微核醣核酸（microRNAs）是一non-coding小片段RNA，透過降解mRNA或抑制mRNA轉譯而抑制標的基因的表現。在植物及非脊椎動物中，miRNA是先天性抗病毒免疫反應佔有重要一環，但仍不清楚miRNA在哺乳動物中是否也扮演類似的角色。C型肝炎病毒（hepatitis C virus, HCV）是隸屬於黃病毒科（Flaviviridae）的唯一成員，其病毒基因體為一條長度約9.6 kb的正股RNA病毒。本研究利用生物資訊分析細胞內miRNA是否會標的在HCV基因體上，並以實驗證明是否調控HCV複製。我們選擇了許多肝臟大量表現的miRNAs，以帶有HCV genome的細胞株進行分析。結果顯示有兩個肝臟大量表現的miRNA過量表現時抑制HCV的表現。為了證明miRNA是標的在HCV基因體上，利用生物資訊預測標的HCV的序列，並且將標的序列進行突變。實驗結果顯示，其中一個miRNA標的HCV序列突變之後使得HCV基因表現回復。另外，miRNA可標的的宿主細胞基因的表現並不影響HCV基因表現。 總結上述的結果，我們發現一個肝臟大量表現的miRNA藉由直接標的在HCV基因體上，進而抑制HCV基因的表現。
MicroRNAs (miRNAs) are small non-coding RNAs which inhibit the expression of target genes by promoting mRNA degradation or inhibiting mRNA translation. Although miRNAs represent a vital component of the innate antiviral immune response in plants and invertebrate animals, it is not clear whether they play the similar roles in the defense of viral infection in mammalian organisms. Hepatitis C virus (HCV) is the only member of the hepacivirus genus in Flaviviridiae. It contains a 9.6 kb single–stranded RNA genome with positive polarity. In this study, bioinformatics analysis was used to investigate whether cellular miRNAs target the HCV genome and modulate HCV replication. Several liver- abundant miRNAs were selected to characterize the effects on HCV subgenomic cells. Our data showed that two liver-abundant miRNAs can down-regulate HCV gene expression in HCV replicon cells. To elucidate whether the miRNA targets on HCV genome, several bioinformatics predicted target sites on HCV genome were mutated by in vitro mutagenesis assay. One mutated target sites significantly reversed the effect of miRNA on HCV gene expression. Knock down the host gene that is targeted by the miRNA showed no effect on expression of HCV. Taken together, we demonstrate a liver abundant miRNA which can down-regulate HCV gene expression by directly targeting on HCV genome.
