RESUMO
Hepatitis C virus (HCV) replication requires annealing of a liver specific small-RNA, miR-122 to 2 sites on 5' untranslated region (UTR). Annealing has been reported to (a) stabilize the genome, (b) stimulate translation and (c) promote the formation of translationally active Internal Ribosome Entry Site (IRES) RNA structure. In this report, we map the RNA element to which small RNA annealing promotes HCV to nucleotides 1-44 and identify the relative impact of small RNA annealing on virus translation promotion and genome stabilization. We mapped the optimal region on the HCV genome to which small RNA annealing promotes virus replication to nucleotides 19-37 and found the efficiency of viral RNA accumulation decreased as annealing moved away from this region. Then, by using a panel of small RNAs that promote replication with varying efficiencies we link the efficiency of lifecycle promotion with translation stimulation. By contrast small RNA annealing stabilized the viral genome even if they did not promote virus replication. Thus, we propose that miR-122 annealing promotes HCV replication by annealing to an RNA element that activates the HCV IRES and stimulates translation, and that miR-122 induced HCV genome stabilization is insufficient alone but enhances virus replication.
Assuntos
Instabilidade Genômica/genética , Hepatite C/genética , MicroRNAs/genética , Biossíntese de Proteínas , Regiões 5' não Traduzidas/genética , Proteínas Argonautas/genética , Genoma Viral/genética , Hepacivirus/genética , Hepacivirus/patogenicidade , Hepatite C/virologia , Humanos , Sítios Internos de Entrada Ribossomal/genética , Estabilidade de RNA/genética , Sequências Reguladoras de Ácido Nucleico/genética , Replicação Viral/genéticaRESUMO
Hepatitis C virus (HCV) replication requires annealing of a liver specific microRNA, miR-122 to 2 sites on 5' untranslated region (UTR). While, microRNAs downregulate gene expression by binding to the 3' untranslated region of the target mRNA, in this case, the microRNA anneals to the 5'UTR of the viral genomes and upregulates the viral lifecycle. In this review, we explore the current understandings of the mechanisms by which miR-122 promotes the HCV lifecycle, and its contributions to pathogenesis. Annealing of miR-122 has been reported to (a) stimulate virus translation by promoting the formation of translationally active internal ribosome entry site (IRES) RNA structure, (b) stabilize the genome, and (c) induce viral genomic RNA replication. MiR-122 modulates lipid metabolism and suppresses tumor formation, and sequestration by HCV may influence virus pathogenesis. We also discuss the possible use of miR-122 as a biomarker for chronic hepatitis and as a therapeutic target. Finally, we discuss roles for miR-122 and other microRNAs in promoting other viruses.
Assuntos
Hepacivirus/fisiologia , Fígado/metabolismo , Fígado/virologia , MicroRNAs/metabolismo , Replicação Viral/fisiologia , Animais , Hepacivirus/genética , Humanos , MicroRNAs/genética , Especificidade de Órgãos , TropismoRESUMO
Annealing of the liver-specific microRNA, miR-122, to the Hepatitis C virus (HCV) 5' UTR is required for efficient virus replication. By using siRNAs to pressure escape mutations, 30 replication-competent HCV genomes having nucleotide changes in the conserved 5' untranslated region (UTR) were identified. In silico analysis predicted that miR-122 annealing induces canonical HCV genomic 5' UTR RNA folding, and mutant 5' UTR sequences that promoted miR-122-independent HCV replication favored the formation of the canonical RNA structure, even in the absence of miR-122. Additionally, some mutant viruses adapted to use the siRNA as a miR-122-mimic. We further demonstrate that small RNAs that anneal with perfect complementarity to the 5' UTR stabilize and promote HCV genome accumulation. Thus, HCV genome stabilization and life-cycle promotion does not require the specific annealing pattern demonstrated for miR-122 nor 5' end annealing or 3' overhanging nucleotides. Replication promotion by perfect-match siRNAs was observed in Ago2 knockout cells revealing that other Ago isoforms can support HCV replication. At last, we present a model for miR-122 promotion of the HCV life cycle in which miRNA annealing to the 5' UTR, in conjunction with any Ago isoform, modifies the 5' UTR structure to stabilize the viral genome and promote HCV RNA accumulation.