Phosphorylation at serine 28 and acetylation at lysine 9 of histone H3 induced by trichostatin A

Tributyrin Mitigates Ethanol-Induced Lysine Acetylation of Histone-H3 and p65-NFκB Downregulating CCL2 Expression and Consequent Liver Inflammation and Injury

PURPOSE

Chemokine-driven leukocyte infiltration and sustained inflammation contribute to alcohol-associated liver disease (ALD). Elevated hepatic CCL2 expression, seen in ALD, is associated with disease severity. However, mechanisms of CCL2 regulation are not completely elucidated. Post-translational modifications (PTMs) of proteins, particularly acetylation, modulate gene expression. This study examined the acetylation changes of promoter-associated histone-H3 and key transcription factor-NFκB in regulating hepatic CCL2 expression and subsequent inflammation and injury. Further, the effect of therapeutic modulation of the acetylation state by tributyrin (TB), a butyrate prodrug, was assessed.

METHODS

Hepatic CCL2 expression was assessed in mice fed control (PF) or an ethanol-containing Lieber-DeCarli (5% v/v, EF) diet for 7 weeks with or without oral administration of tributyrin (TB, 2 g/kg, 5 days/week). A chromatin immunoprecipitation (ChIP) assay evaluated promoter-associated modifications. Nuclear association between SIRT1, p300, and NFκB-p65 and acetylation changes of p65 were determined using immunoprecipitation and Western blot analyses. A Student's t-test and one-way ANOVA determined the significance.

RESULTS

Ethanol significantly increased promoter-associated histone-H3-lysine-9 acetylation (H3K9Ac), reflecting a transcriptionally permissive state with a resultant increase in hepatic CCL2 mRNA and protein expression. Moreover, increased lysine-310-acetylation of nuclear RelA/p65 decreased its association with SIRT1, a class III HDAC, but concomitantly increased with p300, a histone acetyltransferase. This further led to enhanced recruitment of NF-κB/p65 and RNA polymerase-II to the CCL2 promoter. Oral TB administration prevented ethanol-associated acetylation changes, thus downregulating CCL2 expression, hepatic neutrophil infiltration, and inflammation/ injury.

CONCLUSION

The modulation of a protein acetylation state via ethanol or TB mechanistically regulates hepatic CCL2 upregulation in ALD.

Histone phosphorylation integrates the hepatic glucagon-PKA-CREB gluconeogenesis program in response to fasting

The glucagon-PKA signal is generally believed to control hepatic gluconeogenesis via the CREB transcription factor. Here we uncovered a distinct function of this signal in directly stimulating histone phosphorylation for gluconeogenic gene regulation in mice. In the fasting state, CREB recruited activated PKA to regions near gluconeogenic genes, where PKA phosphorylated histone H3 serine 28 (H3S28ph). H3S28ph, recognized by 14-3-3ζ, promoted recruitment of RNA polymerase II and transcriptional stimulation of gluconeogenic genes. In contrast, in the fed state, more PP2A was found near gluconeogenic genes, which counteracted PKA by dephosphorylating H3S28ph and repressing transcription. Importantly, ectopic expression of phosphomimic H3S28 efficiently restored gluconeogenic gene expression when liver PKA or CREB was depleted. These results together highlight a different functional scheme in regulating gluconeogenesis by the glucagon-PKA-CREB-H3S28ph cascade, in which the hormone signal is transmitted to chromatin for rapid and efficient gluconeogenic gene activation.

The Prospective Application of Melatonin in Treating Epigenetic Dysfunctional Diseases

In the past, different human disorders were described by scientists from the perspective of either environmental factors or just by genetically related mechanisms. The rise in epigenetic studies and its modifications, i.e., heritable alterations in gene expression without changes in DNA sequences, have now been confirmed in diseases. Modifications namely, DNA methylation, posttranslational histone modifications, and non-coding RNAs have led to a better understanding of the coaction between epigenetic alterations and human pathologies. Melatonin is a widely-produced indoleamine regulator molecule that influences numerous biological functions within many cell types. Concerning its broad spectrum of actions, melatonin should be investigated much more for its contribution to the upstream and downstream mechanistic regulation of epigenetic modifications in diseases. It is, therefore, necessary to fill the existing gaps concerning corresponding processes associated with melatonin with the physiological abnormalities brought by epigenetic modifications. This review outlines the findings on melatonin’s action on epigenetic regulation in human diseases including neurodegenerative diseases, diabetes, cancer, and cardiovascular diseases. It summarizes the ability of melatonin to act on molecules such as proteins and RNAs which affect the development and progression of diseases.

Design, synthesis and biological evaluation of a novel spiro oxazolidinedione as potent p300/CBP HAT inhibitor for the treatment of ovarian cancer

Histone acetylation is one of the most essential parts of epigenetic modification, mediating a variety of complex biological functions. In these procedure, p300/CBP could catalyze the acetylation of lysine 27 on histone 3 (H3K27ac), and had been reported to mediate tumorigenesis and development in a variety of tumors by enhancing chromatin transcription activity. Ovarian cancer, as an extremely malignant tumor, has also been observed to undergo abnormal acetylation of histones. However, whether the treatment of ovarian cancer could be achieved by inhibiting the acetylation activity of p300/CBP on H3K27 has not been well investigated. In this article, we modified the structure of p300/CBP HAT domain inhibitor A-485 and obtained a highly active small molecule known as 13f, which has an IC₅₀ value of 0.49 nM for inhibiting the in vitro enzyme activity of p300, as well as the anti-proliferation IC₅₀ value on ovarian cancer cell line OVCAR-3 was 153 nM. In addition, 13f had strong acetylase family selectivity, good metabolic stability and promising in vivo anti-tumor activity in OVCAR-3 xenograft model. The discovery of 13f revealed a more active chemical entity of the HATs domain of p300/CBP and provided a novel idea for the application of epigenetic inhibitors in the treatment of ovarian cancer.

The inflammatory effect of epigenetic factors and modifications in type 2 diabetes

Inflammation has a central role in the etiology of type 2 diabetes (T2D) and its complications. Both genetic and epigenetic factors have been implicated in the development of T2D-associated inflammation. Epigenetic mechanisms regulate the function of several components of the immune system. Diabetic conditions trigger aberrant epigenetic alterations that contribute to the progression of insulin resistance and β-cell dysfunction by induction of inflammatory responses. Thus, targeting epigenetic factors and modifications, as one of the underlying causes of inflammation, could lead to the development of novel immune-based strategies for the treatment of T2D. The aim of this review is to provide an overview of the epigenetic mechanisms involved in the propagation and perpetuation of chronic inflammation in T2D. We also discuss the possible anti-inflammatory approaches that target epigenetic factors for the treatment of T2D.

Epigenetic regulation of astrocyte function in neuroinflammation and neurodegeneration

Epigenetic mechanisms control various functions throughout the body, from cell fate determination in development to immune responses and inflammation. Neuroinflammation is one of the prime contributors to the initiation and progression of neurodegeneration in a variety of diseases, including Alzheimer's and Parkinson's diseases. Because astrocytes are the largest population of glial cells, they represent an important regulator of CNS function, both in health and disease. Only recently have studies begun to identify the epigenetic mechanisms regulating astrocyte responses in neurodegenerative diseases. These epigenetic mechanisms, along with the epigenetic marks involved in astrocyte development, could elucidate novel pathways to potentially modulate astrocyte-mediated neuroinflammation and neurotoxicity. This review examines the known epigenetic mechanisms involved in regulation of astrocyte function, from development to neurodegeneration, and links these mechanisms to potential astrocyte-specific roles in neurodegenerative disease with a focus on potential opportunities for therapeutic intervention.

Abnormal expression of TFIIIB subunits and RNA Pol III genes is associated with hepatocellular carcinoma

The levels of the products of RNA polymerase III-dependent genes (Pol III genes), including tRNAs and 5S rRNA, are elevated in transformed and tumor cells, which potentiate tumorigenesis. TFIIB-related factor 1 (Brf1) is a key transcription factor and specifically regulates the transcription of Pol III genes. In vivo and in vitro studies have demonstrated that a decrease in Brf1 reduces Pol III gene transcription and is sufficient for inhibiting cell transformation and tumor formation. Emerging evidence indicates that dysregulation of Brf1 and Pol III genes is linked to the development of hepatocellular carcinoma (HCC) in humans and animals. We have reported that Brf1 is overexpressed in human liver cancer patients and that those with high Brf1 levels have shorter survivals. This review summarizes the effects of dysregulation of these genes on HCC and their regulation by signaling pathways and epigenetics. These novel data should help us determine the molecular mechanisms of HCC from a different perspective and guide the development of therapeutic approaches for HCC patients.

Epigenetic Activation of μ-Opioid Receptor Gene via Increased Expression and Function of Mitogen- and Stress-Activated Protein Kinase 1

Since the discovery of μ-opioid receptor (MOR) gene two decades ago, various regulatory factors have been shown to interact with the MOR promoter and modulate transcript levels. However, the majority of early transcriptional studies on MOR gene have not addressed how intracellular signaling pathways mediate extracellular modulators. In this study, we demonstrate that MOR epigenetic regulation requires multiple coordinated signals converging at the MOR promoter, involving mitogen-activated protein kinase (MAPK) activation and mitogen- and stress-activated protein kinase 1 (MSK1)-ranges of intracellular signaling pathways similar to those activated by opioid agonists. Inhibiting p38 MAPK or extracellular signal-regulated kinase (ERK) 1/2 MAPK (upstream activators of MSK1) reduced MOR expression levels; accordingly, the functional role of MSK1, but not MSK2, was demonstrated using genetic approaches. However, for maximal MSK1 effect, an open chromatin configuration was required, because in vitro CpG methylation of the MOR promoter abolished MSK1 activity. Finally, endogenous MSK1 levels concomitantly increased to regulate MOR gene expression during neuronal differentiation of P19 cells, suggesting a conserved role of this kinase in the epigenic activation of MOR in neurons. Taken together, our findings indicate that the expression of MOR gene requires the activity of intracellular signaling pathways that have been implicated in the behavioral outcomes of opioid drugs, which suggests that an autoregulatory mechanism may function in opioid systems.

A Nanoprinted Model of Interstitial Cancer Migration Reveals a Link between Cell Deformability and Proliferation

Metastatic progression of tumors requires the coordinated dissemination of cancerous cells through interstitial tissues and their replication in distant body locations. Despite their importance in cancer treatment decisions, key factors, such as cell shape adaptation and the role it plays in dense tissue invasion by cancerous cells, are not well understood. Here, we employ a 3D electrohydrodynamic nanoprinting technology to generate vertical arrays of topographical pores that mimic interstitial tissue resistance to the mesenchymal migration of cancerous cells, in order to determine the effect of nuclear size, cell deformability, and cell-to-substrate adhesion on tissue invasion efficiency. The high spatial and temporal resolution of our analysis demonstrates that the ability of cells to deform depends on the cell cycle phase, peaks immediately after mitosis, and is key to the invasion process. Increased pore penetration efficiency by cells in early G1 phase also coincided with their lower nuclear volume and higher cell deformability, compared with the later cell cycle stages. Furthermore, artificial decondensation of chromatin induced an increase in cell and nuclear deformability and improved pore penetration efficiency of cells in G1. Together, these results underline that along the cell cycle cells have different abilities to dynamically remodel their actin cytoskeleton and induce nuclear shape changes, which determines their pore penetration efficiency. Thus, our results support a mechanism in which cell proliferation and pore penetration are functionally linked to favor the interstitial dissemination of metastatic cells.

Involvement of histone H3 phosphorylation through p38 MAPK pathway activation in casticin-induced cytocidal effects against the human promyelocytic cell line HL-60

The effect of casticin was investigated by focusing on cell viability, apoptosis induction and cell cycle arrest in HL-60 cells. Casticin induced a dose- and time-dependent decrease in cell viability associated with apoptosis induction and G2/M cell cycle arrest. The addition of SB203580, an inhibitor for p38 mitogen-activated protein kinase (MAPK), but not SP600125 [c-Jun NH2-terminal protein kinase (JNK) inhibitor] and PD98059 [extracellular signal-regulated kinase (ERK) inhibitor], abrogated casticin-induced cell cycle arrest and apoptosis associated with the activation of caspases including caspase-8, -9 and -3. Endogenous p38 MAPK activation was observed in untreated cells based on the detection of the expression levels of phospho-p38 MAPK, whereas casticin did not affect the degree of p38 MAPK activation. Interestingly, the addition of SB203580 suppressed casticin-induced phosphorylation of histone H3, a downstream molecule of the p38 MAPK signaling pathway and known to be involved in chromosome condensation during mitosis. More importantly, casticin induced upregulation of intracellular ATP levels. Although casticin induced intracellular reactive oxygen species, antioxidants failed to block casticin-mediated cytotoxicity, indicating that casticin-induced cytotoxicity appears to be independent of reactive oxygen species generation. Based on the fact that SB203580 has been reported to compete with ATP for binding to the active form of p38 MAPK, and consequently blocks the p38 MAPK activity in activating downstream molecules, these results suggest that casticin induces cytotoxicity associated with apoptosis and cell cycle arrest in HL-60 cells through the p38 MAPK pathway, in which intracellular ATP levels and phosphorylation of histone H3 play critical roles.

Role of phosphorylated histone H3 serine 10 in DEN-induced deregulation of Pol III genes and cell proliferation and transformation

The products of Pol III genes (RNA polymerase III-dependent genes), such as tRNAs and 5S rRNA, are elevated in both transformed and tumor cells suggesting that they play a crucial role in tumorigenesis. An increase in Brf1 (TFIIIB-related factor 1), a subunit of TFIIIB, augments Pol III gene transcription and is sufficient for cell transformation and tumor formation. We have demonstrated that enhancement of Brf1 and Pol III gene expression is associated with the occurrences of hepatocellular carcinoma (HCC) in mice. This suggests that Brf1 may be a key molecule during HCC development. Diethylnitrosamine (DEN), a chemical carcinogen, has been used to induce HCC in rodents. To determine the role of Brf1 and the epigenetic-regulating events in cell proliferation and transformation, hepatocytes were treated with DEN. The results indicate that DEN increases proliferation and transformation of AML-12 cells. DEN enhanced Brf1 expression and tRNA(Leu) and 5S rRNA transcription, as well as H3S10ph (phosphorylation of histone H3 serine 10). Interestingly, DEN-induced Pol III gene transcription and H3S10ph in tumor cells of liver are significantly higher than in non-tumor cells. Inhibition of H3S10ph by H3S10A attenuates the induction of Brf1 and Pol III genes. Further analysis indicates that H3S10ph occupies the promoters of Brf1 and Pol III genes to modulate their expression. Blocking H3S10ph represses cell proliferation and transformation. These results demonstrate that DEN induces H3S10ph, which mediate Brf1 expression, including but not limited Brf1-dependent genes, to upregulate Pol III gene transcription, resulting in an increase in cell proliferation and transformation.

HDAC inhibitors prevent the induction of the immediate-early gene FOSL1, but do not alter the nucleosome response

Dynamic histone acetylation, catalyzed by lysine acetyltransferases and HDACs, is critical to IEG expression. Expression of IEGs, such as FOSL1, is induced by several signal transduction pathways resulting in activation of the protein kinase MSK and phosphorylation of histone H3 at serine 10 of nucleosomes (the nucleosome response) at the upstream promoter and regulatory region of target genes. HDAC inhibitors prevent FOSL1 gene induction and the association of HDAC1, 2 and 3 with the gene body. However, HDAC inhibitors did not prevent the nucleosome response. Thus HDAC inhibitors perturb events downstream of the nucleosome response required for FOSL1 transcription initiation.

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.

Histone H3 phosphorylation (Ser10, Ser28) and phosphoacetylation (K9S10) are differentially associated with gene expression in liver of rats treated in vivo with acute ethanol

The epigenetic histone modification by ethanol is emerging as one of the mechanisms for its deleterious effects in the liver. In this context, we have investigated the role of histone H3 phosphorylation at Ser10 (P-H3-Ser10), and Ser28 (P-H3-Ser28) in liver after acute ethanol treatment in vivo. Ethanol was administered intraperitoneally in male Sprague-Dawley rats. Ethanol dose-response (1-5 g/kg body weight) and time-course (1-4 h) experiments were conducted, and various parameters were monitored. Steatosis and necrosis (serum alanine aminotransferase) of the liver increased in 4 h, suggesting liver injury. There were differences between P-H3-Ser10 and P-H3-Ser28 at 1 h, with the latter being more sensitive to lower ethanol doses. It was noteworthy that phosphorylation of both serines disappeared at the highest dose used (5 g/kg). We also examined phosphoacetylation of histone H3 at K9S10 and observed a dramatic increase. The changes in histone H3 phosphorylation and phosphoacetylation were also accompanied with expression of early response genes (c-fos, c-jun, mitogen-activated protein kinase phosphatase-1). Chromatin immunoprecipitation assays in samples from 1.5 and 4 h of ethanol administration indicated that increased histone H3 phosphorylation at Ser28 was associated with the promoters of c-jun and plasminogen activator inhibitor-1. In conclusion, this study demonstrates for the first time that in vivo exposure of liver to acute ethanol induced phosphorylation and phosphoacetylation of histone H3, and these modifications are differentially involved in the mRNA expression of genes.

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.

Novel electrostatic mechanism for mode of action by N-acetylated proteins: cell signaling and phosphorylation

Although extensive literature exists for N-acetylated proteins, scant knowledge is available concerning resultant mode of action. This review presents a novel mechanism based on electrostatics and cell signaling. There is substantial increase in the amide dipole and electrostatic field (EF) in contrast with the primary amino of the lysine precursor. The EF might serve as a bridge in electron transfer and cell signaling or energetics may play a role. The relationship between N-acetylation and phosphorylation is addressed. EFs may be important in the case of phosphates. Involvement of cell signaling is addressed including mechanistic aspects. As is the case for many aspects of bioaction, an integrated approach involving electrochemistry and cell signaling seems reasonable.

Phosphorylation of histone H3 serine 28 modulates RNA polymerase III-dependent transcription

Deregulation of RNA polymerase III (Pol III) transcription enhances cellular tRNAs and 5S rRNA production, leading to an increase in translational capacity to promote cell proliferation, transformation and tumor formation. Phosphorylation of histone H3 (H3ph) is induced by tumor promoters (EGF, UV and TPA) and immediate early genes, such as c-myc, c-jun and c-fos. However, it remains to be determined whether H3ph is involved in RNA Pol III transcription. Here, we report that EGF strongly induced H3ph at serine 28 (H3S28ph). EGF significantly increased transcription of RNA Pol III-dependent genes (Pol III genes), tRNA^Leu, tRNA^Tyr, 5S rRNA, and 7SL RNA. Inhibition of EGFR, but not PI3K, reduced both H3S28ph and tRNA^Leu and 5S rRNA transcription. EGF enhanced occupancy of H3S28ph in the promoters of tRNA^Leu and 5S rRNA. Further analysis indicates that EGF augmented cellular levels of protein and mRNA of TFIIIB subunits, Brf1 and TBP. Brf1 is a specific transcription factor for RNA Pol III genes. EGF enhanced occupancy of H3S28ph in the Brf1 and TBP promoters. Inhibition of H3S28ph by mutant H3S28A repressed Brf1, TBP and tRNA^Leu and 5S rRNA expression and decreased occupancy of H3S28ph in their promoters. Reduction of Brf1 significantly decreased tRNA^Leu and 5S rRNA transcription and repressed EGF-induced anchorage-independent growth. Blocking H3S28ph signaling by using mutant H3S28A reduced EGF-induced cell transformation. Together, these results indicate that EGF activates EGFR signaling to induce H3S28ph, which, in turn, upregulates tRNA^Leu and 5S rRNA transcription through Brf1 and TBP and promotes cell transformation. The studies demonstrate that epigenetic modification of H3S28ph plays a critical role in the activity of Pol III genes.

Autotaxin is induced by TSA through HDAC3 and HDAC7 inhibition and antagonizes the TSA-induced cell apoptosis

Background

Autotaxin (ATX) is a secreted glycoprotein with the lysophospholipase D (lysoPLD) activity to convert lysophosphatidylcholine (LPC) into lysophosphatidic acid (LPA), a bioactive lysophospholipid involved in diverse biological actions. ATX is highly expressed in some cancer cells and contributes to their tumorigenesis, invasion, and metastases, while in other cancer cells ATX is silenced or expressed at low level. The mechanism of ATX expression regulation in cancer cells remains largely unknown.

Results

In the present study, we demonstrated that trichostatin A (TSA), a well-known HDAC inhibitor (HDACi), significantly induced ATX expression in SW480 and several other cancer cells with low or undetectable endogenous ATX expression. ATX induction could be observed when HDAC3 and HDAC7 were down-regulated by their siRNAs. It was found that HDAC7 expression levels were low in the cancer cells with high endogenous ATX expression. Exogenous over-expression of HDAC7 inhibited ATX expression in these cells in a HDAC3-dependent manner. These data indicate that HDAC3 and HDAC7 collaboratively suppress ATX expression in cancer cells, and suggest that TSA induce ATX expression by inhibiting HDAC3 and HDAC7. The biological significance of this regulation mechanism was revealed by demonstrating that TSA-induced ATX protected cancer cells against TSA-induced apoptosis by producing LPA through its lysoPLD activity, which could be reversed by BrP-LPA and S32826, the inhibitors of the ATX-LPA axis.

Conclusions

We have demonstrated that ATX expression is repressed by HDAC3 and HDAC7 in cancer cells. During TSA treatment, ATX is induced due to the HDAC3 and HDAC7 inhibition and functionally antagonizes the TSA-induced apoptosis. These results reveal an internal HDACi-resistant mechanism in cancer cells, and suggest that the inhibition of ATX-LPA axis would be helpful to improve the efficacy of HDACi-based therapeutics against cancer.

Chromosomal position effects on AAV-mediated gene targeting

The effects of chromosomal position and neighboring genomic elements on gene targeting in human cells remain largely unexplored. To study these, we used a shuttle vector system in which murine leukemia virus (MLV)-based proviral targets present at different chromosomal locations and containing mutations in the neomycin phosphotransferase (neo) gene were corrected by adeno-associated virus (AAV)-mediated gene targeting. Sixteen identical target loci present in HT-1080 human sarcoma cells were all successfully corrected by gene targeting. The gene targeting frequencies varied by as much as 10-fold, and there was a clear bias for correction of one of the targets in clones containing two target sites. The targeting frequency at each site was correlated to the proximity and density of various genomic elements, and we found a significant association of higher targeting frequencies at loci near a subset of dinucleotide microsatellite repeats (r = –0.55, P < 0.05), in particular GT repeats (r = –0.87, P < 0.0001). Additionally, there was a correlation between meiotic recombination rates and targeting frequencies at the target loci (r = 0.52, P < 0.05). There was no correlation between surrounding chromosomal transcription units and targeting frequencies. Our results indicate that certain chromosomal positions are preferred sites for gene targeting in human cells.

Lysophosphatidic acid protects cancer cells from histone deacetylase (HDAC) inhibitor-induced apoptosis through activation of HDAC

Histone deacetylases (HDACs) catalyze the removal of acetyl groups from histones and contribute to transcriptional repression. In addition, the HDAC inhibitors induce apoptosis in cancer cells through alterations in histone acetylation and activation of the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) apoptotic pathway. Lysophosphatidic acid (LPA) is a growth factor that promotes survival of cancer cells through activation of G protein-coupled receptors. Here we show that HDAC inhibitors can induce apoptosis through activation of the TRAIL apoptotic pathway, and LPA prevented HDAC inhibitor-induced apoptosis and increased TRAIL receptor DR4 (death receptor 4) protein expression. This was associated with increased HDAC1 recruitment to the DR4 promoter following LPA treatment and a reduction in HDAC inhibitor-induced histone acetylation in the DR4 promoter. In addition, LPA induces HDAC enzyme activity in a dose- and time-dependent manner, and this is associated with HDAC1 activation and increased binding of HDAC1 to HDAC2. Reducing the expression of HDAC1 significantly lowered LPA-induced HDAC activity and increased histone acetylation. LPA induction of HDAC activity was blocked by the LPA receptor antagonist, Ki16425, or by inhibiting receptor activation with pertussis toxin. Reducing the expression of the LPA receptor LPA(1) also blocked LPA-induced HDAC activation. In addition, LPA reduced histone acetyltransferase enzymatic activity. Finally, LPA attenuated the ability of the HDAC inhibitor to reduce HDAC activity. Thus, LPA enhances survival of cancer cells by increasing HDAC activity and reducing histone acetylation.

Sirtuins, nuclear hormone receptor acetylation and transcriptional regulation

Endocrine signaling via nuclear receptors (NRs) is known to play an important role in normal physiology as well as in human tumor progression. Hormones regulate gene expression by altering local chromatin structure and, thereby, accessibility of transcriptional co-regulators to DNA. Recently it has been shown that non-histone proteins involved in hormone signaling, such as nuclear receptors and NR co-activators, are regulated by acetylation, resulting in their altered transcriptional activity. NAD-dependent protein deacetylases, the sirtuins (Sir2-related enzymes), directly modify NRs. Because sirtuins have been shown to regulate tumor cellular growth, aging, metabolic signaling and endocrine hormone signaling, they might play a role in cancer progression. This review focuses on the role of acetylation and the sirtuins in nuclear hormone receptor signaling.

Signaling cascades triggered by bacterial metabolic end products during reactivation of Kaposi's sarcoma-associated herpesvirus

The present studies explore the role of polymicrobial infection in the reactivation of Kaposi's sarcoma-associated herpesvirus (KSHV) and analyze signaling pathways activated upon this induction. We hypothesized that activation of the cellular stress-activated mitogen-activated protein kinase (MAPK) p38 pathway would play a key role in the bacterium-mediated disruption of viral latency similar to that of previously reported results obtained with other inducers of gammaherpesvirus lytic replication. KSHV within infected BCBL-1 cells was induced to replicate following exposure to metabolic end products from gram-negative or -positive bacteria that were then simultaneously exposed to specific inhibitors of signal transduction pathways. We have determined that bacterium-mediated induction of lytic KSHV infection is significantly reduced by the inhibition of the p38 MAPK pathway. In contrast, inhibition of the phosphatidylinositol 3-kinase pathway did not impair induction of lytic replication or p38 phosphorylation. Protein kinase C, though activated, was not the major pathway used for bacterium-induced viral reactivation. Furthermore, hyperacetylation of histones 3 and 4 was detected. Collectively, our results show that metabolic end products from these pathogens induce lytic replication of KSHV in BCBL-1 cells primarily via the activation of a stress-activated MAPK pathway. Importantly, we demonstrate for the first time a mechanism by which polymicrobial bacterial infections result in KSHV reactivation and pathogenesis.

Polybromo-1-bromodomains bind histone H3 at specific acetyl-lysine positions

The human polybromo-1 protein is thought to localize the Polybromo, BRG1-associated factors chromatin-remodeling complex to kinetochores during mitosis via direct interaction of its six tandem bromodomains with acetylated nucleosomes. Bromodomains are acetyl-lysine binding modules roughly 100 amino acids in length originally found in chromatin associated proteins. Previous studies verified acetyl-histone binding by each bromodomain, but site-specificity, a central tenet of the histone code hypothesis, was not examined. Here, the acetylation site-dependence of bromodomain-histone interactions was examined using steady-state fluorescence anisotropy. Results indicate that single bromodomains bind specific acetyl-lysine sites within the histone tail with sub-micromolar affinity. Identification of duplicate target sites suggests that native Pb1 interacts with both copies of histone H3 upon nucleosome assembly. Quantitative analysis of single bromodomain-histone interactions can be used to develop hypotheses regarding the histone acetylation pattern that acts as the binding target of the native polybromo-1 protein.

Human endometrial cytodifferentiation by histone deacetylase inhibitors

Abstract Human uterine endometrium repeats proliferation, differentiation (decidualization) and tissue breakdown during the menstrual period. Appropriate secretion of ovarian steroid hormones regulates these sequential endometrial remodeling cycles. While progesterone replacement therapy is adopted for endometrial dysfunction of differentiation, including recurrent impairment of implantation, no obvious effective results are obtained. Histone reversible acetylation, regulated by histone acetyltransferases and histone deacetylases plays a pivotal role in gene transcription. Although, in cells cultured with histone deacetylase inhibitors (HDACI), the expression of only about 2% of expressed genes is changed twofold or more compared with untreated control cells. Numerous previous works have demonstrated that HDACI affect cell proliferation/apoptosis in a variety of types of cells. To date, several HDACI are in phase I or phase II clinical trials as anticancer drugs. However, no reports have been found that HDACI is useful for transdifferentiation in human endometrium. Recently, we reported that HDACI could induce the expression of differentiation marker proteins, morphological change and functional cytodifferentiation in both human endometrial stromal and epithelial cells. In this review, we summarize the effect of HDACI against the human endometrial cytodifferentiation, indicating the possibility that HDACI can be used not only as an anticancer drug, but also as a transdifferentiation reagent, based on a new strategy.

Effects of histone deacetylase inhibitors on transcriptional regulation of the hsp70 gene in Drosophila

Histone acetyltransferases/deacetylases contribute to the activation or inactivation of transcription by modifying the structure of chromatin. Here we examined the effects of histone deacetylase inhibitors (HDIs), trichostatin A, and sodium butyrate on hsp70 gene transcriptional regulation in Drosophila. The chromatin immunoprecipitation assays revealed that HDI treatments induced the hyperacetylation of histone H3 at the promoter and the transcribing regions of hsp70 gene, increased the accessibility of heat-shock factor to target heat-shock element, and promoted the RNA polymerase II-mediated transcription. Moreover, the quantitative real-time PCR confirmed that the HDI-induced hyperacetylation of histone H3 enhanced both the basal and the inducible expression of hsp70 mRNA level. In addition, the acetylation level of histone H3 at the promoter exhibited a fluctuated change upon the time of heat shock. These experimental data implicated a causal link between histone acetylation and enhanced transcription initiation of hsp70 gene in Drosophila.

Alteration of Developmental Program in Paramecium by Treatment with Trichostatin A: A Possible Involvement of Histone Modification

In the ciliate Paramecium caudatum, the somatic macronucleus for the next generation differentiates from a zygotic germinal micronucleus during conjugation. Subsequently, progeny are programmed to enter a sexually "immature" period, during which cells do not mate. This programming occurs at a critical period during the fifth cell cycle after conjugation. Here, we show that treatment with trichostatin A, a histone deacetylase inhibitor, leads to a partial recovery of mating reactivity in immature cells, suggesting that histone acetylation can affect the developmental program. In addition, immunostaining demonstrated that Lys 4 methylation of histone H3 was absent from or present at an undetectable level in the nascent macronucleus during the first cell cycle after conjugation. The methylation level gradually increased in proportion to de novo DNA synthesis, until the new macronucleus reached the maximum level of methylation, concomitant with its full maturation. A link between gene expression and Lys 4 methylation is indirectly supported by the observation that a transcriptionally active gene was enriched by chromatin immunoprecipitation with an antibody directed against methyl-Lys 4 H3, whereas a silent gene was not. These results provide evidence that histone modification plays a key role in the regulation of gene expression and the developmental programming that determine sexual immaturity after conjugation.

A histone deacetylation-dependent mechanism for transcriptional repression of the gap junction gene cx43 in prostate cancer cells

BACKGROUND

The connexin 43 gene (cx43, GJA1) mediates gap junctional intercellular communication (GJIC), which regulates tissue homeostasis. cx43 is frequently downregulated in prostate cancer. We investigated the role of a histone deacetylase (HDAC)-dependent mechanism in the transcriptional repression of cx43 in a panel of prostate cancer cells.

METHODS

The impact of Trichostatin A (TSA), an inhibitor of HDAC, on exogenous and endogenous cx43 gene transcription was examined by the luciferase assay, Northern blot, nuclear run-on, Western blot, and chromatin immunoprecipitation assays.

RESULTS

Trichostatin A induces transcription of cx43 gene and GJIC. The co-activator p300/CBP synergizes with TSA for cx43 promoter activation. We identified a promoter region where cooperation between Ap1 and Sp1 elements was essential for TSA-induced cx43 transcription. TSA increased the level of hyperacetylated histones bound to cx43 promoter.

CONCLUSION

Our results highlight the potential utility of inhibitors of HDAC to restore cx43 gene expression in prostate cancer.

The role of histone H3 phosphorylation (Ser10 and Ser28) in cell growth and cell transformation

Histones are now regarded as integral and dynamic components of the machinery responsible for regulating gene transcription. Many types of cancer and other diseases are associated with translocations or mutations in chromatin-modifying enzymes and regulatory proteins. Much of the work in our laboratory has focused on identifying novel histone H3 kinases and the role of histone H3 phosphorylation in cell proliferation and transformation. We are beginning to unravel the complexities of gene expression mediated by histone H3 phosphorylation, which is induced by a whole host of diverse stimuli. Dissimilar cells respond differentially to distinct stimuli, and induction of gene expression is dependent on the type of stimuli, duration and strength of stimuli, state of the cell and of course, specific cell type. Thus, regulation of histone modifications and resultant gene expression is not just one- or two-dimensional but multidimensional, encompassing a huge array of factors. Significant findings such as the observation that histone H3 phosphorylation (Ser10) is critical for neoplastic cell transformation suggests that histone H3 may be a crucial target for cancer chemotherapy or genetic therapy in the future.

Histone deacetylase inhibitors induce differentiation of human endometrial adenocarcinoma cells through up-regulation of glycodelin

Histone reversible acetylation, which is controlled by histone acetyltransferases and deacetylases, plays a fundamental role in gene transcription. Histone deacetylase inhibitors (HDACIs), such as trichostatin A (TSA) and suberoylanilide hydroxamic acid (SAHA), have been characterized not only as anticancer drugs, but also as cytodifferentiation-inducing agents. In human endometrium, postovulatory production of progesterone directs estrogen-primed endometrial glandular cells to differentiate and thereby produce a number of unique bioactive substances, including glycodelin, that are critical for implantation at the secretory phase of the menstrual cycle. In this study, we show that TSA and SAHA, belonging to the hydroxamic acid group of HDACIs, can induce the phenotype of a human endometrial adenocarcinoma cell line, Ishikawa (originally derived from the glandular component of the endometrium), to differentiate to closely resemble normal endometrial epithelium in a time- and dose-dependent manner, as determined by morphological changes, synthesis of glycogen, and expression of secretory phase-specific proteins, including glycodelin. The proliferation- and differentiation-modulating effects elicited by TSA and SAHA at their optimal concentrations were comparable or more potent than those exerted by combined treatment with progesterone and estradiol. Furthermore, the gene silencing of glycodelin by small interference RNA resulted in the blockade of HDACI-induced differentiation in Ishikawa cells, suggesting the requirement for glycodelin for endometrial epithelial differentiation. Our results collectively indicate that TSA and SAHA are potent differentiation inducers for endometrial glandular cells, providing a clue for a possible therapeutic strategy to modulate endometrial function by targeting glycodelin.

Histone modifications as a platform for cancer therapy

Tumorigenesis and metastasis are a progression of events resulting from alterations in the processing of the genetic information. These alterations result from stable genetic changes (mutations) involving tumor suppressor genes and oncogenes (e.g., ras, BRAF) and potentially reversible epigenetic changes, which are modifications in gene function without a change in the DNA sequence. Mutations of genes coding for proteins that directly or indirectly influence epigenetic processes will alter the cell's gene expression program. Epigenetic mechanisms often altered in cancer cells are DNA methylation and histone modifications (acetylation, methylation, phosphorylation). This article will review the potential of these reversible epigenetic processes as targets for cancer therapies.

Effects of histone acetylation on sodium iodide symporter promoter and expression of thyroid-specific transcription factors

Inhibitors of histone deacetylases (HDACs) activate the sodium iodide symporter (NIS) expression in thyroid tumor cells. In this study, mechanisms accounting for these effects were investigated. Various human thyroid tumor cell lines (ARO, BCPAP, FRO, TPC-1) were treated with the HDAC inhibitors Na butyrate (NaB) and tricostatin A (TSA), and the effects on the expression of NIS and several thyroid-specific transcription factors together with the activity of NIS promoter were evaluated. TSA and NaB increased NIS mRNA levels in all cell lines. Among thyroid-specific transcription factors, only expression of PAX8 in ARO cells was increased. Down-regulation of thyroid-specific transcription factor-1 expression was observed in BCPAP and TPC-1 cell lines. Thyroid-specific transcription factor-2 mRNA was reduced in FRO, BCPAP, and TPC-1 cells. Histone acetylation had no significant effects on HEX expression. Altogether, these data indicate that the increase of NIS expression is not mediated by modification of expression of thyroid-specific transcription factors. Accordingly, in transfection experiments performed in the HeLa cell line (which does not express thyroid-specific transcription factors), treatment with TSA and NaB increased NIS promoter activity. Stimulation of NIS promoter activity was also obtained by overexpressing histone acetylating proteins pCAF and p300 in HeLa cells. Conversely, overexpression of the HDAC 1 enzyme inhibited basal activity of the NIS promoter. Effects of TSA and NaB on NIS expression were also evaluated in nonthyroid cell lines MCF-7, Hep-G2, and SAOS-2. In all cell lines TSA and NaB greatly increased NIS mRNA levels. We concluded that control of NIS expression by inhibition of HDAC appears not to be mediated by cell-specific mechanisms, suggesting it as a potential strategy to induce radioiodine sensitivity in different human tumors.

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

ERK and p38 MAP kinases, acting through the downstream mitogen- and stress-activated kinase 1/2 (MSK1/2), elicit histone H3 phosphorylation on a subfraction of nucleosomes – including those at Fos and Jun – concomitant with gene induction. S10 and S28 on the H3 tail have both been shown to be phospho-acceptors in vivo. Both phospho-epitopes appear with similar time-courses and both occur on H3 tails that are highly sensitive to TSA-induced hyperacetylation, similarities which might suggest that MSK1/2 phosphorylates both sites on the same H3 tails. Indeed, on recombinant histone octamers in vitro, MSK1 efficiently phosphorylates both sites on the same H3 tail. However, sequential immunoprecipitation studies show that antibodies against phosphorylated S10-H3 recover virtually all this epitope without depletion of phosphorylated S28-H3, and vice versa, indicating that the two phospho-epitopes are not located on the same H3 tail in vivo. Confocal immunocytochemistry confirms the clear physical separation of the two phospho-epitopes in the intact mouse nucleus. Finally, we used transfection-based experiments to test models that might explain such differential targeting. Overexpression and delocalisation of MSK1 does not result in the breakdown of targeting in vivo despite the fact that the ectopic kinase is fully activated by external stimuli. These studies reveal a remarkable level of targeting of S10 and S28 phosphorylation to distinct H3 tails within chromatin in the interphase mouse nucleus. Possible models for such exquisite targeting are discussed.

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.

Lifespan extension and elevated hsp gene expression in Drosophila caused by histone deacetylase inhibitors

The heat shock proteins (Hsps) play a positive role in lifespan determination, and histone acetylation has been shown to be involved in transcription of hsp genes in Drosophila. To further determine if hsp22 and hsp70 expression is correlated with lifespan, and if histone acetylation participates in this process, RNA levels for hsp22 and hsp70 were analyzed throughout the lifespan in the long-lived and short-lived iso-female lines. The results showed that hsp22 and hsp70 RNA levels were higher in long-lived line than in short-lived line and that the long-lived flies responded more rapidly to heat but were more tolerant to high temperature. Moreover, we investigated the influences of histone acetylation modification on longevity and on hsp gene expression by using histone deacetylase (HDAC) inhibitors TSA and BuA. The results demonstrated that both inhibitors were able to extend the lifespan and promote hsp22 and hsp70 expression. However, the optimal concentrations of these inhibitors, and probably the mechanisms of their actions, vary with the genetic background. In addition, we showed that HDAC inhibitors caused the hyperacetylation of core histone H3, implicating the involvement of chromatin modulation in hsp gene transcription. These data suggested a close correlation among histone acetylation, hsp gene expression and longevity in D. melanogaster.

Histone acetylation regulates both transcription initiation and elongation of hsp22 gene in Drosophila

Histone acetylation is associated with transcriptional activation of many genes. However, the role of acetylation in transcriptional regulation of heat shock protein genes (hsp) still remains an obscure issue. Here we examined the effects of histone deacetylase inhibitors (HDIs), trichostatin A, and sodium butyrate, on changes in acetylation level of core histones and on expression of hsp22 gene in Drosophila melanogaster. The results showed that both HDIs elevated the acetylation level of histone H3. By using the chromatin immunoprecipitation, we located the HDI-induced H3 hyperacetylation at both the promoter and the downstream of RNA polymerase II of the transcribing hsp22 gene. Meanwhile, the elevated acetylation level increased the accessibility of heat shock factor to target cis-acting regulatory sites. We conclude that histone acetylation stimulates the transcription initiation and promotes the transcription elongation, thereby up-regulating both basal and inducible expression of hsp22 in D. melanogaster.

Sp1 and Sp3 transcription factors mediate trichostatin A-induced and basal expression of extracellular superoxide dismutase

Extracellular superoxide dismutase (EC-SOD) is the major extracellular antioxidant enzyme and may play a critical role in the pathogenesis of a variety of pulmonary, neurological, and cardiovascular diseases. We report here that exposure to the deacetylase inhibitor trichostatin A (TSA) induces EC-SOD mRNA levels in mIMCD3 and Hepa 1-6 cells, but reduces EC-SOD mRNA levels in MLg cells. To determine the molecular mechanism of TSA-mediated EC-SOD gene regulation, we analyzed EC-SOD's proximal promoter region, which revealed two previously unknown but putative Sp1 cis elements. Transfection of systematically truncated 5'-flanking sequences revealed that the second Sp1 binding site contributes up to 70% of the constitutive EC-SOD promoter activity. Binding of Sp1 and Sp3 transcription factors to this region was confirmed by DNase I footprinting, electrophoretic mobility shift assay, super-shift assay, and chromatin immunoprecipitation. A dominant-negative Sp1 construct considerably reduced EC-SOD promoter activity in mammalian cells, whereas coexpression of Sp1 and Sp3 greatly enhanced reporter activity in SL2 cells. An EC-SOD promoter-reporter construct showed from 5- to 14-fold induction after exposure to TSA, whereas deletion of the Sp1 binding site significantly reduced reporter activation. These results are consistent with Sp1/Sp3 transcription factors providing essential TSA-dependent and basal transcription of the EC-SOD gene and may represent a novel pharmacological pathway for regulating EC-SOD levels in tissue.

The androgen receptor acetylation site regulates cAMP and AKT but not ERK-induced activity

The androgen receptor (AR) regulates ligand-dependent gene transcription upon binding specific DNA sequences. The AR conveys both trans-activation and trans-repression functions, which together contribute to prostate cellular growth, differentiation, and apoptosis. Like histone H3, the AR is post-translationally modified by both acetylation and phosphorylation. The histone acetyltransferase p300 transactivates the AR and directly acetylates the AR in vitro at a conserved motif. Point mutations of the AR acetylation motif that abrogate acetylation reduce trans-activation by p300 without affecting the trans-repression function of the AR. The current studies assessed the functional relationship between acetylation and phosphorylation of the AR. Herein trans-activation of the AR acetylation site mutants were enhanced by the p42/p44 MAPK pathway but were defective in regulation by protein kinase A (PKA) signaling. PKA inhibition augmented ARwt activity but not AR acetylation mutant gene reporter activity and association at an androgen response element in chromatin immunoprecipitation assays. Mutations of the lysine residues at the AR acetylation site reduced trichostatin A (TSA) responsiveness and ligand-induced phosphorylation of the AR. The AR acetylation site mutant formed ligand-induced phosphorylation-dependent isoforms with distinguishable characteristics from wild type AR as determined with two-dimensional electrophoresis. Conversely, point mutation of a subset of AR phosphorylation sites reduced trichostatin A responsiveness and trans-activation by histone acetyltransferases. Together these studies suggest that acetylation and phosphorylation of the AR are linked events and that the conserved AR lysine motif contributes to a select subset of pathways governing AR activity.

Cisplatin-induced post-translational modification of histones H3 and H4

The anti-cancer drug cisplatin kills cells by damaging DNA and inducing apoptosis. Understanding the detailed mechanisms by which cancer cells respond to cisplatin has the potential to improve substantially platinum-based therapy. Post-translational modification of histones alters chromatin structure, facilitating the binding of nuclear factors that mediate DNA repair, transcription, and other processes. In the present study, we have investigated the effects of cisplatin treatment on histone post-translational modification in cancer cells. We discovered that specific phosphorylation of histone H3 at Ser-10, mediated by the p38 MAPK pathway, is induced in response to cisplatin treatment. In addition, hyperacetylation of histone H4 was caused by drug treatment. These findings revealed a link between cisplatin administration and chromosomal structural alterations, providing mechanistic information about how cells respond to platinum-induced stress.