Epstein–Barr virus nuclear antigen 2

Structure

EBNA2 has an acidic activation domain, which can interact with many different general transcription factors and co-activators. Regulation of transcription initiation and elongation by EBNA 2 is done part through cyclin-dependent kinase 9 (CDK9) dependent phosphorylation of the RNA polymerase C-terminal domain.

Mechanism

EBNA2 requires C-promoter binding factor 1 (CBF1) to aid in binding to its cis-responsive DNA element, the C promoter (Cp). Binding occurs during infection, to generate a 120kb transcript that encodes all nuclear antigens required for immortalization by EBV.2 Mutation of EBNA2 amino acid 323 and 324, which are located within a highly conserved amino acid motif, abolished the interaction with CBF1.3 This same mutation also abolished the ability of EBNA-2 to activate the Cp.

EBNA-LP and EBNA2 are the first two proteins expressed in latent infection of primary B lymphocytes. EBNA-LP stimulates EBNA2 activation of the LMP1 promoter and of the LMP1/LMP2B bidirectional transcriptional regulatory element whereas EBNA-LP alone only has a negative effect.

EBNA2 transactivates the promoters of the latent membrane antigens LMP, TP1 and TP2. Additionally, EBNA2 interacts with an EBNA2 responsive cis-element of the TP1 promoter. Interactions with both the TP1 and LMP/TP2 promoters occur at at least one binding site for the cellular repressor protein RBP-Jκ. EBNA2 is tethered to the EBNA2 responsive promoter elements by interacting with RBP-Jκ, a human recombination signal sequence binding protein.

Specific responsive elements that share the core sequence GTGGGAA have been discovered in several of the promoters activated by EBNA2. A similar core sequence has recently been identified as a binding site in RBP-Jκ. The binding of RBP-Jκ is not sufficient for EBNA2-mediated trans activation. An activated form of the Notch receptor can transactivate a reporter construct containing a hexamer of the two RBP-Jκ binding sites of the TP1 promoter. This supports the idea that EBNA2 acts as a functional equivalent of an activated Notch receptor.

EBNA2 also interacts with the human homolog of the yeast transcription factor (SNF5 hSNF5/Ini1) as it coelutes with both hSNF5/Ini1 and BRG1. BRG1 is a human homolog of SWI/SNF2. However, this interaction is restricted to a subpopulation of phosphorylated viral EBNA2. EBNA2-hSNF5/Ini1 interaction adds credit to the idea that EBNA2 facilitates transcriptional transactivation by acting as a transcription adapter molecule. Possibly, EBNA2 engages the hSNF-SWI complex to generate an open chromatin conformation at the EBNA2-responsive target genes. This then potentiates the function of the RBP-JK-EBNA2-polymerase II transcription complex.

References

References

1. (July 1994). "Mediation of Epstein-Barr virus EBNA2 transactivation by recombination signal-binding protein J kappa". Science.
2. (September 1996). "Epstein-Barr virus nuclear protein 2 (EBNA2) binds to a component of the human SNF-SWI complex, hSNF5/Ini1". Journal of Virology.
3. (August 2008). "Regulation of transcription by the Epstein-Barr virus nuclear antigen EBNA 2". Biochemical Society Transactions.
4. (December 1997). "Both Epstein-Barr viral nuclear antigen 2 (EBNA2) and activated Notch1 transactivate genes by interacting with the cellular protein RBP-J kappa". Immunobiology.
5. (October 1993). "The Epstein-Barr virus immortalizing protein EBNA-2 is targeted to DNA by a cellular enhancer-binding protein". Proceedings of the National Academy of Sciences of the United States of America.
6. (September 1997). "Epstein-Barr virus nuclear protein LP stimulates EBNA-2 acidic domain-mediated transcriptional activation". Journal of Virology.
7. (January 1993). "The Epstein-Barr virus nuclear antigen 2 interacts with an EBNA2 responsive cis-element of the terminal protein 1 gene promoter". The EMBO Journal.
8. (December 1994). "The human J kappa recombination signal sequence binding protein (RBP-J kappa) targets the Epstein-Barr virus EBNA2 protein to its DNA responsive elements". The EMBO Journal.