Epstein-Barr Virus BamHI W Repeat Number Limits EBNA2/EBNA-LP Coexpression in Newly Infected B Cells and the Efficiency of B-Cell Transformation: a Rationale for the Multiple W Repeats in Wild-Type Virus Strains

被引:39
作者
Tierney, Rosemary J. [1 ]
Kao, Kuan-Yu [1 ]
Nagra, Jasdeep K. [1 ]
Rickinson, Alan B. [1 ]
机构
[1] Univ Birmingham, Sch Canc Sci, Birmingham Canc Res UK Ctr, Birmingham B15 2TT, W Midlands, England
关键词
LATENT CYCLE PROMOTER; BURKITTS-LYMPHOMA; REPETITIVE POLYPEPTIDE; NUCLEAR PROTEINS; EXPRESSION; LINES; LYMPHOCYTES; BINDING; EBNA2; SEQUENCE;
D O I
10.1128/JVI.06059-11
中图分类号
Q93 [微生物学];
学科分类号
071005 ; 100705 ;
摘要
The genome of Epstein-Barr virus (EBV), a gammaherpesvirus with potent B-cell growth-transforming ability, contains multiple copies of a 3-kb BamHI W repeat sequence; each repeat carries (i) a promoter (Wp) that initiates transformation by driving EBNA-LP and EBNA2 expression and (ii) the W1W2 exons encoding the functionally active repeat domain of EBNA-LP. The W repeat copy number of a virus therefore influences two potential determinants of its transforming ability: the number of available Wp copies and the maximum size of the encoded EBNA-LP. Here, using recombinant EBVs, we show that optimal B-cell transformation requires a minimum of 5 W repeats (5W); the levels of transforming ability fall progressively with viruses carrying 4, 3, and 2 W repeats, as do the levels of Wp-initiated transcripts expressed early postinfection (p.i.), while viruses with 1 copy of the wild-type W repeat (1W) and 0W are completely nontransforming. We therefore suggest that genetic analyses of EBV transforming function should ensure that wild-type and mutant strains have equal numbers (ideally at least 5) of W copies if the analysis is not to be compromised. Attempts to enhance the transforming function of low-W-copy-number viruses, via the activity of helper EBV strains or by gene repair, suggested that the critical defect is not related to EBNA-LP size but to the failure to achieve sufficiently strong coexpression of EBNA-LP and EBNA2 early postinfection. We further show by the results of ex vivo assays that EBV strains in the blood of infected individuals typically have a mean of 5 to 8 W copies, consistent with the view that evolution has selected for viruses with an optimal transforming function.
引用
收藏
页码:12362 / 12375
页数:14
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