Three unrelated viral transforming proteins (vIRF, EBNA2, and E1A) induce the MYC oncogene through the interferon-responsive PRF element by using different transcription coadaptors

Different Mechanisms of Regulation of the Warburg Effect in Lymphoblastoid and Burkitt Lymphoma Cells

Background

The Warburg effect is one of the hallmarks of cancer and rapidly proliferating cells. It is known that the hypoxia-inducible factor 1-alpha (HIF1A) and MYC proteins cooperatively regulate expression of the HK2 and PDK1 genes, respectively, in the Burkitt lymphoma (BL) cell line P493-6, carrying an inducible MYC gene repression system. However, the mechanism of aerobic glycolysis in BL cells has not yet been fully understood.

Methods and Findings

Western blot analysis showed that the HIF1A protein was highly expressed in Epstein–Barr virus (EBV)-positive BL cell lines. Using biochemical assays and quantitative PCR (Q-PCR), we found that—unlike in lymphoblastoid cell lines (LCLs)—the MYC protein was the master regulator of the Warburg effect in these BL cell lines. Inhibition of the transactivation ability of MYC had no influence on aerobic glycolysis in LCLs, but it led to decreased expression of MYC-dependent genes and lactate dehydrogenase A (LDHA) activity in BL cells.

Conclusions

Our data suggest that aerobic glycolysis, or the Warburg effect, in BL cells is regulated by MYC expressed at high levels, whereas in LCLs, HIF1A is responsible for this phenomenon.

Viral epigenetics

DNA tumor viruses including members of the polyomavirus, adenovirus, papillomavirus, and herpes virus families are presently the subject of intense interest with respect to the role that epigenetics plays in control of the virus life cycle and the transformation of a normal cell to a cancer cell. To date, these studies have primarily focused on the role of histone modification, nucleosome location, and DNA methylation in regulating the biological consequences of infection. Using a wide variety of strategies and techniques ranging from simple ChIP to ChIP-chip and ChIP-seq to identify histone modifications, nuclease digestion to genome wide next generation sequencing to identify nucleosome location, and bisulfite treatment to MeDIP to identify DNA methylation sites, the epigenetic regulation of these viruses is slowly becoming better understood. While the viruses may differ in significant ways from each other and cellular chromatin, the role of epigenetics appears to be relatively similar. Within the viral genome nucleosomes are organized for the expression of appropriate genes with relevant histone modifications particularly histone acetylation. DNA methylation occurs as part of the typical gene silencing during latent infection by herpesviruses. In the simple tumor viruses like the polyomaviruses, adenoviruses, and papillomaviruses, transformation of the cell occurs via integration of the virus genome such that the virus's normal regulation is disrupted. This results in the unregulated expression of critical viral genes capable of redirecting cellular gene expression. The redirected cellular expression is a consequence of either indirect epigenetic regulation where cellular signaling or transcriptional dysregulation occurs or direct epigenetic regulation where epigenetic cofactors such as histone deacetylases are targeted. In the more complex herpersviruses transformation is a consequence of the expression of the viral latency proteins and RNAs which again can have either a direct or indirect effect on epigenetic regulation of cellular expression. Nevertheless, many questions still remain with respect to the specific mechanisms underlying epigenetic regulation of the viruses and transformation.

Epstein-Barr virus-mediated transformation of B cells induces global chromatin changes independent to the acquisition of proliferation

Epstein–Barr virus (EBV) infects and transforms human primary B cells inducing indefinite proliferation. To investigate the potential participation of chromatin mechanisms during the EBV-mediated transformation of resting B cells we performed an analysis of global changes in histone modifications. We observed a remarkable decrease and redistribution of heterochromatin marks including H4K20me3, H3K27me3 and H3K9me3. Loss of H4K20me3 and H3K9me3 occurred at constitutive heterochromatin repeats. For H3K27me3 and H3K9me3, comparison of ChIP-seq data revealed a decrease in these marks in thousands of genes, including clusters of HOX and ZNF genes, respectively. Moreover, DNase-seq data comparison between resting and EBV-transformed B cells revealed increased endonuclease accessibility in thousands of genomic sites. We observed that both loss of H3K27me3 and increased accessibility are associated with transcriptional activation. These changes only occurred in B cells transformed with EBV and not in those stimulated to proliferate with CD40L/IL-4, despite their similarities in the cell pathways involved and proliferation rates. In fact, B cells infected with EBNA-2 deficient EBV, which have much lower proliferation rates, displayed similar decreases for heterochromatic histone marks. Our study describes a novel phenomenon related to transformation of B cells, and highlights its independence of the pure acquisition of proliferation.

Review of latent and lytic phase biomarkers in Kaposi's sarcoma

INTRODUCTION

Kaposi's sarcoma (KS) is a vascular neoplasm with distinct clinical-epidemiological subtypes and varied clinical presentations. While the association of KS with human herpesvirus-8 (HHV8, KSHV) infection is well known, additional factors are needed for tumorigenesis. The precise sequence of events involved in KS development, progression and regression continues to be investigated. The discovery of KSHV biomarkers is helpful for diagnostic purposes, for understanding KS pathogenesis and for identifying potential druggable targets.

AREAS COVERED

This article reviews a number of key biomarkers relevant for the diagnosis of KS and HHV8-related pathogenesis. New developments in KS, potential therapeutic targets and the challenges involved in their discovery are highlighted.

EXPERT OPINION

Although there is currently no cure for KS, continued research devoted to uncovering biomarkers and understanding their pathogenic roles remains encouraging. The hope is that sometime soon one of these candidate targets will provide a curative therapy for this enigmatic sarcoma.

Evasion and subversion of interferon-mediated antiviral immunity by Kaposi's sarcoma-associated herpesvirus: an overview

Viral invasion of a host cell triggers immune responses with both innate and adaptive components. The innate immune response involving the induction of type I interferons (alpha and beta interferons [IFN-α and -β]) constitutes the first line of antiviral defenses. The type I IFNs signal the transcription of a group of antiviral effector proteins, the IFN-stimulated genes (ISGs), which target distinct viral components and distinct stages of the viral life cycle, aiming to eliminate invading viruses. In the case of Kaposi's sarcoma-associated herpesvirus (KSHV), the etiological agent of Kaposi's sarcoma (KS), a sudden upsurge of type I IFN-mediated innate antiviral signals is seen immediately following both primary de novo infection and viral lytic reactivation from latency. Potent subversion of these responses thus becomes mandatory for the successful establishment of a primary infection following viral entry as well as for efficient viral assembly and egress. This review gives a concise overview of the induction of the type I IFN signaling pathways in response to viral infection and provides a comprehensive understanding of the antagonizing effects exerted by KSHV on type I IFN pathways wielded at various stages of the viral life cycle. Information garnered from this review should result in a better understanding of KSHV biology essential for the development of immunotherapeutic strategies targeted toward KSHV-associated malignancies.

Cytokine-induced tumor suppressors: a GRIM story

Cytokines belonging to the IFN family are potent growth suppressors. In a number of clinical and preclinical studies, vitamin A and its derivatives like retinoic acid (RA) have been shown to exert synergistic growth-suppressive effects on several tumor cells. We have employed a genome-wide expression-knockout approach to identify the genes critical for IFN/RA-induced growth suppression. A number of novel genes associated with Retinoid-Interferon-induced Mortality (GRIM) were isolated. In this review, we will describe the molecular mechanisms of actions of one, GRIM-19, which participates in multiple pathways for exerting growth control and/or cell death. This protein is emerging as a new tumor suppressor. In addition, GRIM-19 appears to participate in innate immune responses as its activity is modulated by several viruses and bacteria. Thus, GRIMs seem to couple with multiple biological responses by acting at critical nodes.

Kaposi Sarcoma Pathogenesis: A Triad of Viral Infection, Oncogenesis and Chronic Inflammation

Kaposi sarcoma (KS) is a complex cancer that arises from the initial infection of an appropriate endothelial or progenitor cell by Kaposi Sarcoma Herpesvirus/Human Herpesvirus-8 (KSHV/HHV8). However, the majority of KS cases occur when infected patients also suffer from some coincident form of immune deregulation, providing a favorable microenvironment for tumor development. Cellular hallmarks of KS progression include both the hyper-proliferation of KSHV-infected cells and the infiltration of immune modulatory cells into KS lesions, which together result in chronic inflammation, the induction of angiogenesis and tumor growth. This review describes the current understanding of the interactions between KSHV and host responses that result in this unusual cancer, along with existing treatments and prospects for future therapeutic approaches.

Kaposi sarcoma-associated herpesvirus (KSHV): molecular biology and oncogenesis

Kaposi sarcoma-associated herpesvirus (KSHV) is a double-stranded DNA herpesvirus belonging to the gamma-herpesvirinae subfamily. KSHV has been associated with the development of three neoplastic diseases: Kaposi sarcoma (KS), primary effusion lymphoma (PEL), and multicentric Castleman disease (MCD). In this review, we discuss the three KSHV-associated malignancies, KSHV genome, latent and lytic aspects of the viral lifecycle, putative viral oncogenes, as well as therapeutic regimens used for the treatment of KS, PEL, and MCD.

Identification and analysis of putative promoter motifs in Flavivirus genome

The genus Flavivirus comprises medically significant pathogenic virus; causing several infections in humans worldwide. Flavivirus genomes are 10-11 kb approximately and encode both structural and non structural region. The non structural region plays fundamental role in the stability, regulation and cell cycle of virus. The complete genomes of 26 Flavivirus were used for identification of promoter motifs through in silico approaches. The promoter sequences were encoded in merely 16 viruses and 10 viruses could not encode it. All these in silico identified promoter motifs was confirmed and verified with the known experimental data. This analysis suggests that presence of promoter may play a crucial role in the pattern of gene expression, regulation networks, cell specificity and development. It may also be useful for designing efficient expression vector and target specific delivery system in the gene therapy.

Identification of direct transcriptional targets of the Kaposi's sarcoma-associated herpesvirus Rta lytic switch protein by conditional nuclear localization

Lytic reactivation from latency is critical for the pathogenesis of Kaposi's sarcoma-associated herpesvirus (KSHV). We previously demonstrated that the 691-amino-acid (aa) KSHV Rta transcriptional transactivator is necessary and sufficient to reactivate the virus from latency. Viral lytic cycle genes, including those expressing additional transactivators and putative oncogenes, are induced in a cascade fashion following Rta expression. In this study, we sought to define Rta's direct targets during reactivation by generating a conditionally nuclear variant of Rta. Wild-type Rta protein is constitutively localized to cell nuclei and contains two putative nuclear localization signals (NLSs). Only one NLS (NLS2; aa 516 to 530) was required for the nuclear localization of Rta, and it relocalized enhanced green fluorescent protein exclusively to cell nuclei. The results of analyses of Rta NLS mutants demonstrated that proper nuclear localization of Rta was required for transactivation and the stimulation of viral reactivation. RTA with NLS1 and NLS2 deleted was fused to the hormone-binding domain of the murine estrogen receptor to generate an Rta variant whose nuclear localization and ability to transactivate and induce reactivation were tightly controlled posttranslationally by the synthetic hormone tamoxifen. We used this strategy in KSHV-infected cells treated with protein synthesis inhibitors to identify direct transcriptional targets of Rta. Rta activated only eight KSHV genes in the absence of de novo protein synthesis. These direct transcriptional targets of Rta were transactivated to different levels and included the genes nut-1/PAN, ORF57/Mta, ORF56/Primase, K2/viral interleukin-6 (vIL-6), ORF37/SOX, K14/vOX, K9/vIRF1, and ORF52. Our data suggest that the induction of most of the KSHV lytic cycle genes requires additional protein expression after the expression of Rta.

GRIM-19: A Double-edged Sword that Regulates Anti-Tumor and Innate Immune Responses

Gene associated with retinoid-interferon-β-induced mortality (GRIM)-19, was originally identified as a critical regulatory protein necessary for Interferon-β-Retinoic acid-induced cell death. Overexpression of GRIM-19 activates cell death and its suppression or inactivation promotes cell growth. GRIM-19 targets multiple proteins/pathways for exerting growth control and cell death. However, GRIM-19 is also required for normal cellular processes. In addition, viruses 'hijack' GRIM-19 for their survival. Intracellular bacterial infections and bacterial products have been reported to induce the expression of GRIM-19. In this review, we will discuss the current status of GRIM-19 in growth control and innate immune response.

The Neuropathology of HIV/AIDS

The introduction of Highly Active Anti-retroviral Therapy (HAART) has resulted in significant decreases in morbidity and mortality for subjects infected with HIV. The brain is a major target organ for HIV resulting in significant neuropathological changes in most HIV infected subjects and a wide range of clinical neurological symptoms including HIV associated dementia. In the pre-HAART era HIV associated dementia was a common complication of AIDS. However, since the introduction of HAART the incidence of HIV associated dementia has fallen, but the prevelance has actually risen due to the increasing number of infected subjects and increased life expectancy. HIV associated dementia correlates most closely with neuroinflammation rather than directly with viral load or HIV encephalitis. HIV related clinical and neuropathological disorders are more prevalent in drug abusers than in other risk groups. This review focuses on the shifting pathology observed in HIV infected subjects since the introduction of HAART, discussing the clinical manifestations of these and the influence of confounding factors such as drug abuse and Hepatitis C co-infection.

Negative regulation of transcription coactivator p300 by orphan receptor TR3

p300 regulates the transcriptional activity of a variety of transcription factors by forming an activation complex and/or promoting histone acetylation. Here, we show a unique characteristic of orphan receptor TR3 in negatively regulating the function of p300. TR3 was found to interact with p300 and inhibited the acetylation of transcription factors induced by p300, resulting in the repression of their transcriptional activity. Further analysis revealed that both a conserved transcriptional adapter motif (TRAM) in p300 and a specific sequence FLELFIL in TR3 were critical for their interaction. TR3 binding completely covered the histone acetyltransferase (HAT) domain of p300 and resulted in suppression of the HAT activity, as the p300-induced histone H3 acetylation and transcription were inhibited with the presence TR3. Furthermore, an agonist of TR3, a natural octaketide isolated from Dothiorella sp. HTF3 of an endophytical fungus, was shown to be a potent compound for inhibiting p300 HAT activity (IC₅₀ = 1.5 μg/ml) in vivo. More importantly, this agonist could repress the transcriptional activity of transcription factors, and proliferation of cancer cells. Taken together, our results not only delineate a novel transcriptional repressor function for TR3, but also reveal its modulation on p300 HAT activity as the underlying mechanism.

Kaposi's sarcoma after liver transplantation

INTRODUCTION

Kaposi's Sarcoma (KS) is a malignant neoplasm arising from endothelial cells. HHV8-infection represents a key pathogenic determinant for the development of KS. There are no standard criteria to treat KS in immunosuppressed-individuals. Six cases (2.1%) of KS occurred in our Center among 285-recipients who underwent liver transplantation (LT) between October 2000 and November 2006.

METHODS

Patients were four males and two females. Mean age was 57 years (range 44-65). Indication for LT was ESLD associated/non-associated with hepatocellular carcinoma (HCC). The immunosuppressive regimen consisted of cyclosporine/tacrolimus associated with steroids or daclizumab. HHV8-detection was performed by the serological method before LT, and by polymerase chain reaction (PCR)-analysis after KS.

RESULTS

One patient had HCV-related cirrhosis and coinfection from HIV, three had HBV-related cirrhosis, two of these with coexistent HCC. The last two patients had alcoholic-cirrhosis, one with coexistent HCC. Mean time from transplantation to KS was 6.2 months (range 3.8-8.8). Three patients were treated with doxorubicin and three with switch from calcineurin-inhibitors to sirolimus. Three patients expired after 11.5, 8.8, and 7.4 months from KS diagnosis.

DISCUSSION

KS should be treated by a multidisciplinary approach to obtain an early diagnosis and best management. Effective treatment with immunosuppression reduction or switch to sirolimus is mandatory and can induce complete regression.

GRIM-19 associates with the serine protease HtrA2 for promoting cell death

We have isolated a novel interferon (IFN)-retinoid regulated cell death regulatory protein genes associated with retinoid-IFN-induced mortality (GRIM)-19 earlier. To understand its mechanism of action, we have employed a yeast-two-hybrid screen and identified serine protease HtrA2 as its binding partner. GRIM-19 physically interacts with HtrA2 and augments cell death in an IFN/all-trans retinoic acid (RA)-dependent manner. In the presence of GRIM-19, the HtrA2-driven destruction of the antiapoptotic protein X-linked inhibitor of apoptosis (XIAP) is augmented. These interactions were disrupted by an human herpes virus-8 (HHV-8)-coded oncoprotein, vIRF1, and conferred resistance to IFN/RA-induced cell death. These data show a critical role of HtrA2 in a cytokine-induced cell death response for the first time and its inhibition by a viral protein.

Crossing the line between activation and repression

Gene transcription can be activated or repressed. Such seemingly simple decisions reflect the coordinated actions of a wide array of proteins. Activators and co-activators work together to stimulate the assembly and activity of the machinery that transcribes the gene, whereas repressors and co-repressors work to achieve the opposite goal. Recent studies show that many proteins often engage in regulatory activities and interactions that cross the activation-repression divide. This article discusses selected examples to illustrate the dynamic nature of the transcriptional regulation process and highlights the important roles of not only the individual proteins but also their communication system.

The GRIMs: a new interface between cell death regulation and interferon/retinoid induced growth suppression

Cytokines and vitamins play a central role in controlling neoplastic cell growth. The interferon (IFN) family of cytokines regulates antiviral, anti-tumor, antimicrobial, differentiation, and immune responses in mammals. Significant advances have been made with respect to IFN-induced signal transduction pathways and antiviral responses. However, the IFN-induced anti-tumor actions are poorly defined. Although IFNs themselves inhibit tumor growth, combination of IFNs with retinoids (a class of Vitamin A related compounds) strongly potentiates the IFN-regulated anti-tumor action in a number of cell types. To define the molecular mechanisms involved in IFN/retinoid (RA)-induced apoptosis we have employed a genetic approach and identified several critical genes. In this review, I provide the current picture of IFN- RA- and IFN/RA-regulated growth suppressive pathways. In particular, I focus on a novel set of genes, the genes-associated with retinoid-interferon induced mortality (GRIM). GRIMs may be novel types of tumor suppressors, useful as biological response markers and potentially novel targets for drug development.

Overlapping CRE and E box motifs in the enhancer sequences of the bovine leukemia virus 5' long terminal repeat are critical for basal and acetylation-dependent transcriptional activity of the viral promoter: implications for viral latency

Bovine leukemia virus (BLV) infection is characterized by viral latency in a large proportion of cells containing an integrated provirus. In this study, we postulated that mechanisms directing the recruitment of deacetylases to the BLV 5' long terminal repeat (LTR) could explain the transcriptional repression of viral expression in vivo. Accordingly, we showed that BLV promoter activity was induced by several deacetylase inhibitors (such as trichostatin A [TSA]) in the context of episomal LTR constructs and in the context of an integrated BLV provirus. Moreover, treatment of BLV-infected cells with TSA increased H4 acetylation at the viral promoter, showing a close correlation between the level of histone acetylation and transcriptional activation of the BLV LTR. Among the known cis-regulatory DNA elements located in the 5' LTR, three E box motifs overlapping cyclic AMP responsive elements (CREs) in U3 were shown to be involved in transcriptional repression of BLV basal gene expression. Importantly, the combined mutations of these three E box motifs markedly reduced the inducibility of the BLV promoter by TSA. E boxes are susceptible to recognition by transcriptional repressors such as Max-Mad-mSin3 complexes that repress transcription by recruiting deacetylases. However, our in vitro binding studies failed to reveal the presence of Mad-Max proteins in the BLV LTR E box-specific complexes. Remarkably, TSA increased the occupancy of the CREs by CREB/ATF. Therefore, we postulated that the E box-specific complexes exerted their negative cooperative effect on BLV transcription by steric hindrance with the activators CREB/ATF and/or their transcriptional coactivators possessing acetyltransferase activities. Our results thus suggest that the overlapping CRE and E box elements in the BLV LTR were selected during evolution as a novel strategy for BLV to allow better silencing of viral transcription and to escape from the host immune response.

CKII site in Epstein-Barr virus nuclear protein 2 controls binding to hSNF5/Ini1 and is important for growth transformation

Substitution mutagenesis of EBNA2 shows that its interaction with hSNF5/Ini1 involves two sites (286IPP and DQQ313), and a mutation at a CKII phosphorylation site (SS469) is essential for the interaction. An alanine substitution (SS469AA) prevents binding to EBNA2 and diminishes the growth-promotion potential of EBNA2 in the transcomplementation assay.

Expression of an E1A/E7 chimeric protein sensitizes tumor cells to killing by activated macrophages but not NK cells

Adenovirus (Ad) E1A and human papillomavirus (HPV) E7 express homologous conserved regions (CRs) that mediate their shared biological functions. Despite their similarities, the expression of E1A sensitizes tumor cells to killing by NK cells and macrophages but the expression of E7 does not, a factor that may contribute to the dissimilar oncogenicities of Ad and HPV. This study was undertaken to define molecular differences between E1A and E7 that are responsible for the ability of E1A and the inability of E7 to sensitize cells to killing by NK cells and macrophages. Genetic mapping studies using human fibrosarcoma cells (H4) that stably expressed mutant forms of E1A showed that only those forms of E1A that interacted with the transcriptional coadaptor protein p300 sensitized cells to killing by NK cells and macrophages. E7 lacks the N-terminal p300-binding region present in E1A. Therefore, a chimeric E1A/E7 gene was constructed that included the N terminus and the CR1 (p300-binding) domain of E1A fused to CR2 and the C-terminal sequences of E7. The E1A/E7 protein interacted with p300 and pRb and immortalized primary mouse embryo fibroblasts (MEF). The expression of E1A/E7 sensitized H4 and MEF cells to killing by activated macrophages but not to killing by NK cells. Therefore, N-terminal differences between E1A and E7 that map to the E1A-p300 binding region accounted for differences in their abilities to sensitize cells to killing by macrophages. However, regions in addition to the E1A-p300 binding region are required to sensitize cells to killing by NK cells.

Alternate interferon signaling pathways

More than a half a century ago, interferons (IFN) were identified as antiviral cytokines. Since that discovery, IFN have been in the forefront of basic and clinical cytokine research. The pleiotropic nature of these cytokines continues to engage a large number of investigators to define their actions further. IFN paved the way for discovery of Janus tyrosine kinase (JAK)-signal transducing activators of transcription (STAT) pathways. A number of important tumor suppressive pathways are controlled by IFN. Several infectious pathogens counteract IFN-induced signaling pathways. Recent studies indicate that IFN activate several new protein kinases, including the MAP kinase family, and downstream transcription factors. This review not only details the established IFN signaling paradigms but also provides insights into emerging alternate signaling pathways and mechanisms of pathogen-induced signaling interference.

Strategic attack on host cell gene expression during adenovirus infection

To understand the interaction between the virus and its host, we used three sources of cDNA microarrays to examine the expression of 12,309 unique genes at 6 h postinfection of HeLa cells with high multiplicities of adenovirus type 2. Seventy-six genes with significantly changed expression ratios were identified, suggesting that adenovirus only modulates expression of a limited set of cellular genes. Quantitative real-time PCR analyses on selected genes were performed to confirm the microarray results. Significantly, a pronounced transcriptional activation by the promiscuous E1A-289R transcriptional activator was not apparent. Instead, promoter sequences in 45% of the upregulated genes harbored a potential E2F binding site, suggesting that the ability of the amino-terminal domain of E1A to regulate E2F-dependent transcription may be a major pathway for regulation of cellular gene expression. CDC25A was the only upregulated gene directly involved in cell cycle control. In contrast, several genes implicated in cell growth arrest were repressed. The transforming growth factor beta superfamily was specifically affected in the expression of both the upstream ligand and an intracellular regulator. In agreement with previous reports, adenovirus also targeted the innate immune response by downregulating several cytokines, including CLL2, CXCL1, and interleukin-6. Finally, stress response genes encoding GADD45B, ATF3, and TP53AP1 were upregulated. Importantly, we also found a novel countermeasure-activation of the apoptosis inhibitor survivin.

Repression of c-Myc and inhibition of G1 exit in cells conditionally overexpressing p300 that is not dependent on its histone acetyltransferase activity

p300 and cAMP response element binding protein (CREB)-binding protein (CBP) are two highly homologous, conserved transcriptional coactivators, and histone acetyltransferases (HATs) that link chromatin remodeling with transcription. Cell transformation by viral oncogene products such as adenovirus E1A and SV40 large T antigen depends on their ability to inactivate p300 and CBP. To investigate the role of p300 in cell-cycle progression, we constructed stable rat cell lines, which conditionally overexpress p300 from a tetracycline-responsive promoter. When p300 was induced in these cells, serum-stimulated S-phase entry was significantly inhibited. The inhibition of S-phase induction was associated with down-regulation of c-Myc, but not of c-Fos or c-Jun. Simultaneous overexpression of c-Myc and p300 before serum stimulation reversed the inhibition of S-phase induction to a significant level, indicating that the inhibition of c-Myc to a large extent is responsible for the p300 inhibition of G1 exit. Similar studies with stable rat cell lines that overexpress a mutant p300, which lacks the HAT activity, showed that the intrinsic HAT activity of p300 is not required for the negative regulation of c-Myc or G1. These findings, and our previously published results (Kolli, S., Buchmann, A. M., Williams, J., Weitzman, S. & Thimmapaya, B. (2001) Proc. Natl. Acad. Sci. USA 98, 4646-4651), establish an important negative regulatory role for p300 in c-Myc expression that may be important in maintaining the cells in the G0/G1 phase of the cell cycle.

Differential hyperacetylation of histones H3 and H4 upon promoter-specific recruitment of EBNA2 in Epstein-Barr virus chromatin

Epstein-Barr virus nuclear antigen 2 (EBNA2) is a transcriptional activator involved in the immortalization of B lymphocytes by the virus. EBNA2 is targeted to the promoters of its responsive genes, via interaction with cellular DNA-binding proteins. Using chromatin immunoprecipitation assays, we show for the first time the conditional recruitment of EBNA2 on two specific viral promoters in vivo and demonstrate a correlation between this recruitment and a local change in the acetylation of histones H3 and H4, which is promoter dependent.

Molecular genetics of Kaposi's sarcoma-associated herpesvirus (human herpesvirus-8) epidemiology and pathogenesis

Kaposi's sarcoma had been recognized as unique human cancer for a century before it manifested as an AIDS-defining illness with a suspected infectious etiology. The discovery of Kaposi's sarcoma-associated herpesvirus (KSHV), also known as human herpesvirus-8, in 1994 by using representational difference analysis, a subtractive method previously employed for cloning differences in human genomic DNA, was a fitting harbinger for the powerful bioinformatic approaches since employed to understand its pathogenesis in KS. Indeed, the discovery of KSHV was rapidly followed by publication of its complete sequence, which revealed that the virus had coopted a wide armamentarium of human genes; in the short time since then, the functions of many of these viral gene variants in cell growth control, signaling apoptosis, angiogenesis, and immunomodulation have been characterized. This critical literature review explores the pathogenic potential of these genes within the framework of current knowledge of the basic herpesvirology of KSHV, including the relationships between viral genotypic variation and the four clinicoepidemiologic forms of Kaposi's sarcoma, current viral detection methods and their utility, primary infection by KSHV, tissue culture and animal models of latent- and lytic-cycle gene expression and pathogenesis, and viral reactivation from latency. Recent advances in models of de novo endothelial infection, microarray analyses of the host response to infection, receptor identification, and cloning of full-length, infectious KSHV genomic DNA promise to reveal key molecular mechanisms of the candidate pathogeneic genes when expressed in the context of viral infection.

Transcription mapping of human herpesvirus 8 genes encoding viral interferon regulatory factors

The human herpesvirus 8 (HHV-8) genome contains four tandemly arranged genes encoding viral interferon regulatory factors (vIRF-1 to 4) located between genes 57 and 58. Transcript mapping techniques were employed to determine the sizes, ends and splicing patterns of mRNAs specified by these genes in HHV-8-infected cell lines untreated or chemically induced into the lytic growth cycle. Depending on the cell line used, vIRF-3 transcription was minimally or not induced (i.e. expressed with latent kinetics), whereas the other vIRFs were inducible (i.e. expressed with lytic kinetics). Each gene possessed its own promoter (or promoters) and polyadenylation sites, and all but vIRF-1 were spliced from two exons. vIRF-1 was transcribed in uninduced and induced cells from a single initiation site preceded by a TATA box, with the possible use of an additional TATA box and initiation site in uninduced cells. In induced cells, vIRF-2 was transcribed from a single major initiation site preceded by a TATA box, and vIRF-4 was expressed from two sites each preceded by a TATA box. Transcripts for these genes were insufficiently abundant in uninduced cells to map the 5'-ends. vIRF-3 lacks an obvious TATA box and exhibited heterogeneous 5'-ends in uninduced and induced cells. These data clarify and extend our understanding of the structure and transcription of the HHV-8 vIRF genes.

Auto-activation of the transforming viral interferon regulatory factor encoded by Kaposi's sarcoma-associated herpesvirus (human herpesvirus-8)

Kaposi's sarcoma-associated herpesvirus (KSHV)/human herpesvirus-8-encoded viral interferon regulatory factor (vIRF) transforms NIH3T3 cells, represses interferon signal transduction and regulates the expression of other KSHV genes. Here, we have shown that vIRF is a transcriptional activator and auto-activates its own expression. Ectopic expression of vIRF activated the vIRF promoter in KSHV-negative 293, COS7, HeLa and BJAB cell lines in a dose-dependent fashion in a reporter assay and the expression of vIRF transcripts from endogenous viral genomes in BCBL-1 and BC-1 cells latently infected with KSHV. Deletion analysis identified two cis elements, named Vac1 and Vac2, in the vIRF promoter that were responsive to vIRF activation. vIRF auto-activation via Vac1 but not Vac2 was repressed by Tis, a transcriptional silencer in the vIRF promoter. Neither Vac1 nor Vac2 contain any interferon-stimulated response element (ISRE)-like sequences and are unresponsive to induction with interferon-beta and -gamma. These results indicate that KSHV uses the mechanism of auto-activation to regulate the expression of a viral transforming protein to efficiently evade host tumour suppressor pathways.

Immune evasion strategies of Kaposi's sarcoma-associated herpesvirus

To establish lifelong infection in the presence of an active host immune system, herpesviruses have acquired an impressive array of immune modulatory mechanisms that contribute to their success as long-term parasites. Kaposi's sarcoma-associated herpesvirus (KSHV) is the most recently discovered human tumor virus and is associated with the pathogenesis of Kaposi's sarcoma, primary effusion lymphoma, and multicentric Castleman's disease. KSHV has acquired a battery of genes to assist in viral survival against the host immune response. These viral gene products target a variety of host immune surveillance mechanisms, including the cytokine-mediated immune response, apoptosis, natural killer (NK) cell killing and T cell-mediated responses. This review summarizes our understanding of the role of these viral proteins in the escape from host immune surveillance, which ultimately contributes to lifelong infection and pathogenesis of KSHV.

Characterization of monoclonal antibodies against GRIM-19, a novel IFN-beta and retinoic acid-activated regulator of cell death

A combination of interferon-beta (IFN-beta) and all-trans retinoic acid (IFN/RA) induces tumor cell apoptosis via some unknown mechanisms. Apoptosis is a gene-directed process that limits the proliferation of undesired cells. Several genes are required to regulate cell death in the higher-order animals. Earlier, we employed a gene expression knockout technique to isolate cell death-related genes. A novel gene, the gene associated with retinoid-interferon-induced mortality-19 (GRIM-19), was found to be essential for tumor cell death induced by IFN/RA. Here, we describe the development and characterization of three monoclonal antibodies (mAbs) against GRIM-19. GRIM-19 is present in the nucleus and cytoplasm. Its expression is induced by the IFN/RA combination. We also show that GRIM-19 inhibits the cell-transforming property of viral oncogenic protein viral IFN regulatory factor-1 (vIRF-1) via a physical interaction. mAbs developed in this study should be useful for studying the other physiologic roles of GRIM-19 and serve as a potent tool for studying tumor responses to IFN/RA therapy.

Epstein-Barr virus EBNA2 blocks Nur77- mediated apoptosis

Epstein-Barr virus infection in vitro immortalizes primary B cells. EBNA2 is an Epstein-Barr virus-encoded transcriptional transactivator that mimics the effects of activated Notch signaling and is essential for this proliferative response. An assay using Sindbis virus (SV) as a cell death inducer revealed that, like Notch, EBNA2 also has antiapoptotic activity. We show that Nur77 is a mediator of SV-induced cell death and that EBNA2 antiapoptotic activity results from interaction with Nur77. EBNA2 colocalized with Nur77 in transfected cells and coprecipitated with Nur77 in IB4 B cells. EBNA2 binds to Nur77 through sequences in the EBNA2 amino acid 123-147 conserved domain and an EBNA2 mutant unable to bind Nur77 also lost the ability to protect cells from SV-induced apoptosis. EBNA2 exerted its antideath function by retaining Nur77 in the nucleus and preventing Nur77 from targeting mitochondria in response to apoptotic stimuli. Thus, targeting of Nur77 can be added to the list of strategies used by viruses to counter apoptosis.

The molecular pathology of Kaposi's sarcoma-associated herpesvirus

Kaposi's sarcoma (KS)-associated herpesvirus (KSHV) is the eighth and most recently identified human herpesvirus (HHV-8). KSHV was discovered in 1994 by Chang et al. who used representational difference analysis to search for DNA sequences present in AIDS-associated KS but not in adjacent normal skin [1]. The virus has since been shown to be specifically associated with all forms of this disease and has fulfilled all of Hill's criteria for causation (reviewed in ). KSHV is also found in all cases of primary effusion lymphoma and in a plasmablastic variant of multicentric Castleman's disease. Over the last few years a wealth of data has been gained on the role of KSHV genes during infection. This review is an attempt to assemble this information into a more complete picture of how KSHV may cause disease.

Adenovirus E1A requires the yeast SAGA histone acetyltransferase complex and associates with SAGA components Gcn5 and Tra1

The budding yeast Saccharomyces cerevisiae was used as a model system to study the function of the adenovirus E1A oncoprotein. Previously we demonstrated that expression of the N-terminal 82 amino acids of E1A in yeast causes pronounced growth inhibition and specifically interferes with SWI/SNF-dependent transcriptional activation. Further genetic analysis identified the yeast transcription factor Adr1 as a high copy suppressor of E1A function. Transcriptional activation by Adr1 requires interaction with co-activator proteins Ada2 and Gcn5, components of histone acetyltransferase complexes including ADA and SAGA. Analysis of mutant alleles revealed that several components of the SAGA complex, including proteins from the Ada, Spt, and Taf classes were required for E1A-induced growth inhibition. Growth inhibition also depended on the Gcn5 histone acetyltransferase, and point mutations within the Gcn5 HAT domain rendered cells E1A-resistant. Also required was SAGA component Tra1, a homologue of the mammalian TRRAP protein which is required for c-myc and E1A induced cellular transformation. Additionally, Gcn5 protein could associate with E1A in vitro in a manner that depended on the N-terminal domain of E1A, and Tra1 protein was co-immunoprecipitated with E1A in vivo. These results indicate a strong requirement for intact SAGA complex for E1A to function in yeast, and suggest a role for SAGA-like complexes in mammalian cell transformation.

On the role of IRF in host defense

Transcription factors of the interferon (IFN) regulatory factor (IRF) family have been shown to play an essential role in the regulated expression of type I IFN genes, IFN-stimulated genes (ISG), and other cytokines and chemokines. Three members of the IRF family, IRF-3, IRF-5, and IRF-7, have been identified as acting as direct transducers of virus-mediated signaling. In infected cells, these factors are activated by phosphorylation on the serine residues, transported to the nucleus, where they bind to the promoters of IFNA and IFNB genes and tether histone transacetylases to the transcription complex enhanceosome. IFNB and IFNA subtypes are expressed at different levels in infected cells. The ratio between the relative levels of IRF-3 and IRF-7 was shown to play an essential role in the inducible expression of type I IFN genes, whereas IRF-3 alone is sufficient for expression of the IFNB gene. IRF-5 was identified recently as another inducer of IFNA genes, which has two unique properties: (1) its activation is virus specific, and (2) the profile of IFNA genes induced by IRF-5 is distinct from that induced by IRF-7. Several viruses target functions of IRF to eliminate the early inflammatory response. Kaposi's sarcoma herpesvirus (KSHV) encodes a cluster of four genes with homology to cellular IRF. Three of these vIRF were shown to inhibit induction of IFN genes and ISG in infected cells and function as dominant negative mutants of cellular IRF. The unique properties of previously uncharacterized vIRF-2 and vIRF-3 are discussed.

Functional cooperation of Epstein-Barr virus nuclear antigen 2 and the survival motor neuron protein in transactivation of the viral LMP1 promoter

Epstein-Barr virus nuclear antigen 2 (EBNA2) is essential for viral transformation of B cells and transactivates cellular and viral target genes by binding RBPJkappa tethered to cognate promoter elements. EBNA2 interacts with the DEAD-box protein DP103 (DDX20/Gemin3), which in turn is complexed to the survival motor neuron (SMN) protein. SMN is implicated in RNA processing, but a role in transcriptional regulation has also been suggested. Here, we show that DP103 and SMN are complexed in B cells and that SMN coactivates the viral LMP promoter in the presence of EBNA2 in reporter gene assays and in vivo. Subcellular localization studies revealed that nuclear gems and/or coiled bodies containing DP103 and SMN are targeted by EBNA2. Protein-protein interaction experiments demonstrated that DP103 binds to SMN exon 6 and that both EBNA2 and SMN interact with the C terminus of DP103. Furthermore, a DP103 binding-deficient SMN mutant was released from nuclear gems and/or coiled bodies and further enhanced coactivation. In addition, impaired transactivation of a DP103 binding-deficient EBNA2 mutant was rescued by overexpression of SMN. Testing different promoter constructs in luciferase assays showed that RBPJkappa is required but not sufficient for coactivation by EBNA2 and SMN. Overall, our data suggest that EBNA2 might target spliceosomal complexes by binding to DP103, thereby releasing SMN which subsequently exerts a coactivational function within the RNA-polymerase II transcription complex on the LMP1 promoter.

Genetic analysis of the Epstein-Barr virus-coded leader protein EBNA-LP as a co-activator of EBNA2 function

Co-operation between the Epstein-Barr virus (EBV)-coded leader protein EBNA-LP and the nuclear antigen EBNA2 appears to be critical for efficient virus-induced B cell transformation. Here we report the genetic analysis of EBNA-LP function using two transient co-transfection assays of co-operativity, activation of latent membrane protein 1 (LMP1) expression from a resident EBV genome in Akata-BL cells and activation of an EBNA2-responsive reporter construct. Small deletions were introduced into each of five conserved regions (CRs) of EBNA-LP sequence present in type 1 and type 2 EBV strains and in several primate lymphocryptovirus EBNA-LP homologues. Deletions within all three CRs in the EBNA-LP W1W2 repeat domain completely abrogated function, through inhibition of nuclear localization in the cases of CR1 and CR2 but not of CR3; deletions within CR4 and CR5 in the Y1Y2 unique domain had relatively little effect, yet loss of the whole Y2 sequence blocked activity. Alanine substitution of serine residues within potential phosphorylation sites identified two mutants of particular interest. Substitution of three such residues (S34,36,63) within W1W2 not only abrogated EBNA-LP activity but was associated with a complete loss of EBNA2 detectability in co-transfected cells, implying possible destabilization of the co-expressed EBNA2 protein. More importantly the individual substitution of S36 completely blocked EBNA-LP/EBNA2 co-operativity while retaining EBNA2 expression. We infer critical roles for the CR3 domain and for the S36 residue in EBNA-LP's co-operative function.

The amino acid region 248-382 of the Epstein-Barr virus nuclear protein 2 (EBNA2) is responsible for the EBNA2-induced EBV reactivation

We showed previously that Epstein-Barr virus (EBV) latency is disrupted and the virus-replicative cycle is activated after expression of EBNA2 in the Burkitt's lymphoma-derived Akata cells. Here, an EBNA2 deletion mutant lacking the amino acid residues 248-382, including the region responsible for association with RBP-J kappa, was generated and tested for its ability to activate EBV replication in Akata cells. This mutant was shown clearly deficient in inducing the EBV-replicative cycle, suggesting that association with RBP-J kappa is necessary for the EBV activating function of EBNA2. It is thus likely that EBV activation by EBNA2, seemingly in conflict with its involvement in lymphocyte immortalization, is nevertheless based on the standard mechanism of transactivation by the protein.

The emerging role of the human herpesvirus 8 (HHV8) in human neoplasia

The human herpesvirus 8 (HHV8) was initially described and characterised in Kaposi's sarcoma tissue. The virus was found in the lesion of most cases of Kaposi's sarcoma. Whilst there is a large body of evidence to implicate its role in the pathogenesis of Kaposi's sarcoma, it has recently been found that the virus may also be important in a number of other human neoplasias. This review will examine the molecular pathology of HHV8 in the pathogenesis of Kaposi's sarcoma and summarise the current evidence and postulated mechanisms in its role in other human neoplasias.

Intranuclear localization of the transcription coadaptor CBP/p300 and the transcription factor RBP-Jk in relation to EBNA-2 and -5 in B lymphocytes

We have studied the expression and the localization of the cellular proteins CBP/p300 and RBP-Jk in in vitro EBV-infected human B lymphocytes in relation to the EBNA-2 and EBNA-5 proteins. We found that the level of CBP/p300 was elevated drastically by EBV infection and also after activation by CD40 ligation. Thus the increase in CBP/p300 expression in the EBV-infected cells is related to the virus-induced activation and proliferation of the cells. EBNA-2 and RBP-Jk colocalized in the nucleoplasm, which is in accordance with their functional interaction. We confirmed earlier reports about the presence and colocalization of EBNA-5 and CBP in the nuclear POD bodies. On the other hand, neither EBNA-2 nor p300 was detected in the PODs. The expression of these two proteins overlapped in some distinct dots of the nucleoplasm. Taken together, the different patterns of CBP and p300 expression and their different localization in relation to the PML bodies and two EBV-encoded proteins in the B cells may provide some clue to their distinct functional roles.

Nuclear localization of CBF1 is regulated by interactions with the SMRT corepressor complex

The CSL family protein CBF1 is a nuclear mediator of Notch signaling and has been predicted to contain an N-terminal nuclear localization signal in exon 4. Surprisingly, we found that CBF1 carrying mutations at codon 233 or 249 within exon 7 was restricted to the cytoplasm. In mammalian and yeast two-hybrid assays, these mutations were also associated with a loss of CBF1-mediated transcriptional repression and a severely impaired interaction with the corepressors SMRT and CIR. Overexpression of SMRT rescued the ability of mutant CBF1 to target to the nucleus of transfected cells and similarly rescued nuclear targeting of enhanced green fluorescent protein (EGFP)-CBF1 exons 6 to 9 CBF1(6-9)carrying the codon 233 or 249 mutations. Carboxy-terminally truncated SMRT with amino acids (aa) 1291 to 1495 deleted was unable to rescue the nuclear targeting of mutant EGFP-CBF1(6-9). In yeast two-hybrid assays, the SMRT aa 1291 to 1495 domain interacted with SKIP and SMRT aa 1291 to 1495 colocalized with SKIP within the nuclei of cotransfected cells. Comparison of the intracellular localization of CBF1(6-9) with that of CBF1(5-9) further supported the suggestion that nuclear targeting of CBF1 is dependent on the formation of a CBF1-SMRT-SKIP corepressor complex. These observations suggest that nuclear targeting of CBF1 is itself a component of CBF1-mediated gene regulation and that in the absence of signaling, CBF1 enters the nucleus precommitted to a transcriptional repression function. The activators NotchIC (the intracellular domain of Notch) and Epstein-Barr virus EBNA2 also mediated nuclear targeting of mutant CBF1, consistent with the competition model for activator versus corepressor binding to CBF1.

The transcriptional activity of cAMP response element-binding protein-binding protein is modulated by the latency associated nuclear antigen of Kaposi's sarcoma-associated herpesvirus

A multifunctional transcription co-activator, cAMP response element-binding protein-binding protein (CBP)interacts with a number of cellular factors and participates in cell growth, transformation, and development. It is also targeted by many viral proteins for their transcriptional activity or for the regulation of cellular processes. Here, we report that the C/H3 region of CBP is targeted by the latency associated nuclear antigen (LANA) of Kaposi's sarcoma-associated herpesvirus (KSHV). LANA interferes with the interaction between CBP and c-Fos, a representative C/H3 region binding, cellular transcription factor, in vivo and in vitro. In addition, we found that LANA inhibits the transcriptional activity and the in vitro histone acetyltransferase activity of CBP, suggesting that LANA modulates the global transcriptional activities of infected cells through the interaction with CBP. These results indicate that KSHV follows one of the conserved strategies, which other viruses utilize for influencing the cellular processes.

Inhibition of p53 tumor suppressor by viral interferon regulatory factor

The irreversible cell cycle arrest and apoptosis induced by p53 are part of the host surveillance mechanisms for viral infection and tumor induction. Kaposi's sarcoma-associated herpesvirus (KSHV), the most recently discovered human tumor virus, is associated with the pathogenesis of Kaposi's sarcoma, primary effusion lymphoma, and multicentric Castleman's disease. The K9 open reading frame of KSHV encodes a viral interferon (IFN) regulatory factor (vIRF) which functions as a repressor for cellular IFN-mediated signal transduction and as an oncoprotein to induce cell growth transformation. Here, we demonstrate that KSHV vIRF interacts with the cellular p53 tumor suppressor through the putative DNA binding region of vIRF and the central region of p53. This interaction suppresses the level of phosphorylation and acetylation of p53 and inhibits transcriptional activation of p53. As a consequence, vIRF efficiently prevents p53-mediated apoptosis. These results suggest that KSHV vIRF interacts with and inhibits the p53 tumor suppressor to circumvent host growth surveillance and to facilitate uncontrolled cell proliferation.

Notch1IC partially replaces EBNA2 function in B cells immortalized by Epstein-Barr virus

Immortalization of B cells by Epstein-Barr virus (EBV) depends on the virally encoded EBNA2 protein. Although not related by sequence, the cellular Notch protein and EBNA2 share several biochemical and functional properties, such as interaction with CBF1 and the ability to activate transcription of a number of cellular and viral genes. Whether these similarities are coincidental or exemplify EBNA2 mimicry of evolutionarily conserved cellular signaling pathways is unclear. We therefore investigated whether activated forms of Notch could substitute for EBNA2 in maintaining the immortalized phenotype of EBV-infected B cells. To address this question, we devised a transcomplementation system using EREB2.5 cells. EREB2.5 cells are immortalized by EBV expressing a conditional estrogen receptor EBNA2 fusion protein (EREBNA2), and cellular proliferation is dependent on the availability of estrogen. Withdrawal of estrogen results in inactivation of EREBNA2, leading to growth arrest and eventually to cell death. Transduction of EREB2.5 cells with a lentiviral vector expressing wild-type EBNA2 rescued EREB2.5 cells from the growth-inhibitory effects of estrogen deprivation, in contrast to transduction with the lentivirus vector alone. EREB2.5 cells were also rescued by enforced expression of human Notch1IC after estrogen starvation, but this effect was restricted to cells expressing high levels of the transcription factor. Compared to wild-type EBNA2-expressing EREB2.5 cells, the Notch-expressing cells expanded more slowly after estrogen starvation, and once established, they continued to display a lower proliferation rate. Analysis of viral and cellular gene expression from transduced EREB2.5 cells after estrogen withdrawal indicated that both wild-type EBNA2- and Notch1IC-positive cells expressed c-Myc at levels similar to those found in parental EREB2.5 cells. However, the latter cells expressed LMP-1 far less efficiently than cells transduced with the wild-type EBNA2 gene. Cells rescued by either wild-type EBNA2 or Notch1IC expressed surface CD21 and CD23 proteins, but not CD10, indicating that induction of relevant type III latency markers was maintained. The data imply that both Notch and EBNA2 activate an important subset of cellular genes associated with type III latency and B-cell growth, while EBNA2 more efficiently induces important viral genes, such as LMP-1. Thus, exploitation of conserved Notch-related signaling pathways may represent a key mechanism by which EBNA2 contributes to EBV-induced cell immortalization.

Coactivator p300 acetylates the interferon regulatory factor-2 in U937 cells following phorbol ester treatment

Interferon regulatory factor-2 (IRF-2) is a transcription factor of the IRF family that represses interferon-mediated gene expression. In the present study, we show that human monocytic U937 cells express truncated forms of IRF-2 containing the DNA binding domain but lacking much of the C-terminal regulatory domain. U937 cells are shown to respond to phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) to induce expression of histone acetylases p300 and p300/CBP-associated factor (PCAF). In addition, TPA treatment led to the appearance of full-length IRF-2, along with a reduction of the truncated protein. Interestingly, full-length IRF-2 in TPA-treated U937 cells occurred as a complex with p300 as well as PCAF and was itself acetylated. Consistent with these results, recombinant IRF-2 was acetylated by p300 and to a lesser degree by PCAF in vitro. Another IRF member, IRF-1, an activator of interferon-mediated transcription, was also acetylated in vitro by these acetylases. Finally, we demonstrate that the addition of IRF-2 but not IRF-1 inhibits core histone acetylation by p300 in vitro. The addition of IRF-2 also inhibited acetylation of nucleosomal histones in TPA-treated U937 cells. Acetylated IRF-2 may affect local chromatin structure in vivo by inhibiting core histone acetylation and may serve as a mechanism by which IRF-2 negatively regulates interferon-inducible transcription.

Molecular piracy of Kaposi's sarcoma associated herpesvirus

Kaposi's Sarcoma associated Herpesvirus (KSHV) is the most recently discovered human tumor virus and is associated with the pathogenesis of Kaposi's sarcoma, primary effusion lymphoma, and Multicentric Casttleman's disease. KSHV contains numerous open reading frames with striking homology to cellular genes. These viral gene products play a variety of roles in KSHV-associated pathogenesis by disrupting cellular signal transduction pathways, which include interferon-mediated anti-viral responses, cytokine-regulated cell growth, apoptosis, and cell cycle control. In this review, we will attempt to cover our understanding of how viral proteins deregulate cellular signaling pathways, which ultimately contribute to the conversion of normal cells to cancerous cells.

Positive regulatory domain I binding factor 1 silences class II transactivator expression in multiple myeloma cells

The major histocompatibility complex (MHC) class II transactivator (CIITA) acts as a master switch to activate expression of the genes required for MHC-II antigen presentation. During B-cell to plasma cell differentiation, MHC-II expression is actively silenced, but the mechanism has been unknown. In plasma cell tumors such as multiple myeloma the repression of MHC-II is associated with the loss of CIITA. We have identified that positive regulatory domain I binding factor 1 (PRDI-BF1), a transcriptional repressor, inhibits CIITA expression in multiple myeloma cell lines. Repression of CIITA depends on the DNA binding activity of PRDI-BF1 and its specific binding site in the CIITA promoter. Deletion of a histone deacetylase recruitment domain in PRDI-BF1 does not inhibit repression of CIITA nor does blocking histone deacetylase activity. This is in contrast to PRDI-BF1 repression of the c-myc promoter. Repression of CIITA requires either the N-terminal acidic and conserved PR motif or the proline-rich domain. PRDI-BF1 has been shown to be a key regulator of B-cell and macrophage differentiation. These findings now indicate that PRDI-BF1 has at least two mechanisms of repression whose function is dependent on the nature of the target promoter. Importantly, PRDI-BF1 is defined as the key molecule in silencing CIITA and thus MHC-II in multiple myeloma cells.

Molecular virology of Kaposi's sarcoma-associated herpesvirus

Kaposi's sarcoma-associated herpesvirus (KSHV), the most recently discovered human tumour virus, is the causative agent of Kaposi's sarcoma, primary effusion lymphoma and some forms of Castleman's disease. KSHV is a rhadinovirus, and like other rhadinoviruses, it has an extensive array of regulatory genes obtained from the host cell genome. These pirated KSHV proteins include homologues to cellular CD21, three different beta-chemokines, IL-6, BCL-2, several different interferon regulatory factor homologues, Fas-ligand ICE inhibitory protein (FLIP), cyclin D and a G-protein-coupled receptor, as well as DNA synthetic enzymes including thymidylate synthase, dihydrofolate reductase, DNA polymerase, thymidine kinase and ribonucleotide reductases. Despite marked differences between KSHV and Epstein-Barr virus, both viruses target many of the same cellular pathways, but use different strategies to achieve the same effects. KSHV proteins have been identified which inhibit cell-cycle regulation checkpoints, apoptosis control mechanisms and the immune response regulatory machinery. Inhibition of these cellular regulatory networks app ears to be a defensive means of allowing the virus to escape from innate antiviral immune responses. However, due to the overlapping nature of innate immune and tumour-suppressor pathways, inhibition of these regulatory networks can lead to unregulated cell proliferation and may contribute to virus-induced tumorigenesis.

Suppression of oncogenic viral interferon regulatory factor (vIRF) of Kaposi's sarcoma-associated herpesvirus by ribozyme-mediated cleavage

Kaposi's sarcoma-associated herpesvirus/human herpesvirus 8 (KSHV/HHV8) has been etiologically associated with several malignancies including Kaposi's sarcoma and primary effusion lymphoma. Oncogenic viral interferon regulatory factor (vIRF) encoded by KSHV ORF-K9 is a homologue of cellular interferon regulatory factor (IRF), and has been demonstrated to inhibit type I/II interferon signal transduction and transform NIH3T3 cells through the interactions with IRF-1, IRF-3, and CBP/p300 proteins. To counteract vIRF's pathogenic role, we have developed five ribozymes targeting ORF-K9 mRNA to suppress vIRF expression. The vIRF RNA substrates were cleaved up to 80% in a substrate-specific manner in transcript cleavage assays in vitro. In a transient transfection assay, two of the ribozymes efficiently suppressed the expression of vIRF protein measured by dual-color immunofluorescence assay that simultaneously detects the expression of both vIRF protein and ribozyme. Flow cytometry analysis showed that these ribozymes reduced vIRF expression up to 76%. A mutant ribozyme had no cleavage activity in vitro, but exhibited antisense effect in vivo. These results suggest that the ribozymes may provide a new approach for functional knockout of vIRF gene, and are potential candidates of antiviral therapy for KSHV-related malignancies.

Detection of Epstein--Barr virus-determined nuclear antigen-2 mRNA by in situ hybridization

A mRNA in situ hybridization method was developed to detect mRNA of Epstein--Barr virus-determined nuclear antigen-2 (EBNA2). Strong in situ hybridization signals were detected in EBNA2-transfected cells with the antisense probe but not with the sense probe of this mRNA. Hybridization signals were also found in formalin-fixed paraffin-embedded tissue samples from patients with invasive uterine cervical cancer and with cervical intraepithelial neoplasia. The sensitivity of mRNA in situ hybridization was higher than that of Northern blotting, and almost the same as that of immunofluorescence staining using monoclonal anti-EBNA2 antibody. It is concluded that this method is useful for sensitive and convenient detection of EBNA2.