Epstein-Barr virus-infected B-chronic lymphocyte leukemia cells express the virally encoded nuclear proteins but they do not enter the cell cycle.
OBJECTIVE
To understand the mechanism for the refractoriness of B-chronic lymphocyte leukemia (B-CLL) cells for EBV-induced immortalization.


METHODS
Cells from four B-CLL patients were infected with Epstein-Barr virus (EBV). Noninfected and infected aliquots were exposed to CD40L. Five days later, the cultures were analyzed for cell survival, activation, DNA synthesis, and expression of EBV-encoded and of cellular regulatory proteins retinoblastoma (Rb), p53, recombinant sequence binding protein (RBP)Jk, and PU.1. The proteins were detected by immunoblotting and by immunofluorescence.


RESULTS
A proportion of the cells were activated and expressed Epstein-Barr nuclear antigens (EBNAs) and elevated Rb level but not latent membrane protein (LMP)-1 and p53. They did not enter the cell cycle. Exposure to CD40L induced DNA synthesis but it did not modify the expression of the EBNAs.


CONCLUSIONS
The virus could activate CLL cells, but the full course of the early events that leads to immortalization--as seen in normal B cells--did not proceed beyond a certain point. Compared to B lymphocytes, the critical point is between activation and initiation of the cell cycle.
Teramoto
N
N
Microbiology and Tumor Biology Center, Karolinska Institute, Stockholm, Sweden. terra@med.okayama-u.ac.jp
Gogolák
P
P
Nagy
N
N
Maeda
A
A
Kvarnung
K
K
Björkholm
T
T
Klein
E
E
D001402:B-Lymphocytes / Q000378:metabolism / Q000821:virology*; D015153:Blotting, Western; D002453:Cell Cycle; D004268:DNA-Binding Proteins / Q000032:analysis; D019309:Epstein-Barr Virus Nuclear Antigens / Q000032:analysis; D005434:Flow Cytometry; D004854:Herpesvirus 4, Human; D006801:Humans; D051819:Immunoglobulin J Recombination Signal Sequence-Binding Protein; D007150:Immunohistochemistry; D019394:Ki-67 Antigen / Q000032:analysis; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000276:immunology*; D008213:Lymphocyte Activation; D009687:Nuclear Proteins; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000032:analysis; D014763:Viral Matrix Proteins / Q000032:analysis
D004268:DNA-Binding Proteins; C037662:EBV-associated membrane antigen, Epstein-Barr virus; D019309:Epstein-Barr Virus Nuclear Antigens; D051819:Immunoglobulin J Recombination Signal Sequence-Binding Protein; D019394:Ki-67 Antigen; D009687:Nuclear Proteins; C497570:RBPJ protein, human; D016159:Tumor Suppressor Protein p53; D014763:Viral Matrix Proteins