Genetic analysis of the role of Epstein-Barr virus nuclear antigen leader protein (EBNA-LP) in B cell transformation.

Abstract

Epstein-Barr virus (EBV) is a gammaherpesvirus that causes infectious mononucleosis and is associated with several human malignancies. In vitro, EBV induces the activation and continuous proliferation of primary human B cells, which carry the viral genome as a latent episome. One of the latency-associated proteins is the EBV nuclear antigen leader protein (EBNA-LP). EBNA-LP is strongly expressed at the initiation of the transformation process and has been previously reported to assist the activation of genes by EBNA-2. To investigate the role and mechanism of action of EBNA-LP in the context of viral infection and B cell transformation, I have generated EBNA-LP knockout EBVs (LP-KO i) and their revertants (LP-REV i) by recombineering in the B95.8 bacterial artificial chromosome (BAC). We found that B cells infected with LP-KO i were able to undergo limited proliferation. However, we were not able to establish LCLs after infection of EBV-negative B cells. We also found that LP-REV i was somewhat impaired in its transforming ability. We identified four nucleotide changes in EBNA-LP’s introns in both LP-KO i and LP-REV i that may influence transforming abilities. Therefore, new EBNA-LP knockouts (LP-KO w) containing wild-type intronic sequences were constructed. LP-KO w initially induced proliferation of adult B cells but then slowed around 5-14 days post infection, after which the cells recovered and established LCLs. However, in cord blood, LP-KO w failed to establish LCLs. Transcript level analysis in primary B cell infections showed that EBNA-LP can regulate the EBNA-2-regulated viral genes LMP-1 and LMP-2, as well as the EBER-2 gene, which is EBNA-2-independent. EBNA-LP has also a more limited role in modulating the EBNA-2-targeted host gene HES-1.