H3 Phosphorylation Research Articles

Abstract B82: G-protein coupled estrogen receptor (GPER) agonist G-1 inhibits growth of human granulosa cell tumor cells via blocking microtubule assembly

Abstract Accumulating evidence indicates that the G-protein coupled estrogen receptor (GPER) mediates the non-genomic actions of estrogen in many different cells and tissues. The selective GPER agonist G-1 (1-[4-(6-bromobenzo[1,3]dioxol-5yl)-3a,4,5,9b-tetrahydro- 3H-cyclopenta[c]quinolin-8-yl]-ethanone) was developed to distinguish estrogen actions mediated by GPER from those mediated by the traditional nuclear estrogen receptors. Our recent data showed that G-1 suppresses the growth of breast and ovarian cancer cells in a GPER-independent manner. However, the mechanisms underlying the suppressive actions of G-1 on cancer cell growth are still unclear. The aim of the present study was to explore potential mechanisms of G-1 action in human ovarian granulosa tumor cells. The KGN cell line, a cell line derived from a metastatic adult ovarian granulosa cell tumor (aGCT), and the COV434 cell line, a cell line derived from a juvenile granulosa cell tumor (jGCT), were used as cellular models. Cell proliferation and viability were determined by cell number counting and MTT assay, respectively. Cell cycle analysis was monitored by flow cytometry. Key proteins associated with cell cycle progression were analyzed with Western blot. Cell apoptosis was detected by analysis of caspase activity and DNA integrity. Cellular cytoskeleton changes were monitored by fluorescent immunocytochemistry, confocal microscopy and in vitro microtubule assembly assays. Consistent with our previous results, the putative GPER agonist G-1 suppressed proliferation in a concentration- and time-dependent manner in both KGN and COV434 cells. G-1 inhibited GCT cell growth via suppressing cell viability, which was indicated by a significant decrease in the MTT metabolism, an increase in DNA fragmentation, and an increase in PARP cleavage. G-1 treatment did not affect the expression of cyclin D1, cyclin D2 and cyclin E, suggesting that G-1 treatment had no effect on the early stage cell cycle progression, a result further confirmed by flow cytometry. However, flow cytometry showed that G-1 treatment arrested the cell cycle in the G2/M phase. G2/M phase arrest of KGN cells was confirmed by a significant increase in the phosphorylation of histone H3 after G-1 treatment. Surprisingly, the Western blot analysis showed that G-1 treatment did not affect the activation of mitotic promoting factors (MPF) and had no effect on G2/M entry checkpoint proteins and kinases. Fluorescent immunocytochemistry and confocal microscopy showed that G-1 treatment disrupted the segregation of chromosomes during mitosis, an effect that may be attributed to the abnormal assembly of microtubules. In vitro microtubule assembly assays demonstrated that G-1 treatment indeed suppressed tubulin polymerization and thereby inhibited the assembly of the microtubules. In conclusion, our results from the present study demonstrate that G-1, the putative GPER agonist, suppresses GCT cell proliferation and induces tumor cell death via blocking microtubule assembly. The ability of G-1 to suppress tumor cell proliferation and induce tumor cell apoptosis by targeting microtubules makes it a promising candidate drug for the treatment of GCT. Citation Format: Xiangmin Lv, Guohua Hua, Chunbo He, John S Davis, Cheng Wang. G-protein coupled estrogen receptor (GPER) agonist G-1 inhibits growth of human granulosa cell tumor cells via blocking microtubule assembly. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: From Concept to Clinic; Sep 18-21, 2013; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2013;19(19 Suppl):Abstract nr B82.

Higher anti‐tumour efficacy of platinum(IV) complex LA‐12 is associated with its ability to bypass M‐phase entry block induced in oxaliplatin‐treated human colon cancer cells

Therapeutic potential of conventionally used platinum-based drugs in treatment of colorectal tumours has been limited due to high incidence of tumour resistance to them and to their severe side effects. This evokes a search for more suitable anti-cancer drugs. We have compared ability of oxaliplatin and a novel platinum(IV) complex, LA-12, to modulate the cell cycle and induce apoptosis in human colon adenocarcinoma HCT116 wt and p53/p21 null cells, and have investigated molecular mechanisms involved. Cell cycle-related changes were analysed by flow cytometry (bromodeoxyuridine/propidium iodide staining, histone H3 phosphorylation). Apoptosis was detected using flow cytometry (assays monitoring caspase activity) and fluorescence microscopy (nuclear morphology). Changes in levels of genes/proteins involved in cell cycle and apoptosis regulation were examined by RT-PCR and western blotting. Our results highlight the outstanding ability of LA-12 to induce effective elimination of colon cancer cells independently of p53/p21, and in significantly lower doses compared to oxaliplatin. While oxaliplatin induced p53- and p21-dependent G2 -phase arrest associated with downregulation of cyclin B1 and Cdk1, LA-12 allowed cells to enter M-phase of the cell cycle regardless of p53/p21 status. Higher malignant cell toxicity and ability to bypass cell cycle arrest important for the cell damage repair suggest LA-12 to be a more effective candidate for elimination of colon tumours from a variety of genetic backgrounds, compared with oxaliplatin.

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.

Corticosteroids Inhibit Sphingosine 1-Phosphate–Induced Interleukin-6 Secretion from Human Airway Smooth Muscle via Mitogen-Activated Protein Kinase Phosphatase 1–Mediated Repression of Mitogen and Stress-Activated Protein Kinase 1

Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid that plays an important proinflammatory role in asthmatic airways. Corticosteroids are first-line antiinflammatories in asthma; however, their repressive effects on S1P-induced cytokine secretion have not been investigated. To address this, our in vitro study reveals the molecular mechanisms by which corticosteroids inhibit S1P-induced IL-6 expression in the pivotal immunomodulatory cell type, airway smooth muscle (ASM). We first uncover the cellular signaling pathways responsible: S1P activates a cyclic adenosine monophosphate/cAMP response-element-binding protein (CREB)/CRE-dependent pathway to induce IL-6 transcription, concomitant with stimulation of the mitogen-activated protein kinase (MAPK) superfamily and downstream mitogen and stress-activated protein kinase 1 (MSK1) and histone H3 phosphorylation. In this way, S1P stimulates parallel signaling pathways to induce IL-6 secretion via CRE-driven transcription of the IL-6 gene promoter in a relaxed chromatin environment achieved through histone H3 phosphorylation. Second, we investigated how corticosteroids mediate their repressive effects. The corticosteroid dexamethasone inhibits S1P-induced IL-6 protein secretion and mRNA expression, but CREB/CRE transrepression, inhibition of IL-6 mRNA stability, or subcellular relocation of MSK1 were not responsible for the repressive effects of dexamethasone. Rather, we show that dexamethasone rapidly induces up-regulation of the MAPK deactivator MAPK phosphatase 1 (MKP-1) and that MKP-1 blocks the MAPK-driven activation of MSK1 and phosphorylation of histone H3. This was confirmed by treatment with triptolide, an inhibitor of MKP-1 up-regulation, where repressive effects of corticosteroids were reversed. Our study reveals the molecular mechanism underlying the antiinflammatory capacity of corticosteroids to repress proinflammatory functions induced by the potent bioactive sphingolipid S1P in the lung.

Epigenetics by flow!

RECENT advances in the field of cancer epigenetics (heritable changes in gene expression that occur without alteration in DNA sequence) with the increased understanding of the mechanisms of epigenetic silencing of tumor suppressor genes and activation of oncogenes—island methylation patterns, histone modifications, and dysregulation of DNA binding proteins-present great promise for future identification of novel biomarkers of application to cancer detection, prognosis, and therapy response (1,2). In particular, histones are essential for chromatin stability. They undergo many modifications, which seem to play important roles in transcriptional regulation and therefore potentially oncogenic if, for example, deregulation leads to the loss of expression of a tumor suppressor gene. Indeed, anomalous patterns of histone modifications are recognized as a hallmark of cancer (3). Histone H3 phosphorylation at serine 10 (and serine 28) occurs at mitosis and the Aurora Kinases that perform this H3 phosphorylation are frequently implicated in cancer (4). Similarly, signatures of histone modifications patterns, such as trimethyl-k9H3, are associated with patient prognosis in acute myeloid leukemia (AML) (5). Epigenetic biomarkers can be detected in tissue samples as well as in biofluids. Chromatin immunoprecipitation (ChIP) using antibodies raised against individual histone marks represents a useful tool for identification of epigenetic biomarkers in basic research and highly specific ChIP grade antibodies are readily available (6). However, this technology does not allow the characterization of epigenetic patterns in heterogeneous clinical samples. Multiparameter flow cytometry, in contrast, allows one to evaluate the expression of markers of interest on a per cell bases. As early as the late 1990s, we developed flow cytometric techniques to identify modifications in cells undergoing mitosis (H3S10 phosphorylation) that have been proven useful not only to identify mitotic cells, but also to study molecular mechanisms associated with the G2 to M transition and as a tool to screen in vivo Aurora Kinase inhibitors (7,8). However, and as noted in the work by Watson et al. (page 78) in the present issue of Cytometry A, condensed chromatin may negatively affect accessibility of antibodies to histone modifications involved in epigenetic regulation. Initial attempts to detect histone marks by flow cytometry were done in cell lines by Obier et al. (9). The authors in the present report extended this work by utilizing antibodies available for ChIP and adapting a protocol that allowed simultaneous measurement of surface immune phenotype, light scatter, and intracellular antigens for normal and leukemic blood evaluation (10). Increased trimethylation of histone H3 Lysine 27 (H3K27me3) has also been associated with tumorigenesis since can silence tumor suppressor genes despite the drop in methylation of the gene’s CpG island (an event that normally activates genes) (11). Interestingly, this is one of the clinically relevant histone marks tested in the Watson’s paper. As presented, the overall MFIs of the leukemic blast samples compared to any of the normal blood cell population seems to indicate increased trimethylation in at least some of the AML samples despite the clear heterogeneity observed. Although, further refinements in the fixation/staining protocol may be needed, this study represents a genuinely novel approach to cancer epigenetics using flow cytometry as the analytical tool. One can only expect an increased number of additional antibodies and applications in the future. The innovative work by Watson et al. in this issue of Cytometry A describes an approach to epigenetics that allows for the study of heterogeneous cell populations on a cell-bycell bases. The authors took advantage of antibodies

O-Linked N-Acetylglucosamine Cycling Regulates Mitotic Spindle Organization

Any defects in the correct formation of the mitotic spindle will lead to chromosomal segregation errors, mitotic arrest, or aneuploidy. We demonstrate that O-linked N-acetylglucosamine (O-GlcNAc), a post-translational modification of serine and threonine residues in nuclear and cytoplasmic proteins, regulates spindle function. In O-GlcNAc transferase or O-GlcNAcase gain of function cells, the mitotic spindle is incorrectly assembled. Chromosome condensation and centrosome assembly is impaired in these cells. The disruption in spindle architecture is due to a reduction in histone H3 phosphorylation by Aurora kinase B. However, gain of function cells treated with the O-GlcNAcase inhibitor Thiamet-G restored the assembly of the spindle and partially rescued histone phosphorylation. Together, these data suggest that the coordinated addition and removal of O-GlcNAc, termed O-GlcNAc cycling, regulates mitotic spindle organization and provides a potential new perspective on how O-GlcNAc regulates cellular events.

Abstract 115: Nuclear CaMKII is a Histone H3 Kinase that Remodels Chromatin During Cardiac Hypertrophy

Background and Purpose: Calcium/calmodulin-dependent protein kinase II (CaMKII) is a ubiquitous serine/threonine kinase implicated in pathological events such as cardiac hypertrophy. In this study we investigated the role of a specific nuclear isoform of CaMKII in chromatin remodeling and in transcriptional regulation in cardiac muscle. Methods: Comprehensive experimental approaches performed in primary cardiomyocyte cultures were used including chromatin immunoprecipitation assays (ChIP), q-PCR, chromatin remodeling assays, in vitro phosphorylation/transcription assays, production of recombinant adenovirus, siRNA technology, fluorescence microscopy and mass spectrometry. Results: We found that CaMKIIδB targets specific components of chromatin during cardiac hypertrophy and binds to nucleosomes through its association domain in a cooperative model. CaMKIIδB also increased chromatin relaxation, and this action was dependent on its kinase activity. The observation that CaMKIIδB interacts with chromatin suggested to us that histones maybe novel substrates of the kinase in cardiac muscle. To test this hypothesis, we performed in vitro kinase assays and found that histone H3 is a bona fide CaMKIIδB substrate and Ser-10 appears to be a predominant phosphorylation site. Increased histone H3 Ser-10 phosphorylation was observed following hypertrophic stimulation and was not associated with cellular proliferation, whereas depletion of CaMKIIδB significantly reduced histone H3 Ser-10 phosphorylation in primary cardiomyocytes. Interestingly, we found that H3 S10 phosphorylation and recruitment of CaMKIIδB occur at promoters of fetal cardiac genes. To establish the functional link between H3 phosphorylation by CaMKIIδB, chromatin remodeling and transcription activation, we developed an in vitro transcription system and using it we found that CaMKIIδB increased chromatin accessibility and mediated transcription of the Mef2 transcription factor. Conclusion: Taken together, these findings highlight a new role of CaMKIIδB as relevant histone H3 kinase and link for the first time epigenetic changes by CaMKII to cardiac hypertrophy.

Distribution pattern of histone H3 phosphorylation at serine 10 during mitosis and meiosis in Brachiaria species

Histones are the major eukaryotic DNA-binding proteins. Posttranslational modifications on N-terminal tails of histones that form nucleosomes are often associated with distinct biological functions. Some theories suggest that one of these modifications, the phosphorylation of histone H3 at serine 10 (H3S10ph) plays a role in both chromosome condensation and sister chromatid cohesion. Although histones and some of their modifications are highly conserved, studies have shown that role and distribution of H3S10ph may differ between species. We evaluated the pattern of H3 phosphorylation using immunodetection during mitosis and meiosis in both diploid and tetraploid genotypes of Brachiaria species. Results revealed differences in chromosome distribution of H3S10ph when mitosis and meiosis were compared. Whole chromosomes were phosphorylated during meiosis I, whereas phosphorylation was restricted to the pericentromeric region in both meiosis II and mitosis. There was no variation in phosphorylation patterns between Brachiaria species and diploid and tetraploid genotypes. Regarding spatiotemporal coordination in the Brachiaria species evaluated, H3S10ph is related to maintenance of sister chromatid cohesion during cell divisions.

Prognostic significance of phospho-histone H3 in prostate carcinoma

Prostate cancer is the second most common cancer in men and the sixth most common cause of death from cancer in men worldwide. Currently, a sufficient pathological distinction between patients requiring further treatment and those for which active surveillance remains an option is still lacking, which leads to the problem of overtreatment. Cell proliferation is routinely assessed by detecting Ki-67 antigen. While Ki-67 is expressed throughout the interphase of proliferating cells, phosphorylation of the chromatin constituent histone H3 occurs only during the late G2 phase and mitosis thus providing a more strict assessment of the mitotic activity. We undertook this study to test whether expression of the recently introduced proliferation marker phospho-histone H3 (pHH3) in prostate carcinoma tissue sections exhibits prognostic significance in comparison with Ki-67. Protein expression of pHH3 and Ki-67 was assessed on TMA consisting of paraffin-embedded tissue from men that had undergone radical prostatectomy. The analysis included triplicate tissue cores of a total of 339 tumor foci. Immunohistochemical staining of pHH3 and Ki-67 was performed and analyzed using Definiens imaging software. Prostate cancer tissue exhibited a significantly higher frequency of pHH3-positive cells compared to benign prostate tissue. pHH3 expression was significantly correlated with Ki-67 expression. Furthermore, statistical analysis revealed positive correlation between pHH3 expression and PSA levels at diagnosis and in addition negatively correlated with overall survival. In contrast to Ki-67 staining, pHH3 expression did not correlate with Gleason grade. Our data point to a conceivable role of pHH3 as prognostic biomarker in prostate carcinoma.

Differentially Expressed Epigenome Modifiers, Including Aurora Kinases A and B, in Immune Cells in Rheumatoid Arthritis in Humans and Mouse Models

To identify epigenetic factors that are implicated in the pathogenesis of rheumatoid arthritis (RA), and to explore the therapeutic potential of the targeted inhibition of these factors. Polymerase chain reaction (PCR) arrays were used to investigate the expression profile of genes that encode key epigenetic regulator enzymes. Mononuclear cells from RA patients and mice were monitored for gene expression changes, in association with arthritis development in murine models of RA. Selected genes were further characterized by quantitative reverse transcription-PCR, Western blot, and flow cytometry methods. The targeted inhibition of the up-regulated enzymes was studied in arthritic mice. A set of genes with arthritis-specific expression was identified by the PCR arrays. Aurora kinases A and B, both of which were highly expressed in arthritic mice and treatment-naive RA patients, were selected for detailed analysis. Elevated aurora kinase expression was accompanied by increased phosphorylation of histone H3, which promotes proliferation of T lymphocytes. Treatment with VX-680, a pan-aurora kinase inhibitor, promoted B cell apoptosis, provided significant protection against disease onset, and attenuated inflammatory reactions in arthritic mice. Arthritis development is accompanied by changes in expression of a number of epigenome-modifying enzymes. Drug-induced down-regulation of the aurora kinases, among other targets, seems to be sufficient to treat experimental arthritis. Development of new therapeutics that target aurora kinases can potentially improve RA management.

P53 Ser15 phosphorylation and histone modifications contribute to IR-induced miR-34a transcription in mammary epithelial cells

Previous studies have demonstrated that miR-34a is a direct transcriptional target of tumor suppressor p53 and plays a crucial role in p53-mediated biological processes, such as cell cycle arrest, apoptosis and senescence. However, the role of p53 phosphorylation at Ser15 and histone modifications in ionizing radiation (IR)-induced miR-34a transcription in human mammary epithelial cells remains unknown. The present study showed that IR triggers miR-34a induction in rat mammary gland tissue and human mammary epithelial cells in a dose- and time-dependent fashion. Gene copy number and CpG methylation exhibit no effect on IR-inducible miR-34a expression, while the levels of phosphorylated p53 at Ser15 are markedly elevated in human mammary epithelial cells 96 h post-IR, which correlates with IR-inducible miR-34a transcription and the p38 MAPK pathway. Conversely, suppression of p38 MAPK with SB239063 inhibits IR-induced p53 phosphorylation at Ser15 and miR-34a expression in a dose-dependent manner. Our study found that wild-type p53 is enriched at miR-34a promoter, and luciferase activity of miR-34a promoter reporter is attenuated by either mutant p53 (Ser15Ala) or mutant miR-34a promoter. Furthermore, IR also triggers phosphorylation, tri-methylation and acetylation of histone H3 and acetylation of histone H4, which correlates with IR-inducible miR-34a transcription, while SAHA potentiates IR-inducible miR-34a expression. Moreover, acetyl-histone H3 is significantly enriched at miR-34a promoter in IR-exposed HMEC cells. Yet, we show that there is no correlation between IR-inducible miR-34a expression and IR-induced rapid and transient G2/M arrest. In sum, our novel data for the first time demonstrate that IR-induced p53 Ser15 phosphorylation via p38 MAPK is essential for its functional regulation of IR-inducible miR-34a transcription in human mammary epithelial cells, and that histone modifications may also play a key role in IR-inducible miR-34a expression.

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.

Alterations of Histone H1 Phosphorylation During Bladder Carcinogenesis

There is a crucial need for development of prognostic and predictive biomarkers in human bladder carcinogenesis in order to personalize preventive and therapeutic strategies and improve outcomes. Epigenetic alterations, such as histone modifications, are implicated in the genetic dysregulation that is fundamental to carcinogenesis. Here we focus on profiling the histone modifications during the progression of bladder cancer. Histones were extracted from normal human bladder epithelial cells, an immortalized human bladder epithelial cell line (hTERT), and four human bladder cancer cell lines (RT4, J82, T24, and UMUC3) ranging from superficial low-grade to invasive high-grade cancers. Liquid chromatography-mass spectrometry (LC-MS) profiling revealed a statistically significant increase in phosphorylation of H1 linker histones from normal human bladder epithelial cells to low-grade superficial to high-grade invasive bladder cancer cells. This finding was further validated by immunohistochemical staining of the normal epithelium and transitional cell cancer from human bladders. Cell cycle analysis of histone H1 phosphorylation by Western blotting showed an increase of phosphorylation from G0/G1 phase to M phase, again supporting this as a proliferative marker. Changes in histone H1 phosphorylation status may further clarify epigenetic changes during bladder carcinogenesis and provide diagnostic and prognostic biomarkers or targets for future therapeutic interventions.

Pim kinases phosphorylate Chk1 and regulate its functions in acute myeloid leukemia

Phosphorylation by Akt on Ser 280 was reported to induce cytoplasmic retention and inactivation of CHK1 with consequent genetic instability in PTEN-/- cells. In acute myeloid leukemia cells carrying the FLT3-internal tandem duplication (ITD) mutation, we observed high rates of FLT3-ITD-dependent CHK1 Ser 280 phosphorylation. Pharmacological inhibition and RNA interference identified Pim1/2, not Akt, as effectors of this phosphorylation. Pim1 catalyzed Ser 280 phosphorylation in vitro and ectopic expression of Pim1/2-induced CHK1 phosphorylation. Ser 280 phosphorylation did not modify CHK1 localization, but facilitated its cell cycle and resistance functions in leukemic cells. FLT3, PIM or CHK1 inhibitors synergized with DNA-damaging agents to induce apoptosis, allowing cells to bypass the etoposide-induced G2/M arrest. Consistently, etoposide-induced CHK1-dependent phosphorylations of CDC25C on Ser 216 and histone H3 on Thr11 were decreased upon FLT3 inhibition. Accordingly, ectopic expression of CHK1 improved the resistance of FLT3-ITD cells and maintained histone H3 phosphorylation in response to DNA damage, whereas expression of unphosphorylated Ser 280Ala mutant did not. Finally, FLT3- and Pim-dependent phosphorylation of CHK1 on Ser 280 was confirmed in primary blasts from patients. These results identify a new pathway involved in the resistance of FLT3-ITD leukemic cells to genotoxic agents, and they constitute the first report of CHK1 Ser 280 regulation in myeloid malignancies.

Formation of a Functional Maize Centromere after Loss of Centromeric Sequences and Gain of Ectopic Sequences

The maize (Zea mays) B centromere is composed of B centromere-specific repeats (ZmBs), centromere-specific satellite repeats (CentC), and centromeric retrotransposons of maize (CRM). Here we describe a newly formed B centromere in maize, which has lost CentC sequences and has dramatically reduced CRM and ZmBs sequences, but still retains the molecular features of functional centromeres, such as CENH3, H2A phosphorylation at Thr-133, H3 phosphorylation at Ser-10, and Thr-3 immunostaining signals. This new centromere is stable and can be transmitted to offspring through meiosis. Anti-CENH3 chromatin immunoprecipitation sequencing revealed that a 723-kb region from the short arm of chromosome 9 (9S) was involved in the formation of the new centromere. The 723-kb region, which is gene poor and enriched for transposons, contains two abundant DNA motifs. Genes in the new centromere region are still transcribed. The original 723-kb region showed a higher DNA methylation level compared with native centromeres but was not significantly changed when it was involved in new centromere formation. Our results indicate that functional centromeres may be formed without the known centromere-specific sequences, yet the maintenance of a high DNA methylation level seems to be crucial for the proper function of a new centromere.

Ethanol inhibits retinal and CNS differentiation due to failure of cell cycle exit via an apoptosis-independent pathway

Alcohol exposure during embryogenesis results in a variety of developmental disorders. Here, we demonstrate that continuous exposure to 1.5% ethanol causes substantial apoptosis and abrogated retinal and CNS development in zebrafish embryos. Chronic exposure to ethanol for 24h before hatching also induces apoptosis and retinal disorder. After the 2-day post-fertilization (dpf) stage, chronic exposure to ethanol continued to induce apoptosis, but did not block retinal differentiation. Although continuous ethanol exposure induces substantial accumulation of reactive oxygen species (ROS) and increases p53 expression, depletion of p53 did not eliminate ethanol-induced apoptosis. On the other hand, sequestering ROS with the antioxidant reagent N-acetylcysteine (NAC) successfully inhibited ethanol-associated apoptosis, suggesting that the ethanol-induced cell death primarily results from ROS accumulation. Continuous ethanol treatment of embryos reduced expression of the mature neural and photoreceptor markers elavl3/huC, rho, and crx; in addition, expression of the neural and retinal progenitor markers ascl1b and pax6b was maintained at the undifferentiated stage, indicating that retinal and CNS neural progenitor cells failed to undergo further differentiation. Moreover, ethanol treatment enhanced BrdU incorporation, histone H3 phosphorylation, and pcna expression in neural progenitor cells, thereby maintaining a high rate of proliferation. Ethanol treatment also resulted in sustained transcription of ccnd1/cyclin D1 and ccne/cyclin E throughout development in neural progenitor cells, without an appropriate increase of cdkn1b/p27 and cdkn1c/p57 expression, suggesting that these cells failed to exit from the cell cycle. Although NAC was able to mitigate ethanol-mediated apoptosis, it was unable to ameliorate the defects in visual and CNS neural differentiation, suggesting that abrogated neural development in ethanol-exposed embryos is unlikely to arise from excessive apoptosis. In conclusion, we demonstrate that the pathological effect of ethanol on zebrafish embryos is partially attributable to cell death and inhibition of visual and CNS neuron differentiation. Excessive apoptosis largely results from the accumulation of ROS, whereas abrogated neural development is caused by failure of cell cycle arrest, which in turn prevents a successful transition from proliferation to differentiation.

Prometaphase arrest-dependent phosphorylation of Bcl-2 family proteins and activation of mitochondrial apoptotic pathway are associated with 17α-estradiol-induced apoptosis in human Jurkat T cells

In Jurkat T cell clone (JT/Neo), G2/M arrest, apoptotic sub-G1 peak, mitochondrial membrane potential (Δψm) loss, and TUNEL-positive DNA fragmentation were induced following exposure to 17α-estradiol (17α-E2), whereas none of these events (except for G2/M arrest) were induced in Jurkat cells overexpressing Bcl-2 (JT/Bcl-2). Under these conditions, phosphorylation at Thr161 and dephosphorylation at Tyr15 of Cdk1, upregulation of cyclin B1 level, histone H1 phosphorylation, Cdc25C phosphorylation at Thr-48, Bcl-2 phosphorylation at Thr-56 and Ser-70, Mcl-1 phosphorylation, and Bim phosphorylation were detected in the presence of Bcl-2 overexpression. However, the 17α-E2-induced upregulation of Bak levels, activation of Bak, activation of caspase-3, and PARP degradation were abrogated by Bcl-2 overexpression. In the presence of the G1/S blocking agent hydroxyurea, 17α-E2 failed to induce G2/M arrest and all apoptotic events including Cdk1 activation and phosphorylation of Bcl-2, Mcl-1 and Bim. The 17α-E2-induced phosphorylation of Bcl-2 family proteins and mitochondrial apoptotic events were suppressed by a Cdk1 inhibitor but not by aurora A and aurora B kinase inhibitors. Immunofluorescence microscopic analysis showed that an aberrant bipolar microtubule array, incomplete chromosome congression at the metaphase plate, and prometaphase arrest, which was reversible, were the underlying factors for 17α-E2-induced mitotic arrest. The in vitro microtubule polymerization assay showed that 17α-E2 could directly inhibit microtubule formation. These results show that the apoptogenic activity of 17α-E2 was due to the impaired mitotic spindle assembly causing prometaphase arrest and prolonged Cdk1 activation, the phosphorylation of Bcl-2, Mcl-1 and Bim, and the activation of Bak and mitochondria-dependent caspase cascade.

6,7-Dimethoxy-3-(3-methoxyphenyl)isoquinolin-1-amine induces mitotic arrest and apoptotic cell death through the activation of spindle assembly checkpoint in human cervical cancer cells

Previously, we reported that 6,7-dimethoxy-3-(3-methoxyphenyl)isoquinolin-1-amine (CWJ-082) has potent cytotoxic effects on various cancer cells, but the underlying molecular mechanism responsible was not determined. In the present study, CWJ-082 caused cervical cancer cell cycle arrest at the G2/M phase and subsequent caspase-dependent apoptosis. The mitotic arrest caused by CWJ-082 found to be due to increases in the activation of cyclin-dependent kinase 1/cyclin B1 complex and the phosphorylation of histone H3. In addition, CWJ-082 induced the phosphorylation of BubR1 and the association between mitotic arrest deficient 2 (Mad2) and cell division cycle protein 20. These findings suggested that CWJ-082 activated the mitotic spindle checkpoint. Furthermore, knockdown of the spindle checkpoint proteins BubR1 or Mad2 using specific small interfering RNAs significantly reduced CWJ-082-induced mitotic cell accumulation and apoptosis. In addition, CWJ-082 induced the appearance of spindle abnormalities by inducing α-tubulin polymerization. In BALB/c(nu/nu) mice bearing a HeLa xenograft, CWJ-082 significantly inhibited tumor growth. Taken together, these results suggest that CWJ-082 inhibits cell growth via mitotic arrest by activating the mitotic spindle checkpoint and by inducing α-tubulin polymerization and that these events ultimately lead to the apoptosis of human cervical cancer cells and inhibit tumor growth in HeLa xenograft mice.

High glucose and insulin differentially modulates proliferation in MCF-7 and MDA-MB-231 cells

Various preclinical and clinical studies have linked diabetes and breast cancer, but little is known regarding the molecular mechanism involved. This study aimed to investigate the effect of high glucose and insulin in breast cancer cells (MCF-7: non-invasive, hormone dependent, and MDA-MB-231: invasive, hormone independent). In contrast to MCF-7 cells, high glucose augmented proliferation of MDA-MB-231 cells as observed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and bromodeoxyuridine assays. The high-glucose condition led to increased expression of cyclin D1, de-phosphorylation of p38, and increased phosphorylation of ERK in MDA-MB-231 cells but not in MCF-7 cells. Interestingly, we observed increased phosphorylation of GSK-3β, NF-κB, and ERα only in MCF-7 cells, highlighting their role as potential targets in prevention of progression of breast cancer under a high-glucose and insulin condition. Furthermore, insulin treatment under a high-glucose condition resulted in increased histone H3 phosphorylation and de-acetylation only in MDA-MB-231 cells. Taken together, we provide the first evidence that high glucose and insulin promotes proliferation of MDA-MB-231 cells by differential alteration of GSK-3β, NF-κB, and ERα expression and histone H3 modifications, which may directly or indirectly modulate the expression of genes involved in its proliferation.

Unliganded progesterone receptor-mediated targeting of an RNA-containing repressive complex silences a subset of hormone-inducible genes

A close chromatin conformation precludes gene expression in eukaryotic cells. Genes activated by external cues have to overcome this repressive state by locally changing chromatin structure to a more open state. Although much is known about hormonal gene activation, how basal repression of regulated genes is targeted to the correct sites throughout the genome is not well understood. Here we report that in breast cancer cells, the unliganded progesterone receptor (PR) binds genomic sites and targets a repressive complex containing HP1γ (heterochromatin protein 1γ), LSD1 (lysine-specific demethylase 1), HDAC1/2, CoREST (corepressor for REST [RE1 {neuronal repressor element 1} silencing transcription factor]), KDM5B, and the RNA SRA (steroid receptor RNA activator) to 20% of hormone-inducible genes, keeping these genes silenced prior to hormone treatment. The complex is anchored via binding of HP1γ to H3K9me3 (histone H3 tails trimethylated on Lys 9). SRA interacts with PR, HP1γ, and LSD1, and its depletion compromises the loading of the repressive complex to target chromatin-promoting aberrant gene derepression. Upon hormonal treatment, the HP1γ-LSD1 complex is displaced from these constitutively poorly expressed genes as a result of rapid phosphorylation of histone H3 at Ser 10 mediated by MSK1, which is recruited to the target sites by the activated PR. Displacement of the repressive complex enables the loading of coactivators needed for chromatin remodeling and activation of this set of genes, including genes involved in apoptosis and cell proliferation. These results highlight the importance of the unliganded PR in hormonal regulation of breast cancer cells.