The cytoplasmic C-terminal domain but not the N-terminal domain of latent membrane protein 1 of Epstein-Barr virus is essential for B cell activation.
The Epstein-Barr virus (EBV) latent membrane protein 1 (LMP-1) is essential for EBV-induced immortalization of human primary B cells, transforms rodent fibroblasts and induces the up-regulation of several B cell activation markers when transiently expressed in primary B cells. The biochemical function of LMP-1 is unclear and limited information is available on the involvement of different domains of the protein in B cell activation. The present study describes the characterization of LMP-1 N- and C-terminal deletion mutants in terms of their cell surface distribution and ability to induce activation markers in primary human B cells and in the type I Burkitt's lymphoma cell line DG75. The C-terminal deletion mutant was detected by immunofluorescence via antibodies targeted against an eight amino acid FLAG epitope substituted for the entire predicted cytoplasmic C-terminal domain. Our findings show that N-terminal deletion mutants of LMP-1 are unable to attain their usual patched distribution on the plasma membrane but retain the ability to activate B cells. In contrast, the C-terminal deletion mutant shows the same patched cell surface distribution as wild-type LMP-1 but is unable to activate B cells. The patched distribution of LMP-1 in the plasma membrane is therefore not sufficient nor necessary for the induction of B cell activation and the results rule out patching as a direct mechanism in LMP-1-induced activation. This is the first study addressing the role of the LMP-1 C-terminal domain in lymphocytes and our results show that this domain is essential for B cell activation and therefore likely to be important for the early events of B cell immortalization by EBV.
Peng-Pilon
M
M
Department of Cell and Molecular Biology, University of Umea, Sweden.
Ruuth
K
K
Lundgren
E
E
Brodin
P
P
D015703:Antigens, CD / Q000276:immunology; D000944:Antigens, Differentiation, B-Lymphocyte / Q000276:immunology; D001402:B-Lymphocytes / Q000166:cytology / Q000276:immunology*; D048429:Cell Size; D002478:Cells, Cultured; D003593:Cytoplasm; D017353:Gene Deletion; D004854:Herpesvirus 4, Human / Q000235:genetics / Q000276:immunology*; D006801:Humans; D018799:Intercellular Adhesion Molecule-1 / Q000276:immunology; D008213:Lymphocyte Activation / Q000276:immunology*; D011990:Receptors, Transferrin; D013154:Spleen / Q000166:cytology; D013329:Structure-Activity Relationship; D014162:Transfection; D014763:Viral Matrix Proteins / Q000737:chemistry* / Q000235:genetics / Q000276:immunology*
D015703:Antigens, CD; D000944:Antigens, Differentiation, B-Lymphocyte; C068126:CD71 antigen; C037662:EBV-associated membrane antigen, Epstein-Barr virus; D011990:Receptors, Transferrin; D014763:Viral Matrix Proteins; D018799:Intercellular Adhesion Molecule-1