Viral replication and the coactivators p300 and CBP

Silencing of Unintegrated Retroviral DNAs

Retroviral infection delivers an RNA genome into the cytoplasm that serves as the template for the synthesis of a linear double-stranded DNA copy by the viral reverse transcriptase. Within the nucleus this linear DNA gives rise to extrachromosomal circular forms, and in a key step of the life cycle is inserted into the host genome to form the integrated provirus. The unintegrated DNA forms, like those of DNAs entering cells by other means, are rapidly loaded with nucleosomes and heavily silenced by epigenetic histone modifications. This review summarizes our present understanding of the silencing machinery for the DNAs of the mouse leukemia viruses and human immunodeficiency virus type 1. We consider the potential impact of the silencing on virus replication, on the sensing of the virus by the innate immune system, and on the formation of latent proviruses. We also speculate on the changeover to high expression from the integrated proviruses in permissive cell types, and briefly consider the silencing of proviruses even after integration in embryonic stem cells and other developmentally primitive cell types.

SARS-CoV-2 Exposed Mesenchymal Stromal Cell from Congenital Pulmonary Airway Malformations: Transcriptomic Analysis and the Expression of Immunomodulatory Genes

The inflammatory response plays a central role in the complications of congenital pulmonary airway malformations (CPAM) and severe coronavirus disease 2019 (COVID-19). The aim of this study was to evaluate the transcriptional changes induced by SARS-CoV-2 exposure in pediatric MSCs derived from pediatric lung (MSCs-lung) and CPAM tissues (MSCs-CPAM) in order to elucidate potential pathways involved in SARS-CoV-2 infection in a condition of exacerbated inflammatory response. MSCs-lung and MSCs-CPAM do not express angiotensin-converting enzyme 2 (ACE2) and transmembrane serine protease 2 (TRMPSS2). SARS-CoV-2 appears to be unable to replicate in MSCs-CPAM and MSCs-lung. MSCs-lung and MSCs-CPAM maintained the expression of stemness markers MSCs-lung show an inflammatory response (IL6, IL1B, CXCL8, and CXCL10), and the activation of Notch3 non-canonical pathway; this route appears silent in MSCs-CPAM, and cytokine genes expression is reduced. Decreased value of p21 in MSCs-lung suggested no cell cycle block, and cells did not undergo apoptosis. MSCs-lung appears to increase genes associated with immunomodulatory function but could contribute to inflammation, while MSCs-CPAM keeps stable or reduce the immunomodulatory receptors expression, but they also reduce their cytokines expression. These data indicated that, independently from their perilesional or cystic origin, the MSCs populations already present in a patient affected with CPAM are not permissive for SARS-CoV-2 entry, and they will not spread the disease in case of infection. Moreover, these MSCs will not undergo apoptosis when they come in contact with SARS-CoV-2; on the contrary, they maintain their staminality profile.

p300 promotes cell proliferation through suppressing Kaposi's sarcoma-associated herpesvirus (KSHV) reactivation in the infected B-lymphoma cells

Primary Effusion Lymphoma (PEL) is a B-cell lymphoma associated with Kaposi's sarcoma herpesvirus (KSHV) infection. However, the mechanism of oncogenesis of PEL is still unclear. Studies have shown that the cellular transcriptional coactivator p300 regulates the interaction between host and virus, which plays a vital role in viral replication. In this study, we investigated the role of p300 in BCBL1 cells during the KSHV life cycle. We found that p300 knockout resulted in an overall increase for the early lytic genes and changed the expression of genes associated with tumor development, proliferation, and the immune response in the KSHV infected B cells. However, knockout of p300 significantly inhibited the expression of the immediate-early gene RTA and the late lytic gene K8 after KSHV lytic activation. Additionally, the intracellular KSHV genome copy number and the virion production were reduced. These results demonstrated that p300 plays a crucial role in suppressing KSHV viral replication in BCBL1. Furthermore, we observed that the growth of BCBL1 was inhibited by knockout of p300, which confirmed our findings that p300 promotes cell proliferation. This study further provided evidence that p300 plays an important role in the pathogenesis of BCBL1, which might lead to the oncogenesis of PEL caused by KSHV infection.

Global landscape of mouse and human cytokine transcriptional regulation

Cytokines are cell-to-cell signaling proteins that play a central role in immune development, pathogen responses, and diseases. Cytokines are highly regulated at the transcriptional level by combinations of transcription factors (TFs) that recruit cofactors and the transcriptional machinery. Here, we mined through three decades of studies to generate a comprehensive database, CytReg, reporting 843 and 647 interactions between TFs and cytokine genes, in human and mouse respectively. By integrating CytReg with other functional datasets, we determined general principles governing the transcriptional regulation of cytokine genes. In particular, we show a correlation between TF connectivity and immune phenotype and disease, we discuss the balance between tissue-specific and pathogen-activated TFs regulating each cytokine gene, and cooperativity and plasticity in cytokine regulation. We also illustrate the use of our database as a blueprint to predict TF-disease associations and identify potential TF-cytokine regulatory axes in autoimmune diseases. Finally, we discuss research biases in cytokine regulation studies, and use CytReg to predict novel interactions based on co-expression and motif analyses which we further validated experimentally. Overall, this resource provides a framework for the rational design of future cytokine gene regulation studies.

Somatic EP300-G211S mutations are associated with overall somatic mutational patterns and breast cancer specific survival in triple-negative breast cancer

PURPOSE

We have compared the mutational profiles of human breast cancer tumor samples belonging to all major subgroups with special emphasis on triple-negative breast cancer (TNBC). Our major goal was to identify specific mutations that could be potentially used for clinical decision making in TNBC patients.

PATIENTS AND METHODS

Primary tumor specimens from 149 Norwegian breast cancer patients were available. We analyzed the tissue samples for somatic mutations in 44 relevant breast cancer genes by targeted next-generation sequencing. As a second confirmatory technique, we performed pyrosequencing on selected samples.

RESULTS

We observed a distinct subgroup of TNBC patients, characterized by an almost completely lack of pathogenic somatic mutations. A point mutation in the adenoviral E1A binding protein p300 (EP300-G211S) was significantly correlated to this TNBC subgroup. The EP300-G211S mutation was exclusively found in the TNBC patients and its presence reduced the chance for other pathological somatic mutations in typical breast cancer genes investigated in our gene panel by 94.9% (P < 0.005). Interestingly, the EP300-G211S mutation also predicted a lower risk for relapses and decreased breast cancer-specific mortality during long-term follow-up of the patients.

CONCLUSION

Next-generation sequencing revealed specific mutations in EP300 to be associated with the mutational patterns in typical breast cancer genes and long-term outcome of triple-negative breast cancer patients.

Structural Insights in Multifunctional Papillomavirus Oncoproteins

Since their discovery in the mid-eighties, the main papillomavirus oncoproteins E6 and E7 have been recalcitrant to high-resolution structure analysis. However, in the last decade a wealth of three-dimensional information has been gained on both proteins whether free or complexed to host target proteins. Here, we first summarize the diverse activities of these small multifunctional oncoproteins. Next, we review the available structural data and the new insights they provide about the evolution of E6 and E7, their multiple interactions and their functional variability across human papillomavirus (HPV) species.

Functional Screening Identifies Human miRNAs that Modulate Adenovirus Propagation in Prostate Cancer Cells

Oncolytic adenoviruses represent a novel class of anticancer agents. Their efficacy in killing cancer cells is variable, suggesting that there is room for improvement. Host miRNAs have been shown to play important roles in susceptibility of cells to replication of different viruses. This study investigated if adenovirus replication in human prostate cancer cells is influenced by host cell miRNA expression. To this end, human miRNA expression in response to adenovirus infection was analyzed, and functional screens for lytic adenovirus replication were performed using synthetic miRNA mimic and inhibitor libraries. Adenovirus infection generally reduced miRNA expression. On top of this nonspecific interference with miRNA biogenesis, a set of miRNAs, including in particular miR-222, was found specifically reduced. Another set of miRNAs was found to promote adenovirus-induced death of prostate cancer cells. In most cases, this did not stimulate adenovirus propagation. The exception was miR-26b. Overexpression of miR-26b inhibited adenovirus-induced NF-κB activation, augmented adenovirus-mediated cell death, increased adenovirus progeny release, and promoted adenovirus propagation and spread in several human prostate cancer cell lines. This suggests that miR-26b is particularly useful to be combined with oncolytic adenovirus for more effective treatment of prostate cancer.

Role of Intrinsic Protein Disorder in the Function and Interactions of the Transcriptional Coactivators CREB-binding Protein (CBP) and p300

The transcriptional coactivators CREB-binding protein (CBP) and p300 undergo a particularly rich set of interactions with disordered and partly ordered partners, as a part of their ubiquitous role in facilitating transcription of genes. CBP and p300 contain a number of small structured domains that provide scaffolds for the interaction of disordered transactivation domains from a wide variety of partners, including p53, hypoxia-inducible factor 1α (HIF-1α), NF-κB, and STAT proteins, and are the targets for the interactions of disordered viral proteins that compete with cellular factors to disrupt signaling and subvert the cell cycle. The functional diversity of the CBP/p300 interactome provides an excellent example of the power of intrinsic disorder to facilitate the complexity of living systems.

Advancements in the development of HIF-1α-activated protein switches for use in enzyme prodrug therapy

While gene-directed enzyme prodrug therapy has shown potential as a cancer therapeutic in animal and clinical trials, concerns over the efficacy, selectivity, and safety of gene delivery vehicles have restricted its advance. In an attempt to relieve some of the demands on targeted gene delivery vehicles and achieve the full potential of enzyme prodrug therapy, cancer-targeted activity can be engineered into the enzyme itself. We previously engineered a switchable prodrug-activating enzyme that selectively kills human cancer cells accumulating the cancer marker hypoxia-inducible factor-1α (HIF-1α). This HIF-1α-activated protein switch (Haps59) is designed to increase its ability to convert the prodrug 5-fluorocytosine into the chemotherapeutic 5-fluorouracil in a HIF-1α-dependent manner. However, in cancer cell lines expressing Haps59 the 5FC sensitivity difference between the presence and absence of HIF-1α was not as large as desired. In this work, we aimed to improve the cancer specificity of this switch via a directed evolution approach utilizing random mutagenesis, linker mutagenesis, and random insertion and circular permutation. We identified improved HIF-1α-activated protein switches that confer E. coli with modest increases in HIF-1α-dependent 5FC toxicity. Additionally, the current bottleneck in the development of improved HIF-1α-activated protein switches is screening switch candidates in mammalian cells. To accommodate higher throughput and reduce experimental variability, we explored the use of Flp recombinase-mediated isogenic integration in 293 cells. These experiments raised the possibility that Haps59 can be activated by other interactors of the CH1 domain, and experiments in E. coli indicated that CITED2 can also activate Haps59. Although many CH1 binding partners are also oncogenes, CH1's promiscuous binding and subsequent off-target activation of Haps59 needs to be examined under normal physiological conditions to identify off-target activators. With aberrant activating molecules identified, further directed evolution can be performed to improve the cancer specificity of HIF-1α-activated protein switches.

The high-risk HPV16 E7 oncoprotein mediates interaction between the transcriptional coactivator CBP and the retinoblastoma protein pRb

The oncoprotein E7 from human papillomavirus (HPV) strains that confer high cancer risk mediates cell transformation by deregulating host cellular processes and activating viral gene expression through recruitment of cellular proteins such as the retinoblastoma protein (pRb) and the cyclic-AMP response element binding binding protein (CBP) and its paralog p300. Here we show that the intrinsically disordered N-terminal region of E7 from high-risk HPV16 binds the TAZ2 domain of CBP with greater affinity than E7 from low-risk HPV6b. HPV E7 and the tumor suppressor p53 compete for binding to TAZ2. The TAZ2 binding site in E7 overlaps the LxCxE motif that is crucial for interaction with pRb. While TAZ2 and pRb compete for binding to a monomeric E7 polypeptide, the full-length E7 dimer mediates an interaction between TAZ2 and pRb by promoting formation of a ternary complex. Cell-based assays show that expression of full-length HPV16 E7 promotes increased pRb acetylation and that this response depends both on the presence of CBP/p300 and on the ability of E7 to form a dimer. These observations suggest a model for the oncogenic effect of high-risk HPV16 E7. The disordered region of one E7 molecule in the homodimer interacts with the pocket domain of pRb, while the same region of the other E7 molecule binds the TAZ2 domain of CBP/p300. Through its ability to dimerize, E7 recruits CBP/p300 and pRb into a ternary complex, bringing the histone acetyltransferase domain of CBP/p300 into proximity to pRb and promoting acetylation, leading to disruption of cell cycle control.

Lysine acetyltransferases CBP and p300 as therapeutic targets in cognitive and neurodegenerative disorders

Neuropsychiatric pathologies, including neurodegenerative diseases and neurodevelopmental syndromes, are frequently associated with dysregulation of various essential cellular mechanisms, such as transcription, mitochondrial respiration and protein degradation. In these complex scenarios, it is difficult to pinpoint the specific molecular dysfunction that initiated the pathology or that led to the fatal cascade of events that ends with the death of the neuron. Among the possible original factors, epigenetic dysregulation has attracted special attention. This review focuses on two highly related epigenetic factors that are directly involved in a number of neurological disorders, the lysine acetyltransferases CREB-binding protein (CBP) and E1A-associated protein p300 (p300). We first comment on the role of chromatin acetylation and the enzymes that control it, particularly CBP and p300, in neuronal plasticity and cognition. Next, we describe the involvement of these proteins in intellectual disability and in different neurodegenerative diseases. Finally, we discuss the potential of ameliorative strategies targeting CBP/p300 for the treatment of these disorders.

Inhibiting the HIV integration process: past, present, and the future

HIV integrase (IN) catalyzes the insertion into the genome of the infected human cell of viral DNA produced by the retrotranscription process. The discovery of raltegravir validated the existence of the IN, which is a new target in the field of anti-HIV drug research. The mechanism of catalysis of IN is depicted, and the characteristics of the inhibitors of the catalytic site of this viral enzyme are reported. The role played by the resistance is elucidated, as well as the possibility of bypassing this problem. New approaches to block the integration process are depicted as future perspectives, such as development of allosteric IN inhibitors, dual inhibitors targeting both IN and other enzymes, inhibitors of enzymes that activate IN, activators of IN activity, as well as a gene therapy approach.

Two independent regions of simian virus 40 T antigen increase CBP/p300 levels, alter patterns of cellular histone acetylation, and immortalize primary cells

Simian virus 40 (SV40) large T antigen (SVT) interferes with normal cell regulation and thus has been used to identify cellular components controlling proliferation and homeostasis. We have previously shown that SVT-mediated transformation requires interaction with the histone acetyltransferases (HATs) CBP/p300 and now report that the ectopic expression of SVT in several cell types in vivo and in vitro results in a significant increase in the steady-state levels of CBP/p300. Furthermore, SVT-expressing cells contain higher levels of acetylated CBP/p300, a modification that has been linked to increased HAT activity. Concomitantly, the acetylation levels of histone residues H3K56 and H4K12 are markedly increased in SVT-expressing cells. Other polyomavirus-encoded large T antigens also increase the levels of CBP/p300 and sustain a rise in the acetylation levels of H3K56 and H4K12. SVT does not affect the transcription of CBP/p300, but rather, alters their overall levels through increasing the loading of CBP/p300 mRNAs onto polysomes. Two distinct regions within SVT, one located in the amino terminus and one in the carboxy terminus, can independently alter both the levels of CBP/p300 and the loading of CBP/p300 transcripts onto polysomes. Within the amino-terminal fragment, a functional J domain is necessary for increasing CBP/p300 and specific histone acetylation levels, as well as for immortalizing primary cells. These studies uncover the action of polyomavirus T antigens on cellular CBP/p300 and suggest that additional mechanisms are used by T antigens to induce cell immortalization and transformation.

Live-cell studies of p300/CBP histone acetyltransferase activity and inhibition

Histone acetyltransferase enzymes (HATs) are important therapeutic targets, but there are few cell-based assays available for evaluating the pharmacodynamics of HAT inhibitors. Here we present the application of a FRET-based reporter, Histac, in live-cell studies of p300/CBP HAT inhibition, by both genetic and pharmacologic disruption. shRNA knockdown of p300/CBP led to increased Histac FRET, thus suggesting a role for p300/CBP in the acetylation of the histone H4 tail. Additionally, we describe a new p300/CBP HAT inhibitor, C107, and show that it can also increase cellular Histac FRET. Taken together, these studies provide a live-cell strategy for identifying and evaluating p300/CBP inhibitors.

Herpes simplex virus type 1 infection activates the Epstein-Barr virus replicative cycle via a CREB-dependent mechanism

The reactivation of latent Epstein-Barr virus (EBV) to lytic replication is important in pathogenesis and requires virus-host cellular interactions. However, the mechanism underlying the reactivation of EBV is not yet fully understood. In the present study, herpes simplex virus type 1 (HSV-1) was shown to induce the reactivation of latent EBV by triggering BZLF1 expression. The BZLF1 promoter (Zp) was not activated by HSV-1 essential glycoprotein-induced membrane fusion. Nevertheless, Zp was activated within 6 h post HSV-1 infection in virus entry-dependent and replication-independent manners. Using a panel of Zp deletion mutants, HSV-1 was shown to promote Zp through a cyclic adenosine monophosphate (cAMP) response element (CRE) located in ZII. The phosphorylated cAMP response element-binding (phos-CREB) protein, the cellular transactivator that binds to CRE, also increased after HSV-1 infection. By transient transfection, cAMP-dependent protein kinase A and HSV-1 US3 protein were found to be capable of activating Zp in CREB- and CRE-dependent manners. The relationship between EBV activation and HSV-1 infection revealed a possible common mechanism that stimulated latent EBV into lytic cycles in vivo.

Epigenetic displacement of HP1 from heterochromatin by HIV-1 Vpr causes premature sister chromatid separation

Although pericentromeric heterochromatin is essential for chromosome segregation, its role in humans remains controversial. Dissecting the function of HIV-1-encoded Vpr, we unraveled important properties of heterochromatin during chromosome segregation. In Vpr-expressing cells, hRad21, hSgo1, and hMis12, which are crucial for proper chromosome segregation, were displaced from the centromeres of mitotic chromosomes, resulting in premature chromatid separation (PCS). Interestingly, Vpr displaced heterochromatin protein 1-α (HP1-α) and HP1-γ from chromatin. RNA interference (RNAi) experiments revealed that down-regulation of HP1-α and/or HP1-γ induced PCS, concomitant with the displacement of hRad21. Notably, Vpr stimulated the acetylation of histone H3, whereas p300 RNAi attenuated the Vpr-induced displacement of HP1-α and PCS. Furthermore, Vpr bound to p300 that was present in insoluble regions of the nucleus, suggesting that Vpr aberrantly recruits the histone acetyltransferase activity of p300 to chromatin, displaces HP1-α, and causes chromatid cohesion defects. Our study reveals for the first time centromere cohesion impairment resulting from epigenetic disruption of higher-order structures of heterochromatin by a viral pathogen.

Lysine acetylation sites in bovine foamy virus transactivator BTas are important for its DNA binding activity

Cellular acetylation signaling is important for viral gene regulation, particularly during the transactivation of retroviruses. The regulatory protein of bovine foamy virus (BFV), BTas, is a transactivator that augments viral gene transcription from both the long terminal repeat (LTR) promoter and the internal promoter (IP). In this study, we report that the histone acetyltransferase (HAT), p300, specifically acetylates BTas both in vivo and in vitro. Further studies demonstrated that BTas acetylation markedly enhances its transactivation activity. Mutagenesis analysis identified three lysines at positions 66, 109 and 110 in BTas that are acetylated by p300. The K110R mutant lost its binding to BFV promoter as well as its ability to activate BFV promoter. The acetylation of K66 and K109 may contribute to increased BTas binding ability. These results suggest that the p300-acetylated lysines of BTas are important for transactivation of BFV promoters and therefore have an important role in BFV replication.

Gene expression and transcription factor profiling reveal inhibition of transcription factor cAMP-response element-binding protein by gamma-herpesvirus replication and transcription activator

Herpesvirus replication involves the expression of over 80 viral genes in a well ordered sequence, leading to the production of new virions. Viral genes expressed during the earliest phases of replication often regulate both viral and cellular genes. Therefore, they have the potential to bring about dramatic functional changes within the cell. Replication and transcription activator (RTA) is a potent immediate early transcription activator of the gamma-herpesvirus family. This family includes Epstein-Barr virus and Kaposi sarcoma-associated herpesvirus, human pathogens associated with malignancy. Here we combine gene array technology with transcription factor profiling to identify the earliest DNA promoter and cellular transcription factor targets of RTA in the cellular genome. We find that expression of RTA leads to both activation and inhibition of distinct groups of cellular genes. The identity of the target genes suggests that RTA rapidly changes the cellular environment to counteract cell death pathways, support growth factor signaling, and also promote immune evasion of the infected cell. Transcription factor profiling of the target gene promoters highlighted distinct pathways involved in gene activation at specific time points. Most notable throughout was the high level of cAMP-response element-binding protein (CREB)-response elements in RTA target genes. We find that RTA can function as either an activator or an inhibitor of CREB-response genes, depending on the promoter context. The association with CREB also highlights a novel connection and coordination between viral and cellular "immediate early" responses.

Complexes of HIV-1 integrase with HAT proteins: multiscale models, dynamics, and hypotheses on allosteric sites of inhibition

A new and very promising strategy for HIV drug discovery consists in blocking the multiple functional interactions between HIV-1 integrase (IN) and its cellular cofactors. At present, this line of action is hindered by the absence of three-dimensional structures of IN in complex with any of them. In this article, we developed a full-length three-dimensional structure of IN, including the highly flexible terminal residues 270-288, which are not experimentally solved. Additionally, we built models of IN complexed to the human acetyltransferases GCN5 and p300 based on available structural and mutagenesis data. Then, we studied the dynamical behavior of these models by means of the Coarse-Grained Molecular Dynamics (CGMD) and Essential Dynamics (ED) to locate and characterize the nature of the largest collective motions. We found correlated motions involving distant regions of IN. Moreover, we found that these are influenced by the binding with the acetyltransferases (HATs). Taken together these findings suggest a way to affect the acetyltransferase binding by an allosteric type of inhibition and provide an important new approach for the drug design against HIV disease.

Blocking interactions between HIV-1 integrase and cellular cofactors: an emerging anti-retroviral strategy

HIV-1 integrase (IN) executes the insertion of proviral DNA into the host cell genome, an essential step in the retroviral life cycle. This is a multi-step process that starts in the cytosol and culminates in the nucleus of the infected cell. It is becoming increasingly clear that IN interacts with a wide range of different host-cell proteins throughout the viral life cycle. These cellular cofactors are exploited for various functions, including nuclear import, DNA target-site selection and virion assembly. The disruption of key interactions between IN and direct cellular cofactors affords a novel therapeutic approach for the design and development of new classes of anti-retroviral agents. Here, we will discuss the rationale behind this emerging and promising therapeutic strategy for HIV drug discovery. Our discussion includes the identified IN cellular cofactors, key research developments in the field and the implications this approach will have on the current HIV treatment regimen.

Histone acetyltransferase p300 promotes the activation of human WT1 promoter and intronic enhancer

The Wilms' tumor gene-1 (WT1) encodes a zinc finger protein involved in gene regulation during kidney, gonad, and heart development. In addition to its promoter, a 258 bp intronic enhancer is required for tissue-specific expression of WT1 gene. p300 is a histone acetyltransferase (HAT) and exerts essential functions in gene regulation. Here, we show that p300 increased the expression of endogenous WT1 mRNA and promoted the activation of the WT1 promoter and intronic enhancer. The results also revealed that the adenovirus E1A repressed the p300 function, while the p300-binding defective E1A delta 2-36 did not, and p300 HAT activity was important for its function since p300 mutant with the HAT domain deleted partially abrogated its ability to activate the WT1 promoter and intronic enhancer. Furthermore, p300 and c-Myb synergistically activated the expression of WT1 gene. This study revealed that p300 and its HAT activity were involved in regulation of WT1 transcription.

Human T lymphotropic virus type 1 accessory protein p12I modulates calcium-mediated cellular gene expression and enhances p300 expression in T lymphocytes

Human T-lymphotropic virus type 1 (HTLV-1) is the etiologic agent of adult T cell leukemia/lymphoma (ATLL), an aggressive CD4+ T lymphocyte malignancy. Activation of T lymphocytes is required for effective retroviral integration into the host cell genome and subsequent viral replication, but the molecular mechanisms involved in HTLV-1-mediated T cell activation remain unclear. HTLV-1 encodes various accessory proteins such as p12I, which has been demonstrated to be critical for HTLV-1 infectivity in vivo in rabbits and in vitro in quiescent primary human T lymphocytes. This hydrophobic protein localizes in the endoplasmic reticulum, increases intracellular calcium, and activates nuclear factor of activated T cell-mediated transcription. To further elucidate the role of p12I in regulation of cellular gene expression, we performed gene array analysis on stable p12I-expressing Jurkat T cells, using Affymetrix U133A arrays. Our data indicate that p12I altered the expression of genes associated with a network of interrelated pathways including T cell signaling, cell proliferation, and apoptosis. Expression of several calcium-regulated genes was found to be altered by p12I, consistent with known properties of the viral protein. Gene array findings were confirmed by semiquantitative RT-PCR in Jurkat T cells and primary CD4+ T lymphocytes. Furthermore, dose-dependent expression of p12I in Jurkat T cells resulted in significant increases in p300 and p300-dependent transcription. This is the first report of a viral protein influencing the transcription of p300, a rate-limiting coadapter critical in HTLV-1-mediated T cell activation. Collectively, our data strongly indicate that HTLV-1 p12I modulates cellular gene expression patterns to hasten the activation of T lymphocytes and thereby promote efficient viral infection.

The Vpr protein from HIV-1: distinct roles along the viral life cycle

The genomes of human and simian immunodeficiency viruses (HIV and SIV) encode the gag, pol and env genes and contain at least six supplementary open reading frames termed tat, rev, nef, vif, vpr, vpx and vpu. While the tat and rev genes encode regulatory proteins absolutely required for virus replication, nef, vif, vpr, vpx and vpu encode for small proteins referred to "auxiliary" (or "accessory"), since their expression is usually dispensable for virus growth in many in vitro systems. However, these auxiliary proteins are essential for viral replication and pathogenesis in vivo. The two vpr- and vpx-related genes are found only in members of the HIV-2/SIVsm/SIVmac group, whereas primate lentiviruses from other lineages (HIV-1, SIVcpz, SIVagm, SIVmnd and SIVsyk) contain a single vpr gene. In this review, we will mainly focus on vpr from HIV-1 and discuss the most recent developments in our understanding of Vpr functions and its role during the virus replication cycle.

Coactivators p300 and PCAF physically and functionally interact with the foamy viral trans-activator

Background

Foamy virus Bel1/Tas trans-activators act as key regulators of gene expression and directly bind to Bel1 response elements (BRE) in both the internal and the 5'LTR promoters leading to strong transcriptional trans-activation. Cellular coactivators interacting with Bel1/Tas are unknown to date.

Results

Transient expression assays, co-immunoprecipitation experiments, pull-down assays, and Western blot analysis were used to demonstrate that the coactivator p300 and histone acetyltransferase PCAF specifically interact with the retroviral trans-activator Bel1/Tas in vivo. Here we show that the Bel1/Tas-mediated trans-activation was enhanced by the coactivator p300, histone acetyltransferases PCAF and SRC-1 based on the crucial internal promoter BRE. The Bel1/Tas-interacting region was mapped to the C/H1 domain of p300 by co-immunoprecipitation and pull-down assays. In contrast, coactivator SRC-1 previously reported to bind to the C-terminal domain of p300 did not directly interact with the Bel1 protein but nevertheless enhanced Bel1/Tas-mediated trans-activation. Cotransfection of Bel1/Tas and p300C with an expression plasmid containing the C/H1domain partially inhibited the p300C-driven trans-activation.

Conclusions

Our data identify p300 and PCAF as functional partner molecules that directly interact with Bel1/Tas. Since the acetylation activities of the three coactivators reside in or bind to the C-terminal regions of p300, a C/H1 expression plasmid was used as inhibitor. This is the first report of a C/H1 domain-interacting retroviral trans-activator capable of partially blocking the strong Bel1/Tas-mediated activation of the C-terminal region of coactivator p300. The potential mechanisms and functional roles of the three histone and factor acetyltransferases p300, PCAF, and SRC-1 in Bel1/Tas-mediated trans-activation are discussed.

Bovine leukemia virus alters growth properties and casein synthesis in mammary epithelial cells

Bovine leukemia virus (BLV) is widespread in US dairy herds, yet only about 1% of infected cattle develop bovine leukosis and are culled from the herd. A major concern is whether BLV infection of dairy cows alters milk yield. Although several studies have examined the effect of BLV on milk production in vivo, the results were inconclusive. No in vitro studies have been done. The discovery of BLV in mammary epithelial cells (MEC) of infected cows raises the possibility that the virus could affect these cells directly. The purpose of this study was to use an in vitro system to determine if BLV could alter milk yield by altering cell number and/or milk production per cell. A short-term cell line established from the MEC of a BLV-negative cow, and a proven casein-producer mouse cell line, Comma D, were stably transfected with a plasmid containing the entire BLV genome. Untransfected parental lines served as negative controls. The BLV-containing bovine MEC line has a reduced population-doubling time, higher saturation density, and increased longevity. The Comma D line is an already-transformed cell line, and growth properties did not change after transfection with BLV. Under appropriate differentiation conditions, both the bovine and mouse MEC transfected with BLV displayed decreased casein production and mRNA synthesis compared with control cell lines without BLV. Our results suggest that effects of BLV infection on milk production may not be related solely to overall animal health but may also be mediated directly at a cellular level.

BRCA1 augments transcription by the NF-kappaB transcription factor by binding to the Rel domain of the p65/RelA subunit

BRCA1 is a tumor suppressor gene mutated in cases of hereditary breast and ovarian cancer. BRCA1 protein is involved in apoptosis and growth/tumor suppression. In this study, we present evidence that p65/RelA, one of the two subunits of the transcription factor NF-kappaB, binds to the BRCA1 protein. Treatment of 293T cells with the cytokine tumor necrosis factor-alpha induces an interaction between endogenous p65/RelA and BRCA1. GST-protein affinity assay experiments reveal that the Rel homology domain of the p65/RelA subunit of NF-kappaB interacts with multiple sites within the N-terminal region of BRCA1. Transient transfection of BRCA1 significantly enhances the ability of the tumor necrosis factor-alpha or interleukin-1beta to activate transcription from the promoters of NF-kappaB target genes. Mutation of the NF-kappaB-binding sites in the NF-kappaB reporter blocks the effect of BRCA1 on transcription. Also the ability of BRCA1 to activate NF-kappaB target genes is inhibited by a super-stable inhibitor of NF-kappaB and by the chemical inhibitor SN-50. These data indicate that BRCA1 acts as a co-activator with NF-kappaB. In addition, we show that cells infected with an adenovirus expressing BRCA1 up-regulate the endogenous expression of NF-kappaB target genes Fas and interferon-beta. Together, this information suggests that BRCA1 may play a role in cell life-death decisions following cell stress by modulation of the activity of NF-kappaB.

CAF-mediated human immunodeficiency virus (HIV) type 1 transcriptional inhibition is distinct from alpha-defensin-1 HIV inhibition

CD8(+) T lymphocytes can inhibit human immunodeficiency virus type 1 (HIV-1) replication by secreting a soluble factor(s) known as CD8(+) T-lymphocyte antiviral factor (CAF). One site of CAF action is inhibition of HIV-1 RNA transcription, particularly at the step of long terminal repeat (LTR)-driven gene expression. The inhibitory effect of CAF on HIV-1 LTR activation is mediated through STAT1 activation. A recent study reports that alpha-defensins 1 to 3 account for CAF activity against HIV-1. Here, we address whether alpha-defensins, particularly alpha-defensin-1, contribute to CAF-mediated inhibition of HIV-1 transcription. Both recombinant alpha-defensin-1 and CAF derived from herpesvirus saimiri (HVS)-transformed CD8(+) cells inhibited HIV-1 infection and gene expression. For both factors, the inhibition of HIV-1 infection did not occur at the level of viral entry. Pretreatment of cells with alpha-defensin-1 followed by a washing out prior to infection blocked infection by HIV-1, indicating that direct inactivation of virions was not required for its inhibitory effect. In contrast to CAF, alpha-defensin-1 did not inhibit phorbol myristate acetate- or Tat-mediated HIV-1 LTR activation in a transient transfection system, nor did it activate STAT1 tyrosine phosphorylation. Furthermore, alpha-defensins 1 to 3 were below the level of detection in a panel of HVS-transformed CD8(+) cells with potent HIV-1 inhibitory activity and a neutralizing antibody against alpha-defensins 1 to 3 did not reverse the inhibitory effect of CAF on HIV-1 gene expression in infected cells and on HIV-1 LTR activation in transfected cells. Taken together, our results suggest that alpha-defensin-1 inhibits HIV-1 infection following viral entry but that alpha-defensins 1 to 3 are not responsible for the HIV-1 transcriptional inhibition by CAF.

Human immunodeficiency virus type 1 (HIV-1) accessory protein Vpr induces transcription of the HIV-1 and glucocorticoid-responsive promoters by binding directly to p300/CBP coactivators

The accessory Vpr protein of human immunodeficiency virus type 1 (HIV-1) is a promiscuous activator of viral and cellular promoters. We report that Vpr enhances expression of the glucocorticoid receptor-induced mouse mammary tumor virus (MMTV) promoter and of the Tat-induced HIV-1 long terminal repeat promoter by directly binding to p300/CBP coactivators. In contrast, Vpr does not bind to p/CAF or to members of the p160 family of nuclear receptor coactivators, such as steroid receptor coactivator 1a and glucocorticoid receptor (GR)-interacting protein 1. Vpr forms a stable complex with p300 and also interacts with the ligand-bound glucocorticoid receptor in vivo. Mutation analysis showed that the C-terminal part of Vpr binds to the C-terminal portion of p300/CBP within amino acids 2045 to 2191. The same p300 region interacts with the p160 coactivators and with the adenovirus E1A protein. Accordingly, E1A competed for binding to p300 in vitro. Coexpression of E1A or of small fragments of p300 containing the Vpr binding site resulted in inhibition of Vpr's transcriptional effects. The C-terminal part of p300 containing the transactivating region is required for Vpr transactivation, whereas the histone acetyltransferase enzymatic region is dispensable. Vpr mutants that bind p300 but not the GR did not activate expression of the MMTV promoter and had dominant-negative effects. These results indicate that Vpr activates transcription by acting as an adapter linking transcription components and coactivators.

Activation of cellular and heterologous promoters by the human herpesvirus 8 replication and transcription activator

The key regulator of the switch from latent to lytic replication of the human herpesvirus 8 (HHV-8; KSHV) is the replication and transcription activator (Rta). The ability of Rta to regulate cellular gene expression was examined by transient transfection into cells that were not infected with HHV-8. Rta induced some, but not all, NF-kappa B-responsive reporters through mechanisms that did not involve activation of classic forms of NF-kappa B. Furthermore, transfection of the NF-kappa B subunit Rel A inhibited the ability of Rta to transactivate some but not all reporters. For example, Rel A inhibited the ability of Rta to transactivate the IL-6 promoter, but only when sequences upstream of the NF-kappa B site were present. The ability of Rel A to inhibit Rta-mediated transactivation was not dependent on a functional NF-kappa B site within the promoter, suggesting an indirect mechanism for inhibition. These studies suggest that Rta expression during lytic reactivation of HHV-8 would lead to expression of some cellular genes, including IL-6, whereas activation of NF-kappa B could inhibit some responses to Rta.

T antigens of simian virus 40: molecular chaperones for viral replication and tumorigenesis

Simian virus 40 (SV40) is a small DNA tumor virus that has been extensively characterized due to its relatively simple genetic organization and the ease with which its genome is manipulated. The large and small tumor antigens (T antigens) are the major regulatory proteins encoded by SV40. Large T antigen is responsible for both viral and cellular transcriptional regulation, virion assembly, viral DNA replication, and alteration of the cell cycle. Deciphering how a single protein can perform such numerous and diverse functions has remained elusive. Recently it was established that the SV40 T antigens, including large T antigen, are molecular chaperones, each with a functioning DnaJ domain. The molecular chaperones were originally identified as bacterial genes essential for bacteriophage growth and have since been shown to be conserved in eukaryotes, participating in an array of both viral and cellular processes. This review discusses the mechanisms of DnaJ/Hsc70 interactions and how they are used by T antigen to control viral replication and tumorigenesis. The use of the DnaJ/Hsc70 system by SV40 and other viruses suggests an important role for these molecular chaperones in the regulation of the mammalian cell cycle and sheds light on the enigmatic SV40 T antigen-a most amazing molecule.

The H1 and H2 regions of the activation domain of herpes simplex virion protein 16 stimulate transcription through distinct molecular mechanisms

BACKGROUND

The Herpes Simplex Virion Protein 16 (VP16) contains a strong activation domain which can be subdivided into two regions, H1 and H2, both of which independently activate transcription in vivo. Several components of the basal transcription machinery have been shown to interact with the activation domain of VP16, mostly through the H1 region.

RESULTS

We show that the H2 region binds directly to histone acetyltransferase, CBP (CREB (cAMP Responsive Element Binding Protein) Binding Protein) both in vivo and in vitro. The sites of interaction with the H2 region were mapped to both the amino- and carboxy-terminal segments of CBP. A mutation in the H2 region disrupts the interaction with CBP and abolishes the ability of VP16 to mediate in vitro transactivation from chromatin templates in an acetyl-CoA dependent manner. In contrast, human Mediator, another co-activator complex, binds specifically to both the H1 and H2 regions.

CONCLUSION

The H1 and H2 regions of the VP16 activation domain activate transcription via distinct pathways. The H2 requires CBP for activation, whereas the H1 may function through Mediator and general transcription factors.

The Kaposi's sarcoma-associated herpesvirus K8 protein interacts with CREB-binding protein (CBP) and represses CBP-mediated transcription

Kaposi's sarcoma-associated herpesvirus (KSHV) open reading frame K8 encodes a basic region-leucine zipper protein of 237 amino acids that homodimerizes with its bZIP domain. KSHV K8 shows significant homology to the Epstein-Barr virus (EBV) immediate-early protein Zta, a key regulator in the reactivation and replication of EBV. In this study, we report that K8, like its homolog EBV Zta, interacts with cellular CREB-binding protein (CBP) in vivo and in vitro. This interaction requires the C/H3 domain of CBP and the basic region of K8. K8 represses CBP-mediated transcription by competing with limited amounts of cellular CBP, exemplified by the reduced expression from the AP-1 and human immunodeficiency virus long terminal repeat promoters.

A small domain of CBP/p300 binds diverse proteins: solution structure and functional studies

The transcriptional coactivators CBP and p300 are critical regulators of metazoan gene expression. They associate with many different DNA-bound transcription factors through small, conserved domains. We have identified a compactly folded 46 residue domain in CBP and p300, the IRF-3 binding domain (IBiD), and we have determined its structure by NMR. It has a helical framework containing an apparently flexible polyglutamine loop that participates in ligand binding. Spectroscopic data indicate that induced folding accompanies association of IBiD with its partners, which exhibit no evident sequence similarities. We demonstrate the significance both in vitro and in vivo of interactions between IBiD and a number of diverse partners. Thus, IBiD is an important contributor to signal integration by CBP and p300.