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J. Virol., Feb 1995, 675-683, Vol 69, No. 2
KM Kaye, KM Izumi, G Mosialos and E Kieff
Recombinant Epstein-Barr viruses (EBVs) were made with mutated latent
membrane protein 1 (LMP1) genes that express only the LMP1 amino- terminal
cytoplasmic and six transmembrane domains (MS187) or these domains and the
first 44 amino acids of the 200-residue LMP1 carboxy- terminal domain
(MS231). After infection of primary B lymphocytes with virus stocks having
small numbers of recombinant virus and large numbers of P3HR-1 EBV which is
transformation defective but wild type (WT) for LMP1, all lymphoblastoid
cell lines (LCLs) that had MS187 or MS231 LMP1 also had WT LMP1 provided by
the coinfecting P3HR-1 EBV. Lytic virus infection was induced in these
coinfected LCLs, and primary B lymphocytes were infected. In over 200
second-generation LCLs, MS187 LMP1 was never present without WT LMP1.
Screening of over 600 LCLs infected with virus from MS231 recombinant
virus-infected LCLs identified two LCLs which were infected with an MS231
recombinant without WT LMP1. The MS231 recombinant virus could growth
transform primary B lymphocytes when cells were grown on fibroblast
feeders. Even after 6 months on fibroblast feeder layers, cells transformed
by the MS231 recombinant virus died when transferred to medium without
fibroblast feeder cells. These data indicate that the LMP1 carboxy terminus
is essential for WT growth-transforming activity. The first 44 amino acids
of the carboxy-terminal cytoplasmic domain probably include an essential
effector of cell growth transformation, while a deletion of the rest of
LMP1 can be complemented by growth on fibroblast feeder layers. LMP1
residues 232 to 386 therefore provide a growth factor-like effect for the
transformation of B lymphocytes. This effect may be indicative of the
broader role of LMP1 in cell growth transformation.
Copyright © 1995, American Society for Microbiology
The Epstein-Barr virus LMP1 cytoplasmic carboxy terminus is essential for B-lymphocyte transformation; fibroblast cocultivation complements a critical function within the terminal 155 residues
Department of Medicine, Harvard Medical School, Boston, Massachusetts 02115.
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