title: The ATM/ATR signaling effector Chk2 is targeted by Epstein-Barr virus nuclear antigen 3C to release the G2/M cell cycle block.
abstract: 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.
authors.affiliation: Department of Microbiology and the Tumor Virology Program, Abramson Comprehensive Cancer Center, University of Pennsylvania School of Medicine, 201E Johnson Pavilion, 3610 Hamilton Walk, Philadelphia, PA 19104, USA.
authors.forename: Tathagata
authors.initials: T
authors.lastname: Choudhuri
authors.forename: Subhash C
authors.initials: SC
authors.lastname: Verma
authors.forename: Ke
authors.initials: K
authors.lastname: Lan
authors.forename: Masanao
authors.initials: M
authors.lastname: Murakami
authors.forename: Erle S
authors.initials: ES
authors.lastname: Robertson
mesh_terms: D048948:14-3-3 Proteins / Q000378:metabolism*; D000956:Antigens, Viral / Q000737:chemistry*; D064007:Ataxia Telangiectasia Mutated Proteins; D001402:B-Lymphocytes / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002455:Cell Division; D064447:Checkpoint Kinase 2; D003593:Cytoplasm / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D019309:Epstein-Barr Virus Nuclear Antigens / Q000378:metabolism*; D016195:G2 Phase; D015967:Gene Expression Regulation, Viral; D006801:Humans; D008954:Models, Biological; D015739:Nocodazole / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D025521:Tumor Suppressor Proteins / Q000378:metabolism*; D020687:cdc25 Phosphatases / Q000378:metabolism*
chemical_list: D048948:14-3-3 Proteins; D000956:Antigens, Viral; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C498774:EBNA-3C, epstein-barr virus; D019309:Epstein-Barr Virus Nuclear Antigens; D025521:Tumor Suppressor Proteins; D064447:Checkpoint Kinase 2; C576324:ATM protein, human; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C578634:CHEK2 protein, human; D017346:Protein Serine-Threonine Kinases; C517009:CDC25C protein, human; D020687:cdc25 Phosphatases; D015739:Nocodazole