Epstein-Barr virus nuclear protein 2 mutations define essential domains for transformation and transactivation

Epstein-Barr virus (EBV) nuclear protein 2 (EBNA-2) is essential for B-lymphocyte growth transformation. EBNA-2 transactivates expression of the EBV latent membrane protein (LMP-1) and also transactivates expression of the B-lymphocyte proteins CD21 and CD23. In order to analyze the functional domains of EBNA-2, we constructed 11 linker-insertion and 15 deletion mutations. Each of the mutant EBNA-2 proteins localized to the nucleus, and each was expressed at levels similar to wild-type EBNA-2. Deletion of both EBNA-2 basic domains was required to prevent nuclear localization, indicating that either is sufficient for nuclear translocation. The mutant EBNA-2 genes were assayed for lymphocyte transformation after recombination with the EBNA-2-deleted P3HR-1 EBV genome and for LMP-1 transactivation following transfection into P3HR-1-infected B-lymphoma cells. Cell lines transformed by recombinant EBV carrying EBNA-2 mutations were assayed for growth properties and LMP-1, CD21, and CD23 expression. The mutational analysis indicates that at least four separate EBNA-2 domains are essential for lymphocyte transformation. Two other domains are necessary for the full transforming phenotype. Two deletion and eight linker-insertion mutations did not reduce transforming activity. Mutations which diminish or abolish lymphocyte transformation also diminish or abolish LMP-1 transactivation, respectively. Cells transformed by recombinant EBV carrying EBNA-2 genes with diminished or normal transforming activity all expressed high levels of LMP-1, CD23, and CD21. These findings suggest that transactivation of these viral and cellular genes by EBNA-2 plays a critical role in lymphocyte transformation by EBV. Furthermore, these results indicate that the transformation and transactivation functions of EBNA-2 may not be separable.