Abstract LB211: Epstein-Barr virus BART lncRNAs induceIKZF3/Aiolos to maintain EBV latency and promote tumorigenicity in nasopharyngeal carcinoma

Abstract

Epstein-Barr virus (EBV) maintains latency in its associated tumors, including nasopharyngeal carcinoma (NPC), expressing very few viral proteins but abundant levels of noncoding RNAs (mainly EBERs and BARTs) in NPC cells. We found that IKZF3/Aiolos is a downstream target of BART lncRNAs in NPC cells. The functions of BART lncRNAs and IKZF3 in EBV latency and pathogenesis of NPC remain elusive. In this study, meta-analysis of eight EBV-associated studies showed that IKZF3/Aiolos was consistently upregulated in EBV-infected NPC cells. Our study further showed that transcription of IKZF3/Aiolos is highly upregulated in EBV-infected NPC cells and clinical tissue samples due to the action of EBV encoded BART lncRNAs, with IKZF3/Aiolos was expressed at higher levels in late stage (stage III & IV) NPC patients than in early stage (stage I & II) disease. Secondly, we found that IKZF3/Aiolos was upregulated in BART-activated NPC cells but downregulated in BART-knockdown NPC cells. In addition, this study further demonstrated that IKZF3/Aiolos modulates transcription of EBV BZLF1 and the cellular gene, LRIG1, to maintain EBV latency and promote NPC tumorigenesis in vitro and in vivo. Our results showed that the EBV lytic reactivator BZLF1 was upregulated in IKZF3/Aiolos knockout or Aiolos inhibitor-treated NPC cells. ChIP-qPCR, immunoprecipitation and immunofluorescence analyses further revealed that IKZF3/Aiolos induces H3K27 deacetylation to silence expression of BZLF1 and maintain EBV latency in NPC cells. Moreover, functional analyses and western blotting showed that IKZF3/Aiolos inhibited the tumor suppressor, LRIG1, to upregulate expression and phosphorylation of the cellular proto-oncogene Erb-B2 for NPC pathogenesis. Sphere- and colony-formation assays demonstrated that IKZF3/Aiolos enhances growth of NPC cells in vitro, and in vivo experiments further showed that IKZF3/Aiolos promotes tumorigenicity of NPC cells in NOD mice. Mechanically, we found that the expression of EBV lytic reactivator BZLF1 and cellular LRIG1 were negatively regulated by BART lncRNA/IKZF3/Aiolos regulatory machinery in NPC cells, while Erb-B2 was positively regulated, which indicated that IKZF3/Aiolos is a new biomarker for NPC and may lead to the development of novel diagnostic tests and treatments for NPC. Citation Format: Songtao He, Jiayan Liu, Bobo Wing-Yee Mok, Sai Wah Tsao, Honglin Chen. Epstein-Barr virus BART lncRNAs induce IKZF3/Aiolos to maintain EBV latency and promote tumorigenicity in nasopharyngeal carcinoma. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3748.