Role of Viral and Host Micrornas in Immune Regulation of Epstein-Barr Virus-Associated Diseases

Epstein-Barr virus (EBV) is an oncogenic human herpes virus that was discovered in 1964. Viral non-coding RNAs, such as BamHI-A rightward fragment-derived microRNAs (BART miRNAs) or BamHI-H rightward fragment 1-derived miRNAs (BHRF1 miRNA) in EBV-infected cells have been recently reported. Host miRNAs are also upregulated upon EBV infection. Viral and host miRNAs are important in maintaining viral infection and evasion of host immunity. Although miRNAs in EBV-infected cells often promote cell proliferation by targeting apoptosis or cell cycle, this review focuses on the regulation of the recognition of the host immune system. This review firstly describes the location and organization of two clusters of viral miRNAs, then describes evasion from host immune surveillance systems by modulating viral gene expression or inhibiting innate and acquired immunity by viral miRNAs as well as host miRNAs. Another topic is the enigmatic depletion of viral miRNAs in several types of EBV-infected tumor cells. Finally, this review introduces the strong correlation of nasopharyngeal cancer cases with a newly identified single nucleotide polymorphism that enhances BART miRNA promoter activity.