Department of Molecular Genetics, University of Toronto, Toronto, Ontario, Canada.
J Virol. 2012 Jan;86(1):60-8. doi: 10.1128/JVI.05623-11. Epub 2011 Oct 19.
Approximately 10% of gastric carcinomas (GC) are comprised of cells latently infected with Epstein-Barr virus (EBV); however, the mechanism by which EBV contributes to the development of this malignancy is unclear. We have investigated the cellular effects of the only EBV nuclear protein expressed in GC, EBNA1, focusing on promyelocytic leukemia (PML) nuclear bodies (NBs), which play important roles in apoptosis, p53 activation, and tumor suppression. AGS GC cells infected with EBV were found to contain fewer PML NBs and less PML protein than the parental EBV-negative AGS cells, and these levels were restored by silencing EBNA1. Conversely, EBNA1 expression was sufficient to induce the loss of PML NBs and proteins in AGS cells. Consistent with PML functions, EBNA1 expression decreased p53 activation and apoptosis in response to DNA damage and resulted in increased cell survival. In addition, EBNA1 mutants unable to bind CK2 kinase or ubiquitin-specific protease 7 had decreased ability to induce PML loss and to interfere with p53 activation. PML levels in EBV-positive and EBV-negative GC biopsy specimens were then compared by immunohistochemistry. Consistent with the results in the AGS cells, EBV-positive tumors had significantly lower PML levels than EBV-negative tumors. The results indicate that EBV infection of GC cells leads to loss of PML NBs through the action of EBNA1, resulting in impaired responses to DNA damage and promotion of cell survival. Therefore, PML disruption by EBNA1 is one mechanism by which EBV may contribute to the development of gastric cancer.
大约 10%的胃癌（GC）是由潜伏感染 EBV 的细胞组成的；然而，EBV 促进这种恶性肿瘤发展的机制尚不清楚。我们研究了在 GC 中唯一表达的 EBV 核蛋白 EBNA1 的细胞效应，重点关注在细胞凋亡、p53 激活和肿瘤抑制中起重要作用的早幼粒细胞白血病（PML）核体（NBs）。发现感染 EBV 的 AGS GC 细胞比母系 EBV 阴性的 AGS 细胞含有更少的 PML NBs 和更少的 PML 蛋白，而沉默 EBNA1 则可以恢复这些水平。相反，EBNA1 的表达足以诱导 AGS 细胞中 PML NBs 和蛋白的丢失。与 PML 功能一致，EBNA1 的表达降低了 DNA 损伤后 p53 的激活和凋亡，导致细胞存活增加。此外，不能结合 CK2 激酶或泛素特异性蛋白酶 7 的 EBNA1 突变体诱导 PML 丢失和干扰 p53 激活的能力降低。然后通过免疫组织化学比较 EBV 阳性和 EBV 阴性 GC 活检标本中的 PML 水平。与 AGS 细胞的结果一致，EBV 阳性肿瘤的 PML 水平明显低于 EBV 阴性肿瘤。结果表明，EBV 感染 GC 细胞会导致 PML NBs 通过 EBNA1 的作用丢失，从而导致对 DNA 损伤的反应受损并促进细胞存活。因此，EBNA1 破坏 PML 是 EBV 可能促进胃癌发展的一种机制。
