Changes in SUMO-modified proteins in Epstein-Barr virus infection identifies reciprocal regulation of TRIM24/28/33 complexes and the lytic switch BZLF1

SUMO modifications regulate the function of many proteins and are important in controlling herpesvirus infections. We performed a site-specific proteomic analysis of SUMO1- and SUMO2-modified proteins in Epstein-Barr virus (EBV) latent and lytic infection to identify proteins that change in SUMO modification status in response to EBV reactivation. Major changes were identified in all three components of the TRIM24/TRIM28/TRIM33 complex, with TRIM24 being rapidly degraded and TRIM33 being phosphorylated and SUMOylated in response to EBV lytic infection. Further experiments revealed TRIM24 and TRIM33 repress expression of the EBV BZLF1 lytic switch gene, suppressing EBV reactivation. However, BZLF1 was shown to interact with TRIM24 and TRIM33, resulting in disruption of TRIM24/TRIM28/TRIM33 complexes, degradation of TRIM24 and modification followed by degradation of TRIM33. Therefore, we have identified TRIM24 and TRIM33 as cellular antiviral defence factors against EBV lytic infection and established the mechanism by which BZLF1 disables this defence.

Virology under the Microscope-a Call for Rational Discourse

Viruses have brought humanity many challenges: respiratory infection, cancer, neurological impairment and immunosuppression to name a few. Virology research over the last 60+ years has responded to reduce this disease burden with vaccines and antivirals. Despite this long history, the COVID-19 pandemic has brought unprecedented attention to the field of virology. Some of this attention is focused on concern about the safe conduct of research with human pathogens. A small but vocal group of individuals has seized upon these concerns - conflating legitimate questions about safely conducting virus-related research with uncertainties over the origins of SARS-CoV-2. The result has fueled public confusion and, in many instances, ill-informed condemnation of virology. With this article, we seek to promote a return to rational discourse. We explain the use of gain-of-function approaches in science, discuss the possible origins of SARS-CoV-2 and outline current regulatory structures that provide oversight for virological research in the United States. By offering our expertise, we - a broad group of working virologists - seek to aid policy makers in navigating these controversial issues. Balanced, evidence-based discourse is essential to addressing public concern while maintaining and expanding much-needed research in virology.

Virology under the Microscope-a Call for Rational Discourse

Viruses have brought humanity many challenges: respiratory infection, cancer, neurological impairment and immunosuppression to name a few. Virology research over the last 60+ years has responded to reduce this disease burden with vaccines and antivirals. Despite this long history, the COVID-19 pandemic has brought unprecedented attention to the field of virology. Some of this attention is focused on concern about the safe conduct of research with human pathogens. A small but vocal group of individuals has seized upon these concerns - conflating legitimate questions about safely conducting virus-related research with uncertainties over the origins of SARS-CoV-2. The result has fueled public confusion and, in many instances, ill-informed condemnation of virology. With this article, we seek to promote a return to rational discourse. We explain the use of gain-of-function approaches in science, discuss the possible origins of SARS-CoV-2 and outline current regulatory structures that provide oversight for virological research in the United States. By offering our expertise, we - a broad group of working virologists - seek to aid policy makers in navigating these controversial issues. Balanced, evidence-based discourse is essential to addressing public concern while maintaining and expanding much-needed research in virology.

Virology under the Microscope-a Call for Rational Discourse

Viruses have brought humanity many challenges: respiratory infection, cancer, neurological impairment and immunosuppression to name a few. Virology research over the last 60+ years has responded to reduce this disease burden with vaccines and antivirals. Despite this long history, the COVID-19 pandemic has brought unprecedented attention to the field of virology. Some of this attention is focused on concern about the safe conduct of research with human pathogens. A small but vocal group of individuals has seized upon these concerns - conflating legitimate questions about safely conducting virus-related research with uncertainties over the origins of SARS-CoV-2. The result has fueled public confusion and, in many instances, ill-informed condemnation of virology. With this article, we seek to promote a return to rational discourse. We explain the use of gain-of-function approaches in science, discuss the possible origins of SARS-CoV-2 and outline current regulatory structures that provide oversight for virological research in the United States. By offering our expertise, we - a broad group of working virologists - seek to aid policy makers in navigating these controversial issues. Balanced, evidence-based discourse is essential to addressing public concern while maintaining and expanding much-needed research in virology.

Flavivirus Capsid Proteins Inhibit the Interferon Response

Zika virus (ZIKV) establishes persistent infections in multiple human tissues, a phenomenon that likely plays a role in its ability to cause congenital birth defects and neurological disease. Multiple nonstructural proteins encoded by ZIKV, in particular NS5, are known to suppress the interferon (IFN) response by attacking different steps in this critical antiviral pathway. Less well known are the potential roles of structural proteins in affecting the host immune response during ZIKV infection. Capsid proteins of flaviviruses are of particular interest because a pool of these viral proteins is targeted to the nuclei during infection and, as such, they have the potential to affect host cell gene expression. In this study, RNA-seq analyses revealed that capsid proteins from six different flaviviruses suppress expression of type I IFN and IFN-stimulated genes. Subsequent interactome and in vitro ubiquitination assays showed that ZIKV capsid protein binds to and prevents activating ubiquitination of RIG-I CARD domains by TRIM25, a host factor that is important for the induction arm of the IFN response. The other flavivirus capsid proteins also interacted with TRIM25, suggesting that these viral proteins may attenuate antiviral signaling pathways at very early stages of infection, potentially even before nonstructural proteins are produced.

Characterization of a cancer-associated Epstein-Barr virus EBNA1 variant reveals a novel interaction with PLOD1 and PLOD3

Whole genome sequence analysis of Epstein-Barr virus genomes from tumours and healthy individuals identified three amino acid changes in EBNA1 that are strongly associated with gastric carcinoma and nasopharyngeal carcinoma. Here we show that, while these mutations do not impact EBNA1 plasmid maintenance function, one of them (Thr85Ala) decreases transcriptional activation and results in a gain of function interaction with PLOD1 and PLOD3. PLOD family proteins are strongly linked to multiple cancers, and PLOD1 is recognized as a prognostic marker of gastric carcinoma. We identified the PLOD1 binding site in EBNA1as the N-terminal transactivation domain and show that lysine 83 is critical for this interaction. The results provide a novel link between EBV infection and the cancer-associated PLOD proteins.

Epstein-Barr virus: Current questions and challenges

Epstein-Barr virus (EBV) infects most people worldwide and persists for life due to complicated interplay between lytic infection and multiple types of latent infections. While usually asymptomatic, EBV is a causative agent in several types of cancer and has a strong association with multiple sclerosis. Exactly how EBV promotes these diseases and why they are rare consequences of infection are incompletely understood. Here I will discuss current ideas on disease induction by EBV, including the importance of lytic protein expression in the context of latent infection as well as the possible importance of specific EBV variants in disease induction.

A Conserved Mechanism of APOBEC3 Relocalization by Herpesviral Ribonucleotide Reductase Large Subunits

An integral part of the antiviral innate immune response is the APOBEC3 family of single-stranded DNA cytosine deaminases, which inhibits virus replication through deamination-dependent and -independent activities. Viruses have evolved mechanisms to counteract these enzymes, such as HIV-1 Vif-mediated formation of a ubiquitin ligase to degrade virus-restrictive APOBEC3 enzymes. A new example is Epstein-Barr virus (EBV) ribonucleotide reductase (RNR)-mediated inhibition of cellular APOBEC3B (A3B). The large subunit of the viral RNR, BORF2, causes A3B relocalization from the nucleus to cytoplasmic bodies and thereby protects viral DNA during lytic replication. Here, we use coimmunoprecipitation and immunofluorescence microscopy approaches to ask whether this mechanism is shared with the closely related gammaherpesvirus Kaposi's sarcoma-associated herpesvirus (KSHV) and the more distantly related alphaherpesvirus herpes simplex virus 1 (HSV-1). The large RNR subunit of KSHV, open reading frame 61 (ORF61), coprecipitated multiple APOBEC3s, including A3B and APOBEC3A (A3A). KSHV ORF61 also caused relocalization of these two enzymes to perinuclear bodies (A3B) and to oblong cytoplasmic structures (A3A). The large RNR subunit of HSV-1, ICP6, also coprecipitated A3B and A3A and was sufficient to promote the relocalization of these enzymes from nuclear to cytoplasmic compartments. HSV-1 infection caused similar relocalization phenotypes that required ICP6. However, unlike the infectivity defects previously reported for BORF2-null EBV, ICP6 mutant HSV-1 showed normal growth rates and plaque phenotypes. Combined, these results indicate that both gamma- and alphaherpesviruses use a conserved RNR-dependent mechanism to relocalize A3B and A3A and furthermore suggest that HSV-1 possesses at least one additional mechanism to neutralize these antiviral enzymes.IMPORTANCE The APOBEC3 family of DNA cytosine deaminases constitutes a vital innate immune defense against a range of different viruses. A novel counterrestriction mechanism has recently been uncovered for the gammaherpesvirus EBV, in which a subunit of the viral protein known to produce DNA building blocks (ribonucleotide reductase) causes A3B to relocalize from the nucleus to the cytosol. Here, we extend these observations with A3B to include a closely related gammaherpesvirus, KSHV, and a more distantly related alphaherpesvirus, HSV-1. These different viral ribonucleotide reductases also caused relocalization of A3A, which is 92% identical to A3B. These studies are important because they suggest a conserved mechanism of APOBEC3 evasion by large double-stranded DNA herpesviruses. Strategies to block this host-pathogen interaction may be effective for treating infections caused by these herpesviruses.

The Epstein-Barr Virus BMRF1 Protein Activates Transcription and Inhibits the DNA Damage Response by Binding NuRD

The BMRF1 protein of Epstein-Barr virus (EBV) has multiple roles in viral lytic infection, including serving as the DNA polymerase processivity factor, activating transcription from several EBV promoters and inhibiting the host DNA damage response to double-stranded DNA breaks (DSBs). Using affinity purification coupled to mass spectrometry, we identified the nucleosome remodeling and deacetylation (NuRD) complex as the top interactor of BMRF1. We further found that NuRD components localize with BMRF1 at viral replication compartments and that this interaction occurs through the BMRF1 C-terminal region previously shown to mediate transcriptional activation. We identified an RBBP4 binding motif within this region that can interact with both RBBP4 and MTA2 components of the NuRD complex and showed that point mutation of this motif abrogates NuRD binding as well as the ability of BMRF1 to activate transcription from the BDLF3 and BLLF1 EBV promoters. In addition to its role in transcriptional regulation, NuRD has been shown to contribute to DSB signaling in enabling recruitment of RNF168 ubiquitin ligase and subsequent ubiquitylation at the break. We showed that BMRF1 inhibited RNF168 recruitment and ubiquitylation at DSBs and that this inhibition was at least partly relieved by loss of the NuRD interaction. The results reveal a mechanism by which BMRF1 activates transcription and inhibits DSB signaling and a novel role for NuRD in transcriptional activation in EBV.IMPORTANCE The Epstein-Barr virus (EBV) BMRF1 protein is critical for EBV infection, playing key roles in viral genome replication, activation of EBV genes, and inhibition of host DNA damage responses (DDRs). Here we show that BMRF1 targets the cellular nucleosome remodeling and deacetylation (NuRD) complex, using a motif in the BMRF1 transcriptional activation sequence. Mutation of this motif disrupts the ability of BMRF1 to activate transcription and interfere with DDRs, showing the importance of the NuRD interaction for BMRF1 functions. BMRF1 was shown to act at the same step in the DDR as NuRD, suggesting that it interferes with NuRD function.

Epstein–Barr virus: overcoming the DNA damage response

Infections by DNA viruses including, Epstein–Barr virus (EBV), typically induce cellular DNA damage responses (DDR), in particular double-stranded break signaling. To avoid apoptosis associated with constitutive DDR signaling, downstream steps of this pathway must be inactivated. EBV has developed multiple ways of disabling the DDR using several different viral proteins expressed at various stages of EBV infection. Here the interplay between EBV and host DDRs is discussed at each stage of EBV infection, along with the EBV proteins and miRNAs that are known to interfere with DDR signaling. The newly discovered APOBEC editing of EBV DNA and protection from this mutation is also discussed.

USP7 Regulates Cytokinesis through FBXO38 and KIF20B

The ubiquitin specific protease 7 (USP7 or HAUSP) is known to regulate a variety of cellular processes by binding and deubiquitylating specific target proteins. To gain a more comprehensive understanding of its interactions and functions, we used affinity purification coupled to mass spectrometry to profile USP7 interactions. This revealed a novel interaction with FBXO38, a poorly characterized F-box protein. We showed that USP7 stabilizes FBXO38 dependent on its catalytic activity by protecting FBXO38 from proteasomal degradation. We used a BioID approach to profile the protein interactions (and putative functions) of FBXO38, revealing an interaction with KIF20B, a Kinesin-6 protein required for efficient cytokinesis. FBXO38 was shown to function independently from an SCF complex to stabilize KIF20B. Consequently, depletion of either FBXO38 or USP7 led to dramatic decreases in KIF20B levels and KIF20B at the midbody, which were manifested in cytokinetic defects. Furthermore, cytokinetic defects associated with USP7 silencing were rescued by restoring FBXO38 or KIF20B. The results indicate a novel mechanism of regulating cytokinesis through USP7 and FBXO38.

Epstein-Barr virus BORF2 inhibits cellular APOBEC3B to preserve viral genome integrity

The APOBEC family of single-stranded (ss)DNA cytosine deaminases provides innate immunity against virus and transposon replication^1–4. A well-studied mechanism is APOBEC3G restriction of HIV-1, which is counteracted by a virus-encoded degradation mechanism^1–4. Accordingly, most work has focused on retroviruses with obligate ssDNA replication intermediates and it is unclear whether large double-stranded (ds)DNA viruses may be similarly susceptible to restriction. Here, we show that the large dsDNA herpesvirus Epstein-Barr virus (EBV), which is the causative agent of infectious mononucleosis and multiple cancers⁵, utilizes a two-pronged approach to counteract restriction by APOBEC3B. The large subunit of the EBV ribonucleotide reductase, BORF2^6,7, bound to APOBEC3B in proteomics studies and immunoprecipitation experiments. Mutagenesis mapped the interaction to the APOBEC3B catalytic domain, and biochemical studies demonstrated that BORF2 stoichiometrically inhibits APOBEC3B DNA cytosine deaminase activity. BORF2 also caused a dramatic relocalization of nuclear APOBEC3B to perinuclear bodies. Upon lytic reactivation, BORF2-null viruses were susceptible to APOBEC3B-mediated deamination as evidenced by lower viral titers, lower infectivity, and hypermutation. The Kaposi’s sarcoma herpesvirus (KSHV) homolog, ORF61, also bound APOBEC3B and mediated relocalization. These data support a model in which the genomic integrity of human γ-herpesviruses is maintained by active neutralization of the antiviral enzyme APOBEC3B.

Identification and Characterization of USP7 Targets in Cancer Cells

The ubiquitin specific protease, USP7, regulates multiple cellular pathways relevant for cancer through its ability to bind and sometimes stabilize specific target proteins through deubiquitylation. To gain a more complete profile of USP7 interactions in cancer cells, we performed affinity purification coupled to mass spectrometry to identify USP7 binding targets in gastric carcinoma cells. This confirmed reported associations of USP7 with USP11, PPM1G phosphatase and TRIP12 E3 ubiquitin ligase as well as identifying novel interactions with two DEAD/DEAH-box RNA helicases, DDX24 and DHX40. Using USP7 binding pocket mutants, we show that USP11, PPM1G, TRIP12 and DDX24 bind USP7 through its TRAF domain binding pocket, while DHX40 interacts with USP7 through a distinct binding pocket in the Ubl2 domain. P/A/ExxS motifs in USP11 and DDX24 that are critical for USP7 binding were also identified. Modulation of USP7 expression levels and inhibition of USP7 catalytic activity in multiple cells lines showed that USP7 consistently stabilizes DDX24, DHX40 and TRIP12 dependent on its catalytic activity, while USP11 and PPM1G levels were not consistently affected. Our study better defines the mechanisms of USP7 interaction with known targets and identifies DDX24 and DHX40 as new targets that are specifically bound and regulated by USP7.

A genome-wide screen of Epstein-Barr virus proteins that modulate host SUMOylation identifies a SUMO E3 ligase conserved in herpesviruses

Many cellular processes pertinent for viral infection are regulated by the addition of small ubiquitin-like modifiers (SUMO) to key regulatory proteins, making SUMOylation an important mechanism by which viruses can commandeer cellular pathways. Epstein-Barr virus (EBV) is a master at manipulating of cellular processes, which enables life-long infection but can also lead to the induction of a variety of EBV-associated cancers. To identify new mechanisms by which EBV proteins alter cells, we screened a library of 51 EBV proteins for global effects on cellular SUMO1 and SUMO2 modifications (SUMOylation), identifying several proteins not previously known to manipulate this pathway. One EBV protein (BRLF1) globally induced the loss of SUMOylated proteins, in a proteasome-dependent manner, as well as the loss of promeylocytic leukemia nuclear bodies. However, unlike its homologue (Rta) in Kaposi's sarcoma associated herpesvirus, it did not appear to have ubiquitin ligase activity. In addition we identified the EBV SM protein as globally upregulating SUMOylation and showed that this activity was conserved in its homologues in herpes simplex virus 1 (HSV1 UL54/ICP27) and cytomegalovirus (CMV UL69). All three viral homologues were shown to bind SUMO and Ubc9 and to have E3 SUMO ligase activity in a purified system. These are the first SUMO E3 ligases discovered for EBV, HSV1 and CMV. Interestingly the homologues had different specificities for SUMO1 and SUMO2, with SM and UL69 preferentially binding SUMO1 and inducing SUMO1 modifications, and UL54 preferentially binding SUMO2 and inducing SUMO2 modifications. The results provide new insights into the function of this family of conserved herpesvirus proteins, and the conservation of this SUMO E3 ligase activity across diverse herpesviruses suggests the importance of this activity for herpesvirus infections.

Expression of flavivirus capsids enhance the cellular environment for viral replication by activating Akt-signalling pathways

Flaviviruses depend on multiple host pathways during their life cycles and have evolved strategies to avoid the innate immune response. Previously, we showed that the West Nile virus capsid protein plays a role in this process by blocking apoptosis. In this study, we examined how expression of capsid proteins from several flaviviruses affects apoptosis and other host processes that impact virus replication. All of the tested capsid proteins protected cells from Fas-dependent apoptosis through a mechanism that requires activated Akt. Capsid expression upregulated other Akt-dependent cellular processes including expression of glucose transporter 1 and mitochondrial metabolism. Protein phosphatase 1, which is known to inactivate Akt, was identified as a DENV capsid interacting protein. This suggests that DENV capsid expression activates Akt by sequestering phosphatases that downregulate phospho-Akt. Capsid-dependent upregulation of Akt would enhance downstream signalling pathways that affect cell survival and metabolism, thus providing a favourable environment for virus replication.

Proceedings of the 7th Biannual International Symposium on Nasopharyngeal Carcinoma 2015

A1 Hope and despair in the current treatment of nasopharyngeal cancer

IB Tan

I1 NPC international incidence and risk factors

Ellen T Chang

I2 Familial nasopharyngeal carcinoma and the use of biomarkers

Chien-Jen Chen, Wan-Lun Hsu, Yin-Chu Chien

I3 Genetic susceptibility risk factors for sporadic and familial NPC: recent findings

Allan Hildesheim

I5 Genetic and environmental risk factors for nasopharyngeal cancer in Southeast Asia

James D McKay, Valerie Gaborieau, Mohamed Arifin Bin Kaderi, Dewajani Purnomosari, Catherine Voegele, Florence LeCalvez-Kelm, Graham Byrnes, Paul Brennan, Beena Devi

I6 Characterization of the NPC methylome identifies aberrant epigenetic disruption of key signaling pathways and EBV-induced gene methylation

Li L, Zhang Y, Fan Y, Sun K, Du Z, Sun H, Chan AT, Tsao SW, Zeng YX, Tao Q

I7 Tumor exosomes and translational research in NPC

Pierre Busson, Claire Lhuillier, Olivier Morales, Dhafer Mrizak, Aurore Gelin, Nikiforos Kapetanakis, Nadira Delhem

I8 Host manipulations of the Epstein-Barr virus EBNA1 protein

Sheila Mansouri, Jennifer Cao, Anup Vaidya, and Lori Frappier

I9 Somatic genetic changes in EBV-associated nasopharyngeal carcinoma

Lo Kwok Wai

I10 Preliminary screening results for nasopharyngeal carcinoma with ELISA-based EBV antibodies in Southern China

Sui-Hong Chen, Jin-lin Du, Ming-Fang Ji, Qi-Hong Huang, Qing Liu, Su-Mei Cao

I11 EBV array platform to screen for EBV antibodies associated with NPC and other EBV-associated disorders

Denise L. Doolan, Anna Coghill, Jason Mulvenna, Carla Proietti, Lea Lekieffre, Jeffrey Bethony, and Allan Hildesheim

I12 The nasopharyngeal carcinoma awareness program in Indonesia

Renske Fles, Sagung Rai Indrasari, Camelia Herdini, Santi Martini, Atoillah Isfandiari, Achmad Rhomdoni, Marlinda Adham, Ika Mayangsari, Erik van Werkhoven, Maarten Wildeman, Bambang Hariwiyanto, Bambang Hermani, Widodo Ario Kentjono, Sofia Mubarika Haryana, Marjanka Schmidt, IB Tan

I13 Current advances and future direction in nasopharyngeal cancer management

Brian O’Sullivan

I14 Management of juvenile nasopharyngeal cancer

Enis Ozyar

I15 Global pattern of nasopharyngeal cancer: correlation of outcome with access to radiotherapy

Anne WM Lee

I16 The predictive/prognostic biomarker for nasopharyngeal carcinoma

Mu-Sheng Zeng

I17 Effect of HLA and KIR polymorphism on NPC risk

Xiaojiang Gao, Minzhong Tang, Pat Martin, Yi Zeng, Mary Carrington

I18 Exploring the Association between Potentially Neutralizing Antibodies against EBV Infection and Nasopharyngeal Carcinoma

Anna E Coghill, Wei Bu, Hanh Nguyen, Wan-Lun Hsu, Kelly J Yu, Pei-Jen Lou, Cheng-Ping Wang, Chien-Jen Chen, Allan Hildesheim, Jeffrey I Cohen

I19 Advances in MR imaging in NPC

Ann D King

O1 Epstein-Barr virus seromarkers and risk of nasopharyngeal carcinoma: the gene-environment interaction study on nasopharyngeal carcinoma in Taiwan

Yin-Chu Chien, Wan-Lun Hsu, Kelly J Yu, Tseng-Cheng Chen, Ching-Yuan Lin, Yung-An Tsou, Yi-Shing Leu, Li-Jen Laio, Yen-Liang Chang, Cheng-Ping Wang, Chun-Hun Hua, Ming-Shiang Wu, Chu-Hsing Kate Hsiao, Jehn-Chuan Lee, Ming-Hsui Tsai, Skye Hung-Chun Cheng, Pei-Jen Lou, Allan Hildesheim, Chien-Jen Chen

O2 Familial tendency and environmental co-factors of nasopharyngeal carcinoma: the gene-environment interaction study on nasopharyngeal carcinoma in Taiwan

Wan-Lun Hsu, Kelly J Yu, Yin-Chu Chien, Tseng-Cheng Chen, Ching-Yuan Lin, Yung-An Tsou, Yi-Shing Leu, Li-Jen Liao, Yen-Liang Chang, Tsung-Lin Yang, Chun-Hun Hua, Ming-ShiangWu, Chu-Hsing Kate Hsiao, Jehn-ChuanLee, Ming-Hsui Tsai, Skye Hung-Chun Cheng, Jenq-Yuh Ko, Allan Hildesheim, Chien-Jen Chen

O3 The genetic susceptibility and prognostic role of TERT-CLPTM1L and genes in DNA damage pathways in NPC

Josephine Mun Yee Ko, Wei Dai, Dora Kwong, Wai Tong Ng, Anne Lee, Roger Kai Cheong Ngan, Chun Chung Yau, Stewart Tung, Maria Li Lung

O4 Long term effects of NPC screening

Mingfang Ji, Wei Sheng, Mun Hon Ng, Weimin Cheng, Xia Yu, Biaohua Wu, Kuangrong Wei, Jun Zhan, Yi Xin Zeng, Su Mei Cao, Ningshao Xia, Yong Yuan

O5 Risk prediction of nasopharyngeal carcinoma by detecting host genetic and Epstein-Barr virus variation in saliva

Qian Cui, Miao Xu, Jin-Xin Bei, Yi-Xin Zeng

O6 Patterns of care study in Turkish nasopharyngeal cancer patients (NAZOTURK): A Turkish Radiation Oncology Association Head and Neck Cancer Working Group Study

B Şahin, A Dizman, M Esassolak, A Saran İkizler, HC Yıldırım, M Çaloğlu, B Atalar, F Akman, C Demiroz, BM Atasoy, E Canyilmaz, S Igdem, G Ugurluer, T Kütük, M Akmansoy, E Ozyar

O7 Long term outcome of intensity modulated radiotherapy in nasopharyngeal carcinoma in National Cancer Centre Singapore

Kiattisa Sommat, Fu Qiang Wang, Li-Lian Kwok, Terence Tan, Kam Weng Fong, Yoke Lim Soong, Shie Lee Cheah, Joseph Wee

O8 International phase II randomized study on the addition of docetaxel to the combination of cisplatin and 5-fluorouracil in the induction treatment for nasopharyngeal carcinoma in children and adolescents

M Casanova, E Özyar, C Patte, D Orbach, A Ferrari, VF Cristine, H Errihani, J Pan, L Zhang, S Liji, K Grzegorzewski, L Gore, A Varan

O9 Prognostic impact of metastatic status in patients with nasopharyngeal carcinoma

Susanna Hilda Hutajulu, Guntara Khuzairi, Camelia Herdini, Henry Kusumo, Mardiah Suci Hardianti, Kartika Widayati Taroeno-Hariadi, Ibnu Purwanto, Johan Kurnianda

O10 Development of small molecule inhibitors of latent Epstein-Barr virus infection for the treatment of nasopharyngeal carcinoma

Troy E. Messick, Kimberly Malecka, Lois Tolvinski, Samantha Soldan, Julianna Deakyne, Hui Song, Antonio van den Heuvel, Baiwei Gu, Joel Cassel, Mark McDonnell, Garry R Smith, Venkata Velvadapu, Haiyan Bian, Yan Zhang, Marianne Carlsen, Shuai Chen, Alastair Donald, Christian Lemmen, Allen B Reitz, Paul M Lieberman

O11 Therapeutic targeting of cancer stem-like cells using a Wnt modulator, ICG-001, enhances the treatment outcome of EBV-positive nasopharyngeal carcinoma

King Chi Chan, Lai Sheung Chan, Kwok Wai Lo, Timothy Tak Chun Yip, Roger Kai Cheong Ngan, Michael Kahn, Maria Li Lung, Nai Ki Mak

O12 Role of micro-RNA in NPC biology

Fei-Fei Liu

O13 Expansion of EBNA1- and LMP2-specific effector T lymphocytes from patients with nasopharyngeal carcinoma without enhancement of regulatory T cells

Wafa Khaali; Juliette Thariat; Laurence Fantin; Flavia Spirito; Meriem Khyatti; El Khalil Ben Driss; Sylvain Olivero; Janet Maryanski; Alain Doglio

O14 The experience of patients’ life after amifostine radiotherapy treatment (ART) for nasopharyngeal carcinoma (NPC)

Mengxue Xia, Yunfei Xia, Hui Chang, Rachel Shaw

O15 Analysis of mitochondrial DNA mutation in latent membrane protein-1 positive nasopharyngeal carcinoma

Pudji Rahaju

O16 Factors influencing treatment adherence of nasopharyngeal cancer and the clinical outcomes: a hospital-based study

Mardiah Suci Hardianti, Sindhu Wisesa, Kartika Widayati Taroeno-Harijadi, Ibnu Purwanto, Bambang Hariwiyanto, Wigati Dhamiyati, Johan Kurnianda

O17 Chromosomal breaks mediated by bile acid-induced apoptosis in nasopharyngeal epithelial cells: in relation to matrix association region/scaffold attachment region

Sang-Nee Tan, Sai-Peng Sim

O18 Expression of p53 (wild type) on nasopharyngeal carcinoma stem cell that resistant to radiotherapy

Muhtarum Yusuf, Ahmad C Romdhoni, Widodo Ario K, Fedik Abdul Rantam

O19 Mathematical model of nasopharyngeal carcinoma in cellular level

Sugiyanto, Lina Aryati, Fajar Adi-Kusumo, Mardiah Suci Hardianti

O20 Differential expression of microRNA-21 on nasopharyngeal carcinoma plasma patient

SY Bintoro, R Oktriani, C. Herawati, A Surono, Sofia M. Haryana

O21 Therapeutic targeting of an oncogenic fibroblast growth factor-FGF19, which promotes proliferation and induces EMT of carcinoma cells through activating ERK and AKT signaling

L. Zhong, L. Li, B. B. Ma, A. T. Chan, Q. Tao

O22 Resist nasopharyngeal carcinoma (NPC): next generation T cells for the adoptive immunotherapy of NPC

M. Kalra, M. Ngo, S. Perna, A. Leen, N. Lapteva, C. M. Rooney, S. Gottschalk

O23 The correlation of heat shock protein 70 expressions and staging of nasopharyngeal carcinoma

Elida Mustikaningtyas, Sri Herawati, Achmad C Romdhoni

O24 Epstein-Barr virus serological profiles of nasopharyngeal carcinoma - A tribute to Werner Henle

Mingfang Ji, YaruiXu, Weimin Cheng, ShengxiangGe, Fugui Li, M. H. Ng

O25 Targeting the apoptosis pathway using combination TLR3 agonist with anti-survivin molecule (YM-155) in nasopharyngeal carcinoma

Louise SY Tan, Benjamin Wong, CM Lim

O26 The resistance mechanism of nasopharyngeal cancer stem cells to cisplatin through expression of CD44, Hsp70, p53 (wild type), Oct-4, and ß-catenin encoded-genes

Achmad C Romdhoni, Fedik A. Rantam, Widodo Ario Kentjono

P1 Prevalence of nasopharyngeal carcinoma patients at Departement of Otorhinolaringology-Head and Neck Surgery, Dr. Hasan Sadikin general hospital, Bandung, Indonesia in 2010-2014

Deasy Z Madani, Nur Akbar, Agung Dinasti Permana

P2 Case report on pediatric nasopharyngeal carcinoma at Dr. Sardjito Hospital, Yogyakarta

Camelia Herdini, Sagung Rai Indrasari, Jajah Fachiroh, Dwi Hartati, T. Baning Rahayudjati

P3 Report on loco regionally advanced nasopharyngeal cancer patients treated with induction chemotherapy followed by concurrent chemo-radiation therapy

Iswandi Darwis, Susanna Hilda Hutajulu, Bambang Hariwiyanto, Wigati Dhamiyati, Ibnu Purwanto, Kartika Widayati Taroeno-Hariadi, Johan Kurnianda

P4 Sex and age differences in the survival of patients with nasopharyngeal carcinoma

Sindhu Wisesa, Mardiah Suci Hardianti, Susanna Hilda Hutajulu, Kartika Widayati Taroeno-Harijadi, Ibnu Purwanto, Camelia Herdini, Wigati Dhamiyati, Johan Kurnianda

P5 Impact of delayed diagnosis and delayed therapy in the treatment outcome of patients with nasopharyngeal carcinoma

Khoirul Anwar, Susanna Hilda Hutajulu, Sagung Rai Indrasari, Sri Retna Dwidanarti, Ibnu Purwanto, Kartika Widayati Taroeno-Hariadi, Johan Kurnianda

P6 Anaysis of pretreatment anemia in nasopharyngeal cancer patients undergoing neoadjuvant therapy

Dominicus Wendhy Pramana, Susanna Hilda Hutajulu, Bambang Hariwiyanto, Wigati Dhamiyati, Ibnu Purwanto, Kartika Widayati Taroeno-Hariadi, Johan Kurnianda

P7 Results of treatment with neoadjuvant cisplatin-5FU in locally advanced nasopharyngeal carcinoma: a local experience

Diah Ari Safitri, Susanna Hilda Hutajulu, Camelia Herdini, Sri Retna Dwi Danarti, Ibnu Purwanto, Kartika Widayati Taroeno-Hariadi, Johan Kurnianda

P8 Geriatrics with nasopharyngeal cancer

Suryo A Taroeno, Sindhu Wisesa, Kartika Widayati Taroeno-Hariadi, Ibnu Purwanto, Bambang Hariwiyanto, Wigati Dhamiyati, Johan Kurnianda

P9 Correlation of lymphocyte to monocyte and neutrophil to lymphocyte ratio to the response of cisplatin chemoradiotheraphy in locally advance nasopharyngeal carcinoma

I. Wijaya, A. Oehadian, D. Prasetya

P10 Prediction of nasopharyngeal carcinoma risk by Epstein-Barr virus seromarkers and environmental co-factors: the gene-environment interaction study on nasopharyngeal carcinoma in Taiwan

Wan-Lun Hsu, Yin-Chu Chien, Kelly J Yu, Cheng-Ping Wang, Ching-Yuan Lin, Yung-An Tsou, Yi-Shing Leu, Li-Jen Liao, Yen-Liang Chang^191,192, Jenq-Yuh Ko, Chun-Hun Hua, Ming-Shiang Wu, Chu-Hsing Kate Hsiao, Jehn-Chuan Lee, Ming-Hsui Tsai, Skye Hung-Chun Cheng, Pei-Jen Lou, Allan Hildesheim, Chien-Jen Chen

P11 Non-viral risk factors for nasopharyngeal carcinoma in West Sumatra, Indonesia

Sukri Rahman, Bestari J. Budiman, Novialdi, Rahmadona, Dewi Yuri Lestari

P12 New prototype Vidas EBV IgA quick: performance on Chinese and Moroccan populations

C. Yin, A. Foussadier, E. Blein, C. Chen, N. Bournet Ammour, M. Khiatti, S. Cao

P13 The expression of EBV-LMP1 and VEGF as predictors and plasma EBV-DNA levels as early marker of distant metastasis after therapy in nasopharyngeal cancer

Dewi Syafriyetti Soeis Marzaini

P14 Characteristics and factors influencing subjects refusal for blood samples retrieval: lesson from NPC case control study in Yogyakarta – Indonesia

Dwi Hartati, Baning Rahayujati, Camelia Herdini, Jajah Fachiroh

P15 Expression of microRNA BART-7-3p and mRNA PTEN on blood plasma of patients with nasopharyngeal carcinoma

L. Gunawan, S. Mubarika Haryana, A. Surono, C. Herawati

P16 IgA response to native early antigen (IgA-EAext) of Epstein-Barr virus (EBV) in healthy population and nasopharyngeal carcinoma (NPC) patients: the potential for diagnosis and screening tools

Michael Hartono, Jajah Fachiroh, Umi Intansari, Dewi Kartikawati Paramita

P17 IgA responses against Epstein-Barr Virus Early Antigen (EBV-EA) peptides as potential candidates of nasopharyngeal carcinoma detection marker

Akmal Akbar, Jajah Fachiroh, Dewi Kartikawati Paramita

P18 Association between smoking habit and IgA-EBV titer among healthy individuals in Yogyakarta, Indonesia

Benny Hermawan, T Baning Rahayudjati, Dewi K Paramita, Jajah Fachiroh

P19 Epstein-Barr virus IgA titer comparison of healthy non-family individuals and healthy first degree family of NPV patients

Gabriella Argy, Jajah Fachiroh, Dewi Kartikawati Paramita, Susanna Hilda Hutajulu

P20 Identification of EBV Early Antigen (EA) derived peptides for NPC diagnosis

Theodora Caroline Sihotang, Jajah Fachiroh, Umi Intansari, Dewi Kartikawati Paramita

P21 Host-pathogen study: relative expression of mRNA BRLF1 Epstein-Barr virus as a potential biomarker for tumor progressivity and polymorphisms of TCRBC and TCRGC2 host genes related to genetic susceptibility on nasopharyngeal carcinoma

Daniel Joko Wahyono, Purnomo Soeharso, Dwi Anita Suryandari, Lisnawati, Zanil Musa, Bambang Hermani

P22 In vitro efficacy of silvestrol and episilvestrol, isolated from Borneo, on nasopharyngeal carcinoma, a major cancer in Borneo

Maelinda Daker, Yeo Jiun Tzen, Norhasimah Bakar, Asma’ Saiyidatina Aishah Abdul Rahman, Munirah Ahmad, Yeo Tiong Chia, Alan Khoo Soo Beng

P23 The expression of mir-141 in patients with nasopharyngeal cancer

Widyandani Sasikirana, Tirta Wardana, Muhammad Radifar, Cita Herawati, Agus Surono, Sofia Mubarika Haryana

Identification of RNF168 as a PML nuclear body regulator

Promyelocytic leukemia (PML) protein forms the basis of PML nuclear bodies (PML NBs), which control many important processes. We have screened an shRNA library targeting ubiquitin pathway proteins for effects on PML NBs, and identified RNF8 and RNF168 DNA-damage response proteins as negative regulators of PML NBs. Additional studies confirmed that depletion of either RNF8 or RNF168 increased the levels of PML NBs and proteins, whereas overexpression induced loss of PML NBs. RNF168 partially localized to PML NBs through its UMI/MIU1 ubiquitin-interacting region and associated with NBs formed by any PML isoform. The association of RNF168 with PML NBs resulted in increased ubiquitylation and SUMO2 modification of PML. In addition, RNF168 was found to associate with proteins modified by SUMO2 and/or SUMO3 in a manner dependent on its ubiquitin-binding sequences, suggesting that hybrid SUMO-ubiquitin chains can be bound. In vitro assays confirmed that RNF168, preferentially, binds hybrid SUMO2-K63 ubiquitin chains compared with K63-ubiquitin chains or individual SUMO2. Our study identified previously unrecognized roles for RNF8 and RNF168 in the regulation of PML, and a so far unknown preference of RNF168 for hybrid SUMO-ubiquitin chains.

EBNA1

Epstein-Barr nuclear antigen 1 (EBNA1) plays multiple important roles in EBV latent infection and has also been shown to impact EBV lytic infection. EBNA1 is required for the stable persistence of the EBV genomes in latent infection and activates the expression of other EBV latency genes through interactions with specific DNA sequences in the viral episomes. EBNA1 also interacts with several cellular proteins to modulate the activities of multiple cellular pathways important for viral persistence and cell survival. These cellular effects are also implicated in oncogenesis, suggesting a direct role of EBNA1 in the development of EBV-associated tumors.

A role for the nucleosome assembly proteins TAF-Iβ and NAP1 in the activation of BZLF1 expression and Epstein-Barr virus reactivation

The reactivation of Epstein-Barr virus (EBV) from latent to lytic infection begins with the expression of the viral BZLF1 gene, leading to a subsequent cascade of viral gene expression and amplification of the EBV genome. Using RNA interference, we show that nucleosome assembly proteins NAP1 and TAF-I positively contribute to EBV reactivation in epithelial cells through the induction of BZLF1 expression. In addition, overexpression of NAP1 or the β isoform of TAF-I (TAF-Iβ) in AGS cells latently infected with EBV was sufficient to induce BZLF1 expression. Chromatin immunoprecipitation experiments performed in AGS-EBV cells showed that TAF-I associated with the BZLF1 promoter upon lytic induction and affected local histone modifications by increasing H3K4 dimethylation and H4K8 acetylation. MLL1, the host protein known to dimethylate H3K4, was found to associate with the BZLF1 promoter upon lytic induction in a TAF-I-dependent manner, and MLL1 depletion decreased BZLF1 expression, confirming its contribution to lytic reactivation. The results indicate that TAF-Iβ promotes BZLF1 expression and subsequent lytic infection by affecting chromatin at the BZLF1 promoter.

Ubiquitin-specific protease 7 is a regulator of ubiquitin-conjugating enzyme UbE2E1

Ubiquitin-specific protease 7 (USP7) is a deubiquitinating enzyme found in all eukaryotes that catalyzes the removal of ubiquitin from specific target proteins. Here, we report that UbE2E1, an E2 ubiquitin conjugation enzyme with a unique N-terminal extension, is a novel USP7-interacting protein. USP7 forms a complex with UbE2E1 in vitro and in vivo through the ASTS USP7 binding motif within its N-terminal extension in an identical manner with other known USP7 binding proteins. We show that USP7 attenuates UbE2E1-mediated ubiquitination, an effect that requires the N-terminal ASTS sequence of UbE2E1 as well as the catalytic activity of USP7. Additionally, USP7 is critical in maintaining the steady state levels of UbE2E1 in cells. This study reveals a new cellular mechanism that couples the opposing activities of the ubiquitination machinery and a deubiquitinating enzyme to maintain and modulate the dynamic balance of the ubiquitin-proteasome system.

EBNA1 and host factors in Epstein-Barr virus latent DNA replication

Epstein-Barr virus episomes (EBV) replicate once per cell cycle during latent infection from the latent origin, oriP. This replication requires the viral EBNA1 protein, which specifically recognizes sequences in oriP and recruits cellular proteins to this origin. Replication from oriP requires the cellular origin recognition and MCM helicase complexes and also involves telomeric factors (including TRF2) that associate with repeated nonameric sequences at the origin. Replication from oriP occurs late in S-phase and this timing appears to be important for efficient replication. Replication from oriP has proven to be a valuable system for elucidating cellular proteins and mechanisms of origin activation.

Contributions of Epstein-Barr nuclear antigen 1 (EBNA1) to cell immortalization and survival

Epstein–Barr virus (EBV) immortalizes host cells as part of its latent mode of infection. As a result of this ability to promote cell proliferation and survival, EBV infection contributes to the development of several kinds of B-cell lymphomas and epithelial tumours. The EBV Epstein–Barr nuclear antigen 1 (EBNA1) protein is the only EBV protein expressed in all EBV-associated tumours and plays multiple important roles in EBV latency. In addition to its well-studied roles in viral DNA replication, segregation and transcriptional activation, several studies have identified roles of EBNA1 in manipulating cellular processes that result in reduced apoptosis and increased cell survival. This review discusses these cellular effects of EBNA1 and mechanisms by which they occur.

The MCM-associated protein MCM-BP is important for human nuclear morphology

Mini-chromosome maintenance complex-binding protein (MCM-BP) was discovered as a protein that is strongly associated with human MCM proteins, known to be crucial for DNA replication in providing DNA helicase activity. The Xenopus MCM-BP homologue appears to play a role in unloading MCM complexes from chromatin after DNA synthesis; however, the importance of MCM-BP and its functional contribution to human cells has been unclear. Here we show that depletion of MCM-BP by sustained expression of short hairpin RNA (shRNA) results in highly abnormal nuclear morphology and centrosome amplification. The abnormal nuclear morphology was not seen with depletion of other MCM proteins and was rescued with shRNA-resistant MCM-BP. MCM-BP depletion was also found to result in transient activation of the G2 checkpoint, slowed progression through G2 and increased replication protein A foci, indicative of replication stress. In addition, MCM-BP depletion led to increased cellular levels of MCM proteins throughout the cell cycle including soluble MCM pools. The results suggest that MCM-BP makes multiple contributions to human cells that are not limited to unloading of the MCM complex.

The Epstein-Barr Virus EBNA1 Protein

Epstein-Barr virus (EBV) is a widespread human herpes virus that immortalizes cells as part of its latent infection and is a causative agent in the development of several types of lymphomas and carcinomas. Replication and stable persistence of the EBV genomes in latent infection require the viral EBNA1 protein, which binds specific DNA sequences in the viral DNA. While the roles of EBNA1 were initially thought to be limited to effects on the viral genomes, more recently EBNA1 has been found to have multiple effects on cellular proteins and pathways that may also be important for viral persistence. In addition, a role for EBNA1 in lytic infection has been recently identified. The multiple roles of EBNA1 in EBV infection are the subject of this paper.

Nuclear body formation and PML body remodeling by the human cytomegalovirus protein UL35

The human cytomegalovirus (HCMV) UL35 gene encodes two proteins, UL35 and UL35a. Expression of UL35 in transfected cells results in the formation of UL35 nuclear bodies that associate with promyelocytic leukemia (PML) protein. PML forms the basis for PML nuclear bodies that are important for suppressing viral lytic gene expression. Given the important relationship between PML and viral infection, we have further investigated the association of UL35 with PML bodies. We demonstrate that UL35 bodies form independently of PML and subsequently recruit PML, Sp100 and Daxx. In contrast, UL35a did not form bodies; however, it could bind UL35 and inhibit the formation of UL35 bodies. The HCMV tegument protein pp71 promoted the formation of UL35 bodies and the cytoplasmic localization of UL35a. Similarly, UL35a shifted pp71 to the cytoplasm. These results indicate that the interplay between UL35, UL35a and pp71 affects their subcellular localization and likely their functions throughout infection.

Gene expression control by protein deubiquitinases

Protein ubiquitylation is involved in the regulation of virtually all aspects of eukaryotic cell biology, including gene expression. The central function of E3 ubiquitin ligases in target selection is well established. More recently, it has become appreciated that deubiquitylating enzymes (DUBs) are crucial components of ubiquitin-regulated cellular switches. Here, we discuss advances in our understanding of how DUBs regulate chromatin dynamics and gene expression. DUBs are integral components of the transcription machinery, involved in both gene activation and repression. They modulate the ubiquitylation status of histones H2A and H2B, which play pivotal roles in a cascade of molecular events that determine chromatin status. A DUB module in the SAGA coactivator complex is required for gene activation, whereas other DUBs are part of the Polycomb gene-silencing machinery. DUBs also control the level or subcellular compartmentalization of selective transcription factors, including the tumour suppressor p53. Typically, DUB specificity and activity are defined by its partner proteins, enabling remarkably versatile and sophisticated regulation. Recent findings not only underscore the pervasive and pivotal role of DUBs in gene expression control, but also raise paradoxical questions concerning the molecular mechanisms involved.

Viral disruption of promyelocytic leukemia (PML) nuclear bodies by hijacking host PML regulators

Epstein-Barr virus (EBV) latent infection promotes cell survival and proliferation, in some cases contributing to tumourigenesis. EBV-immortalized cells and EBV-induced tumours express the viral EBNA1 protein which, in addition to its roles in replicating and maintaining EBV genomes, can alter cellular processes, including the disruption of promyelocytic leukemia (PML) nuclear bodies (NBs) through the degradation of PML proteins. PML NBs are based on PML proteins and mediate several cellular processes including apoptosis, DNA repair and antiviral responses. Accordingly, EBNA1 expression decreases apoptosis and DNA repair which may contribute to malignant transformation. The ability of EBNA1 to disrupt PML NBs has recently been shown to require EBNA1 binding to two host proteins, the protein kinase CK2 and deubiquitylating protein USP7/HAUSP, both of which are known to be partially associated with PML NBs. EBNA1 increases the association of both CK2 and USP7 with PML NBs and, as a result, increases phosphorylation of PML proteins by CK2, a modification that is known to trigger PML polyubiquitylation and degradation. Recent data also implicates USP7 as a negative regulator of PML proteins and nuclear bodies by a mechanism independent of its intrinsic ubiquitin cleavage activity. The results suggest that EBNA1 usurps two host PML regulators in order to promote degradation of PML proteins and loss of PML NBs.

MCM-BP regulates unloading of the MCM2-7 helicase in late S phase

Origins of DNA replication are licensed by recruiting MCM2-7 to assemble the prereplicative complex (pre-RC). How MCM2-7 is inactivated or removed from chromatin at the end of S phase is still unclear. Here, we show that MCM-BP can disassemble the MCM2-7 complex and might function as an unloader of MCM2-7 from chromatin. In Xenopus egg extracts, MCM-BP exists in a stable complex with MCM7, but is not associated with the MCM2-7 hexameric complex. MCM-BP accumulates in nuclei in late S phase, well after the loading of MCM2-7 onto chromatin. MCM-BP immunodepletion in Xenopus egg extracts inhibits replication-dependent MCM dissociation without affecting pre-RC formation and DNA replication. When excess MCM-BP is incubated with Xenopus egg extracts or immunopurified MCM2-7, it binds to MCM proteins and promotes disassembly of the MCM2-7 complex. Recombinant MCM-BP also releases MCM2-7 from isolated late-S-phase chromatin, but this activity is abolished when DNA replication is blocked. MCM-BP silencing in human cells also delays MCM dissociation in late S phase. We propose that MCM-BP plays a key role in the mechanism by which pre-RC is cleared from replicated DNA in vertebrate cells.

USP7/HAUSP promotes the sequence-specific DNA binding activity of p53

The p53 tumor suppressor invokes cellular responses to stressful stimuli by coordinating distinct gene expression programs. This function relies heavily on the ability of p53 to function as a transcription factor by binding promoters of target genes in a sequence specific manner. The DNA binding activity of the core domain of p53 is subject to regulation via post-translational modifications of the C-terminal region. Here we show that the ubiquitin specific protease, USP7 or HAUSP, known to stabilize p53, also regulates the sequence-specific DNA binding mediated by the core domain of p53 in vitro. This regulation is contingent upon interaction between USP7 and the C-terminal regulatory region of p53. However, our data suggest that this effect is not mediated through the N-terminal domain of USP7 previously shown to bind p53, but rather involves the USP7 C-terminal domain and is independent of the deubiquitylation activity of USP7. Consistent with our in vitro observations, we found that overexpression of catalytically inactive USP7 in cells promotes p53 binding to its target sequences and p21 expression, without increasing the levels of p53 protein. We also found that the USP7 C-terminal domain was sufficient for p21 induction. Our results suggest a novel mode of regulation of p53 function by USP7, which is independent of USP7 deubiquitylating activity.

Further insight into substrate recognition by USP7: structural and biochemical analysis of the HdmX and Hdm2 interactions with USP7

Ubiquitin-specific protease 7 (USP7) catalyzes the deubiquitination of several substrate proteins including p53 and Hdm2. We have previously shown that USP7, and more specifically its amino-terminal domain (USP7-NTD), interacts with distinct regions on p53 and Hdm2 containing P/AxxS motifs. The ability of USP7 to also deubiquitinate and control the turnover of HdmX was recently demonstrated. We utilized a combination of biochemistry and structural biology to identify which domain of USP7 interacts with HdmX as well as to identify regions of HdmX that interact with USP7. We showed that USP7-NTD recognized two of six P/AxxS motifs of HdmX ((8)AQCS(11) and (398)AHSS(401)). The crystal structure of the USP7-NTD:HdmX(AHSS) complex was determined providing the molecular basis of complex formation between USP7-NTD and the HdmX(AHSS) peptide. The HdmX peptide interacted within the same residues of USP7-NTD as previously demonstrated with p53, Hdm2, and EBNA1 peptides. We also identified an additional site on Hdm2 ((397)PSTS(400)) that interacts with USP7-NTD and determined the crystal structure of this complex. Finally, analysis of USP7-interacting peptides on filter arrays confirmed the importance of the serine residue at the fourth position for the USP7-NTD interaction and showed that phosphorylation of serines within the binding sequence prevents this interaction. These results lead to a better understanding of the mechanism of substrate recognition by USP7-NTD.

Mitotic chromosome interactions of Epstein-Barr nuclear antigen 1 (EBNA1) and human EBNA1-binding protein 2 (EBP2)

The Epstein-Barr nuclear antigen 1 (EBNA1) protein enables the stable persistence of Epstein-Barr virus episomal genomes during latent infection, in part by tethering the episomes to the cellular chromosomes in mitosis. A host nucleolar protein, EBNA1-binding protein 2 (EBP2), has been shown to be important for interactions between EBNA1 and chromosomes in metaphase and to associate with metaphase chromosomes. Here, we examine the timing of the chromosome associations of EBNA1 and EBP2 through mitosis and the regions of EBNA1 that mediate the chromosome interactions at each stage of mitosis. We show that EBP2 is localized to the nucleolus until late prophase, after which it relocalizes to the chromosome periphery, where it remains throughout telophase. EBNA1 is associated with chromosomes early in prophase through to telophase and partially colocalizes with chromosomal EBP2 in metaphase through to telophase. Using EBNA1 deletion mutants, the chromosome association of EBNA1 at each stage of mitosis was found to be mediated mainly by a central glycine-arginine region, and to a lesser degree by N-terminal sequences. These sequence requirements for chromosome interaction mirrored those for EBP2 binding. Our results suggest that interactions between EBNA1 and chromosomes involve at least two stages, and that the contribution of EBP2 to these interactions occurs in the second half of mitosis.

Epstein-Barr nuclear antigen 1 contributes to nasopharyngeal carcinoma through disruption of PML nuclear bodies

Latent Epstein-Barr virus (EBV) infection is strongly associated with several cancers, including nasopharyngeal carcinoma (NPC), a tumor that is endemic in several parts of the world. We have investigated the molecular basis for how EBV latent infection promotes the development of NPC. We show that the viral EBNA1 protein, previously known to be required to maintain the EBV episomes, also causes the disruption of the cellular PML (promyelocytic leukemia) nuclear bodies (or ND10s). This disruption occurs both in the context of a native latent infection and when exogenously expressed in EBV-negative NPC cells and involves loss of the PML proteins. We also show that EBNA1 is partially localized to PML nuclear bodies in NPC cells and interacts with a specific PML isoform. PML disruption by EBNA1 requires binding to the cellular ubiquitin specific protease, USP7 or HAUSP, but is independent of p53. We further observed that p53 activation, DNA repair and apoptosis, all of which depend on PML nuclear bodies, were impaired by EBNA1 expression and that cells expressing EBNA1 were more likely to survive after induction of DNA damage. The results point to an important role for EBNA1 in the development of NPC, in which EBNA1-mediated disruption of PML nuclear bodies promotes the survival of cells with DNA damage.

Epstein-Barr virus (EBV) infects most people worldwide and is associated with several types of cancer due to its ability to induce cell proliferation. Only one viral protein, EBNA1, is expressed in all forms of EBV-associated tumors. Here, we have investigated whether EBNA1 directly contributes to the development of nasopharyngeal carcinoma (NPC), the most common EBV-associated tumor. We found that EBNA1 disrupts structures in the cell nucleus, called PML bodies, that are known to inhibit malignant transformation and to be important for cells to repair DNA that has been damaged due to exposure to carcinogenic agents. We show that EBNA1 interacts with and degrades the principal component of PML bodies. As a result, cells expressing EBNA1 are less able to repair their DNA and more likely to survive with DNA damage that could result in malignant transformation.

Genome-wide screen of three herpesviruses for protein subcellular localization and alteration of PML nuclear bodies

Herpesviruses are large, ubiquitous DNA viruses with complex host interactions, yet many of the proteins encoded by these viruses have not been functionally characterized. As a first step in functional characterization, we determined the subcellular localization of 234 epitope-tagged proteins from herpes simplex virus, cytomegalovirus, and Epstein–Barr virus. Twenty-four of the 93 proteins with nuclear localization formed subnuclear structures. Twelve of these localized to the nucleolus, and five at least partially localized with promyelocytic leukemia (PML) bodies, which are known to suppress viral lytic infection. In addition, two proteins disrupted Cajal bodies, and 19 of the nuclear proteins significantly decreased the number of PML bodies per cell, including six that were shown to be SUMO-modified. These results have provided the first functional insights into over 120 previously unstudied proteins and suggest that herpesviruses employ multiple strategies for manipulating nuclear bodies that control key cellular processes.

Herpes simplex virus, Epstein–Barr virus, and cytomegalovirus are three types of human herpesviruses that infect most people for their entire life and, under some circumstances, cause significant diseases. Each virus encodes a large number of proteins that function to manipulate the host cell to the best advantage of the virus; however, many of these encoded proteins have never been studied. We have generated constructs to express most of the proteins encoded by these three viruses in human cells and have determined the precise localization of each in the cell. We have also examined how each viral protein affects host nuclear structures called PML bodies, which are part of the cellular response to suppress viral replication. We identified several proteins from all three viruses that disrupt PML bodies, suggesting that they would enable viral infection. Our study has given the first information on the potential function of 120 previously unstudied viral proteins and shows that each virus has multiple mechanisms to disrupt PML bodies that were not previously recognized.

Kinetically driven refolding of the hyperstable EBNA1 origin DNA-binding dimeric beta-barrel domain into amyloid-like spherical oligomers

The Epstein-Barr nuclear antigen 1 (EBNA1) is essential for DNA replication and episome segregation of the viral genome, and participates in other gene regulatory processes of the Epstein-Barr virus in benign and malignant diseases related to this virus. Despite the participation of other regions of the protein in evading immune response, its DNA binding, dimeric beta-barrel domain (residues 452-641) is necessary and sufficient for the main functions. This domain has an unusual topology only shared by another viral origin binding protein (OBP), the E2 DNA binding domain of papillomaviruses. Both the amino acid and DNA target sequences are completely different for these two proteins, indicating a link between fold conservation and function. In this work we investigated the folding and stability of the DNA binding domain of EBNA1 OBP and found it is extremely resistant to chemical, temperature, and pH denaturation. The thiocyanate salt of guanidine is required for obtaining a complete transition to a monomeric unfolded state. The unfolding reaction is extremely slow and shows a marked uncoupling between tertiary and secondary structure, indicating the presence of intermediate species. The Gdm.SCN unfolded protein refolds to fully soluble and spherical oligomeric species of 1.2 MDa molecular weight, with identical fluorescence centre of spectral mass but different intensity and different secondary structure. The refolded spherical oligomers are substantially less stable than the native recombinant dimer. In keeping with the substantial structural rearrangement in the oligomers, the spherical oligomers do not bind DNA, indicating that the DNA binding site is either disrupted or participates in the oligomerization interface. The puzzling extreme stability of a dimeric DNA binding domain from a protein from a human infecting virus in addition to a remarkable kinetically driven folding where all molecules do not return to the most stable original species suggests a co-translational and directional folding of EBNA1 in vivo, possibly assisted by folding accessory proteins. Finally, the oligomers bind Congo red and thioflavin-T, both characteristic of repetitive beta-sheet elements of structure found in amyloids and their soluble precursors. The stable nature of the "kinetically trapped" oligomers suggest their value as models for understanding amyloid intermediates, their toxic nature, and the progress to amyloid fibers in misfolding diseases. The possible role of the EBNA1 spherical oligomers in the virus biology is discussed.

Viral proteomics

Viruses have long been studied not only for their pathology and associated disease but also as model systems for molecular processes and as tools for identifying important cellular regulatory proteins and pathways. Recent advances in mass spectrometry methods coupled with the development of proteomic approaches have greatly facilitated the detection of virion components, protein interactions in infected cells, and virally induced changes in the cellular proteome, resulting in a more comprehensive understanding of viral infection. In addition, a rapidly increasing number of high-resolution structures for viral proteins have provided valuable information on the mechanism of action of these proteins as well as aided in the design and understanding of specific inhibitors that could be used in antiviral therapies. In this paper, we discuss proteomic studies conducted on all eukaryotic viruses and bacteriophages, covering virion composition, viral protein structures, virus-virus and virus-host protein interactions, and changes in the cellular proteome upon viral infection.

East-West Symposium on nasopharyngeal cancer

BACKGROUND

To achieve greater understanding of the epidemiology, pathogenesis, molecular oncology, diagnostic, and therapeutic aspects of nasopharyngeal cancer (NPC), an international meeting was held in June 2005, Toronto, Canada.

RESULTS

Further insights were obtained into the role of EBV in NPC development, with its diverse effects ranging from proliferative signals via NF-kB, to immunesuppression, to angiogenic gene regulation. Subsequently, multiple pathways are dysregulated in NPC as revealed by expression array analyses, including apoptosis, integrin, and B-catenin cascades. Advances have been made in the diagnosis and monitoring of NPC, using transoral brushings and plasma levels of EBV transcripts, which may not directly correlate with the number of circulating tumor cells, but is nevertheless informative in predicting and tracking disease response. Many novel therapies have promising results, particularly in the areas of immunotherapies, and the exploration of molecularly targeted approaches such as cetuximab or histone deacetylase inhibitors.

CONCLUSIONS

The results from large randomized trials and meta-analyses have consistently demonstrated the benefit of concurrent chemotherapy with curative radiation therapy, but at a cost of greater acute and late-tissue toxicities. Further advances are required to achieve an improved understanding on the inter-relationship between environmental and genetic determinants in NPC development, to reduce the global burden of this disease. At the same time, novel therapeutic approaches are necessary to increase curability of NPC, but with reduced long-term toxicities.

Identification and characterization of a novel component of the human minichromosome maintenance complex

Minichromosome maintenance (MCM) complex replicative helicase complexes play essential roles in DNA replication in all eukaryotes. Using a tandem affinity purification-tagging approach in human cells, we discovered a form of the MCM complex that contains a previously unstudied protein, MCM binding protein (MCM-BP). MCM-BP is conserved in multicellular eukaryotes and shares limited homology with MCM proteins. MCM-BP formed a complex with MCM3 to MCM7, which excluded MCM2; and, conversely, hexameric complexes of MCM2 to MCM7 lacked MCM-BP, indicating that MCM-BP can replace MCM2 in the MCM complex. MCM-BP-containing complexes exhibited increased stability under experimental conditions relative to those containing MCM2. MCM-BP also formed a complex with the MCM4/6/7 core helicase in vitro, but, unlike MCM2, did not inhibit this helicase activity. A proportion of MCM-BP bound to cellular chromatin in a cell cycle-dependent manner typical of MCM proteins, and, like other MCM subunits, preferentially associated with a cellular origin in G(1) but not in S phase. In addition, down-regulation of MCM-BP decreased the association of MCM4 with chromatin, and the chromatin association of MCM-BP was at least partially dependent on MCM4 and cdc6. The results indicate that multicellular eukaryotes contain two types of hexameric MCM complexes with unique properties and functions.

Mechanism of DNA Recognition at a Viral Replication Origin

Recognition of the DNA origin by the Epstein-Barr nuclear antigen 1 (EBNA1) protein is the primary event in latentphase genome replication of the Epstein-Barr virus, a model for replication initiation in eukaryotes. We carried out an extensive thermodynamic and kinetic characterization of the binding mechanism of the DNA binding domain of EBNA1, EBNA1452-641, to a DNA fragment containing a single specific origin site. The interaction displays a binding energy of 12.7 kcal mol-1, with 11.9 kcal mol-1 coming from the enthalpic change with a minimal entropic contribution. Formation of the EBNA1452-641.DNA complex is accompanied by a heat capacity change of -1.22 kcal mol-1 K-1, a very large value considering the surface area buried, which we assign to an unusually apolar protein-DNA interface. Kinetic dissociation experiments, including fluorescence anisotropy and a continuous native electrophoretic mobility shift assay, confirmed that two EBNA1.DNA complex conformers are in slow equilibrium; one dissociates slowly (t1/2 approximately 41 min) through an undissociated intermediate species and the other corresponds to a fast twostep dissociation route (t1/2 approximately 0.8 min). In line with this, at least two parallel association events from two populations of protein conformers are observed, with on-rates of 0.25-1.6x10(8) m-1 s-1, which occur differentially either in excess protein or DNA molecules. Both parallel complexes undergo subsequent firstorder rearrangements of approximately 2.0 s-1 to yield two consolidated complexes. These parallel association and dissociation routes likely allow additional flexible regulatory events for site recognition depending on site availability according to nucleus environmental conditions, which may lock a final recognition event, dissociate and re-bind, or slide along the DNA.

Regulation of the EBNA1 Epstein-Barr virus protein by serine phosphorylation and arginine methylation

The Epstein-Barr virus (EBV) EBNA1 protein is important for the replication and mitotic segregation of EBV genomes in latently infected cells and also activates the transcription of some of the viral latency genes. A Gly-Arg-rich region between amino acids 325 and 376 is required for both the segregation and transcriptional activation functions of EBNA1. Here we show that this region is modified by both arginine methylation and serine phosphorylation. Mutagenesis of the four potentially phosphorylated serines in this region indicated that phosphorylation of multiple serines contributes to the efficient segregation of EBV-based plasmids by EBNA1, at least in part by increasing EBNA1 binding to hEBP2. EBNA1 was also found to bind the arginine methyltransferases PRMT1 and PRMT5. Multiple arginines in the 325-376 region were methylated in vitro by PRMT1 and PRMT5, as was an N-terminal Gly-Arg-rich region between amino acids 41 and 50. EBNA1 was also shown to be methylated in vivo, predominantly in the 325-376 region. Treatment of cells with a methylation inhibitor or down-regulation of PRMT1 altered EBNA1 localization, resulting in the formation of EBNA1 rings around the nucleoli. The results indicate that EBNA1 function is influenced by both serine phosphorylation and arginine methylation.

The role of BiP in endoplasmic reticulum-associated degradation of major histocompatibility complex class I heavy chain induced by cytomegalovirus proteins

Human cytomegalovirus (HCMV1) US11 and US2 proteins cause rapid degradation of major histocompatibility complex (MHC) molecules, apparently by ligating cellular endoplasmic reticulum (ER)-associated degradation machinery. Here, we show that US11 and US2 bind the ER chaperone BiP. Four related HCMV proteins, US3, US7, US9, and US10, which do not promote degradation of MHC proteins, did not bind BiP. Silencing BiP reduced US11- and US2-mediated degradation of MHC class I heavy chain (HC) without altering the synthesis or translocation of HC into the ER or the stability of HC in the absence of US11 or US2. Induction of the unfolded protein response (UPR) did not affect US11-mediated HC degradation and could not explain the stabilization of HC when BiP was silenced. Unlike in yeast, BiP did not act by maintaining substrates in a retrotranslocation-competent form. Our studies go beyond previous observations in mammalian cells correlating BiP release with degradation, demonstrating that BiP is functionally required for US2- and US11-mediated HC degradation. Further, US2 and US11 bound BiP even when HC was absent and degradation of US2 depended on HC. These data were consistent with a model in which US2 and US11 bridge HC onto BiP promoting interactions with other ER-associated degradation proteins.

Molecular recognition of p53 and MDM2 by USP7/HAUSP

The ubiquitin-specific protease, USP7, has key roles in the p53 pathway whereby it stabilizes both p53 and MDM2. We show that the N-terminal domain of USP7 binds two closely spaced 4-residue sites in both p53 and MDM2, falling between p53 residues 359-367 and MDM2 residues 147-159. Cocrystal structures with USP7 were determined for both p53 peptides and for one MDM2 peptide. These peptides bind the same surface of USP7 as Epstein-Barr nuclear antigen-1, explaining the competitive nature of the interactions. The structures and mutagenesis data indicate a preference for a P/AXXS motif in peptides that bind USP7. Contacts made by serine are identical and crucial for all peptides, and Trp165 in the peptide-binding pocket of USP7 is also crucial. These results help to elucidate the mechanism of substrate recognition by USP7 and the regulation of the p53 pathway.

Expression Profiling of Herpesvirus and Vaccinia Virus Proteins Using a High-Throughput Baculovirus Screening System

We have developed a high-throughput system for generating baculoviruses and testing the expression, solubility, and affinity column purification of encoded proteins. We have used this system to generate baculoviruses for and analyze the expression of 337 proteins from three different herpesviruses (HSV-1, EBV, and CMV) and vaccinia virus. Subsets of these proteins were also tested for expression and solubility in E. coli. Comparisons of the results in the two systems are presented for each virus.

EBP2 plays a key role in Epstein-Barr virus mitotic segregation and is regulated by aurora family kinases

Epstein-Barr virus (EBV) genomes persist indefinitely in latently infected human cells, in part due to their ability to stably segregate during cell division. This process is mediated by the viral EBNA1 protein, which tethers the viral episomes to the cellular mitotic chromosomes. We have previously identified a mitotic chromosomal protein, human EBNA1 binding protein 2 (hEBP2), which binds to EBNA1 and enables EBNA1 to partition EBV-based plasmids in Saccharomyces cerevisiae. Using an RNA silencing approach, we show that hEBP2 is essential for the proliferation of human cells and that repression of hEBP2 severely decreases the ability of EBNA1 and EBV-based plasmids to bind mitotic chromosomes. When expressed in yeast, hEBP2 undergoes the same cell cycle-regulated association with the mitotic chromatin as in human cells, and using yeast temperature-sensitive mutant strains, we found that the attachment of hEBP2 to mitotic chromosomes was dependent on the Ipl1 kinase. Both RNA silencing of the Ipl1 orthologue in human cells (Aurora B) and specific inhibition of the Aurora B kinase activity with a small molecule confirmed a role for this kinase in enabling hEBP2 binding to human mitotic chromosomes, suggesting that this kinase can regulate EBV segregation.

Structure of the p53 binding domain of HAUSP/USP7 bound to Epstein-Barr nuclear antigen 1 implications for EBV-mediated immortalization

USP7/HAUSP is a key regulator of p53 and Mdm2 and is targeted by the Epstein-Barr nuclear antigen 1 (EBNA1) protein of Epstein-Barr virus (EBV). We have determined the crystal structure of the p53 binding domain of USP7 alone and bound to an EBNA1 peptide. This domain is an eight-stranded beta sandwich similar to the TRAF-C domains of TNF-receptor associated factors, although the mode of peptide binding differs significantly from previously observed TRAF-peptide interactions in the sequence (DPGEGPS) and the conformation of the bound peptide. NMR chemical shift analyses of USP7 bound by EBNA1 and p53 indicated that p53 binds the same pocket as EBNA1 but makes less extensive contacts with USP7. Functional studies indicated that EBNA1 binding to USP7 can protect cells from apoptotic challenge by lowering p53 levels. The data provide a structural and conceptual framework for understanding how EBNA1 might contribute to the survival of Epstein-Barr virus-infected cells.

HAUSP/USP7 as an Epstein-Barr virus target

USP7 (also called HAUSP) is a de-ubiquitinating enzyme recently identified as a key regulator of the p53-mdm2 pathway, which stabilizes both p53 and mdm2. We have discovered that the Epstein-Barr nuclear antigen 1 protein of Epstein-Barr virus binds with high affinity to USP7 and disrupts the USP7-p53 interaction. The results have important implications for the role of Epstein-Barr nuclear antigen 1 in the cellular immortalization that is typical of an Epstein-Barr virus latent infection.

Functional characterization of EBV-encoded nuclear antigen 1-specific CD4+ helper and regulatory T cells elicited by in vitro peptide stimulation

CD4(+) helper and regulatory T (Treg) cells play important but opposing roles in regulating host immune responses against cancer and other diseases. However, very little is known about the antigen specificity of CD4(+) Treg cells. Here we describe the generation of a panel of EBV-encoded nuclear antigen 1 (EBNA1)-specific CD4(+) T-cell lines and clones that recognize naturally processed EBNA1-P(607-619) and -P(561-573) peptides in the context of HLA-DQ2 and HLA-DR11, -DR12, and -DR13 molecules, respectively. Phenotypic and functional analyses of these CD4(+) T cells revealed that they represent EBNA1-specific CD4(+) T helper as well as Treg cells. CD4(+) Treg cells do not secrete interleukin (IL)-10 and transforming growth factor beta cytokines but express CD25, the glucocorticoid-induced tumor necrosis factor receptor-related protein (GITR), and Forkhead Box P3 (Foxp3), and are capable of suppressing the proliferative responses of naive CD4(+) and CD8(+) T cells to stimulation with mitogenic anti-CD3 antibody. The suppressive activity of these CD4(+) Treg cells is mediated via cell-cell contact or in part by a cytokine-dependent manner. Importantly, these Treg cells suppress IL-2 secretion by CD4(+) effector T cells specific for either EBNA1 or a melanoma antigen, suggesting that these CD4(+) Treg cells induce immune suppression. These observations suggest that the success of peptide-based vaccines against EBV-associated cancer and other diseases may likely depend upon our ability to identify antigens/peptides that preferentially activate helper T cells and/or to design strategies to regulate the balance between CD4(+) helper and Treg cells.

Methods for measuring the replication and segregation of Epstein-Barr virus-based plasmids

Plasmids containing the Epstein-Barr virus (EBV) latent origin of replication, OriP, are stably maintained in human cells expressing the viral EBNA-1 protein. This stable maintenance is owing to the ability of EBNA-1 to activate DNA replication from OriP and to facilitate the segregation of the plasmids during cell division. Methods for quantifying the replication and stable maintenance of EBV-based plasmids in human cells are presented here, as is a reconstituted segregation system in yeast that enables the segregation activity of EBNA1 to be measured independently from its replication activity.