but also induced hyperacetylation of both histone H3 and H4 within the nucleosome. Moreover, we identified a novel crosstalk pathway between H3 phosphorylation and H4 acetylation on K12. Involvement of these acetyl marks in MSK1-mediated transcription was further confirmed by chromatin immunoprecipitation assays, thus validating the biological relevance of the BICON results. These studies serve as proof-of-principle for this new technical approach, and demonstrate that BICON can be further adapted to study PTMs and crosstalks associated with other histone-modifying enzymes.

A mutational mimic analysis of histone H3 post-translational modifications: specific sites influence the conformational state of H3/H4, causing either positive or negative supercoiling of DNA

Histone H3 has specific sites of post-translational modifications that serve as epigenetic signals to cellular machinery to direct various processes. Mutational mimics of these modifications (glutamine for acetylation, methionine and leucine for methylation, and glutamic acid for phosphorylation) were constructed at the relevant sites of the major histone variant, H3.2, and their effects on the conformational equilibrium of the H3/H4 tetramer at physiological ionic strength were determined when bound to or free of DNA. The deposition vehicle used for this analysis was NAP1, nucleosome assembly protein 1. Acetylation mimics in the N-terminus preferentially stabilized the left-handed conformer (DNA negatively supercoiled), and mutations within the globular region preferred the right-handed conformer (DNA positively supercoiled). The methylation mimics in the N-terminus tended to maintain characteristics similar to those of wild-type H3/H4; i.e., the conformational equilibrium maintains similar levels of both left- and right-handed conformers. Phosphorylation mimics facilitated a mixed effect, i.e., when at serines, the left-handed conformer, and at threonines, a mixture of both conformers. When double mutations were present, the conformational equilibrium was shifted dramatically, either leftward or rightward depending on the specific sites. In contrast, these mutations tended not to affect the direction and extent of supercoiling for variants H3.1 and H3.3. Variant H3.3 promoted only the left-handed conformer, and H3.1 tended to maintain both conformers. Additional experiments indicate the importance of a propagation mechanism for ensuring the formation of a particular superhelical state over an extended region of the DNA. The potential relevance of these results to the maintenance of epigenetic information on a gene is discussed.

Histone phosphorylation: a chromatin modification involved in diverse nuclear events

Histone posttranslational modifications are key components of diverse processes that modulate chromatin structure. These marks function as signals during various chromatin-based events, and act as platforms for recruitment, assembly or retention of chromatin-associated factors. The best-known function of histone phosphorylation takes place during cellular response to DNA damage, when phosphorylated histone H2A(X) demarcates large chromatin domains around the site of DNA breakage. However, multiple studies have also shown that histone phosphorylation plays crucial roles in chromatin remodeling linked to other nuclear processes. In this review, we summarize the current knowledge of histone phosphorylation and describe the many kinases and phosphatases that regulate it. We discuss the key roles played by this histone mark in DNA repair, transcription and chromatin compaction during cell division and apoptosis. Additionally, we describe the intricate crosstalk that occurs between phosphorylation and other histone modifications and allows for sophisticated control over the chromatin remodeling processes.

H3S10 phosphorylation marks constitutive heterochromatin during interphase in early mouse embryos until the 4-cell stage

Phosphorylation of histone H3 at Ser10 (H3S10P) has been linked to a variety of cellular processes, such as chromosome condensation and gene activation/silencing. Remarkably, in mammalian somatic cells, H3S10P initiates in the pericentromeric heterochromatin during the late G2 phase, and phosphorylation spreads throughout the chromosomes arms in prophase, being maintained until the onset of anaphase when it gets dephosphorylated. Considerable studies have been carried out about H3S10P in different organisms; however, there is little information about this histone modification in mammalian embryos. We hypothesized that this epigenetic modification could also be a marker of pericentromeric heterochromatin in preimplantation embryos. We therefore followed the H3S10P distribution pattern in the G1/S and G2 phases through the entire preimplantation development in in vivo mouse embryos. We paid special attention to its localization relative to another pericentromeric heterochromatin marker, HP1β and performed immunoFISH using specific pericentromeric heterochromatin probes. Our results indicate that H3S10P presents a remarkable distribution pattern in preimplantation mouse embryos until the 4-cell stage and is a better marker of pericentromeric heterochromatin than HP1β. After the 8-cell stage, H3S10P kinetic is more similar to the somatic one, initiating during G2 in chromocenters and disappearing upon telophase. Based on these findings, we believe that H3S10P is a good marker of pericentromeric heterochromatin, especially in the late 1- and 2-cell stages as it labels both parental genomes and that it can be used to further investigate epigenetic regulation and heterochromatin mechanisms in early preimplantation embryos.

Inner workings and regulatory inputs that control Polycomb repressive complex 2

Polycomb repressive complex 2 (PRC2) is a conserved multisubunit enzyme that methylates histone H3 on lysine-27. This chromatin modification is a hallmark of target genes transcriptionally silenced by the Polycomb system. At its core, PRC2 activity depends upon the SET domain active site of its catalytic subunit, EZH2, as well as critical stimulatory inputs from noncatalytic subunits, especially EED and SU(Z)12. We review recent progress on this core PRC2 machinery, including key features of the active site, control mechanisms that operate via EZH2 phosphorylation, and subunit elements and architectures that influence PRC2 function. Among these, we highlight work identifying an EED regulatory site that enables PRC2 to bind pre-existing methylated H3-K27 and stimulate enzyme output. These advances illuminate basic inner workings of PRC2 and also provide insights that could aid design of PRC2 inhibitors. The chromatin landscape that PRC2 encounters in vivo is decorated with many histone modifications that accompany active transcription, such as H3-K4 methylation. It has long been assumed that these "active" modifications oppose PRC2 at some level but, until recently, mechanisms of this antagonistic cross-talk have been elusive. We discuss new findings that illuminate how H3-K4 and H3-K36 methylation, H3-K27 acetylation, and H3-S28 phosphorylation each exert a negative impact on PRC2 function. The emerging picture presents PRC2 as a cooperative multipart machine, intricately outfitted to sense and respond to the local chromatin environment and other cues. This PRC2 design ensures flexibility and fine tuning of its fundamental gene silencing roles in diverse biological contexts.

Histone H3 phosphorylation, immediate-early gene expression, and the nucleosomal response: a historical perspective1This article is part of Special Issue entitled Asilomar Chromatin and has undergone the Journal’s usual peer review process

Histone H3 is modified at serines 10 and 28 in interphase cells following activation of the RAS-MAPK or p38-MAPK pathways by growth factors or stress. These modifications are involved in the regulation of immediate-early genes, including Jun and Fos, whose increased expression is a trademark of various cancers. This review outlines the series of discoveries that led to the characterization of these modifications, the kinase, MSK1/2, which is activated by both MAPK pathways and directs phosphorylation of H3, and the mechanistic function of these modifications in transcriptional activation. Research examining the effect of deregulated MSK1/2 in human disorders, namely cancer, is evaluated. Recently, a number of reports proposed novel, intervening pathways leading to enrichment of phosphorylated serine 10 and 28 and the activation of MSK1/2. These novel pathways predict an even more complicated signalling mechanism for cell growth, apoptosis, and the immune response, suggesting that MSK1/2 is intrinsically responsible for an even greater number of biological processes. This review proposes that MSK1/2 is an optimal target for cancer therapy, based on its fundamental role in transmitting external signals into varied responses involved in cancer development.

A chromatin-modifying function of JNK during stem cell differentiation

Signaling mediates cellular responses to extracellular stimuli. The c-Jun NH(2)-terminal kinase (JNK) pathway exemplifies one subgroup of the mitogen-activated protein (MAP) kinases, which, besides having established functions in stress response, also contribute to development by an unknown mechanism. We show by genome-wide location analysis that JNK binds to a large set of active promoters during the differentiation of stem cells into neurons. JNK-bound promoters are enriched with binding motifs for the transcription factor NF-Y but not for AP-1. NF-Y occupies these predicted sites, and overexpression of dominant-negative NF-YA reduces the JNK presence on chromatin. We find that histone H3 Ser10 (H3S10) is a substrate for JNK, and JNK-bound promoters are enriched for H3S10 phosphorylation. Inhibition of JNK signaling in post-mitotic neurons reduces phosphorylation at H3S10 and the expression of target genes. These results establish MAP kinase binding and function on chromatin at a novel class of target genes during stem cell differentiation.

When signaling kinases meet histones and histone modifiers in the nucleus

Signaling pathways involve cascades of protein phosphorylation and ultimately affect regulation of transcription in the nucleus. However, most of the kinases in these pathways have not been generally considered to directly modulate transcription thus far. Here, recent significant progress in the field elucidating direct modifications of histones and histone modifiers by upstream kinases is summarized, and future directions are discussed.

Quantitative phosphoproteomics identifies substrates and functional modules of Aurora and Polo-like kinase activities in mitotic cells

Mitosis is a process involving a complex series of events that require careful coordination. Protein phosphorylation by a small number of kinases, in particular Aurora A, Aurora B, the cyclin-dependent kinase-cyclin complex Cdk1/cyclinB, and Polo-like kinase 1 (Plk1), orchestrates almost every step of cell division, from entry into mitosis to cytokinesis. To discover more about the functions of Aurora A, Aurora B, and kinases of the Plk family, we mapped mitotic phosphorylation sites to these kinases through the combined use of quantitative phosphoproteomics and selective targeting of kinase activities by small-molecule inhibitors. Using this integrated approach, we connected 778 phosphorylation sites on 562 proteins with these enzymes in cells arrested in mitosis. By connecting the kinases to protein complexes, we associated these kinases with functional modules. In addition to predicting previously unknown functions, this work establishes additional substrate-recognition motifs for these kinases and provides an analytical template for further use in dissecting kinase signaling events in other areas of cellular signaling and systems biology.

Squamocin modulates histone H3 phosphorylation levels and induces G1 phase arrest and apoptosis in cancer cells

Background

Histone modifications in tumorigenesis are increasingly recognized as important epigenetic factors leading to cancer. Increased phosphorylation levels of histone H3 as a result of aurora B and pMSK1 overexpression were observed in various tumors. We selected aurora B and MSK1 as representatives for testing various compounds and drugs, and found that squamocin, a bis-tetrahydrofuran annonaceous acetogenin, exerted a potent effect on histone H3 phosphorylation.

Methods

GBM8401, Huh-7, and SW620 cells were incubated with 15, 30, and 60 μM squamocin for 24 h. The expressions of mRNA and proteins were analyzed by qRT-PCR and Western blotting, respectively. The cell viability was determined by an MTT assay. Cell cycle distribution and apoptotic cells were analyzed by flow cytometry.

Results

Our results showed that squamocin inhibited the proliferation of GBM8401, Huh-7, and SW620 cells, arrested the cell cycle at the G₁ phase, and activated both intrinsic and extrinsic pathways to apoptosis. In addition, we demonstrated that squamocin had the ability to modulate the phosphorylation levels of H3S10 (H3S10p) and H3S28 (H3S28p) in association with the downregulation of aurora B and pMSK1 expressions.

Conclusions

This study is the first to show that squamocin affects epigenetic alterations by modulating histone H3 phosphorylation at S10 and S28, providing a novel view of the antitumor mechanism of squamocin.

Histone code pathway involving H3 S28 phosphorylation and K27 acetylation activates transcription and antagonizes polycomb silencing

Histone H3 phosphorylation is a critical step that couples signal transduction pathways to gene regulation. To specifically assess the transcriptional regulatory functions of H3 phosphorylation, we developed an in vivo targeting approach and found that the H3 kinase MSK1 is a direct and potent transcriptional activator. Targeting of this H3 kinase to the endogenous c-fos promoter is sufficient to activate its expression without the need of upstream signaling. Moreover, targeting MSK1 to the α-globin promoter induces H3 S28 phosphorylation and reactivates expression of this polycomb-silenced gene. Importantly, we discovered a mechanism whereby H3 S28 phosphorylation not only displaces binding of the polycomb-repressive complexes, but it also induces a methyl-acetylation switch of the adjacent K27 residue. Our findings show that signal transduction activation can directly regulate polycomb silencing through a specific histone code-mediated mechanism.

Emerging mass spectrometry-based technologies for analyses of chromatin changes: analysis of histones and histone modifications

Mass spectrometry (MS) is rapidly becoming an indispensable tool for the analysis of posttranslational modifications (PTMs) of proteins, and particularly histone PTMs that regulate physiological processes. The more traditional bottom-up approach of searching for modifications on peptides rather than intact proteins (top-down) has proven useful for finding phosphorylation, acetylation, and ubiquitination sites. With the use of modern instrumentation and various MS-based techniques, peptides and their PTMs can be characterized in a high-throughput manner while still maintaining high sensitivity and specificity. In complement to bottom-up MS, recent advances in MS technology, such as high-field Fourier transform ion cyclotron resonance (FTICR)-mass spectrometry, have permitted the study of intact proteins and their modifications. On-line and off-line protein separation instruments coupled to FTICR-MS allow the characterization of PTMs previously undetectable with bottom-up approaches. The use of unique fragmentation techniques in FTICR-MS provides a viable option for the study of labile modifications. In this chapter, we provide a detailed description of the analytical tools - mass spectrometry in particular - that are used to characterize modifications on peptides and proteins. We also examine the applicability of these mass spectrometric techniques to the study of PTMs on histones via both the bottom-up and top-down proteomics approaches.

Multisite phosphorylation of Erk5 in mitosis

The MAP kinase Erk5 plays important roles in cellular proliferation, and has recently been implicated in the regulation of mitosis. The classic pathway of Erk5 activation involves dual phosphorylation at its TEY microdomain by the upstream regulating kinase MEK5. Here we describe a second pathway that controls Erk5 phosphorylation. This pathway is activated in mitotic cells and involves kinase activities distinct from MEK5. Studies aimed at identifying these kinases suggested that CDK1 activity is required to sustain Erk5 phosphorylation in mitosis, as treatment with RO3306, a CDK1 inhibitor, reversed mitotic phosphorylation of Erk5. Moreover, CDK1 co-precipitated with Erk5 in mitotic cells. The mitotic phosphorylation of Erk5 occurs at multiple sites located at its unique C-terminal region, within an Erk5 subdomain that has formerly been implicated in the control of the subcellular location of Erk5. Furthermore, molecular studies indicated that phosphorylation at these sites may participate in the control of the transit of Erk5 between the cytosol and the nucleus, in addition to regulating its transcriptional activity. Together, our results demonstrate the existence of a second Erk5 phosphorylation pathway, that is activated in mitosis, and that may participate in the regulation of Erk5 functions.

Stability of histone modifications across mammalian genomes: implications for 'epigenetic' marking

The combination of chromatin immunoprecipitation (ChIP) with microarray analysis (ChIP-chip) or high-throughput sequencing (ChIP-seq and ChIP-SAGE) has provided maps of a wide variety of site-specific histone modifications across mammalian genomes in various cell types. Although distinct genomic regions and functional elements have been strongly associated with specific histone modifications, an overwhelming number of combinatorial patterns have also been observed across the genome. While peaks of enrichment in ChIP-chip and ChIP-seq data may suggest stable and predictive 'landmarks' across the genomic landscape, studies from transcribed genes indicate a more dynamic model of how these data may be interpreted. In light of such studies, which show highly dynamic methylation, acetylation and phosphorylation of histone H3 during gene transcription, we consider the extent to which genome-wide maps of chromatin state could be interpreted as 'snapshots' of heterogeneous profiles deriving from dynamic modification processes. Rather than acting as static 'epigenetic' landmarks, histone modifications may function as dynamic and transient operational marks supporting specific steps in diverse processes throughout the mammalian genome.

Promoter chromatin remodeling of immediate-early genes is mediated through H3 phosphorylation at either serine 28 or 10 by the MSK1 multi-protein complex

Upon activation of the ERK and p38 MAPK pathways, the MSK1/2-mediated nucleosomal response, including H3 phosphorylation at serine 28 or 10, is coupled with the induction of immediate-early (IE) gene transcription. The outcome of this response, varying with the stimuli and cellular contexts, ranges from neoplastic transformation to neuronal synaptic plasticity. Here, we used sequential co-immunoprecipitation assays and sequential chromatin immunoprecipitation (ChIP) assays on mouse fibroblast 10T1/2 and MSK1 knockdown 10T1/2 cells to show that H3 serine 28 and 10 phosphorylation leads to promoter remodeling. MSK1, in complexes with phospho-serine adaptor 14-3-3 proteins and BRG1 the ATPase subunit of the SWI/SNF remodeler, is recruited to the promoter of target genes by transcription factors such as Elk-1 or NF-kappaB. Following MSK1-mediated H3 phosphorylation, BRG1 associates with the promoter of target genes via 14-3-3 proteins, which act as scaffolds. The recruited SWI/SNF remodels nucleosomes at the promoter of IE genes enabling the binding of transcription factors like JUN and the onset of transcription.

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-response element-binding protein (CREB) controls MSK1-mediated phosphorylation of histone H3 at the c-fos promoter in vitro

The rapid induction of the c-fos gene correlates with phosphorylations of histone H3 and HMGN1 by mitogen- and stress-activated protein kinases. We have used a cell-free system to dissect the mechanism by which MSK1 phosphorylates histone H3 within the c-fos chromatin. Here, we show that the reconstituted c-fos chromatin presents a strong barrier to histone H3 phosphorylation by MSK1; however, the activators (serum response factor, Elk-1, cAMP-response element-binding protein (CREB), and ATF1) bound on their cognate sites recruit MSK1 to phosphorylate histone H3 at Ser-10 within the chromatin. This activator-dependent phosphorylation of histone H3 is enhanced by HMGN1 and occurs preferentially near the promoter region. Among the four activators, CREB plays a predominant role in MSK1-mediated phosphorylation of histone H3, and the phosphorylation of Ser-133 in CREB is essential for this process. Mutational analyses of MSK1 show that its N-terminal inhibition domain is critical for the kinase to phosphorylate chromatin-embedded histone H3 in a CREB-dependent manner, indicating the presence of an intricate regulatory network for MSK1-mediated phosphorylation of histone H3.

MSK1 regulates the transcription of IL-1ra in response to TLR activation in macrophages

The activity of the pro-inflammatory cytokine IL (interleukin)-1 is closely regulated in vivo via a variety of mechanisms, including both the control of IL-1 production and secretion as well as naturally occurring inhibitors of IL-1 function, such as IL-1ra (IL-1 receptor antagonist). IL-1ra is homologous with IL-1, and is able to bind but not activate the IL-1 receptor. IL-1ra can be produced by a variety of cell types, and its production is stimulated by inflammatory signals. In the present study, we show that in macrophages the TLR (Toll-like receptor)-mediated induction of IL-1ra from both its proximal and distal promoters involves the p38 and ERK1/2 (extracellular-signal-regulated kinase 1/2) MAPK (mitogen-activated protein kinase) cascades. In addition, we show that MSK1 and 2 (mitogen- and stress-activated kinase 1 and 2), kinases activated by either ERK1/2 or p38 in vivo, are required for the induction of both IL-1ra mRNA and protein. MSKs regulate IL-1ra transcription via both IL-10-dependent and -independent mechanisms in cells. Consistent with this, knockout of MSK in mice was found to result in a decrease in IL-1ra production following LPS (lipopolysaccharide) injection. MSKs therefore act as important negative regulators of inflammation following TLR activation.