CREB-binding protein/p300 are transcriptional coactivators of p65

Evaluation of the immune humoral response of Brazilian patients with Rubinstein-Taybi syndrome

Rubinstein-Taybi syndrome (RTS) is a rare developmental disorder characterized by craniofacial dysmorphisms, broad thumbs and toes, mental and growth deficiency, and recurrent respiratory infections. RTS has been associated with CREBBP gene mutations, but EP300 gene mutations have recently been reported in 6 individuals. In the present study, the humoral immune response in 16 RTS patients with recurrent respiratory infections of possible bacterial etiology was evaluated. No significant differences between patients and 16 healthy controls were detected to explain the high susceptibility to respiratory infections: normal or elevated serum immunoglobulin levels, normal salivary IgA levels, and a good antibody response to both polysaccharide and protein antigens were observed. However, most patients presented high serum IgM levels, a high number of total B cell and B subsets, and also high percentiles of apoptosis, suggesting that they could present B dysregulation. The CREBBP/p300 family gene is extremely important for B-cell regulation, and RTS may represent an interesting human model for studying the molecular mechanisms involved in B-cell development.

Kinome profiling of myxoid liposarcoma reveals NF-kappaB-pathway kinase activity and casein kinase II inhibition as a potential treatment option

BACKGROUND

Myxoid liposarcoma is a relatively common malignant soft tissue tumor, characterized by a (12;16) translocation resulting in a FUS-DDIT3 fusion gene playing a pivotal role in its tumorigenesis. Treatment options in patients with inoperable or metastatic myxoid liposarcoma are relatively poor though being developed and new hope is growing.

RESULTS

Using kinome profiling and subsequent pathway analysis in two cell lines and four primary cultures of myxoid liposarcomas, all of which demonstrated a FUS-DDIT3 fusion gene including one new fusion type, we aimed at identifying new molecular targets for systemic treatment. Protein phosphorylation by activated kinases was verified by Western Blot and cell viability was measured before and after treatment of the myxoid liposarcoma cells with kinase inhibitors. We found kinases associated with the atypical nuclear factor-kappaB and Src pathways to be the most active in myxoid liposarcoma. Inhibition of Src by the small molecule tyrosine kinase inhibitor dasatinib showed only a mild effect on cell viability of myxoid liposarcoma cells. In contrast, inhibition of the nuclear factor-kappaB pathway, which is regulated by the FUS-DDIT3 fusion product, in myxoid liposarcoma cells using casein kinase 2 inhibitor 4,5,6,7-tetrabromobenzotriazole (TBB) showed a significant decrease in cell viability, decreased phosphorylation of nuclear factor-kappaB pathway proteins, and caspase 3 mediated apoptosis. Combination of dasatinib and TBB showed an enhanced effect.

CONCLUSION

Kinases associated with activation of the atypical nuclear factor-kappaB and the Src pathways are the most active in myxoid liposarcoma in vitro and inhibition of nuclear factor-kappaB pathway activation by inhibiting casein kinase 2 using TBB, of which the effect is enhanced by Src inhibition using dasatinib, offers new potential therapeutic strategies for myxoid liposarcoma patients with advanced disease.

Vitamin D3 upregulated protein 1 suppresses TNF-α-induced NF-κB activation in hepatocarcinogenesis

Vitamin D(3) upregulated protein 1 (VDUP1) is a candidate tumor suppressor, the expression of which is dramatically reduced in various tumor tissues. In this study, we found that VDUP1 expression is suppressed during human hepatic carcinogenesis, and mice lacking VDUP1 are much more susceptible to diethylnitrosamine-induced hepatocarcinogenesis compared with wild type mice. VDUP1-deficient tumors proliferated significantly more than wild type tumors and had corresponding changes in the expression of key cell cycle regulatory proteins. In addition, the hepatomitogen-induced response was associated with a considerable increase in the release of TNF-α and subsequent enhancement of NF-κB activation in VDUP1-deficient mice. When cells were treated with TNF-α, the VDUP1 level was markedly reduced, concomitant with elevated NF-κB activation. Furthermore, the overexpression of VDUP1 resulted in the robust suppression of TNF-α-activated NF-κB activity via association with HDAC1 and HDAC3. These results indicate that VDUP1 negatively regulates hepatocarcinogenesis by suppressing TNF-α-induced NF-κB activation.

Innate and adaptive factors regulating human immunodeficiency virus type 1 genomic activation

Over the past decade, antiretroviral therapy targeting the viral entry process, reverse transcriptase, integrase, and protease, has prolonged the lives of people infected with human immunodeficiency virus type 1 (HIV-1). However, despite the development of more effective therapeutic strategies, reservoirs of viral infection remain. This review discusses molecular mechanisms surrounding the development of latency from the site of integration to pre- and post-integration maintenance of latency, including epigenetic factors. In addition, an overview of innate and adaptive cells important to HIV-1 infection are examined from the viewpoint of cytokines released and cytokines that act on these cells to explore an overall understanding of HIV-1 proviral genome activation. Finally, this review is discussed from the viewpoint of how an understanding of the interplay of all of these factors will help guide the next generation of therapies.

Porcine reproductive and respiratory syndrome virus non-structural protein 1 suppresses tumor necrosis factor-alpha promoter activation by inhibiting NF-κB and Sp1

The objective of this study was to identify porcine reproductive and respiratory syndrome virus (PRRSV)-encoded proteins that are responsible for the inhibition of TNF-α expression and the mechanism(s) involved in this phenomenon. Using a TNF-α promoter reporter system, the non-structural protein 1 (Nsp1) was found to strongly suppress the TNF-α promoter activity. Such inhibition takes place especially at the promoter's proximal region. Both Nsp1α and Nsp1β, the two proteolytic fragments of Nsp1, were shown to be involved in TNF-α promoter suppression. Furthermore, using reporter plasmids specific for transcription factors (TFs) that bind to TNF-α promoter, Nsp1α and Nsp1β were demonstrated to inhibit the activity of the TFs that bind CRE-κB(3) and Sp1 elements respectively. Subsequent analyses showed that Nsp1α moderately inhibits NF-κB activation and that Nsp1β completely abrogates the Sp1 transactivation. These findings reveal one of the important mechanisms underlying the innate immune evasion by PRRSV during infection.

NF-kappaB p65 subunit mediates lipopolysaccharide-induced Na(+)/I(-) symporter gene expression by involving functional interaction with the paired domain transcription factor Pax8

The Gram-negative bacterial endotoxin lipopolysaccharide (LPS) elicits a variety of biological responses. Na(+)/I(-) symporter (NIS)-mediated iodide uptake is the main rate-limiting step in thyroid hormonogenesis. We have recently reported that LPS stimulates TSH-induced iodide uptake. Here, we further analyzed the molecular mechanism involved in the LPS-induced NIS expression in Fisher rat thyroid cell line 5 (FRTL-5) thyroid cells. We observed an increase in TSH-induced NIS mRNA expression in a dose-dependent manner upon LPS treatment. LPS enhanced the TSH-stimulated NIS promoter activity denoting the NIS-upstream enhancer region (NUE) as responsible for the stimulatory effects. We characterized a novel putative conserved kappaB site for the transcription factor nuclear factor-kappaB (NF-kappaB) within the NUE region. NUE contains two binding sites for the transcription factor paired box 8 (Pax8), main regulator of NIS transcription. A physical interaction was observed between the NF-kappaB p65 subunit and paired box 8 (Pax8), which appears to be responsible for the synergic effect displayed by these transcription factors on NIS gene transcription. Moreover, functional blockage of NF-kappaB signaling and site-directed mutagenesis of the kappaB cis-acting element abrogated LPS stimulation. Silencing expression of p65 confirmed its participation as an effector of LPS-induced NIS stimulation. Furthermore, chromatin immunoprecipitation corroborated that NIS is a novel target gene for p65 transactivation in response to LPS. Moreover, we were able to corroborate the LPS-stimulatory effect on thyroid cells in vivo in LPS-treated rats, supporting that thyrocytes are capable of responding to systemic infections. In conclusion, our results reveal a new mechanism involving p65 in the LPS-induced NIS expression, denoting a novel aspect in thyroid cell differentiation.

KappaB-Ras is a nuclear-cytoplasmic small GTPase that inhibits NF-kappaB activation through the suppression of transcriptional activation of p65/RelA

NF-κB is an important transcription factor involved in various biological responses, including inflammation, cell differentiation, and tumorigenesis. κB-Ras was identified as an IκB-interacting small GTPase and is reported to disturb cytokine-induced NF-κB activation. In this study, we established that κB-Ras is a novel type of nuclear-cytoplasmic small GTPase that mainly binds to GTP, and its localization seemed to be regulated by its GTP/GDP-binding state. Unexpectedly, the GDP-binding form of the κB-Ras mutant exhibited a more potent inhibitory effect on NF-κB activation, and this inhibitory effect seemed to be due to suppression of the transactivation of a p65/RelA NF-κB subunit. κB-Ras suppressed phosphorylation at serine 276 on the p65/RelA subunit, resulting in decreased interaction between p65/RelA and the transcriptional coactivator p300. Interestingly, the GDP-bound κB-Ras mutant exhibited higher interactive affinity with p65/RelA and inhibited the phosphorylation of p65/RelA more potently than wild-type κB-Ras. Taken together, these findings suggest that the GDP-bound form of κB-Ras in cytoplasm suppresses NF-κB activation by inhibiting its transcriptional activation.

Adiponectin increases BMP-2 expression in osteoblasts via AdipoR receptor signaling pathway

Adiponectin is a protein hormone secreted predominantly by differentiated adipocytes and involved in energy homeostasis. Bone morphogenetic protein (BMP) plays important roles in osteoblastic differentiation and bone formation. However, the effects of adiponectin on BMPs expression in cultured osteoblasts are largely unknown. Here we found that adiponectin increased mRNA expression of BMP-2 but not other BMPs in cultured osteoblastic cells. Stimulation of osteoblasts with adiponectin also increased protein levels of BMP-2 by Western blot and ELISA assay. Adiponectin-mediated BMP-2 expression was attenuated by 5'-AMP-activated protein kinase (AMPK) small interference RNA and AMPK inhibitor (araA and compound C). Activations of p38 and NF-kappaB pathways after adiponectin treatment were demonstrated, and adiponectin-induced expression of BMP-2 was inhibited by the specific inhibitor and mutant of p38 and NF-kappaB cascades. Taken together, our results provide evidence that adiponectin enhances BMP-2 expression in osteoblastic cells, and AdipoR1 receptor, AMPK, p38 and NF-kappaB signaling pathways may be involved in increasing BMP-2 expression by adiponectin.

TNF-alpha induces matrix metalloproteinase-9 expression in A549 cells: role of TNFR1/TRAF2/PKCalpha-dependent signaling pathways

Matrix metalloproteinases (MMPs), in particular MMP-9, have been shown to be induced by cytokines, including TNF-alpha and contributes to airway inflammation. However, the mechanisms underlying TNF-alpha-induced MMP-9 expression in human A549 cells remain unclear. Here, we report that TNF-alpha-induced MMP-9 gene expression was mediated through the TNFR1/TRAF2/PKCalpha-dependent signaling pathways in A549 cells, determined by zymographic, RT-PCR, and Western blotting analyses. TNF-alpha-induced MMP-9 expression was reduced by pretreatment with a TNFR Ab. Furthermore, TNF-alpha-induced TNFR1 and TRAF2 complex formation was revealed by immunoprecipitation using an anti-TNFR1 Ab followed by Western blot analysis against an anti-TRAF2 or anti-TNFR1 Ab. In addition, TNF-alpha-induced MMP-9 expression was also reduced by pretreatment with the inhibitor of PKCalpha (Gö6983), c-Src (PP1), EGFR (AG1478), or PI3K (LY294002) or transfection with siRNAs of PKCalpha, Src, EGFR, Akt, p65, p300, and c-Jun. On the other hand, TNF-alpha stimulated the phosphorylation of c-Src, EGFR, Akt, JNK1/2, and c-Jun, which were inhibited by pretreatment with Gö6983. We also showed that TNF-alpha induced Akt translocation and the formation of an Akt/p65/p300 complex. Pretreatment with the inhibitor of JNK1/2 (SP600125) but not the inhibitor of MEK1/2 (U0126), p38 MAPK (SB202190), or PI3K (LY294002), markedly inhibited TNF-alpha-induced c-Jun mRNA levels. Taken together, these data suggest that in A549 cells, TNF-alpha induces MMP-9 expression via the TNFR1/TRAF2/PKCalpha-dependent JNK1/2/c-Jun and c-Src/EGFR/PI3K/Akt pathways.

Regulation of NF-kappaB circuitry by a component of the nucleosome remodeling and deacetylase complex controls inflammatory response homeostasis

The MTA1 coregulator (metastatic tumor antigen 1), a component of the nucleosome remodeling and deacetylase (NuRD) complex, has been intimately linked with human cancer, but its role in inflammatory responses remains unknown. Here, we discovered that MTA1 is a target of inflammation, and stimulation of macrophages with Escherichia coli lipopolysaccharide (LPS) stimulates MTA1 transcription via the NF-kappaB pathway. Unexpectedly, we found that MTA1 depletion in LPS-stimulated macrophages impairs NF-kappaB signaling and expression of inflammatory molecules. MTA1 itself acts as a transcriptional coactivator of inflammatory cytokines in LPS-stimulated macrophages, and in contrast, it acts as a corepressor in resting primary macrophages as its depletion induced cytokine expression. LPS stimulates S-nitrosylation of histone deacetylase 2 (HDAC2) and interferes with its binding to MTA1, which, in turn, resulted in the loss of corepressor behavior of MTA1.HDAC complex in activated macrophages. Consequently, the net levels of inflammatory cytokines in LPS-stimulated macrophages from MTA1(-/-) mice were high compared with wild-type mice. Accordingly, MTA1(-/-) mice were much more susceptible than control mice to septic shock induced by LPS, revealing that MTA1 protects mice from deregulated host inflammatory response. These findings reveal a previously unrecognized, critical homeostatic role of MTA1, both as a target and as a component of the NF-kappaB circuitry, in the regulation of inflammatory responses.

A novel fluid resuscitation strategy modulates pulmonary transcription factor activation in a murine model of hemorrhagic shock

INTRODUCTION

Combining the hemodynamic and immune benefits of hypertonic saline with the anti-inflammatory effects of the phosphodiesterase inhibitor pentoxifylline (HSPTX) as a hemorrhagic shock resuscitation strategy reduces lung injury when compared with the effects of Ringer's lactate (RL). We hypothesized that HSPTX exerts its anti-inflammatory effects by interfering with nuclear factor kappa B/cAMP response element-binding protein (NF-kappaB-CREB) competition for the coactivator CREB-binding protein (CBP) in lung tissue, thus affecting pro-inflammatory mediator production.

METHODS

Male Sprague-Dawley rats underwent 60 minutes of hemorrhagic shock to reach a mean arterial blood pressure of 35 mmHg followed by resuscitation with either RL or HSPTX (7.5% HS + 25 mg/kg PTX). After four hours, lung samples were collected. NF-kappaB activation was assessed by measuring the levels of phosphorylated cytoplasmic inhibitor of kappa B (I-kappaB) and nuclear NF-kappaB p65 by western blot. NF-kappaB and CREB DNA-binding activity were measured by electrophoretic mobility shift assay (EMSA). Competition between NF-kappaB and CREB for the coactivator CBP was determined by immunoprecipitation. Interleukin-8 (IL-8) levels in the lung were measured by ELISA.

RESULTS

RL resuscitation produced significantly higher levels of lung IL-8 levels, I-kappaB phosphorylation, p65 phosphorylation, and NF-kappaB DNA binding compared with HSPTX. NF-kappaB-CBP-binding activity was similar in both groups, whereas CREB-CBP-binding activity was significantly increased with HSPTX. CREB-DNA binding-activity increased to a greater level with HSPTX compared with RL.

DISCUSSION

HSPTX decreases lung inflammation following hemorrhagic shock compared with conventional resuscitation using RL through attenuation of NF-kappaB signaling and increased CREB-DNA binding activity. HSPTX may have therapeutic potential in the attenuation of ischemia-reperfusion injury observed after severe hemorrhagic shock.

The role of epigenetics in the pathology of diabetic complications

Diabetes is associated with significantly accelerated rates of several debilitating microvascular complications such as nephropathy, retinopathy, and neuropathy, and macrovascular complications such as atherosclerosis and stroke. While several studies have been devoted to the evaluation of genetic factors related to type 1 and type 2 diabetes and associated complications, much less is known about epigenetic changes that occur without alterations in the DNA sequence. Environmental factors and nutrition have been implicated in diabetes and can also affect epigenetic states. Exciting research has shown that epigenetic changes in chromatin can affect gene transcription in response to environmental stimuli, and changes in key chromatin histone methylation patterns have been noted under diabetic conditions. Reports also suggest that epigenetics may be involved in the phenomenon of metabolic memory observed in clinic trials and animal studies. Further exploration into epigenetic mechanisms can yield new insights into the pathogenesis of diabetes and its complications and uncover potential therapeutic targets and treatment options to prevent the continued development of diabetic complications even after glucose control has been achieved.

Regulation of MCP-1 chemokine transcription by p53

BACKGROUND

Our previous studies showed that the expression of the monocyte-chemoattractant protein (MCP)-1, a chemokine, which triggers the infiltration and activation of cells of the monocyte-macrophage lineage, is abrogated in human papillomavirus (HPV)-positive premalignant and malignant cells. In silico analysis of the MCP-1 upstream region proposed a putative p53 binding side about 2.5 kb upstream of the transcriptional start. The aim of this study is to monitor a physiological role of p53 in this process.

RESULTS

The proposed p53 binding side could be confirmed in vitro by electrophoretic-mobility-shift assays and in vivo by chromatin immunoprecipitation. Moreover, the availability of p53 is apparently important for chemokine regulation, since TNF-alpha can induce MCP-1 only in human keratinocytes expressing the viral oncoprotein E7, but not in HPV16 E6 positive cells, where p53 becomes degraded. A general physiological role of p53 in MCP-1 regulation was further substantiated in HPV-negative cells harboring a temperature-sensitive mutant of p53 and in Li-Fraumeni cells, carrying a germ-line mutation of p53. In both cases, non-functional p53 leads to diminished MCP-1 transcription upon TNF-alpha treatment. In addition, siRNA directed against p53 decreased MCP-1 transcription after TNF-alpha addition, directly confirming a crosstalk between p53 and MCP-1.

CONCLUSION

These data support the concept that p53 inactivation during carcinogenesis also affects immune surveillance by interfering with chemokine expression and in turn communication with cells of the immunological compartment.

Transcriptome remodeling in hypoxic inflammation

Hypoxia is an integral component of the inflamed tissue microenvironment. Today, the influence of hypoxia on the natural evolution of inflammatory responses is widely accepted; however, many molecular and cellular mechanisms mediating this relationship remain to be clarified. Hypoxic stress affects several independent transcriptional regulators related to inflammation in which HIF-1 and NF-kappaB play central roles. Transcription factors interact with both HATs and HDACs, which are components of large multiprotein co-regulatory complexes. This review summarizes the current knowledge on hypoxia-responsive transcriptional pathways in inflammation and their importance in the etiology of chronic inflammatory diseases, with the primary focus on transcriptional co-regulators and histone modifications in defining gene-specific transcriptional responses in hypoxia, and on the recent progress in the understanding of hypoxia-mediated epigenetic reprogramming. Furthermore, this review discusses the molecular cross-talk between glucocorticoid anti-inflammatory pathways and hypoxia.

Transcription factor Egr-1 is essential for maximal matrix metalloproteinase-9 transcription by tumor necrosis factor alpha

Matrix metalloproteinase-9 (MMP-9) is involved in a wide range of normal and pathologic conditions, including inflammation, tissue repair, tumor invasion, and metastasis. Tumor necrosis factor alpha (TNFalpha) is a major proinflammatory cytokine that plays crucial roles in tumor progression, including tumor invasion and metastasis in the tumor microenvironment. Egr-1 is a member of the zinc-finger transcription factor family induced by diverse stimuli, including TNFalpha. However, the role of Egr-1 in MMP-9 expression was previously unknown. This study shows that Egr-1 directly binds to the MMP-9 promoter and plays an essential role for TNFalpha induction of MMP-9 transcription. Furthermore, Egr-1 together with NF-kappaB can synergistically activate both basal and TNFalpha-induced MMP-9 promoter activities in the presence of p300. We found that Egr-1 mediates extracellular signal-regulated kinase and c-jun NH(2)-terminal kinase mitogen-activated protein kinase-dependent MMP-9 transcription on TNFalpha stimulation. The requirement for Egr-1 in MMP-9 expression is further supported by the fact that HeLa cells expressing Egr-1 siRNA and Egr-1-null mouse embryonic fibroblasts were refractory to TNFalpha-induced MMP-9 expression. This report establishes that Egr-1 is essential for MMP-9 transcription in response to TNFalpha within the tumor microenvironment.

Epigenetics of diabetic complications

Type 1 and Type 2 diabetes are complex diseases associated with multiple complications, and both genetic and environmental factors have been implicated in these pathologies. While numerous studies have provided a wealth of knowledge regarding the genetics of diabetes, the mechanistic pathways leading to diabetes and its complications remain only partly understood. Studying the role of epigenetics in diabetic complications can provide valuable new insights to clarify the interplay between genes and the environment. DNA methylation and histone modifications in nuclear chromatin can generate epigenetic information as another layer of gene transcriptional regulation sensitive to environmental signals. Recent evidence shows that key biochemical pathways and epigenetic chromatin histone methylation patterns are altered in target cells under diabetic conditions and might also be involved in the metabolic memory phenomenon noted in clinical trials and animal studies. New therapeutic targets and treatment options could be uncovered from an in-depth study of the epigenetic mechanisms that might perpetuate diabetic complications despite glycemic control.

Molecular control of HIV-1 postintegration latency: implications for the development of new therapeutic strategies

The persistence of HIV-1 latent reservoirs represents a major barrier to virus eradication in infected patients under HAART since interruption of the treatment inevitably leads to a rebound of plasma viremia. Latency establishes early after infection notably (but not only) in resting memory CD4⁺ T cells and involves numerous host and viral trans-acting proteins, as well as processes such as transcriptional interference, RNA silencing, epigenetic modifications and chromatin organization. In order to eliminate latent reservoirs, new strategies are envisaged and consist of reactivating HIV-1 transcription in latently-infected cells, while maintaining HAART in order to prevent de novo infection. The difficulty lies in the fact that a single residual latently-infected cell can in theory rekindle the infection. Here, we review our current understanding of the molecular mechanisms involved in the establishment and maintenance of HIV-1 latency and in the transcriptional reactivation from latency. We highlight the potential of new therapeutic strategies based on this understanding of latency. Combinations of various compounds used simultaneously allow for the targeting of transcriptional repression at multiple levels and can facilitate the escape from latency and the clearance of viral reservoirs. We describe the current advantages and limitations of immune T-cell activators, inducers of the NF-κB signaling pathway, and inhibitors of deacetylases and histone- and DNA- methyltransferases, used alone or in combinations. While a solution will not be achieved by tomorrow, the battle against HIV-1 latent reservoirs is well- underway.

Crosstalk in inflammation: the interplay of glucocorticoid receptor-based mechanisms and kinases and phosphatases

Glucocorticoids (GCs) are steroidal ligands for the GC receptor (GR), which can function as a ligand-activated transcription factor. These steroidal ligands and derivatives thereof are the first line of treatment in a vast array of inflammatory diseases. However, due to the general surge of side effects associated with long-term use of GCs and the potential problem of GC resistance in some patients, the scientific world continues to search for a better understanding of the GC-mediated antiinflammatory mechanisms. The reversible phosphomodification of various mediators in the inflammatory process plays a key role in modulating and fine-tuning the sensitivity, longevity, and intensity of the inflammatory response. As such, the antiinflammatory GCs can modulate the activity and/or expression of various kinases and phosphatases, thus affecting the signaling efficacy toward the propagation of proinflammatory gene expression and proinflammatory gene mRNA stability. Conversely, phosphorylation of GR can affect GR ligand- and DNA-binding affinity, mobility, and cofactor recruitment, culminating in altered transactivation and transrepression capabilities of GR, and consequently leading to a modified antiinflammatory potential. Recently, new roles for kinases and phosphatases have been described in GR-based antiinflammatory mechanisms. Moreover, kinase inhibitors have become increasingly important as antiinflammatory tools, not only for research but also for therapeutic purposes. In light of these developments, we aim to illuminate the integrated interplay between GR signaling and its correlating kinases and phosphatases in the context of the clinically important combat of inflammation, giving attention to implications on GC-mediated side effects and therapy resistance.

Histone acetyltransferase p300 is a coactivator for transcription factor REL and is C-terminally truncated in the human diffuse large B-cell lymphoma cell line RC-K8

Human c-Rel (REL) is a member of the NF-kappaB family of transcription factors. REL's normal physiological role is in the regulation of B-cell proliferation and survival. The REL gene is amplified in many human B-cell lymphomas and overexpression of REL can transform chicken lymphoid cells. In this report, histone acetyltransferase p300 enhanced REL-induced transactivation and interacted with REL both in vitro and in REL-transformed chicken spleen cells and the B-lymphoma cell line RC-K8, in which REL is constitutively active and required for proliferation. However, due to a deletion in the EP300 locus, only a C-terminally truncated form of p300 is expressed in RC-K8 cells. These results suggest a role for p300 in REL-mediated oncogenic activity in B lymphoma.

HIV reservoirs, latency, and reactivation: prospects for eradication

Current antiretroviral therapy effectively suppresses but does not eradicate HIV-1 infection. During therapy patients maintain a persistent low-level viremia requiring lifelong adherence to antiretroviral therapies. This viremia may arise from latently infected reservoirs such as resting memory CD4+ T-cells or sanctuary sites where drug penetration is suboptimal. Understanding the mechanisms of HIV latency will help efforts to eradicate the infection. This review examines the dynamics of persistent viremia, viral reservoirs, the mechanisms behind viral latency, and methods to purge the viral reservoirs. This article forms part of a special issue of Antiviral Research marking the 25th anniversary of antiretroviral drug discovery and development, vol. 85, issue 1, 2010.

NF-kappaB activity is constitutively elevated in c-Abl null fibroblasts

The c-abl proto-oncogene encodes a nonreceptor tyrosine kinase involved in many cellular processes, including signaling from growth factor and antigen receptors, remodeling the cytoskeleton, and responding to DNA damage and oxidative stress. Many downstream pathways are affected by c-Abl. Elevated c-Abl kinase activity can inhibit NF-kappaB activity by stabilizing the inhibitory protein IkappaB alpha, raising the possibility that c-Abl-deficient cells might have increased NF-kappaB activity. We examined the levels of NF-kappaB activity in primary mouse embryonic fibroblasts (MEFs) derived from wild-type and c-Abl knockout mice and found that the knockout MEFs indeed exhibited elevated NF-kappaB activity in response to stimulation as well as constitutively elevated NF-kappaB activity. Thus, endogenous c-Abl is a negative regulator of basal and inducible NF-kappaB activity. Examination of various points of NF-kappaB regulation revealed that unstimulated c-Abl knockout MEFs do not exhibit an increase in IkappaB alpha degradation, p65/RelA nuclear translocation, or DNA binding of NF-kappaB subunits. They do, however, show reduced levels of the histone deacetylase HDAC1, a negative regulator of basal NF-kappaB activity. Unstimulated c-Abl knockout MEFs are less responsive to induction of NF-kappaB activity by trichostatin A, an HDAC inhibitor, suggesting that c-Abl might play a role in the HDAC-mediated repression of basal NF-kappaB activity.

Epidithiodiketopiperazines block the interaction between hypoxia-inducible factor-1alpha (HIF-1alpha) and p300 by a zinc ejection mechanism

The hypoxic response in humans is regulated by the hypoxia-inducible transcription factor system; inhibition of hypoxia-inducible factor (HIF) activity has potential for the treatment of cancer. Chetomin, a member of the epidithiodiketopiperazine (ETP) family of natural products, inhibits the interaction between HIF-alpha and the transcriptional coactivator p300. Structure-activity studies employing both natural and synthetic ETP derivatives reveal that only the structurally unique ETP core is required and sufficient to block the interaction of HIF-1alpha and p300. In support of both cell-based and animal work showing that the cytotoxic effect of ETPs is reduced by the addition of Zn(2+) through an unknown mechanism, our mechanistic studies reveal that ETPs react with p300, causing zinc ion ejection. Cell studies with both natural and synthetic ETPs demonstrated a decrease in vascular endothelial growth factor and antiproliferative effects that were abrogated by zinc supplementation. The results have implications for the design of selective ETPs and for the interaction of ETPs with other zinc ion-binding protein targets involved in gene expression.

CARM1 but not its enzymatic activity is required for transcriptional coactivation of NF-kappaB-dependent gene expression

Coactivator-associated arginine methyltransferase 1 (CARM1) belongs to the protein arginine methyltransferase family. It was reported to methylate histone as well as non-histone proteins and thus to be involved in transcriptional activation and mRNA degradation/stability. Here we report the genetic complementation of carm1-/- cells with wild-type CARM1 or an enzymatic inactive mutant of CARM1 to investigate the requirement of CARM1 and its enzymatic activity for nuclear factor kappaB (NF-kappaB)-dependent gene expression. Using custom microarray and quantitative reverse transcription PCR, we could define a subset of NF-kappaB target genes that required CARM1 for their proper expression. Although several tumor necrosis factor-alpha- and phorbol-12-myristate-13-acetate/ionomycin-induced NF-kappaB target genes are CARM1 dependent, CARM1 enzymatic activity was dispensable for gene expression. Interestingly, CARM1 was not required for the stimulus-dependent recruitment of RelA/p65 to chromatin, suggesting that CARM1 is rather contributing in protein complex stabilization. Together, our results confirm the importance of CARM1 as transcriptional cofactor without the involvement of its catalytic activity.

Thioredoxin interacting protein (TXNIP) induces inflammation through chromatin modification in retinal capillary endothelial cells under diabetic conditions

Chronic hyperglycemia and activation of receptor for advanced glycation end products (RAGE) are known risk factors for microvascular disease development in diabetic retinopathy. Thioredoxin-interacting protein (TXNIP), an endogenous inhibitor of antioxidant thioredoxin (TRX), plays a causative role in diabetes and its vascular complications. Herein we investigate whether HG and RAGE induce inflammation in rat retinal endothelial cells (EC) under diabetic conditions in culture through TXNIP activation and whether epigenetic mechanisms play a role in inflammatory gene expression. We show that RAGE activation by its ligand S100B or HG treatment of retinal EC induces the expression of TXNIP and inflammatory genes such as Cox2, VEGF-A, and ICAM1. TXNIP silencing by siRNA impedes RAGE and HG effects while stable over-expression of a cDNA for human TXNIP in EC elevates inflammation. p38 MAPK-NF-kappaB signaling pathway and histone H3 lysine (K) nine modifications are involved in TXNIP-induced inflammation. Chromatin immunoprecipitation (ChIP) assays reveal that TXNIP over-expression in EC abolishes H3K9 tri-methylation, a marker for gene inactivation, and increases H3K9 acetylation, an indicator of gene induction, at proximal Cox2 promoter bearing the NF-kappaB-binding site. These findings have important implications toward understanding the molecular mechanisms of ocular inflammation and endothelial dysfunction in diabetic retinopathy.

Cigarette smoke extract induces COX-2 expression via a PKCalpha/c-Src/EGFR, PDGFR/PI3K/Akt/NF-kappaB pathway and p300 in tracheal smooth muscle cells

Exposure to cigarette smoke extract (CSE) leads to airway or lung inflammation, which may be mediated through cyclooxygenase-2 (COX-2) expression and its product prostaglandin E2 (PGE2) synthesis. The aim of this study was to investigate the molecular mechanisms underlying CSE-induced COX-2 expression in human tracheal smooth muscle cells (HTSMCs). Here, we describe that COX-2 induction is dependent on PKCalpha/c-Src/EGFR, PDGFR/PI3K/Akt/NF-kappaB signaling in HTSMCs. CSE stimulated the phosphorylation of c-Src, EGFR, PDGFR, and Akt, which were inhibited by pretreatment with the inhibitor of PKCalpha (Gö6976 or Gö6983), c-Src (PP1), EGFR (AG1478), PDGFR (AG1296), or PI3K (LY294002). Moreover, CSE induced a significant increase in COX-2 expression, which was reduced by pretreatment with these inhibitors or transfection with siRNA of PKCalpha, Src, or Akt. Furthermore, CSE-stimulated NF-kappaB p65 phosphorylation and translocation were also attenuated by pretreatment with Gö6976, PP1, AG1478, AG1296, or LY294002. CSE-induced COX-2 expression was also mediated through the recruitment of p300 associated with NF-kappaB in HTSMCs, revealed by coimmunoprecipitation and Western blot analysis. In addition, pretreatment with the inhibitors of NF-kappaB (helenalin) and p300 (garcinol) or transfection with p65 siRNA and p300 siRNA markedly inhibited CSE-regulated COX-2 expression. However, CSE-induced PGE2 generation was reduced by pretreatment with the inhibitor of COX-2 (NS-398). These results demonstrated that in HTSMCs, CSE-induced COX-2-dependent PGE2 generation was mediated through PKCalpha/c-Src/EGFR, PDGFR/PI3K/Akt leading to the recruitment of p300 with NF-kappaB complex.

CpG methylation controls reactivation of HIV from latency

DNA methylation of retroviral promoters and enhancers localized in the provirus 5' long terminal repeat (LTR) is considered to be a mechanism of transcriptional suppression that allows retroviruses to evade host immune responses and antiretroviral drugs. However, the role of DNA methylation in the control of HIV-1 latency has never been unambiguously demonstrated, in contrast to the apparent importance of transcriptional interference and chromatin structure, and has never been studied in HIV-1-infected patients. Here, we show in an in vitro model of reactivable latency and in a latent reservoir of HIV-1-infected patients that CpG methylation of the HIV-1 5' LTR is an additional epigenetic restriction mechanism, which controls resistance of latent HIV-1 to reactivation signals and thus determines the stability of the HIV-1 latency. CpG methylation acts as a late event during establishment of HIV-1 latency and is not required for the initial provirus silencing. Indeed, the latent reservoir of some aviremic patients contained high proportions of the non-methylated 5' LTR. The latency controlled solely by transcriptional interference and by chromatin-dependent mechanisms in the absence of significant promoter DNA methylation tends to be leaky and easily reactivable. In the latent reservoir of HIV-1-infected individuals without detectable plasma viremia, we found HIV-1 promoters and enhancers to be hypermethylated and resistant to reactivation, as opposed to the hypomethylated 5' LTR in viremic patients. However, even dense methylation of the HIV-1 5'LTR did not confer complete resistance to reactivation of latent HIV-1 with some histone deacetylase inhibitors, protein kinase C agonists, TNF-alpha, and their combinations with 5-aza-2deoxycytidine: the densely methylated HIV-1 promoter was most efficiently reactivated in virtual absence of T cell activation by suberoylanilide hydroxamic acid. Tight but incomplete control of HIV-1 latency by CpG methylation might have important implications for strategies aimed at eradicating HIV-1 infection.

Oxidative stress induced lung cancer and COPD: opportunities for epigenetic therapy

Reactive oxygen species (ROS) form as a natural by-product of the normal metabolism of oxygen and play important roles within the cell. Under normal circumstances the cell is able to maintain an adequate homeostasis between the formation of ROS and its removal through particular enzymatic pathways or via antioxidants. If however, this balance is disturbed a situation called oxidative stress occurs. Critically, oxidative stress plays important roles in the pathogenesis of many diseases, including cancer. Epigenetics is a process where gene expression is regulated by heritable mechanisms that do not cause any direct changes to the DNA sequence itself, and disruption of epigenetic mechanisms has important implications in disease. Evidence is emerging that histone deacetylases (HDACs) play decisive roles in regulating important cellular oxidative stress pathways including those involved with sensing oxidative stress and those involved with regulating the cellular response to oxidative stress. In particular aberrant regulation of these pathways by HDACs may play critical roles in cancer progression. In this review we discuss the current evidence linking epigenetics and oxidative stress and cancer, using chronic obstructive pulmonary disease and non-small cell lung cancer to illustrate the importance of epigenetics on these pathways within these disease settings.

Pharmacologic resuscitation: cell protective mechanisms of histone deacetylase inhibition in lethal hemorrhagic shock

BACKGROUND

We have demonstrated that valproic acid (VPA), a histone deacetylase inhibitor (HDACI), can improve animal survival after hemorrhagic shock, and protect neurons from hypoxia-induced apoptosis. This study investigated whether VPA treatment works through the c-Jun N-terminal kinase (JNK)/Caspase-3 survival pathways.

METHODS

Wistar-Kyoto rats underwent hemorrhagic shock (60% blood loss over 60 min) followed by post-shock treatment with VPA (300 mg/kg), without any additional resuscitation fluids. The experimental groups were: (1) Sham (no hemorrhage, no resuscitation), (2) no resuscitation (hemorrhage, no resuscitation), and (3) VPA treatment. The animals were sacrificed at 1, 6, or 24h (n=3/timepoint), and liver tissue was harvested. Cytosolic and nuclear proteins were isolated and analyzed for acetylated histone-H3 at lysine-9 (Ac-H3K9), total and phosphorylated JNK, and activated caspase-3 by Western blot.

RESULTS

Hemorrhaged animals were in severe shock, with mean arterial pressures of 25-30 mmHg and lactic acid 7-9 mg/dL. As expected, only the VPA treated animals survived to the 6- and 24-h timepoints; none of the non-resuscitated animals survived to these time points. Treatment of hemorrhaged animals with VPA induced acetylation of histone H3K9, which peaked at 1h and returned back to normal by 24h. Hemorrhage induced phosphorylation of JNK (active form) and increased activated caspase-3 levels, representing a commitment to subsequent cell death. Treatment with VPA decreased the phospho-JNK (P=0.06) expression at 24h, without changing the total levels of JNK (P=0.89), and this correlated with attenuation of activated caspase-3 at 24h (P=0.04), compared with the non-resuscitated animals.

CONCLUSION

Treatment with HDACI, induces acetylation of histone H3K9, and reduces JNK phosphorylation and subsequent caspase-3 activation. This discovery establishes for the first time that HDACI may protect cells after severe hemorrhage through modulation of the JNK/caspase-3 apoptotic pathway.

Regulation of chemokine gene expression by hypoxia via cooperative activation of NF-kappaB and histone deacetylase

Hypoxia is a microenvironmental factor frequently associated with tumors and inflammation. This study addresses the question of how hypoxia modulates the basal and IL-1 beta-induced production of cytokines and aims to identify the underlying mechanism of hypoxic transcriptional repression. We found that despite the similarities of the promoter structures of IL-8 and MCP-1, these chemokines were differently regulated by hypoxia (an increase in IL-8, but a decrease in MCP-1 mRNA and protein expression). Such differences were not observed in a reporter gene assay, in which both of the promoters were activated by hypoxia. The difference in the response to hypoxia between MCP-1 expression and the promoter assay was not due to mRNA instability. Using proteosome inhibitor MG132 and I kappaB overexpression we demonstrated that an NF-kappaB-dependent mechanism was involved in both the activation of IL-8 and the repression of MCP-1 mRNA expression in response to hypoxia. The histone deacetylase inhibitor Trihostatin A abolished the inhibitory actions of hypoxia on IL-1 beta-induced MCP-1 gene expression. Furthermore, hypoxia induced histone deacetylase activity in the nuclear extracts. Although stimulation with IL-1 beta and/or hypoxia increased the acetylation of histones H3 and H4 in the presence of Trihostatin A, histone acetylation remained unchanged when the cells were treated without histone deacetylase inhibitor. Collectively, our findings suggest that transiently transfected promoters are not subject to the same NF-kappaB regulatory mechanisms as their chromatinized counterparts. NF-kappaB, activated by hypoxia, can act as a transcriptional repressor via a mechanism that involves deacetylation of histones.

Intestinal hormones and growth factors: effects on the small intestine

There are various hormones and growth factors which may modify the intestinal absorption of nutrients, and which might thereby be useful in a therapeutic setting, such as in persons with short bowel syndrome. In part I, we focus first on insulin-like growth factors, epidermal and transferring growth factors, thyroid hormones and glucocorticosteroids. Part II will detail the effects of glucagon-like peptide (GLP)-2 on intestinal absorption and adaptation, and the potential for an additive effect of GLP2 plus steroids.

Loss of CFTR results in reduction of histone deacetylase 2 in airway epithelial cells

Inflammatory cytokines, particularly the neutrophil chemoattractant IL-8, are elevated in the cystic fibrosis (CF) airway, even in the absence of detectable infection. The transcriptional regulation of many inflammatory genes, including IL8 (CXCL8), involves chromatin remodeling through histone acetylation. NF-kappaB is known to facilitate histone acetylation of IL8 and other proinflammatory gene promoters, but we find that increased NF-kappaB activation cannot explain the elevated IL8 expression and promoter acetylation seen in CFTR-deficient cells. Recognized components of the NF-kappaB-coactivator complex, acetyltransferase CBP, p300, and the histone deacetylase HDAC1, are unchanged by CFTR activity. However, we find that the histone acetyltransferase (HAT)/HDAC balance is sensitive to CFTR function, as cells with reduced or absent CFTR function have decreased HDAC2 protein, resulting in hyperacetylation of the IL8 promoter and increased IL8 transcription. Reduced HDAC2 and HDAC2 activity, but not HDAC2 mRNA, is observed in cells deficient in CFTR. Suppressing HDAC2 expression with HDAC2 short hairpin RNA (shRNA) results in increased IL8 expression and promoter acetylation comparable with CFTR-deficient cells. Treating CFTR-deficient cells with N-acetyl-cysteine (NAC) increases HDAC2 expression to near control levels. Our data suggest that there is an intrinsic alteration in the HAT/HDAC balance in cells lacking CFTR function in vitro and in native CF tissue and that oxidative stress is likely contributing to this alteration. This mechanism, found in other inflammatory airway diseases, provides an explanation for the apparent dysregulation of inflammatory mediators seen in the CF airway, as reduced histone deacetylation would potentially influence many genes.

Identification of genes, including the gene encoding p27Kip1, regulated by serine 276 phosphorylation of the p65 subunit of NF-kappaB

Phosphorylation of the p65 subunit of NF-kappaB is required for its transcriptional activity. Recent reports show that phosphorylation of p65 at serine 276 regulates only a subset of genes, such as those encoding IL-6, IL-8, Gro-beta, and ICAM-1. In order to identify additional genes regulated by serine 276 phosphorylation, HepG2 hepatoma cells were infected with adenoviruses encoding either wild-type p65 or the S276A mutant of p65, followed by DNA microarray analysis. The results show that mutation of serine 276 affected the expression of several genes that encode proteins involved in cell cycle regulation, signal transduction, transcription, and metabolism. Notably, expression of S276A increased the mRNA and protein level of p27, a cell cycle inhibitory protein, which led to an increased association of p27 with cdk2, and inhibition of cdk2 activity. Furthermore, while wild-type NF-kappaB is known to increase cell proliferation in a number of different cancer cell lines, our data shows that S276A inhibited cell proliferation. Evidence is mounting that NF-kappaB plays a pivotal role in oncogenesis. Therapeutic agents that regulate the phosphorylation of serine 276 and p27 gene expression, therefore, may be useful as anti-cancer agents in the future.

The DEAD-box RNA helicase DDX1 interacts with RelA and enhances nuclear factor kappaB-mediated transcription

DEAD-box RNA helicases constitute the largest family of RNA helicases and are involved in many aspects of RNA metabolism. In this study, we identified RelA (p65), a subunit of nuclear factor-kappaB (NF-kappaB), as a cellular co-factor of DEAD-box RNA helicase DDX1, through mammalian two hybrid system and co-immunoprecipitation assay. Additionally, confocal microscopy and chromatin immunoprecipitation assays confirmed this interaction. In NF-kappaB dependent reporter gene assay, DDX1 acted as a co-activator to enhance NF-kappaB-mediated transcription activation. The functional domains involved were mapped to the carboxy terminal transactivation domain of RelA and the amino terminal ATPase/helicase domain of DDX1. The DDX1 trans-dominant negative mutant lacking ATP-dependent RNA helicase activity lost it transcriptional inducer activity. Moreover, depletion of endogenous DDX1 by specific small interfering RNAs significantly reduced NF-kappaB-dependent transcription. Taken together, the results suggest that DDX1 may play an important role in NF-kappaB-mediated transactivation, and revelation of this regulatory pathway may help to explore the novel mechanisms for regulating NF-kappaB transcriptional activity.

NF-kappaB serves as a cellular sensor of Kaposi's sarcoma-associated herpesvirus latency and negatively regulates K-Rta by antagonizing the RBP-Jkappa coactivator

Successful viral replication is dependent on a conducive cellular environment; thus, viruses must be sensitive to the state of their host cells. We examined the idea that an interplay between viral and cellular regulatory factors determines the switch from Kaposi's sarcoma-associated herpesvirus (KSHV) latency to lytic replication. The immediate-early gene product K-Rta is the first viral protein expressed and an essential factor in reactivation; accordingly, this viral protein is in a key position to serve as a viral sensor of cellular physiology. Our approach aimed to define a host transcription factor, i.e., host sensor, which modulates K-Rta activity on viral promoters. To this end, we developed a panel of reporter plasmids containing all 83 putative viral promoters for a comprehensive survey of the response to both K-Rta and cellular transcription factors. Interestingly, members of the NF-kappaB family were shown to be strong negative regulators of K-Rta transactivation for all but two viral promoters (Ori-RNA and K12). Recruitment of K-Rta to the ORF57 and K-bZIP promoters, but not the K12 promoter, was significantly impaired when NF-kappaB expression was induced. Many K-Rta-responsive promoters modulated by NF-kappaB contain the sequence of the RBP-Jkappa binding site, a major coactivator which anchors K-Rta to target promoters via consensus motifs which overlap with that of NF-kappaB. Gel shift assays demonstrated that NF-kappaB inhibits the binding of RBP-Jkappa and forms a complex with RBP-Jkappa. Our results support a model in which a balance between K-Rta/RBP-Jkappa and NF-kappaB activities determines KSHV reactivation. An important feature of this model is that the interplay between RBP-Jkappa and NF-kappaB on viral promoters controls viral gene expression mediated by K-Rta.

Structural basis for recruitment of CBP/p300 coactivators by STAT1 and STAT2 transactivation domains

CBP/p300 transcriptional coactivators mediate gene expression by integrating cellular signals through interactions with multiple transcription factors. To elucidate the molecular and structural basis for CBP-dependent gene expression, we determined structures of the CBP TAZ1 and TAZ2 domains in complex with the transactivation domains (TADs) of signal transducer and activator of transcription 2 (STAT2) and STAT1, respectively. Despite the topological similarity of the TAZ1 and TAZ2 domains, subtle differences in helix packing and surface grooves constitute major determinants of target selectivity. Our results suggest that TAZ1 preferentially binds long TADs capable of contacting multiple surface grooves simultaneously, whereas smaller TADs that are restricted to a single contiguous binding surface form complexes with TAZ2. Complex formation for both STAT TADs involves coupled folding and binding, driven by intermolecular hydrophobic and electrostatic interactions. Phosphorylation of S727, required for maximal transcriptional activity of STAT1, does not enhance binding to any of the CBP domains. Because the different STAT TADs recognize different regions of CBP/p300, there is a potential for multivalent binding by STAT heterodimers that could enhance the recruitment of the coactivators to promoters.

Muscle precursor cells isolated from aged rats exhibit an increased tumor necrosis factor- alpha response

Improving muscle precursor cell (MPC, muscle-specific stem cells) function during aging has been implicated as a key therapeutic target for improving age-related skeletal muscle loss. MPC dysfunction during aging can be attributed to both the aging MPC population and the changing environment in skeletal muscle. Previous reports have identified elevated levels of tumor necrosis factor- alpha (TNF- alpha ) in aging, both circulating and locally in skeletal muscle. The purpose of the present study was to determine if age-related differences exist between TNF- alpha -induced nuclear factor-kappa B (NF- kappaB) activation and expression of apoptotic gene targets. MPCs isolated from 32-month-old animals exhibited an increased NF- kappaB activation in response to 1, 5, and 20 ng mL(-1) TNF- alpha, compared to MPCs isolated from 3-month-old animals. No age differences were observed in the rapid canonical signaling events leading to NF- kappaB activation or in the increase in mRNA levels for TNF receptor 1, TNF receptor 2, TNF receptorassociated factor 2 (TRAF2), or Fas (CD95) observed after 2 h of TNF- alpha stimulation. Interestingly, mRNA levels for TRAF2 and the cell death-inducing receptor, Fas (CD95), were persistently upregulated in response to 24 h TNF- alpha treatment in MPCs isolated from 32-month-old animals, compared to 3-month-old animals. Our data indicate that age-related differences may exist in the regulatory mechanisms responsible for NF- kappaB inactivation, which may have an effect on TNF- alpha-induced apoptotic signaling. These findings improve our understanding of the interaction between aged MPCs and the changing environment associated with age, which is critical for the development of potential clinical interventions aimed at improving MPC function with age.

Methyl-CpG targeted recruitment of p300 reactivates tumor suppressor genes in human cancer cells

Aberrant hypermethylation of gene promoters is a major mechanism associated with inactivation of tumor suppressor genes (TSGs) in cancer. We have previously shown that the methyl-CpG targeted transcriptional activation (MeTA) that allows re-expression of TSGs in human cancer cells is accomplished by combining a methyl-CpG binding domain (MBD) with a NFkappaB transcriptional activation domain (AD), accompanied by histone H3K9/K14 acetylation. Herein we demonstrate that p300 histone acetyltransferase (HAT), one of the NFkappaB (AD)-associated coactivators, reactivates epigenetically silenced MLH1 in 293T cells. Interestingly, the HAT domain of p300 is not essential for the reactivation of MLH1; instead, the C-terminal transactivation domain (C-TAD) but not the N-terminal one (N-TAD) reactivates MLH1. Furthermore, all ten of the cancer-related genes analyzed in three types of cancer cells were reactivated by the effect of p300 linked to MBD. These results demonstrate that it is possible to reactivate epigenetically silenced TSGs in human cancer cells by direct targeting of a transcriptional coactivator at highly methylated promoters.

Control of stochastic gene expression by host factors at the HIV promoter

The HIV promoter within the viral long terminal repeat (LTR) orchestrates many aspects of the viral life cycle, from the dynamics of viral gene expression and replication to the establishment of a latent state. In particular, after viral integration into the host genome, stochastic fluctuations in viral gene expression amplified by the Tat positive feedback loop can contribute to the formation of either a productive, transactivated state or an inactive state. In a significant fraction of cells harboring an integrated copy of the HIV-1 model provirus (LTR-GFP-IRES-Tat), this bimodal gene expression profile is dynamic, as cells spontaneously and continuously flip between active (Bright) and inactive (Off) expression modes. Furthermore, these switching dynamics may contribute to the establishment and maintenance of proviral latency, because after viral integration long delays in gene expression can occur before viral transactivation. The HIV-1 promoter contains cis-acting Sp1 and NF-κB elements that regulate gene expression via the recruitment of both activating and repressing complexes. We hypothesized that interplay in the recruitment of such positive and negative factors could modulate the stability of the Bright and Off modes and thereby alter the sensitivity of viral gene expression to stochastic fluctuations in the Tat feedback loop. Using model lentivirus variants with mutations introduced in the Sp1 and NF-κB elements, we employed flow cytometry, mRNA quantification, pharmacological perturbations, and chromatin immunoprecipitation to reveal significant functional differences in contributions of each site to viral gene regulation. Specifically, the Sp1 sites apparently stabilize both the Bright and the Off states, such that their mutation promotes noisy gene expression and reduction in the regulation of histone acetylation and deacetylation. Furthermore, the NF-κB sites exhibit distinct properties, with κB site I serving a stronger activating role than κB site II. Moreover, Sp1 site III plays a particularly important role in the recruitment of both p300 and RelA to the promoter. Finally, analysis of 362 clonal cell populations infected with the viral variants revealed that mutations in any of the Sp1 sites yield a 6-fold higher frequency of clonal bifurcation compared to that of the wild-type promoter. Thus, each Sp1 and NF-κB site differentially contributes to the regulation of viral gene expression, and Sp1 sites functionally “dampen” transcriptional noise and thereby modulate the frequency and maintenance of this model of viral latency. These results may have biomedical implications for the treatment of HIV latency.

After HIV genome integration into the host chromosome, the viral promoter coordinates a complex set of inputs to control the establishment of viral latency, the onset of viral gene expression, and the ensuing gene expression levels. Among these inputs are chromatin structure at the site of integration, host transcription factors, and the virally encoded transcriptional regulator Tat. Importantly, transcriptional noise from host and viral transcriptional regulators may play a critical role in the decision between replication versus latency, because stochastic fluctuations in gene expression are amplified by a Tat-mediated positive transcriptional feedback loop. To evaluate the individual contributions of key transcription factor binding elements in gene expression dynamics, we employ model HIV viruses with mutations introduced into numerous promoter elements. Extensive analysis of gene expression dynamics and transcription factor recruitment to the viral promoter reveals that each site differentially contributes to viral gene expression and to the establishment of a low expression state that may contribute to viral latency. This systems-level approach elucidates the synergistic contributions of host and viral factors to the dynamics, magnitudes, and stochastic effects in viral gene expression, as well as provides insights into mechanisms that contribute to proviral latency.

Increased migration of Langerhans cells in response to HPV16 E6 and E7 oncogene silencing: role of CCL20

Human papillomavirus (HPV) infection, particularly type 16, is causally associated with cancer of the uterine cervix. The persistence or progression of cervical lesions suggests that viral antigens are not adequately presented to the immune system. This hypothesis is reinforced by the observation that most squamous intraepithelial lesions (SILs) show quantitative and functional alterations of Langerhans cells (LC). The infiltration of immature LC in the squamous epithelium is mainly controlled by Macrophage Inflammatory Protein 3alpha/CCL20. After having shown that CCL20 production is altered in HPV-transformed keratinocytes (KC), the possible role of HPV16 E6 and E7 viral oncoproteins in the reduced CCL20 levels observed in SILs was investigated by silencing HPV16 E6 and E7 oncogenes by RNA interference (siRNA). This treatment not only increased CCL20 secretion but also resulted in the modulation of NF-kappaB p50, p52 and p65 precursor localization. Moreover, silencing of E6 and E7 oncogenes in HPV16-transformed KC induced a significantly higher migratory capacity of LC in a Boyden chamber assay and in an in vitro formed (pre)neoplastic epithelium reminiscent of high-grade SILs. Anti-CCL20 neutralizing antibody experiments showed that the increased migration of LC is due to the re-expression of CCL20 in E6 and E7 siRNA transfected KC. These data suggest that HPV16 E6/E7-induced down-regulation of CCL20 observed during the cervical carcinogenesis may contribute to a diminished capacity of the immune system to control HPV infection.

Gamma-secretase-dependent and -independent effects of presenilin1 on beta-catenin.Tcf-4 transcriptional activity

Presenilin1 (PS1) is a component of the gamma-secretase complex mutated in cases of Familial Alzheimer's disease (FAD). PS1 is synthesized as a 50 kDa peptide subsequently processed to two 29 and 20 kDa subunits that remain associated. Processing of PS1 is inhibited by several mutations detected in FAD patients. PS1 acts as negative modulator of beta-catenin.Tcf-4 transcriptional activity. In this article we show that in murine embryonic fibroblasts (MEFs) the mechanisms of action of the processed and non-processed forms of PS1 on beta-catenin.Tcf-4 transcription are different. Whereas non-processed PS1 inhibits beta-catenin.Tcf-4 activity through a mechanism independent of gamma-secretase and associated with the interaction of this protein with plakoglobin and Tcf-4, the effect of processed PS1 is prevented by gamma-secretase inhibitors, and requires its interaction with E- or N-cadherin and the generation of cytosolic terminal fragments of these two cadherins, which in turn destabilize the beta-catenin transcriptional cofactor CBP. Accordingly, the two forms of PS1 interact differently with E-cadherin or beta-catenin and plakoglobin: whereas processed PS1 binds E-cadherin with high affinity and beta-catenin or plakoglobin weakly, the non-processed form behaves inversely. Moreover, contrarily to processed PS1, that decreases the levels of c-fos RNA, non-processed PS1 inhibits the expression c-myc, a known target of beta-catenin.Tcf-4, and does not block the activity of other transcriptional factors requiring CBP. These results indicate that prevention of PS1 processing in FAD affects the mechanism of repression of the transcriptional activity dependent on beta-catenin.

Adenovirus E1A regulates lung epithelial ICAM-1 expression by interacting with transcriptional regulators at its promoter

We focused on the regulation of inflammatory mediator expression by adenovirus E1A in lung epithelial cells and the role of this viral protein in the pathogenesis of chronic obstructive pulmonary disease (COPD). We previously reported that E1A, a well-known regulator of host genes, increased ICAM-1 expression in human bronchial epithelial (HBE) and A549 cells in response to LPS stimulation. In this report, we clarified the mechanism of this regulation. We found NF-kappaB translocation to the nucleus after LPS stimulation in both E1A-positive and -negative HBE cells. ICAM-1 promoter reporter constructs revealed that a mutation in the proximal NF-kappaB binding site completely inhibited increased transcription, whereas the mutation in a distal site did not. We analyzed the participation of E1A in transcriptional complex formation at this promoter using chromatin immunoprecipitation. In E1A-positive HBE and A549 cells, LPS stimulation increased ICAM-1 promoter immunoprecipitation by NF-kappaB p65 and p300 but not activator protein-1 antibodies with a concomitant increase by the E1A antibody. No increase was found in E1A-negative cells except in HBE cells with p65 antibody. The association of E1A with the increased promoter immunoprecipitation with p300 was also observed after TNF-alpha stimulation of A549 cells. These results suggest that adenovirus E1A regulates the ICAM-1 promoter through its proximal NF-kappaB binding site, most likely by interacting with the transcriptional complex that forms at this site. E1A regulation of the LPS response may play a role in acute exacerbations as a consequence of bacterial infections in COPD.

Brd4 coactivates transcriptional activation of NF-kappaB via specific binding to acetylated RelA

Acetylation of the RelA subunit of NF-kappaB, especially at lysine-310, is critical for the transcriptional activation of NF-kappaB and the expression of inflammatory genes. In this study, we demonstrate that bromodomains of Brd4 bind to acetylated lysine-310. Brd4 enhances transcriptional activation of NF-kappaB and the expression of a subset of NF-kappaB-responsive inflammatory genes in an acetylated lysine-310-dependent manner. Bromodomains of Brd4 and acetylated lysine-310 of RelA are both required for the mutual interaction and coactivation function of Brd4. Finally, we demonstrate that Brd4 further recruits CDK9 to phosphorylate C-terminal domain of RNA polymerase II and facilitate the transcription of NF-kappaB-dependent inflammatory genes. Our results identify Brd4 as a novel coactivator of NF-kappaB through specifically binding to acetylated lysine-310 of RelA. In addition, these studies reveal a mechanism by which acetylated RelA stimulates the transcriptional activity of NF-kappaB and the NF-kappaB-dependent inflammatory response.

Tcl1 functions as a transcriptional regulator and is directly involved in the pathogenesis of CLL

B cell chronic lymphocytic leukemia (B-CLL) is the most common human leukemia. Deregulation of the T cell leukemia/lymphoma 1 (TCL1) oncogene in mouse B cells causes a CD5-positive leukemia similar to aggressive human B-CLLs. To examine the mechanisms by which Tcl1 protein exerts oncogenic activity in B cells, we investigated the effect of Tcl1 expression on NF-kappaB and activator protein 1 (AP-1) activity. We found that Tcl1 physically interacts with c-Jun, JunB, and c-Fos and inhibits AP-1 transcriptional activity. Additionally, Tcl1 activates NF-kappaB by physically interacting with p300/CREB binding protein. We then sequenced the TCL1 gene in 600 B-CLL samples and found 2 heterozygous mutations: T38I and R52H. Importantly, both mutants showed gain of function as AP-1 inhibitors. The results indicate that Tcl1 overexpression causes B-CLL by directly enhancing NF-kappaB activity and inhibiting AP-1.

A dimer-specific function of the transcription factor NFATp

The transcription factor NFATp integrates multiple signal transduction pathways through coordinate binding with basic-region leucine zipper (bZIP) proteins and other transcription factors. The NFATp monomer, even in the absence of its activation domains, recruits bZIP proteins to canonical NFAT-bZIP composite DNA elements. By contrast, the NFATp dimer and its bZIP partner bind noncooperatively to the NFAT-bZIP element of the tumor necrosis factor (TNF) gene promoter. This observation raises the possibility that the function of the activation domains of NFATp is dimer-specific. Here, we determine the consensus DNA binding site of the NFATp dimer, describe monomer- and dimer-specific NFATp-DNA contact patterns, and demonstrate that NFATp dimerization and dimer-specific activation subdomains are required for transcriptional activation from the TNF NFAT-bZIP element. We also show that these NFATp subdomains interact with the coactivator CBP (CREB-binding protein), which is required for NFATp-dependent TNF gene transcription. Thus, the context-specific function of the activation domains of NFAT can be potentiated by DNA-directed dimerization.

Transcriptional activation of human matrix metalloproteinase-9 gene expression by multiple co-activators

Matrix metalloproteinase-9 (MMP-9), a proteolytic enzyme for matrix proteins, chemokines and cytokines, is a major target in cancer and autoimmune diseases, since it is aberrantly upregulated. To control MMP-9 expression in pathological conditions, it is necessary to understand the regulatory mechanisms of MMP-9 expression. MMP-9 gene expression is regulated primarily at the transcriptional level. In this study, we investigated the role of multiple co-activators in regulating MMP-9 transcription. We demonstrate that multiple transcriptional co-activators are involved in MMP-9 promoter activation, including CBP/p300, PCAF, CARM1 and GRIP1. Furthermore, enhancement of MMP-9 promoter activity requires the histone acetyltransferase activity of PCAF but not that of CBP/p300, and the methyltransferase activity of CARM1. More importantly, these co-activators are able to activate MMP-9 promoter activity independently, and function in a synergistic manner. Significant synergy was observed among CARM1, p300 and GRIP1, which is dependent on the interaction of p300 and CARM1 with the AD1 and AD2 domains of GRIP1, respectively. This suggests the formation of a ternary co-activator complex on the MMP-9 promoter. Chromatin immunoprecipitation assays demonstrate that these co-activators associate with the endogenous MMP-9 promoter, and that siRNA knockdown of expression of these co-activators reduces endogenous MMP-9 expression. Taken together, these studies demonstrate a new level of transcriptional regulation of MMP-9 expression by the cooperative action of co-activators.