Radiation and Cisplatin activation of EBV in nasopharyngeal cancer: Understanding the oncolytic potential of EBV

Proc Amer Assoc Cancer Res, Volume 47, 2006 823 Introduction: The Epstein Barr Virus (EBV) is highly associated with Nasopharyngeal Cancer (NPC) where it exists in a state of latency (type II), expressing a limited number of genes. Upon stress activation however, the EBV profile switches to a lytic phase, associated with the expression of several critical EBV genes including BRLF1 and BZLF1. The events regulating this switch are not completely understood, but insights into this process may lead to the development of novel therapeutic strategies given the intimate relationship between EBV and NPC. Materials & Methods: The EBV positive cell line C666-1 was treated with ionizing radiation, RT (15Gy) and/or Cisplatin (50ug/mL). Gene expression data was determined using quantitative real-time PCR. Dominant-negative experiments were performed using dN-NF-YA (kindly provided by R. Manotvani) and over-expression analysis used the pNF-YA construct (Origene). Transactivation ability of NF-Y was determined on nuclear lysates using ELISA-based analyses (Active Motif). Chromatin immunoprecipiation (ChIP) experiments were performed using NF-YA and NF-YB antibodies (Active Motif, Santa Cruz) and primers designed for the appropriate NF-Y consensus regions. Results: C666-1 cells were treated with RT and/or Cisplatin, and a time and dose-dependent activation of BRLF1 and BZLF1 were observed. Increases in BRLF1 were observed as early as two hours post-treatment, followed by BZLF1 expression between 8 and 24 hours. The expression of both lytic genes increased in a time-dependent manner to 72 hours post-treatment. These same treatments were also associated with the increased expression of the transcription factor Nuclear Factor Y (NF-Y) and immediate nuclear transactivation. Introduction of dN-NF-YA significantly reduced BRLF1 expression after RT and Cisplatin treatment by 5-fold. Consistent with these observations, overexpression of NF-YA resulted in at least a 10-fold increase in both BRLF1 and BZLF1 expression. In silico analysis reveals that putative NF-Y consensus binding sequences are located in the promoter region of BZLF1 and BRLF1, suggesting a potential transcriptional regulatory role of NF-Y. Preliminary results using chromatin immunoprecipitation (ChIP) confirm the physical interaction between NF-Y and the promoter region of critical EBV lytic genes. Conclusion: Taken together, these data suggest the novel finding that NF-Y appears to be a major mediator of the EBV stress response in switching from a latent to lytic state. Manipulations which could increase NF-Y expression, thereby facilitating the expression of lytic EBV genes in human NPC, might offer a potential therapeutic strategy to enhance NPC response to RT and Cisplatin.