The ATM/ATR signaling effector Chk2 is targeted by Epstein-Barr virus nuclear antigen 3C to release the G2/M cell cycle block

J Virol. 2007 Jun;81(12):6718-30. doi: 10.1128/JVI.00053-07. Epub 2007 Apr 4.


Epstein-Barr virus (EBV) infects most of the human population and persists in B lymphocytes for the lifetime of the host. The establishment of latent infection by EBV requires the expression of a unique repertoire of genes. The product of one of these viral genes, the EBV nuclear antigen 3C (EBNA3C), is essential for the growth transformation of primary B lymphocytes in vitro and can regulate the transcription of a number of viral and cellular genes important for the immortalization process. This study demonstrates an associated function of EBNA3C which involves the disruption of the G2/M cell cycle checkpoint. We show that EBNA3C-expressing lymphoblastoid cell lines treated with the drug nocodazole, which is known to block cells at the G2/M transition, did not show a G2/M-specific checkpoint arrest. Analyses of the cell cycles of cells expressing EBNA3C demonstrated that the expression of this essential EBV nuclear antigen is capable of releasing the G2/M checkpoint arrest induced by nocodazole. This G2/M arrest in response to nocodazole was also abolished by caffeine, suggesting an involvement of the ATM/ATR signaling pathway in the regulation of this cell cycle checkpoint. Importantly, we show that the direct interaction of EBNA3C with Chk2, the ATM/ATR signaling effector, is responsible for the release of this nocodazole-induced G2/M arrest and that this interaction leads to the serine 216 phosphorylation of Cdc25c, which is sequestered in the cytoplasm by 14-3-3. Overall, our data suggest that EBNA3C can directly regulate the G2/M component of the host cell cycle machinery, allowing for the release of the checkpoint block.

Publication types

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

MeSH terms

  • 14-3-3 Proteins / metabolism*
  • Antigens, Viral / chemistry*
  • Ataxia Telangiectasia Mutated Proteins
  • B-Lymphocytes / metabolism
  • Cell Cycle Proteins / metabolism*
  • Cell Division
  • Checkpoint Kinase 2
  • Cytoplasm / metabolism
  • DNA-Binding Proteins / metabolism*
  • Epstein-Barr Virus Nuclear Antigens / metabolism*
  • G2 Phase
  • Gene Expression Regulation, Viral*
  • Humans
  • Models, Biological
  • Nocodazole / pharmacology
  • Protein Serine-Threonine Kinases / metabolism*
  • Tumor Suppressor Proteins / metabolism*
  • cdc25 Phosphatases / metabolism*


  • 14-3-3 Proteins
  • Antigens, Viral
  • Cell Cycle Proteins
  • DNA-Binding Proteins
  • EBNA-3C, epstein-barr virus
  • Epstein-Barr Virus Nuclear Antigens
  • Tumor Suppressor Proteins
  • Checkpoint Kinase 2
  • ATM protein, human
  • ATR protein, human
  • Ataxia Telangiectasia Mutated Proteins
  • CHEK2 protein, human
  • Protein Serine-Threonine Kinases
  • CDC25C protein, human
  • cdc25 Phosphatases
  • Nocodazole