title: The EBV nuclear antigen 1 (EBNA1) enhances B cell immortalization several thousandfold.
abstract: The Epstein-Barr virus (EBV) nuclear antigen 1 (EBNA1) is one of the earliest viral proteins expressed after infection and is the only latent protein consistently expressed in viral-associated tumors. EBNA1's crucial role in viral DNA replication, episomal maintenance, and partitioning is well examined whereas its importance for the immortalization process and the tumorgenicity of EBV is unclear. To address these open questions, we generated, based on the maxi-EBV system, an EBNA1-deficient EBV mutant and used this strain to infect primary human B cells. Surprisingly, lymphoblastoid cell lines (LCL) emerged from these experiments, although with very low frequency. These cell lines were indistinguishable from normal LCLs with respect to proliferation and growth conditions. A detailed analysis indicated that the entire viral DNA was integrated into the cellular genome. At least 5 of the 11 latent EBV proteins were expressed, indicating the integrity of the EBV genome. EBNA1-positive and DeltaEBNA1-EBV-LCLs were injected into severe combined immunodeficient (SCID) mice to examine their tumorgenicity in comparison. Both groups supported tumor growth, indicating that EBNA1 is not mandatory for EBV's oncogenic potential. The results shown provide genetic evidence that EBNA1 is not essential to establish LCLs but promotes the efficiency of this process significantly.
authors.affiliation: Department of Gene Vectors, GSF-National Research Center for Environment and Health, Marchioninistrasse 25, 81377 Munich, Germany.
authors.forename: Sibille
authors.initials: S
authors.lastname: Humme
authors.forename: Gilbert
authors.initials: G
authors.lastname: Reisbach
authors.forename: Regina
authors.initials: R
authors.lastname: Feederle
authors.forename: Henri-Jacques
authors.initials: HJ
authors.lastname: Delecluse
authors.forename: Kristine
authors.initials: K
authors.lastname: Bousset
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Hammerschmidt
authors.forename: Aloys
authors.initials: A
authors.lastname: Schepers
mesh_terms: D001402:B-Lymphocytes / Q000166:cytology*; D015139:Blotting, Southern; D015153:Blotting, Western; D002460:Cell Line; D002472:Cell Transformation, Viral / Q000502:physiology*; D004279:DNA, Viral / Q000032:analysis; D019309:Epstein-Barr Virus Nuclear Antigens / Q000502:physiology*; D004854:Herpesvirus 4, Human / Q000235:genetics / Q000502:physiology; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D010957:Plasmids
chemical_list: D004279:DNA, Viral; D019309:Epstein-Barr Virus Nuclear Antigens; C417029:EBV-encoded nuclear antigen 1