Activated Notch1 can transiently substitute for EBNA2 in the maintenance of proliferation of LMP1-expressing immortalized B cells.
Epstein-Barr virus (EBV) nuclear antigen 2 (EBNA2) and latent membrane protein 1 (LMP1) are essential for immortalization of human B cells by EBV. EBNA2 and activated Notch transactivate genes by interacting with the cellular transcription factor RBP-Jkappa/CBF1. Therefore, EBNA2 can be regarded as a functional homologue of activated Notch. We have shown previously that the intracellular domain of Notch1 (Notch1-IC) is able to transactivate EBNA2-regulated viral promoters and to induce phenotypic changes in B cells similar to those caused by EBNA2. Here we investigated whether Notch1-IC can substitute for EBNA2 in the maintenance of B-cell proliferation. Using an EBV-immortalized lymphoblastoid cell line in which EBNA2 function can be regulated by estrogen, we demonstrate that murine Notch1-IC, in the absence of functional EBNA2, is unable to maintain LMP1 expression and to maintain cell proliferation. However, in a lymphoblastoid cell line expressing LMP1 independently of EBNA2, murine Notch1-IC can transiently maintain proliferation after EBNA2 inactivation. After 4 days, cell numbers do not increase further, and cells in the G2 phase of the cell cycle start to die. In contrast to EBNA2, murine Notch1-IC is unable to upregulate the expression of the c-myc gene in these cells.
Höfelmayr
H
H
Institute for Clinical Molecular Biology and Tumor Genetics, GSF National Research Center of Environment and Health, D-81377 Munich, Germany.
Strobl
L J
LJ
Marschall
G
G
Bornkamm
G W
GW
Zimber-Strobl
U
U
D000818:Animals; D001402:B-Lymphocytes / Q000502:physiology*; D002453:Cell Cycle / Q000502:physiology; D002455:Cell Division / Q000502:physiology; D002461:Cell Line, Transformed; D019309:Epstein-Barr Virus Nuclear Antigens / Q000235:genetics / Q000378:metabolism*; D004967:Estrogens / Q000494:pharmacology; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D051881:Receptor, Notch1; D011956:Receptors, Cell Surface; D015398:Signal Transduction; D014157:Transcription Factors; D014162:Transfection; D014763:Viral Matrix Proteins / Q000378:metabolism*; D014764:Viral Proteins
C402641:EBNA-2 protein, Human herpesvirus 4; C037662:EBV-associated membrane antigen, Epstein-Barr virus; D019309:Epstein-Barr Virus Nuclear Antigens; D004967:Estrogens; D008565:Membrane Proteins; C497761:NOTCH1 protein, human; C497762:Notch1 protein, mouse; D051881:Receptor, Notch1; D011956:Receptors, Cell Surface; D014157:Transcription Factors; D014763:Viral Matrix Proteins; D014764:Viral Proteins