Epstein-Barr virus utilizes Ikaros in regulating its latent-lytic switch in B cells

J Virol. 2014 May;88(9):4811-27. doi: 10.1128/JVI.03706-13. Epub 2014 Feb 12.


Ikaros is a zinc finger DNA-binding protein that regulates chromatin remodeling and the expression of genes involved in the cell cycle, apoptosis, and Notch signaling. It is a master regulator of lymphocyte differentiation and functions as a tumor suppressor in acute lymphoblastic leukemia. Nevertheless, no previous reports described effects of Ikaros on the life cycle of any human lymphotropic virus. Here, we demonstrate that full-length Ikaros (IK-1) functions as a major factor in the maintenance of viral latency in Epstein-Barr virus (EBV)-positive Burkitt's lymphoma Sal and MutuI cell lines. Either silencing of Ikaros expression by small hairpin RNA (shRNA) knockdown or ectopic expression of a non-DNA-binding isoform induced lytic gene expression. These effects synergized with other lytic inducers of EBV, including transforming growth factor β (TGF-β) and the hypoxia mimic desferrioxamine. Data from chromatin immunoprecipitation (ChIP)-quantitative PCR (qPCR) and ChIP-sequencing (ChIP-seq) analyses indicated that Ikaros did not bind to either of the EBV immediate early genes BZLF1 and BRLF1. Rather, Ikaros affected the expression of Oct-2 and Bcl-6, other transcription factors that directly inhibit EBV reactivation and plasma cell differentiation, respectively. IK-1 also complexed with the EBV immediate early R protein in coimmunoprecipitation assays and partially colocalized with R within cells. The presence of R alleviated IK-1-mediated transcriptional repression, with IK-1 then cooperating with Z and R to enhance lytic gene expression. Thus, we conclude that Ikaros plays distinct roles at different stages of EBV's life cycle: it contributes to maintaining latency via indirect mechanisms, and it may also synergize with Z and R to enhance lytic replication through direct association with R and/or R-induced alterations in Ikaros' functional activities via cellular signaling pathways.

Importance: This is the first report showing that the cellular protein Ikaros, a known master regulator of hematopoiesis and critical tumor suppressor in acute lymphoblastic leukemia, also plays important roles in the life cycle of Epstein-Barr virus in B cells.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • B-Lymphocytes / virology*
  • Cell Line, Tumor
  • Chromatin Immunoprecipitation
  • Gene Expression Regulation, Viral*
  • Gene Knockdown Techniques
  • Herpesvirus 4, Human / physiology*
  • Host-Pathogen Interactions*
  • Humans
  • Ikaros Transcription Factor / metabolism*
  • Protein Binding
  • Virus Latency*


  • IKZF1 protein, human
  • Ikaros Transcription Factor