Gene regulation by Epstein-Barr virus EBNA2 type 1 and type 2

Abstract

Epstein-Barr virus, EBV, is a human herpes virus that establishes a life long, persistent, latent infection in B lymphocytes. In vitro, EBV readily transforms and immortalizes primary B cells. EBV exists in two types, named EBV type 1 and type 2. These are defined on the basis of polymorphism in the EBNA2 locus. The EBNA2 gene encodes a viral transcription factor that controls viral and cell genes and is absolutely required for B cell transformation. EBV type 1 strains are much more efficient than EBV type 2 at transforming B cells and the enhanced transformation efficiency was previously mapped to the EBNA2 gene. A transfection assay was devised to compare the ability of type 1 and type 2 EBNA2 to sustain cell proliferation in EREB2.5 lymphoblastoid cells, which contain a ΔEBNA2-Epstein-Barr virus and express a conditional EBNA2. The reduced proliferation in cells expressing type 2 EBNA2 correlated with loss of expression of some cell genes that are known to be targets of type 1 EBNA2. Microarray analysis of EBNA2 target genes in stably transfected Burkitt lymphoma cells identified a small number of genes that are more strongly induced by type 1 than type 2 EBNA2 and one of these genes (CXCR7) was shown to be required for proliferation of lymphoblastoid cell lines. The Epstein-Barr virus LMP1 gene is directly induced by EBNA2 and is critically involved in B cell transformation. In Daudi Burkitt lymphoma cells, EBNA2 type 1 induced LMP1 much more strongly than EBNA2 type 2, although both reached comparable levels after 48 hours. The results show that differential gene regulation by Epstein-Barr virus type 1 and type 2 EBNA2 is likely to be the basis for the much weaker B cell transformation activity of type 2 Epstein-Barr virus strains compared to type 1 strains.