title: The NP9 protein encoded by the human endogenous retrovirus HERV-K(HML-2) negatively regulates gene activation of the Epstein-Barr virus nuclear antigen 2 (EBNA2).
abstract: Epstein-Barr virus (EBV) is a human tumour virus that efficiently growth-transforms primary human B-lymphocytes in vitro. The viral nuclear antigen 2 (EBNA2) is essential for immortalisation of B-cells and stimulates viral and cellular gene expression through interaction with DNA-bound transcription factors. Like its cellular homologue Notch, it associates with the DNA-bound repressor RBPJκ (CSL/CBF1) thereby converting RBPJκ into the active state. For instance, both EBNA2 and Notch activate the cellular HES1 promoter. In EBV-transformed lymphocytes, the RNA of the NP9 protein encoded by human endogenous retrovirus HERV-K(HML-2) Type 1 is strongly up-regulated. The NP9 protein is detectable both in EBV-positive Raji cells, a Burkitt's lymphoma cell line, and in IB4, an EBV-transformed human lymphoblastoid cell line. NP9 binds to LNX that forms a complex with the Notch regulator Numb. Therefore, the function of NP9 vis-à-vis Notch and EBNA2 was analysed. Here, we show that NP9 binds to EBNA2 and negatively affects the EBNA2-mediated activation of the viral C- and LMP2A promoters. In contrast, NP9 did neither interfere in the activation of the HES1 promoter by Notch nor the induction of the viral LMP1 promoter by EBNA2. In an electrophoretic mobility shift analysis, NP9 reduced the binding of EBNA2 to DNA-bound RBPJκ by about 50%. The down-regulation of EBNA2-activity by NP9 might represent a cellular defence mechanism against viral infection or could, alternatively, represent an adaptation of the virus to prevent excessive viral protein production that might otherwise be harmful for the infected cell.
authors.affiliation: Institut für Virologie, Universitätsklinikum des Saarlandes, 66421 Homburg, Germany.
authors.forename: Henrik
authors.initials: H
authors.lastname: Gross
authors.forename: Stephanie
authors.initials: S
authors.lastname: Barth
authors.forename: Thorsten
authors.initials: T
authors.lastname: Pfuhl
authors.forename: Vivienne
authors.initials: V
authors.lastname: Willnecker
authors.forename: Andreas
authors.initials: A
authors.lastname: Spurk
authors.forename: Vladimir
authors.initials: V
authors.lastname: Gurtsevitch
authors.forename: Marlies
authors.initials: M
authors.lastname: Sauter
authors.forename: Bin
authors.initials: B
authors.lastname: Hu
authors.forename: Elfriede
authors.initials: E
authors.lastname: Noessner
authors.forename: Nikolaus
authors.initials: N
authors.lastname: Mueller-Lantzsch
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Kremmer
authors.forename: Friedrich A
authors.initials: FA
authors.lastname: Grässer
mesh_terms: D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D015153:Blotting, Western; D002051:Burkitt Lymphoma / Q000235:genetics / Q000378:metabolism; D019556:COS Cells; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D024202:Electrophoretic Mobility Shift Assay; D019309:Epstein-Barr Virus Nuclear Antigens / Q000235:genetics* / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D015967:Gene Expression Regulation, Viral; D015686:Gene Products, env / Q000235:genetics / Q000378:metabolism*; D004854:Herpesvirus 4, Human / Q000254:growth & development; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D047468:Immunoprecipitation; D008156:Luciferases / Q000378:metabolism; D008214:Lymphocytes / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011485:Protein Binding; D051881:Receptor, Notch1 / Q000378:metabolism; D012045:Regulatory Sequences, Nucleic Acid; D000072056:Transcription Factor HES-1; D015533:Transcriptional Activation; D014763:Viral Matrix Proteins / Q000235:genetics; D014764:Viral Proteins / Q000235:genetics* / Q000378:metabolism*
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D019309:Epstein-Barr Virus Nuclear Antigens; D015686:Gene Products, env; D018398:Homeodomain Proteins; D008156:Luciferases; D051881:Receptor, Notch1; D000072056:Transcription Factor HES-1; D014763:Viral Matrix Proteins; D014764:Viral Proteins; C402641:EBNA-2 protein, Human herpesvirus 4; C037662:EBV-associated membrane antigen, Epstein-Barr virus; C469430:Np9 protein, HERV-K, human; C078493:HES1 protein, human