Epstein-Barr Virus Latent Gene Expression in Nasopharyngeal And Gastric Carcinoma

Cláudia Sofia da Silva Oliveira EPSTEIN-BARR VIRUS LATENT GENE EXPRESSION IN NASOPHARYNGEAL AND GASTRIC CARCINOMA Dissertação de Candidatura ao grau de Mestre em Oncologia submetida ao Instituto de Ciências Biomédicas de Abel Salazar da Universidade do Porto. Orientador – Doutor Hugo Sousa Categoria – Técnico Superior de Saúde Afiliação – Serviço de Virologia, IPO Porto FG EPE Co-orientador – Mestre Joana Ribeiro Categoria – Bolseira de Investigação Afiliação – Grupo Oncologia Molecular e Patologia Viral, IPO Porto FG EPE Cláudia Oliveira | MSc Oncology Epstein-Barr virus latent gene expression in nasopharyngeal and gastric carcinoma | I PREFACE This study was realized in the Molecular Oncology & Viral Pathology Group of the Portuguese Oncology Institute of Porto (IPO Porto). A systematic review of literature is being prepared to be published: Ribeiro J, Oliveira C, Sousa H. EBV LATENCY PATTERN IN GASTRIC CARCINOMAS: A SYSTEMATIC REVIEW. The results obtained in this study are being prepared to be included in different publications to be submitted in the near future. Cláudia Oliveira | MSc Oncology Epstein-Barr virus latent gene expression in nasopharyngeal and gastric carcinoma | III AGRADECIMENTOS Esta tese não teria certamente sido possível, sem o apoio, motivação e encorajamento, que fui tendo ao longo da sua realização. Deixo aqui os meus agradecimentos a todos, que de uma forma ou de outra, contribuíram para a sua execução. Em primeiro lugar gostaria de agradecer ao meu orientador, Doutor Hugo Sousa por me ter aceite no Grupo de Oncologia Molecular e Patologia Viral do Instituto Português de Oncologia do Porto (IPO Porto FG EPE), pelos novos conhecimentos adquiridos, por toda a ajuda e disponibilidade fornecida e por ter deste modo ter enriquecido o meu percurso académico. Não menos importante, á minha co-orientadora, Mestre Joana Ribeiro, por ter de igual forma ter contribuído para que este projeto fosse possível. Queria também agradecer ao serviço de Anatomia Patológica do IPO-PORTO, em especial ao Dr. Luis Pedro, á Dra. Ana Gallaghar, ao Dr. Manuel Jácome, á Técnica Fernanda Silva e a Técnica Ana tavares, por toda a ajuda e disponibilidade que forneceram, que tornaram este trabalho possível. Às minhas companheiras de laboratório, Nádia Neto e Ana Bela Campos, pelos momentos de desespero passados em conjunto, pelas horas infindáveis a moldar os sofás da entrada, mas principalmente pelas gargalhadas e por todas as situações de descontração que tornaram este ano muito mais fácil de aguentar. Um especial agradecimento também á Mariana Malta, que na altura do aperto, foi uma ajuda preciosa no laboratório. Aos meus amigos, pelos convívios, pelas saídas, por todos os bons momentos, mas mais importante do que isso, por todo o apoio que ao longo destes anos todos nunca falhou. Aos meus pais e família, por terem permitido que eu realizasse todo este percurso sem nunca terem duvidado de mim. Por último, quero agradecer àqueles que ao longo deste ano aturaram todo o meu mau humor e, que á sua maneira, sempre souberam sempre como o mudar. A todos, um sincero obrigada! Cláudia Oliveira | MSc Oncology Epstein-Barr virus latent gene expression in nasopharyngeal and gastric carcinoma | V RESUMO O EBV é um vírus associado a cancro que infecta cerca de 90% da população mundial, sem causar sintomas na maioria dos portadores ao longo da vida. A infeção por EBV pode adotar quatro diferentes padrões de latência, a latência 0, I, II, e III, que parecem estar correlacionados com os diferentes tipos de doenças associadas ao EBV. . No entanto, há algumas dúvidas sobre a expressão de genes latentes do EBV em diferentes doenças tais como o carcinoma nasofaríngeo e o carcinoma gástrico. Foi realizado um estudo retrospetivo com 23 casos de carcinoma da nasofaringe e 9 casos de carcinoma gástrico associados ao EBV, a fim de avaliar a expressão de proteínas do EBV nos diferentes tumores e tentar estabelecer uma correlação clínica entre a latência viral e a malignidade. A deteção do EBV foi feita por EBER-IHS e a deteção de proteínas do EBV (LMP1 e LMP2a) foi realizada por imuno-histoquímica. Todos os casos utilizados neste estudo foram EBV positivos. LMP1 esteve presente em 95,5% dos casos de carcinoma da nasofaringe, mas nenhum dos casos de carcinoma gástrico mostrou ter expressão LMP1. Em relação á LMP2a, ela foi expressa em 100% dos casos de carcinoma da nasofaringe, enquanto no carcinoma gástrico estava presente em 44,4%. A expressão proteica de cada um dos tumores levou a diferentes tipos de latência. No carcinoma da nasofaringe, 21 casos (95,5%), apresentaram expressão de LMP1 e LMP2a, o que corresponde a um padrão de latência II, e apenas 1 caso (4,5%) expressou um padrão de latência distinto semelhante à latência II, mas sem a expressão de LMP1. No carcinoma gástrico, 5 casos (55,5%) não apresentavam expressão de LMP1 e LMP2a, que corresponde a um padrão de latência I. Os restantes 4 casos, tiveram o mesmo padrão de latência que um caso de carcinoma da nasofaringe onde há expressão de LMP2a, mas não de LMP1. Esses dados confirmam os padrões de latência associados ao carcinoma da nasofaringe (latência II) e com o carcinoma gástrico (latência I). Identificou-se também um padrão de latência novo e ainda não aceite (latency II-like) que é especialmente importante no carcinoma gástrico, e é caracterizado por a expressão de EBNA 1 e LMP2a. Este foi o primeiro estudo realizado em Portugal para caracterizar os padrões de latência do EBV em diferentes neoplasias. Em conclusão, mesmo com a confirmação que o carcinoma da nasofaringe expressa tipicamente um padrão Latência II e o carcinoma gástrico a latência I, observou-se também que alguns casos expressam um perfil de latência diferente. Portanto, há uma necessidade de uma determinação correta da expressão de proteínas do EBV para um conhecimento correto sobre os mecanismos de Cláudia Oliveira | MSc Oncology VI | Epstein-Barr virus latent gene expression in nasopharyngeal and gastric carcinoma transformação. A literatura suporta a necessidade de reestruturação dos padrões de latência, considerando a expressão de todos os tipos de expressão de proteínas. Cláudia Oliveira | MSc Oncology Epstein-Barr virus latent gene expression in nasopharyngeal and gastric carcinoma | VII ABSTRACT EBV is a human cancer-associated virus that infects about 90% of the global population, without causing major symptoms in the majority of lifelong carriers trough the establishment of a viral latent state. EBV infection can adopt four different patterns of latency, named type 0, I, II, and III, which seem to be correlated with the different types of EBV associated disease. Nevertheless, there is some doubt on the differential expression of EBV latent genes in different diseases such as Nasopharyngeal Carcinoma and Gastric Carcinoma. We have performed a retrospective study with 23 NPC and 9 EBVaGC cases, in order to evaluate the expression of EBV proteins in different tumors and try to establish a clinical correlation between the viral latency and the malignances. The identification of EBV was made by EBER-ISH and the detection of EBV proteins (LMP1 and LMP2a) was performed by immunohistochemistry. All cases used in this study were EBV positive LMP1 was present in 95.5% of NPC cases, but in none EBVaGC was shown LMP1 expression. Regarding the LMP2a, it was expressed in 100% of NPC cases, while in GC it was present in 44.4%. The protein expression that each of the tumour presented led to different latency types. In NPC, 21 cases (95.5%), had the expression of both LMP1 and LMP2a, which corresponds to a latency II pattern, and only 1 case (4.5%) expressed a distinct latency pattern similar to latency II, but without the expression of LMP1. In GC, 5 cases (55.5%) had no expression of LMP1 and LMP2a, wich corresponds to a latency I pattern. The remaining 4 cases, had the same latency pattern as one case of NPC were there is expression of LMP2a, but not LMP1. These data confirm the latency patterns associated with NPC (latency II) and with EBVaGC (latency I). We also identified a novel and yet not accepted latency (latency II-like) that is especially important in EBVaGC, characterized by the expression of EBNA1 and LMP2a. This was the first study in Portugal to characterize the latency patterns of EBV in different diseases. In conclusion, even with the confirmation of NPC as typically expressing a Latency II pattern and EBVaGC a latency I, we observed that some cases express a different latency profile. Hence, there is an urge in the correct determination of EBV profile expression for a correct knowledge on the mechanisms of transformation. The literature supports the need for restructuring the latency patterns, considering the expression of all types of protein expression. Cláudia Oliveira | MSc Oncology Epstein-Barr virus latent gene expression in nasopharyngeal and gastric carcinoma | XV INDEX PREFACE _______________________________________________________ I AGRADECIMENTOS ______________________________________________ III RESUMO _______________________________________________________ V ABSTRACT ____________________________________________________ VII ABREVIATIONS LIST _____________________________________________ IX FIGURE LIST ____________________________________________________ XI TABLE LIST ____________________________________________________ XIII INDEX ________________________________________________________ XV I. INTRODUCTION ______________________________________________ 1 1. Epstein-Barr Virus ________________________________________________ 3 1.1. Historical Background__________________________________________________ 3 1.2. EBV Structure and Genome _____________________________________________ 3 1.3. EBV Infection ________________________________________________________ 5 1.4. Viral gene expression __________________________________________________ 6 1.4.1. Lytic genes ______________________________________________________ 6 1.4.1.1. Immediate-Early Lytic Proteins _____________________________________ 6 1.4.1.2. Early Lytic Proteins ______________________________________________ 7 1.4.1.3. Late Lytic Proteins ______________________________________________ 8 1.4.2. Latent genes _____________________________________________________ 8 1.4.2.1 EBV-nuclear antigens _________________________________________ 9 1.4.2.1. Latent membrane proteins ____________________________________ 10 1.4.3. Other transcripts __________________________________________________ 11 2. EBV-Associated Malignancies ______________________________________ 13 2.1. Burkitt’s Lymphoma __________________________________________________ 13 2.2. Hodgkin’s Lymphoma _________________________________________________ 15 2.3. Post-transplant lymphoproliferative disease _______________________________ 16 2.4. Nasopharyngeal Carcinoma ____________________________________________ 17 2.5. Gastric Carcinoma ___________________________________________________ 19 3. EBV Latency ____________________________________________________ 21 3.1. Latency 0 __________________________________________________________ 21 3.2. Latency I ___________________________________________________________ 21 3.3. Latency II __________________________________________________________ 22 3.4. Latency III __________________________________________________________ 22 3.5. Other types of latency_________________________________________________ 22 II. AIMS OF THE STUDY _________________________________________ 25 III. MATERIAL AND METHODS __________________________________ 29 1. Population and Type of study ______________________________________ 29 2. Sample collection and processing ____________________________________ 30 3. EBV detection (EBER-ISH) __________________________________________ 30 4. EBV proteins expression analysis _____________________________________ 32 Cláudia Oliveira | MSc Oncology XVI | Epstein-Barr virus latent gene expression in nasopharyngeal and gastric carcinoma 5. Quality control ____________________________________________________ 33 6. Data analysis ____________________________________________________ 33 IV. RESULTS _________________________________________________ 37 1. EBER-ISH _______________________________________________________ 37 2. Protein expression _______________________________________________ 37 2.1. LMP1 _____________________________________________________________ 37 2.2. LMP2A ____________________________________________________________ 38 3. EBV latency _____________________________________________________ 39 3.1. NPC ______________________________________________________________ 39 3.2. EBVaGC ___________________________________________________________ 39 V. DISCUSSION ______________________________________________ 39 VI. CONCLUSION _____________________________________________ 47 VII. REFERENCES _____________________________________________ 51 VIII. APPENDIX ________________________________________________ 63 I. INTRODUCTION Cláudia Oliveira | MSc Oncology Epstein-Barr virus latent gene expression in nasopharyngeal and gastric carcinoma | 3 1. Epstein-Barr Virus 1.1. Historical Background In 1958, Denis Burkitt identified a frequent cancer among children in Equatorial Africa [1, 2]. This tumour was dependent on climatic and geographical conditions, which led to the possibility that it could be associated with a vector-borne agent [1]. Later, in 1964, Anthony Epstein, Yvonne Barr and Bert Achong using electronic microscopy discovered typical herpesvirus particles in biopsies of the named Burkitt’s Lymphoma (BL), which they have called Epstein-Barr Virus (EBV). In the late 1960s, studies revealed that BL patients had higher antibody titers to EBV antigens [3, 4] These serological assays also allowed the identification of EBV as the etiological agent of infectious mononucleosis (IM) and nasopharyngeal carcinoma (NPC) [5, 6]. 1.2. EBV Structure and Genome EBV also recognized as Human Herpesvirus 4 (HHV4), belongs to the Herpesviridae family, Gammaherpesvirinae subfamily and is the only human virus from the Lymphocryptovirus genus [7]. The virion of EBV is about 120-300 nm in diameter and consists of a toroid shaped protein core wrapped with linear double stranded DNA with approximately 172 kilobase pairs (kb) in an icosahedral nucleocapsid with 162 capsomeres, an outer envelope with external glycoprotein spikes and a tegument protein between the nucleocapsid and envelope (Figure 1) [8-11]. Figure 1: EBV virion structure (adapted from http://viralzone.expasy.org/viralzone/all_by_species/185.html) EBV genome has several terminal repeats (TRs) and internal repeat sequences (IRs) that divide the genome into short and long unique sequence domains (Figure 2) [12]. The EBV genome is linear, but once it reaches the nucleus of the infected cell, it adopts an Cláudia Oliveira | MSc Oncology 4 | Epstein-Barr virus latent gene expression in nasopharyngeal and gastric carcinoma episomal structure through the binding of the TRs, which is required for replication of the viral genome [13]. Only a very small fraction of the EBV genome that enters the cell is able to reach the nucleus and an even smaller fraction is able to circularize. During cellular proliferation, linear viral genomes are gradually lost while circular DNA is maintained [14, 15] Indeed, during latency, EBV DNA acts like the celular DNA, being associated with histones and replicating once during the S phase, depending only on the cellular machinery and being equally transmitted to daughter cells [13]. By gene sequencing of different EBV isolates it was possible to identify two different EBV subtypes, which were classified as type 1 and type 2 (or type A and type B, respectively) [16]. The difference between these two subtypes are mainly on genetic polymorphism in the Epstein Barr Nuclear Antigens (EBNAs), but other single base changes may be observed in other regions of the genome [9, 17-19]. Type 1 is observed in almost all populations, being predominant in Europe, America, South America and Asia; while type 2 is mainly found in Central Africa, New Guinea and in Alaskan Eskimos [20]. The influence of these EBV subtypes in disease development is not yet understood, but type 1 virus seems to prevail in most EBV positive associated diseases, whereas type 2 is mainly associated with immunocompromised patients [21]. Figure 2: Map of EBV genome (Straus, 1993) Cláudia Oliveira | MSc Oncology Epstein-Barr virus latent gene expression in nasopharyngeal and gastric carcinoma | 5 1.3. EBV Infection EBV infection is restricted to humans, and is transmitted almost exclusively by saliva [5]. The primary infection usually occurs early in life and the family is frequently responsible for the transmission, although in developed countries this infection can be delayed until adolescence or adulthood and here it can lead to the development of a strong immune response medically known as IM [5, 22, 23]. After controlled, the infection is asymptomatic due to the establishment of a viral latency within the memory B lymphocytes [24]. In fact, EBV establishes a persistent lifelong infection, in most cases without consequences, in more than 90% of the world population [25, 26]. It is assumed that the primary infection occurs in the oropharynx, due to the interaction of the viral membrane glycoprotein gp85/42, with a Major histocompatibility complex (MHC) class II receptor on the surface of lymphoepithelial cells of the Waldeyer's ring [27]. Subsequently, EBV starts a short period of lytic replication, after which it is released into the saliva and infects adjacent epithelial cells (Figure 3) [27]. Figure 3: Interactions between Epstein–Barr virus and host cells (Young, 2004) Cláudia Oliveira | MSc Oncology 6 | Epstein-Barr virus latent gene expression in nasopharyngeal and gastric carcinoma Then, after the infection of epithelial cells in the oropharynx, EBV infects immature B lymphocytes that are nearby, process only possible due to the binding of EVB's membrane glycoprotein gp350 / 220 with the CD21 molecule of B lymphocytes [28]. The infected Blymphocytes will be transformed into lymphoblastoid cells with latent EBV, proliferating without control. Many of these proliferating cells are killed by cytotoxic T-lymphocyte response, nevertheless some escape through downregulation of antigen expression and the establishment of a stable reservoir of memory B lymphocytes where viral antigen expression is almost nonexistent [29]. 1.4. Viral gene expression As all other herpesviruses, EBV has a life cycle with different viral gene expression programs: a latent one, on which no viral particles are formed; and a lytic one, on which new infectious viruses are produced [16]. There are more than 90 viral proteins coded by the EBV genome and the great majority has no known function [30]. 1.4.1. Lytic genes EBV establishes a latent persistent lifelong infection in most cases, nevertheless, for reasons not yet understood, the virus can reactivate and restart its lytic cycle in specific conditions [24]. By analogy with other herpesviruses, the proteins expressed in this phase are classified as immediate-early, early, and late lytic proteins: Immediate-early genes are transcribed after infection in the presence of protein synthesis inhibitors; Early genes are expressed in the presence of viral DNA synthesis inhibitors; and late genes are not transcribed when these inhibitors are present. EBV lytic genes are named by BamHI fragment within which they are located, whether they are expressed in a leftward (L) or rightward direction (R), and the number of their position in the BamHI fragment. For example, BZLF1 is the first transcript expressed in the leftward direction in the BamHI Z fragment of EBV (Figure 4) [31]. 1.4.1.1. Immediate-Early Lytic Proteins Immediate-early genes are important for regulating gene expression in the virus. The major immediate-early proteins of EBV are encoded by BZLF1 and BRLF1, also named by Z Epstein–Barr replication activator (ZEBRA) or Zta and Rta, respectively. BZLF1 and BRLF1 proteins activate transcription of viral early genes [32, 33]. BZLF1 protein inhibits transcription from the EBNA Cp promoter and may facilitate the switch from latent to lytic Cláudia Oliveira | MSc Oncology Epstein-Barr virus latent gene expression in nasopharyngeal and gastric carcinoma | 7 infection [34]. BZLF1 protein also downregulates the interferon gamma receptor and inhibits the ability of interferon gamma to activate its target genes including IRF-1, CIITA, and MHC class II [31]. Figure 4: EBV lytic cycle activation 1.4.1.2. Early Lytic Proteins EBV early lytic proteins include enzymes that are important for viral DNA replication, inhibition of apoptosis, and activation of gene expression. Six viral proteins have been identified as replication proteins originated by the lytic origin of replication (ori-lyt) [35]. These replication proteins are the viral DNA polymerase, encoded by BALF5, the DNA polymerase processivity factor, encoded by BMRF1, the single-stranded DNA-binding protein homolog, encoded by BALF2, the primase homolog, encoded by BSLF1, the helicase homolog, encoded by BBLF4, and the helicase-primase homolog, encoded by BBLF2/3. The viral thymidine kinase, encoded by BXLF1, phosphorylates acyclovir and results in activation of the drug with inhibition of the viral DNA polymerase and viral DNA replication0 [35]. Other early viral proteins important for viral DNA replication are the ribonucleotide reductase proteins encoded by BORF2 and BARF1 and the uracil DNA glycosylase encoded by BKRF3 [35]. Cláudia Oliveira | MSc Oncology 14 | Epstein-Barr virus latent gene expression in nasopharyngeal and gastric carcinoma There are several forms of BL according to its geographic distribution, incidence magnitude and risk factors (Table 1). BL is a B-cell lymphoma genetically characterized by a chromosomal translocation that results in deregulation of the c-MYC oncogene [133]. Characteristics Endemic BL Sporadic BL HIV associated BL Epidemiology Equatorial Median age 7 yrs Associated with malaria/Climate Median age 30yrs Children (30%) Older adults (1%) Low Socio Economical Status HIV risk groups Median age 10-19 yrs Clinical Presentation Facial skeleton (50%), Central Nervous System (33%), other organs Abdominal, ileo-coecal (80%) Bone marrow (20%) Other organs also affected Organ and nodal presentation Pathology/Morphology Germinal centre B-cell Chromosomal translocations Monomorphic medium sized B cells with basophilic cytoplasm and multiple mitotic figures EBV association 95-100% 30% 30-50% Endemic BL (eBL) is the disease originally described by Burkitt and 95% of the cases are found in equatorial Africa (Figure 6), characteristically affecting the facial skeleton in children between ages two to nine [134]. Sporadic Burkitt’s lymphoma (sBL) is the form usually described outside the endemic region and accounts for 1–2% of adult lymphoma in Western Europe and America. It is morphologically similar to eBL but affects mainly abdominal viscera. sBL can be detected at any age and no specific co-factor has been described [134]. A third subtype of BL has been proposed based on its association with the human immunodeficiency virus (HIV) infection. Though well described in the developed world and known among HIV positive adults in Africa, the childhood form of the disease among HIV positive children has not been well characterized [132]. Table 1: Overview of Burkitt’s lymphoma clinical variants. Figure 6: Map of Africa showing the 'lymphoma belt' in which eBL occurs at high incidence. Cláudia Oliveira | MSc Oncology Epstein-Barr virus latent gene expression in nasopharyngeal and gastric carcinoma | 15 BL has a very close association with EBV, with approximately 95% of eBL showing the presence of the EBV genome in their tumour cells, while the other form are associated with EBV in 30-50% of all cases [135]. EBV plays a role in the pathogenesis of BL by deregulation of c-MYC activity and clonal expansion, direct mutagenesis and immune inactivation. Indeed, EBV is known to transform resting B cells into latently infected lymphoblastoid cells [132]. The majority of BL’s, show EBV latency I pattern. This cells carry a wild-type EBV genome and express only EBNA1 from the latent promoter Qp [136]. However, around 15% of endemic tumours, carry an EBNA2 gene-deleted genome and express EBNA1, -3A, -3B, and -3C from the Wp latent promoter [137]. 2.2. Hodgkin’s Lymphoma Hodgkin lymphoma (HL) was first discribed it in 1832 by Doctor Thomas Hodgkin. HL is rare type of cancer, being only diagnosed 66,000 new cases of Hodgkin lymphoma worldwide in 2012, accounting to 0.5% of total cancer cases. HL has a global spread, being more common in Asia and Europe (Figure 7) [138] HL is characterized by the presence of malignant multinucleated Reed Sternberg cells in a background of reactive inflammatory cells [13]. HL exists in five forms: mixed-cellularity, nodular-sclerosis, lymphocyterich, lymphocyte-depleted and lymphocyte-predominant (LPHL) subtypes. LPHL is the only one not associated with EBV [13]. HL presentation can be very different, since, it can appear in all lymphoid nodes in the body (Figure 8). The most common place for Hodgkin lymphoma is in the lymph nodes in the neck, and >50% of diagnosis are at stage I or II (Appendix II) [139]. Figure 7: Hodgkin Lymphoma incidence worldwide, both sexes, all ages, Globocan 2012 Cláudia Oliveira | MSc Oncology 16 | Epstein-Barr virus latent gene expression in nasopharyngeal and gastric carcinoma Studies suggest that 40% of HL cases, are associated with EBV. In these EBV infection exhibits a type II form of latency, being limited to the EBERs, EBNA1, LMP1, LMP2, and BARTs [140]. 2.3. Post-transplant lymphoproliferative disease Post-transplant lymphoproliferative disease (PTLD) is a well-recognized complication of both solid organ transplantation and allogeneic hematopoietic stem cell transplantation [13]. This terms is used to describe lymphoproliferations, that are not always monoclonal and whose morphologic features often differ from those of lymphomas [141]. PTLD are the second most frequent neoplasia in transplant patients, and its incidence varies depending on the organ transplanted, and ranges from 0.5% in adult kidney or liver recipients to more than 10% in lung, intestinal recipients or pediatric transplant patients (table 2) [142]. Organ Recipient Age 1 year (%) 3 years (%) 5 years (%) >5 years (%) Kidney Adulta) 0.46 0.87 1.18 ND Pediatric a) 1.73 2.45 ND ND Liver Adult a) 1.1 3 4 4.7 Pediatric a) ND ND 6 ND Heart Adult b) 0.67 ND 1.3 2.0 Pediatric b) 1.7 ND 4.6 7.9 Lung Adult b) 1.6 ND 2.1 5.6 Pediatric b) 4.8 ND 11.1 10.3 *NDNot Described; a) ISHLT 2008; b) French PTLD registry Table 2: Reported incidence of PTLD by organ system and recipient age Figure 8: Hodgkin Lymphoma body locations, from cancer research UK Cláudia Oliveira | MSc Oncology Epstein-Barr virus latent gene expression in nasopharyngeal and gastric carcinoma | 17 Literature suggest that EBV infection has a major pathogenic role in PTLDs, infecting 60%-80% of PTLD patients, including 100% of early-onset PTLD patients [28]. Up to 2/3 of PTLD cases are associated with EBV infection of B cells, either because of reactivation of the virus or from primary EBV infection [13, 102]. Recipients who are EBV seronegative have a higher risk of developing EBV-induced lymphoma, particularly pediatric patients [143, 144]. Literature suggest that EBV infection has a major pathogenic role in PTLDs, infecting 60%-80% of PTLD patients, including 100% of early-onset PTLD patients [28]. In most cases of PTLD, tumour cells express the latency III pattern, with some cells undergoing lytic replication [145]. However, there is variability between individuals once latency type I and II patterns have also been detected in PTLD biopsies. In these cases additional genetic or epigenetic changes are probably required for tumour outgrowth [146, 147]. 2.4. Nasopharyngeal Carcinoma NPC is a rare type of head and neck cancer that affects the upper part of oropharynx, the nasopharynx (Figure 9) [139]. NPC has been reported in almost all parts of the world, however, most cases are found in South East Asia, Southern China, North Africa and in the Eskimo population of Alaska (Figure 10) [148-150]. In 2012 it was reported 87 000 new cases of NPC at a global level, corresponding to 0.6% of all cases of cancer [138]. Because the nasopharynx is a deep-seated structure and the nasal and aural symptoms are nonspecific, a large portion of patients with NPC are only diagnosed when the tumour has reached advanced stages, III and IV (Appendix II) [139]. Figure 9: Nasopharynx location from cancer research UK Cláudia Oliveira | MSc Oncology 18 | Epstein-Barr virus latent gene expression in nasopharyngeal and gastric carcinoma Taking into account 2003 WHO classification NPC can be divided in three main types: keratinizing squamous cell carcinoma, non-keratinizing carcinoma, which can be divided diferentiated and undifferentiated, finally in basaloid squamous cell carcinoma respectively [151, 152]. NPC as several risk factors, such as EBV infection and classic head and neck aetiological factors including alcohol and tobacco [153]. Even though here is no doubt that NPC has a definite association with EBV, it is still not clear the specific pathogenic mechanism by which EBV causes NPC. A gap in the explanation of the EBV pathogenesis in the tumour is the fact that mature nasopharyngeal cells are not usually infected with EBV, though tumours have been shown to be infected before transformation [154]. It has been shown that the immature epithelial cells carry CD21 and can be infected by the virus. It is therefore postulated that EBV infects nasopharyngeal cells that have been stimulated by other environmental factors [155-157]. It appears that latency gene expression in NPC is intermediate between what is seen in latency I and latency II. The expression of EBNA1 and the EBERs are present in all EBVpositive NPC cases [158, 159]. It also appears that LMP2A can be detected in about 50% of NPC [160, 161]. In other hand, LMP1 is identified readily in only 35% of cases. LMP1 has been identified in all pre invasive lesions, suggesting that its expression is necessary in early lesions but may not be as essential in established carcinomas [162]. Figure 10: Nasopharyngeal carcinoma incidence worldwide, both sexes, all ages, Globocan 2012 Cláudia Oliveira | MSc Oncology Epstein-Barr virus latent gene expression in nasopharyngeal and gastric carcinoma | 19 2.5. Gastric Carcinoma GC is the sixth most common malignancy in both sexes worldwide with 952.000 new cases estimated in 2012, corresponding to 6.8% of all cases of cancer [138]. The incidence rates are almost twice higher in male (8.5%) than in female (4.8%) with about 631.000 and 320.000 new cases per year, respectively [138]. More than 70% of total cases occur in developing regions like Eastern Asia, Eastern Europe and Latin America. In contrast, the lowest incidence rates are observed in United States, Australia and some North European countries (figure 11) [138]. Adenocarcinomas are about 95% of all GC and the other cases include: Squamous cells cancers; lymphoma; gastrointestinal stromal tumours (GIST); and neuroendocrine tumours (NET). Histologically, GC can be classified by two different classifications, World Health Organization (WHO) and Lauren (Table 3) [163, 164] Table 3: Comparison of Lauren’s and WHO classification systems [153,154] WHO (2010) Lauren (1965) Papillary adenocarcinoma Intestinal Type Tubular adenocarcinoma Mucinous adenocarcinoma Signet-ring cell carcinoma Diffuse Type Poorly cohesive carcinoma Mixed carcinoma Indeterminate Uncommon variants - Figure 11: Gastric cancer incidence worldwide, both sexes, all ages, Globocan 2012 Cláudia Oliveira | MSc Oncology 20 | Epstein-Barr virus latent gene expression in nasopharyngeal and gastric carcinoma Anatomically, GC is divided into proximal and distal tumours depending on their localization of stomach. Proximal tumours are found in cardia region whereas distal carcinomas are often located in the antrum/pyloric region (Figure 12). Gastric carcinogenesis is a multistep process, where different factors are involved, including EBV [165]. EBV-positive GC is present in 10% of all GCs [166, 167]. EBV infection has been detected in different types of gastric cancer: gastric adenocarcinomas and lymphoepithelioma-like gastric carcinomas (LELC) [168]. LELC represents about 4% of all gastric carcinomas and more than approximately 80% of cases have EBV-infected cells [168]. Actually, scientific community is still debating the role of EBV infection on gastric carcinoma, and recent studies have suggested that EBVaGC is a distinct subgroup of gastric cancers with specific molecular features [169, 170]. The evidence for involvement of EBV in gastric carcinoma is based on the specific presence of viral gene products such as EBERs in tumour cells but not in the surrounding non-neoplastic epithelium [171], the presence of clonal EBV in tumour cells [172] and elevated EBV antibodies in prediagnostic sera of patients with EBV-associated gastric carcinoma [173]. EBVaGC has typically a latency I pattern in which only EBNA1, EBERs and BARTs are expressed. Even though, in some cases it can also express a small amount of LMP2A, while LMP1 is rarely expressed in EBVaGC. In these cases, the genes expressed do not correspond to any classification of latency patterns described in the literature [167]. Figure 12: Illustrative scheme of the stomach regions from cancer research UK Cláudia Oliveira | MSc Oncology Epstein-Barr virus latent gene expression in nasopharyngeal and gastric carcinoma | 21 3. EBV Latency EBV infection can adopt mainly four different programs of latency, named type 0, I, II, and III latency (table 4) (Figure 13) [106]. The different latency programs adopted, are dependent on several cell-specific factors such as epigenetic events, which include DNA methylation, histone modifications and chromatin organization. EBV latency within B cells usually progresses from Latency III to Latency II to Latency I. [174, 175]. Moreover, latency programs have also been shown to correlate with the type of EBV associated disease, and they impose different phenotypic and functional properties on the viral genome carrying B cell [176, 177]. Table 4: EBV gene latency programmes Latency type Transcripts EBV-associated disease EBERS EBNA1 EBNA2 EBNA3 FAMILY EBNALP LMP1 LMP2 Latency 0 + - - - - - - Memory B cells in healthy individuals Latency I + + - - - - - Burkitt lymphoma, Gastric Carcinoma Latency II + + - - - + + Hodgkin lymphoma, Nasopharyngeal Carcinoma Latency III + + + + + + + Post-transplant lymphoproliferative disease 3.1. Latency 0 Although EBV-infected proliferating B cells are eliminated by cytotoxic T cells in vivo, the virus is not totally eliminated from the body. Instead, EBV is able to establish in vivo latency, called latency 0 in memory B cells [2]. The switch from proliferation to latency 0 in memory B cells is still poorly understood. In this type of latency no viral gene expression is found [178]. 3.2. Latency I In type I latency only EBNA1 is expressed from the Qp promoter, while all the other latency-associated promoters remain silent [137]. Although the mechanism behind the switch in promoters is not completely understood, the repression of the Cp promoter during this period seems to be related to DNA methylation [174]. During type I latency, transcription of the viral transcripts EBERs and BARTs has also been described [30]. This type of latency is mainly associated with BL and GC. Cláudia Oliveira | MSc Oncology 22 | Epstein-Barr virus latent gene expression in nasopharyngeal and gastric carcinoma 3.3. Latency II Another main type of latency, type II, is characterized by the expression of the following viral genes: EBNA1, LMP1 and LMP2, EBERs and BARTs. This type of expression was first detected in NPC in epithelial cells [179]. This type of latency can also be found in EBV positive Reed/Sternberg cells of HL of B cell origin [140, 180]. 3.4. Latency III Type latency III expresses all latent genes and can be found in PTLD. The EBV’s role in cell growth is most evident in latency III, as EBNA2, EBNALP, EBNA3A and EBNA3C coordinately upregulate cMyc expression and cell proliferation, and EBV LMP1 enhances cell survival [76, 84, 181-184]. 3.5. Other types of latency Additionally to these thoroughly studied three latency programs, other types of EBV latency have also been described such as, a pattern which is found in some gastric and nasopharyngeal carcinomas in which EBNA1 and LMP2A are the only genes detected. This pattern is is described by the majority of authors as latency II-like, however, in some studies focused on only NPC the denomination latency IIb is also found [167, 185-189]. In a group of BL tumours, another pattern of latent gene expression has been described in which the expression of EBNA1, -3A, -3B, -3C and truncated EBNALP is observed, but not the expression of EBNA2 or LMPs. Since this latency program was found to be associated with the exclusive transcription from the Wp promoter, it was therefore called "Wp-restricted latency"[137, 190]. Another type of latency named latency IIb which lacks LMP1 but expresses EBNA2, was first seen in B-Chronic Lymphocytic Leukemia (B-CLL) cells infected with EBV in vitro [191]. Figure 13: EBV cycle and latent states (Thorley-Lawson, 2008) II. AIMS OF THE STUDY Cláudia Oliveira | MSc Oncology 30 | Epstein-Barr virus latent gene expression in nasopharyngeal and gastric carcinoma The group of EBVaGC cases, included 9 cases that were diagnosed in 2011, and it consisted of 7 males and 2 females with median age of 69 years old (Table 6). 2. Sample collection and processing Tumour tissues were collected from the institution archives and histological sections (3 µm slides) were obtained from formalin-fixed paraffin-embedded (FFPE) tissue blocks. 3. EBV detection (EBER-ISH) Tissue samples were dewaxed in xylene for 2 x 3 minutes. After dewaxing, slides were sequentially hydrated in 100% v/v ethanol for 2 x 3 minutes, 96% v/v ethanol for 3 minutes and distilled water for 2 x 3 minutes. Proteolytic treatment was performed by addition of 10 Variable Gender n(%) Male 7 (77.8) Female 2 (22.2) Age Median 69 ± 10,994 Minimum 52 Maximum 82 Surgical Procedure n(%) Subtotal Gastrectomy 2 (22.2) Total Gastrectomy 7 (78.8) Histology n(%) WHO 2010 Mixed Adenocarcinoma 2 (22.2) Tubular Adenocarcinoma 5 (55.6) Carcinoma with lymphoid stroma 2 (22.2) Lauren (1965) Intestinal types 5 (55.6) Indeterminate types 2 (22.2) lymphoepithelioma-like carcinoma 2 (22.2) Invasion pattern n(%) Expansive 6 (33.3) Infiltrative 3 (67.7) Table 6: Characterization of gastric carcinoma cases Cláudia Oliveira | MSc Oncology Epstein-Barr virus latent gene expression in nasopharyngeal and gastric carcinoma | 31 mM proteinase K and incubation at 37ºC during 30 minutes. Finished the incubation time, endogenous peroxidase activity was blocked by incubating the slides in 3% hydrogen peroxide (H2O2) for 10 minutes at room temperature, then solution the slides were immersed in distilled water for 2 x 3 minutes and then dehydrated in 96% v/v ethanol followed 100% v/v ethanol for 3 minutes to facilitate air drying. Epstein-Barr virus was identified by in situ hybridization (ISH) for detection of EBVencoded small RNA (EBER). Hybridization results in duplex formation of sequence present in EBV infected cells (EBERs) and specific probe. The BondTM Ready-to-use ISH EBER Probe (Leica, Newcastle upon Tyne, UK) was used with a volume of 20 µl for each slide. Slides were covered with coverslip, and then incubated at 37ºC for 2 hours. Nonspecific antibody binding was block using UltraVision Large Volume Detection System AntiPolyvalent, HRP (THERMO SCIENTIFIC, Fremont, USA). It was incubated for 10 minutes at room temperature and washing was performed with TBS, 0.1% v/v Trinton X-100 (TBST) 2x 5 minutes. EBERs detection was performed with BondTM Anti-Fluorescein Antibody (Leica, Newcastle upon Tyne, UK) diluted 1:150 in TBS, 3% m/v BSA, 0.1% v/v Trinton X-100 with incubation at room temperature for 30 minutes. After washing 2 x 3 minutes with TBS, the revelation of hybrids was performed with the UltraVision Large Volume Detection System Anti-Polyvalent, HRP (THERMO SCIENTIFIC, Fremont, USA). Briefly, the Biotinylated Goat Anti-Polyvalent Antibody (THERMO SCIENTIFIC, Fremont, USA) was added at room temperature for 10 minutes, washed with TBS-T 2 x 5 minutes followed by the addition of Streptavidin Peroxidase (THERMO SCIENTIFIC, Fremont, USA) with incubation for 10 minutes at room temperature. Streptavidin shows high affinity with several secondary antibody-conjugated biotin molecules providing a good revelation signal. Detection of hybrids is achieved by enzymatic reaction using a specific substrate to peroxidase. ImmPACTTM DAB, Peroxidase Substrate (VECTOR, Burlingame, CA USA) was used during 4 minutes at room temperature and diluted 3:100. The final washing was performed with distillated water 2 x 5 minutes. Mayer’s hemalum solution (Millipore, Darmstadt, Germany) was used as counterstain for 10-20 seconds, depending of dye’s use. After coloration, slides were washed in running water for 5 minutes and the following step was sequential dehydration in 70% v/v ethanol for 2 x 4 minutes, 96% v/v ethanol for 2 x 4 minutes, 100% v/v ethanol for 2 x 4 minutes and xylene for 2 x 4 minutes. Mounting was performed with Microscopy Entellan (MERCK, Darmstadt, Germany). Cláudia Oliveira | MSc Oncology 32 | Epstein-Barr virus latent gene expression in nasopharyngeal and gastric carcinoma 4. EBV proteins expression analysis Epstein-Barr virus latent proteins were identified by immunohistochemistry (IHC) technique, which detects them in FFPE tissue, blocks using specific antibodies for each protein (table 7). IHC is a method for localizing specific antigens in FFPE tissues based on antigen–antibody interaction. The technique is widely used in dermatologic diagnostics and research, and its applications continue to be extended because of its ease of use, reliability, and versatility. In IHC an antigen–antibody construct is visualized through light microscopy by means of a colour signal. Protein Primary Antibody Dilution Incubation Positive expression in carcinoma cells LMP1 NCL-EBV-CS1-4, Leica, Newcastle upon Tyne, UK 1:100 3h, room temperature Cytoplasm LMP2A 15F9, THERMO SCIENTIFIC, Fremont, USA 1:250 Overnight, 4ºC Cytoplasm and membrane Tissue samples were dewaxed in xylene for 2 x 4 minutes. After dewaxing, slides were sequentially hydrated in 100% v/v ethanol for 2 x 4 minutes, 96% v/v ethanol for 2x4 minutes; 70% v/v ethanol for 4 minutes and water for 5 minutes. Antigen retrieval was performed using a heat induced epitope retrieval method, where the slides were submersed a citrate-based antigen unmasking solution (VECTOR, Burlingame, CA USA) and heated in the microwave for 15 minutes at medium power. Slides were allowed to cold down to room temperature, rinsed in the unmasking solution for almost 20 minutes and then washed in Tris-buffer saline containing 0.02% Tween 20 (TBS-T), and the endogenous peroxidase was blocked with 3% hydrogen peroxide (H2O2) for 10 minutes. Subsequently, the slides were washed in TBS-T 2x 5 minutes, treated with UV-block solution from UltraVision Large Volume Detection System Anti-Polyvalent, HRP (THERMO SCIENTIFIC, Fremont, USA) for 10 minutes, to block nonspecific protein binding and incubated with the specific EBV latent protein antibodies (the specific conditions of each antibody are described in table 6). After being rinsed in TBS-T, Biotinylated Goat Anti-Polyvalent Antibody (THERMO SCIENTIFIC, Fremont, USA) was added and incubated in a humid chamber at room temperature for 10 minutes. The next step was washing with TBS-T 2 x 5 minutes following the addition of Streptavidin Peroxidase (THERMO SCIENTIFIC, Fremont, USA) with Table 7: Antibodies and conditions used for the detection of different EBV proteins Cláudia Oliveira | MSc Oncology Epstein-Barr virus latent gene expression in nasopharyngeal and gastric carcinoma | 33 incubation for 10 minutes at room temperature. Detection of hybrids is achieved by enzymatic reaction using a specific substrate to peroxidase, 3, 3'-diaminobenzidine (DAB) ImmPACTTM DAB (VECTOR, Burlingame, CA USA) was used during 4 minutes at room temperature and diluted 3:100. The final washing was performed with water 2 x 5 minutes. Mayer’s hemalum solution (Millipore, Darmstadt, Germany) was used as counterstain for 10-30 seconds, depending of dye’s use. After coloration, slides were washed in running water for 5 minutes and the following step was sequential dehydration in 70% v/v ethanol for 4 minutes, 96% v/v ethanol for 2 x 4 minutes, 100% v/v ethanol for 2 x 4 minutes and xylene for 2 x 4 minutes. Mounting was performed with Microscopy Entellan (MERCK, Darmstadt, Germany). 5. Quality control Positive and negative tissues controls were used in order to ensure the quality of the protocol. As a positive control for EBV proteins, PTLD FFPE tissue samples were used, once this malignancy expresses all EBV proteins. As for negative control, it was used GC or NPC FFPE tissue samples that lacked the specific antigen. 6. Data analysis The clinicopathological characteristics of the tumour were compared to the expression of EBV latency proteins and consequently to the EBV latency pattern in GC and NPC pacients. IV. RESULTS Cláudia Oliveira | MSc Oncology Epstein-Barr virus latent gene expression in nasopharyngeal and gastric carcinoma | 37 1. EBER-ISH In all 9 cases of GC and 23 cases of NPC included in this study, a reconfirmation of the presence of EBV was preformed using the EBER-ISH technique. Of the 23 EBV positive NPC cases, a case has shown to have insufficient tumour tissue for performing the remaining tests and therefore, this case is going to be excluded from other tests, in this manner NPC cases were reduced to 22. In figure 14 it is represented the results of EBERISH in tumor samples. Figure 14: EBER-ISH Results A) GC EBV positive; B) NPC EBV positive; C) Negative control 2. Protein expression 2.1. LMP1 None of the cases of GC showed to be positive for LMP1. As for NPC, 21 (95.5%) of the examined cases have showed to be positive for LMP1 (Figure 15). In figure 16 it is represented LPM1 immunohistochemestry results in tumour samples. Negative 100% GC Positive Negative Positive 95,5% Negative 4,5% NPC Positive Negative Figure 15: LMP1 results Cláudia Oliveira | MSc Oncology 38 | Epstein-Barr virus latent gene expression in nasopharyngeal and gastric carcinoma Figure 16: IHC LMP1 results A) GC case negative for LMP1; B) NPC case positive for LMP1; C) NPC case negative for LMP1; D) Positive Control; E) Negative control 2.2. LMP2A Of all cases of GC, only 4 proved to be positive for LMP2a. As for NPC, all 22 cases examined proved to be positive for LMP2a (Figure 17). In figure 18 it is represented LPM1 immunohistochemestry results in tumour samples. Positive 44,4% Negative 55,6% GC Positive Negative Positive 100% NPC Positive Negative Figure 17: LMP2a results Cláudia Oliveira | MSc Oncology Epstein-Barr virus latent gene expression in nasopharyngeal and gastric carcinoma | 39 Figure 18: IHC LMP2a results A) GC case positive for LMP2a; B) GC case negative for LMP2a; C) NPC case positive for LMP2a; D) Positive control; E) Negative control 3. EBV latency Assuming that EBNA1 is expressed in all EBV associated tumours, it was given to each of the cases used in this study an EBV latency pattern based on the expression of LMP1 and LMP2a. 3.1. NPC Table 8 describes the principal baseline characteristics of each NPC case used in this study, including sex, age, histological type and expressed proteins. The majority of cases, 21 (95.5%), had the expression of both LMP1 and LMP2a, which corresponds to a latency II pattern. Only 1 case (4.5%) expressed a distinct latency pattern similar to latency II, but without the expression of LMP1. This pattern is going to be referred as “latency IIlike”. 3.2. EBVaGC Table 9 describes the principal baseline characteristics of each EBVaGC case used in this study, including sex, age, tumour location, histological type and expressed proteins. From all 9 cases of GC, 5 (55.6%) had no expression of LMP1 and LMP2a. In these, a latency I pattern is observed. The remaining 4 cases, had the expression of LMP2a, but not LMP1. These cases presented a “latency II-like” pattern. VI. CONCLUSION Cláudia Oliveira | MSc Oncology Epstein-Barr virus latent gene expression in nasopharyngeal and gastric carcinoma | 49 EBV infection can adopt different patterns of latency, and these have a close correlation with the different types of EBV associated diseases. With this study it was possible to confirm that in our population, NPC is characterized by a latency II pattern, while EBVaGC shows a latency I pattern. We were also able to identify a novel, and yet not accepted, latency pattern associated mainly associated with EBVaGC, but also described in one case of NPC. We described that latency pattern as latency II-like, and it is characterized by the expression of EBNA1 and LMP2a. This is the first study regarding latency patterns of NPC and EBVaGC in Portugal and further studies are required to confirm these evidences, especially with more cases and ideally from different regions of Portugal. It also important to increase the panel of proteins studied so we can correctly describe the different latency patterns, and in order to better understand the role of each protein in tumour carcinogenesis, functional assays would also be important. VII. REFERENCES Cláudia Oliveira | MSc Oncology Epstein-Barr virus latent gene expression in nasopharyngeal and gastric carcinoma | 53 1. Burkitt, D., Determining the climatic limitations of a children's cancer common in Africa. 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APPENDIX Cláudia Oliveira | MSc Oncology Epstein-Barr virus latent gene expression in nasopharyngeal and gastric carcinoma | 65 Appendix I Cláudia Oliveira | MSc Oncology Epstein-Barr virus latent gene expression in nasopharyngeal and gastric carcinoma | 67 Appendix II Apendix II – Sistematic review flow Diagram PRISMA 2009 Flow Diagram Records identified through database searching (n =233) Screening Included Eligibility Identification Additional records identified through other sources (n =0) Records after duplicates removed (n =0) Records screened (n =233) Full-text articles assessed for eligibility (n =56) Full-text articles excluded (n =31)  Do not evaluate the expression of EBV proteins (n=14)  In vitro studies (n=3)  Articles in Chinese (n=4)  Case report (n=1)  No access to full-text (n=5)  Replicated data (n=3)  Related to MALT lymphoma (n=1)   Studies included in qualitative synthesis (n = 25) Records excluded (n =177)  Do not evaluate the expression of EBV proteins (n=36)  In vitro studies (n=48)  Not related with gastric cancer (n=39)  Review (n=54)