Choudhuri Tathagata, Verma Subhash C, Lan Ke, Murakami Masanao, Robertson Erle S
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.
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.
爱泼斯坦-巴尔病毒（EBV）感染了大多数人类，并在宿主的B淋巴细胞中终身持续存在。EBV建立潜伏感染需要表达一组独特的基因。这些病毒基因之一的产物，即EBV核抗原3C（EBNA3C），对于体外原代B淋巴细胞的生长转化至关重要，并且可以调节许多对永生化过程重要的病毒和细胞基因的转录。本研究证明了EBNA3C的一种相关功能，即涉及破坏G2/M细胞周期检查点。我们发现，用诺考达唑处理表达EBNA3C的淋巴母细胞系，已知该药物会在G2/M期转换时阻断细胞，但这些细胞并未表现出G2/M特异性检查点阻滞。对表达EBNA3C的细胞的细胞周期分析表明，这种重要的EBV核抗原的表达能够解除由诺考达唑诱导的G2/M检查点阻滞。咖啡因也消除了对诺考达唑的这种G2/M阻滞，这表明ATM/ATR信号通路参与了该细胞周期检查点的调节。重要的是，我们表明EBNA3C与ATM/ATR信号效应器Chk2的直接相互作用负责解除这种由诺考达唑诱导的G2/M阻滞，并且这种相互作用导致Cdc25c的丝氨酸216磷酸化，Cdc25c被14-3-3隔离在细胞质中。总体而言，我们的数据表明EBNA3C可以直接调节宿主细胞周期机制的G2/M成分，从而解除检查点阻滞。
