Role of Misfolded N-CoR Mediated Transcriptional Deregulation of Flt3 in Acute Monocytic Leukemia (AML)-M5 Subtype

The nuclear receptor co-repressor (N-CoR) is a key component of the generic multi-protein complex involved in transcriptional control. Flt3, a key regulator of hematopoietic cell growth, is frequently deregulated in AML (acute myeloid leukemia). Here, we report that loss of N-CoR-mediated transcriptional control of Flt3 due to misfolding, contributes to malignant growth in AML of the M5 subtype (AML-M5). An analysis of hematopoietic genes in AML cells led to the identification of Flt3 as a transcriptional target of N-CoR. Flt3 level was inversely related to N-CoR status in various leukemia cells. N-CoR was associated with the Flt3 promoter in-vivo, and a reporter driven by the Flt3 promoter was effectively repressed by N-CoR. Blocking N-CoR loss with Genistein; an inhibitor of N-CoR misfolding, significantly down-regulated Flt3 levels regardless of the Flt3 receptor mutational status and promoted the differentiation of AML-M5 cells. While stimulation of the Flt3 receptor with the Flt3 ligand triggered N-CoR loss, Flt3 antibody mediated blockade of Flt3 ligand-receptor binding led to N-CoR stabilization. Genetic ablation of N-CoR potentiated Flt3 ligand induced proliferation of BA/F3 cells. These findings suggest that N-CoR-induced repression of Flt3 might be crucial for limiting the contribution of the Flt3 signaling pathway on the growth potential of leukemic cells and its deregulation due to N-CoR loss in AML-M5, could contribute to malignant growth by conferring a proliferative advantage to the leukemic blasts. Therapeutic restoration of N-CoR function could thus be a useful approach in restricting the contribution of the Flt3 signaling pathway in AML-M5 pathogenesis

Trichostatin A Selectively Suppresses the Cold-Induced Transcription of the ZmDREB1 Gene in Maize

Post-translational modifications of histone proteins play a crucial role in responding to environmental stresses. Histone deacetylases (HDACs) catalyze the removal of an acetyl group from histones and are generally believed to be a transcriptional repressor. In this paper, we report that cold treatment highly induces the up-regulation of HDACs, leading to global deacetylation of histones H3 and H4. Treatment of maize with the HDAC inhibitor trichostatin A (TSA) under cold stress conditions strongly inhibits induction of the maize cold-responsive genes ZmDREB1 and ZmCOR413. However, up-regulation of the ZmICE1 gene in response to cold stress is less affected. The expression of drought and salt induced genes, ZmDBF1 and rab17, is almost unaffected by TSA treatment. Thus, these observations show that HDACs may selectively activate transcription. The time course of TSA effects on the expression of ZmDREB1 and ZmCOR413 genes indicates that HDACs appear to directly activate the ZmDREB1 gene, which in turn modulates ZmCOR413 expression. After cold treatment, histone hyperacetylation and DNA demethylation occurs in the ICE1 binding region, accompanied by an increase in accessibility to micrococcal nuclease (MNase). The two regions adjacent to the ICE1 binding site remain hypoacetylated and methylated. However, during cold acclimation, TSA treatment increases the acetylation status and accessibility of MNase and decreases DNA methylation at these two regions. However, TSA treatment does not affect histone hyperacetylation and DNA methylation levels at the ICE1 binding regions of the ZmDREB1 gene. Altogether, our findings indicate that HDACs positively regulate the expression of the cold-induced ZmDREB1 gene through histone modification and chromatin conformational changes and that this activation is both gene and site selective

Induction of interferon-stimulated genes on the IL-4 response axis by Epstein-Barr virus infected human b cells; relevance to cellular transformation.

Epstein-Barr virus (EBV) is an oncogenic virus that is associated with the pathogenesis of several human lymphoid malignancies, including Hodgkin's lymphoma. Infection of normal resting B cells with EBV results in activation to lymphoblasts that are phenotypically similar to those generated by physiological stimulation with CD40L plus IL-4. One important difference is that infection leads to the establishment of permanently growing lymphoblastoid cell lines, whereas CD40L/IL-4 blasts have finite proliferation lifespans. To identify early events which might later determine why EBV infected blasts go on to establish transformed cell lines, we performed global transcriptome analyses on resting B cells and on EBV and CD40L/IL-4 blasts after 7 days culture. As anticipated there was considerable overlap in the transcriptomes of the two types of lymphoblasts when compared to the original resting B cells, reflecting common changes associated with lymphocyte activation and proliferation. Of interest to us was a subset of 255 genes that were differentially expressed between EBV and CD40L/IL-4 blasts. Genes which were more highly expressed in EBV blasts were substantially and significantly enriched for a set of interferon-stimulated genes which on further in silico analyses were found to be repressed by IL-4 in other cell contexts and to be up-regulated in micro-dissected malignant cells from Hodgkin's lymphoma biopsies when compared to their normal germinal center cell counterparts. We hypothesized that EBV and IL-4 were targeting and discordantly regulating a common set of genes. This was supported experimentally in our B cell model where IL-4 stimulation partially reversed transcriptional changes which follow EBV infection and it impaired the efficiency of EBV-induced B cell transformation. Taken together, these data suggest that the discordant regulation of interferon and IL-4 pathway genes by EBV that occurs early following infection of B cells has relevance to the development or maintenance of an EBV-associated malignancy

Molecular Biomarkers of Vascular Dysfunction in Obstructive Sleep Apnea

Untreated and long-lasting obstructive sleep apnea (OSA) may lead to important vascular abnormalities, including endothelial cell (EC) dysfunction, hypertension, and atherosclerosis. We observed a correlation between microcirculatory reactivity and endothelium-dependent release of nitric oxide in OSA patients. Therefore, we hypothesized that OSA affects (micro)vasculature and we aimed to identify vascular gene targets of OSA that could possibly serve as reliable biomarkers of severity of the disease and possibly of vascular risk. Using quantitative RT-PCR, we evaluated gene expression in skin biopsies of OSA patients, mouse aortas from animals exposed to 4-week intermittent hypoxia (IH; rapid oscillations in oxygen desaturation and reoxygenation), and human dermal microvascular (HMVEC) and coronary artery endothelial cells (HCAEC) cultured under IH. We demonstrate a significant upregulation of endothelial nitric oxide synthase (eNOS), tumor necrosis factor-alpha-induced protein 3 (TNFAIP3; A20), hypoxia-inducible factor 1 alpha (HIF-1α?? and vascular endothelial growth factor (VEGF) expression in skin biopsies obtained from OSA patients with severe nocturnal hypoxemia (nadir saturated oxygen levels [SaO2]<75%) compared to mildly hypoxemic OSA patients (SaO2 75%–90%) and a significant upregulation of vascular cell adhesion molecule 1 (VCAM-1) expression compared to control subjects. Gene expression profile in aortas of mice exposed to IH demonstrated a significant upregulation of eNOS and VEGF. In an in vitro model of OSA, IH increased expression of A20 and decreased eNOS and HIF-1α expression in HMVEC, while increased A20, VCAM-1 and HIF-1αexpression in HCAEC, indicating that EC in culture originating from distinct vascular beds respond differently to IH stress. We conclude that gene expression profiles in skin of OSA patients may correlate with disease severity and, if validated by further studies, could possibly predict vascular risk in OSA patients

A20 Modulates Lipid Metabolism and Energy Production to Promote Liver Regeneration

Background: Liver Regeneration is clinically of major importance in the setting of liver injury, resection or transplantation. We have demonstrated that the NF-$\kappa$B inhibitory protein A20 significantly improves recovery of liver function and mass following extended liver resection (LR) in mice. In this study, we explored the Systems Biology modulated by A20 following extended LR in mice. Methodology and Principal Findings: We performed transcriptional profiling using Affymetrix-Mouse 430.2 arrays on liver mRNA retrieved from recombinant adenovirus A20 (rAd.A20) and rAd.$\beta$galactosidase treated livers, before and 24 hours after 78% LR. A20 overexpression impacted 1595 genes that were enriched for biological processes related to inflammatory and immune responses, cellular proliferation, energy production, oxidoreductase activity, and lipid and fatty acid metabolism. These pathways were modulated by A20 in a manner that favored decreased inflammation, heightened proliferation, and optimized metabolic control and energy production. Promoter analysis identified several transcriptional factors that implemented the effects of A20, including NF-$\kappa$B, CEBPA, OCT-1, OCT-4 and EGR1. Interactive scale-free network analysis captured the key genes that delivered the specific functions of A20. Most of these genes were affected at basal level and after resection. We validated a number of A20's target genes by real-time PCR, including p21, the mitochondrial solute carriers SLC25a10 and SLC25a13, and the fatty acid metabolism regulator, peroxisome proliferator activated receptor alpha. This resulted in greater energy production in A20-expressing livers following LR, as demonstrated by increased enzymatic activity of cytochrome c oxidase, or mitochondrial complex IV. Conclusion: This Systems Biology-based analysis unravels novel mechanisms supporting the pro-regenerative function of A20 in the liver, by optimizing energy production through improved lipid/fatty acid metabolism, and down-regulated inflammation. These findings support pursuit of A20-based therapies to improve patients' outcomes in the context of extreme liver injury and extensive LR for tumor treatment or donation

O-Glycosylation Regulates Ubiquitination and Degradation of the Anti-Inflammatory Protein A20 to Accelerate Atherosclerosis in Diabetic ApoE-Null Mice

Background: Accelerated atherosclerosis is the leading cause of morbidity and mortality in diabetic patients. Hyperglycemia is a recognized independent risk factor for heightened atherogenesis in diabetes mellitus (DM). However, our understanding of the mechanisms underlying glucose damage to the vasculature remains incomplete. Methodology/Principal Findings: High glucose and hyperglycemia reduced upregulation of the NF-κB inhibitory and atheroprotective protein A20 in human coronary endothelial (EC) and smooth muscle cell (SMC) cultures challenged with Tumor Necrosis Factor alpha (TNF), aortae of diabetic mice following Lipopolysaccharide (LPS) injection used as an inflammatory insult and in failed vein-grafts of diabetic patients. Decreased vascular expression of A20 did not relate to defective transcription, as A20 mRNA levels were similar or even higher in EC/SMC cultured in high glucose, in vessels of diabetic C57BL/6 and FBV/N mice, and in failed vein grafts of diabetic patients, when compared to controls. Rather, decreased A20 expression correlated with post-translational O-Glucosamine-N-Acetylation (O-GlcNAcylation) and ubiquitination of A20, targeting it for proteasomal degradation. Restoring A20 levels by inhibiting O-GlcNAcylation, blocking proteasome activity, or overexpressing A20, blocked upregulation of the receptor for advanced glycation end-products (RAGE) and phosphorylation of PKCβII, two prime atherogenic signals triggered by high glucose in EC/SMC. A20 gene transfer to the aortic arch of diabetic ApoE null mice that develop accelerated atherosclerosis, attenuated vascular expression of RAGE and phospho-PKCβII, significantly reducing atherosclerosis. Conclusions: High glucose/hyperglycemia regulate vascular A20 expression via O-GlcNAcylation-dependent ubiquitination and proteasomal degradation. This could be key to the pathogenesis of accelerated atherosclerosis in diabetes

In vitro nuclear interactome of the HIV-1 Tat protein

<p>Abstract</p> <p>Background</p> <p>One facet of the complexity underlying the biology of HIV-1 resides not only in its limited number of viral proteins, but in the extensive repertoire of cellular proteins they interact with and their higher-order assembly. HIV-1 encodes the regulatory protein Tat (86–101aa), which is essential for HIV-1 replication and primarily orchestrates HIV-1 provirus transcriptional regulation. Previous studies have demonstrated that Tat function is highly dependent on specific interactions with a range of cellular proteins. However they can only partially account for the intricate molecular mechanisms underlying the dynamics of proviral gene expression. To obtain a comprehensive nuclear interaction map of Tat in T-cells, we have designed a proteomic strategy based on affinity chromatography coupled with mass spectrometry.</p> <p>Results</p> <p>Our approach resulted in the identification of a total of 183 candidates as Tat nuclear partners, 90% of which have not been previously characterised. Subsequently we applied <it>in silico </it>analysis, to validate and characterise our dataset which revealed that the Tat nuclear interactome exhibits unique signature(s). First, motif composition analysis highlighted that our dataset is enriched for domains mediating protein, RNA and DNA interactions, and helicase and ATPase activities. Secondly, functional classification and network reconstruction clearly depicted Tat as a polyvalent protein adaptor and positioned Tat at the nexus of a densely interconnected interaction network involved in a range of biological processes which included gene expression regulation, RNA biogenesis, chromatin structure, chromosome organisation, DNA replication and nuclear architecture.</p> <p>Conclusion</p> <p>We have completed the <it>in vitro </it>Tat nuclear interactome and have highlighted its modular network properties and particularly those involved in the coordination of gene expression by Tat. Ultimately, the highly specialised set of molecular interactions identified will provide a framework to further advance our understanding of the mechanisms of HIV-1 proviral gene silencing and activation.</p

Mad proteins contain a dominant transcription repression domain.

Transcription repression by the basic region-helix-loop-helix-zipper (bHLHZip) protein Mad1 requires DNA binding as a ternary complex with Max and mSin3A or mSin3B, the mammalian orthologs of the Saccharomyces cerevisiae transcriptional corepressor SIN3. The interaction between Mad1 and mSin3 is mediated by three potential amphipathic alpha-helices: one in the N terminus of Mad (mSin interaction domain, or SID) and two within the second paired amphipathic helix domain (PAH2) of mSin3A. Mutations that alter the structure of the SID inhibit in vitro interaction between Mad and mSin3 and inactivate Mad's transcriptional repression activity. Here we show that a 35-residue region containing the SID represents a dominant repression domain whose activity can be transferred to a heterologous DNA binding region. A fusion protein comprising the Mad1 SID linked to a Ga14 DNA binding domain mediates repression of minimal as well as complex promoters dependent on Ga14 DNA binding sites. In addition, the SID represses the transcriptional activity of linked VP16 and c-Myc transactivation domains. When fused to a full-length c-Myc protein, the Mad1 SID specifically represses both c-Myc's transcriptional and transforming activities. Fusions between the GAL DNA binding domain and full-length mSin3 were also capable of repression. We show that the association between Mad1 and mSin3 is not only dependent on the helical SID but is also dependent on both putative helices of the mSin3 PAH2 region, suggesting that stable interaction requires all three helices. Our results indicate that the SID is necessary and sufficient for transcriptional repression mediated by the Mad protein family and that SID repression is dominant over several distinct transcriptional activators

A complex containing N-CoR, mSin3 and histone deacetylase mediates transcriptional repression.

Transcriptional repression by nuclear receptors has been correlated to binding of the putative co-repressor, N-CoR. A complex has been identified that contains N-CoR, the Mad presumptive co-repressor mSin3, and the histone deacetylase mRPD3, and which is required for both nuclear receptor- and Mad-dependent repression, but not for repression by transcription factors of the ets-domain family. These data predict that the ligand-induced switch of heterodimeric nuclear receptors from repressor to activator functions involves the exchange of complexes containing histone deacetylases with those that have histone acetylase activity

Transcriptional repression by the methyl-CpG-binding protein MeCP2 involves a histone deacetylase complex.

Cytosine residues in the sequence 5'CpG (cytosine-guanine) are often postsynthetically methylated in animal genomes. CpG methylation is involved in long-term silencing of certain genes during mammalian development and in repression of viral genomes. The methyl-CpG-binding proteins MeCP1 and MeCP2 interact specifically with methylated DNA and mediate transcriptional repression. Here we study the mechanism of repression by MeCP2, an abundant nuclear protein that is essential for mouse embryogenesis. MeCP2 binds tightly to chromosomes in a methylation-dependent manner. It contains a transcriptional-repression domain (TRD) that can function at a distance in vitro and in vivo. We show that a region of MeCP2 that localizes with the TRD associates with a corepressor complex containing the transcriptional repressor mSin3A and histone deacetylases. Transcriptional repression in vivo is relieved by the deacetylase inhibitor trichostatin A, indicating that deacetylation of histones (and/or of other proteins) is an essential component of this repression mechanism. The data suggest that two global mechanisms of gene regulation, DNA methylation and histone deacetylation, can be linked by MeCP2