Transcription of Epstein–Barr Virus-Encoded Nuclear Antigen 1 Promoter Qp Is Repressed by Transforming Growth Factor-β via Smad4 Binding Element in Human BL Cells

In Epstein–Barr virus (EBV)-infected BL cells, the oncogenic EBV-encoded nuclear antigen 1 (EBNA 1) gene is directed from the latent promoter Qp. Yeast one-hybrid screen analysis using the −50 to −37 sequence of Qp as the bait was carried out to identify transcriptional factors that may control Qp activity. Results showed that Smad4 binds the −50 to −37 sequence of Qp, indicating that this promoter is potentially regulated by TGF-β. The association of Smad4 with Qp was further confirmed by supershift of EMSA complexes using Smad4-specific antibody. The transfection of a Qp reporter construct in two EBV(+) BL cell lines, Rael and WW2, showed that Qp activity is repressed in response to the TGF-β treatment. This repression involves the interaction of a Smad3/Smad4 complex and the transcriptional repressor TGIF, as determined by cotransfection assay and coimmunoprecipitation analysis. Results suggest that TGF-β may transcriptionally repress Qp through the Smad4-binding site in human BL cells.