Epstein–Barr virus nuclear antigen 2

The Epstein–Barr virus nuclear antigen 2 (EBNA-2) is one of the six EBV viral nuclear proteins expressed in latently infected B lymphocytes is a transactivator protein. EBNA2 is involved in the regulation of latent viral transcription and contributes to the immortalization of EBV infected cells.^[1][2] EBNA2 acts as an adapter molecule that binds to cellular sequence-specific DNA-binding proteins, JK recombination signal-binding protein (RBP-JK), and PU.1 as well as working with multiple members of the RNA polymerase II transcription complex.^[1]

EBNA2 has an acidic activation domain, which can interact with many different general transcription factors and co-activators.^[3] 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.^[3]

EBNA2 requires C-promoter binding factor 1 (CBF1) to aid in binding to its cis-responsive DNA element, the C promoter (Cp).^[1][4] 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.^[5]

EBNA-LP and EBNA2 are the first two proteins expressed in latent infection of primary B lymphocytes.^[6] 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.^[6]

EBNA2 transactivates the promoters of the latent membrane antigens LMP, TP1 and TP2.^[7] Additionally, EBNA2 interacts with an EBNA2 responsive cis-element of the TP1 promoter.^[7] Interactions with both the TP1 and LMP/TP2 promoters occur at at least one binding site for the cellular repressor protein RBP-Jκ.^[4] EBNA2 is tethered to the EBNA2 responsive promoter elements by interacting with RBP-Jκ, a human recombination signal sequence binding protein.^[4][8]

Specific responsive elements that share the core sequence GTGGGAA have been discovered in several of the promoters activated by EBNA2.^[8] A similar core sequence has recently been identified as a binding site in RBP-Jκ.^[8] The binding of RBP-Jκ is not sufficient for EBNA2-mediated trans activation.^[4] 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.^[4] This supports the idea that EBNA2 acts as a functional equivalent of an activated Notch receptor.^[4]

EBNA2 also interacts with the human homolog of the yeast transcription factor (SNF5 hSNF5/Ini1) as it coelutes with both hSNF5/Ini1 and BRG1.^[7] BRG1 is a human homolog of SWI/SNF2.^[2] However, this interaction is restricted to a subpopulation of phosphorylated viral EBNA2.^[2] EBNA2-hSNF5/Ini1 interaction adds credit to the idea that EBNA2 facilitates transcriptional transactivation by acting as a transcription adapter molecule.^[2] Possibly, EBNA2 engages the hSNF-SWI complex to generate an open chromatin conformation at the EBNA2-responsive target genes.^[2] This then potentiates the function of the RBP-JK-EBNA2-polymerase II transcription complex.^[2]