title: Differential stimulation of hepatitis C virus RNA translation by microRNA-122 in different cell cycle phases.
abstract: Hepatitis C virus (HCV) replicates preferentially in the liver, and in most cases the HCV infection becomes chronic and often results in hepatocellular carcinoma. When the HCV plus-strand RNA genome has been delivered to the cytosol of the infected cell, its translation is directed by the Internal Ribosome Entry Site (IRES) in the 5'-untranslated region (5'-UTR) of the viral RNA. Thereby, IRES activity is modulated by several host factors. In particular, the liver-specific microRNA-122 (miR-122) interacts with two target sites in the HCV 5'-UTR and stimulates HCV translation, thereby most likely contributing to HCV liver tropism. Here we show that HCV IRES-dependent translation efficiency in the hepatoma cell line Huh7 is highest during the G₀ and G₁ phases of the cell cycle but significantly drops during the S phase and even more in the G₂/M phase. The superimposed stimulation of HCV translation by ectopic miR-122 works best during the G₀, G₁ and G₂/M phases but is lower during the S phase. However, the levels of Ago2 protein do not substantially change during cell cycle phases, indicating that other cellular factors involved in HCV translation stimulation by miR-122 may be differentially expressed in different cell cycle phases. Moreover, the levels of endogenously expressed miR-122 in Huh7 cells are lowest in the S phase, indicating that the predominant G₀/G₁ state of non-dividing hepatocytes in the liver facilitates high expression of the HCV genome and stimulation by miR-122, with yet unknown factors involved in the differential extent of stimulation by miR-122.
authors.affiliation: Institute of Biochemistry, Faculty of Medicine, Justus-Liebig-University, Giessen, Germany.
authors.forename: Carmen
authors.initials: C
authors.lastname: Fehr
authors.forename: K Dominik
authors.initials: KD
authors.lastname: Conrad
authors.forename: Michael
authors.initials: M
authors.lastname: Niepmann
mesh_terms: D060565:Argonaute Proteins / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D015870:Gene Expression; D015967:Gene Expression Regulation, Viral; D017930:Genes, Reporter; D005814:Genes, Viral; D016174:Hepacivirus / Q000235:genetics / Q000502:physiology*; D006526:Hepatitis C / Q000821:virology; D006801:Humans; D007399:Interphase; D035683:MicroRNAs / Q000235:genetics / Q000378:metabolism*; D014176:Protein Biosynthesis; D034622:RNA Interference; D012342:RNA, Small Nuclear / Q000378:metabolism; D012367:RNA, Viral / Q000235:genetics*
chemical_list: C466422:AGO2 protein, human; D060565:Argonaute Proteins; C531907:MIRN122 microRNA, human; D035683:MicroRNAs; D012342:RNA, Small Nuclear; D012367:RNA, Viral; C405486:U6 small nuclear RNA