title: hTERT inhibition triggers Epstein-Barr virus lytic cycle and apoptosis in immortalized and transformed B cells: a basis for new therapies.
abstract: OBJECTIVE
  Induction of viral lytic cycle, which induces death of host cells, may constitute a useful adjunct to current therapeutic regimens for Epstein-Barr virus (EBV)-driven malignancies. Human telomerase reverse transcriptase (hTERT), essential for the oncogenic process, may modulate the switch from latent to lytic infection. The possible therapeutic role of hTERT inhibition combined with antiviral drugs was investigated.
  
  
  METHODS
  EBV-negative BL41 and convertant EBV-positive BL41/B95.8 Burkitt's lymphoma cell lines and lymphoblastoid cell lines (LCL) were infected with retroviral vector encoding short hairpin RNA (shRNA) anti-hTERT and cultured with or without the prodrug ganciclovir. The effects on EBV lytic replication, cell proliferation, and apoptosis were characterized.
  
  
  RESULTS
  hTERT silencing by shRNA induced the expression of BZLF1, EA-D, and gp350 EBV lytic proteins and triggered a complete lytic cycle. This effect was associated with downregulation of BATF, a negative regulator of BZLF1 transcription. hTERT silencing also resulted in antiproliferative and proapoptotic effects. In particular, hTERT inhibition induced an accumulation of cells in the S-phase, an effect likely due to the dephosphorylation of 4E-BP1, an AKT1-dependent substrate, which results in a decreased availability of proteins needed for cell-cycle progression. Besides inducing cell death through activation of complete EBV lytic replication, hTERT inhibition triggered AKT1/FOXO3/NOXA-dependent apoptosis in EBV-positive and -negative Burkitt's lymphoma cells. Finally, ganciclovir enhanced the apoptotic effect induced by hTERT inhibition in EBV-positive Burkitt's lymphomas and LCLs.
  
  
  CONCLUSIONS
  These results suggest that combination of antiviral drugs with strategies able to inhibit hTERT expression may result in therapeutically relevant effects in patients with EBV-related malignancies.
authors: Department of Surgery, Oncology and Gastroenterology, Section of Oncology and Immunology, University of Padova, Italy.
authors: Silvia
authors: S
authors: Giunco
authors: Riccardo
authors: R
authors: Dolcetti
authors: Sonia
authors: S
authors: Keppel
authors: Andrea
authors: A
authors: Celeghin
authors: Stefano
authors: S
authors: Indraccolo
authors: Jessica
authors: J
authors: Dal Col
authors: Katy
authors: K
authors: Mastorci
authors: Anita
authors: A
authors: De Rossi
mesh_terms: D000998:Antiviral Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics*; D001402:B-Lymphocytes / Q000187:drug effects / Q000378:metabolism* / Q000821:virology; D050976:Basic-Leucine Zipper Transcription Factors / Q000235:genetics; D015153:Blotting, Western; D002461:Cell Line, Transformed; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D005434:Flow Cytometry; D015774:Ganciclovir / Q000494:pharmacology; D015967:Gene Expression Regulation, Viral; D004854:Herpesvirus 4, Human / Q000235:genetics* / Q000502:physiology; D054884:Host-Pathogen Interactions / Q000235:genetics; D006801:Humans; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics; D034622:RNA Interference; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000235:genetics; D019098:Telomerase / Q000235:genetics* / Q000378:metabolism; D015534:Trans-Activators / Q000235:genetics; D014775:Virus Activation / Q000187:drug effects
chemical_list: D000998:Antiviral Agents; C099359:BATF protein, human; C063676:BZLF1 protein, Herpesvirus 4, Human; D050976:Basic-Leucine Zipper Transcription Factors; D015534:Trans-Activators; C494918:AKT1 protein, human; D051057:Proto-Oncogene Proteins c-akt; C509186:TERT protein, human; D019098:Telomerase; D015774:Ganciclovir