Expression of Epstein-Barr nuclear antigen 1 in gastric carcinoma cells is associated with enhanced tumorigenicity and reduced cisplatin sensitivity.
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.
Cheng
Tse-Chou
TC
Departments of Surgery, Chi-Mei Medical Center, Liu-Ying Campus, Tainan, Taiwan, R.O.C.
Hsieh
Shan-Shan
SS
Hsu
Wen-Lin
WL
Chen
Yu-Fang
YF
Ho
Hwei-Hon
HH
Sheu
Lai-Fa
LF
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis; D002277:Carcinoma / Q000378:metabolism* / Q000821:virology*; D045744:Cell Line, Tumor; D002470:Cell Survival; D002471:Cell Transformation, Neoplastic; D002945:Cisplatin / Q000494:pharmacology*; D019309:Epstein-Barr Virus Nuclear Antigens / Q000096:biosynthesis*; D015972:Gene Expression Regulation, Neoplastic; D015967:Gene Expression Regulation, Viral; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D009368:Neoplasm Transplantation; D013274:Stomach Neoplasms / Q000378:metabolism* / Q000821:virology*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
D000970:Antineoplastic Agents; D019309:Epstein-Barr Virus Nuclear Antigens; D016159:Tumor Suppressor Protein p53; C417029:EBV-encoded nuclear antigen 1; D002945:Cisplatin