E2F1 mediated apoptosis induced by the DNA damage response is blocked by EBV nuclear antigen 3C in lymphoblastoid cells

PLoS Pathog. 2012;8(3):e1002573. doi: 10.1371/journal.ppat.1002573. Epub 2012 Mar 15.

Abstract

EBV latent antigen EBNA3C is indispensible for in vitro B-cell immortalization resulting in continuously proliferating lymphoblastoid cell lines (LCLs). EBNA3C was previously shown to target pRb for ubiquitin-proteasome mediated degradation, which facilitates G1 to S transition controlled by the major transcriptional activator E2F1. E2F1 also plays a pivotal role in regulating DNA damage induced apoptosis through both p53-dependent and -independent pathways. In this study, we demonstrate that in response to DNA damage LCLs knocked down for EBNA3C undergo a drastic induction of apoptosis, as a possible consequence of both p53- and E2F1-mediated activities. Importantly, EBNA3C was previously shown to suppress p53-induced apoptosis. Now, we also show that EBNA3C efficiently blocks E2F1-mediated apoptosis, as well as its anti-proliferative effects in a p53-independent manner, in response to DNA damage. The N- and C-terminal domains of EBNA3C form a stable pRb independent complex with the N-terminal DNA-binding region of E2F1 responsible for inducing apoptosis. Mechanistically, we show that EBNA3C represses E2F1 transcriptional activity via blocking its DNA-binding activity at the responsive promoters of p73 and Apaf-1 apoptosis induced genes, and also facilitates E2F1 degradation in an ubiquitin-proteasome dependent fashion. Moreover, in response to DNA damage, E2F1 knockdown LCLs exhibited a significant reduction in apoptosis with higher cell-viability. In the presence of normal mitogenic stimuli the growth rate of LCLs knockdown for E2F1 was markedly impaired; indicating that E2F1 plays a dual role in EBV positive cells and that active engagement of the EBNA3C-E2F1 complex is crucial for inhibition of DNA damage induced E2F1-mediated apoptosis. This study offers novel insights into our current understanding of EBV biology and enhances the potential for development of effective therapies against EBV associated B-cell lymphomas.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Antigens, Viral / genetics
  • Antigens, Viral / metabolism*
  • Apoptosis / genetics*
  • Cell Line
  • Cell Line, Tumor
  • Cell Proliferation
  • DNA Damage
  • E2F1 Transcription Factor / antagonists & inhibitors
  • E2F1 Transcription Factor / metabolism*
  • Epstein-Barr Virus Infections / genetics
  • Epstein-Barr Virus Infections / metabolism*
  • Epstein-Barr Virus Infections / virology
  • Epstein-Barr Virus Nuclear Antigens
  • Gene Expression Regulation, Viral
  • HEK293 Cells
  • Humans
  • Lymphocytes / metabolism
  • Lymphocytes / pathology
  • Lymphocytes / virology*
  • Lymphoma, B-Cell / immunology
  • Lymphoma, B-Cell / virology
  • Osteoblasts / immunology
  • Osteoblasts / virology
  • Transfection

Substances

  • Antigens, Viral
  • E2F1 Transcription Factor
  • E2F1 protein, human
  • EBNA-3C, epstein-barr virus
  • Epstein-Barr Virus Nuclear Antigens