Latent Nuclear Antigen Research Articles

Nuclear respiratory factor 1 promotes the progression of EBV-associated gastric cancer and maintains EBV latent infection.

This study aimed to investigate the association of Epstein-Barr virus (EBV) with nuclear respiratory factor 1 (NRF1) and the biological function of NRF1 in EBV-associated gastric cancer (EBVaGC). Western blot and qRT-PCR were used to assess the effect of latent membrane protein 2A (LMP2A) on NRF1 expression after transfection with LMP2A plasmid or siLMP2A. The effects of NRF1 on the migration and apoptosis ability of GC cells were investigated by transwell assay and flow cytometry apoptosis analysis in vitro, respectively. In addition, we determined the regulatory role of NRF1 in EBV latent infection by western blot and droplet digital PCR (ddPCR). LMP2A upregulated NRF1 expression by activating the NF-κB pathway. Moreover, NRF1 upregulated the expression of N-Cadherin and ZEB1 to promote cell migration. NRF1 promoted the expression of Bcl-2 to increase the anti-apoptotic ability of cells. In addition, NRF1 maintained latent infection of EBV by promoting the expression of the latent protein Epstein-Barr nuclear antigen 1 (EBNA1) and inhibiting the expression of the lytic proteins. Our data indicated the role of NRF1 in EBVaGC progression and the maintenance of EBV latent infection. This provided a new theoretical basis for further NRF1-based anti-cancer therapy.

EBNA2-EBF1 complexes promote MYC expression and metabolic processes driving S-phase progression of Epstein-Barr virus–infected B cells

Epstein-Barr virus (EBV) is a human tumor virus which preferentially infects resting human B cells. Upon infection invitro, EBV activates and immortalizes these cells. The viral latent protein EBV nuclear antigen 2 (EBNA2) is essential for B cell activation and immortalization; it targets and binds the cellular and ubiquitously expressed DNA-binding protein CBF1, thereby transactivating a plethora of viral and cellular genes. In addition, EBNA2 uses its N-terminal dimerization (END) domain to bind early B cell factor 1 (EBF1), a pioneer transcription factor specifying the B cell lineage. We found that EBNA2 exploits EBF1 to support key metabolic processes and to foster cell cycle progression of infected B cells in their first cell cycles upon activation. The α1-helix within the END domain was found to promote EBF1 binding. EBV mutants lacking the α1-helix in EBNA2 can infect and activate B cells efficiently, but activated cells fail to complete the early S phase of their initial cell cycle. Expression of MYC, target genes of MYC and E2F, as well as multiple metabolic processes linked to cell cycle progression are impaired in EBVΔα1-infected B cells. Our findings indicate that EBF1 controls B cell activation via EBNA2 and, thus, has a critical role in regulating the cell cycle of EBV-infected B cells. This is a function of EBF1 going beyond its well-known contribution to B cell lineage specification.

CASE REPORT OF AN EPITHELIOID VARIANT OF KAPOSI SARCOMA: A RARE MIMIC OF ANGIOSARCOMA

Cutaneous Kaposi sarcoma (KS) is a vascular neoplasm with a broad spectrumclinicopathology. An epithelioid morphology, a rare recent variant of KS, with many variants of KS that may mimic other vascular neoplasms poses a diagnostic challenge. We report on a 75-year-old Saudi man HIV- negative who had been diagnosed with classical KS on the right foot 8 years before the present episode. Histopathological findings of the new lesion included areas showing epithelioid cells with moderate pleomorphism, growing in solid sheets. The epithelioid cells show nuclear enlargement and hyperchromasia mimicking angiosarcoma. Immunohistochemistry shows a strong diffuse nuclear staining pattern for HHV-8 latent nuclear antigen-1 (LNA-1) in the epithelioid as well as the classical spindle cells. A diagnosis of epithelioid Kaposi sarcoma is made, which should be included within the known histological variants of KS. Prior to this case, the epithelioid variant of Kaposi sarcoma has been reported only three times in the literature. Since this variant shares similar clinical and histological features with angiosarcoma, integration of clinical findings and context, histopathologic features and immunohistochemical results is critical in obtaining the correct diagnosis and treatment.

Rate of Epstein-Barr Virus in Gastric Adenocarcinoma in Egyptian Patients in View of the WHO Classification and Correlation with p16 Immunoreactivity

BACKGROUND AND AIM: Gastric cancer (GC) is one of the top causes of cancer-related deaths worldwide. According to the Cancer Genome Atlas, there are four subtypes of GC, with the Epstein-Barr virus (EBV) subtype accounting for about 10% of cases. EBV infection causes EBV-associated GC (EBVaGC). The previous research suggested that the presence of the EBV viral genome in gastric carcinomas could be used as a surrogate marker for targeted therapy and optimal GC treatment. AIM: We aimed to explore the rate of EBV involvement in gastric carcinogenesis from molecular perspective view and to evaluate the role of the tumor-suppressor protein p16 as a marker for diagnosis in GC Egyptian patients in relation to EBV infection. METHODS: One hundred-four surgically resected GC cases were analyzed. Two methods including quantitative real-time polymerase chain reaction (qPCR) for detecting EBV-derived latent membrane protein-1 (LMP-1) and Epstein-Barr nuclear antigen-1 (EBNA-1) genes as well as immunohistochemistry (IHC) detection of LMP-1 protein and p16 protein on paraffinized tissue blocks were applied. RESULTS: Using IHC, p16 protein was presented in 90/104 (86.5%) of the GC cases, and EBV LMP-1 was detected in 4 cases (3.84%). qPCR detected 14 cases positive for EBV (13.46%). In EBV positive cases detected using qPCR, no expression of p16 was detected. CONCLUSION: EBVaGC has a low incidence in Egypt; loss of p16 expression was recognized in EBVaGC and could be considered as a promising biomarker of EBVaGC. The combination of the two methods IHC and qPCR in addition to p16 is recommended for improving the accuracy of identification of infected cancer.

Human Herpesvirus 8 seroprevalence among blood donors in Mali.

In sub-Saharan Africa, the Human Herpesvirus 8 (HHV-8) is endemic but with disparities between regions and population studied. Although the virus remains mostly latent, there is some evidence that blood transfusion may represents one of the transmission way for this virus. Here, we evaluated HHV-8 seroprevalence among blood donors in Mali. This cross-sectional study recruited blood donors from the Blood Transfusion Center at Gabriel Touré Hospital, Bamako. Serum was used for the detection of latent HHV-8 immunoglobulin G directed against latent associated nuclear antigen 1 by an indirect immunofluorescence assay.Human immunodeficiency virus 1(HIV-1), Hepatitis B Virus (HBV), HCV, and Treponema pallidum were also screened.HHV-8 seroprevalence was 10.4% in Malian blood donors. None of the sociodemographic characteristics were associated with HHV-8 infection, although there is a tendency of a higher HHV-8 seroprevalence among participants living in Bamako than those not living there. One individual had coinfection HHV-8/HBV, another HHV-8/HCV while another had HCV and T.pallidum. None has been tested positive for HIV infection. This intermediate seroprevalence in Malian blood donors suggests that the risk of HHV-8 transmission by transfusion should be considered. Further investigations are needed to assess impact of HHV-8 in polytransfused patients residing in an endemic area for this virus.

Antibody response to herpes simplex virus-1 is increased in autoimmune encephalitis.

Antibody response to herpes simplex virus-1 is increased in autoimmune encephalitis.

Epstein-Barr Virus, But Not Human Papillomavirus, Is Associated With Preinvasive and Invasive Ocular Surface Squamous Neoplasias in Zambian Patients.

BackgroundThe etiopathogenesis of ocular surface squamous neoplasia (OSSN) is not fully understood. We assessed the frequency of oncogenic viruses in OSSN by immunohistochemistry (IHC) and polymerase chain reaction (PCR) for human papillomavirus (HPV), Epstein–Barr virus (EBV), Merkel cell polyomavirus (MCPyV), Kaposi sarcoma virus, and adenovirus. Cases from Zambia were prospectively enrolled using a cross-sectional study design between November 2017 and March 2020.MethodsDemographic and clinical data [age, sex, HIV status, antiretroviral therapy (ART) history, CD4 count, plasma viral load] and tumor biopsies were collected from 243 consenting patients. Tumor samples were bisected, and half was used for DNA isolation, while the other half was formalin fixed and paraffin embedded (FFPE) for histopathology analysis. The expressions of latent EBV nuclear antigen 1 (EBNA1), CDKN2A/p16INK4A (p16), and MCPyV large T-antigen (LT) were tested by IHC. Multiplex PCR was used to detect 16 HPV genotypes and four other DNA tumor viruses [Kaposi’s sarcoma-associated herpesvirus (KSHV), EBV, MCPyV, and adenovirus]. Relationships between HIV status, viral DNA and protein expression, and tumor grades were determined by statistical analysis.ResultsOSSN tumors from patients were 29.6% preinvasive and 70.4% invasive. Patients presented with unilateral tumors that were 70.4% late stage (T3/T4). OSSN patients were HIV positive (72.8%). IHC on 243 FFPE biopsies resulted in the detection of EBNA1 (EBV), p16 high-risk HPV (HR-HPV), and MCPyV LT expression in 89.0%, 4.9%, and 0.0%, respectively. EBNA1 was expressed in all grades of preinvasive [cornea–conjunctiva intraepithelial neoplasia (CIN)1, 100%; CIN2, 85.7%; CIN3, 95.8%; and carcinoma in situ (CIS), 83.8%] and in invasive (89.2%) OSSN. PCR on 178 samples detected EBV, HR-HPV, and MCPyV in 80.3%, 9.0%, and 13.5% of tumors, respectively. EBV was detected in all grades of preinvasive and invasive OSSN. EBV detection was associated with high HIV viral loads (p = 0.022). HR-HPV was detected in 0.0% CIN1, 0.0% CIN2, 5.6% CIN3, 13.0% CIS, and 7.0% invasive OSSN.ConclusionsOur findings of EBV DNA and EBNA1 protein in all the grades of preinvasive and especially invasive OSSN are consistent with a potential causal role for EBV in OSSN. A role of HPV in OSSN was not clearly established in this study.

The Role of Epstein-Barr Virus in Modulating Key Tumor Suppressor Genes in Associated Malignancies: Epigenetics, Transcriptional, and Post-Translational Modifications.

Epstein-Barr virus (EBV) is ubiquitous and carried by approximately 90% of the world’s adult population. Several mechanisms and pathways have been proposed as to how EBV facilitates the pathogenesis and progression of malignancies, such as Hodgkin’s lymphoma, Burkitt’s lymphoma, nasopharyngeal carcinoma, and gastric cancers, the majority of which have been linked to viral proteins that are expressed upon infection including latent membrane proteins (LMPs) and Epstein-Barr virus nuclear antigens (EBNAs). EBV expresses microRNAs that facilitate the progression of some cancers. Mostly, EBV induces epigenetic silencing of tumor suppressor genes, degradation of tumor suppressor mRNA transcripts, post-translational modification, and inactivation of tumor suppressor proteins. This review summarizes the mechanisms by which EBV modulates different tumor suppressors at the molecular and cellular levels in associated cancers. Briefly, EBV gene products upregulate DNA methylases to induce epigenetic silencing of tumor suppressor genes via hypermethylation. MicroRNAs expressed by EBV are also involved in the direct targeting of tumor suppressor genes for degradation, and other EBV gene products directly bind to tumor suppressor proteins to inactivate them. All these processes result in downregulation and impaired function of tumor suppressors, ultimately promoting malignances.

Immunohistochemical characterization of KS cases seen in Nnewi Anambra state using HHV-8 LNA1 and HIV-1P24 antibodies

Introduction: Kaposi sarcoma (KS) is of public health significance in sub-Saharan Africa, including Nigeria, especially in the era of HIV/AIDS. Several works have been done on the prevalence and patterns of KS both in Nigeria and other parts of Africa, with a reported significant prevalence. We employed immunohistochemistry to characterise the morphologic KS cases seen in Nnewi. Materials and Methods: The Formalin Fixed, Paraffin Embedded (FFPE) tissue blocks of all haematoxylin and eosin (H&E) diagnosed cases of KS seen in the archives of histopathology facilities in Nnewi, Anambra State over 15 year period were retrieved. Fresh sections were made from the tissue blocks of the 82 cases that met the inclusion criteria for the study, and were subjected to immunohistochemistry using HHV-8 LNA1 (Human Herpes Virus-8 Latent nuclear antigen1) and HIV-1p24 antibodies and reviewed. Results: A total of 82 KS cases were studied, 69 of which were confirmed KS cases on immunohistochemistry. KS accounted for 1.20% and 14.47% of solid malignancies and sarcomas respectively. Nearly 80% of these were HIV/AIDS-associated, 59.3% of which occurred in females. KS occurred more in the third decade with an age range of 7-74years. Conclusion: KS is quite common in our environment and is largely HIV/AIDS associated. Reducing the burden of HIV/AIDS will invariably reduce KS burden.

Establishment of Tree Shrew Animal Model for Kaposi's Sarcoma-Associated Herpesvirus (HHV-8) Infection.

Kaposi’s sarcoma-associated herpesvirus (KSHV) is the most common cause of Kaposi’s sarcoma (KS) and other malignant growths in humans. However, the lack of a KSHV-infected small animal model has hampered understanding of the mechanisms of KSHV infection, virus replication, pathogenesis, and persistence. This study was designed to explore the susceptibility of tree shrews as a possible KSHV-infected small animal model. A recombinant GFP (latent)/RFP (lytic)-positive rKSHV.219 strain was used to infect primary cells cultured from different tissues of tree shrews as an in vitro model and adult tree shrews as an in vivo model. KSHV latent nuclear antigen (LANA) and DNA were successfully detected in primary cells of tree shrews. Among them, tree shrew kidney epithelial cells (TSKEC) were the most susceptible cells to KSHV infection compared to other cells. KSHV genomic DNA, mRNA, and KSHV-specific proteins were readily detected in the TSKEC cultured up to 32 dpi. Moreover, KSHV DNA and mRNA transcription were also readily detected in the peripheral blood mononuclear cells (PBMCs) and various tissues of tree shrews infected with KSHV. Haematoxylin and eosin (HE) staining showed lymphocyte infiltration, lymphoid tissue focal aggregation, alveolar wall thickening, hepatocyte edema, hepatic necrosis in the spleen, lung, and liver of KSHV-infected animals. Additionally, immune-histochemical (IHC) staining showed that LANA or ORF62-positive cells were present in the spleen, lung, liver, and kidney of KSHV-infected tree shrews. Here, we have successfully established in vitro and in vivo KSHV latent infection in tree shrews. This small animal model is not only useful for studying the pathogenesis of KSHV in vivo but can also be a useful model to study transmission routes of viral infection and a useful platform to characterize the novel therapeutics against KSHV.

NDRG1 facilitates lytic replication of Kaposi's sarcoma-associated herpesvirus by maintaining the stability of the KSHV helicase.

The presumed DNA helicase encoded by ORF44 of Kaposi’s sarcoma-associated herpesvirus (KSHV) plays a crucial role in unwinding viral double-stranded DNA and initiating DNA replication during lytic reactivation. However, the regulatory mechanism of KSHV ORF44 has not been fully elucidated. In a previous study, we identified that N-Myc downstream regulated gene 1 (NDRG1), a host scaffold protein, facilitates viral genome replication by interacting with proliferating cell nuclear antigen (PCNA) and the latent viral protein latency-associated nuclear antigen (LANA) during viral latency. In the present study, we further demonstrated that NDRG1 can interact with KSHV ORF44 during viral lytic replication. We also found that the mRNA and protein levels of NDRG1 were significantly increased by KSHV ORF50-encoded replication and transcription activator (RTA). Remarkably, knockdown of NDRG1 greatly decreased the protein level of ORF44 and impaired viral lytic replication. Interestingly, NDRG1 enhanced the stability of ORF44 and inhibited its ubiquitin-proteasome-mediated degradation by reducing the polyubiquitination of the lysine residues at positions 79 and 368 in ORF44. In summary, NDRG1 is a novel binding partner of ORF44 and facilitates viral lytic replication by maintaining the stability of ORF44. This study provides new insight into the mechanisms underlying KSHV lytic replication.

Functional interplay of Epstein-Barr virus oncoproteins in a mouse model of B cell lymphomagenesis

Epstein-Barr virus (EBV) is a B cell transforming virus that causes B cell malignancies under conditions of immune suppression. EBV orchestrates B cell transformation through its latent membrane proteins (LMPs) and Epstein-Barr nuclear antigens (EBNAs). We here identify secondary mutations in mouse B cell lymphomas induced by LMP1, to predict and identify key functions of other EBV genes during transformation. We find aberrant activation of early B cell factor 1 (EBF1) to promote transformation of LMP1-expressing B cells by inhibiting their differentiation to plasma cells. EBV EBNA3A phenocopies EBF1 activities in LMP1-expressing B cells, promoting transformation while inhibiting differentiation. In cells expressing LMP1 together with LMP2A, EBNA3A only promotes lymphomagenesis when the EBNA2 target Myc is also overexpressed. Collectively, our data support a model where proproliferative activities of LMP1, LMP2A, and EBNA2 in combination with EBNA3A-mediated inhibition of terminal plasma cell differentiation critically control EBV-mediated B cell lymphomagenesis.

Design and molecular docking studies of new inhibitor candidates for EBNA1 DNA binding site: a computational study

ABSTRACTEpstein-Barr virus (EBV), a member of human herpesvirus, causes infectious mononucleosis, Burkitt’s lymphoma, nasopharyngeal carcinoma, gastric carcinoma and Hodgkin lymphomas. Epstein-Barr Nuclear Antigen 1, one of antigens encoded by EBV, comprises 641 amino acid residues. Among the latent infection Epstein-Barr Nuclear Antigen 1 acts in DNA replication, transcription of viral and cellular genes and in immortalisation of B lymphocytes. These special roles of Epstein-Barr Nuclear Antigen 1 make it an important drug target. Therefore, in this study, we create a ligand set of totally 2068 ligands to block binding DNA to Epstein-Barr Nuclear Antigen 1 antigen. After applying Lipinski’s Rule of Five filter to these ligands, 1637 ligands which are suitable to be a drug were run into molecular docking studies. It was seen that designed ligands show more activity to prevent binding DNA to Epstein-Barr Nuclear Antigen 1 antigen rather than ligands selected from the literature which are also studied in vitro and in silico.

Human herpesvirus-8 latent nuclear antigen-1 expression in kaposi's sarcoma cases as seen in Nnewi, Anambra State: (A 10-year retrospective study)

Background: Human herpesvirus-8 (HHV-8) is a recognized major causative agent of Kaposi sarcoma (KS). Latent nuclear antigen-1 (LNA-1) is constitutively expressed in all HHV-8-infected cells. The index study emphasizes the role of immunohistochemistry in the diagnosis of KS in Nnewi, Anambra State, Nigeria. After thorough searches in Google Scholar and PubMed, we discovered that our study is the first to employ HHV-8 LNA-1 immunohistochemistry in the diagnosis of KS in Nigeria and other parts of Africa. Materials and Methods: It is a 10-year retrospective analysis of all histopathologically diagnosed KS cases from the archives of both Nnamdi Azikiwe University Teaching Hospital and Pathocon Specialist Clinic and Research Institute Nnewi. Pathology report forms of all KS cases and their blocks were retrieved and recut, and the recut slides were reviewed to confirm the cases. Of the 69 cases of KS retrieved, only 58 that met the inclusion criteria were analyzed using HHV-8 LNA-1 immunohistochemical stains. Results: Of these 58 cases, 20.7' were KS mimickers misdiagnosed as KS while 79.3' were true KS. Confirmed or HHV-8 LNA-1-positive KS cases accounted for 1.3' of all solid malignancies and 15.7' of all sarcomas, with majority presenting as cutaneous lesions mainly involving the lower limb (52.2') and predominantly (69.6') in nodular stage. Conclusion: HHV-8 LNA-1 is an important immunohistochemical marker in confirming diagnosis of KS.

Kaposi Sarcoma in Mantled Guereza.

We identified a novel Kaposi’s sarcoma herpesvirus–related rhadinovirus (Colobine gammaherpesvirus 1) in a mantled guereza (Colobus guereza kikuyensis). The animal had multiple oral tumors characterized by proliferation of latent nuclear antigen 1–positive spindle cells and was not co-infected with immunosuppressive simian viruses, suggesting that it had Kaposi sarcoma caused by this novel rhadinovirus.

Gastric Kaposi Sarcoma Discovered in a Immunocompromised Renal Transplant Patient

Kaposi sarcoma (KS) is an angioproliferative tumor associated with human herpesvirus 8. Lesions in the gastrointestinal tract (GI) are the most common extracutaneous location and can even occur in the absence of cutaneous lesions. They are often clinically silent; however, patients can present with abdominal pain, nausea, vomiting, anemia, GI bleeding and, in rare cases, mechanical obstruction, intussusception, and perforation. The purpose of this case study is to share a case of a gastric KS to help illustrate the clinical presentation and endoscopic description of this rare finding. A 61-year-old male post renal transplant for end state renal disease was admitted to the hospital from clinic secondary to worsening anasarca and lethargy. His vitals were stable upon presentation and laboratory evaluation revealed acute kidney injury with a Creatinine of 2.5 (baseline of 1.5) and acute anemia with hemoglobin at 6.8 (baseline of 13). GI was consulted with concern of occult GI bleeding for which an esophagogastroduodenoscopy (EGD) and colonoscopy was performed. On EGD, a large 3x3cm friable mass was found in the gastric antrum thought to be a contributing cause of the patient's anemia. Pathology demonstrated positive CD31 and CD34 staining confirming the vascular origin of the tumor. Further assessment revealed spindle cell proliferation and confirmatory immunohistochemical testing for human herpes virus 8 latent nuclear antigen consistent with a diagnosis of gastric KS. His colonoscopy incidentally demonstrated a diminutive tubular adenoma and a small lipoma. After further work-up, including negative HIV testing, it was felt that the patient's presentation was a result of his immunosuppression from his renal transplant. Oncology was consulted who did not feel chemotherapy was indicated. His tacrolimus was reduced and he was taken off his mycophenolate mofetil. He was discharged home with close follow up with his nephrologist and primary care provider. Although rare, the GI tract is the most common extracutaneous site involved in KS. Endoscopic appearance of KS lesions includes cratered, ulcerated, flat, polypoid/nodular masses. It is usually associated with immunosuppression. Treatment should be focused on reconstitution of the patient's immune system and joint decision making with oncology. Endoscopic examinations are often useful for assisting in therapeutic decision-making and evaluating therapy outcomes.2635 Figure 1. Approximately 3 x 3cm large friable mass in right gastric antrum representing Kaposi sarcoma.

Molecular Grading of Oral Squamous Cell Carcinomas Infected with EBV

BackgroundSquamous Cell Carcinoma (SCC) is a type of cancer that is often found in oral cavity and areas of the head and neck. Viruses are major etiological factors through production of factors that can disturb proliferation and apoptosis regulators such as p53i, c-myc and bcl-2. This study aimed to determine the molecular grading of oral squamous cell carcinoma (OSCCs) infected with the Epstein-Barr Virus (EBV).MethodsTwenty-seven OSCC patients underwent biopsy to detect EBV infection through in situ hybridization for RNA EBV (EBER) and immunohistochemical analysis of latent membrane protein-1 (LMP-1) and EBV nuclear antigen-1 (EBNA-1). To assess molecular grades, cell proliferation and apoptosis regulator expression i.e. inactive p53 (p53i), c-myc and bcl-2, were immunohistochemically analysed.ResultsThe cases were divided into two groups; infected and non-infected by EBV. Regression analysis showed that only EBNA-1 expression could affect p53i expression. Based on regression equations molecular grading of OSCCs infected by EBV was divided into three: Grade I (low), EBNA-1 expression was 7.60, and p53i expression was 9.74-17.5; Grade II (medium), EBNA-1 expression was 7.61-19.7, and p53i 17.5-30.1; Grade III (high), EBNA-1 expression was 19.71, and p53i ≥ 30.1.ConclusionIn OSCC infected with EBV, only EBNA-1 expression can influence p53i expression.

An essential EBV latent antigen 3C binds Bcl6 for targeted degradation and cell proliferation.

The latent EBV nuclear antigen 3C (EBNA3C) is required for transformation of primary human B lymphocytes. Most mature B-cell malignancies originate from malignant transformation of germinal center (GC) B-cells. The GC reaction appears to have a role in malignant transformation, in which a major player of the GC reaction is Bcl6, a key regulator of this process. We now demonstrate that EBNA3C contributes to B-cell transformation by targeted degradation of Bcl6. We show that EBNA3C can physically associate with Bcl6. Notably, EBNA3C expression leads to reduced Bcl6 protein levels in a ubiquitin-proteasome dependent manner. Further, EBNA3C inhibits the transcriptional activity of the Bcl6 promoter through interaction with the cellular protein IRF4. Bcl6 degradation induced by EBNA3C rescued the functions of the Bcl6-targeted downstream regulatory proteins Bcl2 and CCND1, which resulted in increased proliferation and G1-S transition. These data provide new insights into the function of EBNA3C in B-cell transformation during GC reaction, and raises the possibility of developing new targeted therapies against EBV-associated cancers.

KSHV episomes: rugged individualists on the factory floor

We have recently developed tools to study Kaposi’s sarcoma-associated virus (KSHV) reactivation at the single-episome level. Using immunofluorescent labeling of latent nuclear antigen (LANA) protein to localize viral episomes, combined with fluorescence in situ RNA hybridization (RNA-FISH) of an intron region of immediate early transcripts, we have visualized active transcription of viral genomes in infected cells. At this level, we observed that not all episomes within a single cell were uniformly transcribed following reactivation stimuli. However, those episomes that were transcribed, formed large aggregates containing a significant fraction of cellular RNA polymerase II (RNAPII), foci consistent with previously described viral transcriptional factories. This focal assembly of RNAPII on viral episomes was accompanied by an overall decrease in the pool of cellular RNAPII. Additionally, the viral transcriptional factories localized with replicating viral genomic DNAs. This co-localization suggests that KSHV may assemble an “all-in-one” workroom for both gene transcription and DNA replication. While previous studies have reported on the variable response of individual KSHV infected cells or episomes derived from a population during reactivation, our results expose this variation further by demonstrating heterogeneity in the response of individual KSHV episomes within a single reactivating cell.

Kaposi's Sarcoma-Associated Herpesvirus Hijacks RNA Polymerase II To Create a Viral Transcriptional Factory.

ABSTRACTLocally concentrated nuclear factors ensure efficient binding to DNA templates, facilitating RNA polymerase II recruitment and frequent reutilization of stable preinitiation complexes. We have uncovered a mechanism for effective viral transcription by focal assembly of RNA polymerase II around Kaposi's sarcoma-associated herpesvirus (KSHV) genomes in the host cell nucleus. Using immunofluorescence labeling of latent nuclear antigen (LANA) protein, together with fluorescence in situ RNA hybridization (RNA-FISH) of the intron region of immediate early transcripts, we visualized active transcription of viral genomes in naturally infected cells. At the single-cell level, we found that not all episomes were uniformly transcribed following reactivation stimuli. However, those episomes that were being transcribed would spontaneously aggregate to form transcriptional “factories,” which recruited a significant fraction of cellular RNA polymerase II. Focal assembly of “viral transcriptional factories” decreased the pool of cellular RNA polymerase II available for cellular gene transcription, which consequently impaired cellular gene expression globally, with the exception of selected ones. The viral transcriptional factories localized with replicating viral genomic DNAs. The observed colocalization of viral transcriptional factories with replicating viral genomic DNA suggests that KSHV assembles an “all-in-one” factory for both gene transcription and DNA replication. We propose that the assembly of RNA polymerase II around viral episomes in the nucleus may be a previously unexplored aspect of KSHV gene regulation by confiscation of a limited supply of RNA polymerase II in infected cells.IMPORTANCE B cells infected with Kaposi's sarcoma-associated herpesvirus (KSHV) harbor multiple copies of the KSHV genome in the form of episomes. Three-dimensional imaging of viral gene expression in the nucleus allows us to study interactions and changes in the physical distribution of these episomes following stimulation. The results showed heterogeneity in the responses of individual KSHV episomes to stimuli within a single reactivating cell; those episomes that did respond to stimulation, aggregated within large domains that appear to function as viral transcription factories. A significant portion of cellular RNA polymerase II was trapped in these factories and served to transcribe viral genomes, which coincided with an overall decrease in cellular gene expression. Our findings uncover a strategy of KSHV gene regulation through focal assembly of KSHV episomes and a molecular mechanism of late gene expression.