Enhancement of nuclear factor-kappa B acetylation by coactivator p300 and HIV-1 Tat proteins

Enhanced NF-κB activation via HIV-1 Tat-TRAF6 cross-talk

The Tat proteins of HIV-1 and simian immunodeficiency virus (SIV) are essential for activating viral transcription. In addition, Tat stimulates nuclear factor κB (NF-κB) signaling pathways to regulate viral gene expression although its molecular mechanism is unclear. Here, we report that Tat directly activates NF-κB through the interaction with TRAF6, which is an essential upstream signaling molecule of the canonical NF-κB pathway. This interaction increases TRAF6 oligomerization and auto-ubiquitination, as well as the synthesis of K63-linked polyubiquitin chains to further activate the NF-κB pathway and HIV-1 transcription. Moreover, ectopic expression of TRAF6 significantly activates HIV-1 transcription, whereas TRAF6 knockdown inhibits transcription. Furthermore, Tat-mediated activation of NF-κB through TRAF6 is conserved among HIV-1, HIV-2, and SIV isolates. Our study uncovers yet another mechanism by which HIV-1 subverts host transcriptional pathways to enhance its own transcription.

The role of B-Cell Lymphoma-3 (BCL-3) in enabling the hallmarks of cancer: implications for the treatment of colorectal carcinogenesis

With its identification as a proto-oncogene in chronic lymphocytic leukaemia and central role in regulating NF-κB signalling, it is perhaps not surprising that there have been an increasing number of studies in recent years investigating the role of BCL-3 (B-Cell Chronic Lymphocytic Leukaemia/Lymphoma-3) in a wide range of human cancers. Importantly, this work has begun to shed light on our mechanistic understanding of the function of BCL-3 in tumour promotion and progression. Here, we summarize the current understanding of BCL-3 function in relation to the characteristics or traits associated with tumourigenesis, termed ‘Hallmarks of Cancer’. With the focus on colorectal cancer, a major cause of cancer related mortality in the UK, we describe the evidence that potentially explains why increased BCL-3 expression is associated with poor prognosis in colorectal cancer. As well as promoting tumour cell proliferation, survival, invasion and metastasis, a key emerging function of this proto-oncogene is the regulation of the tumour response to inflammation. We suggest that BCL-3 represents an exciting new route for targeting the Hallmarks of Cancer; in particular by limiting the impact of the enabling hallmarks of tumour promoting inflammation and cell plasticity. As BCL-3 has been reported to promote the stem-like potential of cancer cells, we suggest that targeting BCL-3 could increase the tumour response to conventional treatment, reduce the chance of relapse and hence improve the prognosis for cancer patients.

Post-translational Modification-Based Regulation of HIV Replication

Human immunodeficiency virus (HIV) relies heavily on the host cellular machinery for production of viral progeny. To exploit cellular proteins for replication and to overcome host factors with antiviral activity, HIV has evolved a set of regulatory and accessory proteins to shape an optimized environment for its replication and to facilitate evasion from the immune system. Several cellular pathways are hijacked by the virus to modulate critical steps during the viral life cycle. Thereby, post-translational modifications (PTMs) of viral and cellular proteins gain increasingly attention as modifying enzymes regulate virtually every step of the viral replication cycle. This review summarizes the current knowledge of HIV-host interactions influenced by PTMs with a special focus on acetylation, ubiquitination, and phosphorylation of proteins linked to cellular signaling and viral replication. Insights into these interactions are surmised to aid development of new intervention strategies.

TSG-6 secreted by bone marrow mesenchymal stem cells attenuates intervertebral disc degeneration by inhibiting the TLR2/NF-κB signaling pathway

Inflammation has been correlated with intervertebral disc degeneration (IDD). Recent evidence suggests that TNF-α-stimulated gene 6 protein (TSG-6) secreted by bone marrow mesenchymal stem cells (BMSCs) displays a remarkable ability to inhibit inflammatory processes in a variety of diseases. However, it is unknown whether BMSCs exert their therapeutic effect against IDD by secreting TSG-6. Here we investigated the effects of BMSCs and TSG-6 on IDD and explored the possible underlying mechanisms in vitro and in vivo. We found that BMSCs and TSG-6 reduced the expression of MMP-3 and MMP-13, and increased the expression of collagen II and aggrecan in the IL-1β-treated nucleus pulposus cells (NPCs), but the protective effects of BMSCs and TSG-6 were attenuated when TSG-6 expression was silenced. We also found that the activation of the TLR2/NF-κB pathway was inhibited by BMSCs and TSG-6. The levels of IL-6 and TNF-α in the degenerated NPCs were reduced and the proliferation of IL-1β-treated NPCs was increased in the presence of BMSCs and TSG-6. Furthermore, in vivo experiments showed that BMSCs and TSG-6 restored the MRI T2-weighted signal intensity and increased collagen II and aggrecan expression in the degenerated nucleus pulposus (NP) tissues. Finally, our results showed that BMSCs and TSG-6 downregulated the TLR2/NF-κB signaling and reduced the expression of MMPs and inflammatory cytokines in the degenerated NP tissues. The present study is the first to demonstrate the involvement of TLR2/NF-κB pathway in the potential anti-IDD therapeutic effect of TSG-6, and the results provide new insight into the beneficial effect of BMSCs in the treatment of IDD.

Functional Studies of CCAAT/Enhancer Binding Protein Site Located Downstream of the Transcriptional Start Site

Previous studies have identified a CCAAT/enhancer binding protein (C/EBP) site located downstream of the transcriptional start site (DS3). The role of the DS3 element with respect to HIV-1 transactivation by Tat and viral replication has not been characterized. We have demonstrated that DS3 was a functional C/EBPβ binding site and mutation of this site to the C/EBP knockout DS3-9C variant showed lower HIV-1 long terminal repeat (LTR) transactivation by C/EBPβ. However, it was able to exhibit similar or even higher transcription levels by Tat compared to the parental LTR. C/EBPβ and Tat together further enhanced the transcription level of the parental LAI-LTR and DS3-9C LTR, with higher levels in the DS3-9C LTR. HIV molecular clone viruses carrying the DS3-9C variant LTR demonstrated a decreased replication capacity and delayed rate of replication. These results suggest that DS3 plays a role in virus transcriptional initiation and provides new insight into C/EBP regulation of HIV-1.

HADC5 deacetylates MKL1 to dampen TNF-α induced pro-inflammatory gene transcription in macrophages

Macrophage-dependent inflammatory response on the one hand functions as a key line of defense in host immunity but on the other hand underlies the pathogenesis of a host of human pathologies when aberrantly activated. Our previous investigations have led to the identification of megakaryocytic leukemia 1 (MKL1) as a key co-factor of NF-κB/p65 participating in TNF-α induced pro-inflammatory transcription in macrophages. How post-translational modifications contribute to the modulation of MKL1 activity remains an underexplored subject matter. Here we report that the lysine deacetylase HDAC5 interacts with and deacetylates MKL1 in cells. TNF-α treatment down-regulates HDAC5 expression and expels HDAC5 from the promoters of pro-inflammatory genes in macrophages. In contrast, over-expression of HDAC5 attenuates TNF-α induced pro-inflammatory transcription. Mechanistically, HDAC5-mediated MKL1 deacetylation disrupts the interaction between MKL1 and p65. In addition, deacetylation of MKL1 by HDAC5 blocks its nuclear translocation in response to TNF-α treatment. In conclusion, our work has identified an important pathway that contributes to the regulation of pro-inflammatory response in macrophages.

The anti-inflammatory role of extranuclear apurinic/apyrimidinic endonuclease 1/redox effector factor-1 in reactive astrocytes

Apurinic/apyrimidinic endonuclease 1 (APE1), a ubiquitous multipurpose protein, is also known as redox effector factor-1 (Ref-1). It is involved in DNA repair and redox signaling and, in turn, oxidative stress-induced neurodegeneration. Although previous studies have demonstrated that APE1/Ref-1 functions as a negative regulator of inflammatory response via several mechanisms in neuronal cells, little is known about the roles of APE1/Ref-1 in glial cells. In this study, we found that cytoplasmic APE1/Ref-1 expression was upregulated in reactive astrocytes of the kainic acid- or lipopolysaccharide (LPS)-injected hippocampus. Analysis of the inflammatory response induced by extranuclear APE1/Ref-1 (ΔNLS-Ref-1) in cultured primary astrocytes revealed that it markedly suppressed inducible nitric oxide synthase (iNOS) expression and tumor necrosis factor-α (TNF-α) secretion induced by LPS to a similar extent as did wild type APE1/Ref-1 (WT-Ref-1), supporting the concept an anti-inflammatory role of extranuclear APE1/Ref-1 in astrocytes. Additionally, overexpression of WT- and ΔNLS-Ref-1 suppressed the transcriptional activity of nuclear factor-κB (NF-κB), although it effectively enhanced activator protein 1 (AP-1) activity. The blunting effect of APE1/Ref-1 on LPS-induced NF-κB activation was not mediated by IκB kinase (IKK) activity. Instead, APE1/Ref-1 inhibited p300-mediated acetylation of p65 by suppressing intracellular reactive oxygen species (ROS) levels following LPS treatment. Taken together, our results showed that altered expression and/or subcellular distribution of APE1/Ref-1 in activated astrocytes regulated the neuroinflammatory response to excitotoxin and endotoxin insults used in model of neurodegenerative brain diseases.

Histone Deacetylase Inhibitor RGFP109 Overcomes Temozolomide Resistance by Blocking NF-κB-Dependent Transcription in Glioblastoma Cell Lines

Glioblastoma (GBM) is the most frequent and aggressive tumour in the central nervous system. Many studies have demonstrated that upregulation of the NF-κB onco-pathway is accompanied by the acquisition of Temozolomide (TMZ) resistance in GBM cells. Here, we show that RGFP109, a selective histone deacetylase (HDAC1 and HDAC3) inhibitor, overcomes TMZ resistance and downregulates the expression of NF-κB-regulated pro-survival genes in a TMZ-resistant (TR) GBM cell line. RGFP109 did not alter the phosphorylation levels of NF-κB/p65 or inhibitory κBα (IκBα). Immunofluorescence microscopy showed that RGFP109 does not block the nuclear translocation of NF-κB/p65. However, co-immunoprecipitation assays revealed that RGFP109 induces the hyperacetylation of NF-κB/p65 and histones, and blocks interactions between NF-κB/p65 and its coactivators, p300 and p300/CBP-associated factor (PCAF). These results indicate that RGFP109-mediated post-translational nuclear acetylation may be involved in the regulation of NF-κB. Electrophoretic mobility shift assays revealed that RGFP109 reduces NF-κB/p65 binding to κB-DNA and decreased the transcriptional level of κB-mediated genes, suggesting that RGFP109-induced hyperacetylation leads to attenuated transcription of the κB gene. In addition, RGFP109 elevates the expression of inhibitor of growth 4 (ING4), which is typically downregulated in GBM cells. Importantly, we found that RGFP109 enhances ING4 recognition and binding to NF-κB/p65, which may be positively correlated with reduced interactions between NF-κB/p65 and p300/PCAF, thereby effecting transcription of the κB gene. Finally, we show that knockdown of ING4 with plasmids containing pcDNA3.1-ING4 shRNA abolished the effect of RGFP109. Therefore, ING4 may act as a corepressor and facilitate RGFP109-triggered suppression of the NF-κB pathway. Taken together, our data show that RGFP109, an HDAC inhibitor, in combination with TMZ may be a therapeutic candidate for patients with temozolomide-resistant GBM.

Mechanisms of transcription factor acetylation and consequences in hearts

Acetylation of proteins as a post-translational modification is gaining rapid acceptance as a cellular control mechanism on par with other protein modification mechanisms such as phosphorylation and ubiquitination. Through genetic manipulations and evolving proteomic technologies, identification and consequences of transcription factor acetylation is beginning to emerge. In this review, we summarize the field and discuss newly unfolding mechanisms and consequences of transcription factor acetylation in normal and stressed hearts. This article is part of a Special Issue entitled: The role of post-translational protein modifications on heart and vascular metabolism edited by Jason R.B. Dyck & Jan F.C. Glatz.

HIV replication: a game of hide and sense

PURPOSE OF REVIEW

The goal of this review is to summarize recent progress in our understanding of innate sensing of HIV. Furthermore, we present the mechanisms that HIV has evolved to attenuate innate immune responses and discuss open questions.

RECENT FINDINGS

Toll-like receptors (TLRs) and various cytosolic sensors induce an antiviral interferon response upon detection of genomic HIV RNA or intermediates of reverse transcription. HIV limits activation of these sensing pathways by interfering with TLR signaling and by cloaking viral nucleic acids in the cytoplasm, before proviral dsDNA translocates into the nucleus. Furthermore, the viral accessory protein Vpu mitigates antiviral gene expression by inhibiting canonical nuclear factor kappa B (NF-κB) signaling. These evasion mechanisms, however, are imperfect and HIV infection almost inevitably triggers the activation of IRF3, NF-κB and other key transcription factors of antiviral immunity. Notably, the interplay of these processes plays a critical role in the induction of chronic inflammation that drives progression to AIDS.

SUMMARY

HIV has evolved sophisticated but imperfect mechanisms to evade and counteract innate sensing. Whether virus-induced immune activation represents merely a suboptimal adaptation of HIV to its human host or even facilitates HIV replication, for example by increasing the number of viral target cells, remains to be clarified.

The Multifaceted Contributions of Chromatin to HIV-1 Integration, Transcription, and Latency

The capacity of the human immunodeficiency virus (HIV-1) to establish latent infections constitutes a major barrier to the development of a cure for HIV-1. In latent infection, replication competent HIV-1 provirus is integrated within the host genome but remains silent, masking the infected cells from the activity of the host immune response. Despite the progress in elucidating the molecular players that regulate HIV-1 gene expression, the mechanisms driving the establishment and maintenance of latency are still not fully understood. Transcription from the HIV-1 genome occurs in the context of chromatin and is subjected to the same regulatory mechanisms that drive cellular gene expression. Much like in eukaryotic genes, the nucleosomal landscape of the HIV-1 promoter and its position within genomic chromatin are determinants of its transcriptional activity. Understanding the multilayered chromatin-mediated mechanisms that underpin HIV-1 integration and expression is of utmost importance for the development of therapeutic strategies aimed at reducing the pool of latently infected cells. In this review, we discuss the impact of chromatin structure on viral integration, transcriptional regulation and latency, and the host factors that influence HIV-1 replication by regulating chromatin organization. Finally, we describe therapeutic strategies under development to target the chromatin-HIV-1 interplay.

Post-translational Serine/Threonine Phosphorylation and Lysine Acetylation: A Novel Regulatory Aspect of the Global Nitrogen Response Regulator GlnR in S. coelicolor M145

Soil-dwelling Streptomyces bacteria such as S.coelicolor have to constantly adapt to the nitrogen (N) availability in their habitat. Thus, strict transcriptional and post-translational control of the N-assimilation is fundamental for survival of this species. GlnR is a global response regulator that controls transcription of the genes related to the N-assimilation in S. coelicolor and other members of the Actinomycetales. GlnR represents an atypical orphan response regulator that is not activated by the phosphorylation of the conserved aspartate residue (Asp 50). We have applied transcriptional analysis, LC-MS/MS analysis and electrophoretic mobility shift assays (EMSAs) to understand the regulation of GlnR in S. coelicolor M145. The expression of glnR and GlnR-target genes was revisited under four different N-defined conditions and a complex N-rich condition. Although, the expression of selected GlnR-target genes was strongly responsive to changing N-concentrations, the glnR expression itself was independent of the N-availability. Using LC-MS/MSanalysis we demonstrated that GlnR was post-translationally modified. The post-translational modifications of GlnR comprise phosphorylation of the serine/threonine residues and acetylation of lysine residues. In the complex N-rich medium GlnR was phosphorylated on six serine/threonine residues and acetylated on one lysine residue. Under defined N-excess conditions only two phosphorylated residues were detected whereas under defined N-limiting conditions no phosphorylation was observed. GlnR phosphorylation is thus clearly correlated with N-rich conditions. Furthermore, GlnR was acetylated on four lysine residues independently of the N-concentration in the defined media and on only one lysine residue in the complex N-rich medium. Using EMSAs we demonstrated that phosphorylation inhibited the binding of GlnR to its targets genes, whereas acetylation had little influence on the formation of GlnR-DNA complex. This study clearly demonstrated that GlnR DNA-binding affinity is modulated by post-translational modifications in response to changing N-conditions in order to elicit a proper transcriptional response to the latter.

Aberrant lysine acetylation in tumorigenesis: Implications in the development of therapeutics

The 'language' of covalent histone modifications translates environmental and cellular cues into gene expression. This vast array of post-translational modifications on histones are more than just covalent moieties added onto a protein, as they also form a platform on which crucial cellular signals are relayed. The reversible lysine acetylation has emerged as an important post-translational modification of both histone and non-histone proteins, dictating numerous epigenetic programs within a cell. Thus, understanding the complex biology of lysine acetylation and its regulators is essential for the development of epigenetic therapeutics. In this review, we will attempt to address the complexities of lysine acetylation in the context of tumorigenesis, their role in cancer progression and emphasize on the modalities developed to target lysine acetyltransferases towards cancer treatment.

NFKB1: a suppressor of inflammation, ageing and cancer

The pleiotropic consequences of nuclear factor of kappa light polypeptide gene enhancer in B-cells (NF-κB) pathway activation result from the combinatorial effects of the five subunits that form the homo- and heterodimeric NF-κB complexes. Although biochemical and gene knockout studies have demonstrated overlapping and distinct functions for these proteins, much is still not known about the mechanisms determining context-dependent functions, the formation of different dimer complexes and transcriptional control in response to diverse stimuli. Here we discuss recent results that reveal that the nuclear factor of kappa light polypeptide gene enhancer in B-cells 1 (NFKB1) (p105/p50) subunit is an important regulator of NF-κB activity in vivo. These effects are not restricted to being a dimer partner for other NF-κB subunits. Rather p50 homodimers have a critical role as suppressors of the NF-κB response, while the p105 precursor has a variety of NF-κB-independent functions. The importance of Nfkb1 function can be seen in mouse models, where Nfkb1(-/-) mice display increased inflammation and susceptibility to certain forms of DNA damage, leading to cancer, and a rapid ageing phenotype. In humans, low expression of Kip1 ubiquitination-promoting complex 1 (KPC1), a ubiquitin ligase required for p105 to p50 processing, was shown to correlate with a reduction in p50 and glioblastoma incidence. Therefore, while the majority of research in this field has focused on the upstream signalling pathways leading to NF-κB activation or the function of other NF-κB subunits, such as RelA (p65), these data demonstrate a critical role for NFKB1, potentially revealing new strategies for targeting this pathway in inflammatory diseases and cancer.

Manipulation of the host protein acetylation network by human immunodeficiency virus type 1

Over the past 15 years, protein acetylation has emerged as a globally important post-translational modification that fine-tunes major cellular processes in many life forms. This dynamic regulatory system is critical both for complex eukaryotic cells and for the viruses that infect them. HIV-1 accesses the host acetylation network by interacting with several key enzymes, thereby promoting infection at multiple steps during the viral life cycle. Inhibitors of host histone deacetylases and bromodomain-containing proteins are now being pursued as therapeutic strategies to enhance current antiretroviral treatment. As more acetylation-targeting compounds are reaching clinical trials, it is time to review the role of reversible protein acetylation in HIV-infected CD4(+) T cells.

Therapeutic doses of irradiation activate viral transcription and induce apoptosis in HIV-1 infected cells

The highly active antiretroviral therapy reduces HIV-1 RNA in plasma to undetectable levels. However, the virus continues to persist in the long-lived resting CD4(+) T cells, macrophages and astrocytes which form a viral reservoir in infected individuals. Reactivation of viral transcription is critical since the host immune response in combination with antiretroviral therapy may eradicate the virus. Using the chronically HIV-1 infected T lymphoblastoid and monocytic cell lines, primary quiescent CD4(+) T cells and humanized mice infected with dual-tropic HIV-1 89.6, we examined the effect of various X-ray irradiation (IR) doses (used for HIV-related lymphoma treatment and lower doses) on HIV-1 transcription and viability of infected cells. Treatment of both T cells and monocytes with IR, a well-defined stress signal, led to increase of HIV-1 transcription, as evidenced by the presence of RNA polymerase II and reduction of HDAC1 and methyl transferase SUV39H1 on the HIV-1 promoter. This correlated with the increased GFP signal and elevated level of intracellular HIV-1 RNA in the IR-treated quiescent CD4(+) T cells infected with GFP-encoding HIV-1. Exposition of latently HIV-1infected monocytes treated with PKC agonist bryostatin 1 to IR enhanced transcription activation effect of this latency-reversing agent. Increased HIV-1 replication after IR correlated with higher cell death: the level of phosphorylated Ser46 in p53, responsible for apoptosis induction, was markedly higher in the HIV-1 infected cells following IR treatment. Exposure of HIV-1 infected humanized mice with undetectable viral RNA level to IR resulted in a significant increase of HIV-1 RNA in plasma, lung and brain tissues. Collectively, these data point to the use of low to moderate dose of IR alone or in combination with HIV-1 transcription activators as a potential application for the "Shock and Kill" strategy for latently HIV-1 infected cells.

WNT/β-catenin signaling inhibits CBP-mediated RelA acetylation and expression of proinflammatory NF-κB target genes

The discovery of functional crosstalk between WNT and nuclear factor κB (NF-κB) signaling has established a more complex role for these two pathways in inflammation and cancer. However, the molecular mechanisms of the crosstalk and its biological consequences are largely unknown. Here, we show that WNT/β-catenin signaling selectively inhibits the expression of a proinflammatory subset of IL-1β-induced NF-κB target genes. WNT/β-catenin signaling does not affect nuclear translocation of the RelA subunit of NF-κB or its association with CBP (also known as CREBBP), but reduces CBP-mediated acetylation and chromatin recruitment of RelA. Thus, β-catenin selectively regulates NF-κB gene expression through its negative effects on RelA acetylation. This anti-inflammatory effect may be relevant for cancer treatment.

Pharmacology of cognitive enhancers for exposure-based therapy of fear, anxiety and trauma-related disorders

Pathological fear and anxiety are highly debilitating and, despite considerable advances in psychotherapy and pharmacotherapy they remain insufficiently treated in many patients with PTSD, phobias, panic and other anxiety disorders. Increasing preclinical and clinical evidence indicates that pharmacological treatments including cognitive enhancers, when given as adjuncts to psychotherapeutic approaches [cognitive behavioral therapy including extinction-based exposure therapy] enhance treatment efficacy, while using anxiolytics such as benzodiazepines as adjuncts can undermine long-term treatment success. The purpose of this review is to outline the literature showing how pharmacological interventions targeting neurotransmitter systems including serotonin, dopamine, noradrenaline, histamine, glutamate, GABA, cannabinoids, neuropeptides (oxytocin, neuropeptides Y and S, opioids) and other targets (neurotrophins BDNF and FGF2, glucocorticoids, L-type-calcium channels, epigenetic modifications) as well as their downstream signaling pathways, can augment fear extinction and strengthen extinction memory persistently in preclinical models. Particularly promising approaches are discussed in regard to their effects on specific aspects of fear extinction namely, acquisition, consolidation and retrieval, including long-term protection from return of fear (relapse) phenomena like spontaneous recovery, reinstatement and renewal of fear. We also highlight the promising translational value of the preclinial research and the clinical potential of targeting certain neurochemical systems with, for example d-cycloserine, yohimbine, cortisol, and L-DOPA. The current body of research reveals important new insights into the neurobiology and neurochemistry of fear extinction and holds significant promise for pharmacologically-augmented psychotherapy as an improved approach to treat trauma and anxiety-related disorders in a more efficient and persistent way promoting enhanced symptom remission and recovery.

HIV-1 Tat induces DNMT over-expression through microRNA dysregulation in HIV-related non Hodgkin lymphomas

BACKGROUND

A close association between HIV infection and the development of cancer exists. Although the advent of highly active antiretroviral therapy has changed the epidemiology of AIDS-associated malignancies, a better understanding on how HIV can induce malignant transformation will help the development of novel therapeutic agents.

METHODS

HIV has been reported to induce the expression of DNMT1 in vitro, but still no information is available about the mechanisms regulating DNMT expression in HIV-related B-cell lymphomas. In this paper, we investigated the expression of DNMT family members (DNMT1, DNMT3a/b) in primary cases of aggressive B-cell lymphomas of HIV-positive subjects.

RESULTS

Our results confirmed the activation of DNMT1 by HIV in vivo, and reported for the first time a marked up-regulation of DNMT3a and DNMT3b in HIV-positive aggressive B-cell lymphomas. DNMT up-regulation in HIV-positive tumors correlated with down-regulation of specific microRNAs, as the miR29 family, the miR148-152 cluster, known to regulate their expression. Literature reports the activation of DNMTs by the human polyomavirus BKV large T-antigen and adenovirus E1a, through the pRb/E2F pathway. We have previously demonstrated that the HIV Tat protein is able to bind to the pocket proteins and to inactivate their oncosuppressive properties, resulting in uncontrolled cell proliferation. Therefore, we focused on the role of Tat, due to its capability to be released from infected cells and to dysregulate uninfected ones, using an in vitro model in which Tat was ectopically expressed in B-cells.

CONCLUSIONS

Our findings demonstrated that the ectopic expression of Tat was per se sufficient to determine DNMT up-regulation, based on microRNA down-regulation, and that this results in aberrant hypermethylation of target genes and microRNAs. These results point at a direct role for Tat in participating in uninfected B-cell lymphomagenesis, through dysregulation of the epigenetical control of gene expression.

Mass spectrometry-based proteomic approaches for discovery of HIV-host interactions

A molecular understanding of viral infection requires a multi-disciplinary approach. Mass spectrometry has emerged as an indispensable tool to investigate the complex and dynamic interactions between HIV-1 and its host. It has been employed to study protein associations, changes in protein abundance and post-translational modifications occurring after viral infection. Here, we review and provide examples of mass spectrometry-based proteomic approaches currently used to explore virus-host interaction. Efforts in this area are certain to accelerate the discovery of the unique molecular strategies utilized by the virus to commandeer the cell as well as mechanisms of host defense.

AEG-1/MTDH/LYRIC: signaling pathways, downstream genes, interacting proteins, and regulation of tumor angiogenesis

Astrocyte elevated gene-1 (AEG-1), also known as metadherin (MTDH) and lysine-rich CEACAM1 coisolated (LYRIC), was initially cloned in 2002. AEG-1/MTDH/LYRIC has emerged as an important oncogene that is overexpressed in multiple types of human cancer. Expanded research on AEG-1/MTDH/LYRIC has established a functional role of this molecule in several crucial aspects of tumor progression, including transformation, proliferation, cell survival, evasion of apoptosis, migration and invasion, metastasis, angiogenesis, and chemoresistance. The multifunctional role of AEG-1/MTDH/LYRIC in tumor development and progression is associated with a number of signaling cascades, and recent studies identified several important interacting partners of AEG-1/MTDH/LYRIC in regulating cancer promotion and other biological functions. This review evaluates the current literature on AEG-1/MTDH/LYRIC function relative to signaling changes, interacting partners, and angiogenesis and highlights new perspectives of this molecule, indicating its potential as a significant target for the clinical treatment of various cancers and other diseases.

Transcriptional control of HIV latency: cellular signaling pathways, epigenetics, happenstance and the hope for a cure

Replication-competent latent HIV-1 proviruses that persist in the genomes of a very small subset of resting memory T cells in infected individuals under life-long antiretroviral therapy present a major barrier towards viral eradication. Multiple molecular mechanisms are required to repress the viral trans-activating factor Tat and disrupt the regulatory Tat feedback circuit leading to the establishment of the latent viral reservoir. In particular, latency is due to a combination of transcriptional silencing of proviruses via host epigenetic mechanisms and restrictions on the expression of P-TEFb, an essential co-factor for Tat. Induction of latent proviruses in the presence of antiretroviral therapy is expected to enable clearance of latently infected cells by viral cytopathic effects and host antiviral immune responses. An in-depth comprehensive understanding of the molecular control of HIV-1 transcription should inform the development of optimal combinatorial reactivation strategies that are intended to purge the latent viral reservoir.

O-GlcNAc transferase inhibits LPS-mediated expression of inducible nitric oxide synthase through an increased interaction with mSin3A in RAW264.7 cells

O-linked N-acetylglucosamine (O-GlcNAc) transferase (OGT), which catalyzes the addition of a single β-N-GlcNAc unit to target proteins, has been shown to act as a transcriptional regulator. In the current study, we discovered that OGT exerted inhibitory effects on the LPS-driven activation of NF-κB and inducible nitric oxide synthase (iNOS). In response to LPS, OGT exhibited an increased interaction with the transcriptional corepressor mammalian Sin3A (mSin3A). Furthermore, mSin3A, histone deacetylase (HDAC)1, and HDAC2 displayed increased binding to the iNOS promoter in response to LPS. Treatment with GlcN, in contrast, inhibits LPS-induced inflammation and decreased LPS-mediated recruitment of OGT, mSin3A, and HDACs. LPS treatment also resulted in the hypo-O-GlcNAcylation of mSin3A, which was reversed by GlcN. When the effect of the HDAC inhibitor trichostatin A (TSA) on LPS- and/or GlcN-mediated iNOS protein/mRNA induction was investigated, the results revealed that TSA dose dependently enhanced iNOS expression in response to LPS and/or GlcN. In addition, histone acetyltransferases, p300, and cAMP response element-binding protein-binding protein (CBP) enhanced LPS- and/or GlcN-induced iNOS protein expression. These results collectively suggest that OGT inhibits LPS-driven NF-κB activation and subsequent iNOS transcription by modulating histone acetylation either directly or indirectly.

T cell factor 4 is a pro-catabolic and apoptotic factor in human articular chondrocytes by potentiating nuclear factor κB signaling

T cell factor/lymphoid enhancer factor (TCF/LEF) transcription factors are downstream effectors of Wnt/β-catenin signaling, which has been implicated in the development and progression of osteoarthritis (OA). This study aimed to investigate the role of TCF/LEF transcription factors in human articular chondrocytes. Primary human osteoarthritic cartilage predominantly expressed TCF4 and to a lesser extent, LEF1 and TCF3 mRNA. Overexpression of TCF4, but not of TCF3 or LEF1, induced MMP-1, -3, and -13 expression and generic MMP activity in human chondrocytes. This was due to potentiating NF-κB signaling by a protein-protein interaction between TCF4 and NF-κB p65 activating established NF-κB target genes such as MMPs and IL-6. LEF1 competed with TCF4 for binding to NF-κB p65. IκB-α was able to counteract the effect of TCF4 on NF-κB target gene expression. Finally, we showed that TCF4 mRNA expression was elevated in OA cartilage compared with healthy cartilage and induced chondrocyte apoptosis at least partly through activating caspase 3/7. Our findings suggest that increased TCF4 expression may contribute to cartilage degeneration in OA by augmenting NF-κB signaling.

tat Exon 1 exhibits functional diversity during HIV-1 subtype C primary infection

Human immunodeficiency virus type 1 (HIV-1) Tat is a mediator of viral transcription and is involved in the control of virus replication. However, associations between HIV-1 Tat diversity and functional effects during primary HIV-1 infection are still unclear. We estimated selection pressures in tat exon 1 using the mixed-effects model of evolution with 672 viral sequences generated from 20 patients infected with HIV-1 subtype C (HIV-1C) over 500 days postseroconversion. tat exon 1 residues 3, 4, 21, 24, 29, 39, and 68 were under positive selection, and we established that specific amino acid signature patterns were apparent in primary HIV-1C infection compared with chronic infection. We assessed the impact of these mutations on long terminal repeat (LTR) activity and found that Tat activity was negatively affected by the Ala(21) substitution identified in 13/20 (65%) of patients, which reduced LTR activity by 88% (± 1%) (P < 0.001). The greatest increase in Tat activity was seen with the Gln(35)/Lys(39) double mutant that resulted in an additional 49% (± 14%) production of LTR-driven luciferase (P = 0.012). There was a moderate positive correlation between Tat-mediated LTR activity and HIV-1 RNA in plasma (P = 0.026; r = 0.400) after 180 days postseroconversion that was reduced by 500 days postseroconversion (P = 0.043; r = 0.266). Although Tat activation of the LTR is not a strong predictor of these clinical variables, there are significant linear relationships between Tat transactivation and patients' plasma viral loads and CD4 counts, highlighting the complex interplay between Tat mutations in early HIV-1C infection.

The coactivator role of histone deacetylase 3 in IL-1-signaling involves deacetylation of p65 NF-κB

Histone deacetylase (HDAC) 3, as a cofactor in co-repressor complexes containing silencing mediator for retinoid or thyroid-hormone receptors (SMRT) and nuclear receptor co-repressor (N-CoR), has been shown to repress gene transcription in a variety of contexts. Here, we reveal a novel role for HDAC3 as a positive regulator of IL-1-induced gene expression. Various experimental approaches involving RNAi-mediated knockdown, conditional gene deletion or small molecule inhibitors indicate a positive role of HDAC3 for transcription of the majority of IL-1-induced human or murine genes. This effect was independent from the gene regulatory effects mediated by the broad-spectrum HDAC inhibitor trichostatin A (TSA) and thus suggests IL-1-specific functions for HDAC3. The stimulatory function of HDAC3 for inflammatory gene expression involves a mechanism that uses binding to NF-κB p65 and its deacetylation at various lysines. NF-κB p65-deficient cells stably reconstituted to express acetylation mimicking forms of p65 (p65 K/Q) had largely lost their potential to stimulate IL-1-triggered gene expression, implying that the co-activating property of HDAC3 involves the removal of inhibitory NF-κB p65 acetylations at K122, 123, 314 and 315. These data describe a novel function for HDAC3 as a co-activator in inflammatory signaling pathways and help to explain the anti-inflammatory effects frequently observed for HDAC inhibitors in (pre)clinical use.

The BET bromodomain inhibitor JQ1 activates HIV latency through antagonizing Brd4 inhibition of Tat-transactivation

Latent HIV reservoirs are the primary hurdle to eradication of infection. Identification of agents, pathways and molecular mechanisms that activate latent provirus may, in the presence of highly active antiretroviral therapy, permit clearance of infected cells by the immune system. Promoter-proximal pausing of RNA polymerase (Pol) II is a major rate-limiting step in HIV gene expression. The viral Tat protein recruits human Super Elongation Complex (SEC) to paused Pol II to overcome this limitation. Here, we identify the bromodomain protein Brd4 and its inhibition of Tat-transactivation as a major impediment to latency reactivation. Brd4 competitively blocks the Tat-SEC interaction on HIV promoter. The BET bromodomain inhibitor JQ1 dissociates Brd4 from the HIV promoter to allow Tat recruitment of SEC to stimulate HIV elongation. JQ1 synergizes with another latency activator prostratin, which promotes Pol II loading onto the viral promoter. Because JQ1 activates viral latency without inducing global T cell activation, this and other closely related compounds and their antagonization of Brd4 to promote Tat-SEC interaction merit further investigations as effective agents/strategies for eliminating latent HIV.

ISSLS prize winner: inhibition of NF-κB activity ameliorates age-associated disc degeneration in a mouse model of accelerated aging

STUDY DESIGN

NF-κB activity was pharmacologically and genetically blocked in an accelerated aging mouse model to mitigate age-related disc degenerative changes.

OBJECTIVE

To study the mediatory role of NF-κB-signaling pathway in age-dependent intervertebral disc degeneration.

SUMMARY OF BACKGROUND DATA

Aging is a major contributor to intervertebral disc degeneration (IDD), but the molecular mechanism behind this process is poorly understood. NF-κB is a family of transcription factors that play a central role in mediating cellular response to damage, stress, and inflammation. Growing evidence implicates chronic NF-κB activation as a culprit in many aging-related diseases, but its role in aging-related IDD has not been adequately explored. We studied the effects of NF-κB inhibition on IDD, using a DNA repair-deficient mouse model of accelerated aging (Ercc1 mice) previously been reported to exhibit age-related IDD.

METHODS

Systemic inhibition of NF-κB activation was achieved either genetically by deletion of 1 allele of the NF-κB subunit p65 (Ercc1p65 mice) or pharmacologically by chronic intraperitoneal administration of the Nemo Binding Domain (8K-NBD) peptide to block the formation of the upstream activator of NF-κB, IκB Inducible Kinase (IKK), in Ercc1 mice. Disc cellularity, total proteoglycan content and proteoglycan synthesis of treated mice, and untreated controls were assessed. RESULTS.: Decreased disc matrix proteoglycan content, a hallmark feature of IDD, and elevated disc NF-κB activity were observed in discs of progeroid Ercc1 mice and naturally aged wild-type mice compared with young wild-type mice. Systemic inhibition of NF-κB by the 8K-NBD peptide in Ercc1 mice increased disc proteoglycan synthesis and ameriolated loss of disc cellularity and matrix proteoglycan. These results were confirmed genetically by using the p65 haploinsufficient Ercc1p65 mice.

CONCLUSION

These findings demonstrate that the IKK/NF-κB signaling pathway is a key mediator of age-dependent IDD and represents a therapeutic target for mitigating disc degenerative diseases associated with aging.

Impact of Tat Genetic Variation on HIV-1 Disease

The human immunodeficiency virus type 1 (HIV-1) promoter or long-terminal repeat (LTR) regulates viral gene expression by interacting with multiple viral and host factors. The viral transactivator protein Tat plays an important role in transcriptional activation of HIV-1 gene expression. Functional domains of Tat and its interaction with transactivation response element RNA and cellular transcription factors have been examined. Genetic variation within tat of different HIV-1 subtypes has been shown to affect the interaction of the viral transactivator with cellular and/or viral proteins, influencing the overall level of transcriptional activation as well as its action as a neurotoxic protein. Consequently, the genetic variability within tat may impact the molecular architecture of functional domains of the Tat protein that may impact HIV pathogenesis and disease. Tat as a therapeutic target for anti-HIV drugs has also been discussed.

NF-κB inhibition delays DNA damage-induced senescence and aging in mice

The accumulation of cellular damage, including DNA damage, is thought to contribute to aging-related degenerative changes, but how damage drives aging is unknown. XFE progeroid syndrome is a disease of accelerated aging caused by a defect in DNA repair. NF-κB, a transcription factor activated by cellular damage and stress, has increased activity with aging and aging-related chronic diseases. To determine whether NF-κB drives aging in response to the accumulation of spontaneous, endogenous DNA damage, we measured the activation of NF-κB in WT and progeroid model mice. As both WT and progeroid mice aged, NF-κB was activated stochastically in a variety of cell types. Genetic depletion of one allele of the p65 subunit of NF-κB or treatment with a pharmacological inhibitor of the NF-κB-activating kinase, IKK, delayed the age-related symptoms and pathologies of progeroid mice. Additionally, inhibition of NF-κB reduced oxidative DNA damage and stress and delayed cellular senescence. These results indicate that the mechanism by which DNA damage drives aging is due in part to NF-κB activation. IKK/NF-κB inhibitors are sufficient to attenuate this damage and could provide clinical benefit for degenerative changes associated with accelerated aging disorders and normal aging.

Molecular mechanisms of HIV-1 infection in neonatal target cells

HIV-1-infected neonates and infants have a higher viral load and progress to symptomatic AIDS more rapidly than their own infected mothers, as well as other infected adults, with differences in clinical manifestations, recurrent bacterial infections and CNS disorders. Two major reasons have been attributed to this differential HIV pathogenesis and disease; the relative immaturity of the neonate’s immune system and it’s inability to contain the highly replicating and mutating HIV-1, and the more efficient replication of HIV-1 in neonatal cells than in adult target cells. In this context, it has been demonstrated that HIV-1 replicates more efficiently in neonatal (cord) blood monocytes/macrophages and T lymphocytes – including naive and memory T lymphocytes – compared with adult blood cells. We have also determined the mechanisms of the differential HIV-1 replication in cord versus adult blood monocytes/macrophages and T lymphocytes (naive and memory), finding that it was influenced at the level of HIV-1 gene expression. The increased HIV-1 gene expression in neonatal versus adult target cells was regulated by differential expression of host factors, transcription factors (NF-κB, E2F, HAT-1, TFIIE, Cdk9 and Cyclin T1), signal transducers (STAT3 and STAT5A) and cytokines (IL-1β, IL-6 and IL-10). We also showed that nuclear extracts from cord cells interacted with HIV-1 long terminal repeat cis-acting sequences, including NF-κB, NFAT, AP1 and NF-IL6, to a greater extent when compared with adult peripheral blood mononuclear cell nuclear extracts. Additionally, shRNA of retroviral origin for STAT3 and IL-6 downregulated both their own gene expression as well as that of HIV-1, indicating that these factors influenced the differential expression of HIV-1 genes in cord cells compared with adult cells. In addition, HIV-1 integration plays an important role in differential HIV-1 replication and gene expression in neonatal versus adult cells by integrating into more actively transcribed genes in neonates compared with adults. We characterized 468 HIV-1 integration sites within cord and adult blood T lymphocytes and monocytes/macrophages, including genes coding for cellular components, and those involved with maintenance of the intracellular environment, enzyme regulation, cellular metabolism, catalytic activity and cation transport, as well as several potential transcription factor binding sites at the sites of integration. Additionally, the genes at the integration sites, transcription factors and transcription binding sites were expressed at higher levels in cord than adult target cells. In summary, the increased HIV-1 gene expression and replication in neonatal target cells due to differential expression of host factors all contribute to an increased viral load and faster disease progression in neonates and infants when compared with similar situations in adult patients. Based on these findings, it may be possible to identify new viral and host targets for use in developing strategies for the treatment and prevention of HIV-1.

NF-κB and epigenetic mechanisms as integrative regulators of brain resilience to anoxic stress

Brain cells display an amazing ability to respond to several different types of environmental stimuli and integrate this response physiologically. Some of these responses can outlive the original stimulus by days, weeks or even longer. Long-lasting changes in both physiological and pathological conditions occurring in response to external stimuli are almost always mediated by changes in gene expression. To effect these changes, cells have developed an impressive repertoire of signaling systems designed to modulate the activity of numerous transcription factors and epigenetic mechanisms affecting the chromatin structure. Since its initial characterization in the nervous system, NF-κB has shown to respond to multiple signals and elicit pleiotropic activities suggesting that it may play a pivotal role in integration of different types of information within the brain. Ample evidence demonstrates that NF-κB factors are engaged in and necessary for neuronal development and synaptic plasticity, but they also regulate brain response to environmental noxae. By focusing on the complexity of NF-κB transcriptional activity in neuronal cell death, it emerged that the composition of NF-κB active dimers finely tunes the neuronal vulnerability to brain ischemia. Even though we are only beginning to understand the contribution of distinct NF-κB family members to the regulation of gene transcription in the brain, an additional level of regulation of NF-κB activity has emerged as operated by the epigenetic mechanisms modulating histone acetylation. We will discuss NF-κB and epigenetic mechanisms as integrative regulators of brain resilience to anoxic stress and useful drug targets for restoration of brain function. This article is part of a Special Issue entitled: Brain Integration.

Insights on the acetylated NF-κB transcription factor complex with DNA from molecular dynamics simulations

The nuclear factor-κB (NF-κB) is a DNA sequence-specific regulator of many important biological processes, whose activity is modulated by enzymatic acetylation. In one of the best functionally characterized NF-κB complexes, the p50/p65 heterodimer, acetylation of K221 at p65 causes a decrease of DNA dissociation rate, whilst the acetylation of K122 and K123, also at p65, markedly decreases the binding affinity for DNA. By means of molecular dynamics simulations based on the X-ray structure of the p50/p65 complex with DNA, we provide insights on the structural determinants of the acetylated complexes in aqueous solution. Lysine acetylation involves the loss of favorable electrostatic interactions between DNA and NF-κB, which is partially compensated by the reduction of the desolvation free-energy of the two binding partners. Acetylation at both positions K122 and K123 is associated with a decrease of the electrostatic potential at the p65/DNA interface, which is only partially counterbalanced by an increase of the local Na(+) concentration. It induces the disruption of base-specific and nonspecific interactions between DNA and NF-κB and it is consistent with the observed decrease of binding affinity. In contrast, acetylation at position K221 results in the loss of nonspecific protein-DNA interactions, but the DNA recognition sites are not affected. In addition, the loss of protein-DNA interactions is likely to be counterbalanced by an increase of the configurational entropy of the complex, which provides, at a speculative level, a justification for the observed decrease of NF-κB/DNA dissociation rate.

Control of HIV latency by epigenetic and non-epigenetic mechanisms

Intensive antiretroviral therapy successfully suppresses viral replication but is unable to eradicate the virus. HIV persists in a small number of resting memory T cells where HIV has been transcriptionally silenced. This review will focus on recent insights into the HIV transcriptional control mechanisms that provide the biochemical basis for understanding latency. There are no specific repressors of HIV transcription encoded by the virus, instead latency arises when the regulatory feedback mechanism driven by HIV Tat expression is disrupted. Small changes in transcriptional initiation, induced by epigenetic silencing, lead to profound restrictions in Tat levels and force the entry of proviruses into latency. In resting memory T cells, which carry the bulk of the latent viral pool, additional restrictions, especially the limiting cellular levels of the essential Tat cofactor P-TEFb and the transcription initiation factors NF-κB and NFAT ensure that the provirus remains silenced unless the host cell is activated. The detailed understanding of HIV transcription is providing a framework for devising new therapeutic strategies designed to purge the latent viral pool. Importantly, the recognition that there are multiple restrictions imposed on latent proviruses suggest that proviral reactivation will not be achieved when only a single reactivation step is targeted and that any optimal activation strategy will require both removal of epigenetic blocks and the activation of P-TEFb.

HDAC1/NFκB pathway is involved in curcumin inhibiting of Tat-mediated long terminal repeat transactivation

Chromatin remodeling, especially in relation to the transactivator Tat, is an essential event for human immunodeficiency virus-1 (HIV-1) transcription. Curcumin has been shown to suppress pathways linked to HIV-1 replication. We investigated whether curcumin had the potential to inhibit Tat-induced long terminal repeat region (LTR) transactivation. As we shown, curcumin inhibited Tat-induced LTR transcativation, while knockdown of histone deacetylase 1 (HDAC1) by siRNA potentiated Tat-induced HIV-1 transcativation. Curcumin reversed Tat-induced down-regulation of HDAC1 expression in multinuclear activation of galactosidase indicator (MAGI) cells. Treatment with curcumin reversed Tat-induced dissociation of HDAC1 from LTR; and curcumin caused a decline in the binding of p65/NFκB to LTR promoters stimulated by Tat. Curcumin attenuated Tat-induced p65 phosphorylation and IKK phosphorylation. Curcumin reversed Tat-mediated reduction in AMPK activation and downstream acetyl-CoA carboxylase (ACC) activation. Collectively, our data provide new insights into understanding of the molecular mechanisms of curcumin inhibited Tat-regulated transcription, suggesting that targeting AMPK/HDAC1/NFκB pathway could serve as new anti-HIV-1 agents.

Curcumin enhances the efficacy of chemotherapy by tailoring p65NFκB-p300 cross-talk in favor of p53-p300 in breast cancer

Breast cancer cells often develop multiple mechanisms of drug resistance during tumor progression, which is the major reason for the failure of breast cancer therapy. High constitutive activation of NFκB has been found in different cancers, creating an environment conducive for chemotherapeutic resistance. Here we report that doxorubicin-induced SMAR1-dependent transcriptional repression and SMAR1-independent degradation of IkBα resulted in nuclear translocation of p65NFκB and its association with p300 histone acetylase and subsequent transcription of Bcl-2 to impart protective response in drug-resistant cells. Consistently SMAR1-silenced drug-resistant cells exhibited IkBα-mediated inhibition of p65NFκB and induction of p53-dependent apoptosis. Interestingly, curcumin pretreatment of drug-resistant cells alleviated SMAR1-mediated p65NFκB activation and hence restored doxorubicin sensitivity. Under such anti-survival condition, induction of p53-p300 cross-talk enhanced the transcriptional activity of p53 and intrinsic death cascade. Importantly, promyelocyte leukemia-mediated SMAR1 sequestration that relieved the repression of apoptosis-inducing genes was indispensable for such chemo-sensitizing ability of curcumin. A simultaneous decrease in drug-induced systemic toxicity by curcumin might also have enhanced the efficacy of doxorubicin by improving the intrinsic defense machineries of the tumor-bearer. Overall, the findings of this preclinical study clearly demonstrate the effectiveness of curcumin to combat doxorubicin-resistance. We, therefore, suggest curcumin as a potent chemo-sensitizer to improve the therapeutic index of this widely used anti-cancer drug. Taken together, these results suggest that curcumin can be developed into an adjuvant chemotherapeutic drug.

Infectious agents and lymphoma

In the past 25 years revelations on the genesis of human cancer have come at an increasing pace. Research on oncogenic infectious agents, especially viruses, has helped us to understand the process of malignant transformation of cells because the cellular events in viral-driven transformation mirror, often brilliantly, basic cellular processes that culminate in cancer, even those not associated with viruses. Infectious agents, especially viruses, account for several of the most common malignancies-up to 20% of all cancers. Some of these cancers are endemic, with a high incidence in certain geographic locations, but sporadic/lower incidence in other parts of the world. Lymphomas arise frequently in association with infectious agents such as Epstein-Barr virus, human immunodeficiency virus, human herpes virus 8, Helicobacter pylori, and hepatitis C virus. In this review, we will focus on the association between infectious agents and lymphomas, with a look at the molecular mechanisms they use to disturb cell regulation and eventually result in cancer.

Paradoxical enhancement of fear extinction memory and synaptic plasticity by inhibition of the histone acetyltransferase p300

It is well established that the coordinated regulation of activity-dependent gene expression by the histone acetyltransferase (HAT) family of transcriptional coactivators is crucial for the formation of contextual fear and spatial memory, and for hippocampal synaptic plasticity. However, no studies have examined the role of this epigenetic mechanism within the infralimbic prefrontal cortex (ILPFC), an area of the brain that is essential for the formation and consolidation of fear extinction memory. Here we report that a postextinction training infusion of a combined p300/CBP inhibitor (Lys-CoA-Tat), directly into the ILPFC, enhances fear extinction memory in mice. Our results also demonstrate that the HAT p300 is highly expressed within pyramidal neurons of the ILPFC and that the small-molecule p300-specific inhibitor (C646) infused into the ILPFC immediately after weak extinction training enhances the consolidation of fear extinction memory. C646 infused 6 h after extinction had no effect on fear extinction memory, nor did an immediate postextinction training infusion into the prelimbic prefrontal cortex. Consistent with the behavioral findings, inhibition of p300 activity within the ILPFC facilitated long-term potentiation (LTP) under stimulation conditions that do not evoke long-lasting LTP. These data suggest that one function of p300 activity within the ILPFC is to constrain synaptic plasticity, and that a reduction in the function of this HAT is required for the formation of fear extinction memory.

Histone acetyltransferases are crucial regulators in NF-κB mediated inflammation

Post-translational modifications of proteins, such as acetylation, are important regulatory events in eukaryotic cells. Reversible acetylations of histones and non-histone proteins regulate gene expression and protein activity. Acetylation levels of proteins are regulated by a dynamic equilibrium between acetylation by (histone) acetyltransferases and deacetylation by (histone) deacetylases. Alterations in this equilibrium can result in pathological states. Inflammation is a physiological response that, under certain conditions, turns into a disease. This review focuses on the crucial regulatory roles of protein acetylation in NF-κB-mediated inflammation and the potential applications of small-molecule inhibitors of acetylation for the treatment of inflammatory diseases.

Modulation of NF-κB signalling by microbial pathogens

The nuclear factor-κB (NF-κB) family of transcription factors plays a central part in the host response to infection by microbial pathogens, by orchestrating the innate and acquired host immune responses. The NF-κB proteins are activated by diverse signalling pathways that originate from many different cellular receptors and sensors. Many successful pathogens have acquired sophisticated mechanisms to regulate the NF-κB signalling pathways by deploying subversive proteins or hijacking the host signalling molecules. Here, we describe the mechanisms by which viruses and bacteria micromanage the host NF-κB signalling circuitry to favour the continued survival of the pathogen.

The peroxisome proliferator-activated receptor β/δ (PPARβ/δ) agonist GW501516 prevents TNF-α-induced NF-κB activation in human HaCaT cells by reducing p65 acetylation through AMPK and SIRT1

Nuclear factor (NF)-κB is a ubiquitously expressed transcription factor controlling the expression of numerous genes involved in inflammation. The aim of this study was to evaluate whether activation of the peroxisome proliferator-activated receptor (PPAR) β/δ prevented TNF-α-induced NF-κB activation in human HaCaT keratinocytes and, if so, to determine the mechanism involved. The PPARβ/δ agonist GW501516 inhibited the increase caused by TNF-α in the mRNA levels of the NF-κB target genes interleukin 8 (IL-8), TNF-α and thymic stromal lymphopoietin (TSLP). Likewise, GW501516 prevented the increase in NF-κB DNA-binding activity observed in cells exposed to TNF-α. The reduction in NF-κB activity following GW501516 treatment in cells stimulated with TNF-α did not involve either increased IκBα protein levels or a reduction in the translocation of the p65 subunit of NF-κB. In contrast, GW501516 treatment decreased TNF-α-induced p65 acetylation. Acetylation of p65 is mainly regulated by p300, a transcriptional co-activator that binds to and acetylates p65. Of note, AMP kinase (AMPK) activation phosphorylates p300 and reduces its binding to p65. GW501516 increased AMPK phosphorylation and the subsequent p300 phosphorylation, leading to a marked reduction in the association between p65 and this transcriptional co-activator. In addition, treatment with the PPARβ/δ agonist increased SIRT1 protein levels. Finally, the reduction in IL-8 mRNA levels following GW501516 treatment in TNF-α-stimulated cells was abolished in the presence of the PPARβ/δ antagonist GSK0660, the AMPK inhibitor compound C and the SIRT1 inhibitor sirtinol, indicating that the effects of GW501516 on NF-κB activity were dependent on PPARβ/δ, AMPK and SIRT1, respectively.

Specification of DNA binding activity of NF-kappaB proteins

Nuclear factor-kappaB (NF-kappaB) is a pleiotropic mediator of inducible and specific gene regulation involving diverse biological activities including immune response, inflammation, cell proliferation, and death. The fine-tuning of the NF-kappaB DNA binding activity is essential for its fundamental function as a transcription factor. An increasing body of literature illustrates that this process can be elegantly and specifically controlled at multiple levels by different protein subsets. In particular, the recent identification of a non-Rel subunit of NF-kappaB itself provides a new way to understand the selective high-affinity DNA binding specificity of NF-kappaB conferred by a synergistic interaction within the whole complex. Here, we review the mechanism of the specification of DNA binding activity of NF-kappaB complexes, one of the most important aspects of NF-kappaB transcriptional control.

Combinatorial latency reactivation for HIV-1 subtypes and variants

The eradication of HIV-1 will likely require novel clinical approaches to purge the reservoir of latently infected cells from a patient. We hypothesize that this therapy should target a wide range of latent integration sites, act effectively against viral variants that have acquired mutations in their promoter regions, and function across multiple HIV-1 subtypes. By using primary CD4(+) and Jurkat cell-based in vitro HIV-1 latency models, we observe that single-agent latency reactivation therapy is ineffective against most HIV-1 subtypes. However, we demonstrate that the combination of two clinically promising drugs-namely, prostratin and suberoylanilide hydroxamic acid (SAHA)-overcomes the limitations of single-agent approaches and can act synergistically for many HIV-1 subtypes, including A, B, C, D, and F. Finally, by identifying the proviral integration position of latent Jurkat cell clones, we demonstrate that this drug combination does not significantly enhance the expression of endogenous genes nearest to the proviral integration site, indicating that its effects may be selective.

Differential expression and interaction of host factors augment HIV-1 gene expression in neonatal mononuclear cells

We have previously shown a higher level of HIV-1 replication and gene expression in neonatal (cord) blood mononuclear cells (CBMC) compared with adult blood cells (PBMC), which could be due to differential expression of host factors. We performed the gene expression profile of CBMC and PBMC and found that 8013 genes were expressed at higher levels in CBMC than PBMC and 8028 genes in PBMC than CBMC, including 1181 and 1414 genes upregulated after HIV-1 infection in CBMC and PBMC, respectively. Several transcription factors (NF-kappaB, E2F, HAT-1, TFIIE, Cdk9, Cyclin T1), signal transducers (STAT3, STAT5A) and cytokines (IL-1beta, IL-6, IL-10) were upregulated in CBMC than PBMC, which are known to influence HIV-1 replication. In addition, a repressor of HIV-1 transcription, YY1, was down regulated in CBMC than PBMC and several matrix metalloproteinase (MMP-7, -12, -14) were significantly upregulated in HIV-1 infected CBMC than PBMC. Furthermore, we show that CBMC nuclear extracts interacted with a higher extent to HIV-1 LTR cis-acting sequences, including NF-kappaB, NFAT, AP1 and NF-IL6 compared with PBMC nuclear extracts and retroviral based short hairpin RNA (shRNA) for STAT3 and IL-6 down regulated their own and HIV-1 gene expression, signifying that these factors influenced differential HIV-1 gene expression in CBMC than PBMC.

Acetylation of p65 at lysine 314 is important for late NF-kappaB-dependent gene expression

Background

NF-κB regulates the expression of a large number of target genes involved in the immune and inflammatory response, apoptosis, cell proliferation, differentiation and survival. We have earlier reported that p65, a subunit of NF-κB, is acetylated in vitro and in vivo at three different lysines (K310, K314 and K315) by the histone acetyltransferase p300.

Results

In this study, we describe that site-specific mutation of p65 at lysines 314 and 315 enhances gene expression of a subset of NF-κB target genes including Mmp10 and Mmp13. Increased gene expression was mainly observed three hours after TNFα stimulation. Chromatin immunoprecipitation (ChIP) experiments with an antibody raised against acetylated lysine 314 revealed that chromatin-bound p65 is indeed acetylated at lysine 314.

Conclusions

Together, our results establish acetylation of K314 as an important regulatory modification of p65 and subsequently of NF-κB-dependent gene expression.