Epstein-Barr virus BZLF1 gene is activated by transforming growth factor-β through cooperativity of smads and c-Jun/c-Fos proteins

Induction of Epstein-Barr virus (EBV) production in an EBV-positive cell is achieved by expression of the gene BZLF1 that switches the latent state into a lytic state. The expression of the BZLF1 gene is initiated from the promoter Zp, which is normally suppressed in EBV-transformed B cells. The BZLF1 gene can be induced for expression by activating agents, such as transforming growth factor-β (TGF-β) and 12-O-tetradecanoylphorbol-13-acetate. The 12-o-tetradecanoylphorbol-13-acetate-responsive element located in the Zp is the AP-1 motif. The TGF-β-responsive element, however, has not been determined. We demonstrated that the Smad4-binding element site, GTCTG, from -233 to -229, was located in the regulatory region of the Zp relative to the BZLF1 transcription initiation site and was physically associated with Smad4. This association was important for the TGF-β induction of Zp. We also showed from the results of co-transfection experiments and electrophoretic mobility shift assays that both the AP-1 motif and Smad4-binding element site appeared to be required for the TGF-β-induced activation of Zp. This effect was mediated through the cooperation of Smad3/ Smad4 and c-Jun/c-Fos that formed a complex. TGF-β treatment of Rael cells induced production of infectious EBV particles that was capable of infecting EBV-negative CA46 cells and transforming normal cord blood B cells, in vitro. Those data support a mechanism that TGF-β induces the latent EBV in cells to enter the viral lytic cycle through regulation of key viral proteins by TGF-β signal transducers. Those findings also suggest a role of TGF-β in EBV-associated diseases.