Departments of Surgery, Chi-Mei Medical Center, Liu-Ying Campus, Tainan, Taiwan, R.O.C.
Int J Oncol. 2010 Jan;36(1):151-60.
Epstein-Barr nuclear antigen 1 (EBNA-1) is consistently expressed in all EBV-associated gastric carcinomas. We explored its biological effects in gastric carcinoma cells by expressing the protein in two Epstein-Barr virus (EBV)-negative gastric carcinoma cell lines (SCM1 and TMC1). EBNA1-expressing SCM1 and TMC1 cells displayed no significant differences in growth rates, respectively, compared to those of vector-transfected SCM1 and TMC1 cells in vitro. However, EBNA1 was able to enhance tumorigenicity, the growth rate and the malignant histopathological grade in a xenograft nude mice test. We also evaluated whether EBNA1 caused EBNA1-expressing cells to have enhanced tumorigenicity in an immunocompetent host. We showed that EBNA1-expressing LL/2 cells (derived from lung carcinoma of a Swiss mouse) had enhanced tumorigenicity and growth ability in the immunocompetent allograft Balb/c mice test. These results support the expression of EBNA1 in EBV-associated gastric carcinoma being able to provide advantages of EBV-mediated cell growth and transformation, and to enhance the malignant potential in vivo. In a clonogenic assay, we showed that EBNA1 could reduce the sensitivity of gastric carcinoma cells (SCM1 cells) harboring wild-type p53 to cisplatin, but this was not found in mutant p53-bearing TMC1 cells. In addition, we demonstrated that EBNA1-expressing SCM1 cells, but not EBNA1-expressing TMC1 cells, were associated with reduced expression levels of p53. These findings are compatible with EBNA1 efficiently competing with p53 for binding to ubiquitin-specific protease 7, which causes p53 to degrade by the ubiquitin/proteasome system. These findings suggest that EBNA1 expression is able to reduce the p53 protein level, resulting in the inhibition of its functional activities. Finally, our results suggest that EBV infection with EBNA1 expression in gastric carcinomas provides advantages for host cell survival, growth ability and transformation potential involving escape from immunosurveillance and a reduction in the sensitivity to DNA damage or other apoptotic stress stimuli mediated by suppression of the wild-type p53 protein level; these are distinct from the pathogenesis of EBV-negative gastric carcinomas.
Epstein-Barr 核抗原 1（EBNA-1）在所有与 EBV 相关的胃癌中均持续表达。我们通过在两种 EBV 阴性胃癌细胞系（SCM1 和 TMC1）中表达该蛋白来研究其在胃癌细胞中的生物学效应。EBNA1 表达的 SCM1 和 TMC1 细胞与转染载体的 SCM1 和 TMC1 细胞相比，体外生长速度无明显差异。然而，EBNA1 能够增强异种移植裸鼠试验中的致瘤性、生长速度和恶性组织病理学分级。我们还评估了 EBNA1 是否导致 EBNA1 表达细胞在免疫活性宿主中具有更强的致瘤性。我们表明，EBNA1 表达的 LL/2 细胞（源自瑞士鼠肺癌）在免疫活性同种异体 Balb/c 小鼠试验中具有更强的致瘤性和生长能力。这些结果支持 EBV 相关胃癌中 EBNA1 的表达能够提供 EBV 介导的细胞生长和转化优势，并增强体内的恶性潜能。在集落形成试验中，我们表明 EBNA1 可以降低携带野生型 p53 的胃癌细胞（SCM1 细胞）对顺铂的敏感性，但在携带突变型 p53 的 TMC1 细胞中未发现这种情况。此外，我们证明，与表达 EBNA1 的 TMC1 细胞不同，表达 EBNA1 的 SCM1 细胞与 p53 表达水平降低有关。这些发现与 EBNA1 有效竞争与泛素特异性蛋白酶 7 的结合，导致 p53 通过泛素/蛋白酶体系统降解相一致。这些发现表明，EBNA1 表达能够降低 p53 蛋白水平，从而抑制其功能活性。最后，我们的结果表明，EBV 感染并表达 EBNA1 可提供宿主细胞存活、生长能力和转化潜力的优势，包括逃避免疫监视以及降低对野生型 p53 蛋白水平抑制介导的 DNA 损伤或其他凋亡应激刺激的敏感性；这些与 EBV 阴性胃癌的发病机制不同。
